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The relative effects of intake and compression generated turbulence on I.C. engine combustion duration Dohring, Klaus 1986

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THE RELATIVE EFFECTS OF INTAKE AND COMPRESSION GENERATED TURBULENCE ON I.C.ENGINE COMBUSTION DURATION by KLAUS DOHRING D i p l . I n g . Technische U n i v e r s i t a t Braunschweig (1983) A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Mechanical E n g i n e e r i n g We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA March 1986 © Klaus Dohring, 1986 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the The U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree that permission f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permi s s i o n . Department of Mechanical E n g i n e e r i n g The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada . V6T 1W5 Date: March 1986 - i i -ABSTRACT: A Rapid Intake and Compression Machine was designed and b u i l t , which makes i t p o s s i b l e to simulate the p i s t o n motion of a r e c i p r o c a t i n g i n t e r n a l combustion engine at 1000 rpm. The compression s t r o k e can be run by i t s e l f or f o l l o w i n g the intake s t r o k e . Hot Wire Anemometer measurements were made at s e v e r a l l o c a t i o n s i n s i d e the combustion chamber d u r i n g intake and compression stroke and d u r i n g the compression stroke by i t s e l f . Under s i m i l a r o p e r a t i n g c o n d i t i o n s a combustible mixture was drawn i n and i g n i t e d with v a r y i n g i g n i t i o n times a f t e r s i m u l a t i n g the intake and compression s t r o k e together and a f t e r s i m u l a t i n g the compression stroke by i t s e l f . The mass f r a c t i o n burned curves versus time were c a l c u l a t e d from the pre s s u r e t r a c e . The v e l o c i t y measurements were compared to the combustion t e s t r e s u l t s and the one st r o k e r e s u l t s were compared to the r e s u l t s found from the two st r o k e t e s t s . I t was found that the compression s t r o k e run by i t s e l f generates very l i t t l e flow motion i n a f l a t d i s k combustion chamber without s w i r l , compared to the intake and compression s t r o k e run to g e t h e r . The i g n i t i o n d elay p e r i o d as w e l l as the main combustion d u r a t i o n were c o n s i d e r a b l y s h o r t e r a f t e r the intake and compression s t r o k e compared to the compression s t r o k e by i t s e l f . In the case of intake and compression s t r o k e more advanced i g n i t i o n t i m i n g reduced the i g n i t i o n d elay p e r i o d as w e l l as the main combustion durat i o n . I t i s concluded that under the present engine c o n d i t i o n s the compression s t r o k e generates p r a c t i c a l l y no t u r b u l e n c e . Thus the c o n t r i b u t i o n of the compression stroke to the flow c o n d i t i o n s around i g n i t i o n time i s l i m i t e d to c o u n t e r a c t i n g the decay of i n t a k e generated turb u l e n c e through compression e f f e c t s . - i v-TABLE OF CONTENTS: Page: ABSTRACT i i LIST OF TABLES vi LIST OF FIGURES v i i ACKNOWLEDGEMENT i X NOMENCLATURE X CHAPTER 1 1 INTRODUCTION 1 1.1 REVIEW OF PREVIOUS WORK 3 1.2 OBJECTIVE OF THIS WORK 5 CHAPTER 2 2 EXPERIMENTAL APPARATUS 7 2.1 HISTORY OF THE RAPID COMPRESSION MACHINE _ j 2.2 DESCRIPTION OF THE RAPID INTAKE AND COMPRESSION MACHINE 12 CHAPTER 3 3 EXPERIMENTS 18 3.1 HOT-WIRE ANEMOMETRY MEASUREMENTS 19 3.1.1 EQUIPMENT AND PROCEDURE 19 3.1.2 LIMITATIONS OF HOT-WIRE ANEMOMETRY IN INTERNAL COMBUSTION ENGINES 24 3.2 COMBUSTION TESTS 29 3.3 DATA ACQUISITION 30 CHAPTER 4 4 DATA PROCESSING AND RESULTS 32 4.1 HOT-WIRE ANEMOMETER DATA 32 .1 RAW INSTANTANEOUS VELOCITY DATA -V-4.1.2 DATA REDUCTION 34 4.1.3 HOT-WIRE ANEMOMETER RESULTS 38 4.2 COMBUSTION DATA 44 4.2.1 PRESSURE DATA 44 4.2.2 DATA PROCESSING AND REDUCTION 45 4.2.3 COMBUSTION RESULTS 50 CHAPTER 5 5 CONCLUSIONS 53 BIBLIOGRAPHY 56 APPENDIX A - HOT WIRE ANEMOMETER DATA ANALYSIS PROGRAMMES. .90 a. Hot Wire Anemometer C a l i b r a t i o n Programme 91 b. Data S e p a r a t i o n and S c a l i n g Programme 92 c. Instantaneous V e l o c i t y Programme 94 d. Data Reduction Programme 96 APPENDIX B - COMBUSTION DATA ANALYSIS PROGRAMMES 99 a. Data Sepa r a t i o n and S c a l i n g Programme 100 b. Data Reduction and R e s c a l i n g Programme 102 c. Mass F r a c t i o n Burned Programme 104 d. Data Reduction Programme 105 APPENDIX C - DESIGN OUTLINE AND LIMITATIONS OF THE RAPID INTAKE AND COMPRESSION MACHINE 107 a. I n t r o d u c t i o n 108 b. O u t l i n e of the Design Process 109 c. L i m i t a t i o n s of C r i t i c a l Components 116 d. L i m i t a t i o n s of the Rapid Intake- and Compression Machine 121 APPENDIX D - MANUAL AND MAINTENANCE PLAN FOR THE RAPID INTAKE AND COMPRESSION MACHINE 123 a. Operation Manual f o r the Rapid Intake and Compression Machine 124 b. Maintenance Plan 129 APPENDIX E - ESTIMATE OF THE EFFECT OF COMPRESSION ON EXISTING VORTICITY 130 - v i -LIST OF TABLES; Page: Table 1 Bas i c Dimensions of the Rapid Intake and Compression Machine 59 Table 2 Hot-Wire Anemometer Equipment 60 Table 3 Ensemble Averaged Mass F r a c t i o n Burned 61 - v i i -LIST OF FIGURES: Page: F i g u r e 1 Rapid Compression Machine Mounting Outlay 62 Fi g u r e 2 Rapid Compression Machine Crank Box 63 Fi g u r e 3 Rapid Compression Machine Assembly with Intake Valve D r i v e T r a i n 64 Fi g u r e 4 Rack and P i s t o n V e l o c i t y , Intake and Compression Stroke 65 F i g u r e 5 Rack and P i s t o n V e l o c i t y , Compression Stroke only 66 Fi g u r e 6 Hot-wire Anemometer Measurement L o c a t i o n s 67 F i g u r e 7a Example of Instantaneous V e l o c i t y , One Stroke..68 F i g u r e 7b Example of Instantaneous V e l o c i t y , Two Strokes 69 F i g u r e 7c Example of the Window Averaging and I n t e r p o l a t i o n Technique used 70 Fi g u r e 8a Ensemble Averaged Mean V e l o c i t i e s / T i m e , Two Strokes 71 F i g u r e 8b Ensemble Averaged Mean V e l o c i t i e s / D e g r e e Crank Angle, Two Strokes 72 F i g u r e 9a Ensemble Averaged Turbulence I n t e n s i t i e s / T i m e , Two Strokes 73 F i g u r e 9b Ensemble Averaged Turbulence I n t e n s i t i e s / D e g r e e Crank Angle, Two Strokes ... .74 F i g u r e 10a Ensemble Averaged C y c l i c V a r i a t i o n I n t e n s i t i e s / T i m e , Two Strokes 75 F i g u r e 10b Ensemble Averaged C y c l i c V a r i a t i o n I n t e n s i t i e s / D e g r e e Crank Angle, Two Strokes ... .76 F i g u r e 11a Ensemble Averaged Mean V e l o c i t i e s / T i m e , One Stroke 77 F i g u r e 11b Ensemble Averaged Mean V e l o c i t i e s / D e g r e e Crank Angle, One Stroke 78 - v i i i -F i g u r e 12a Ensemble Averaged Turbulence I n t e n s i t i e s / T i m e , One Stroke 79 F i g u r e 12b Ensemble Averaged Turbulence I n t e n s i t i e s / D e g r e e Crank Angle, One Stroke 80 F i g u r e 13a Ensemble Averaged C y c l i c V a r i a t i o n I n t e n s i t i e s / T i m e , One Stroke 81 F i g u r e 13b Ensemble Averaged C y c l i c V a r i a t i o n I n t e n s i t i e s / D e g r e e Crank Angle, One Stroke 82 F i g u r e 14a Example of C y l i n d e r Pressure Trace, One Stroke 83 F i g u r e 14b Example of C y l i n d e r Pressure Trace, Two Strokes 84 F i g u r e 15a Example of Mass F r a c t i o n Burned Curves, One Stroke 85 F i g u r e 15b Example of Mass F r a c t i o n Burned Curves, Two Strokes 85 F i g u r e 16 Pressure Trace Averaged versus Mass F r a c t i o n Burned Averaged 87 F i g u r e 17 Ensemble Averaged Mass F r a c t i o n Burned Curves, One and Two Strokes 88 F i g u r e 18 Pressure Increase due to Combustion and C a l c u l a t e d Mass F r a c t i o n Burned 89 F i g u r e 19 V a l v i n g on the d r i v i n g s i d e of the Rapid Intake and Compression Machine 127 F i g u r e 20 V a l v i n g on the b r a k i n g s i d e of the Rapid Intake and Compression Machine 128 F i g u r e 21 Schematic of the Approximation of Change i n Pressure 135 F i g u r e 22 Schematic of the Change in Turbulence I n t e n s i t y due to Compression and Decay 136 - i x -ACKNOWLEDGEMENT: The presented work would not have been p o s s i b l e without the c o n t r i b u t i o n s of my s u p e r v i s o r Dr.R.Evans, r e s e a r c h a s s i s t a n t A.Jones and the machining s k i l l s of J.Hoar, L.Drakes and B.Hansen, a l l of whom I would l i k e to thank here. I would a l s o l i k e to thank Drs.Daneshyar, Hauptmann and H i l l f o r t h e i r v a l u a b l e c o n t r i b u t i o n s i n v a r i o u s d i s c u s s i o n s . -X-NOMENCLATURE: M T Prong T 9 T W a l l U(t,n) 0 ( t w , n ) 0(t,n) u(t,n) u'(t,n) 0 E ( t ) u £ ( t ) U c ( t , n ) U£<t> 0 ( 5 ,n) u c (6,n) U E ( e ) O E ( 0 ) mean wire temperature, prong temperature, bulk gas temperature, c y l i n d e r w a l l temperature, instantaneous gas v e l o c i t y of run n at time t , window averaged mean v e l o c i t y of run n at time t w , i n t e r p o l a t e d mean v e l o c i t y of run n at time t , f l u c t u a t i n g v e l o c i t y of run n at time t , turbule n c e i n t e n s i t y of run n at time t , ensemble averaged mean v e l o c i t y at time t , ensemble averaged t u r b u l e n c e inten500y at time t , c y c l i c v a r i a t i o n v e l o c i t y of run n at time t, c y c l i c v a r i a t i o n i n t e n s i t y at time t , mean v e l o c i t y of run n at crank angle 6, c y c l i c v a r i a t i o n v e l o c i t y of run n at crank angle 6, c y c l i c v a r i a t i o n i n t e n s i t y at crank angle 8, ensemble averaged mean v e l o c i t y at crank angle 6, - x i -u'(8rn) t u r b u l e n c e i n t e n s i t y of run n a t crank a n g l e 8, u E ( c 5 ) ensemble averaged t u r b u l e n c e i n t e n s i t y a t crank a n g l e 8, T time a v e r a g i n g window, N number of r u n s , k t h e r m a l c o n d u c t i v i t y of the w i r e , A c r o s s s e c t i o n a l a r e a of the w i r e , d w i r e d i a m e t e r , h mean c o n v e c t i v e heat t r a n s f e r c o e f f i c i e n t , I w i r e c u r r e n t , p w i r e r e s i s t i v i t y , 1 w i r e l e n g t h , R w i r e r e s i s t e n c e , Nu N u s s e l t number, k „ c o n d u c t i v i t y of the gas, gas Re Reynolds number, v gas v e l o c i t y , v k i n e m a t i c v i s c o s i t y of the gas, A,B,n w i r e c a l i b r a t i o n c o n s t a n t s , dQ heat exchange w i t h the w a l l i n time increment d t , AR s u r f a c e a r e a exposed t o heat t r a n s f e r , BO c y l i n d e r b o r e , a,b,c heat t r a n s f e r e q u a t i o n c o n s t a n t s , M f b ( t , n ) mass f r a c t i o n burned a t time t of run n, - x i i -Mfb(t) ensemble averaged mass f r a c t i o n burned at time t , P(t,n) c y l i n d e r pressure at time t of run n, P(t) ensemble averaged c y l i n d e r p r e s s u r e at time t, -1-1 INTRODUCTION: T r a n s p o r t a t i o n of people and goods i s a key f a c t o r i n d i v e r s i f i e d s o c i e t i e s . Our present t r a n s p o r t a t i o n systems are mostly powered by i n t e r n a l combustion engines, which use f u e l s d e r i v e d from crude o i l . The p o l i t i c a l s i d e of t h i s dependence on crude o i l was r e a l i z e d by the p u b l i c i n 1973 dur i n g the s o - c a l l e d " O i l - C r i s i s " , when a part of the supply of crude o i l seemed to become u n c e r t a i n and p r i c e s i n c r e a s e d d r a s t i c a l l y . I t was then that many a l t e r n a t e - f u e l s programmes came i n t o being. Emission c o n t r o l measures can be another reason to c o n s i d e r f u e l s with d i f f e r e n t p r o p e r t i e s . N a t u r a l gas, mainly c o n s i s t i n g of methane, i s one a l t e r n a t i v e f u e l f o r i n t e r n a l combustion engines i n c o u n t r i e s that e i t h e r have n a t u r a l gas f i e l d s or import methane i n s u f f i c i e n t q u a n t i t i e s . Conversion k i t s are a v a i l a b l e f o r SI engines, which enable the engine to run e i t h e r on g a s o l i n e or on n a t u r a l gas. Since present SI engines are designed f o r the use of g a s o l i n e , they do not achieve the performance p o s s i b l e with a m o d i f i e d engine, when running on n a t u r a l gas. In order to modify the SI engine f o r the optimum use of t h i s new f u e l , a good understanding of the r e l a t i o n between engine and f u e l i s e s s e n t i a l . One major disadvantage of n a t u r a l gas i s i t s slower burning v e l o c i t y i n comparison to g a s o l i n e , causing a decrease i n e f f i c i e n c y . The e f f i c i e n c y decreases because the -2-combustion process moves away from a constant-volume combustion towards a c o n s t a n t - p r e s s u r e combustion, with the constant-volume process having a higher e f f i c i e n c y than the co n s t a n t - p r e s s u r e process, Van Wylen and Sonntag [ 1 ] , Turbulence i n the combustion chamber i s known to i n c r e a s e the burning v e l o c i t y , Lancaster and K r i e g e r [ 2 ] , Thus by enhancing the tu r b u l e n c e i n s i d e the combustion .engine the r a t e of combustion can be i n c r e a s e d . Besides i n c r e a s i n g the e f f i c i e n c y , f a s t e r combustion can a l s o reduce the problem of knock because any gas pockets that otherwise might a u t o - i g n i t e due to i n c r e a s i n g p r essure and temperature are consumed by the flame before they have the time to a u t o - i g n i t e . The c y c l e - b y - c y c l e f l u c t u a t i o n i n the combustion p r e s s u r e of a r e c i p r o c a t i n g combustion engine i s b e l i e v e d to be r e l a t e d to the flow c o n d i t i o n s i n s i d e the combustion chamber as w e l l , Winsor and Pa t t e r s o n [3]. Reduced c y c l e - b y - c y c l e f l u c t u a t i o n s would allow engine o p e r a t i o n with leaner mixtures, which i s d e s i r a b l e i n terms of engine emissions and f u e l e f f i c i e n c y . At the present time the mechanism by which the flow motion a f f e c t s the combustion process i s not yet f u l l y understood. -3-1.1 REVIEW OF PREVIOUS WORK Semenov [4] was the f i r s t t o p u b l i s h a comprehensive study on the f l o w c o n d i t i o n s i n s i d e - a combustion e n g i n e . He used a temperature-compensated hot w i r e anemometer t o measure t h e f l o w f i e l d i n a o n e - c y l i n d e r CFR engine d u r i n g the i n t a k e and compression s t r o k e . Large v e l o c i t y g r a d i e n t s d u r i n g the i n t a k e p r o c e s s l e d him t o the c o n c l u s i o n t h a t the v e l o c i t y g r a d i e n t s c r e a t e d by the i n t a k e j e t a r e the main s o u r c e s of t u r b u l e n c e d u r i n g the compre s s i o n s t r o k e . D e s p i t e the r a p i d decay of t u r b u l e n t motion due t o v i s c o s i t y he found the t u r b u l e n t energy per u n i t volume t o re a c h a maximum around t o p dead c e n t r e , which i s caused by the decrease i n c y l i n d e r volume d u r i n g the co m p r e s s i o n s t r o k e . D i s a b l i n g the v a l v e s , Semenov found t h a t i n a compre s s i o n s t r o k e f o l l o w i n g a c y c l e w i t h o u t the i n t a k e p r o c e s s the t u r b u l e n t f l u c t u a t i o n s almost d i s a p p e a r near t o p dead c e n t r e and the f l o w has o n l y about 10% of the k i n e t i c energy of a normal c y c l e . L a n c a s t e r [5] used a m o d i f i e d t r i - a x i a l hot w i r e probe w i t h a thermocouple i n a CFR e n g i n e . L o o k i n g at the d i r e c t i o n a l components of the f l o w , he found a n i s o t r o p i c c o n d i t i o n s d u r i n g the i n t a k e s t r o k e and e a r l y p o r t i o n of the com p r e s s i o n s t r o k e . D u r i n g c o m p r e s s i o n the t u r b u l e n c e tended toward i s o t r o p y and reached i s o t r o p y near t o p dead c e n t r e . -4-Witze [6] employed an L-head Wisconsin engine and a s i n g l e wire probe, i n v e s t i g a t i n g the s p a t i a l d i s t r i b u t i o n of t u r b u l e n c e . He found the t u r b u l e n t s t r u c t u r e to be inhomogeneous in the c l e a r a n c e volume. The measured i n c r e a s e in mean v e l o c i t y and t u r b u l e n c e d u r i n g compression was a t t r i b u t e d to the p i s t o n motion e n l a r g i n g the intake generated turbulence v i a compression e f f e c t s and a d d i t i o n a l bulk gas motion. Turbulence p r o d u c t i o n by the s q u i s h motion was concluded to be i n s i g n i f i c a n t i n comparison to the compression stroke enhancement of intake generated t u r b u l e n c e . C a t a n i a and M i t t i c a [ 7 ] , using a standard hot wire anemometer i n a s i n g l e - c y l i n d e r d i r e c t - i n j e c t i o n D i e s e l engine, found the t u r b u l e n c e to tend toward i s o t r o p y d u r i n g the l a s t p a r t of the i n t a k e process and the main part of compression, based on changing the wire o r i e n t a t i o n from 0 to 45 to 90 ° with r e s p e c t to the c y l i n d e r a x i s . V a r y i n g the s i z e of the averaging window i n t h e i r data r e d u c t i o n technique, p r a c t i c a l l y i d e n t i c a l r e s u l t s were obtained f o r the mean v e l o c i t y with windows between 4 and 16 degree crank a n g l e . The t u r b u l e n c e i n t e n s i t y estimate d i d not vary c o n s i d e r a b l y f o r window s i z e s between 8 and 20 degree crank a n g l e . E l i m i n a t i n g some of the inherent shortcomings of the i n t r u s i v e hot wire anemometer measurement technique, l a s e r doppler v e l o c i m e t r y has become a popular i n v e s t i g a t i v e t o o l . -5-Using t h i s r e l a t i v e l y new technique i n an L-head engine, Rask [8] concluded that c y c l e - b y - c y c l e a n a l y s i s i s important in order to separate c y c l i c v a r i a t i o n from t u r b u l e n t f l u c t u a t i o n s . The turbulence was found to be p r a c t i c a l l y constant d u r i n g the compression s t r o k e . L i o u and S a n t a v i c c a [9] used l a s e r doppler v e l o c i m e t r y i n a CFR engine with a f l a t d i s k combustion chamber with and without s w i r l . In order to allow f o r o p t i c a l a c c e s s , the engine was equipped with a t r a n s p a r e n t head and p o r t s i n the c y l i n d e r w a l l s f o r the gas exchange. The t u r b u l e n c e i n t e n s i t y was found to be r e l a t i v e l y homogeneous near top dead c e n t r e with and without s w i r l , and to i n c r e a s e with s w i r l . During the compression stroke the t u r b u l e n c e i n t e n s i t y decreased with and without s w i r l . Comparing t h e i r r e s u l t s t o the ones from v a l v e d engines, they support the hypothesis that the t u r b u l e n c e at top dead c e n t r e i s r e l a t i v e l y i n s e n s i t i v e to the d e t a i l s of the i n t a k e p r o c e s s . 