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An evaluation of partially stratified charge ignition in a direct injection natural gas engine Gorby, David 2007

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A N EVALUATION OF PARTIALLY STRATIFIED CHARGE IGNITION IN A DIRECT INJECTION N A T U R A L GAS ENGINE by DAVID GORBY B.A.Sc, the University of British Columbia, 2000  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE F A C U L T Y OF GRADUATE STUDIES (Mechanical Engineering)  THE UNIVERSITY OF BRITISH COLUMBIA April 2007  © David Gorby, 2007  ABSTRACT The challenge of reducing tailpipe emissions, while retaining performance, continues to motivate new engine technologies.  To this end, natural gas shows promise as a clean burning alternative  fuel. However, an efficiency penalty of conventional spark ignited engines persists when these are fuelled by natural gas.  This penalty is due to pumping losses, which arise as the intake  mixture is throttled to maintain stoichiometry over the engine's operating range. Direct injection (DI), used to create a globally lean stratified charge, provides a load control method which is decoupled from throttling. Previous work has shown this concept to be viable, but plagued by poor fuel usage and high emissions of unburned hydrocarbons.  Partially Stratified Charge (PSC) technology is a novel high-energy ignition method. It involves a standard spark plug, modified such that a small portion of natural gas (<5% of the total fuel charge) is injected directly into the vicinity of the electrodes. The intention is to surround these with an easily ignitable mixture, thus ensuring a strong flame kernel that propagates through a marginal bulk charge. PSC has already been shown to improve combustion stability in ultra-lean, homogeneous mixtures. This study was conducted to determine if PSC can be combined with direct injection to improve combustion stability in a stratified charge engine.  A single cylinder research engine was modified to include a natural gas direct injector, as well as PSC ignition. Experiments were conducted over a wide range of fuel injection timings, as well as different angles between the fuel jet and ignition source.  Engine performance was poor at  stratified charge operating conditions and results indicate that PSC did not reliably improve combustion.  Experimental evidence suggests that the PSC system was not igniting the pilot  charge as expected.  Very high concentration gradients at the boundaries of the PSC and DI  ii  plumes m a y be the cause o f the negative result. These m a k e it difficult to r e l i a b l y ensure that the spark p l u g discharges into the n a r r o w and transient regions o f c o m b u s t i b l e m i x t u r e .  A secondary i n v e s t i g a t i o n w a s conducted i n w h i c h a v e r y dilute p r e m i x e d fuel c o m p o n e n t was added to the intake air.  T h i s assured reliable i g n i t i o n o f the P S C p i l o t charge; and i n this  configuration, stratified charge c o m b u s t i o n at late direct injection t i m i n g s p r o d u c e d stable engine operation.  iii  TABLE OF CONTENTS Abstract  it  Table o f Contents...  iv  ;  L i s t o f Tables  vi  L i s t o f Figures  vii  Nomenclature  ix  Acknowledgements  1.  INTRODUCTION  ••  xii  1  1.1  BACKGROUND  1  1.2  RESEARCH OBJECTIVES  6  2.  EXPERIMENTAL APPARATUS 2.1  R E S E A R C H ENGINE  2.2  D I R E C T INJECTION S Y S T E M  9 9 10  2.2.1  Direct Injector  10  2.2.2  Cylinder Head Modifications  11.  2.2.3  Jet Development.  12  2.2.4  Injector Characterization  13  2.3  P S C SYSTEM  14  2.3.1  PSC Timing Characterization  15  2.3.2  PSC verification  20  2.4  INSTRUMENTATION A N D D A T A ACQUISITION  23  2.5  ENGINE C O N T R O L S Y S T E M  27  2.6  DATA PROCESSING  28  2.7  STATISTICAL P I L O T S T U D Y  29  2.8  UNCERTAINTY ANALYSIS  31  2.9  CLOSING REMARKS  33  3.  METHODOLOGY  34  3.1  DEFINITIONS: E A R L Y A N D L A T E D I R E C T INJECTION  34  3.2  Dl TIMING S W E E P S  35  3.2.1  PSC Settings  .36  iv  3.2.2  Air Fuel Ratio  36  3.2.3  Direct Injector Jet Angle  37  3.3 4.  PILOT C H A R G E STUDY RESULTS A N D DISCUSSION  4.1  5.  39  DI TIMING SWEEPS  39  4.1.1  Results  39  4.1.2  Discussion  41  PILOT C H A R G E STUDY  50  4.2  4.3  37  4.2.1  Results  50  4.2.2  Discussion  51  SUMMARY CONCLUSIONS AND RECOMMENDATIONS  57 59  5.1  CONCLUSIONS  59  5.2  RECOMMENDATIONS FOR FUTURE W O R K  60  REFERENCES  63  APPENDIX A: DESIGN D O C U M E N T A T I O N  66  APPENDIX  76  B: S A M P L E C A L C U L A T I O N S  APPENDIX C: ENGINE O P E R A T I N G PROCEDURES  82  A P P E N D I X D: F U E L C O M P O S I T I O N  87  v  LIST O F T A B L E S  Table 1-1 Hydrogen to Carbon Ratios  1  Table 2-1 Ricardo Hydra SI Configuration Geometry  10  Table 2-2 PSC Specifications  15  Table 2-3 PSC Verification Operating Parameters  21  Table 2-4 Ricardo Hydra Instrumentation  24  Table 2-5 Statistical Pilot Study Operating Condition  29  Table 2-6 Statistical Pilot Study Sample Sizes  29  Table 2-7 Measurement Uncertainty  31  Table 3-1 Fuelling Contributions  :  38  Table 4-1 Partial Combustion: Weak Mixture with PSC  55  Table 4-2 Average BSFC and Ignition Delay  —-57  Table D-l B C Natural Gas Composition Table D-2 Mixture Properties  87 •  87  vi  LIST OF FIGURES Figure 1.1 E s t i m a t e d  F u e l C o n s u m p t i o n Penalty for N a t u r a l G a s v s . D i e s e l  Figure 1.2 F u e l E f f i c i e n c y o f L o a d C o n t r o l Strategies  3 8  Figure 2.1 S I C y l i n d e r H e a d M o d i f i e d for J43 D i r e c t Injector  11  Figure 2.2 D I Jet A n g l e A d j u s t m e n t R a n g e  12  Figure 2.3 J43 P u l s e W i d t h C h a r a c t e r i z a t i o n  13  Figure 2.4 P S C S p a r k P l u g  14  Figure 2.5 P S C T i m i n g C h a r a c t e r i z a t i o n Process F l o w D i a g r a m  16  Figure 2.6 P S C T i m i n g C h a r a c t e r i z a t i o n - 8 bar S u p p l y Pressure  17  Figure 2.7 P S C T i m i n g C h a r a c t e r i z a t i o n - 15 bar S u p p l y Pressure  18  Figure 2.8 P S C T i m i n g C h a r a c t e r i z a t i o n - 2 0 bar S u p p l y Pressure  18  Figure 2.9  19  P S C C h a r a c t e r i z a t i o n , 8 bar, C o a r s e T i m e s c a l e  Figure 2.10 C h a r a c t e r i z a t i o n , Figure 2.11  15 bar, Coarse T i m e s c a l e  20  C h a r a c t e r i z a t i o n , 2 0 bar, C o a r s e T i m e s c a l e  20  Figure 2.12 H i s t o g r a m Figure 2.13  o f Integrated Heat Release  D y n o c l i e n t Interface W i n d o w  Figure 2.14 Pressureclient Figure 2.15  Figure 2.17 S p e e d Figure 2.18  25  Interface W i n d o w  T i m i n g C o n t r o l l e r Interface W i n d o w  Figure 2.16 T o r q u e  H a l f - l e n g t h o f CI  H a l f - l e n g t h o f CI  95  95  at V a r y i n g S a m p l e Sizes at V a r y i n g S a m p l e S i z e s  F u e l F l o w H a l f - l e n g t h o f CI  95  22  at V a r y i n g S a m p l e S i z e s  26 27 30 30 30  Figure 3.1 H y p o t h e t i c a l D I F u e l E f f i c i e n c y w i t h T i m i n g  35  Figure 4.1 D I T i m i n g S w e e p B S F C R e s u l t ( 0 ° Injector A n g l e )  40  Figure 4.2 D I T i m i n g S w e e p B S F C Results ( 8 ° Injector A n g l e )  40  vii  Figure 4.3 Histogram of Net Heat Release (0° Injector Angle)  42  Figure 4.4 Histogram of Net Heat Release (8° Injector Angle)  43  Figure 4.5 Misfire with DI Timing (0° Injector Angle)  44  Figure 4.6 Misfire with DI Timing (0° Injector Angle)  44  Figure 4.7 BSFC with Misfire (0° Injector Angle)  45  Figure 4.8 BSFC with Misfire (8° Injector Angle)  46  Figure 4.9 tHC with Misfire (0° Injector Angle)  47  Figure 4.10 tHC with Misfire (8° Injector Angle)  47  Figure 4.11 BSFC with tHC (0° Injector Angle)  48  Figure 4.12 BSFC with tHC (8° Injector Angle)...  49  Figure 4.13 Pilot Charge Study Fuel Efficiency Results  :  50  Figure 4.14 Histogram of Net Heat Release for all pilot charge study conditions  51  Figure 4.15 In-Cylinder Pressure Trace Comparison: Motored and with PSC  52  Figure 4.16 Net Heat Release Rate Comparison: Motored and with PSC  52  Figure 4.17 In-Cylinder Pressure Trace Comparison: With and Without PSC  54  Figure 4.18 Net Heat Release Rate Comparison: Weak Mixture With and Without PSC  54  Figure 4.19 BSFC Comparison: Pilot Charge Study With Timing Sweeps  56  Figure A . l Aluminium SI Cylinder Head Solid Model  66  Figure A.2 G E A Analysis of Stress Due to Combustion Seal Pre-Load  67  Figure A.3 DI Head Modification Fabrication Drawings Figure A.4 Geometry: Piston # 476P by Federal Mogul for Ford Fiesta (1978-80)  r  74 75  viii  NOMENCLATURE SYMBOLS A  R e l a t i v e air fuel ratio  Sample M e a n S  S a m p l e Standard D e v i a t i o n  n  N u m b e r o f S a m p l e Points  w  Uncertainty  B  F i x e d U n c e r t a i n t y due to Instrument E r r o r  P  Statistical U n c e r t a i n t y (95% C o n f i d e n c e Interval)  x  M e a s u r e d Parameter  m  M a s s F l o w Rate  P  Brake Power  b  x  b  Brake Torque  N  E n g i n e Speed  /  Fuel  ABBREVIATIONS ABDC  A f t e r B o t t o m D e a d Centre  BMEP  B r a k e M e a n E f f e c t i v e Pressure  BSFC  Brake Specific Fuel Consumption  BTDC  B e f o r e T o p D e a d Centre  CAD  C r a n k A n g l e Degrees  CI  C o n f i d e n c e Interval  CL  Confidence L i m i t  CO  Carbon Monoxide  C0  2  Carbon Dioxide  COV  Coefficient o f Variation  DC  Direct Current  DI  D i r e c t Injection  DISC  D i r e c t Injection Stratified C h a r g e  DOE  Department o f Energy  EGR  Exhaust Gas Recirculation  Ex Vlv.  