1.2 OBJECTIVE OF THIS WORK: Depending on the engine geometry and o p e r a t i n g c o n d i t i o n s , r e s e a r c h e r s have found the t u r b u l e n c e i n t e n s i t y to i n c r e a s e [4,..6], remain f a i r l y constant [5,7,8,36] or to decrease [9,37] d u r i n g the compression s t r o k e of a r e c i p r o c a t i n g i n t e r n a l combustion engine. The flow f i e l d around top dead c e n t r e a f t e r compression c o n s i s t s of flow generated d u r i n g the intake p r o c e s s , subject to decay due to -6-v i s c o u s a c t i o n and s u b j e c t t o change due t o c o m p r e s s i o n , and of f l o w g e n e r a t e d d u r i n g the compre s s i o n s t r o k e by the p i s t o n m o t i o n . No one has so f a r been a b l e t o determine e x p e r i m e n t a l l y how much f l o w a c t i v i t y the compre s s i o n s t r o k e by i t s e l f g e n e r a t e s , s t a r t i n g w i t h the gas a t r e s t . Semenov [4] has come c l o s e s t by d i s a b l i n g the v a l v e s and l o o k i n g a t the p i s t o n - i n d u c e d f l o w m o t i o n , y e t i n h i s experiment the gas i n s i d e the c y l i n d e r i s not a t r e s t b e f o r e c o m p r e s s i o n . Adding s q u i s h can be e x p e c t e d t o a l t e r the f l o w f i e l d as w e l l . The o b j e c t i v e of t h i s work was t o dete r m i n e the r e l a t i v e r o l e s of the i n t a k e and compre s s i o n s t r o k e s i n g e n e r a t i n g t u r b u l e n c e i n the combustion chamber and t o examine the e f f e c t s of the t u r b u l e n c e on combustion d u r a t i o n . T h i s was done by o b t a i n i n g c o m p a r a t i v e e x p e r i m e n t a l d a t a of the t u r b u l e n c e i n t e n s i t y and combustion d u r a t i o n f o r the i n t a k e and co m p r e s s i o n s t r o k e and f o r the compression s t r o k e by i t s e l f i n a o n e - c y l i n d e r s p a r k - i g n i t e d r a p i d i n t a k e and compression machine w i t h a f l a t - d i s k combustion chamber, r u n n i n g on a methane-air m i x t u r e under d e f i n e d o p e r a t i n g c o n d i t i o n s . I t s h o u l d be noted t h a t u s i n g a f l a t - d i s k combustion chamber w i t h o u t s q u i s h s h o u l d be ta k e n o n l y as the f i r s t s t e p i n a s e r i e s of d i f f e r e n t e x p e r i m e n t s i n which s q u i s h and p o s s i b l y s w i r l a r e g r a d u a l l y i n t r o d u c e d and t h e i r e f f e c t on the combustion d u r a t i o n i n v e s t i g a t e d . -7-2 EXPERIMENTAL APPARATUS Since i t i s very d i f f i c u l t to s t a r t and stop a running combustion engine w i t h i n m i l l i s e c o n d s , i t was decided to b u i l d a machine capable of s i m u l a t i n g the intake and compression stroke under e n g i n e - l i k e c o n d i t i o n s at 1000 r e v o l u t i o n s per minute, s t a r t i n g from and sto p p i n g at zero v e l o c i t y . Such an engine would a l s o allow c l o s e c o n t r o l of the engine o p e r a t i o n parameters such as in t a k e m a n i f o l d p r e s s u r e , simulated r e v o l u t i o n s , mixture composition and i g n i t i o n t i m i n g . I t was c a l l e d a r a p i d i ntake and compression machine i n analogy t o machines used to study the i g n i t i o n temperature of f u e l s under near a d i a b a t i c r a p i d compression. A b r i e f h i s t o r y of these machines i s given here. 2.1 HISTORY OF THE RAPID COMPRESSION MACHINE: The f i r s t use of an " A d i a b a t i c Compression Apparatus" was r e p o r t e d by F a l k [10] i n 1906, i n v e s t i g a t i n g the i g n i t i o n temperature of homogeneous hydrogen-oxygen mixtures. A f a l l i n g weight drove a p i s t o n i n t o a v e r t i c a l c y l i n d e r with a bore of 25 mm and 44 mm i n a second apparatus. I t d i d not i n c o r p o r a t e an a r r e s t mechanism, so that the p i s t o n and the weight were d r i v e n back up by the pre s s u r e due to combustion of the compressed mixture. N e g l e c t i n g i g n i t i o n d e l a y and i n e r t i a of the moving p a r t s , the i g n i t i o n temperature was c a l c u l a t e d from the i n i t i a l -8-c o n d i t i o n s and the po i n t of rebound, which was measured by a s l i p - r i n g on the p i s t o n rod. One year l a t e r Falk [11] p u b l i s h e d r e s u l t s obtained by the same method using d i f f e r e n t gas mixtures. In 1914 Dixon, Bradshaw and Cambell [12] r e p o r t e d experiments about "The F i r i n g of Gases by A d i a b a t i c Compression", i n which they used a f a l l i n g pendulum, which drove a p i s t o n h o r i z o n t a l l y i n t o a g l a s s tube, which was f i l l e d w ith premixed gases. The compression r a t i o c o u l d be v a r i e d by stopping the pendulum at v a r i o u s l o c a t i o n s by means of a wooden blo c k . Using a g l a s s tube, which ruptured upon pressure r i s e due to the combustion, they were able to take flame photographs. In a second p a r t under the same t i t l e Dixon and C r o f t s [13] d e s c r i b e a second r a p i d compression machine, i n which a f a l l i n g weight d r i v e s a p i s t o n v e r t i c a l l y i n t o a c y l i n d e r , f o l l o w i n g F a l k ' s concept. In 1922 and 1926 T i z a r d and Pye [14] p u b l i s h e d t h e i r i n v e s t i g a t i o n of the a u t o - i g n i t i o n of premixed gases i n a r a p i d compression machine, i n which an a r r e s t i n g c l u t c h , d r i v e n by a f l y w h e e l , drove the p i s t o n and was r e l e a s e d at top dead c e n t e r . With a p i s t o n diameter of 3 inches ([21] quotes 4.5 inches) and a s t r o k e of 8 inches they achieved a compression time of about 140 ms. -9-Between 1939 and 1943 J o s t and Roegener [15] and Scheuermayer and S t e i g e r w a l d [16] repo r t e d experiments using compressed a i r to d r i v e the p i s t o n and a r r e s t i n g the p i s t o n at the end of the compression stroke m e c h a n i c a l l y . P i s t o n v e l o c i t i e s of up to 60 m/s c o u l d be achieved, but stopping the p i s t o n without rebound or mechanical f r a c t u r e was a s e r i o u s problem. The M.I.T. r a p i d compression machine from 1948, Leary et a l . [17] and T a y l o r [18], overcame t h i s problem by using a gas c u s h i o n i n g d e v i c e to brake and a r r e s t the p i s t o n . Thus compression times of l e s s than 10 ms c o u l d be achieved without p i s t o n damage. Ni t r o g e n was used to d r i v e and brake the d r i v i n g p i s t o n , i n - l i n e with the compression p i s t o n . In 1961 Rogowski [19] designed another M.I.T. r a p i d compression machine with three p i s t o n s i n t h r e e c y l i n d e r s arranged along a common s h a f t . One p i s t o n was d r i v e n p n e u m a t i c a l l y ; one p i s t o n moved through h y d r a u l i c f l u i d i n a s o - c a l l e d snubbing chamber, thus c o n t r o l l i n g the speed and br a k i n g , and the t h i r d p i s t o n compressed the mixture under i n v e s t i g a t i o n . With a bore of 4 inches and a str o k e of 18 inches the compression time was about 30 ms. The sh a f t was a r r e s t e d m e c h a n i c a l l y at the end of compression to ensure constant-volume combustion. The same p r i n c i p l e , i f not the i d e n t i c a l machine, was used by R i f e and Heywood [20], 1974, s t u d y i n g d i e s e l combustion, and Matekunas [21], 1979,who looked at SI engine -10-combust i o n . Beeley, G r i f f i t s and Gray [22], 1980, e x p e r i m e n t a l l y a n a l y s i n g the spontaneous i g n i t i o n of i s o p r o p y l n i t r a t e , a l s o used the same p r i n c i p l e with a s l i g h t l y d i f f e r e n t p i s t o n arrangement and achieved a compression time of 25 ms with a 193 mm s t r o k e . In 1969 A f f l e c k and Thomas [23] p u b l i s h e d a study on preflame r e a c t i o n s u s i n g an opposed-piston r a p i d compression machine, i n which two p i s t o n s , coming from o p p o s i t e s i d e s , compressed the a i r - f u e l mixture. Both p i s t o n s , using Rogowski's idea, were d r i v e n p n e u m a t i c a l l y and speed c o n t r o l l e d and stopped by h y d r a u l i c means with an i n - l i n e d e s i g n . With a p i s t o n diameter of 1.5 inches they reached compression times of about 10 ms. Zigan [24], 1977, l o o k i n g at D i e s e l combustion, used compressed a i r to d r i v e a d r i v i n g p i s t o n , which was mounted on a common s h a f t with the compression p i s t o n . A mechanical device was used f o r b r a k i n g . For a s t r o k e of up to 750 mm a time f o r compression of about 130 ms was measured. A l a r g e r a p i d compression machine was used by Kaminoto et a l . [25], 1981, to study D i e s e l combustion with a bore of 200 mm and a stroke of 560 mm. Again, u s i n g Rogowski's concept, i t was d r i v e n by compressed n i t r o g e n and c o n t r o l l e d h y d r a u l i c a l l y with three p i s t o n s on one s h a f t i n - l i n e . V i b r a t i o n problems l i m i t e d the compression time t o 150 to -11-160 ms. A d i f f e r e n t k i n d of r a p i d c o m p r e s s i o n machine was used by Ikegami et a l . [ 2 6 ] , 1981, i n t h e i r study of i g n i t i o n and combustion of a D i e s e l s p r a y , i n which a v e r y l i g h t f r e e p i s t o n w i t h 50 mm d i a m e t e r was d r i v e n by compressed n i t r o g e n and stopped a f t e r a s t r o k e of up t o 300 mm by ramming i n t o a s t o p p e r - r i n g . Due t o the damage t h a t t h i s s t o p p i n g p r o c e d u r e caused, the p i s t o n crown had t o be r e p l a c e d a f t e r each e x p e r i m e n t . U s i n g a b u r s t i n g diaphram between the p r e s s u r i z e d n i t r o g e n and the p i s t o n t o s t a r t the m o t i o n , a c o m p r e s s i o n time of about 10 ms i s r e p o r t e d . Kono et a l . [ 2 7 ] , 1983, e x p e r i m e n t a l l y d e t e r m i n i n g knock i n t e n s i t y , a l s o used a b u r s t i n g diaphram on the pneumatic d r i v i n g s i d e t o i n i t i a t e the m o t i o n . B r a k i n g and. s t o p p i n g was done by m e c h a n i c a l means. The time of c o m p r e s s i o n was found t o be around 10 ms. A l l the r a p i d compression machine's d e s c r i b e d so f a r can o n l y do one s t r o k e , namely the compression s t r o k e . In 1984 Hayasui e t a l . [28] p u b l i s h e d a p h o t o g r a p h i c i n v e s t i g a t i o n of the knock phenomena, done w i t h a r a p i d c o m p r e s s i o n and e x p a n s i o n machine, d e v e l o p e d a t Toyota's C e n t r a l R e s e a r c h and Development L a b o r a t o r i e s . T h i s s o p h i s t i c a t e d new type of machine can do up t o f i v e c o n t i n u o u s r e c i p r o c a t i o n s of c o m p r e s s i o n and e x p a n s i o n s t r o k e s , s i m u l a t i n g an e q u i v a l e n t e n g ine r e v o l u t i o n of up t o 1200 rpm w i t h a maximun p i s t o n v e l o c i t y of 5 m/s. -12-Compression and d r i v i n g p i s t o n are i n - l i n e with the d r i v i n g p i s t o n being moved h y d r a u l i c a l l y with pressure from a r e s e r v o i r a p p l i e d on e i t h e r s i d e . Fast response s o l e n o i d v a l v e s and an e l e c t r o n i c c o n t r o l system c o n t r o l the p i s t o n motion. The c y l i n d e r bore was 85 mm with a str o k e of 90 mm. Intake and exhaust v a l v e s c o u l d be o p t i o n a l l y i n s t a l l e d , thus e n a b l i n g the machine to simulate the f u l l f o u r - s t r o k e engine c y c l e or any d e s i r e d p a r t of i t . Even though r a p i d compression machines have been used as r e s e a r c h t o o l s f o r q u i t e some time, the one designed and b u i l t f o r the present work i s unique i n the resp e c t that i t i s the f i r s t one to simulate the intake and compression s t r o k e of a r e c i p r o c a t i n g engine. 2.2 DESCRIPTION OF THE RAPID INTAKE AND COMPRESSION MACHINE Since i t i s c o n s i d e r a b l y e a s i e r to c o n t r o l a t r a n s l a t i o n a l motion along one l i n e without motion r e v e r s a l , the concept of an i n - l i n e t r a n s l a t i o n a l d r i v e t r a i n was chosen, using a crank s h a f t to t r a n s f e r the t r a n s l a t o r y i n t o a r o t a t i o n a l motion. F i g u r e 1 shows a schematic of the r a p i d intake and compression machine. The machine i s d r i v e n by the pneumatic d r i v i n g c y l i n d e r on the r i g h t hand s i d e , which i s p r e s s u r i z e d from a separate pressure tank. The c y l i n d e r rod d r i v e s a rack, which runs through the crank box of the r a p i d intake and compression machine. The c y l i n d e r rod of the -13-h y d r a u l i c b r a k i n g c y l i n d e r i s a t t a c h e d t o the o t h e r s i d e of the r a c k . The movement and thus speed of the rack i s c o n t r o l l e d by c o n t r o l l i n g the amount of f l u i d r e l e a s e d from the h y d r a u l i c b r a k i n g c y l i n d e r . The h y d r a u l i c system i n i t i a l l y b e i n g c l o s e d , the pneumatic s i d e can be p r e s s u r i z e d w i t h o u t r a c k movement. T h i s h e l p s t o ensure f a s t a c c e l e r a t i o n . Movement i s i n i t i a t e d by t r i g g e r i n g a s o l e n o i d v a l v e on t h e h y d r a u l i c s i d e , which r e l e a s e s a s m a l l amount of f l u i d above a c a r t r i d g e v a l v e , thus e n a b l i n g the c a r t r i d g e v a l v e t o move and open l a r g e f l o w a r e a s f o r f a s t a c c e l e r a t i o n . The f l u i d i s f o r c e d t h r o u g h an o r i f i c e t o c o n t r o l t h e maximum v e l o c i t y the r a c k can r e a c h . B r a k i n g s t a r t s w i t h i n a p p r o x i m a t e l y 20 mm from the end of the rack s t r o k e on the h y d r a u l i c s i d e . A p i n on the h y d r a u l i c p i s t o n moves i n t o the o u t f l o w h o l e , r e s t r i c t i n g the f l o w and thus r e d u c i n g t h e amount of f l u i d r e l e a s e d . The geometry of the b r a k i n g p i n was s e l e c t e d w i t h the a i d of a b r a k i n g s i m u l a t i o n programme. F i g u r e 2 shows the c r a n k box of the r a p i d i n t a k e and c o m p r e s s i o n machine. The r a c k , r u n n i n g t h r o u g h the crank box, d r i v e s a p i n i o n , which i s mounted a t the end of a crank s h a f t . The c r a n k s h a f t i n t u r n moves a p i s t o n v i a a c o n n e c t i n g r o d . S t a r t i n g w i t h the rack a t the b e g i n n i n g of i t s s t r o k e , the r a p i d i n t a k e and c o m p r e s s i o n machine w i l l p e r f o r m the i n t a k e and c ompression s t r o k e , w h i l e s t a r t i n g w i t h the rack -14-h a l f way down the rack s t r o k e , the machine w i l l p e r f o r m the compres s i o n s t r o k e o n l y . I f d e s i r e d , any s t a r t i n g p o s i t i o n between b e g i n n i n g and end of the rack s t r o k e can be chosen. By c h a n g i n g the gear s e t t i n g between rack and crank s h a f t , any c o m b i n a t i o n of s t r o k e s can be s i m u l a t e d , as l o n g as they c o v e r 382 c o n s e c u t i v e degrees cr a n k a n g l e . G i v e n a c o n s t a n t rack v e l o c i t y , the crank s h a f t w i l l r o t a t e a t a c o n s t a n t rpm. Wi t h the g i v e n d i m e n s i o n s a ra c k v e l o c i t y of a p p r o x i m a t e l y 4 m/s t r a n s l a t e s i n t o 1000 rpm crank s h a f t r e v o l u t i o n s . The p i s t o n crown i s removable f o r easy change of combustion chamber geometry. A f l a t d i s k combustion chamber was used f o r the p r e s e n t e x p e r i m e n t s . The compres s i o n r a t i o can be v a r i e d by r e p l a c i n g a r i n g . In the p r e s e n t work a c o n s t a n t c o m p r e s s i o n r a t i o of 8.0 was used w i t h a c l e a r a n c e h e i g h t of a p p r o x i m a t e l y 14.3 m i l l i m e t e r a t t o p dead c e n t r e . T a b l e 1 g i v e s some b a s i c d i m e n s i o n s of the r a p i d i n t a k e and c o m p r e s s i o n machine. F i g u r e 3 shows the i n t a k e v a l v e d r i v e t r a i n which o p e r a t e s t h e i n t a k e v a l v e . A p l a t e i s mounted on the r a c k , i n t o which a groove was m i l l e d w i t h a n u m e r i c a l l y c o n t r o l l e d machine. A p i n runs i n t h i s g r o o v e , f o r c i n g a s m a l l p l a t e t o f o l l o w i t s l i f t , t hus p u s h i n g the push r o d , the r o c k e r arm, the v a l v e cap and the i n t a k e v a l v e . The v a l v e l i f t c h a r a c t e r i s t i c s were taken from the R i c a r d o Hydra engine a t the Department of M e c h a n i c a l E n g i n e e r i n g a t -15-UBC, but problems w i t h the d i s c o n n e c t i o n of the i n t a k e v a l v e d r i v e t r a i n r e s u l t e d i n an i n c r e a s e i n v a l v e p l a y . With a s m a l l v a l v e p l a y the i n t a k e v a l v e would bounce and s h o r t l y reopen d u r i n g the p r o c e s s of v a l v e d r i v e t r a i n d i s c o n n e c t i o n . The problem was reduced by i n c r e a s i n g the v a l v e p l a y . The v a l v e t i m i n g and l i f t a r e l i s t e d i n T a b l e 1. The p o s i t i o n of the i n t a k e v a l v e i n the c y l i n d e r head i s d e s i g n e d such t h a t p a r t of the c y l i n d e r head t o p c o u l d be r e p l a c e d by a q u a r t z g l a s s window e n a b l i n g o p t i c a l a c c e s s t o h a l f of t h e combustion chamber. A s l o t t e d d i s k i s mounted on t h e upper end of the crank s h a f t w i t h an o p t i c a l p i c k - u p d e v i c e a t the s i d e . I t reads a s t e p w i s e v o l t a g e change ev e r y two degrees crank a n g l e , which g i v e s the r e f e r e n c e w i t h r e s p e c t t o crank s h a f t p o s i t i o n and p i s t o n p o s i t i o n f o r the r e c o r d e d d a t a . A c c e s s t o the combustion chamber f o r the h o t - w i r e probe i s from t h r e e s i d e s h a l f way between p i s t o n t o p and c y l i n d e r head a t t h e t o p dead c e n t r e p o s i t i o n , see a l s o F i g u r e 6. A p r e s s u r e t r a n s d u c e r i s mounted i n the c y l i n d e r head i n o r d e r t o r e a d the c y l i n d e r p r e s s u r e . For the combustion t e s t s a spark p l u g w i t h c e n t r a l spark p l u g p o s i t i o n was used. An o p t i c a l p i c k - u p was used t o t r i g g e r the d a t a a c q u i s i t i o n system, which i n t u r n was a c t i v a t e d by a s m a l l p l a t e a t t a c h e d t o the r a c k . T h i s way the d a t a r e c o r d i n g s t a r t e d a t a s e t r a c k l o c a t i o n w i t h known r e f e r e n c e t o degrees c r a n k a n g l e . -16-F i g u r e 4 shows the r a c k v e l o c i t y v e r s u s degrees crank a n g l e i n the upper graph and the a c t u a l p i s t o n v e l o c i t y ( d o t t e d l i n e ) and the i d e a l p i s t o n v e l o c i t y ( s o l i d l i n e ) a t 1000 rpm v e r s u s degrees crank a n g l e i n the lower graph f o r the i n t a k e and compression s t r o k e . At the b e g i n n i n g and the end of the r a c k t r a v e l i t runs s l o w e r than the d e s i r e d v e l o c i t y of 4 m/s and compensates f o r t h a t by r u n n i n g s l i g h t l y f a s t e r i n between. The i n i t i a l l e v e l i n g o f f of the rack v e l o c i t y between a p p r o x i m a t e l y 15 t o 45 degrees crank a n g l e i s most l i k e l y due t o some p r e s s u r e l o s s on the p r e s s u r e s i d e of the pneumatic d r i v i n g c y l i n d e r , s i n c e the c y l i n d e r volume on t h a t s i d e i s s m a l l a t the b e g i n n i n g of the rack s t r o k e and a i r f l o w i n from the p r e s s u r e tank has t o be e s t a b l i s h e d . As can be seen i n the lower graph of F i g u r e 4 the a c t u a l p i s t o n v e l o c i t y i s lower than the i d e a l one d u r i n g the f i r s t and l a s t - a p p r o x i m a t e l y 90 degrees crank a n g l e of the p i s t o n t r a v e l and s l i g h t l y h i g h e r between a p p r o x i m a t e l y 90 t o 270 degrees c r a n k a n g l e . The o v e r a l l time of r a c k t r a v e l i s a p p r o x i m a t e l y 75 m i l l i s e c o n d s f o r the i n t a k e and the c o m p r e s s i o n s t r o k e t o g e t h e r . F i g u r e 5 shows the rack v e l o c i t y v e r s u s degrees crank a n g l e and t h e a c t u a l ( d o t t e d l i n e ) and i d e a l p i s t o n v e l o c i t y ( s o l i d l i n e ) v e r s u s degrees cr a n k a n g l e f o r the one s t r o k e c a s e , namely compression s t r o k e o n l y . A g a i n the a c t u a l p i s t o n v e l o c i t y i s l e s s than the i d e a l one a t the b e g i n n i n g and the end of the run and i s s l i g h t l y h i g h e r i n between. -17-The o v e r a l l time of rack t r a v e l i s a p p r o x i m a t e l y 40 m i l l i s e c o n d s f o r the compression s t r o k e o n l y . -18-3 EXPERIMENTS In order to be able to determine the e f f e c t of the flow c o n d i t i o n s on the combustion d u r a t i o n i t was necessary to o b t a i n data of both the flow f i e l d and the combustion. Thus two s e r i e s of experiments were run, one i n which the instantaneous gas v e l o c i t y i n s i d e the combustion chamber was measured i n a i r , using hot-wire anemometry, and the other i n which a combustible mixture was drawn i n , i g n i t e d and the pressure t r a c e recorded. Both compression s t r o k e only and in t a k e and compression stroke were run f o r both s e r i e s . U s u a l l y 10 repeated runs were made f o r each t e s t . The i n i t i a l p r e s sure f o r the two-stroke experiments i n the small tank, out of which the gas was drawn during the intake process, was ambient p r e s s u r e . The i n i t i a l pressure i n the c y l i n d e r at bottom dead c e n t r e f o r the one stroke experiments was set to be 381 mm Hg so that the pre s s u r e s at top dead c e n t r e f o r the one and the two stroke cases would be as c l o s e as p o s s i b l e . The value of 381 mm Hg was found by t r i a l and e r r o r and used throughout the experiments. -19-3.1 HOT-WIRE ANEMOMETRY MEASUREMENTS 3.1.1 EQUIPMENT AND PROCEDURE Tabl e 2 g i v e s a l i s t of the h o t - w i r e anemometer equipment used. The w i r e s were spot welded, heat t r e a t e d and c a l i b r a t e d by the a u t h o r . The heat t r e a t m e n t took u s u a l l y 7 t o 8 hours and ensured t h a t the w i r e r e s i s t a n c e had s t a b i l i z e d and would not drop d u r i n g the e x p e r i m e n t s . The b r i d g e was b a l a n c e d a c c o r d i n g t o the D i s a manual and the anemometer c a l i b r a t e d i n a wind t u n n e l f o r a i r speeds between t y p i c a l l y 0.5 t o 16 m/s. The lower l i m i t comes from the i n s e n s i t i v i t y of the p i t o t tube and manometer t o re a d a t low v e l o c i t i e s and the upper l i m i t r e p r e s e n t s the maximum wind t u n n e l speed. The z e r o v e l o c i t y v o l t a g e r e a d i n g was not used f o r the c a l i b r a t i o n c u r v e , because buoyancy e f f e c t s due t o f r e e c o n v e c t i o n become i m p o r t a n t a t v e r y low v e l o c i t i e s . At low Reynolds numbers the N u s s e l t / R e y n o l d s number r e l a t i o n of e q u a t i o n (14) f o r f o r c e d c o n v e c t i o n does not h o l d , see C o l l i s and W i l l i a m s [ 3 4 ] . The w i r e was o p e r a t e d a t 600° C e l s i u s . The w i r e o r i e n t a t i o n i n s i d e the engine was always p a r a l l e l t o the p i s t o n t o p s u r f a c e s i n c e the main f l o w d i r e c t i o n was ex p e c t e d t o f o l l o w the p i s t o n m o t i o n . The w i r e o r i e n t a t i o n was not changed, because the t u r b u l e n c e i n t e n s i t y can be ex p e c t e d t o be i s o t r o p i c near t o p dead c e n t r e , Chapter 1.1. The gas v e l o c i t y was measured a t f i v e d i f f e r e n t l o c a t i o n s -20-i n s i d e the combustion chamber, as shown in F i g u r e 6. A l l l o c a t i o n s are i n one plane h a l f way between the p i s t o n top and the c y l i n d e r head at top dead c e n t r e . L o c a t i o n 1 i s s i t u a t e d i n the c e n t r e of the combustion chamber, l o o k i n g at i t from the top view. L o c a t i o n 3 and 5 are 10 mm away from the w a l l and l o c a t i o n s 2 and 4 are h a l f way between 1 and 3 and 1 and 5 r e s p e c t i v e l y . Measurement l o c a t i o n 1 i s exposed d i r e c t l y to the intake valve j e t d u r i n g the intake process. The bridge output v o l t a g e was f i l t e r e d with a D i s a f i l t e r at 20 kHz to a v o i d problems of a l i a s i n g . The value of 20 kHz was chosen because i t i s l e s s than h a l f of the data sampling frequency of 62.5 kHz and thus no a l i a s i n g should be expected, see Bendat and P i e r s o l [ 3 8 ] . Since the c o n d i t i o n s i n s i d e the combustion chamber vary r a p i d l y i n terms of temperature and d e n s i t y and are very d i f f e r e n t from the c a l i b r a t i o n c o n d i t i o n s i n the wind t u n n e l , the o r i g i n a l v e l o c i t y / v o l t a g e c a l i b r a t i o n curve can not be used d i r e c t l y to r e l a t e measured anemometer v o l t a g e s i n s i d e the engine to flow v e l o c i t y . The method used to overcome t h i s problem has been d e s c r i b e d i n d e t a i l by Cameron [29]. N e g l e c t i n g r a d i a t i o n , the heat t r a n s f e r equation f o r the sensor i s e s t a b l i s h e d as by Lancaster [ 5 ] , assuming a one-dimensional temperature d i s t r i b u t i o n along the wire, constant c o n d u c t i v i t y and heat t r a n s f e r -21-c o e f f i c i e n t and constant f l u i d p r o p e r t i e s along the wire: d 2T ( 1 ) -kA -+ 7rhd(T -T ) = I 2(p/A) dx 2 W 9 where: k = thermal c o n d u c t i v i t y of the wire A = c r o s s s e c t i o n a l area of the wire T w = l o c a l wire temperature d = wire diameter h = mean c o n v e c t i v e heat t r a n s f e r c o e f f i c i e n t Tg = bulk gas temperature I = wire c u r r e n t p = wire r e s i s t i v i t y . Assuming a symmetrical temperature p r o f i l e a long the wire l e n g t h , the boundary c o n d i t i o n s a r e : dT (2) — = 0 at x=0 dx and ( 3 ) TW = T P r o n g a t x = 1 / 2 with x=0 at the wire midpoint and 1 being the wire l e n g t h . The r e s i s t i v i t y i s assumed to have the form: (4) p = p 0 (1 + a (T - T 0 ) ) , where: a = temperature c o e f f i c i e n t of the wire r e s i s t i v i t y p 0 = r e f e r e n c e r e s i s t i v i t y -22-T 0 = r e f e r e n c e temperature p = r e s i s t i v i t y a t w i r e temperature T. From (E5) R = Jpdx i t f o l l o w s t h a t : (E6) R 0 = ( 4 p 0 D / ( 7 r d 2 ) where R 0 i s the r e f e r e n c e w i r e r e s i s t e n c e . The s o l u t i o n t o the heat t r a n s f e r e q u a t i o n E1 i s : (E7) T„ = T p r o n g C l c o s h C 2 x + C, w c o s h C 2 l / 2 where: (E8) C, = ( 7 r d l h T g + l 2 R 0 ( l - a T 0 ) ) / ( ?rdhl-I 2 R 0 a ) and (E9) C 2 = 4h/kd - ( 4 I 2 R 0 a ) / ( k l 7 r d 2 ) The mean w i r e t e m p e r a t u r e T M i s found by a v e r a g i n g the tem p e r a t u r e over the w i r e l e n g t h : 1/2 (E10) T M = ^ / T w d x ; -1/2 which y i e l d s : T —C ( E l 1) T M = 2 P r o n g t a n h ( C 2 l / 2 ) + C, M C 21 The w i r e p a r a m e t e r s a r e e i t h e r g i v e n by the s p e c i f i c a t i o n s of the w i r e p r o d u c e r o r by the w i r e o p e r a t i n g c o n d i t i o n s . -23-The gas p r o p e r t i e s were c a l c u l a t e d from the measured p r e s s u r e assuming p o l y t r o p i c c o m p r e s s i o n . E q u a t i o n (11) was used t o c a l c u l a t e the heat t r a n s f e r c o e f f i c e n t h i t e r a t i v e l y . The c a l i b r a t i o n c u r v e was i n i t i a l l y used t o e s t a b l i s h a r e l a t i o n between the N u s s e l t and the Reynolds numbers, d e f i n e d by: (12) Nu = h d / k g a s where k„ „ i s the c o n d u c t i v i t y of the gas and gas u (13) Re = vd/V where v i s the i n s t a n t a n e o u s gas v e l o c i t y and v i s the k i n e m a t i c gas v i s c o s i t y . The N u s s e l t / R e y n o l d s number r e l a t i o n was assumed t o be of the form: (14) Nu = A + B R e n where A,B and n a r e c o n s t a n t s d e t e r m i n e d by c u r v e f i t t i n g from the c a l i b r a t i o n c o n d i t i o n s . The form i n e q u a t i o n (14) assumes a c o n s t a n t P r a n d l number, as s t a t e d by H o r v a t i n and Hussman [ 3 1 ] , and a l s o n e g l e c t s the s o - c a l l e d temperature l o a d i n g f a c t o r d e r i v e d by C o l l i s and W i l l i a m s [ 3 4 ] . The l a t e r a s sumption i s j u s t i f i e d by the f a c t t h a t i t i s s m a l l due t o the n a t u r e of i t s exponent of -0.17. E q u a t i o n (14) was a l s o used i n t h i s form by W i t z e [6] and Cameron [ 2 9 ] . I t -24-should be noted t h a t , f o l l o w i n g Witzes recommendation, a l l gas p r o p e r t i e s were eva l u a t e d at the free-stream c o n d i t i o n s . Based on the computed heat t r a n s f e r c o e f f i c i e n t h the Nuss e l t number i s c a l c u l a t e d . The Reynolds number i s found from the N u s s e l t number using equation (14). The instantaneous gas v e l o c i t y i s f i n a l l y c a l c u l a t e d from the Reynolds number. 3.1.2 LIMITATIONS OF HOT-WIRE ANEMOMETRY IN INTERNAL  COMBUSTION ENGINES Two major problems are encountered using constant-temperature hot-wire anemometry i n i n t e r n a l combustion engines: o p e r a t i o n o u t s i d e of the c a l i b r a t i o n range and d i r e c t i o n a l ambiguity. In s i d e a r e c i p r o c a t i n g combustion engine the c y l i n d e r volume, p r e s s u r e and temperature vary r a p i d l y . I t i s not p r a c t i c a l to c a l i b r a t e a hot-wire anemometer f o r a l l the pressure/temperature c o n d i t i o n s i t w i l l encounter i n s i d e the combustion chamber, s i n c e the wire o p e r a t i n g l i f e time i s l i m i t e d due to the r e l a t i v e l y high o p e r a t i n g temperature needed so th a t the wire operates above the gas temperature i n s i d e the engine. Not only i s the anemometer operated under c o n d i t i o n s i t i s not c a l i b r a t e d f o r , but these c o n d i t i o n s are not known -25-a c c u r a t e l y . The gas p r o p e r t i e s i n s i d e the combustion chamber, i n p a r t i c u l a r the temperature, are p r e s e n t l y estimated from the measured pressure t r a c e assuming a p o l y t r o p i c r e l a t i o n with a p o l y t r o p i c exponent of 1.35. The v a l i d i t y of c a l c u l a t i n g the gas temperature from the pressure measurements through a p o l y t r o p i c r e l a t i o n has been demonstrated by Lancaster [ 5 ] , who measured the gas temperature with a 5.0 micrometer diameter r e s i s t a n c e thermometer and compared i t to v a l u e s c a l c u l a t e d from the pressure measurements. The value of 1.35, as a l s o used by Hor v a t i n and Hussman [31], seemed a reasonable compromise between assuming a d i a b a t i c c o n d i t i o n s , Witze [ 6 ] , and a l l o w i n g f o r some heat exchange with the w a l l s . In the present a n a l y s i s the f i r s t p r e s s u r e data reading was taken to correspond to ambient temperature and the known r e f e r e n c e p r e s s u r e , which was measured with a s e n s i t i v e manometer. From there on the gas p r o p e r t i e s f o r the intake and compression stroke and f o r the case of the compression stroke by i t s e l f were c a l c u l a t e d from the c y l i n d e r p r essure using the p o l y t r o p i c r e l a t i o n . T h i s a l s o a l l o w s f o r some temperature drop due to the expansion e f f e c t s d u r i n g the intake s t r o k e , while other r e s e a r c h e r s assumed ambient temperature at bottom dead c e n t r e , Cameron [29]. The temperature d i s t r i b u t i o n was assumed to be uniform throughout the measurement l o c a t i o n s , thus l i m i t i n g the heat exchange to a region very c l o s e to the w a l l s . Using a r e s i s t a n c e thermometer with a 8.0 micrometer wire, Semenov -26-[4] found t h a t the t h e r m a l boundary l a y e r was about 1.5 t o 2 mm t h i c k , j u s t i f y i n g the assumption of u n i f o r m b u l k gas t e m p e r a t u r e throughout the combustion chamber o u t s i d e the t h e r m a l boundary l a y e r . S i n c e the a c t u a l gas t e m p e r a t u r e i s not known, t h e r e i s no i n f o r m a t i o n on the p o s s i b i l i t y of h i g h f r e q u e n c y temperature f l u c t u a t i o n s which would appear as v e l o c i t y f l u c t u a t i o n s s i n c e t h e h o t - w i r e anemometer can not d i s t i n g u i s h between the two. On the o t h e r hand any p o s s i b l e h i g h f r e q u e n c y t e m p e r a t u r e f l u c t u a t i o n t r a v e l i n g by the sensor would do so by means of mass f l u x w i t h a c e r t a i n v e l o c i t y a s s o c i a t e d w i t h i t . In the case of an eddy w i t h a t e m p e r a t u r e g r a d i e n t , which has been shed from the w a l l , the temperature f l u c t u a t i o n would change the i n d i c a t e d v e l o c i t y f l u c t u a t i o n q u a n t i t a t i v e l y but not q u a l i t a t i v e l y . A s e n s i t i v i t y a n a l y s i s was made l o o k i n g a t the e f f e c t of changes i n the b u l k gas v e l o c i t y on the c a l c u l a t e d i n s t a n t a n e o u s v e l o c i t y by v a r y i n g the p o l y t r o p i c exponent from 1.35 t o 1.30 and 1.40. I t was found t h a t w i t h the c a l c u l a t e d t e mperature a t t o p dead c e n t r e v a r y i n g a p p r o x i m a t e l y 27 K the computed gas v e l o c i t y would v a r y l e s s than 23%. I t s h o u l d be noted t h a t the e f f e c t of c h a n g i n g the p o l y t r o p i c exponent on the v e l o c i t y i s most pronounced a t t o p dead c e n t r e w i t h the c a l c u l a t e d temperature a t a maximum, so t h a t the v a l u e of 23% r e p r e s e n t s a worst case e s t i m a t e . -27-At a given wire o r i e n t a t i o n the standard (one wire) hot-wire anemometer can not d i s t i n g u i s h flow d i r e c t i o n s . T h i s i s c a l l e d d i r e c t i o n a l ambiguity. In the s t r i c t sense i t f a l l s under the category of o p e r a t i o n away from the c a l i b r a t i o n c o n d i t i o n s s i n c e d i r e c t i o n a l ambiguity only occurs with a flow d i r e c t i o n d i f f e r e n t from the one d u r i n g c a l i b r a t i o n . In an i s o t r o p i c t u r b u l e n t flow with some known mean v e l o c i t y the flow d i r e c t i o n at a measurement p o i n t i s v a r i e d by the t u r b u l e n t v e l o c i t y f l u c t u a t i o n s i n a l l three p r i n c i p a l d i r e c t i o n s . The s i n g l e wire can not d i s t i n g u i s h between d i f f e r e n t flow d i r e c t i o n s . The r e s u l t i n g measurement e r r o r i n c r e a s e s with i n c r e a s i n g f l u c t u a t i o n s and d e c r e a s i n g mean v e l o c i t y . I n s i d e a combustion engine the flow c o n d i t i o n s can vary s t r o n g l y with l a r g e f l u c t u a t i o n s and, i n some cases, p r a c t i c a l l y no mean flow. In t h i s work the wire was o r i e n t e d p a r a l l e l to the c y l i n d e r a x i s , assuming that the mean flow, being generated by the p i s t o n motion, would f o l l o w the p i s t o n motion. The s p a t i a l r e s o l u t i o n of the order of the wire l e n g t h and the frequency r e s o l u t i o n , given by the mean v e l o c i t y and the wire l e n g t h , are gen e r a l l i m i t a t i o n s shared with other users, who operate the anemometer under constant ambient c o n d i t i o n s . I t i s very d i f f i c u l t to estimate the cumulative e f f e c t of the l i s t e d l i m i t a t i o n s . C a t a n i a and M i t t i c a [7] c l a i m an u n c e r t a i n t y l i m i t of p l u s or minus 10% f o r the computed gas -28-v e l o c i t i e s i n s i d e a combustion e n g i n e , a f t e r t a k i n g g r e a t c a r e t o m i n i m i z e a l l e r r o r s . L a n c a s t e r [5] g i v e s an e s t i m a t e of 20% u n c e r t a i n t y f o r h i s v e l o c i t y measurements. For the case of known gas p r o p e r t i e s he e s t i m a t e s an u n c e r t a i n t y of l e s s than 10% i n the computed v e l o c i t y . The a u t h o r p r e f e r s the more c a r e f u l statement by W i t z e [ 6 ] : "Because of t h e s e l i m i t a t i o n s , i t i s n e c e s s a r y t o i n t e r p r e t the v e l o c i t y and t u r b u l e n c e i n t e n s i t y d e t e r m i n e d from the anemometer output as b e i n g merely " r e p r e s e n t a t i v e " measures of the h o t - w i r e response of i t s e nvironment. T h i s i s not t o say t h a t such measurements a r e m e a n i n g l e s s , because they a r e t r u l y r e p r e s e n t a t i v e of the " e f f e c t i v e " mass f l u x c o n d i t i o n s sensed by the probe, such t h a t i n most i n s t a n c e s they g i v e a t the l e a s t a q u a l i t a t i v e i n d i c a t i o n of the f l o w s t r u c t u r e i n the e n g i n e . " Cameron [29] e s t i m a t e d an u n c e r t a i n t y of 35% f o r the c a l c u l a t e d i n s t a n t a n e o u s v e l o c i t y , based on 5% u n c e r t a i n t y e s t i m a t e s f o r the r e f e r e n c e p r e s s u r e and t e m p e r a t u r e . T a k i n g i n t o account t h a t i n the p r e s e n t e d work the i n i t i a l c o n d i t i o n s a r e w e l l known and based on the t e m p e r a t u r e s e n s i t i v i t y a n a l y s i s p e r formed, i t i s e s t i m a t e d t h a t e r r o r i n the c a l c u l a t e d gas p r o p e r t i e s causes of the o r d e r of 20% u n c e r t a i n t y i n the computed gas v e l o c i t i e s . Analogous t o the e s t i m a t e s of C a t a n i a and M i t t i c a [7] and L a n c a s t e r [ 5 ] , an o t h e r 10% u n c e r t a i n t y i n the computed gas v e l o c i t y i s a t t r i b u t e d t o the r e m a i n i n g s o u r c e s of e r r o r such as d i r e c t i o n a l a m b i g u i t y , i n s t r u m e n t e r r o r and e r r o r i n the - 2 9 -p h y s i c a l p r o p e r t i e s and geometry of the w i r e . The t o t a l u n c e r t a i n t y i n the p r e s e n t e d gas v e l o c i t y measurements i s t h e r e f o r e e s t i m a t e d t o be a p p r o x i m a t e l y 30%. 3.2 COMBUSTION TESTS The f o l l o w i n g equipment was used t o measure the p r e s s u r e i n s i d e the combustion chamber: P r e s s u r e - T r a n s d u c e r : K i s t l e r Type 6121, No SN 185071 P r e s s u r e A m p l i f i e r : K i s t l e r 5004 Dual Mode A m p l i f i e r The p r e s s u r e t r a n s d u c e r was r e c e s s e d h a l f of i t s d i a m e t e r t o p r o t e c t i t from the e f f e c t s of t h e r m a l shock, as recommended by Benson and P i c k [ 3 5 ] . A s l i g h t l y l e a n m i x t u r e of methane-air (lambda=1.02) was p r e p a r e d i n a s e p a r a t e tank and used f o r a l l the combustion t e s t s . The m i x t u r e c o m p o s i t i o n was d e t e r m i n e d w i t h a gas chromatograph. T h i s ensured t h a t the same m i x t u r e c o m p o s i t i o n was used throughout a l l of the combustion t e s t s . A s i m p l e b r e a k e r p o i n t i g n i t i o n system was used. The b r e a k e r p o i n t c o n s i s t e d of a c o n t a c t which would be d i s c o n n e c t e d by the rack a t a s e t r a c k p o s i t i o n , r e l a t e d t o a c e r t a i n d e grees crank a n g l e p o s i t i o n . The spark p l u g was l o c a t e d i n the c e n t r e of the c y l i n d e r . I g n i t i o n s e t t i n g s of t o p dead c e n t r e , 10, 20 and 30 degrees crank a n g l e b e f o r e t o p dead c e n t r e were used. The p r e s s u r e d a t a was s c a l e d a c c o r d i n g t o the a m p l i f i e r s e t t i n g . S i n c e the dynamic p r e s s u r e t r a n s d u c e r measures o n l y -30-changes i n p r e s s u r e , the i n i t i a l p r e s s u r e s e t t i n g was measured w i t h a manometer and used as r e f e r e n c e f o r the f i r s t r e c o r d e d p r e s s u r e t r a n s d u c e r r e a d i n g . 