Exhaust V a l v e  GC  Gas Chromatograph  GDI  G a s o l i n e D i r e c t Injection  H/C  H y d r o g e n to C a r b o n R a t i o  HRR  H e a t Release Rate  IC  Internal C o m b u s t i o n  IHR  Integrated H e a t Release  IMEP  Indicated M e a n E f f e c t i v e Pressure  Int V l v .  Intake V a l v e  LML  Lean Misfire Limit  MBT  M i n i m u m A d v a n c e for B e s t T o r q u e  NO  Oxides o f Nitrogen  x  PM  Particulate M a t t e r  PSC  P a r t i a l l y Stratified C h a r g e  PW  Pulse W i d t h  (R+M)/2  A v e r a g e o f R e s e a r c h and M o t o r e d Octane N u m b e r s  RAFR  Relative A i r Fuel Ratio  SAE  S o c i e t y o f A u t o m o t i v e Engineers  rpm  R e v o l u t i o n s per M i n u t e  SC  Stratified C h a r g e  SI  Spark Ignition  SOI  Start o f Injection  tHC  Total Hydrocarbons  UBC  University o f British Columbia  US  U n i t e d States  xi  ACKNOWLEDGEMENTS I w o u l d l i k e to thank m y supervisor, D r . R o b e r t E v a n s , for p r o v i d i n g the opportunity for m e to c o m e b a c k to the W e s t C o a s t and study at U B C .  I w o u l d also l i k e to thank C o n o r R e y n o l d s ,  w h o s e mentorship and g u i d a n c e were i n v a l u a b l e assets d u r i n g this project.  I a m grateful to m y  lab partner, D a v i d W i l l i a m s , and m y other lab-mates M a l c o l m S h i e l d , E d C h a n , James Saunders and A n d r e w M e z o for the g o o d d i s c u s s i o n s and for k e e p i n g me l a u g h i n g throughout.  I a m v e r y grateful to W e s t p o r t Innovations Inc, for p r o v i d i n g the hardware and support that made this thesis p o s s i b l e . I w o u l d p a r t i c u l a r l y l i k e to thank M i k e H e b b s for l e n d i n g his experience and guidance towards getting this project started.  I w o u l d l i k e to thank the M e c h a n i c a l E n g i n e e r i n g faculty and staff, p a r t i c u l a r l y : M a r t i n D a v y , B o b P a r r y , G l e n n J o l l y , M a r k u s F e n g l e r and G o r d W r i g h t for their assistance, a d v i c e and explanations o f things I k n e w n o t h i n g about.  F i n a l l y , I w o u l d l i k e to thank m y w i f e , E r i n , w h o went t h r o u g h this first, then encouraged me to follow.  xii  1. I N T R O D U C T I O N LI  BACKGROUND  The reciprocating internal combustion (IC) engine remains the dominant power-plant of the world's ground based transportation system. As it continuously evolves, the dynamic standard it sets in terms of cost effective performance and reliability has seen challengers relegated to the fringes of market viability. Given the ubiquity of IC engines, the twin challenges of increasing fuel efficiency and reducing tailpipe emissions remain relevant today, as they will into the future.  To this end, natural gas has both economic and environmental benefits as an alternative fuel for IC engines. As a gaseous fuel, long chain hydrocarbons and high molecular weight compounds are absent, thus the atomic ratio of hydrogen to carbon (H/C) is favourable compared to liquid hydrocarbons fuels (Table 1-1).  Table 1-1 Hydrogen to Carbon Ratios Fuel  Molecular H/C Ratio  Gasoline  1.6-2.1  Diesel  -1.8  Natural Gas  3.7-4  Source: US DOE 2006a  These attributes are beneficial for the combustion of natural gas: they contribute to minimizing the production of soot and other particulate matter (PM) (Heywood 1988); and the favourable H/C ratio results in an approximate 25% reduction in C 0 per unit of heat energy released, when 2  compared to gasoline or diesel (BP 2005). Also inherent in natural gas engines is an enhanced potential for reducing the formation of oxides of nitrogen (NOx).  NOx emissions are often  mitigated through use of exhaust gas recirculation (EGR); however, at high EGR ratios the NOx  1  reduction benefits b e c o m e offset b y i n c r e a s i n g l e v e l o f P M . T h e l o w propensity for natural gas to form P M makes it a g o o d candidate for m a x i m i z i n g the N O x r e d u c i n g potential o f E G R ( G o u d i e , D u n n et a l , 2 0 0 4 ) .  F o r the c o n v e n t i o n a l spark ignited engine, o p t i m i z e d for natural gas rather  than gasoline, there is a potential benefit to thermal e f f i c i e n c y . T h i s is due to the potential for increased c o m p r e s s i o n ratios, w h i c h are supported by the higher octane characteristic o f natural gas (gasoline: 86-94, natural gas: 120+, ( R + M ) / 2 , U S D O E 2006a). T h e e c o n o m i c attractiveness o f natural gas results f r o m its current status as the least expensive o f a l l fuels, w h e n evaluated o n a cost per unit energy basis ( U S D O E 2006b).  Despite the potential benefits, there are barriers to the w i d e acceptance o f natural gas by the transportation market.  These are p r i m a r i l y due to the relatively l o w v o l u m e t r i c energy density  inherent i n gaseous fuels, w h i c h subsequently  require more c o m p l e x f u e l l i n g and  on-board  storage systems than are necessary for l i q u i d fuels. T h e c o m p l e x i t y o f these systems varies w i t h the strategy used ( n o r m a l l y c o m p r e s s i o n or liquefaction), but they c a n add s i g n i f i c a n t l y to a v e h i c l e ' s w e i g h t and expense. options.  Progress is needed i n terms o f cost effective, light w e i g h t storage  In a d d i t i o n to the i n i t i a l capital expenditure, the added w e i g h t inherent i n current  gaseous fuel storage decreases v e h i c l e fuel e c o n o m y , e r o d i n g the potential for reductions i n cost and emissions.  C u r r e n t l y , fleet v e h i c l e s are i n the best p o s i t i o n for a transition to natural gas.  T h e potential cost  savings, leveraged o v e r their h i g h fuel use, results i n a substantial m a r g i n for offsetting the increase  in vehicle complexity.  A d d i t i o n a l l y , fleet v e h i c l e s are often  s e r v i c e d by central  refuelling depots and are subsequently less affected b y the l i m i t e d a v a i l a b i l i t y o f p u b l i c natural gas infrastructure.  A m o n g fleet v e h i c l e s , natural gas is a p a r t i c u l a r l y attractive alternative i n  m e d i u m duty d i e s e l a p p l i c a t i o n s ; and indeed as o f 2 0 0 0 , natural gas had penetrated the U S transit bus market m o r e effectively than any other v e h i c l e market ( F r a i l y , C l a r k et a l , 2 0 0 0 ) .  The  2  already substantial size and expense o f these vehicles mileage penalty o f a d d i n g natural gas storage.  further reduces the m a r g i n a l cost and  A d d i t i o n a l l y , the three-way catalyst f o u n d o n  gasoline engines is currently an effective pollutant countermeasure. treatment  on  diesel  engines,  combined  with  their  high  T h e absence o f s u c h after-  P M output,  provides  the  greatest  opportunity for m a x i m i z i n g the e m i s s i o n r e d u c i n g potential o f natural gas.  T h o u g h beneficial in terms o f air quality, there is an efficiency penalty w h e n diesel is replaced by natural gas, u s i n g a c o n v e n t i o n a l spark i g n i t i o n (SI) c y c l e . load,  where  conventional  SI  engines  experience  T h i s penalty is greatest under part  throttling  losses  in  order to  maintain  a  stoichiometric air-fuel ratio. T h e p r o b l e m is further c o m p o u n d e d by the s t o i c h i o m e t r i c m i x t u r e ' s inability to e x p l o i t the t h e r m o d y n a m i c benefits o f excess air, s u c h as higher specific heat ratios, and r e d u c e d heat transfer to the c o m b u s t i o n c h a m b e r w a l l s ( F e r g u s o n a n d K i r k p a t r i c k ,  2001).  Figure  engine  1.1  s h o w s qualitatively the fuel c o n s u m p t i o n penalty o f a t y p i c a l natural gas  c o m p a r e d to a n equivalent diesel.  Torque curves  Speed Figure 1.1 E s t i m a t e d  F u e l C o n s u m p t i o n P e n a l t y for  N a t u r a l G a s vs. D i e s e l ( R i c a r d o , F r o m K u b e s h  2002)  R e d u c t i o n or E l i m i n a t i o n o f this penalty w o u l d enhance market acceptance o f natural gas, further r e a l i z i n g its potential for r e d u c i n g e m i s s i o n s and operating costs.  3  One approach to mitigating this fuel consumption penalty is through a homogenous lean burn strategy, in which engine output is controlled by varying the fuel flow, without throttling the airflow. Germane et al (1983) provides a complete review of the lean burn concept; while others (Gupta and Bell, 1994) have contributed results directly related to lean burn natural gas engines. As a means of load control, this approach is effective near the upper end of an engine's load range, however combustion quality eventually degrades as the relative air fuel ratio (RAFR, denoted: A ) approaches the lean misfire limit (LML - for natural gas A M L ~1.6, Gupta and Bell 1  L  1994). Assuming good combustion until very near L M L , this represents throttleless operation over the engine's upper -35% load range.  In order to achieve throttleless operation over the entire load range, one potential strategy is to operate at global relative air fuel ratios well in excess of the homogeneous lean misfire limit. To achieve this, the fuel/air charge must be stratified such that an ignitable mixture contacts the ignition source at the correct time, though the balance of the working gas is composed of inert dilutent (EGR or Air).  The combusting gasses may be separated physically or aerodynamically  from the working gas, which may be air, recirculated exhaust gas or a combination thereof. Abata (1986) provides a detailed historical review of the stratified charge concept, while Kubesh (2002) provides more current examples of the concept applied in natural gas engines.  