3.3 DATA ACQUISITION A Cyborg I s a a c 2000 d a t a a c q u i s i t i o n system was used t o read d a t a on t h r e e c h a n n e l s a t a sa m p l i n g r a t e of 62.5 kHz. The s a m p l i n g r a t e was kept as h i g h as p o s s i b l e so t h a t a good r e s o l u t i o n i n terms of degrees crank a n g l e p o s i t i o n c o u l d be a c h i e v e d . The d a t a a c q u i s i t i o n system d i g i t i z e d the a n a l o g i n p u t v o l t a g e s i g n a l s i n t o 4 d i g i t i n t e g e r numbers between 0 and 4096 c o r r e s p o n d i n g t o -10 and 10 V o l t r e s p e c t i v e l y . E r r o r s due t o q u a n t i z a t i o n were l e s s than 0.1% i n the worst case f o r the h o t - w i r e anemometer b r i d g e v o l t a g e s i g n a l . The system was t r i g g e r e d by the o p t i c a l p i c k - u p d e v i c e a c t i v a t e d by the r a c k . In the one s t r o k e case 20,000 d a t a p o i n t s were r e a d , c o v e r i n g a p e r i o d of 106.7 m i l l i s e c o n d s , i n the two s t r o k e case 30,000 d a t a p o i n t s were read over a p e r i o d of 160 m i l l i s e c o n d s . D u r i n g h o t - w i r e anemometry measurements the b r i d g e v o l t a g e , p r e s s u r e a m p l i f i e r v o l t a g e and the degrees crank a n g l e o p t i c a l p i c k - u p v o l t a g e were r e c o r d e d . For the combustion t e s t s the p r e s s u r e a m p l i f i e r v o l t a g e , degrees crank a n g l e p i c k - u p v o l t a g e and the v o l t a g e of the p r i m a r y i g n i t i o n c o i l c i r c u i t were r e c o r d e d . A N i c o l e t 3091 o s c i l o s c o p e was used t o view some of the -31-measured parameters dur i n g the course of the experiments. A f t e r each run the s t o r e d data was read from the Isaac data a c q u i s i t i o n system i n t o an IBM Personal Computer and s t o r e d on d i s k e t t e s . L a t e r the data was t r a n s f e r e d to a Vax computer and processed t h e r e . - 3 2 -4 DATA PROCESSING AND RESULTS 4.1 HOT-WIRE ANEMOMETER DATA A f t e r i n i t i a l problems w i t h w i r e breakage the t e s t p r o c e d u r e was m o d i f i e d t o m i n i m i z e w i r e h a n d l i n g , such t h a t i t was p o s s i b l e t o a q u i r e the complete s e t of h o t - w i r e measurement d a t a used i n t h i s work w i t h one w i r e . As mentioned i n Chapter 4.1 the i n s t a n t a n e o u s gas v e l o c i t y i s c a l c u l a t e d from the measured anemometer v o l t a g e u s i n g the N u s s e l t / Reynolds number c a l i b r a t i o n c u r v e , i t e r a t i n g the heat t r a n s f e r c o e f f i c i e n t f o r every measurement p o i n t . In t h i s method heat l o s s due t o c o n d u c t i o n t o the sup p o r t prongs i s i n c l u d e d i n the heat t r a n s f e r e q u a t i o n , Chapter 4.1.1. The measured cr a n k a n g l e p u l s e s were used t o r e l a t e the gas v e l o c i t y t o the cran k a n g l e p o s i t i o n i n degrees cr a n k a n g l e . 4.1.1 RAW INSTANTANEOUS VELOCITY DATA Examples of i n s t a n t a n e o u s gas v e l o c i t y v e r s u s crank a n g l e f o r one run a r e shown i n F i g u r e 7a f o r the o n e - s t r o k e case and i n F i g u r e 7b f o r the t w o - s t r o k e c a s e . I t s h o u l d be not e d t h a t the o r i g i n a l v o l t a g e / v e l o c i t y c a l i b r a t i o n c u r v e of t h e h o t - w i r e anemometer c o v e r s o n l y v e l o c i t i e s between a p p r o x i m a t e l y 0.5 and 16 m/s, so t h a t d a t a p o i n t s o u t s i d e t h a t range a r e e x t r a p o l a t e d and t h e r e f o r e s u b j e c t t o a d d i t i o n a l e r r o r . I t s h o u l d a l s o be noted t h a t i n t h i s work the range of i n t e r e s t i s around t o p dead c e n t r e a f t e r the -33 -compression s t r o k e , s i n c e t h i s i s where i g n i t i o n o c c u r s . Comparing the two examples i n F i g u r e 7a and b i t i s found t h a t the i n s t a n t a n e o u s gas v e l o c i t y i n the case of i n t a k e and compression s t r o k e i s an o r d e r of magnitude l a r g e r than f o r the co m p r e s s i o n s t r o k e by i t s e l f . Both c u r v e s s t a r t a t some non-zero v a l u e , which i s b e l i e v e d t o be p a r t i a l l y due t o the e x t r a p o l a t i o n e r r o r below 0.5 m/s and p a r t i a l l y due t o the f a c t t h a t the da t a a c q u i s i t i o n system was t r i g g e r e d a f t e r the ra c k movement had been i n i t i a t e d , so t h a t the p i s t o n had some non-zero v e l o c i t y a t the f i r s t measurement p o i n t . In the o n e - s t r o k e case i n F i g u r e 7a some h i g h f r e q u e n c y components can be seen s t a r t i n g a t a p p r o x i m a t e l y 275 degrees crank a n g l e . T h i s i s caused by the i n t a k e v a l v e d r i v e t r a i n d i s c o n n e c t i n g from the ra c k and h i t t i n g t he i n t a k e v a l v e i n the p r o c e s s , c a u s i n g i t t o bounce and open m o m e n t a r i l y . I t can be seen from F i g u r e s 11a and b t h a t the mean v e l o c i t y shows a c h a r a c t e r i s t i c bump a t t h a t crank s h a f t p o s i t i o n , which i s most pronounced a t measurement l o c a t i o n 1. T h i s i n d i c a t e s t h a t the v a l v e opened b r i e f l y , r e l e a s i n g some gas, r a t h e r than p u r e l y m e c h a n i c a l probe v i b r a t i o n due t o m e c h a n i c a l shock l o a d i n g . T h i s was s u b s t a n t i a t e d t h r o u g h a t e s t , i n which the c y l i n d e r head was h i t w i t h a hammer. The h o t - w i r e probe s i g n a l d i d not show the h i g h f r e q u e n c y f l u c t u a t i o n s seen i n F i g u r e 7a. These h i g h - f r e q u e n c y components d i s a p p e a r towards h i g h e r crank a n g l e degrees and do not rea c h the range of s p e c i a l -34-i n t e r e s t between 330 degrees crank a n g l e and top dead c e n t r e . The gas v e l o c i t y i n the two s t r o k e case i n F i g u r e 7b e x h i b i t s a wide range of f r e q u e n c i e s . The h i g h e s t v e l o c i t i e s a r e measured around 90 degrees c r a n k a n g l e d u r i n g the i n t a k e s t r o k e w i t h the p i s t o n a t i t s h i g h e s t speed. The gas v e l o c i t y d r ops o f f towards t o p dead c e n t r e a t the end of the comp r e s s i o n s t r o k e . For each measurement l o c a t i o n 10 r e p e t i t i v e runs were made. 4.1.2 DATA REDUCTION Each run was i n d i v i d u a l l y a n a l y s e d by c a l c u l a t i n g a window-averaged mean v e l o c i t y , c u r v e f i t t i n g u s i n g a c u b i c - s p l i n e r o u t i n e and computing the r o o t mean square (rms) v a l u e of the f l u c t u a t i n g v e l o c i t y over t h a t window. In an a l o g y t o C a t a n i a and M i t t i c a [7] the parameters used a r e d e f i n e d as f o l l o w s : W i t h U ( t , n ) b e i n g the i n s t a n t a n e o u s v e l o c i t y of run n at time t , t h e window averaged mean v e l o c i t y of run n a t time t w i s g i v e n by: t w+T/2 (15) 0 ( t w , n ) = 1 f U ( t , n ) d t t w ~ T / 2 w i t h T b e i n g the window. Here a window s i z e of 125 da t a p o i n t s was chosen, c o r r e s p o n d i n g t o 2 m i l l i s e c o n d s or 12 degrees c r a n k a n g l e a t 1000 rpm or a c u t - o f f f r e q u e n c y of 500 Hz. A l l f r e q u e n c y components above 500 Hz a r e a t t r i b u t e d -35-t o t u r b u l e n c e , f r e q u e n c i e s below 500 Hz a r e c o n s i d e r e d t o r e p r e s e n t changes i n mean v e l o c i t y . The chosen v a l u e i s i d e n t i c a l t o the one used by Cameron [29] and i s c l o s e t o the 10 degrees crank a n g l e window s i z e used by W i t z e , M a r t i n and Borgnakke [ 3 6 ] . I t a l s o l i e s w i t h i n the range of 8 t o 20 degrees crank a n g l e recommended by C a t a n i a and M i t t i c a [7] and i s w i t h i n the range of c u t - o f f f r e q u e n c i e s of 300 t o 900 Hz used by L i o u and S a n t a v i c c a [ 9 ] . The d i s c r e e t window-averaged v a l u e s 0 ( t w , n ) a t the c e n t r e of each window were then i n t e r p o l a t e d u s i n g a c u b i c - s p l i n e r o u t i n e w i t h z e r o t e n s i o n , such t h a t the f i t t e d c u r v e f o r 0 ( t , n ) went th r o u g h a l l window-averaged p o i n t s . F i g u r e 7c p i c t u r e s t h i s s c h e m a t i c a l l y . The f l u c t u a t i n g v e l o c i t y u ( t , n ) of run n a t time t i s d e f i n e d by: The t u r b u l e n c e i n t e n s i t y of run n a t time t w i n window T was found from: , The t u r b u l e n c e i n t e n s i t y r e p r e s e n t s the s t a n d a r d d e v i a t i o n of the f l u c t u a t i n g v e l o c i t y i n the i n t e r v a l T. (16) u ( t , n ) = U ( t , n ) - 0 ( t , n ) (17) -36-The ensemble-averaged mean v e l o c i t y a t time t was found from: N (18) D_(t) = 1/N I 0 ( t f n ) E n=1 w i t h N b e i n g the number of r e c o r d s , here u s u a l l y 10. S i m i l a r l y the ensemble-averaged t u r b u l e n c e i n t e n s i t y was d e f i n e d by: N (19) u ' ( t ) = 1/N L u ' ( t , n ) E n=1 The d i f f e r e n c e i n mean v e l o c i t y between d i f f e r e n t c y c l e s was c h a r a c t e r i s e d by the c y c l i c v a r i a t i o n v e l o c i t y : (20) U c ( t , n ) = 0(t,n) - D E ( t ) The c y c l i c v a r i a t i o n i n t e n s i t y r e p r e s e n t s the s t a n d a r d d e v i a t i o n of t h e c y c l i c v a r i a t i o n v e l o c i t i e s over the number of c y c l e s : (21) U£(t) =|l/N ^ U 2 ( t , n ) U s i n g the cra n k a n g l e / t i m e r e f e r e n c e d a t a , the mean v e l o c i t y 0(6?,n) of run n a t crank a n g l e 6 was found from the i n t e r p o l a t e d mean v e l o c i t y 0(t,n) a t the c o r r e s p o n d i n g time t . The c y c l i c v a r i a t i o n v e l o c i t y U^(0,n) was found i n a s i m i l a r f a s h i o n from U r ( t , n ) . -37-The ensemble averaged mean v e l o c i t y at crank angle 6 was given by: The c y c l i c v a r i a t i o n i n t e n s i t y with r e s p e c t to crank angle i s given by: In order to f i n d the t u r b u l e n c e i n t e n s i t y u'(0,n) the u ' ( t w , n ) v a l u e s were i n t e r p o l a t e d using a c u b i c - s p l i n e r o u t i n e . Based on the crank angle/time r e f e r e n c e data, u'(0,n) was found from the i n t e r p o l a t e d u'(t,n) curves. As i n equation 19, the ensemble-averaged turbulence i n t e n s i t y with respect to crank angle i s d e f i n e d by: Note that the window averaging p a r t of the data p r o c e s s i n g was done with r e s p e c t to time, s i n c e the data was recorded at a constant r a t e i n time with v a r y i n g degrees crank angle c o n d i t i o n s due to the a c c e l e r a t i o n and d e c e l e r a t i o n of the crank s h a f t . (22) N 0_ (0) = 1/N I U"(0,n) (23) (24) N u E ( 0 ) = 1/N I u'(6\n) -38-4.1.3 HOT-WIRE ANEMOMETER RESULTS  I n t a k e and Compression S t r o k e Data: F i g u r e 8a shows the ensemble-averaged mean v e l o c i t i e s d u r i n g the i n t a k e and the compre s s i o n s t r o k e a t the f i v e measurement l o c a t i o n s v e r s u s t i m e . F i g u r e 8b shows the same ensemble-averaged mean v e l o c i t i e s v e r s u s crank a n g l e . D u r i n g the i n t a k e s t r o k e the maximum ensemble averaged mean v e l o c i t y i s found a t l o c a t i o n 1 around 90 degrees crank a n g l e , where the h o t - w i r e anemometer i s d i r e c t l y exposed t o the i n t a k e v a l v e j e t and the j e t b e i n g s t r o n g e s t w i t h the p i s t o n a t i t s h i g h e s t speed a t 90 degrees crank a n g l e . Between a p p r o x i m a t e l y 280 and 305 degrees c r a n k a n g l e the ensemble averaged mean v e l o c i t i e s a t l o c a t i o n s 1,2 and 3 show a d i s t i n c t peak. S i n c e the gas i s drawn i n th r o u g h a v a l v e w i t h an e c c e n t r i c p o s i t i o n , some s w i r l i n g motion i n the p l a n e of the c y l i n d e r a x i s and the i n t a k e v a l v e c o u l d o c c u r , a l s o c a l l e d b a r r e l i n g m o t i o n . Such a s w i r l would be compressed d u r i n g the compre s s i o n s t r o k e and, assuming c o n s e r v a t i o n of a n g u l a r momentum, i n t e n s i f i e d i n i t s r o t a t i o n , u n t i l i t b r e a k s up. The peaks of the c u r v e s f o r l o c a t i o n 1,2 and 3 between 280 and 305 degrees c r a n k a n g l e c o u l d p o s s i b l y be caused by such a s w i r l i n g m o t i o n . Towards t o p dead c e n t r e the ensemble-averaged mean v e l o c i t i e s drop o f f and t h e n , l o o k i n g a t F i g u r e 8a, re a c h some c o n s t a n t l e v e l c l o s e t o z e r o a f t e r about 90 m i l l i s e c o n d s . -39-F i g u r e 9a shows the ensemble-averaged t u r b u l e n c e i n t e n s i t i e s d u r i n g the i n t a k e and compr e s s i o n s t r o k e f o r the f i v e measurement l o c a t i o n s v e r s u s time and v e r s u s crank a n g l e i n F i g u r e 9b. Ag a i n the h i g h e s t l e v e l of a c t i v i t y i s measured a t l o c a t i o n 1 d u r i n g most of the i n t a k e s t r o k e . Towards bottom dead c e n t r e a t 180 degrees c r a n k a n g l e the ensemble averaged t u r b u l e n c e i n t e n s i t y a t l o c a t i o n 1 drops r a p i d l y and re a c h e s the same l e v e l as the o t h e r c u r v e s . The c u r v e s f o r a l l f i v e measurement l o c a t i o n s a r e i n a r e l a t i v e l y narrow band d u r i n g the compression s t r o k e , which i n d i c a t e s t h a t the t u r b u l e n c e i n t e n s i t y becomes independent of measurement l o c a t i o n , t h a t i s homogeneous. I t appears t o s t a y homogeneous throughout the c o m p r e s s i o n s t r o k e . A s i m i l a r c o n c l u s i o n was reached by Daneshyar and F u l l e r [ 3 0 ] . The ensemble-averaged t u r b u l e n c e i n t e n s i t i e s m a i n t a i n a n e a r l y c o n s t a n t v a l u e d u r i n g most of the c o m p r e s s i o n s t r o k e and d r o p o f f towards t o p dead c e n t r e . I t appears t h a t d u r i n g most of the compr e s s i o n s t r o k e the decay of t u r b u l e n t motion i s b a l a n c e d by the enhancement of e x i s t i n g t u r b u l e n t motion due t o compr e s s i o n and the g e n e r a t i o n of t u r b u l e n c e through p i s t o n i n d u c e d f l o w m o t i o n . In the g i v e n c o n f i g u r a t i o n the g e n e r a t i o n of t u r b u l e n t motion d u r i n g the c o m p r e s s i o n s t r o k e i s s m a l l , as can be seen from F i g u r e s 12a and b, by comparison t o the l e v e l i n F i g u r e s 9a and b. W i t h the p i s t o n d e c e l e r a t i n g towards t o p dead c e n t r e the r a t e of enhancement and g e n e r a t i o n d e c r e a s e and net decay o c c u r s . -40-F i g u r e 10a shows the c y c l i c v a r i a t i o n i n t e n s i t i e s f o r the f i v e measurement l o c a t i o n s v e r s u s time and v e r s u s crank a n g l e i n F i g u r e 10b. The c y c l i c v a r i a t i o n i n t e n s i t y i s a measure of how w e l l the mean v e l o c i t y i s r e p e a t e d from c y c l e t o c y c l e . Even though t h e e x p e r i m e n t a l c o n d i t i o n s were kept as c o n s t a n t as p o s s i b l e , the v a l u e s f o r the c y c l i c v a r i a t i o n i n t e n s i t i e s average a p p r o x i m a t e l y a q u a r t e r of the v a l u e s f o r t he ensemble averaged mean v e l o c i t i e s , see F i g u r e s 8a and b. The v a l u e s f o r the c y c l i c v a r i a t i o n i n t e n s i t i e s a r e r o u g h l y h a l f of the v a l u e s of the ensemble averaged t u r b u l e n c e i n t e n s i t i e s d u r i n g the i n t a k e s t r o k e , see F i g u r e s 9a and b, and r o u g h l y the same d u r i n g the compres s i o n s t r o k e . T h i s u n d e r l i n e s the need f o r c y c l e - b y - c y c l e d a t a a n a l y s i s i n o r d e r t o be a b l e t o s e p a r a t e c y c l i c v a r i a t i o n from t u r b u l e n c e i n t e n s i t i e s . Compression S t r o k e Only D a t a : F i g u r e 11a shows the ensemble-averaged mean v e l o c i t i e s a t the f i v e measurement l o c a t i o n s f o r the case of compression s t r o k e a l o n e v e r s u s time and v e r s u s c r a n k a n g l e i n F i g u r e 11b. Compared t o the ensemble-averaged mean v e l o c i t i e s f o r the i n t a k e and c o m p r e s s i o n s t r o k e , see F i g u r e s 8a and b, t h e r e i s h a r d l y any f l o w a c t i v i t y i n the case of the com p r e s s i o n s t r o k e by i t s e l f . I t s h o u l d be emphasized a g a i n t h a t the combustion chamber geometry used i n t h i s work r e p r e s e n t s the s i m p l e case of a f l a t d i s k w i t h o u t s q u i s h . S t a r t i n g t he com p r e s s i o n s t r o k e w i t h t h e gas a t r e s t , the -41-p i s t o n motion d u r i n g the compres s i o n s t r o k e g e n e r a t e s v e r y l i t t l e mean f l o w i n the g i v e n e x p e r i m e n t a l c o n f i g u r a t i o n . S t a r t i n g the compression s t r o k e w i t h the gas i n motion due t o the i n t a k e p r o c e s s , a mean f l o w a c t i v i t y a p p r o x i m a t e l y an o r d e r of magnitude l a r g e r i s m a i n t a i n e d d u r i n g most of the compress i o n s t r o k e . The c u r v e s i n F i g u r e s 11a and b s h o u l d s t a r t a t a v a l u e c l o s e t o z e r o s i n c e the gas i s a t r e s t a t the s t a r t of the ex p e r i m e n t . The f a c t t h a t the d a t a a c q u i s i t i o n i s t r i g g e r e d a p p r o x i m a t e l y 8 degrees cr a n k a n g l e a f t e r the p i s t o n motion has been i n i t i a t e d s h o u l d not account f o r some n o t i c e a b l e f l o w motion s i n c e the p i s t o n i s v e r y slow around bottom dead c e n t r e . As mentioned i n Chapter 5.1.1, v e l o c i t y v a l u e s below a p p r o x i m a t e l y 0.5 m/s a r e O u t s i d e the c a l i b r a t i o n range and, b e i n g e x t r a p o l a t e d , a r e s u b j e c t t o a d d i t i o n a l e r r o r . Some d e v i a t i o n i n the l e v e l of the c u r v e s can be seen. In p a r t i c u l a r the c u r v e f o r l o c a t i o n 5 seems t o be s h i f t e d up by a c o n s t a n t f a c t o r i n comparison t o the o t h e r c u r v e s . T h i s i s most l i k e l y caused by some d e v i a t i o n i n the z e r o adjustment of the a u x i l i a r y u n i t , which was used t o f i l t e r t he h o t - w i r e anemometer v o l t a g e s i g n a l . I t i s n o t i c e a b l e here because of the low mean v e l o c i t y l e v e l . The bump i n the ensemble-averaged mean v e l o c i t y f o r l o c a t i o n 1 and 4 around 280 degrees crank a n g l e i s caused by bounc i n g of the i n t a k e v a l v e due t o the i n t a k e v a l v e d r i v e t r a i n d i s c o n n e c t i n g from t h a r a c k . I t appears t h a t the -42-i n t a k e v a l v e has opened a g a i n s l i g h t l y d u r i n g the b o u n c i n g , r e l e a s i n g some gas and t h e r e b y c a u s i n g some mean f l o w a c t i v i t y . A pronounced peak i n t h e ensemble averaged mean v e l o c i t i e s f o r l o c a t i o n 3 can be seen w i t h i t s maximum v a l u e a t a p p r o x i m a t e l y 36 m i l l i s e c o n d s and a f t e r t o p dead c e n t r e . A s i m i l a r but l e s s pronounced peak can be seen f o r measurement l o c a t i o n 5. These peaks p o i n t towards the e x i s t e n c e of a r i n g v o r t e x t h a t i s formed due t o r o l l i n g up of the boundary l a y e r on the c y l i n d e r w a l l , as d e s c r i b e d by Daneshyar, F u l l e r and Dekker [ 3 2 ] . T h i s phenomena appears t o be l i m i t e d t o lower engine r e v o l u t i o n s s i n c e i t depends on the e s t a b l i s h m e n t of a boundary l a y e r a t the c y l i n d e r w a l l . In such a r o l l - u p v o r t e x one c o u l d expect some temperature g r a d i e n t s i n c e the v o r t e x c o n s i s t s of a boundary l a y e r which has been s c r a p e d o f f the c o o l w a l l and r o l l e d up. The t e m p e r a t u r e g r a d i e n t i n s i d e the boundary l a y e r c o u l d be e x p e c t e d t o be p r e s e r v e d t h r o u g h o u t the r o l l - u p p r o c e s s . As mentioned i n Chapter 4.1.2, q u a l i t a t i v e s t a t e m e n t s are not a f f e c t e d by a temperature g r a d i e n t i n a v o r t e x p a s s i n g by the s e n s o r . F i g u r e 12a shows the ensemble averaged t u r b u l e n c e i n t e n s i t i e s f o r the f i v e measurement l o c a t i o n s v e r s u s time and v e r s u s crank a n g l e i n F i g u r e 12b. A l l c u r v e s show pronounced peaks around 280 d e g r e e s crank a n g l e , which , as mentioned b e f o r e i n c h a p t e r 4.1.1, are caused by h i g h - 4 3 -f r e q u e n c y o s c i l l a t i o n s i n t r o d u c e d i n t o the s i g n a l by the v a l v e d r i v e t r a i n d i s c o n n e c t i n g from the rack and h i t t i n g the v a l v e i n the p r o c e s s , as d i s c u s s e d i n Chapter 4.1.1. These h i g h - f r e q u e n c y o s c i l l a t i o n s can a l s o be seen i n the raw v e l o c i t y t r a c e , see F i g u r e 7a. T h i s p a r t of the c u r v e s i s i n t r o d u c e d by the experiment and s h o u l d not be t h e r e . T h i s d i s t u r b a n c e drops o f f f a s t and the c u r v e s r e a c h the p r e v i o u s l e v e l around 345 degrees crank a n g l e . L i k e the ensemble-averaged mean v e l o c i t i e s i n F i g u r e s 11a and b, the ensemble averaged t u r b u l e n c e i n t e n s i t i e s a t l o c a t i o n 3 and 5 show pronounced peaks a f t e r t o p dead c e n t r e . T h i s i n d i c a t e s the pre s e n c e of h i g h - f r e q u e n c y f l o w a c t i v i t i e s , p a s s i n g by the sensor a f t e r the p i s t o n has come t o a s t o p . The v a l u e s of the t u r b u l e n c e i n t e n s i t i e s a r e s m a l l compared t o the v a l u e s of the mean v e l o c i t i e s i n F i g u r e s 11a and b. F i g u r e 13a shows the c y c l i c v a r i a t i o n i n t e n s i t i e s f o r the f i v e measurement l o c a t i o n s v e r s u s time and v e r s u s crank a n g l e i n F i g u r e 13b. The low l e v e l of the c u r v e s up t o a p p r o x i m a t e l y 350 degrees cr a n k a n g l e i n d i c a t e s a good r e p e a t a b i l i t y of the mean f l o w v e l o c i t y over the c y c l e s a t a l l measurement l o c a t i o n s . In the s e f i g u r e s one can a g a i n see a pronounced peak i n the c u r v e s f o r l o c a t i o n 3 and 5 a f t e r t o p dead c e n t r e . I t appears t h a t the f l o w a c t i v i t y a f t e r t o p dead c e n t r e a t t h e s e l o c a t i o n s i s not as -44-r e p e t i t i v e i n i t s magnitude and time of occurance as the mean gas motion over most of the compression s t r o k e . 4.2 COMBUSTION DATA 4.2.1 PRESSURE DATA F i g u r e 14a shows the measured p r e s s u r e i n s i d e the combustion chamber f o r f i v e r e p e t i t i v e runs v e r s u s time f o r the com p r e s s i o n s t r o k e by i t s e l f and f o r the i n t a k e and compres s i o n s t r o k e i n F i g u r e 14b. In both c a s e s the m i x t u r e was i g n i t e d a t 10 degrees crank a n g l e b e f o r e t o p dead c e n t r e , c o r r e s p o n d i n g t o a p p r o x i m a t e l y 29.5 m i l l i s e c o n d s i n F i g u r e 14a and a p p r o x i m a t e l y 69.5 m i l l i s e c o n d s i n F i g u r e 14b. The i g n i t i o n time i s a l s o i n d i c a t e d w i t h a s h o r t v e r t i c a l l i n e i n both graphs. In both graphs an a d d i t i o n a l p r e s s u r e t r a c e w i t h o u t i g n i t i o n i s i n c l u d e d f o r r e f e r e n c e . In F i g u r e 14a the i n c r e a s e i n p r e s s u r e due t o compre s s i o n can be seen between 0 and a p p r o x i m a t e l y 32 m i l l i s e c o n d s . A f t e r t h a t the p r e s s u r e w i t h o u t i g n i t i o n d e c r e a s e s s l o w l y due t o heat l o s s , w h i l e the p r e s s u r e s w i t h i g n i t i o n i n c r e a s e due t o the combustion p r o c e s s . They r e a c h a maximum between about 55 and 59 m i l l i s e c o n d s . In F i g u r e 14b the c y l i n d e r p r e s s u r e s d e c r e a s e i n i t i a l l y d u r i n g the i n t a k e s t r o k e and then i n c r e a s e d u r i n g the comp r e s s i o n s t r o k e , u n t i l t o p dead c e n t r e i s reached a t a p p r o x i m a t e l y 75 m i l l i s e c o n d s . A g a i n the p r e s s u r e w i t h o u t i g n i t i o n d e c r e a s e s i n time due t o heat l o s s , w h i l e the - 4 5 -p r e s s u r e s w i t h i g n i t i o n i n c r e a s e r a p i d l y due t o the combustion. They r e a c h a maximum around about 8 0 m i l l i s e c o n d s . S i n c e d i f f e r e n t amounts of d a t a were taken f o r the one and the two s t r o k e case a t the same sa m p l i n g r a t e , the time s c a l e i s d i f f e r e n t f o r the graphs i n F i g u r e 14a and b. Comparing the two graphs i t becomes apparent t h a t the time between i g n i t i o n and p r e s s u r e maximum f o r the case of the c o m p r e s s i o n s t r o k e by i t s e l f i s between 4 and 5 t i m e s l o n g e r than f o r the i n t a k e and c o m p r e s s i o n s t r o k e . I t a l s o becomes apparent t h a t i n the f a s t e s t b u r n i n g two s t r o k e case h i g h e r peak p r e s s u r e s a r e reached. 4.2.2 DATA PROCESSING AND REDUCTION A mass f r a c t i o n burned programme, d e v e l o p e d and documented by Jones [ 3 3 ] , was m o d i f i e d t o accomodate the r a p i d i n t a k e and c o m p r e s s i o n machine combustion chamber geometry. I t was a l s o changed from c o n s t a n t degrees crank a n g l e increment s t e p s t o c o n s t a n t time s t e p s . The programme c a l c u l a t e s the mass f r a c t i o n burned v e r s u s . time a f t e r i g n i t i o n from the p r e s s u r e t r a c e . The p r e s s u r e d a t a f o r the two s t r o k e c a s e was r e s c a l e d , u s i n g bottom dead c e n t r e as a new s t a r t i n g p o i n t and c u t t i n g o f f the p r e s s u r e t r a c e d u r i n g the i n t a k e s t r o k e , because the mass f r a c t i o n burned programme s t a r t s c a l c u l a t i n g a t bottom dead c e n t r e b e f o r e t h e c o m p r e s s i o n s t r o k e . -46-A new i n p u t parameter was i n t r o d u c e d i n t o the programme, which a l l o w e d a r e d u c t i o n i n the number of d a t a p o i n t s p r o c e s s e d by the programme. T h i s v a r i a b l e d a t a r e d u c t i o n parameter was needed because a h i g h d a t a s a m p l i n g f r e q u e n c y means a s m a l l c a l c u l a t i o n s t e p increment between d a t a p o i n t s i n the mass f r a c t i o n burned programme. I f the c a l c u l a t i o n s t e p i n c r e m e n t s get t o o s m a l l , the programme can not f i n d a s u f f i c i e n t d i f f e r e n c e between s u c c e s s i v e d a t a p o i n t s and w i l l s t o p . The b a s i c assumptions made i n the o r i g i n a l programme a r e : The combustion chamber i s d i v i d e d i n t o two zones by a t h i n , s p h e r i c a l l y expanding flame f r o n t s e p a r a t i n g the burned gas f r a c t i o n from t h e unburned gas f r a c t i o n . - ' Both the burned and unburned gases have v a r y i n g s p e c i f i c h e a t s and obey the i d e a l gas law. The unburned gas i s i s e n t r o p i c a l l y compressed by the expanding burned gas. The p r e s s u r e i s u n i f o r m throughout the combustion chamber. The programme was used w i t h the two b a s i c d i s s o c i a t i o n s t e p s : (25) C0 2 = CO + 0.5 0 2 and (26) H 20 = H 2 + 0.5 0 2 . -47-The programme f e a t u r e s an e m p i r i c a l e q u a t i o n f o r heat l o s s of t h e form proposed by Annand [ 3 9 ] : (27) dQ = a ( k / B O ) ( R e ) b ( T g - T W a l l ) A R d t + C ( T * ~ T ^ a l l ) A R d t where: dQ = heat exchange w i t h the w a l l d u r i n g the time increment dt AR = a r e a of the s u r f a c e exposed t o heat t r a n s f e r k = t h e r m a l c o n d u c t i v i t y of the gas BO = c y l i n d e r bore Re = Reynolds number, based on the mean p i s t o n v e l o c i t y and c y l i n d e r bore Tg = gas temperature T W a l l = temperature d t = time increment a,b,c = c o n s t a n t s Jones [33] and Cameron [29] used a=0.8, b=0.7 and c=0.0 as v a l u e s f o r the c o n s t a n t s . Annand [39] s u g g e s t s s e t t i n g c=0.0 d u r i n g the compression s t r o k e , as t h i s term r e p r e s e n t s the heat exchange due t o r a d i a t i o n and i s s m a l l compared t o the c o n v e c t i v e heat t r a n s f e r . Annand a l s o s u g g e s t s the use of b=0.7, s i n c e t h i s conformed b e s t w i t h e x p e r i m e n t a l d a t a . That l e a v e s the parameter a t o a d j u s t t o the s p e c i f i c c o n d i t i o n s . In the p r e s e n t work i t was found t h a t v a r y i n g the v a l u e of a d i d not s i g n i f i c a n t l y a l t e r t h e r e s u l t of the mass f r a c t i o n burned programme. The v a l u e of a was then s e t t o a=1.2 i n the two s t r o k e case and t o a=1.6 i n the one -48-s t r o k e c a s e , s i n c e t h e s e v a l u e s seemed t o g i v e the h i g h e s t mass f r a c t i o n burned r e s u l t s • under the g i v e n c o n d i t i o n s . A comparison was made between the i n c r e a s e i n c y l i n d e r p r e s s u r e due t o combustion and the c a l c u l a t e d mass f r a c t i o n burned. In o r d e r t o be a b l e t o compare the shape of the two c u r v e s , the p r e s s u r e t r a c e s f o r a one s t r o k e case and a two s t r o k e c a s e , both w i t h i g n i t i o n a t t o p dead c e n t r e , were n o r m a l i z e d u s i n g the lo w e s t p r e s s u r e b e f o r e combustion as the lower r e f e r e n c e v a l u e and the maximum combustion p r e s s u r e as the upper r e f e r e n c e v a l u e . The r e s u l t i n g r e l a t i v e p r e s s u r e i n c r e a s e due t o combustion has a v a l u e of one f o r the peak combustion p r e s s u r e and a v a l u e of z e r o a t the b e g i n n i n g of combustion. The mass f r a c t i o n burned c u r v e s , c a l c u l a t e d w i t h the mass f r a c t i o n burned programme from the same p r e s s u r e t r a c e s , were n o r m a l i z e d as w e l l u s i n g the maximum o b t a i n e d v a l u e of mass f r a c t i o n burned as upper r e f e r e n c e v a l u e and z e r o as lower r e f e r e n c e v a l u e . F i g u r e 18 shows the r e s u l t of t h i s c o m p a r i s o n . S i n c e a l l t h e c u r v e s shown a r e n o r m a l i z e d , they a l l s t a r t a t z e r o and end a t one. In the o n e - s t r o k e case as w e l l as the t w o - s t r o k e case the v a l u e s f o r the p r e s s u r e i n c r e a s e due t o combustion a r e h i g h e r than t h e v a l u e s c a l c u l a t e d from the mass f r a c t i o n burned programme except f o r v a l u e s v e r y c l o s e t o one. Depending on the a c c u r a c y r e q u i r e d , i t may be j u s t i f i e d t o omit the c o m p u t a t i o n of the mass f r a c t i o n burned and use the n o r m a l i z e d p r e s s u r e i n c r e a s e due t o combustion d i r e c t l y . -49-F i g u r e s 15a and b show the r e s u l t i n g mass f r a c t i o n burned c u r v e s v e r s u s t i m e , u s i n g the p r e s s u r e t r a c e s shown i n F i g u r e s 14a and b. F i g u r e 15a a g a i n r e p r e s e n t s the case of the compression s t r o k e by i t s e l f and F i g u r e 15b r e p r e s e n t s the case of i n t a k e and compression s t r o k e . D e f i n i n g the i g n i t i o n d e l a y as the time between i g n i t i o n and 2% mass f r a c t i o n burned and d e f i n i n g the main combustion d u r a t i o n as t h e time between 2% and 80% mass f r a c t i o n burned, i t becomes apparent from F i g u r e s 15a and b t h a t both i g n i t i o n d e l a y and main combustion d u r a t i o n a re s i g n i f i c a n t l y s h o r t e r i n the t w o - s t r o k e case compared t o the o n e - s t r o k e c a s e . The mass f r a c t i o n burned c u r v e s were ensemble averaged over the number of r u n s : N (28) M f b ( t ) = 1/N I M f b ( t , n ) n=1 In the p r e s e n t work a l l p r e s s u r e t r a c e s were a n a l y s e d i n d i v i d u a l l y i n the mass f r a c t i o n burned programme and the r e s u l t i n g mass f r a c t i o n burned c u r v e s were then ensemble averaged. Another way of p r o c e e d i n g used by some r e s e a r c h e r s i s t o ensemble average the p r e s s u r e t r a c e s , see e q u a t i o n 29, and then a n a l y s e the ensemble averaged p r e s s u r e t r a c e i n a mass f r a c t i o n burned programme. N (29) P ( t ) = 1/N Z P ( t , n ) n=1 T h i s has the advantage of r e d u c i n g the amount of computing -50-and d a t a h a n d l i n g , but may i n t r o d u c e some e r r o r . These two methods were compared i n two examples, one f o r the o n e - s t r o k e case and one f o r the t w o - s t r o k e c a s e . F i g u r e 16 shows the r e s u l t of ensemble a v e r a g i n g over the p r e s s u r e t r a c e s b e f o r e c a l c u l a t i n g the mass f r a c t i o n burned a g a i n s t ensemble a v e r a g i n g t h e mass f r a c t i o n burned c u r v e s . The l e f t two c u r v e s a r e f o r the t w o - s t r o k e case w i t h i g n i t i o n a t 30 degrees crank a n g l e b e f o r e t o p dead c e n t r e . The r i g h t two c u r v e s a r e f o r the o n e - s t r o k e case w i t h i g n i t i o n a t 10 degrees crank a n g l e b e f o r e t o p dead c e n t r e . In the l a t t e r case the c u r v e s f o r a v e r a g i n g over the p r e s s u r e t r a c e s and a v e r a g i n g over the mass f r a c t i o n burned c u r v e s superimpose v e r y w e l l , which i s due t o v e r y l i t t l e s c a t t e r i n the p r e s s u r e t r a c e s . In the f i r s t case the c u r v e s do not superimpose as w e l l due t o more s c a t t e r i n the p r e s s u r e d a t a , but s t i l l r e p r e s e n t a s i m i l a r r e s u l t . The two shown c a s e s were chosen because they r e p r e s e n t the two extremes of b e s t and worst f i t . 4.2.3 COMBUSTION RESULTS Ta b l e 3 shows the c a l c u l a t e d v a l u e s of ensemble averaged mean and s t a n d a r d d e v i a t i o n f o r the i g n i t i o n d e l a y and main combustion d u r a t i o n f o r the d i f f e r e n t s e r i e s of e x p e r i m e n t s r u n . F i g u r e 17 shows the ensemble-averaged mass f r a c t i o n burned c u r v e s v e r s u s time a f t e r i g n i t i o n f o r the f o u r -51-i g n i t i o n s e t t i n g s used f o r the compression s t r o k e by i t s e l f i n the r i g h t s i d e of the graph and f o r the i n t a k e and compres s i o n s t r o k e i n the l e f t s i d e of the graph. L o o k i n g a t the c u r v e s f o r the one s t r o k e c a s e , the main d i f f e r e n c e between the c u r v e s f o r v a r i o u s i g n i t i o n s e t t i n g s i s a change i n the i g n i t i o n d e l a y . T a b l e 3 c o n f i r m s t h a t the main combustion d u r a t i o n f o r the case of compre s s i o n s t r o k e o n l y i s not n o t i c e a b l y a f f e c t e d by a change i n the i g n i t i o n time and a l s o r e l a t i v e l y r e p e t i t i v e , i n d i c a t e d by the low v a l u e of the s t a n d a r d d e v i a t i o n w i t h r e s p e c t t o the main combustion d u r a t i o n . The i g n i t i o n d e l a y tends t o i n c r e a s e w i t h e a r l i e r i g n i t i o n t i m i n g . The sum of i g n i t i o n d e l a y and main combustion d u r a t i o n appears t o be l i t t l e a f f e c t e d by changes i n the i g n i t i o n s e t t i n g . The t r e n d of s l i g h t l y i n c r e a s e d o v e r - a l l combustion d u r a t i o n w i t h more advanced i g n i t i o n s e t t i n g i n the o n e - s t r o k e case i s most l i k e l y due t o a lower gas temperature a t i g n i t i o n time f o r more advanced i g n i t i o n . Because t h e r e i s v e r y l i t t l e f l o w a c t i v i t y d u r i n g the compression s t r o k e by i t s e l f , t h e r e i s no b e n e f i t t o more advanced i g n i t i o n s e t t i n g i n terms of h i g h e r t u r b u l e n c e i n t e n s i t y . I n the case of i n t a k e and co m p r e s s i o n s t r o k e i n the l e f t s i d e of t h e graph i n F i g u r e 17 b o t h the i g n i t i o n d e l a y and the main combustion d u r a t i o n d e c r e a s e w i t h e a r l i e r i g n i t i o n , so t h a t the sum of the two i s reduced by about 45% g o i n g from t o p dead c e n t r e i g n i t i o n t o 30 degrees c r a n k a n g l e b e f o r e t o p dead c e n t r e . In the t w o - s t r o k e case t h e r e i s a -52-b e n e f i t to more advanced i g n i t i o n s e t t i n g i n terms of higher turbulence i n t e n s i t y , which outweighs the disadvantage of a lower gas temperature at i g n i t i o n time. -53-5 CONCLUSIONS A r a p i d i n t a k e and compression machine, which can s i m u l a t e the p i s t o n v e l o c i t y of a r e c i p r o c a t i n g i n t e r n a l c ombustion engine a t up t o 1000 rpm over 360 degrees crank a n g l e , was d e s i g n e d and b u i l t . T h i s machine made i t p o s s i b l e t o run the compres s i o n s t r o k e by i t s e l f and compare i t t o r u n n i n g the i n t a k e and compres s i o n s t r o k e t o g e t h e r . I n s i d e t he f l a t - d i s k combustion chamber w i t h o u t s q u i s h and s w i r l t he i n s t a n t a n e o u s f l o w v e l o c i t i e s were measured a t f i v e l o c a t i o n s , u s i n g h o t - w i r e anemometry. Under s i m i l a r o p e r a t i n g c o n d i t i o n s a c o m b u s t i b l e m i x t u r e was drawn i n and i g n i t e d . From the measured p r e s s u r e t r a c e the mass f r a c t i o n burned was computed. The h o t - w i r e anemometry r e s u l t s , c h a p t e r 4.1, have shown t h a t under the g i v e n t e s t c o n d i t i o n s w i t h a f l a t - d i s k c ombustion chamber w i t h o u t s q u i s h the compression s t r o k e by i t s e l f g e n e r a t e s v e r y l i t t l e f l o w motion around i g n i t i o n time compared t o the i n t a k e and co m p r e s s i o n s t r o k e t o g e t h e r . Running i n t a k e and compres s i o n s t r o k e , i t was found t h a t d u r i n g most of the com p r e s s i o n s t r o k e the t u r b u l e n c e i n t e n s i t y remained f a i r l y c o n s t a n t and on a s i m i l a r l e v e l a t a l l measurement l o c a t i o n s . From t h i s i t i s c o n c l u d e d t h a t under the p r e s e n t c o n d i t i o n s d u r i n g most of the compression s t r o k e t he decay of t u r b u l e n t motion due t o v i s c o s i t y i s b a l a n c e d by enhancement of e x i s t i n g v o r t i c i t y due t o co m p r e s s i o n . -54-The combustion e x p e r i m e n t s , c h a p t e r 4.2, have shown t h a t i g n i t i o n d e l a y as w e l l as main combustion d u r a t i o n are c o n s i d e r a b l y s h o r t e r a f t e r i n t a k e and compression s t r o k e t o g e t h e r compared t o the compression s t r o k e by i t s e l f . In the t w o - s t r o k e e x p e r i m e n t s e a r l i e r i g n i t i o n reduced both i g n i t i o n d e l a y and main combustion d u r a t i o n . In the combustion d a t a a n a l y s i s i s was found t h a t the n o r m a l i z e d p r e s s u r e i n c r e a s e due t o combustion g i v e s r e s u l t s s i m i l a r t o the n o r m a l i z e d computed mass f r a c t i o n burned. Depending on the a c c u r a c y r e q u i r e d , i t may t h e r e f o r e be j u s t i f i e d t o omit the l e n g t h y c o m p u t a t i o n of the mass f r a c t i o n burned and use the n o r m a l i z e d p r e s s u r e i n c r e a s e due t o combustion d i r e c t l y . U s i n g a mass f r a c t i o n burned programme, i t was found t h a t ensemble a v e r a g i n g over the p r e s s u r e t r a c e s b e f o r e c a l c u l a t i n g the mass f r a c t i o n burned g i v e s r e s u l t s s i m i l a r t o computing the mass f r a c t i o n burned c u r v e s from the i n d i v i d u a l p r e s s u r e t r a c e s and then ensemble a v e r a g i n g over the mass f r a c t i o n burned c u r v e s . A g a i n depending on the a c c u r a c y r e q u i r e d , i t may be j u s t i f i e d t o ensemble average over the p r e s s u r e t r a c e s b e f o r e computing the mass f r a c t i o n burned. As mentioned i n the i n t r o d u c t i o n , the p r e s e n t work s h o u l d be l o o k e d a t as merely the b e g i n n i n g of a s e r i e s of e x p e r i m e n t s , i n which g r a d u a l l y s q u i s h i s i n t r o d u c e d by changes i n the combustion chamber geometry. I t i s a l s o p o s s i b l e t o i n t r o d u c e s w i r l t h r ough changes i n the i n t a k e -55-system and to i n v e s t i g a t e combinations of s w i r l and s q u i s h . The r a p i d intake and compression machine i s a v e r s a t i l e r e s e a r c h t o o l with many a p p l i c a t i o n s , e n a b l i n g c l o s e c o n t r o l of the o p e r a t i n g c o n d i t i o n s . -56-BIBLIOGRAPHY 1. 