Currently, there is renewed interest in the direct injection (DI) category of stratified charge (SC) engines. In this variation (acronym: DISC), fuel is injected directly into the combustion chamber, where it interacts with surrounding air to form a combustible mixture. Zhao, Harrington et al  L M L is reached when COVI EP>10% (Heywood, 1998). Though leaner combustion is possible, M  this threshold defines the point at which drivability. is said to be adversely affected.  4  (2002) review this concept in its most common application of gasoline direct injection (GDI). Early examples of DI engines were limited by their mechanically controlled fuelling systems. Freed of these limitations by modern advances in electromagnetic actuation and microprocessor based engine management, researchers are now motivated to re-examine the benefits of DISC engines.  The allure of the stratified charge engine is its potential to hybridize spark ignited and compression ignition engine models, combining the advantages of each. However, applications of this concept remain beset by poor fuel usage and high emissions of unburned hydrocarbons, particularly at reduced load.  Managing the interface between the combustible mixture and  working gas remains problematic.  Abata (1986) describes this region as highly dynamic,  influenced by inlet aerodynamics, piston movement and combustion induced fluid motion. More specifically to DISC, Lahbabi et al (1993) describe the free surface of a transient gaseous jet as highly complex, with turbulent structures producing undulations on the order of the jet's half width.  These factors can contribute to separation between the combustible mixture and the  ignition source, resulting in misfire. In addition, local mixing beyond the lean combustion limit leads to flame extinction. Indeed many researchers continue to report difficulty in managing this highly complex phenomenon (Goto and Sato, 2001, Turner, Pearson and Kenchington, 2004, Huang et al 2003)  Local charge stratification has emerged as a sub-set of the stratified charge concept.  In this  variant, a small portion of the overall fuel charge is inducted separately to create a localized pilot region with a distinct composition: an easily ignitable mixture in the vicinity of an ignition source.  When applied as an enhanced ignition system, this has been shown to improve  combustion stability in ultra-lean mixtures, which require greater ignition energy than a stoichiometric charge (Green and Zavier, 1992, Arcoumanis et al., 1997).  In their review of  5  alternative i g n i t i o n methods, D a l e et a l (1997) describe enhanced i g n i t i o n systems as those w h i c h increase i g n i t i o n energy and i m p r o v e its d i s p e r s i o n throughout a c o m b u s t i b l e m i x t u r e . In the case o f l o c a l charge stratification, the spark is augmented b y the added f u e l ' s c h e m i c a l energy, w h i c h is then dispersed b y turbulent m o t i o n .  1.2 RESEARCH  OBJECTIVES  The objective o f the research presented i n this thesis was to determine i f a technique o f local charge stratification, referred to as p a r t i a l l y stratified charge ( P S C ) , can i m p r o v e c o m b u s t i o n stability and fuel usage i n a natural gas p o w e r e d D I S C engine.  P S C is a m e t h o d o f l o c a l charge stratification d e v e l o p e d at T 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 ( E v a n s 2 0 0 0 ) . It i n v o l v e s injecting a small p o r t i o n o f fuel d i r e c t l y into the v i c i n i t y o f a m o d i f i e d spark p l u g ' s electrodes. R e y n o l d s (2001) demonstrated an extension to the lean misfire l i m i t i n a homogeneous charge natural gas engine u s i n g P S C .  F o l l o w i n g these results, B r o w n (2003)  reported s i m i l a r f i n d i n g s i n a d u a l fuel regime, w i t h natural gas as the P S C fuel and port injected gasoline as the m a i n charge.  B r o w n also evaluated a m o n o - f u e l strategy, i n w h i c h a gasoline  direct injector p r o v i d e d the p i l o t charge, and the b u l k charge w a s , again, port injected.  The  results o f the m o n o - f u e l study were not as p o s i t i v e , o w i n g to difficulties i n r e l i a b l y i g n i t i n g the p i l o t charge.  T h i s thesis describes a study i n w h i c h the concept o f l o c a l charge stratification w a s r e m o v e d from its f a m i l i a r context o f h o m o g e n o u s charge engines, and c o m b i n e d w i t h a f u l l y stratified approach. The g o a l w a s to determine i f m i x t u r e enrichment l o c a l to the spark p l u g w o u l d a i d the i g n i t i o n and c o m b u s t i o n o f a stratified D I fuel charge. T h e specific research objectives were to:  6  1.  A d d a natural gas direct injection system to a single c y l i n d e r research engine.  2.  D e t e r m i n e i f j e t g u i d e d stratification, created b y late c y c l e direct injection, w i l l facilitate g l o b a l l y lean operation.  3.  C o m p a r e the d i r e c t l y injected e n g i n e ' s performance w h e n operating w i t h c o n v e n t i o n a l spark i g n i t i o n , to c o m b u s t i o n initiated by P S C .  It was h y p o t h e s i z e d that P S C w o u l d i m p r o v e fuel usage i n the D I S C engine t h r o u g h t w o modes. First, it was thought that the e n f l a m e d p i l o t charge w o u l d be m u c h larger i n v o l u m e than the i o n i z e d r e g i o n p r o d u c e d from a standard spark discharge. T h i s larger v o l u m e o f i n i t i a l l y active chemistry  would  increase  combustible region.  the  p r o b a b i l i t y o f successfully  igniting  the  DI  bulk  plume's  S e c o n d l y , it w a s thought that the extra i g n i t i o n energy o f P S C w o u l d  promote c o m b u s t i o n t h r o u g h regions o f the D I p l u m e where m i x i n g w i t h the w o r k i n g gas has progressed to a n otherwise o v e r l y lean c o m p o s i t i o n .  I f r e a l i z e d , these i m p r o v e m e n t s w o u l d  reduce unburned h y d r o c a r b o n s levels and increase efficiency t h r o u g h i m p r o v e d c o m b u s t i o n and reduced misfire.  A s o u t l i n e d q u a l i t a t i v e l y i n F i g u r e 1.2, this hypothesis supports a n increased range o f un-throttled load c o n t r o l for SI engines.  B r a k e specific fuel c o n s u m p t i o n ( B S F C ) is a measure o f engine  efficiency that describes the amount o f fuel necessary to produce a quantity o f shaft w o r k ; thus l o w e r values are preferred.  B r a k e mean effective pressure ( B M E P ) represents the range o f loads  an engine is expected to operate over. I f successful, the D I S C strategy w o u l d extend the range o f un-throttled l o a d c o n t r o l b e y o n d that o f a h o m o g e n o u s lean b u r n engine.  7  Baseline: Throttled Load Control  BMEP Figure 1.2 Fuel Efficiency of Load Control Strategies (Lean Burn and Lean Burn with PSC Approximated from Reynolds 2004)  2. EXPERIMENTAL APPARATUS T h e experimental i n v e s t i g a t i o n described i n this thesis was p e r f o r m e d o n a R i c a r d o H y d r a , fourstroke, single c y l i n d e r research engine.  T h e H y d r a is a f l e x i b l e engine test-bed, w h i c h is easily  configured to operate w i t h a variety o f fuels and i g n i t i o n methods.  F o r the purposes o f this study,  it w a s m o d i f i e d to support a gaseous direct injector, i n a d d i t i o n to a P S C spark p l u g . A s further described i n this section, the H y d r a is thoroughly instrumented to record a w i d e variety o f performance indicators and e m i s s i o n s data.  2.1 RESEARCH  ENGINE  T h e R i c a r d o H y d r a is p r o d u c e d b y R i c a r d o C o n s u l t i n g E n g i n e e r s o f the U n i t e d K i n g d o m ( R i c a r d o 2006).  It is designed s p e c i f i c a l l y for research, w i t h h i g h l y m o d u l a r components that  enable it to accept a w i d e range o f pistons, c y l i n d e r heads and v a l v e trains. T h i s c a p a b i l i t y a l l o w s the H y d r a to emulate a w i d e variety o f diesel, gasoline, and alternative fuel engines.  F o r this study, the H y d r a was fitted w i t h a cast a l u m i n i u m , spark i g n i t i o n c y l i n d e r head, w i t h t w o vertical v a l v e s actuated b y a s i n g l e overhead c a m shaft. flat  fire-deck  and b o w l - i n - p i s t o n arrangement.  T h e c o m b u s t i o n c h a m b e r consisted o f a  T h e relevant geometry is detailed i n T a b l e 2-1  b e l o w , and a d r a w i n g o f the p i s t o n c r o w n is available i n A p p e n d i x A .  9  Table 2-1  Ricardo Hydra Spark Ignition Configuration Geometry  Bore  81.5  mm  Stroke  88.9  mm  Clearance Volume  54.7  cc  Displaced Volume  463.3  cc  Compression Ratio  9.47:1  Inlet Valve Diameter  36.0  mm  Inlet Valve Open  12°  BTDC  Inlet Valve Close  56°  ABDC  Exhaust Valve Diameter  33.5  mm  Exhaust Valve Open  56°  BBDC  Exhaust Valve Close  12°  ATDC  U B C ' s Hydra is coupled to a D C dynamometer which provides regenerative load absorption, as well as motoring power.  The dynamometer is trunnion mounted, with a swing-arm that is  connected to a load cell for torque measurement.  2.2 DIRECT  INJECTION  SYSTEM  2.2.1 Direct Injector The bulk charge direct injector was a Westport model J43 gaseous mono-fuel injector provided by Westport Innovations Inc. of Vancouver B C . The J43 is an iteration in a line of prototype injectors designed for research purposes, and is not a commercially available product.  