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R.S.BENSON, R.PICK, "Recent Advances i n I n t e r n a l Combustion Engine I n s t r u m e n t a t i o n w i t h P a r t i c u l a r R e f e r e n c e t o H i g h Speed Data A c q u i s i t i o n and Automated Test Bed", SAE 740695 36. P.O.WITZE, J.K.MARTIN, C.BORGNAKKE, "Measurements and P r e d i c t i o n s of the P r e c o m b u s t i o n F l u i d M o t i o n and Combustion Rate i n a S p a r k - I g n i t i o n E n g i n e " , SAE 831697 37. P.O.WITZE, "A C r i t i c a l Comparison of Hot-Wire Anemometry and L a s e r Doppler V e l o c i m e t r y f o r I.C.Engine A p p l i c a t i o n s " , SAE 800132 38. J.S.BENDAT, A.G.PIERSOL, "Random Data: A n a l y s i s and Measurement P r o c e d u r e s " 39. W.ANNAND, "Heat T r a n s f e r i n t h e C y l i n d e r s of R e c i p r o c a t i n g I n t e r n a l Combustion E n g i n e s " , Proc.Intn.Mech.Engrs V o l 177 No36 1963 -59-D r i v i n g C y l i n d e r : Bore 152.5 mm S t r o k e 254 mm Max. Working P r e s s u r e 10 Bar B r a k i n g C y l i n d e r : Bore 37.9 mm S t r o k e 254 mm Max. Working P r e s s u r e 160 Bar Combustion Chamber: Bore 101.6 mm S t r o k e 100 mm Max. Combustion P r e s s u r e 75 Bar I n t a k e V a l v e : Head Diameter 39.4 mm Max. L i f t 9.4 mm V a l v e Opens 24 Deg. ATDC V a l v e C l o s e s 20 Deg. ABDC Compression R a t i o used 8:1 Max. O r i f i c e Diameter 8.0 mm S i m u l a t e d R e v o l u t i o n 1000 RPM TABLE 1 BASIC DIMENSIONS OF THE RAPID INTAKE AND COMPRESSION MACHINE -60-PROBE: TSI MODEL 1226 No 46313 WIRE: TSI PLATINUM IRIDIUM, 6.3 MICROMETER DIAMETER, 1.5 mm LENGTH BRIDGE: DISA TYPE 55M10 CTA STANDARD BRIDGE FILTER: DISA TYPE 55D25 AUXILIARY UNIT, SET TO FILTER AT 20 kHz TABLE 2 HOT-WIRE ANEMOMETRY EQUIPMENT -61-MAIN No IGNITION AT IGNITION DELAY [ms] STANDARD DEVIATION [ms] COMBUSTION DURATION [ms] STANDARD DEVIATION [ms ] OF RUNS 2 STROKE TDC 4.546 0.581 6.806 0.879 1 5 2 STROKE 10°BTDC 3.756 0.440 5.936 1 .030 1 5 2 STROKE 20°BTDC 2.961 1.117 3.789 0.352 15 2 STROKE 30°BTDC 3.084 1 .309 3.256 0.374 1 5 1 STROKE TDC 7. 1 38 0.669 19.337 0.735 1 5 1 STROKE 10°BTDC 7.370 1 . 1 60 19.093 0.964 1 5 1 STROKE 20°BTDC 10.097 1 .605 17.887 0.743 1 5 1 STROKE 30°BTDC 9.072 0.970 19.495 1.414 1 1 TABLE 3 ENSEMBLE AVERAGED MASS FRACTION BURNED TOP VIEW: HVDRAULIC FLUID 0UMP1NC RESERVOIR -HYDRAULIC BRAKINO CrLINOER VALVE ACTUATOR -i X Q Orni O O 0^  - MOUNTING PLATE - CARTRfDOE VALVE HOUSING COMPRESSED AIR SUPPIV PLATES. MOUNTED OH A LATHE BED - PNEUMATIC DRIVINO CYLINDER O o MOUNTING PLATE MECHANICAL ENGINEERING DEPARTMENT I H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A «t«. JO I?. 64 RAPID COMPRESSION MACHINE MOUNTING OUTLAY t cn ro FIGURE 1 Rapid Compression Machine Mounting Outlay FIGURE 2 Rapid Compression Machine Crank Box FIGURE 3 Rapid Compression Machine Intake Valve Drive Train -65-8.0 o o OJ 4.0 0.0 Rack Ve loc i ty : 180 Crank Angle (Degree) 360 Piston Ve loc i ty : 4.0 I—r 180 Crank Angle (Degree) 360 FIGURE 4 Rack and Piston Velocity Intake and Compression Stroke -66-Rack Veloc i ty: 180 Crank Angle (Degree) 360 FIGURE 5 Rack and Piston Veloc i ty Compression Stroke only -67-SIDE VIEW: t X K-Y PISTON TOP DEAD CENTRE FIGURE 6 HOT-WIRE ANEMOMETER MEASUREMENT LOCATIONS 0.8-1 Crank Angle [Degree] FIGURE 7a Example of Instantaneous Velocity Trace One Stroke, Measurement Location 2 20-. Crank Angle [Degree] FIGURE 7b Example of Instantaneous Velocity Two Strokes, Measurement Location 3 -70-T i m e ( M i l l i s e c o n d s ) FIGURE 7 c Example o f the Window A v e r a g i n g and I n t e r p l o a t i o n Techn ique used Locations: L o c a t i o n 1 L o c a t i o n 2 L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 60 75 90 Time [Milliseconds] 105 120 135 FIGURE 8a Ensemble Averaged Mean Velocities Two Strokes, different Measurement Locations 150 Crank Angle [Degree] FIGURe 8b Ensemble Averaged Mean Velocities Two Strokes, different Measurement Locations Locations: L o c a t i o n 1  L o c a t i o n 2 L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 i 1 1 1 1 1 1 r— 0 20 40 60 80 100 120 140 Time [Milliseconds] FIGURE 9a Ensemble Averaged Turbulence Intensities Two Strokes, different Measurement Locations Crank Angle [Degree] FIGURE 9b Ensemble Averaged Turbulence Intensities Two Strokes, different Measurement Locations 6-Locations: L o c q t i o n 1 L o c a t i o n 2 L o c a t i o n 3 L o c a t i o n 4 0 120 60 80 100 Time [Milliseconds] FIGURE 10a Cyclic Variation Intensities Two Strokes, different Measurement Locations 7 Locations: Crank Angle [Degree] FIGURE 10b Cyclic Variation Intensities Two Strokes, different Measurement Locations Locations: A L o c a t i o n 1 X L o c a t i o n 2 • L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 -11 T 8 70 40 50 60 Time [Milliseconds] FIGURE 11a Ensemble Averaged Mean Velocities One Stroke, different Measurement Locations 80 90 100 0.7 0.6H 0.5H 0.4H 0.3 0.2-0.0 Locations: A L o c o t i o n 1 X L o c a t i o n 2 • L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 It 320 FIGURE 11b 240 2 6 0 2 8 0 3 0 0 Crank Angle [Degree] Ensemble Averaged Mean Velocities One Stroke, different Measurement Locations 3 4 0 0.20 0.16-.tr 0.12 to c 0) o c 0.08 0.04-0.00-Locations: L o c a t i o n 1 L o c a t i o n 2 L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 70 40 50 60 Time [Milliseconds] FIGURE 12a Ensemble Averaged Turbulence Intensities One Stroke, different Measurement Locations 80 90 100 i 0.20 0.16-0.12-0.08-0.04-0.00 180 200 220 240 260 280 300 320 Crank Angle [Degree] FIGURE 12b Ensemble Averaged Turbulence Intensities One Stroke, different Measurement Locations 340 360 '</) c C o 0.40-r 0.35 0.30 0.25 0.20H • > o ~o >-O 0.15H o.i(H 0.05 0.00 40 50 60 Time [Milliseconds] 70 Locations: A L o c a t i o n 1 X L o c a t i o n 2 • L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 80 90 FIGURE 13a Cyclic Variation Intensities One Stroke, different Measurement Locations 100 Locations: L o c a t i o n 1 L o c a t i o n 2 L o c a t i o n 3 L o c a t i o n 4 L o c a t i o n 5 IVC 180 200 220 320 240 260 280 300 Crank Angle [Degree] FIGURE 13b Cyclic Variation Intensities One Stroke, different Measurement Locations 340 360 25-1 O i 1 1 1 1 *—•—• —I r-0 20 40 60 80 100 Time [Milliseconds] FIGURE 14a Examples of Cylinder Pressure Traces One Stroke, Ignition 10 Deg before Top Dead Centre 35 Legend: 1 — • 1 i 1 i 1 ' " 1 20 40 60 80 100 120 140 160 Time [Milliseconds] FIGURE 14b Examples of Cylinder Pressure Traces Two Strokes, Ignition at 10 Deg before Top Dead Centre 1 Legend Time after Ignition [Milliseconds] FIGURE 15a Example of Mass Fraction Burned Curves Compression Stroke only Time after Ignition [Milliseconds] FIGURE 15b Examples of Mass Fraction Burned Curves Intake and Compression Stroke Time after Ignition [Milliseconds] FIGURE 16 Pressure Trace Averaged versus Mass Fraction Burned Averaged 1-1 Time after Ignition [Milliseconds] FIGURE 17 Ensemble Averaged Mass Fraction Burned Curves One and Two Strokes, different Ignition Times Time after Ignition [Milliseconds] FIGURE 18 Pressure Increase due to Combustion and Calculated Mass Fraction Burned -90-APPENDIX A: PROGRAMME DESCRIPTIONS: Page: a) Hot-Wire C a l i b r a t i o n Programme HWCAL b) Data S e p a r a t i o n and S c a l i n g Programme SEPARATE c) I n s t a n t a n e o u s V e l o c i t y Programme HWPRO d) Data R e d u c t i o n Programme DATRED Data P r o c e s s i n g F l o w c h a r t : CALIBRATION DATA RAW DATA 1 HWCAL SEPARATE 1_J HWPRO DATRED f RESULTS -91-APPENDIX A: a. Hot-Wire C a l i b r a t i o n Programme HWCAL T h i s programme was w r i t t e n and documented by Cameron [ 2 9 ] , I t uses the wind t u n n e l h o t - w i r e anemometer c a l i b r a t i o n d a t a and t r a n s f e r s i t i n t o N u s s e l t and Reynolds numbers. I t then uses a c u r v e f i t t i n g r o u t i n e t o det e r m i n e the c o n s t a n t s A,B and n t o f i t a c u r v e of the form Nu = A + B R e n t o the d a t a . The i n p u t parameters t o the programme a r e the ambient temperature and p r e s s u r e , o p e r a t i n g and i c e - p o i n t r e s i s t a n c e of the w i r e and the c a l i b r a t i o n d a t a p a i r s of p i t o t tube p r e s s u r e d i f f e r e n t i a l and b r i d g e v o l t a g e . Output parameters are the c o n s t a n t s A,B and n. -92-APPENDIX A: b. Data S e p a r a t i o n and S c a l i n g Programme SEPARATE T h i s programme s e p a r a t e s the s t r i n g of 4 d i g i t i n t e g e r numbers coming from the d a t a a c q u i s i t i o n system i n t o the number of c h a n n e l s used, here t h r e e , and s c a l e s the data a c c o r d i n g t o the measurement i n s t r u m e n t s e t t i n g . I n p u t s i n t o the programme are t h e raw d a t a s t r i n g and the r e f e r e n c e p r e s s u r e , o u t p u t s a r e the cra n k a n g l e / t i m e r e f e r e n c e , the c y l i n d e r p r e s s u r e and the h o t - w i r e anemometer b r i d g e v o l t a g e . The f i r s t c y l i n d e r p r e s s u r e r e a d i n g i s s e t to the v a l u e of the i n p u t r e f e r e n c e p r e s s u r e and a l l f o l l o w i n g p r e s s u r e r e a d i n g s a r e s c a l e d a c c o r d i n g l y . The raw p r e s s u r e d a t a i s smoothed u s i n g a s t a n d a r d smoothing r o u t i n e . The cr a n k a n g l e / t i m e r e f e r e n c e d a t a and the h o t - w i r e v o l t a g e and c y l i n d e r p r e s s u r e data a r e put i n t o s e p a r a t e o u t p u t f i l e s . - 9 3 -Flowchart SEPARATE: RAW INTEGER DATA STRING FROM ISAAC DATA ACQUISITION SYSTEM AMBIENT PRESSURE SEPARATE CHANNELS CRANK ANGLE PULSE BRIDGE VOLTAGE CYLINDER PRESSURE FIND DEGREE CRANK ANGLE t SCALE SCALE CRANK ANGLE/TIME OUTPUT FILE BRIDGE VOLTAGE AND CYLINDER PRESSURE OUTPUT FILE -94-APPENDIX A: c. I n s t a n t a n e o u s V e l i c i t y Programme HWPRO T h i s programme reads i n the h o t - w i r e anemometer b r i d g e v o l t a g e and c y l i n d e r p r e s s u r e d a t a from the programme SEPARATE and t r a n s f e r s i t i n t o i n s t a n t a n e o u s gas v e l o c i t y / t i m e d a t a p a i r s . The time r e f e r e n c e i s based on the se t s a m p l i n g r a t e . The i t e r a t i o n l o o p i s g i v e n i n the f l o w c h a r t . The c o m p u t a t i o n i s v e r y s i m i l a r t o the one i n the h o t - w i r e c a l i b r a t i o n programme HWCAL. The heat t r a n s f e r c o e f f i c i e n t , b e i n g the o n l y unknown parameter, i s found i t e r a t i v e l y . Based on t h i s heat t r a n s f e r c o e f f i c i e n t , the v e l o c i t y i s c a l c u l a t e d from the c a l i b r a t i o n N u s s e l t / R e y n o l d s number r e l a t i o n . Input- parameters a r e the b r i d g e v o l t a g e and c y l i n d e r p r e s s u r e , w i r e s p e c i f i c a t i o n s such as the c a l i b r a t i o n c o n s t a n t s from the programme HWCAL, o p e r a t i n g and ambient w i r e r e s i s t e n c e and the ambient c o n d i t i o n s such as temperature and p r e s s u r e . The gas tempe r a t u r e i s e s t i m a t e d from the c y l i n d e r p r e s s u r e assuming p o l y t r o p i c c o n d i t i o n s w i t h an exponent of 1.35. The gas p r o p e r t i e s were e v a l u a t e d a t the f r e e - s t r e a m c o n d i t i o n s . Output parameters a r e the gas v e l o c i t y / t i m e d a t a p a i r s . -95-F l o w e h a r t HWPRO: HOT-WIRE BRIDGE VOLTAGE CYLINDER PRESSURE A = E V 2 R 0 ( l - a 0 T 0 ) f f d l R T 2 B=EV 2R 0a 0/(7rdlR 2) T g = T 0 ( P / P 0 ) 1 .35 h I = E V 2 R w / ( k 7 T d l ( T w - T ) R T 2 ) ^ 0.8 C 2 = 4 ( h I - B ) / k w d E = t a n h ( / C , 2 l / 2 ) / / T 2 l h = ( A ( 1 - E ) + B ( T W - 2 T 0 E ) ) / ( T w - T +(T - 2 T 0 ) E ) | ( h - h j j / h j | < 0 . 0 1 y e s Nu=hd/k -no -t»»h=h. • p=P/RT V Mg° = Tg°' 7 6 R e = ( ( N u - A ) / B ) l / n t v = n/ p V=Rev/d i gas v e l o c i t y / t i m e - 9 6 -APPENDIX A; d. Data R e d u c t i o n Programme DATRED: T h i s programme reads i n the i n s t a n t a n e o u s gas v e l o c i t y / t i m e d a t a p a i r s from the HWPRO programme and the cran k a n g l e / t i m e r e f e r e n c e d a t a from the SEPARATE programme f o r the number of runs n and c a l c u l a t e s mean v e l o c i t i e s , t u r b u l e n c e i n t e n s i t i e s and c y c l i c v a r i a t i o n v e l o c i t i e s based on a c y c l e - b y - c y c l e a n a l y s i s . The gas v e l o c i t y i s averaged over a window T. A c u r v e i s f i t t e d t h r o ugh the window averaged p o i n t s u s i n g a c u b i c - s p l i n e r o u t i n e . T h i s c u r v e i s d e f i n e d as the mean v e l o c i t y of t h a t r u n . The ensemble averaged mean v e l o c i t y i s found by a v e r a g i n g the mean v e l o c i t y c u r v e s over the number of r u n s . The f l u c t u a t i n g v e l o c i t y i s d e f i n e d as the d i f f e r e n c e between the i n s t a n t a n e o u s and the mean v e l o c i t y of t h a t r u n . The t u r b u l e n c e i n t e n s i t y r e p r e s e n t s the r o o t mean square v a l u e of the f l u c t u a t i n g v e l o c i t y over the window T. The ensemble averaged t u r b u l e n c e i n t e n s i t y i s computed by a v e r a g i n g the t u r b u l e n c e i n t e n s i t y c u r v e s over the number of r u n s . The c y c l i c v a r i a t i o n v e l o c i t y i s d e f i n e d as the d i f f e r e n c e between mean v e l o c i t y of t h a t run and the ensemble averaged mean v e l o c i t y . The c y c l i c v a r i a t i o n i n t e n s i t y r e p r e s e n t s t h e r o o t mean square v a l u e of the c y c l i c v a r i a t i o n v e l o c i t i e s over the number of r u n s . Input parameters a r e the gas v e l o c i t y / t i m e d a t a p a i r s , the crank a n g l e / t i m e r e f e r e n c e d a t a and the number of runs. -97-Output parameters are the ensemble averaged mean v e l o c i t y versus time and versus crank angle, the ensemble averaged t u r b u l e n c e i n t e n s i t y versus time and versus crank angle and the c y c l i c v a r i a t i o n i n t e n s i t y versus time and versus crank a n g l e . -98-Flowe h a r t DATRED: i n s t a n t a n e o u s gas v e l o c i t y U ( t , n ) crank a n g l e / t i m e r e f e r e n c e d a t a WINDOW AVERAGE CURVE FIT: 0 ( t , n ) J I ENSEMBLE AVERAGE:Og(t) u ( t , n ) = U ( t , n ) - 0 ( t , n ) CALCULATE RMS AND CURVE FIT: u ' ( t , n ) ENSEMBLE AVERAGE: u ' ( t ) U c ( t , n ) = 0 ( t , n ) - O p ( t ) CALCULATE RMS AND CURVE F I T : U£(t) RESULTS VERSUS TIME AND RESULTS VERSUS CRANK ANGLE -99-APPENDIX B: PROGRAMME DESCRIPTIONS: Page: a) Data S e p a r a t i o n and S c a l i n g Programme SEPARATE2 b) Data R e d u c t i o n and R e s c a l i n g Programme DATSCALE c) Mass F r a c t i o n Burned Programme MB d) Data R e d u c t i o n Programme MB_AVERAGE Data P r o c e s s i n g F l o w c h a r t : RAW DATA SEPARATE2 L DATSCALE i MB t RESULTS -100-APPENDIX B: a. Data S e p a r a t i n g and S c a l i n g Programme SEPARATE2 T h i s programme i s a m o d i f i e d v e r s i o n of the programme SEPARATE d e s c r i b e d i n appendix A. I t reads i n the raw i n t e g e r d a t a s t r i n g from the ISAAC d a t a a c q u i s i t i o n system, s e p a r a t e s i t i n t o t h r e e c h a n n e l s and s c a l e s the d a t a a c c o r d i n g t o the i n s t r u m e n t s e t t i n g . The t h r e e c h a n n e l s a re the crank a n g l e p o s i t i o n , c y l i n d e r p r e s s u r e and the v o l t a g e of the p r i m a r y c i r c u i t of the i g n i t i o n c o i l , b e i n g used t o d e t e c t i g n i t i o n . Input parameters a r e the raw d a t a and r e f e r e n c e p r e s s u r e , o u t p u t s a r e the cra n k a n g l e / t i m e r e f e r e n c e d a t a , c y l i n d e r p r e s s u r e and time of i g n i t i o n , found from the i g n i t i o n c o i l v o l t a g e . The time r e f e r e n c e a g a i n i s known from the s e t sa m p l i n g r a t e . -101-F l o w c h a r t SEPARATE2: RAW INTEGER DATA STRING FROM ISAAC DATA ACQUISITION SYSTEM AMBIENT PRESSURE 1 SEPARATE CHANNELS IGNITION COIL VOLTAGE CRANK ANGLE PULSE FIND DEGREE CRANK ANGLE CYLINDER PRESSURE T SCALE r FIND IGNITION TIME CRANK ANGLE/TIME OUTPUT F I L E CYLINDER PRESSURE AND IGNITION TIME OUTPUT F I L E -102-APPENDIX B: b. Data R e d u c t i o n and R e s c a l i n g Programme DATSCALE T h i s programme was w r i t t e n i n o r d e r t o b r i n g the data from the programme SEPARATE2 i n t o a form t h a t the programme MB can read w i t h o u t major m o d i f i a t i o n s . DATSCALE reads i n the c y l i n d e r p r e s s u r e and cra n k a n g l e / t i m e r e f e r e n c e d a t a from the programme SEPARATE2, r e s c a l e s the p r e s s u r e d a t a from bar t o kPa and reduces the amount of d a t a by a f a c t o r of 10. C o r r e s p o n d i n g t o a c o n s t a n t time i n c r e m e n t , i t f i n d e s the r e s p e c t i v e c r a n k a n g l e p o s i t i o n by i n t e r p o l a t i o n . The time a x i s i s r e s c a l e d , such t h a t the i n t a k e p r o c e s s i s cut o f f . The new time r e f e r e n c e s t a r t s a t bottom dead c e n t r e , because the programme MB s t a r t s c a l c u l a t i n g a t bottom dead c e n t r e b e f o r e c o m p r e s s i o n . Output parameters a r e the t i m e , c y l i n d e r p r e s s u r e and crank a n g l e p o s i t i o n , s t a r t i n g a t bottom dead c e n t r e and s t o p p i n g a t t o p dead c e n t r e w i t h t h e p i s t o n coming t o a s t o p . -103-F l o w c h a r t DATSCALE: CYLINDER PRESSURE RESCALE REDUCE t CRANK ANGLE/TIME REFERENCE DATA FIND BOTTOM DEAD CENTRE SET REFERENCE TIME ZERO AT BDC FOR CONSTANT TIME INCREMENT FIND CRANK ANGLE POSITION AND CYLINDER PRESSURE TIME CYLINDER PRESSURE CRANK ANGLE POSITION -104-APPENDIX B: c. Mass F r a c t i o n Burned Programme MB: T h i s programme i s a m o d i f i e d v e r s i o n of the programme MB w r i t t e n , used and documented by Jones [ 3 3 ] , I t was changed from a c o n s t a n t crank a n g l e degree s t e p increment t o a c o n s t a n t time i n c r e m e n t , because i n the case of the R a p i d I n t a k e and Compression machine the p i s t o n comes t o a s t o p a t t o p dead c e n t r e . The s u b r o u t i n e VOL was changed t o accomodate the geometry of the R a p i d I n t a k e and Compression machine combustion chamber. The programme c o n t i n u e s c a l c u l a t i o n p a s t t op dead c e n t r e u s i n g c o n s t a n t c y l i n d e r volume. B a s i c assumptions made i n the programme a r e l i s t e d i n Chapter 4.2.2 of t h i s work, f o r f u r t h e r d e s c r i p t i o n see Jones [ 3 3 ] . Input parameters a r e the c y l i n d e r p r e s s u r e , time and crank a n g l e p o s t i o n d a t a from the programme DATSCALE, ambient c o n d i t i o n s , m i x t u r e p a r a m e t e r s , o p e r a t i n g c o n d i t i o n s , geometry and heat t r a n s f e r c o n s t a n t s . Output parameters a r e the mass f r a c t i o n burned v e r s u s t i m e . -105-APPENDIX B; d. Data R e d u c t i o n Programme MB AVERAGE: T h i s programme reads i n the mass f r a c t i o n burned i n f o r m a t i o n of the number of runs and c a l c u l a t e s the ensemble averaged mass f r a c t i o n burned c u r v e . The i g n i t i o n time i s ta k e n as r e f e r e n c e p o i n t f o r the ensemble a v e r a g i n g of the mass f r a c t i o n burned c u r v e s . The mean i g n i t i o n d e l a y and mean main combustion d u r a t i o n a re computed as w e l l as t h e i r s t a n d a r d d e v i a t i o n s , l i s t e d i n TABLE 3 . Input parameters a re the number of r u n s , the mass f r a c t i o n burned c u r v e s from the programme MB and the i g n i t i o n time from the programme SEPARATE2. Output parameters a r e the ensemble averaged mass f r a c t i o n burned c u r v e , the mean i g n i t i o n d e l a y p e r i o d and the mean main combustion d u r a t i o n and t h e i r s t a n d a r d d e v i a t i o n s . -106-F l o w c h a r t MB_AVERAGE: MASS FRACTION BURNED CURVES IGNITION TIMES t RESET TIME SCALE TO ZERO AT IGNITION ENSEMBLE AVERAGE MASS FRACTION BURNED CURVES CALCULATE MEAN IGNITION DELAY AND STANDARD DEVIATION CALCULATE MEAN MAIN COMBUSTION DURATION AND STANDARD DEVIATION w 1 I OUTPUT -107-APPENDIX C: DESIGN OUTLINE AND LIMITATIONS OF THE RAPID INTAKE AND COMPRESSION MACHINE: a. I n t r o d u c t i o n b. O u t l i n e of the Design Process c. L i m i t a t i o n s of C r i t i c a l Components d. L i m i t a t i o n s of the Rapid Intake and Compression Machine -108-APPENDIX C; a. I n t r o d u c t i o n The f o l l o w i n g i s a d e s c r i p t i o n of the d e s i g n p r o c e s s , hardware and l i m i t a t i o n s of the r a p i d i n t a k e and compression machine. A manual f o r o p e r a t i o n i s i n c l u d e d i n appendix d as w e l l as some recommendations r e g a r d i n g maintenance of the machine. I t i s h i g h l y recommended t h a t o p e r a t o r s of the machine f a m i l i a r i z e t h e m s e l f e s w i t h the d e s i g n , f u n c t i o n s and l i m i t a t i o n s of the machine b e f o r e o p e r a t i o n . A complete s e t of d e s i g n drawings i s w i t h Dr.Evans and w i t h John Hoar i n the work shop. Most components of the d r i v e - t r a i n of the machine were bought o f f - t h e - s h e l f and m o d i f i e d when n e c e s s a r y . Most components of the crank box and crank s h a f t were made i n the shop of the Department of M e c h a n i c a l E n g i n e e r i n g a t the U n i v e r s i t y of B r i t i s h C olumbia. -109-APPENDIX C: b. O u t l i n e of the Design P r o c e s s I t i s c o n s i d e r a b l y e a s i e r t o c o n t r o l a t r a n s l a t i o n a l motion a l o n g a l i n e w i t h o u t motion r e v e r s a l than w i t h motion r e v e r s a l . T h e r e f o r e an i n - l i n e t r a n s l a t i o n a l d r i v e - t r a i n c oncept was chosen, u s i n g a crank s h a f t t o t r a n s f e r the t r a n s l a t i o n a l motion i n t o a r o t a t i o n a l m o t i o n , which i n t u r n i s t r a n s f e r e d i n t o the d e s i r e d t r a n s l a t i o n a l motion w i t h motion r e v e r s a l by the crank s h a f t and c o n n e c t i n g r o d . S t a r t i n g w i t h the combustion chamber, i t was d e c i d e d t o use a f l a t - d i s k geometry w i t h o u t s w i r l or s q u i s h f o r the f i r s t s e r i e s of e x p e r i m e n t s , but t o i n c l u d e the o p t i o n of chan g i n g the combustion chamber geometry e a s i l y . T h e r e f o r e the p i s t o n f e a t u r e s a removable p i s t o n crown such t h a t by r e p l a c i n g the p i s t o n crown the combustion chamber geometry can be changed. The co m p r e s s i o n r a t i o can be changed by r e p l a c i n g a r i n g , on which the c y l i n d e r tube r e s t s . The p i s t o n d i a m e t e r was chosen t o be f o u r i n c h e s . T h i s v a l u e i s s l i g h t l y l a r g e r than i n most c a r e n g i n e s and was chosen because a l a r g e r p i s t o n d i a m e t e r makes a c c e s s t o the combustion chamber e a s i e r . Even w i t h the i n t a k e v a l v e mounted, o p t i c a l a c c e s s t o 50% of the combustion chamber can be made p o s s i b l e . The p i s t o n and p i s t o n crown a r e made of aluminum i n o r d e r t o reduce t h e i r w e i g t h . The c h o i c e of f o u r i n c h e s p i s t o n d i a m e t e r was f u r t h e r f a v o u r e d by the f a c t t h a t t u b i n g of -110-t h a t i n n e r d i a m e t e r was a v a i l a b l e o f f - t h e - s h e l f w i t h micro-honed i n s i d e s u r f a c e , which was used f o r the c y l i n d e r . A s p e c i a l s e a l was p l a c e d between the p i s t o n and the c y l i n d e r w a l l , because r e g u l a r p i s t o n r i n g s l e a k . A P a r k e r p i p s e a l was chosen f o r t h i s p u r p o s e , because i t s e a l s both ways and can ta k e h i g h p r e s s u r e s . The m a t e r i a l used i s c o m p a t i b l e w i t h m i n e r a l o i l s and o i l d e r i v e d f u e l s . I t was d e c i d e d t o s t o p the p i s t o n motion a t t o p dead c e n t r e , t h e r e b y c r e a t i n g a co n s t a n t - v o l u m e combustion chamber w i t h p i s t o n - i n d u c e d f l o w m o t i o n . H i g h peak p r e s s u r e s can be reached under th e s e c o n d i t i o n s , because the c y l i n d e r volume i s a t a minimum a t t o p dead c e n t r e and no work i s done. T h e r e f o r e a maximum combustion p r e s s u r e of 100 bar was chosen as i n i t i a l d e s i g n v a l u e . L a t e r t h i s l i m i t was reduced t o 75 bar i n o r d e r t o i n c r e a s e the s a f e t y m a r g i n . A c y l i n d e r p r e s s u r e of 100 b a r , a c t i n g on a p i s t o n of f o u r i n c h e s d i a m e t e r , t r a n s l a t e s i n t o a f o r c e of 81.07 kN or a p p r o x i m a t e l y 8 m e t r i c t o n n e s . T h i s h i g h f o r c e n e c e s s i t a t e s a s t r o n g c r a n k s h a f t and c o n n e c t i n g r o d . I n p a r t i c u l a r the cr a n k s h a f t i s h i g h l y s t r e s s e d under a bending moment and shear l o a d . Because of t h i s h i g h l o a d the crank s h a f t and p i s t o n p i n a r e made out of G43400, hardened and tempered. The crank s h a f t i s p r e s s - f i t t e d t o g e t h e r . S h o u l d a s i t u a t i o n be e n c o u n t e r e d i n which h i g h c o m p r e s s i o n r a t i o s a r e used, e.g. i n the s i m u l a t i o n of D i e s e l engine c o n d i t i o n s , and the l i m i t of 75 bar c y l i n d e r p r e s s u r e may be exceeded, then the o p t i o n of s t o p p i n g the p i s t o n a f t e r t o p -Ill-dead c e n t r e c o u l d be used t o reduce the maximum c y l i n d e r p r e s s u r e . A l l o w i n g the p i s t o n t o move past t o p dead c e n t r e i n c r e a s e s the c y l i n d e r volume and some work i s done. Thus the maximum c y l i n d e r p r e s s u r e i s reduced. The c o n n e c t i n g rod b e a r i n g s a r e p l a i n s p h e r i c a l b e a r i n g s , because r o l l e r b e a r i n g s of s u f f i c i e n t l y s m a l l d i a m e t e r c o u l d not have taken the h i g h s t a t i c l o a d . The crank s h a f t b e a r i n g s , a r e heavy duty c y l i n d r i c a l r o l l e r b e a r i n g s . The c o n n e c t i n g rod can be d i s c o n n e c t e d on e i t h e r end. The w e i g t h of the moving p a r t s l i s t e d so f a r was e s t i m a t e d t o be a p p r o x i m a t e l y 11 kg. In o r d e r t o be a b l e t o a c c e l e r a t e the crank s h a f t s u f f i c i e n t l y f a s t , a h i g h t o r q u e has t o be t r a n s m i t t e d t o the s h a f t . C e r t a i n s i z e s of f i t t i n g r a c k s and p i n i o n s a re a v a i l a b l e c o m m e r c i a l l y . A rack and p i n i o n c o m b i n a t i o n a l l o w s t o t r a n s m i t h i g h l o a d s both ways and t r a n s f o r m s a f o r c e i n t o a torque and v i c e v e r s a . The l i m i t i n g f a c t o r i n terms of maximum l o a d t r a n s m i t t a b l e i s the s t r e s s on the base of the gear t e e t h . S i n c e w i t h s t r a i g h t gears o n l y one t o o t h i s engaged a t a t i m e , one t o o t h c a r r i e s a l l the l o a d . The diam e t e r and w i d t h of the ra c k and p i n i o n c o m b i n a t i o n was chosen a c c o r d i n g t o t h i s l i m i t a t i o n . I n t h i s case the d e c i s i o n was made on the c o n s e r v a t i v e s i d e w i t h a chosen w i d t h of two i n c h e s . The v a l u e s of maximum a c c e l e r a t i o n found i n t h e ex p e r i m e n t s a r e below the v a l u e s assumed i n the c a l c u l a t i o n s , so t h a t a rack and p i n i o n of one and a h a l f i n c h e s w i d t h would have been s u f f i c i e n t . I n the chosen -112-c o n f i g u r a t i o n a rack s t r o k e of 254 mm t r a n s l a t e s i n t o a p p r o x i m a t e l y 382 degrees crank a n g l e r e v o l u t i o n . U s i n g a rac k and p i n i o n has the g r e a t advantage t h a t , depending on the g e a r - t e e t h s p a c i n g , numerous sequences of s t r o k e s can be r u n , as l o n g as they c o v e r 382 c o n s e c u t i v e degrees crank a n g l e . The change from one s i m u l a t e d sequence of s t r o k e s t o a n o t h e r can be a c h i e v e d e a s i l y by d i s c o n n e c t i n g the rack from the p i n i o n , s e t t i n g the crank s h a f t ' a n d p i n i o n i n t o the new d e s i r e d p o s i t i o n and c o n n e c t i n g the rack and p i n i o n a g a i n . The rack and p i n i o n c o n t r i b u t e about 11.5 kg of w e i g h t . I t was chosen t o use a pneumatic system on the d r i v i n g s i d e , because pneumatic systems a re w i d e l y used and c l e a n . P a r t s a r e e a s i l y a v a i l a b l e . A compressor and p r e s s u r e tank were a v a i l a b l e a t the department. The compressor can produce a maximum p r e s s u r e of 150 p s i or 10 b a r . The maximum p r e s s u r e r a t i n g of the tank i s 200 p s i or 13.8 b a r . The tank was used as a p r e s s u r e r e s e r v o i r i n o r d e r t o m a i n t a i n a c o n s t a n t d r i v i n g p r e s s u r e . For the d r i v i n g c y l i n d e r a d i a m e t e r of s i x i n c h e s was chosen, g i v i n g 18.24 kN of d r i v i n g f o r c e a t 10 bar p r e s s u r e . The pneumatic d r i v i n g c y l i n d e r has a b r a k i n g system, which was used i n i t i a l l y . L a t e r i t was found t h a t i t s t a r t e d b r a k i n g t o o e a r l y and i t was d i s a b l e d by removing the p a r t i c u l a r s e a l t h a t e n c l o s e d the b r a k i n g volume. The d r i v i n g c y l i n d e r has a s t r o k e of 254 mm. -113-A h y d r a u l i c system was chosen f o r the b r a k i n g s i d e because of the i n c o m p r e s s i b l e n a t u r e of the h y d r a u l i c f l u i d . By c o n t r o l l i n g the amount of f l u i d r e l e a s e d per t i m e , the motion of the h y d r a u l i c p i s t o n can be c o n t r o l l e d . H y d r a u l i c systems a r e u s u a l l y d e s i g n e d f o r h i g h p r e s s u r e s . I t was d e c i d e d t o use a c y l i n d e r of s m a l l d i a m e t e r and h i g h p r e s s u r e i n o r d e r t o reduce the f l o w r a t e of the f l u i d . A dia m e t e r of 37.9 mm was chosen. In the case of no rack motion and n e g l e c t i n g f r i c t i o n e f f e c t s , a d r i v i n g p r e s s u r e of 10 bar t r a n s l a t e s i n t o a b r a k i n g p r e s s u r e of 160 bar or 2320 p s i . I t was d e c i d e d t o use an o r i f i c e i n o r d e r t o c o n t r o l the amount of h y d r a u l i c f l u i d r e l e a s e d per t i m e . For a g i v e n geometry and f l u i d , the f l o w r a t e t h r o u g h the o r i f i c e i s p r o p o r t i o n a l t o the square r o o t of the p r e s s u r e drop a c r o s s the o r i f i c e . T h i s means t h a t i n i t i a l l y , when s t a r t i n g w i t h the system a t r e s t , t h e r e i s l i t t l e p r e s s u r e d r o p a c r o s s the o r i f i c e because t h e r e i s l i t t l e f l o w t h r o u g h i t . From t h i s i t f o l l o w s t h a t a t the b e g i n n i n g of the rack motion most of the d r i v i n g f o r c e i s a v a i l a b l e f o r f a s t a c c e l e r a t i o n , because t h e b r a k i n g f o r c e i s s m a l l . Once a c e r t a i n rack v e l o c i t y i s reached and the o u t f l o w t h r o u g h the o r i f i c e i s e s t a b l i s h e d , the p r e s s u r e drop a c r o s s i t i n c r e a s e s f a s t and a b a l a n c e i s reached. The f l o w r a t e t h r o u g h the o r i f i c e i s not v e r y s e n s i t i v e t o f l u c t u a t i o n s i n the p r e s s u r e drop a c r o s s i t , e.g. from the motion r e v e r s a l of t h e p i s t o n and c o n n e c t i n g r o d , because of the s q u a r e - r o o t n a t u r e of the -114-r e l a t i o n . F a s t i n i t i a t i o n of rack motion i s d e s i r a b l e . T h e r e f o r e a c o m b i n a t i o n of c a r t r i d g e v a l v e and f a s t response s o l e n o i d v a l v e were chosen t o i n i t i a t e the motion on the h y d r a u l i c s i d e . The pneumatic d r i v i n g s i d e i s p r e s s u r i z e d w i t h o u t a l l o w i n g h y d r a u l i c f l u i d t o escape on the b r a k i n g s i d e . Then the s o l e n o i d v a l v e i s t r i g g e r e d e l e c t r i c a l l y . I t r e l e a s e s a p i l o t volume of 1.6 cm 3 of f l u i d from the c a r t r i d g e v a l v e , w i t h s u b s e q u e n t l y moves r a p i d l y , opening l a r g e f l o w a r e a s i n the p r o c e s s . The response time of the s o l e n o i d v a l v e and c a r t r i d g e v a l v e c o m b i n a t i o n i s a p p r o x i m a t e l y 15 ms. Once the c a r t r i d g e v a l v e has moved and opened l a r g e f l o w a r e a s , the o r i f i c e i s the most r e s t r i c i n g and t h e r e f o r e c o n t r o l l i n g element. The f i n a l b r a k i n g of the machine i s done by a p i n , which i s a t t a c h e d t o the p i s t o n of the h y d r a u l i c c y l i n d e r . T h i s p i n moves i n t o the o u t f l o w h o l e of the c y l i n d e r towards the end of the s t r o k e , t h u s r e s t r i c t i n g t h e o u t f l o w and d e c e l e r a t i n g the d r i v e t r a i n . The s t a n d a r d o u t f l o w h o l e of the o f f - t h e - s h e l f h y d r a u l i c c y l i n d e r was opened up i n o r d e r t o reduce the f l o w r e s t r i c t i o n . A s l e e v e was made f o r the s t a n d a r d b r a k i n g p i n on t h e p i s t o n . A s i m p l e b r a k i n g s i m u l a t i o n programme was w r i t t e n and used t o f i n d the most s u i t a b l e s l e e v e geometry. T h i s programme assumed l i n e a r d e c e l e r a t i o n and i t e r a t i v e l y c a l c u l a t e d the p i n d i a m e t e r needed f o r a g i v e n p o s i t i o n and v e l o c i t y i n o r d e r t o a c h i e v e -115-l i n e a r d e c e l e r a t i o n . The c y l i n d e r head was f i t t e d w i t h an i n t a k e v a l v e , which was chosen from a c a t a l o g e f o r i t s d i m e n s i o n s . I t was p o s i t i o n e d i n the head such t h a t i t would be p o s s i b l e t o r e p l a c e p a r t of the head by a q u a r t z g l a s s window. S t i l l k e e p i n g a r e g u l a r i n t a k e system, e x a c t l y h a l f of the combustion chamber c o u l d be a c c e s s e d o p t i c a l l y . For r e a s o n s of s i m p l i c i t y i t was d e c i d e d t o o p e r a t e the i n t a k e v a l v e w i t h a r o c k e r arm and push r o d . The push rod i t s e l f i s d r i v e n by a p i n , which runs i n a groove i n a p l a t e , which i s mounted on the r a c k . The groove was m i l l e d w i t h a n u m e r i c a l l y c o n t r o l l e d machine and r e p r e s e n t s the v a l v e l i f t c h a r a c t e r i s t i c s of the R i c a r d o Hydra e n g i n e . U n f o r t u n a t e l y a d e s i g n e r r o r was made w i t h the way the p i n d i s c o n n e c t s from the p l a t e . T u r n i n g around a h i n g e , the p l a t e c o n n e c t i n g the p i n and push rod changes i t s p o s i t i o n w h i l e the p i n d i s c o n n e c t s , and h i t s the push r o d . The push rod i n t u r n causes the r o c k e r arm t o h i t the i n t a k e v a l v e . A b e t t e r system of d i s c o n n e c t i n g the p i n from the p l a t e s h o u l d be i n s t a l l e d b e f o r e a new s e r i e s of e x p e r i m e n t s i s begun, which i n v o l v e s the engine i n t a k e p r o c e s s . G r e a t c a r e was taken d u r i n g the assembly p r o c e s s t o e nsure good a l i g n m e n t of the d r i v i n g c y l i n d e r , the r a c k , the c r a n k box and the b r a k i n g c y l i n d e r i n o r d e r t o e l i m i n a t e s i d e f o r c e s on the r a c k and on t h e c y l i n d e r s . -116-APPENDIX C: c. L i m i t a t i o n s of C r i t i c a l Components  Crank s h a f t Due t o the h i g h bending moment on the s h a f t , the maximum c y l i n d e r p r e s s u r e s h o u l d not exceed 75 b a r . The maximum t o r q u e on the crank s h a f t s h o u l d not exceed 500 Nm. P i s t o n s e a l The p i s t o n i s equipped w i t h a r e g u l a r m e t a l p i s t o n r i n g and a P a r k e r p i p s e a l , which s e a l s both ways. The maximum recommended p r e s s u r e f o r the p i p s e a l i s 7000 p s i or 482 bar and i s v e r y much h i g h e r than the maximum c y l i n d e r p r e s s u r e recommended. The polymyte m a t e r i a l i s c o m p a t i b l e w i t h m i n a r a l base o i l s and f u e l s . The temperature rage of the s e a l i s g i v e n w i t h -54°C t o 135°C. No i n f o r m a t i o n was found on the maximum v e l o c i t y recommended f o r the s e a l . P r o p e r l u b r i c a t i o n i s e s s e n t i a l f o r the s e a l l i p s a t the v e l o c i t i e s i t i s exposed t o i n the r a p i d i n t a k e and compres s i o n machine. C o n n e c t i n g r o d The c o n n e c t i n g rod i s under a b u c k l i n g l o a d d u r i n g c o m b u s t i o n . T h i s b u c k l i n g l o a d s h o u l d not exceed 80 kN. E i t h e r end of t h e c o n n e c t i n g r o d i s t h r e a d e d . L o c k - t i g h t was used on bo t h t h r e a d s t o ensure t h a t the c o n n e c t i n g rod c o u l d not l o o s e n d u r i n g o p e r a t i o n . -117-Rack and p i n i o n The maximum f o r c e t r a n s m i t t e d between rack and p i n i o n s h o u l d not exceed 10 kN, t r a n s l a t i n g i n t o a maximum t o r q u e of 380 Nm. The s t r e s s on the base of the gear t e e t h as w e l l as the e x c e n t r i c bending f o r c e on the s h a f t a r e the l i m i t i n g f a c t o r s . The ra c k i s under a b u c k l i n g l o a d . The maximum b u c k l i n g l o a d s h o u l d not exceed 100 kN. Wi t h the p r e s e n t d r i v i n g c y l i n d e r t h i s l i m i t can not be reached. Proper l u b r i c a t i o n of the rack i s i m p o r t a n t , as i t s l i d e s t h r o u g h the cra n k box. Rack d e v i c e s The f o r c e s on the rack d e v i c e s s h o u l d not exceed the maximum d r i v i n g f o r c e of 18.24 kN t h a t the p r e s e n t d r i v i n g c y l i n d e r can produce. In p a r t i c u l a r the d e v i c e on the h y d r a u l i c s i d e s h o u l d not be o v e r l o a d e d . The s a f e t y - p i n s have t o be i n p l a c e a t a l l t i m e s under l o a d . D r i v i n g c y l i n d e r The p r e s s u r e l i m i t on the p r e s e n t d r i v i n g c y l i n d e r i s 150 p s i or 10 b a r . I t has a d i a m e t e r of 152.2 mm and a s t r o k e of 254 mm. The b r a k i n g of the d r i v i n g c y l i n d e r was d i s a b l e d by removing the b r a k i n g s e a l . The maximum recommended v e l o c i t y f o r the c y l i n d e r s e a l s i s 4 m/s. Pro p e r l u b r i c a t i o n i s e s s e n t i a l f o r the s e a l s . The c y l i n d e r r o d s h o u l d not be exposed t o s i d e f o r c e s . F i l t e r i n g of the compressed a i r h e l p s t o reduce the amount of dust and p a r t i c l e s t h a t -118-accumulate i n the d r i v i n g c y l i n d e r and cause wear of the s e a l s . Compressed a i r r e s e r v o i r The r e s e r v o i r used f o r the compressed a i r i s s i m p l y the tank of an a i r compressor w i t h a volume of a p p r o x i m a t e l y 40 l i t e r s . The upper p r e s s u r e l i m i t of the tank i s 200 p s i or 13.8 b a r . The compressor was used t o b r i n g the p r e s s u r e up i n i t i a l l y , then compressed a i r from h i g h - p r e s s u r e c y l i n d e r s was used w i t h a p r e s s u r e r e g u l a t o r t o m a i n t a i n a c o n s t a n t d r i v i n g p r e s s u r e . The f l e x i b l e t u b i n g between the tank and the d r i v i n g c y l i n d e r has an i n n e r d i a m e t e r of 1 1/2 i n c h e s and s h o u l d not be p r e s s u r i z e d beyond 150 p s i or 10 b a r . H y d r a u l i c c y l i n d e r The h y d r a u l i c b r a k i n g c y l i n d e r has an i n n e r d i a m e t e r of 37.9 mm and a s t r o k e of 254 mm. The maximum p r e s s u r e r a t i n g i s 3000 p s i or 207 b a r . Two s t a i n l e s s s t e e l b a l l v a l v e s a r e a t t a c h e d t o the h i g h - p r e s s u r e s i d e of the h y d r a u l i c c y l i n d e r . The v a l v e s e a t s of t h e s e b a l l v a