The  J43's gas  magnetostrictive  needle  is actuated  by an interaction between a magnetic  material, T e r f e n o l - D ™ .  field and the  Terfenol is a ferrous metal alloy with a highly  repeatable response to magnetic fields (Etrema Products Inc 2006). A s coils within the injector become energized, magnetic domains within the Terfenol become realigned, causing the material to expand. This movement opens the injector's gas needle, allowing fuel to flow.  In this study,  fuel was metered by varying the commanded pulse width (PW), which determines the duration of  10  needle lift. Further rate s h a p i n g is possible b y v a r y i n g the J43's needle lift; h o w e v e r , this m e t h o d d i d not suit the desired operating range, so m a x i m u m lift was c o m m a n d e d in all cases.  2.2.2  Cylinder Head Modifications  T h o u g h the U B C H y d r a ' s c o m p l e m e n t  o f c y l i n d e r heads support a w i d e variety o f f u e l l i n g  methods, none a v a i l a b l e w e r e intended for direct injection c o m b i n e d w i t h spark ignition. guidance f r o m W e s t p o r t , a d e s i g n  With  study was undertaken to determine the best a p p r o a c h for  m o d i f y i n g a spare SI h e a d to i n c l u d e a direct injector.  A representation o f the resulting d e s i g n  concept is s h o w n i n F i g u r e 2.1 b e l o w , and further d o c u m e n t a t i o n f r o m the d e s i g n study c a n be f o u n d in A p p e n d i x A .  Figure 2.1  SI C y l i n d e r H e a d M o d i f i e d for  J43 D i r e c t  Injector  11  2.2.3 Jet Development Hill and Ouellette's (1999) review of gaseous jets, as well as follow-on work by Iaconis (2001) served as the main guide for locating and sizing the injector's single gas orifice.  In its base  position, the injection plume was aimed directly towards the ignition source so as to ignite the jet as it exits the injector. This is analogous to the Texaco TCCS engine: a historical example of a DISC engine, described by Abata (1986). As illustrated in Figure 2.2, small adjustments to the rotation angle of the injector's central axis offered a limited degree of control over the concentration of air-fuel mixture directed at the spark plug electrodes.  Small variations in this  angle could alternatively direct the jet's rich core or the more vigorously mixed shear layer at the jet boundary towards the electrodes.  8° Towards Intake Valve  0° (Neutral Angle)  Injector Tip  Spark Plug  Fuel Jet  \  Cylinder Bore  16° Towards Intake Valve  Injector Angle  Figure 2.2 DI Jet Angle Adjustment Range  For the purposes of design, the quasi steady state jet and vortex ball model was assumed for the plume's shape (Turner 1959, from Hill and Ouellette 1999). The jet's central axis was given a 10° down angle relative to the fire deck in its base position. As suggested by Hill and Ouellette, 12  m i n i m a l w a l l interference c o u l d be expected at this angle, p r o v i d e d the pressure ratio across the injector's outlet r e m a i n e d s u f f i c i e n t l y h i g h (>4).  2.2.4 Injector Characterization T h e orifice diameter w a s s i z e d u s i n g the assumptions described by Iaconis (2001).  o f i s e n t r o p i c a l l y e x p a n d e d ideal gas,  In his characterization o f a W e s t p o r t J41 injector (a predecessor to  the J 4 3 ) , Iaconis f o u n d this m o d e l to agree w e l l w i t h experimental results, t h o u g h he went on to evaluate several refinements that attempt to predict losses w i t h i n the injector. F o r the purposes o f this study, internal losses w e r e a p p r o x i m a t e d b y a 10 percent loss i n stagnation pressure, suggested by H i l l and Ouellette; sample calculations are a v a i l a b l e i n A p p e n d i x B .  as  A n orifice  diameter o f 0 . 5 m m w a s f o u n d to match the injector's linear response range to the desired f l o w rates. T h i s is illustrated i n F i g u r e 2.3, w h i c h shows the injector's characterization data, recorded at W e s t p o r t ' s test f a c i l i t y , as w e l l as predicted f l o w rates.  35  •  30 3  Westport J43 Pulse Width Characterization Calculated Flow Rates  • •  25  •  W  X  o  20  l~ 1 ( U B C Hydra)  15  0.  10 5  X~3 ( U B C Hydra) •  CB  s  0 0  1  2  3  4  5  Injection Pulse Width (ms) Figure 2.3 J43 P u l s e W i d t h C h a r a c t e r i z a t i o n  13  2.3 PSC SYSTEM A U S patent has been granted to U B C for the P S C system (Evans 2000). The patent document contains a thorough description of the P S C concept and its intended use in SI engines.  The  particular realization of the P S C concept used in this study is functionally identical to that described by Brown (2003), and changed very little from Reynolds (2001). The reader is referred to these documents for a detailed description of the P S C system; though a representation of a P S C spark plug is shown in Figure 2.4, and a list of the key specifications follow in Table 2-2.  14  Table 2-2 PSC Specifications Spark plug type Bosch XR4CS Heat Range 4 Reach 3/4 in Capillary Tube 1/16 in Stainless Steel Solenoid Omega SV122 Supply Regulator C C A 4922801 -01 -000 Supply Pressure 27 bar  2.3.1 PSC Timing Characterization Previous work on the PSC system had indicated a significant delay between the time an injection command is sent, and the actual start of injection (SOI). A prior understanding of this delay is important, since there is no relevant feedback to indicate the actual SOI while the engine is running. Reynolds (2001) performed a characterization study to quantify this delay; however the solenoid he and Brown used to meter PSC flow failed prior to this study.  Though the  replacement was of the same make and model, Reynolds' results could not be assumed accurate for the new solenoid; thus another study was performed.  The characterization study was performed using the experimental set-up depicted in Figure 2.5. Data was collected and analyzed using the Hydra's data acquisition and processing system, as described further in 2.4 of this thesis. Injection commands were sent to the PSC solenoid at a frequency and duty cycle that were equivalent to engine operation at 2000rpm.  Timing was  measured in terms of crank angle degrees (CAD); thus one crank angle degree was equivalent to 0.083ms.  Pressure data for 100 consecutive cycles was acquired at half crank angle degree  increments.  15  T w o Stage Regulator  From H i g h Pressure Storage  Thermal Mass Flow Meter With Pressure Transducer  P S C Spark Plug  Atmospheric Vent  A l u m i n u m Pressure Jig Enclosed Volume: ~3cc  Piezoelectric Pressure Transducer  T o DAQ Figure 2.5 PSC Timing Characterization Process Flow Diagram  Trials were conducted at supply pressures of 8, 15 and 20 bar(gauge). The two higher pressures were chosen to represent the pressure differential across the capillary tube during moderately early and moderately late PSC injection timings. The lower pressure was selected following an analysis in which the capillary tube flow was modeled assuming Fanno, conditions (Wilcox 2003, White 1994; see Appendix B for a sample calculation). This analysis revealed that, during engine operation, pressure in the combustion chamber during the compression stroke was sufficient to prevent the PSC flow from frictionally choking within the capillary tube. However, pressure differentials representative of engine conditions would result in choking in the characterization test rig, where the back pressure was close to atmospheric. According to the Fanno model, 8 bar(gauge) was near the maximum supply pressure that would not produce frictional choking in the test rig.  This lower pressure trial was conducted as a comparison in which the compressibility  effects, rather than pressure differential, were more closely matched to actual conditions.  16  T h e c o m m a n d e d injection pulse w i d t h s ( P W ) were set to 8.5 C A D (0.71ms) and 8.75 C A D (0.73ms), to c o i n c i d e w i t h t y p i c a l engine operation.  D u e to the coarse c o n t r o l afforded by the  solenoid, f l o w rates at these s i m i l a r durations were substantially different.  T h e results o f the t i m i n g study are s h o w n i n Figures 2.6, 2.7 and 2.8.  T h e i n i t i a l detection o f  increased pressure w a s taken to indicate the S O I ; thus a significant l a g between the t i m i n g c o m m a n d and the actual event was c o n f i r m e d .  T h o u g h the p o o r signal-to-noise ratio makes  precise measurement difficult, the pressure signals appear to d i v e r g e from the baseline data between 35 and 45 C A D (2.92 and 3.75 ms) after the start o f injection.  T h i s result appears  independent o f pressure differential and injection duration.  1.02 +  Background B a c k g r o u n d Smoothed  1.01  A  O  8.5 C A D P W 8.5 C A D P W Smoothed  X  8.75 C A D P W  S3 1.00 -  |  0.99 -  0.98  0.97  0  20  40  60  80  100  T i m i n g - B e g i n n i n g at Injection C o m m a n d ( C A D - 2000 R P M Equivalent)  Figure 2.6  P S C T i m i n g C h a r a c t e r i z a t i o n - 8 bar S u p p l y Pressure  17  1.02  + Background Background Smoothed O 8.5 C A D PW 8.5 C A D P W Smoothed  1.01  X  8.75 C A D P W 8.75 C A D PW Smoothed !  loo  ¥ e  Iin CO  I  0.99  0.98  0.97 Timing - Beginning at Injection Command ( C A D - 2000 R P M Equivalent) Figure 2.7 P S C Timing Characterization - 15 bar Supply Pressure  1.02  +  Background Background Smoothed O 8.5 C A D P W 8.5 C A D P W Smoothed X 8.75 C A D P W 8.75 C A D P W Smoothed <  1.01  ¥  i-oo  s—-  0.99  0.98  0.97 0  10  20  30  40  50  60  70  80  90  100  Timing - Beginning at Injection Command ( C A D - 2000 R P M Equivalent) Figure 2.8 P S C Timing Characterization - 20 bar Supply Pressure  Larger scale graphs (Figures 2.9, 2.10 and 2.11) reveal the injection durations to be greater than an order of magnitude longer than the commanded pulse widths. It is unclear to what extent this is due to signal delays as the control driver amplifies the command pulse, inertia of mechanical components, or pressure build-up within the PSC line. However, it is unlikely that combustion pressures would allow the actual injection event to continue as long as observed in the test rig. Consequently, a characterization of the end of injection is not available from this data. It is interesting to note that the test rig pressure remains high more than 180 CAD after the start of injection. This may warrant further investigation during future PSC work, since it indicates the possibility that gas flow resumes once combustion chamber pressure drops during blow-down.  1.02  1  1.01 -  0.97 H 0  """""Background Smoothed 8.5 CAD PW Smoothed 8.75 CAD PW Smoothed  1  1  1  90  180  270  :  1 360  Timing - Beginning at Injection Command (CAD - 2000 RPM Equivalent) Figure 2.9 PSC Characterization, 8 bar, Coarse Timescale  19  1.02  l.oi i  ¥ e  1  1.00  B a c k g r o u n d Smoothed  % 0.99 cu 0.98 H  8.5 C A D P W Smoothed 8.75 C A D P W Smoothed  0.97 0  90  180  270  360  T i m i n g - B e g i n n i n g at Injection C o m m a n d ( C A D - 2000 R P M Equivalent) F i g u r e 2.10 Characterization, 15 bar, C o a r s e T i m e s c a l e  1.02  1.01  ¥ e  a  *—•  v  I.OO  % 0.99 cu  Background Smoothed 8.5 C A D P W S m o o t h e d  0.98  8.75 C A D P W S m o o t h e d 0.97 0  90  180  270  360  T i m i n g - B e g i n n i n g at Injection C o m m a n d ( C A D - 2 0 0 0 R P M E q u i v a l e n t ) F i g u r e 2.11 Characterization, 20 bar, C o a r s e T i m e s c a l e  2.3.2  PSC verification  D u r i n g the course o f this i n v e s t i g a t i o n a concurrent study, w h i c h i n v o l v e d m o d i f y i n g the H y d r a ' s aspiration system to i n c l u d e an E G R l o o p , was also i n progress. required substantial m o d i f i c a t i o n to the intake and exhaust routes.  T h e a d d i t i o n o f this system T h e resulting effect o n the  H y d r a ' s v o l u m e t r i c e f f i c i e n c y and residual gas fraction were e x p l o r e d i n detail by W i l l i a m s  20  (2006); here it is sufficient to mention that engine characteristics in this regard had changed since the work of Reynolds (2001) and Brown (2003). In light of these changes, the pre-mixed, leanburn application of PSC was revisited before evaluating new applications of the PSC concept. This was undertaken to determine if PSC would still produce the previously documented results, following the engine modifications.  A single operating condition was chosen near the engine's lean misfire limit; Table 2-3 provides a summary of the operating parameters. Ignition timing was adjusted to minimum advance for best torque (MBT) according to the procedure described by Reynolds (2001). Data was collected with unaided spark ignition, and then at the same global air-fuel ratio, but with 2.6% of the fuel injected as PSC.  Table 2-3 PSC Verification Operating Parameters Trial PSC Fuelling (%) Premixed Fuelling (%) Engine Speed (rpm) Overall Relative AFR ( A ) PSC commanded SOI relative to Ignition (CAD) Ignition Timing Throttle Position (% open)  1 0 100 2000 1.6 41 MBT 100  2 2.6 97.4 2000 1.6 41 MBT 100  A significant difference in BSFC was apparent between these two treatments (386 g/kWh with PSC, and 647 g/kWh without). This is likely due to the reduction in partial burn events observed in the PSC case. Figure 2.12 is a histogram showing the distribution of integrated heat release (IHR) for the two conditions. In each case, IHR is individually calculated for 100 consecutive cycles. Partial burn is interpreted as combustion events which fall below the normally distributed peaks concentrated above 800 kJ/m . 3  According to this definition, the PSC data show three  percent partial burn, whereas the non-PSC case shows 32%.  21  Integrated Heat Release (kJ/m) Figure 2.12 Histogram of Integrated Heat Release  The effects of varying PSC injection timing relative to ignition have been described by Reynolds (2001), and are not a major focus of this thesis. The timing of the current PSC system was "tuned" qualitatively to a commanded SOI lead of 41 C A D before ignition. According to the PSC timing study described above, this would produce an actual SOI lead of up to six crank angle degrees. This timing appeared optimal and was adopted for all subsequent PSC experiments. Shorter lead durations were accompanied by a reduction in torque; whereas lengthening the duration by up to 15 C A D had little effect, though a similar drop in performance was noticed beyond this.  The fuel efficiency results suggested that, despite changes to the engine, PSC still produced the significant baseline improvement established in previous studies.  This verification allowed a  more meaningful evaluation of PSC in the current DI application.  22  2.4 INSTRUMENTATION AND DATA ACQUISITION UBC's  Ricardo  Hydra  t h e r m o d y n a m i c research.  is  equipped  with  a  full  instrumentation  package  suitable  for  A n a l o g u e Signals from the instruments are r e c e i v e d b y c o n d i t i o n i n g  boards, where they are filtered and a m p l i f i e d as needed.  A f t e r this i n i t i a l c o n d i t i o n i n g , a data  acquisition c a r d installed i n a P e n t i u m III based computer samples the signals for c o n v e r s i o n to digital data. Fast response instruments, s u c h as the i n - c y l i n d e r pressure transducer, are s a m p l e d i n 0.5 crank-angle degree increments (24 k H z at 2 0 0 0 r p m ) . D a t a that is not evaluated o n a c y c l e to c y c l e basis, s u c h as engine speed and torque, fuel and air f l o w rates, and exhaust e m i s s i o n s are sampled at l o w e r rates.  T h e s e parameters, referred to as " p e r f o r m a n c e data", are s a m p l e d at  approximately 1.3Hz. T a b l e 2-4 p r o v i d e s a list o f the H y d r a ' s instrumentation.  23  T a b l e 2-4 Ricardo Hydra Instrumentation Range  Manufacturer  Model  Intake Air Flow Rate  Meriam  50MW 20-1.5  Intake Air and Exhaust Temperature  Omega  1/8" K-Type  - 2 0 0 - 1250°C  Intake Manifold Pressure Differential  Sensym  LX1803AZ  0 - 3 0 psia  Pressure Transducer (Intake Air Flow Rate)  AutoTran  600 D-014  0 - 20" H20  Exhaust Relative Air-Fuel Ratio  ECM  2400G  1 =0.4- 10.0  In-Cylinder Pressure Transducer  AVL  QC33C  0 - 200 bar  MKS Instruments  1559A-100C-SV  0 - 100 slm  Natural Gas Flow Meter - PSC  MKS Instruments  179A-24-S3BM  0 - 2 0 slm  Natural Gas Flow Meter - Direct Injection  Endress + Hauser  Promass 80A DN02/1/12"  0-20 kg/h  US Digital  H1-360-IE  0 - 10,000 rpm  BLH  Load Beam Transducer  0 - 50 Nm  Carbon Dioxide Emissions  Beckman  880  Hydrocarbon Emissions  Ratfisch  RS-55  0 - 10,000 ppm  Carbon Monoxide Emissions  Siemens  Ultramat21P  0 - 10,000 ppm  API  200AH  Measurement  Natural Gas Flow Meter/Controller - Port Fuel  Engine Crank Angle / Speed Engine Torque  Nitrogen Oxide Emissions  0 - 3 0 scfm  0 - 20%  0 - 4500 ppm  A custom Lab View application, referred to as the Dynoserver, applies gains and offsets as appropriate to convert the data to engineering units before passing it to a remote computer located in an adjacent control room. This second computer operates two Lab View applications, referred to as the Dynoclient (Figure 2.13) and the Pressureclient (Figure 1.2).  These display real-time  operating parameters and the in-cylinder pressure trace respectively; they also record data for subsequent off-line analysis.  24  t> Dynoclient.vi  BMB>|  7"  SPEED]  woo  m4  MAIN PARAMETERS 0.0  1.0  1  y  1  o.'e -—y i  0.5'  A«*aged Torque (Nm)p^™  0,9  2.0 . 1.0  1.0  T_  3.0  _> 1.2 i.s y -> ;  Intake Man. Pressure!  1.1  t: « ' « I  |  1.2  <r —'— 1  0.00  DIAGNOSTICS NG fuel Ficw Rate! 1 , 11.355 kq/hour|  0.01  D9837  1-0.004  2  4  6  8  Oil Pressurel 10  2S.0  50.0  1-0.29  •  »)  100  120  Water Out Temperaturel  150  Intake Man, Tempi  175.8 50 r *  0  50  100  .. |Z9.0  j kg/hourl  J barfgll  Esthaust Man. Tempi  Throttle  ;j|-Z3.0  200 -100 600 800 1r  20  ;25 "  30  35  Barornetrk: Pressurel 0.90  0.95  1.0  1.1  jgSarl  : Test Cei Temperaturel iff  "\  dead  ENGINE A I R Engine Air Temperaturel  MS™  ~«E£l  PSC Irrrectron Ttrmqi  0 4jf  Unused Channell  Jjfo.459  dead  | drocl  bartol  ' | dead  Spark Tirrlno.1  [  :  Unused Teffljyjtue Volumetric Disp  | baKq)l  Oil Temperaturel  T  P5C Pressure} 0.0  : I&.16  *  | baKajl  Exhaust Han, Pressurel  P5C_Ftow Retej :  0.020.03  0  dead  J18.7  Relative HumMltyl  $7T~~ SI Air How Rate (IFOI  ba,(a)|  0,65  Mass tambdaj  |^20(rjffP)l  LFE Air Pressure} MPukeWttnl  ;Jfo5o  Exhaust Lambda]  O.0: ; :  1.0  2.0  3.0  11,0046  [ barjaj  O.OO 0.50 1.00 1.50 2,00  CO] (Other Injection Trming and Pursewridth here)  f-io ppmj •:,  Test# I Ir*akrjC02 O.OOOB |  CH4j  j-1282  (RESERVE SPACE FOR PRESSURE TRACE)  02i • corrals 1-0.003  r-0-27  'A  3lOO  013.010.0-  1-0.01 |  t POINTS  C02J Ko62  5.00.0-  Figure 2.13 Dynoclient Interface Window  25  Intake  Figure 2.14 Pressureclient Interface Window  An exhaust oxygen sensor provided a rough guide for determining the Hydra's air-fuel ratio. However, since the effectiveness of this instrument is reduced by poor combustion quality, airfuel ratios reported in this study are calculated from intake flow measurements.  