l v e s a r e r a t e d up t o 2200 p s i or 152 b a r , the v a l v e b o d i e s a r e r a t e d up t o 2500 p s i or 172 b a r . In t h i s c a s e the v a l v e s a re the l i m i t i n g f a c t o r i n terms of p r e s s u r e . The b r a k i n g c y l i n d e r r o d s h o u l d not be exposed t o s i d e f o r c e s . C a r t r i d g e and s o l e n o i d v a l v e The c a r t r i d g e v a l v e has a p r e s s u r e r a t i n g of up t o 6000 p s i or 413 bar and a f l o w r a t e of up t o 50 gpm or 3154 cm 3/s. At a r a c k v e l o c i t y of 4 m/s the f l o w r a t e i s 4560 c r n 3 / s , -119-e x c e e d i n g the f l o w r a t e l i m i t of the v a l v e . The moving p a r t of the c a r t r i d g e v a l v e was s h o r t e n e d i n o r d e r t o i n c r e a s e the v a l v e l i f t and i n c r e a s e the f l o w r a t e of the v a l v e . I t s h o u l d a l s o be noted t h a t the f l o w t h r o u g h the v a l v e i s h i g h l y unsteady. The response time of the c a r t r i d g e and s o l e n o i d v a l v e was g i v e n t o be about 15 ms. The c a r t r i d g e v a l v e body s h o u l d be h a n d l e d w i t h g r e a t c a r e because the v a l v e s e a l s t h rough a v e r y t i g h t f i t between the v a l v e c y l i n d e r and the v a l v e h o u s i n g . Any d i s t u r b a n c e of the v a l v e s u r f a c e would l e a d t o l e a k a g e of the v a l v e and c r e e p of the r a c k under l o a d . The s o l e n o i d v a l v e opens the c a r t r i d g e v a l v e by dumping a p i l o t volume of 1.6 cm 3. I t i s a 3/2 way d i r e c t i o n a l poppet v a l v e o p e r a t e d by a 120 v o l t s o l e n o i d . The p r e s s u r e r a t i n g i s up t o 9000 p s i or 620 b a r . The maximum f l o w r a t e i s g i v e n t o be 9.5 gpm or 32 1/min. H y d r a u l i c f l u i d T r a n s former i n s u l a t i n g o i l was chosen as h y d r a u l i c f l u i d f o r i t s low v i s c o s i t y and s t a b i l i t y under shear l o a d . The f l u i d i s f o r c e d t h r o u g h the sharp-edged o r i f i c e under a h i g h p r e s s u r e drop and t h u s i s s u b j e c t t o h i g h shear f o r c e s . A s t a b l e and compact m o l e c u l a r s t r u c t u r e of the f l u i d i s r e q u i r e d . So f a r no problems w i t h the f l u i d were e n c o u n t e r e d i n terms of d e t e r i o r a t i o n of t h e f l u i d due t o break-up. -120-O r i f i c e The o r i f i c e i s a t h i n round s h e l l w i t h a h o l e i n the c e n t r e and a h i g h p r e s s u r e drop a c r o s s i t . I n i t i a l c o n c e r n about the s t r e n g t h of the o r i f i c e p r o v e d t o be unfounded. The h o l e d i a m e t e r was i n i t i a l l y e s t i m a t e d based on s i m u l a t i o n and comp u t a t i o n and l a t e r found by t r i a l and e r r o r . P r e s e n t l y a 8 mm d i a m e t e r h o l e i s used. O r i f i c e f a i l u r e c o u l d l e a d t o s e l f - d e s t r u c t i o n of the machine, because w i t h o u t the o r i f i c e the rack speed would i n c r e a s e and the f i n a l b r a k i n g would become even more severe than i t i s a l r e a d y . B r a k i n g The h y d r a u l i c b r a k i n g s t a r t s a p p r o x i m a t e l y 20 mm b e f o r e the end of the rack s t r o k e , w i t h the rack s t i l l h a v i n g a v e l o c i t y of about 3 m/s. The b r a k i n g i s s e v e r e and i t i s q u i t e l i k e l y t h a t the peak p r e s s u r e i n s i d e the h y d r a u l i c c y l i n d e r s h o r t l y exceeds the maximum p r e s s u r e r a t i n g of the c y l i n d e r and the b a l l v a l v e s . The d r i v e - t r a i n runs i n t o the end of i t s s t r o k e w i t h a v e l o c i t y of about 0.5 m/s. The compres s i o n i n s i d e the combustion chamber a s s i s t s the h y d r a u l i c b r a k i n g . -121-APPENDIX C: d. L i m i t a t i o n s of the R a p i d I n t a k e and Compression Machine The peak c y l i n d e r p r e s s u r e s h o u l d not exceed 75 bar i n the p r e s e n t c o n f i g u a r t i o n . S h o u l d a q u a r t z g l a s s window be i n s t a l l e d , then t h i s l i m i t may have t o lowered f u r t h e r . In t he p r e s e n t c o n f i g u r a t i o n an engine r e v o l u t i o n of 1000 rpm i s s i m u l a t e d , u s i n g an o r i f i c e of 8 mm h o l e d i a m e t e r and a d r i v i n g p r e s s u r e of 9 b a r . The maximum rack v e l o c i t y reached i s about 5 m/s. T h i s exceeds the v e l o c i t y l i m i t of the d r i v i n g c y l i n d e r s e a l , thus r e d u c i n g the o p e r a t i n g l i f e span of t h a t component. The b r a k i n g i s s e v e r e . I n c r e a s i n g the d r i v i n g p r e s s u r e t o 10 bar and i n c r e a s i n g the o r i f i c e d i a m e t e r , a h i g h e r r a c k v e l o c i t y c o u l d be r e a c h e d . The time needed f o r a c c e l e r a t i o n and d e c e l e r a t i o n would i n c r e a s e t o o . The h i g h e r the d e s i r e d v e l o c i t y , the more the c u r v e of r a c k v e l o c i t y v e r s u s time would change from an i d e e l r e c t a n g u l a r box-car f u n c t i o n t o a p a r a b o l a w i t h a d e s t i n c t v e l o c i t y maximum a t h a l f s t r o k e . The a c t u a l r a p i d i n t a k e and compres s i o n machine p i s t o n v e l o c i t y would be l e s s and l e s s s i m i l a r t o the p i s t o n v e l o c i t y i t i s i n t e n d e d t o s i m u l a t e . A r e v o l u t i o n of 1000 rpm t r a n s l a t e s i n t o 30 ms time per s t r o k e . P r e s e n t l y the machine com p l e t e s the t w o - s t r o k e run i n about 75 ms and the one,-stroke run i n about 40 ms. A c c e l e r a t i o n and d e c e l e r a t i o n t a k e r o u g h l y 10 ms time each a t t he p r e s e n t . From t h i s i t f o l l o w s d i r e c t l y t h a t the -122-maximum r e v o l u t i o n the p r e s e n t machine c o u l d p o s s i b l y s i m u l a t e i s about 1500 rpm, s i n c e i t would t a k e a t l e a s t 10 ms f o r a c c e l e r a t i o n t o maximum speed and 10 ms f o r d e c e l e r a t i o n . Compromizing i n terms of the shape of the c u r v e of rack v e l o c i t y v e r s u s t i m e , i t i s e s t i m a t e d t h a t i t would be p o s s i b l e t o push the o p e r a t i n g l i m i t s of the machine t o 1200-1300 rpm. The p r e s e n t l y s i m u l a t e d r e v o l u t i o n of 1000 rpm r e p r e s e n t s a good compromise between r u n n i n g the machine as f a s t as p o s s i b l e and y e t c l o s e l y s i m u l a t i n g the p i s t o n motion of an a c t u a l r e c i p r o c a t i n g e n g i n e . The machine has proven t o be r e l i a b l e under the d e s c i b e d o p e r a t i n g c o n d i t i o n s over more than 600 r u n s . No s i g n s of wear or damage were d e t e c t e d a f t e r t h a t number of r u n s . In the p r e s e n t work the i n t a k e and com p r e s s i o n s t r o k e a r e r u n , s t a r t i n g a t 22 degrees crank a n g l e b e f o r e t o p dead c e n t r e and s t o p p i n g a t t o p dead c e n t r e . Depending on the g e a r - t e e t h s p a c i n g of the rack and p i n i o n , v a r i o u s o t h e r sequences of s t r o k e s can be r u n , as l o n g as they c o v e r 382 c o n s e c u t i v e degrees crank a n g l e . -123-APPENDIX D: MANUAL AND MAINTENANCE PLAN FOR THE RAPID INTAKE AND COMPRESSION MACHINE: a. O p e r a t i o n Manual f o r the R a p i d I n t a k e and Compression Machine b. Maintenance P l a n -124-APPENDIX D; a. O p e r a t i o n Manual f o r the R a p i d I n t a k e and Compression  Machine The r a p i d i n t a k e and c o m p r e s s i o n machine s h o u l d be o p e r a t e d o n l y by p e o p l e who have f a m i l i a r i z e d t h e m s e l f e s w i t h the equipment. I t s h o u l d be o p e r a t e d o n l y w i t h the p l e x i g l a s c o v e r s i n p l a c e c o v e r i n g the rack on b oth s i d e s and the l i d b o l t e d down on t o p of the h y d r a u l i c f l u i d r e s e r v o i r . F i g u r e s D.1 and D.2 p i c t u r e the v a l v i n g of the machine s c h e m a t i c a l l y . V a l v e s V1 t o V3 a r e r e g u l a r n e e d l e v a l v e s . V4 i s a 1 1/2 i n c h s t a i n l e s s s t e e l b a l l v a l v e w i t h a 2200 p s i or 152 bar p r e s s u r e l i m i t . V5 i s a 1/2 i n c h b r a s s b a l l v a l v e , r a t e d up t o 1500 p s i or 103 b a r . The v a l v e V6 i s a 1/2 i n c h s t a i n l e s s s t e e l b a l l v a l v e . V7 i s a 3/4 i n c h s t a i n l e s s s t e e l b a l l v a l v e . Both v a l v e s V6 and V7 have a s e a t r a t i n g of 2200 p s i or 152 bar and a v a l v e body r a t i n g of up t o 2500 p s i or 172 b a r . V a l v e V8 r e p r e s e n t s the c a r t r i d g e v a l v e and V9 r e p r e s e n t s the s o l e n o i d v a l v e . The s o l e n o i d v a l v e i s t r i g g e r e d by the t r i g g e r box, which f e a t u r e s an o n / o f f - s w i t c h , a c o n t r o l l i g h t and a t r i g g e r p u s h - b u t t o n . The s o l e n o i d v a l v e i s o n l y o p e r a t e d i f the o n / o f f - s w i t c h i s i n the o n - p o s i t i o n , i n d i c a t e d by the r e d c o n t r o l - l i g h t b e i n g on, and the p u s h-button i s p r e s s e d . The o n / o f f - s w i t c h s h o u l d a l w a y s be i n the o f f - p o s i t i o n except * f o r f i r i n g of the machine i n o r d e r t o a v o i d a c c i d e n t a l a c t i v a t i o n of the s o l e n o i d . -125-The compressor can be used t o b r i n g the compressed a i r r e s e r v o i r up t o p r e s s u r e i n i t i a l l y . For t h a t the v a l v e s s h o u l d be c l o s e d . D u r i n g the runs compressed a i r from h i g h - p r e s s u r e c y l i n d e r s i s used, going t h r o u g h a p r e s s u r e r e g u l a t o r and v a l v e V1. V a l v e VI i s always open d u r i n g e x p e r i m e n t s . W i t h the rack b e i n g a t the b e g i n n i n g of i t s s t r o k e , v a l v e s V6 t o V8 s h o u l d be c l o s e d , i n p a r t i c u l a r v a l v e V6 has t o be always c l o s e d when p r e s s u r i z i n g the system. To p r e s s u r i z e the system, yet w i t h o u t rack m o t i o n , the v a l v e s e t t i n g i s : c l o s e d : V2,V3,V4,V6,V7,V8,V9 open: V1,V5. Opening v a l v e V4 p r e s s u r i z e s the d r i v i n g c y l i n d e r und thus the b r a k i n g c y l i n d e r . The p r e s s u r e i n the d r i v i n g c y l i n d e r i n t he same as i n the p r e s s u r e r e s e r v o i r . S i n c e no h y d r a u l i c f l u i d i s a l l o w e d t o escape y e t , the h i g h p r e s s u r e i n the h y d r a u l i c s i d e b a l a n c e s the d r i v i n g f o r c e and the rack does not move. To i n i t i a t e r a c k m o t i o n , the v a l v e V7 i s opened. At t h i s p o i n t the rack s l o w l y c r e e p s due t o leaka g e a t the c a r t r i d g e v a l v e . P u t t i n g the o n / o f f - s w i t c h of the t r i g g e r box i n t o the o n - p o s i t i o n and p r e s s i n g the pu s h - b u t t o n opens v a l v e s V9 and V8 and the rack moves r a p i d l y t o the end of i t s s t r o k e . A f t e r the t e s t , s e t the o n / o f f - s w i t c h back i n t o the o f f - p o s i t i o n , c l o s e v a l v e s V7, V4 and V5. Now a l l v a l v e s e x c e p t v a l v e V1 a r e c l o s e d . Some s m a l l gas b u b b l e s may form -126-i n t he h y d r a u l i c f l u i d d u r i n g a r un. These gas bubbles s h o u l d be g i v e n the time t o r i o e i n t o the h y d r a u l i c f l u i d r e s e r v o i r b e f o r e the rack i s d r i v e n back. To d r i v e the rack back, the v a l v e V6 i s opened. V a l v e V6 has to be always open t o d r i v e the rack back and has t o be always c l o s e d when the ra c k moves f o r w a r d . Opening v a l v e V2 b l e e d s the p r e s s u r e from the d r i v i n g c y l i n d e r , d e c r e a s i n g the d r i v i n g f o r c e . Opening v a l v e V3 s l o w l y w h i l e s t i l l b l e e d i n g the p r e s s u r e t h r o u g h v a l v e V2, the ra c k w i l l s t a r t t o s l o w l y move back. Pro p e r c o o r d i n a t i o n of the manual o p e r a t i o n of v a l v e s V2 and V3 l e a d s t o a smooth rack m o t i o n . Once the ra c k i s i n the d e s i r e d p o s i t i o n , v a l v e s V2, V3 and V6 a r e c l o s e d . A g a i n , a l l v a l v e s except v a l v e V1 a r e c l o s e d . The p r o c e d u r e s t a r t s a g a i n w i t h p r e s s u r i z i n g the system. To shut-down the machine, a l l v a l v e s a r e c l o s e d . The p r e s s u r e i s r e l e a s e d from the d r i v i n g c y l i n d e r t h r o u g h v a l v e s V2 and V5. For l o n g e r shut-down p e r i o d s , i t i s recommended t o b l e e d the compressed a i r tank as w e l l . F i gu r e 19 V a l v i n g on the d r i v i n g s i d e of the Rapid In take and Compress ion Machine vent c y l i nd er rod bra k i ng c y l i nder b r a k i n g p in f l u i d r e s e r v o i r f l u i d l e v e l V 6 0 i ^ V 7 o r i f i c e V8 V9 r o CO i t r i g g e r box F i g u r e 20 V a l v i n g on the b r a k i n g s i d e of the Rapid I n take and Compress ion Machine -129-APPENDIX D: b. Maintenance P l a n The h y d r a u l i c f l u i d l e v e l i n the r e s e r v o i r has t o be checked from time t o t i m e . A f t e r a p p r o x i m a t e l y 300 runs the h y d r a u l i c f l u i d s h o u l d be r e p l a c e d and the c a r t r i d g e v a l v e and o r i f i c e checked f o r damage. Watch f o r m e t a l c h i p s i n s i d e the h y d r a u l i c system, t h a t would i n d i c a t e damage. A f t e r the h y d r a u l i c system has been opened, a l l gas i n s i d e i t has t o be removed. T h i s can be a c h i e v e d by r u n n i n g the machine w i t h low d r i v i n g p r e s s u r e f o r a few t i m e s . The r a c k s h o u l d be l u b r i c a t e d a t l e a s t e v e r y 300 r u n s , as w e l l as t h e c y l i n d e r w a l l s and p i s t o n s e a l . At t h a t p o i n t the b e a r i n g s s h o u l d be i n s p e c t e d and l u b r i c a t e d as w e l l . A f t e r a p p r o x i m a t e l y every 600 runs the pneumatic c y l i n d e r s h o u l d be opened up, c l e a n e d , i n s p e c t e d and l u b r i c a t e d w i t h grease and p o s s i b l y some o i l . S h o u l d a c o n s i d e r a b l e amount of dust and p a r t i c l e s be found i n s i d e the c y l i n d e r , then the compressed a i r tank s h o u l d be c l e a n e d as w e l l . S i n c e t h e whole machine tends t o s l o w l y move due t o the sev e r e b r a k i n g , i t may have t o be moved back i n t o p l a c e from time t o t i m e . -130-APPENDIX E; E s t i m a t e of the e f f e c t of compression on e x i s t i n g v o r t i c i t y : The f o l l o w i n g i s a crude a p p r o x i m a t i o n of the e f f e c t s t h a t the compr e s s i o n s t r o k e has on the i n t a k e - s t r o k e g e n e r a t e d t u r b u l e n c e . T h i s a p p r o x i m a t i o n e s t i m a t e s the r a t e of decay due t o v i s c o s i t y and b a l a n c e s t h a t w i t h the a m p l i f i c a t i o n e f f e c t of e x i s t i n g v o r t i c i t y due t o c o m p r e s s i o n . Assuming t h a t a g r a d u a l p r e s s u r e i n c r e a s e from a p o i n t 1 t o a p o i n t 3 can be e x p r e s s e d by a r a p i d p r e s s u r e i n c r e a s e from p o i n t 1 t o p o i n t 2 and a c o n s t a n t p r e s s u r e from p o i n t 2 t o p o i n t 3, as s c h e m a t i c a l l y shown i n F i g u r e 21, then the p r i n c i p l e s of the r a p i d d i s t o r t i o n t h e o r y can be a p p l i e d g o i n g from p o i n t 1 t o p o i n t 2. As s c h e m a t i c a l l y shown i n F i g u r e 22 and t o be d e r i v e d soon, the r a p i d compression of v o r t i c i t y l e a d s t o an i n c r e a s e of i t s i n t e n s i t y . In the time A t , g o i n g from p o i n t 2 t o p o i n t 3, the t u r b u l e n c e i n t e n s i t y d e c r e a s e s due t o decay. The e s t i m a t e of a m p l i f i c a t i o n of e x i s t i n g v o r t i c i t y t h r o u g h c o m p r e s s i o n e f f e c t s i s d e r i v e d f o r a s p h e r i c a l v o r t e x as f o l l o w s : c o n s e r v a t i o n of mass: (30) p L 3 = c o n s t a n t where p s t a n d s f o r the d e n s i t y and L f o r a c h a r a c t e r i s t i c -131-l e n g t h s c a l e . T h i s can be r e w r i t t e n a s : 1/3 (31) L / L 0 = (po/p) where 0 i n d i c a t e s some i n i t i a l c o n d i t i o n . C o n s e r v a t i o n of a n g u l a r momentum: (32) u L = c o n s t a n t where u i n d i c a t e s some c h a r a c t e r i s t i c v e l o c i t y . T h i s can be e x p r e s s e d a s : (33) L / L 0 = u 0/u The p o l y t r o p i c compression r e l a t i o n y i e l d s : i/n (34) Po/p = (Po/p) From e q u a t i o n s ( 3 1 ) , (33) and (34) one can f i n d : 1/3n (35) u/u 0 = (p/Po) R e a r r a n g i n g t h i s an e x p r e s s i o n f o r the i n c r e a s e of t u r b u l e n c e i n t e n s i t y due t o compres s i o n e f f e c t s can be found: 2/3n (36) u 2 - u§ = ug ( ( p / p 0 ) " 1) For i s o t r o p i c homogeneous t u r b u l e n c e the r a t e of d i s s i p a t i o n i s g i v e n by: (37) 3 u 2 / 3 t = u 3 / L -132-Assuming s m a l l time i n c r e m e n t s , t h i s i s a p p r o x i m a t e d by: (38) A u 2 / A t = u 3/L The change i n i n t e n s i t y i s r e p r e s e n t e d by: (39) A u 2 = u 2 - ul The d e c r e a s e of i n t e n s i t y i n time At due t o v i s c o s i t y i s t h e r e f o r e a p p r o x i m a t e d by: (40) u? - u i = (u?/L) At The net change of i n t e n s i t y between p o i n t s 1 and 3 i s t h e r e f o r e g i v e n as the d i f f e r e n c e between e q u a t i o n (36) and e q u a t i o n ( 4 0 ) : 2/3n (41) u| - ug = u g ( ( p / p 0 ) - 1) - ( u ? / D At T h i s e q u a t i o n i n d i c a t e s t h a t i n o r d e r t o i n c r e a s e the t u r b u l e n c e i n t e n s i t y a h i g h c o m p r e s s i o n r a t i o and f a s t c o m p r e s s i o n , t h e r e f o r e h i g h engine r e v o l u t i o n , a r e d e s i r a b l e . I t a l s o i n d i c a t e s t h a t a l a r g e i n i t i a l t y p i c a l l e n g t h s c a l e r educes the decay of t u r b u l e n c e due t o v i s c o s i t y . T e s t i n g the d e r i v e d a p p r o x i m a t i o n i n e q u a t i o n (41) a t a p i s t o n p o s i t i o n h a l f way between bottom and t o p dead c e n t r e d u r i n g the c o m p r e s s i o n s t r o k e w i t h a p i s t o n v e l o c i t y of 4 m/s and l o o k i n g a t a time increment At of 1 ms y i e l d s : 1/n ( p / p 0 ) = 64/60 = 1.06667 -133-and u s i n g a c o n s t a n t average v a l u e f o r u 2 of u 2 = 4 m 2/s 2 one f i n d s : L = 45 mm At t h a t p o i n t the c l e a r a n c e h e i g h t i s 60 mm, so t h a t the c a l c u l a t e d v a l u e a p p r o x i m a t e s t h i s v a l u e w i t h i n 25% e r r o r . In a second t e s t case the whole c o m p r e s s i o n stoke i s ap p r o x i m a t e d by u s i n g : 1/n ( p / p 0 ) = 8 and a time increment At of 30 ms as w e l l as a c o n s t a n t average v a l u e f o r u 2 of u 2 = 4 m 2/s 2 a l e n g t h s c a l e of L = 15 mm can be found. At t h a t p o i n t the c l e a r a n c e h e i g h t i s a p p r o x i m a t e l y 14 mm. The e s t i m a t e d v a l u e i s a s t o n i s h i n g l y c l o s e t o the t y p i c a l l e n g t h s c a l e a t t o p dead c e n t r e . Yet i t s h o u l d be kept i n mind t h a t t h i s i s a crude a p p r o x i m a t i o n , i n which a one s i d e a c o n s t a n t l e n g t h s c a l e L i s assumed i n e u a t i o n s (37) and (38) and on the o t h e r s i d e an e q u a t i o n i s d e r i v e d i n ( 3 1 ) , which e x p r e s s e s the change i n l e n g t h s c a l e L, as the d e n s i t y changes. The e s t i m a t i o n a l s o uses one -134-average v a l u e u 2 f o r a l l i n t e n s i t i e s . F u r t h e r r e f i n e m e n t reduce the e s t i m a t i o n e r r o r . Figure 21 Schematic of the Approximation of Change in Pressure Figure 22 Schematic of the Change in Turbulence Intensity due to Compression and Decay 

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