26  2.5 ENGINE CONTROL  SYSTEM  The Hydra's speed and throttle position are set by adjusting potentiometers on a control console. Engine speed is maintained at constant set points by a feedback controller.  Input from the  potentiometer is compared with output from a tachometer coupled to the dynamometer and discrepancies are corrected by the thyristor drive. Input to the throttle potentiometer is mapped through a transfer function, then output to a servomotor that is directly linked to the throttle plate.  Ignition and fuel injection are controlled by a custom built timing system. Commands are entered into a Lab View application (Figure 2.15), which runs on the same computer as the DynoServer. These commands are passed to a counter/timer card, where they are indexed to the crank-shaft's angular position, then output as trigger signals for the hardware drivers. The drivers generate the ignition voltage and current, as well as the lift and hold currents for the PSC injector. The timing, duration and lift commands for the natural gas direct injector are sent to a driver system supplied by Westport.  • M ®| ••]  Timing Control !  *  -90.0  -60.0  -90.0  -60.01  -90.0  -60.0  1  '  '«  0.0  T i m i n g  1 00.0  •  |-36.0  -40.0  -20.0  0.0  20.0  -40.0  -20.0  0.0  20.0  -40.0  -20.0  0.0  20.0  *' '  ™  Trrrr  200.0  D u r a t i o n  300.0  3 1-23.00 3! 3J-56.00 3! 5J194.5  fro  1  400.0450.0  —  ^|8.00 1  ( O N J l9*ion Control  OFF j  NG Stratfied Injector  fl8.25  QFFJ  Main NG Direct Injector  3168.5  OFF)  PortGasolneInjection  1  , Stop ) Figure 2.15 Timing Controller Interface Window  Ported natural gas flow is controlled by an MKS thermal mass flow meter/controller. Set points are input from a remote interface in the control room.  27  2.6 DATA PROCESSING Data recorded during experimentation's imported into a combination of spreadsheets, which partially automate the task of data processing.  Pressure data is recorded in half crank angle  degree increments for 100 consecutive cycles. The spreadsheets calculate the. 100 cycle mean at each half crank angle degree, though data for each cycle is retained for individual analysis if necessary. For performance data, the spreadsheets calculate each parameter's sample mean standard deviation (S ), x  coefficient of variation (COV ) x  (X),  and 95% confidence interval (CI s%) 9  for the mean. The contingent expressions are (Bowker and Lieberman, 1972):  X = -tx  (Eq.2.1)  i  (Eq. 2.2)  (Eq. 2.3)  (Eq. 2.4)  Where  ^ 025 0  «-i '  s m  e  2.5% point of the t distribution with n-1 degrees of freedom. The 95%  confidence interval for the mean is the range that, if calculated repeatedly from multiple samples, would contain the true population mean 95% of the time.  28  2.7 STATISTICAL PILOT STUDY Drift in operating parameters such as engine speed and torque is an observable characteristic of the Hydra test-bed. In order to support the assumption of steady-state conditions while logging data, it is desirable to keep the collection interval short relative to the time scales of drift. Since the logging rate is fixed by the equipment, the number of sample points determines the duration of the collection interval. A pilot study was therefore undertaken to determine a sample size appropriate for characterizing operating conditions quickly, yet with a reasonable level of statistical certainty.  Due to difficulty in modifying the pressure data sampling process, this study was limited to performance data. Trials were conducted at a moderately rough operating point (COVIMEP ~ 5%) so as to support a conservative estimate of the data's spread. Details of the engine parameters are given in Table 2-5 and Table 2-6 below.  T a b l e 2-5 Statistical Pilot Study Operating Condition Engine Speed Load Premixed Fuelling  2000 rpm Wide Open Throttle lkg/hr ( A K 1.3)  PSC Direct Injection  Off Off  T a b l e 2-6 Statistical Pilot Study Sample Sizes Trial 1 2 3 4 5 6 7  Sample Size 11 21 31 41 51 76 101  2.5% point t distribution 2.228 2.086 2.042 2.021 2.009 1.992 1.984  29  Figures 2.16, 2 . 1 7 a n d 2.18 b e l o w s h o w the half-length o f the 9 5 % confidence interval as a function o f sample size f o r several k e y performance indicators. T h e v a l u e s s h o w n are added to and subtracted f r o m the sample m e a n to construct the confidence i n t e r v a l . These are calculated a c c o r d i n g to E q . 2.4, u s i n g each i n d i v i d u a l s a m p l e ' s standard d e v i a t i o n .  0.0  m  11  21  31  41  51  76  101  Number o f Sample Points Figure 2.16 Torque. H a l f - l e n g t h o f CI  at V a r y i n g S a m p l e S i z e s  9}  11  21  31  41  51  76  101  Number o f Sample Points Figure 2.17 Speed H a l f - l e n g t h o f CI  95  at V a r y i n g S a m p l e S i z e s  0.3 ^  0.2 -I  Sli  o  E"33 3  0 1  0.0 11  21  31  41  51  76  101  Number o f Sample Points Figure 2.18 F u e l F l o w H a l f - l e n g t h o f CI  95  at V a r y i n g S a m p l e S i z e s  30  T h e i n c e n t i v e for i n c r e a s i n g the sample size b e y o n d 51 data points w a s m i n i m a l ;  therefore  performance data for a l l subsequent experimentation was s a m p l e d i n sets o f 51 data points.  2.8 UNCERTAINTY  ANALYSIS  T h e uncertainties due to the instrument error associated w i t h each measured parameter  are  p r o v i d e d i n T a b l e 2-7 b e l o w .  T a b l e 2-7 M e a s u r e m e n t U n c e r t a i n t y Measurement  Uncertainty  Intake A i r F l o w R a t e  Pressure T r a n s d u c e r (Intake A i r F l o w Rate)  ± ± ± ±  Exhaust Relative A i r - F u e l Ratio  ± 0.009  Intake A i r and E x h a u s t Temperature Intake M a n i f o l d Pressure Differential  I n - C y l i n d e r Pressure T r a n s d u c e r Natural Gas F l o w Meter - P S G N a t u r a l G a s F l o w M e t e r / C o n t r o l l e r - Port F u e l N a t u r a l G a s F l o w M e t e r - D i r e c t Injection Engine C r a n k A n g l e / Speed Engine Torque Carbon Dioxide Emissions Hydrocarbon Emissions Carbon Monoxide Emissions Nitrogen Oxide Emissions  ± ± ± ± ± ± ± ± ± ±  0.3 scfm 2.2°C 0.6 P s i 0.2" H 2 0 0.4 bar 0.12 s l m 0.6 s l m 0.011 0 . 5 ° / ± 2 . 5 rpm 0.5 N m 0.2% 100 p p m 100 p p m 50 p p m  T h e overall uncertainty for each measured v a r i a b l e is reported as the instrument error, c o m b i n e d in quadrature w i t h the 9 5 % confidence interval, as r e c o m m e n d e d b y the J o u r n a l o f F l u i d s E n g i n e e r i n g ( R o o d a n d T e l o i n i s , 1991). F o r a measured parameter, the o v e r a l l uncertainty w is given by:  w=  V#  2  +P  2  ( E q . 2.5)  W h e r e B is the f i x e d uncertainty due to instrument error, and P is the 9 5 % c o n f i d e n c e interval, calculated as i n s e c t i o n 2.6 a b o v e .  31  For a parameter R, that is calculated from several measured variables R(xi,x , ...x„), the uncertainty 2  of each variable (w w , ...w„), is propagated in the following manner (Holman, 2001): h  2  ( dR  2  w,  (dR  )  2  + {dx w ) + . 2  >  (dR  1  w„  (Eq. 2.6)  2  As an example, BSFC is a fuel efficiency indicator that is particularly relevant in this study; the overall uncertainly for BSFC, at an operating condition that involves DI and PSC fuelling,, is reported in the manner described below. First, BSFC (g/kWh) is defined as:  (Eq. 2.7)  BSFC =  Where m is the total fuel flow (g/h), comprised of DI ( m ) f  DI  m  f  =m  Dl  +m  and PSC ( m  P S C  ) contributions:  (Eq. 2.8)  PSC  and Pb is the brake power (kW), defined as:  *  60  where N is the engine speed (rpm) and r is the brake torque (Nm). So the uncertainty in fuel b  flow according to Eq. 2.6 is:  32  f  m  V  DI  (Eq. 2.10)  PSC  m  m  and the uncertainty in power is:  (Eq. 2.11)  60  so the overall uncertainty for BSFC becomes:  wBSFC  2.9  CLOSING  ^  2  1  p  m  /  +  (  m p2  v  ^  *i  (Eq. 2.12) y  REMARKS  The PSC timing characterization and verification study, as well as the statistical pilot study were conducted as a collaborative effort between the Author and fellow M.A.Sc. Candidate, Mr. David Williams. The Author wishes to recognize Mr. Williams' contribution to these segments of this thesis.  33  3. M E T H O D O L O G Y As further described in this chapter, the experimental investigation was carried out in two parts. A primary study was aimed at characterizing the DI and PSC combustion system in terms of operating characteristics at varying levels of stratification. A secondary study was focused on the viability of the PSC pilot charge; and also involved re-visiting stratified combustion under conditions that guaranteed an ignitable pilot charge.  3.1 DEFINITIONS: EARLY AND LATE DIRECT  INJECTION  One of the goals of this study was to implement a late direct injection strategy for charge stratification. As defined by Abata (1986), this is a combustion system in which heat release is controlled by varying the injection rate. Ignition immediately follows the start of injection; then combustion propagates to engulf the plume as it issues from the injector. In this study, firing the spark plug shortly after the start of injection was the base strategy for igniting the stratified charge; however it was also anticipated that releasing the main fuel jet into the already burning PSC charge would provide more reliable ignition.  Despite the original hypothesis, practical considerations kept most operation biased towards early DI timings. A n early direct injection combustion system is one in which ignition occurs after injection is complete.  Heat release is controlled by mixing processes, as well as the chemical  kinetics of combustion.  Stratification in early direct injection engines, when desired, is  established through wall or air-guided approaches (Zhao 2002). This study did not involve a mechanism for maintaining the stratification of an early DI charge, so early injection timings were expected to produce a relatively homogenized charge.  34  3.2 DI TIMING SWEEPS T h e p r i m a r y i n v e s t i g a t i o n i n v o l v e d s w e e p i n g the direct injection t i m i n g across a range that a l l o w e d for v a r y i n g degrees o f fuel-air m i x i n g before i g n i t i o n . T h e v a r i a b l e o f interest was the injection t i m i n g relative to i g n i t i o n , as this determined the d u r a t i o n a v a i l a b l e for fuel to m i x w i t h the  s u r r o u n d i n g air before  c o m b u s t i o n began.  B e g i n n i n g w i t h early injection t i m i n g s , a  c o m b u s t i o n m o d e close to p r e m i x e d was expected to progress towards a stratified regime as the t i m i n g was d e l a y e d later into the c y c l e .  T h e i g n i t i o n method w a s v a r i e d between an unaided  spark and P S C for e a c h operating c o n d i t i o n . In this manner, it w o u l d b e c o m e apparent i f P S C ignition offered any i m p r o v e m e n t s across the v a r y i n g degrees o f stratification. T h e h y p o t h e s i z e d result is illustrated g r a p h i c a l l y i n F i g u r e 3.1.  A n increase i n B S F C w a s expected at intermediate  t i m i n g s i n w h i c h the m i x i n g interval w o u l d be too short to produce a h o m o g e n e o u s mixture, yet too l o n g to effectively produce a late D I stratified charge.  •Without P S C With P S C  pa  Spark Early (Premixed)  DI Timing  Late (Stratified)  F i g u r e 3.1 H y p o t h e t i c a l D I F u e l E f f i c i e n c y w i t h T i m i n g  35  In practice, the D I t i m i n g range w a s b o u n d early i n the c y c l e b y inlet v a l v e closure, and later i n the c y c l e by severe c o m b u s t i o n degradation. O p e r a t i n g points were established b y f i x i n g the D I t i m i n g i n 10 C A D increments and then adjusting i g n i t i o n t i m i n g to M B T .  F o r completeness,  experiments were attempted at late t i m i n g s , b e y o n d the onset o f severe performance degradation. In these cases, the f u e l l i n g systems were energized l o n g e n o u g h to briefly e x h i b i t results, and then deactivated so that c o n t i n u e d m o t o r i n g c o u l d dilute the h i g h levels o f unburned fuel that were evident at these c o n d i t i o n s . In these cases, c o m b u s t i o n was not stable e n o u g h to proceed safely through the d u r a t i o n r e q u i r e d for data c o l l e c t i o n , w i t h o u t p r o d u c i n g an unacceptable risk o f e x p l o s i o n i n the exhaust m a n i f o l d .  3.2.1  PSC Settings  F o r operating c o n d i t i o n s at w h i c h data was recorded, the c o m m a n d e d P S C S O I was h e l d constant at 41 C A D before i g n i t i o n .  T h i s t i m i n g was selected since it w a s k n o w n to be effective i n the  p r e m i x e d , lean b u r n case where P S C is k n o w n to produce a s i g n i f i c a n t result (see S e c t i o n 2.3). T h e P S C f l o w rate w a s h e l d between 2% and 3 % o f the total fuel charge; precise c o n t r o l w i t h i n this range was not a v a i l a b l e f r o m the c o n t r o l system used. A g a i n , for completeness, the t i m i n g o f P S C relative to i g n i t i o n w a s v a r i e d over a w i d e range ( a p p r o x i m a t e l y 41 ± 3 0 C A D ) at most operating c o n d i t i o n s . Q u a l i t a t i v e o b s e r v a t i o n indicated that v a r y i n g this t i m i n g had no effect, so the relative t i m i n g o f the p r e m i x e d study was adopted for consistency i n r e c o r d i n g data.  3.2.2  Air Fuel Ratio  F o r the t i m i n g sweeps, the g l o b a l relative air-fuel ratio was h e l d constant at A = 1 . 3 ± 0 . 0 8 .  This  moderate air-fuel ratio w a s concentrated e n o u g h to produce r e l i a b l e c o m b u s t i o n i n a homogenous m i x t u r e . K n o w i n g that the g l o b a l m i x t u r e w a s inherently c o m b u s t i b l e , performance degradation observed as the D I t i m i n g w a s retarded c o u l d be attributed to the effects o f stratification; and benefits due to the use o f P S C had the potential to reduce this degradation.  That a globally  36  stoichiometric m i x t u r e was not used is due to safety concerns: as a p r e c a u t i o n against severe backfire r e s u l t i n g from h i g h instances o f m i s f i r e at late t i m i n g s , a lean m i x t u r e w a s preferred.  3.2.3  Direct Injector Jet Angle  T h e D I t i m i n g sweeps w e r e repeated at each o f three jet orientations. These were chosen to direct v a r y i n g concentrations o f air-fuel m i x t u r e towards the electrodes, i n the manner d e s c r i b e d i n section 2.2. A s d i a g r a m m e d p r e v i o u s l y i n F i g u r e 2.2, angles o f 0 ° , 8 ° , and 1 6 ° were selected to direct r i c h , moderate, and lean mixtures respectively towards the electrodes.  T h i s approach to  m i x t u r e c o n t r o l has m o r e v a l i d i t y for late D I , since it depends o n a transient jet structure w h i c h , i n the case o f early i n j e c t i o n , w i l l have dissipated w e l l before i g n i t i o n . T h e angle is d e f i n e d relative to a line b i s e c t i n g the centre o f the injector sac and the centre electrode o f the spark p l u g , as s h o w n i n F i g u r e 2.2.  A l l testing w a s c o n d u c t e d at 2 0 0 0 r p m and w i d e o p e n throttle.  T h e D I s u p p l y pressure was  maintained at 3 0 0 0 p s i , this represents a pressure ratio o f a p p r o x i m a t e l y 12, relative to m a x i m u m motored i n - c y l i n d e r pressure.  3.3 PILOT CHARGE STUDY F o l l o w i n g the p r i m a r y i n v e s t i g a t i o n , it was hypothesised that the P S C charge w a s f a i l i n g to ignite under the c o n d i t i o n s o f the t i m i n g sweep study.  G i v e n the p o s i t i v e results obtained from the  a p p l i c a t i o n o f P S C to h o m o g e n o u s lean burn, it m a y be that the presence o f a s u r r o u n d i n g air-fuel mixture, even v e r y dilute, is required for the P S C charge to ignite. T h e p i l o t charge study was a p r e l i m i n a r y e x p l o r a t i o n o f this hypothesis.  I n i t i a l l y , the engine w a s run o n P S C alone. A f l o w rate and relative t i m i n g t y p i c a l o f that used for the t i m i n g sweeps w a s selected, and pressure arid emissions data w e r e evaluated against motored  37  engine data for i n d i c a t i o n s o f c o m b u s t i o n . through the intake m a n i f o l d .  A v e r y lean b a c k g r o u n d m i x t u r e was then inducted  T h i s mixture w a s too dilute to support c o m b u s t i o n  however, w h e n P S C w a s a p p l i e d , some evidence o f c o m b u s t i o n w a s detected.  throughout;  T h e concentration  o f the b a c k g r o u n d m i x t u r e w a s adjusted to be as w e a k as p o s s i b l e , w h i l e still s u p p o r t i n g a l i m i t e d c o m b u s t i o n event w h e n P S C w a s i n use.  F i n a l l y the shortest burst a v a i l a b l e f r o m the direct  injector's c o n t r o l system w a s introduced. T h i s was t i m e d to l a g the i n j e c t i o n and i g n i t i o n o f the P S C charge.  In i s o l a t i o n , each o f the three fuel sources w o u l d have p r o d u c e d an extremely lean  m i x t u r e ; h o w e v e r , as o u t l i n e d i n T a b l e 3-1, the c o m b i n a t i o n p r o d u c e d a g l o b a l l y r i c h charge.  T a b l e 3-1 F u e l l i n g C o n t r i b u t i o n s F u e l Source DI PSC  F l o w Rate (kg/h)  A (In Isolation)  0.56  2.14  0.029  42.3  Premixed  0.71  1.69  Overall  1.30  0.92  T h e injector orientation was m a i n t a i n e d i n the eight degree p o s i t i o n for the duration o f the p i l o t charge study.  38  4. RESULTS AND DISCUSSION One of the primary research objectives was to determine if jet-guided stratification, created by late direct injection, would facilitate globally lean load control. As will be discussed in this section, a negative result was obtained:  without significant time for premixing, combustion  quality was poor, with high instances of misfire. Results for direct injection timing sweeps are therefore confined to relatively early injection timings in which the directly injected fuel had the opportunity to mix with the surrounding air prior to ignition.  The parallel objective was to compare the directly injected engine's performance when ignited by un-aided spark ignition, to when ignited by PSC. As will be discussed further in this chapter, the results did not reveal a significant difference between these two ignition methods.  4.1 DI TIMING SWEEPS 4.1.1 Results BSFC data.obtained from the zero and eight degree injector angle timing sweeps are presented in Figures 4.1 and 4.2. In keeping with the convention of timing advance increasing in the negative direction, the injector lead is presented in C A D after ignition. For example, a relative timing of 70 C A D indicates that injection began 70 C A D before ignition.  39  900 O B S F C - D I Without P S C O B S F C - With P S C  600  <P  A <>  u OH  i  300  -100  -90  -80  -70  -60  -50  -40  -30  -20  D I S O I T i m i n g Relative to Ignition ( C A D After Ignition) F i g u r e 4.1 D I T i m i n g S w e e p B S F C R e s u l t ( 0 ° Injector A n g l e )  900  O B S F C - D I Without P S C O B S F C - D I With P S C  600  A  CQ  300  -100  -90  -80  -70  -60  -50  -40  -30  D I S O I T i m i n g Relative to Igntion ( C A D After Ignition) F i g u r e 4.2  D I T i m i n g Sweep B S F C Results ( 8 ° Injector A n g l e )  -20  In the zero and eight degree injector angle cases, a r a p i d increase i n B S F C is evident as the S O I lead reaches a m i n i m u m threshold. T h i s threshold is shorter i n the z e r o degree case than for eight degrees.  A t these early t i m i n g s , the j e t ' s i n i t i a l structure w o u l d have dissipated w e l l  before  i g n i t i o n . C o n s e q u e n t l y , the difference i n m i n i m u m threshold is l i k e l y due to the influence o f b u l k f l u i d m o t i o n , intake i n d u c e d or f r o m the D I jet, rather than o n w h i c h c o m p o n e n t o f the jet intersected the spark p l u g .  T h e 1 6 ° angle y i e l d e d such p o o r c o m b u s t i o n at a l l t i m i n g s that data  was not c o l l e c t e d .  T h e fuel efficiency data supports a negative result for the m a i n research questions o f this study. T h e c r i t i c a l d e c l i n e i n performance demonstrates that the direct injection s y s t e m installed was not able to produce a r e l i a b l y ignitable stratified charge.  Furthermore, i n the early direct injection  regime, the data does not s h o w a significant difference between trials c o n d u c t e d w i t h P S C i g n i t i o n and those i g n i t e d b y c o n v e n t i o n a l spark i g n i t i o n . There is i n c o n s i s t e n c y between w h i c h o f these cases d i s p l a y more favourable fuel efficiency; and i n a l l cases there is significant overlap between the uncertainty ranges o f each. These results s h o w that the current P S C system is unable to reduce fuel c o n s u m p t i o n i n a direct injection stratified charge engine.  4.1.2  Discussion  In order to understand the B S F C results, it is useful to b e g i n b y c h a r a c t e r i z i n g the D I data i n terms o f the heat released per engine c y c l e .  S i n c e this is a pressure-based  c a l c u l a t i o n , it is  available for each o f the 100 c y c l e s recorded per operating c o n d i t i o n . H i s t o g r a m s o f heat release for a l l operating c o n d i t i o n s v i s i t e d d u r i n g the t i m i n g sweeps are s h o w n i n F i g u r e s 4.3 and 4.4. These reveal a d i s t i n c t l y b i m o d a l distribution. T h e majority o f c y c l e s are d i v i d e d between the first  peak,  a  sharp  concentration  o c c u r r i n g between  zero  and  80  kJ/m , 3  a p p r o x i m a t e l y n o r m a l d i s t r i b u t i o n , centred o n an average near 1200 k J / m . 3  and  a  second,  T h e first peak is  interpreted as misfire, w h i c h is subsequently defined i n this thesis as c o m b u s t i o n events that y i e l d  41  less than 80 k J / m . 3  P a r t i a l b u r n c y c l e s , w h i c h are characterized b y values that fall between the  t w o p r i m a r y modes, are i n d i c a t e d i n v e r y few cases.  160 140 120 §  100 -  <L>  0  160  320  480  640  800  960  Integrated Heat Release k J / m  Figure 4.3  1120  1280  1440  3  H i s t o g r a m o f N e t H e a t R e l e a s e for A l l T i m i n g S w e e p C o n d i t i o n s ( 0 ° Injector A n g l e )  42  180 160 -140 -120 - =  0  160  320  480  640  800  960  Integrated Heat Release k J / m  Figure 4.4  1120  1280  1440  3  H i s t o g r a m o f N e t H e a t Release for A l l T i m i n g S w e e p C o n d i t i o n s (8° Injector A n g l e )  M i s f i r e , a c c o r d i n g to the above definition, is s h o w n i n F i g u r e s 4.5 and 4.6 relative to D I t i m i n g . T h e trend s o m e w h a t resembles the relationship between B S F C and D I t i m i n g . A g a i n , the t i m i n g sweep data s h o w s n o consistent advantage o f P S C over standard i g n i t i o n .  43  60 O M i s f i r e - D I Without P S C  o  O Misfire - D I With P S C  50  40  I  30  o A  20  o  o  o  o  io H  o  o  o  0 -100  -80  -60  -40  -20  D I S O I T i m i n g Relative to Ignition ( C A D After Ignition)  Figure  4.5 M i s f i r e w i t h D I T i m i n g  (0°  Injector A n g l e )  60 O M i s f i r e - D I Without P S C 50  H  O Misfire - DI With P S C  40  30  20  o  8  10  o <6  -100  -80  o o  -60  -40  -20  DI SOI Timing Relative to Ignition ( C A D After Ignition)  Figure 4.6  Misfire with DI Timing  (0°  Injector A n g l e )  M i s f i r e must certainly contribute to the B S F C trends; h o w e v e r , for the majority o f t i m i n g c o n d i t i o n s , m i s f i r e and B S F C do not correlate w e l l .  F i g u r e s 4.7 and 4.8 s h o w a p o o r l y defined  relationship between B S F C and misfire, as w e l l as a l a c k o f differentiation between P S C and standard i g n i t i o n .  In these figures, the majority o f data is g r o u p e d b e l o w 3 0 % m i s f i r e ; w h e n  these groups are e x a m i n e d separately ( s o l i d trend lines) the c o r r e l a t i o n between B S F C  and  misfire is v e r y poor.  1200 O O  B S F C - D I Without P S C B S F C - DI With P S C  1000  800  u  600  4r  CP  C/)  CQ 400  Linear ( A l l 0 ° D a t a ) y = 12x + 211, R = 0.90 Linear (<30% Misfire) y = 8.6x + 264, R = 0.57 2  200  2  10  20  30  40  50  60  Misfire (%)  Figure  4.7 B S F C w i t h M i s f i r e ( 0 ° Injector A n g l e )  45  1200 O O  1000  B S F C - D I Without P S C B S F C - D I Without P S C Linear ( A l l 8° Data) y == 7.9x + 297, R = 0.72 Linear (< 3 0 % Misfire) y == 4.9x + 321, R = 0.30 2  2  800  u  oo CQ  600  >  400 o 200 1  0 0  10  20  30  40  50  60  Misfire (%)  Figure 4.8 B S F C  w i t h M i s f i r e ( 8 ° Injector A n g l e )  T h e relationship between total h y d r o c a r b o n emissions and m i s f i r e is s i m i l a r to that o f B S F C and misfire.  F i g u r e s 4.9 and 4.10 reveal n o clear difference between P S C and standard i g n i t i o n , and  there is poor c o r r e l a t i o n for data that falls at misfire rates o f less than 3 0 % .  46  140 120  O  t H C - D I Without P S C  O  t H C - DI With P S C  100  1 y  80  X  1  60 40 Linear ( A l l 0° Data) y = 1.9x + 12.4, R = 0.92 2  20 -  Linear (<30% Misfire) y = 1.5x + 17.1, R = 0.66 2  0 50  40  30  20  10  60  Misfire (%)  Figure 4.9  t H C w i t h M i s f i r e ( 0 ° Injector A n g l e )  14U  120  O  t H C - D I Without P S C  O  t H C - D I With P S C L i n e a r ( A l l 8° Data) y = 1.6x + 16.6, R = 0.81 2  100  •Linear (<30% M i s f i r e ) y = 1.5x + 17.9, R = 0.56 2  80 u  60  0  X  40 20  0  0 10  15  20  25  M i s f i r e (%)  Figure  4.10 t H C w i t h M i s f i r e ( 8 ° Injector A n g l e )  30  35  H o w e v e r , B S F C and total hydrocarbons ( t H C ) e x h i b i t a strong c o r r e l a t i o n .  T h i s is plotted i n  Figures 4.11 a n d 4.12 for each t i m i n g sweep. T h e data is plotted w i t h o u t differentiation between P S C and standard i g n i t i o n , since no significant difference was f o u n d between these w h e n B S F C and t H C where e x a m i n e d separately.  1200 B S F C Linear 1000  ^  800  H  600  y = 6.62x + 126 R = 0.99 2  u fcu m  400 200 -I  20  40  60  80  100  120  t H C (g/kWh)  Figure 4.11 B S F C  w i t h t H C ( 0 ° Injector A n g l e )  48  1200  200 0 -j 0  ,  ,  ,  ,  1  1  20  40  60  80  100  120  t H C (g/kWh)  Figure 4.12  B S F C w i t h t H C ( 8 ° Injector A n g l e )  T h e correlation between B S F C and t H C indicates that the D I e n g i n e ' s e f f i c i e n c y was strongly influenced b y m i s f i r e and i n c o m p l e t e c o m b u s t i o n .  T h e l a c k o f c o r r e l a t i o n between m i s f i r e and  B S F C or t H C indicates that e v e n w h e n fuel was successfully i g n i t e d , the c o m b u s t i o n quality was poor.  T h i s suggests p r o b l e m s s u c h as a l a c k o f flame front penetration into o v e r l y lean or r i c h  areas, or i s o l a t i o n o f ignitable regions f r o m active c o m b u s t i o n c h e m i s t r y . I n this case the mixture was not fully  stratified, but characterized b y d i f f e r i n g levels o f heterogeneity;  c o m b u s t i o n p r o b l e m s encountered are also c o m m o n i n stratified charge engines.  however  the  W h e n compared  to c o n v e n t i o n a l spark i g n i t i o n , P S C d i d not e x h i b i t a significant effect o n these p r o b l e m s .  49  4.2 PILOT CHARGE STUDY 4.2.1 Results In the presence o f a w e a k h o m o g e n o u s m i x t u r e (k ~\J,  see T a b l e 3-1 for f u e l l i n g details), late  direct injection, c o m b i n e d w i t h P S C , p r o d u c e d reliable c o m b u s t i o n .  B S F C is plotted at several  direct injection t i m i n g s i n F i g u r e 4.13.  5  10  15  20  25  30  D I S O I T i m i n g Relative to Igntion ( C A D After Igntion)  Figure 4.13 P i l o t  C h a r g e Study F u e l E f f i c i e n c y Results  Perhaps as significant as the B S F C result, is that no m i s f i r e w a s observed as l o n g as P S C was i n use.  T h e histogram o f net heat release for a l l three conditions ( F i g u r e 4.14) reveals a tightly  distributed peak w i t h a n average o f 1370 k J / m . 3  50  70 60 450 4-  | M 0 f 3  20 +  10 + 0 0  160  320  480  640  800  960  Integrated Heat Release k J / m  Figure 4.14  1120  1280  1440  3  H i s t o g r a m o f N e t H e a t Release for a l l p i l o t charge study c o n d i t i o n s  A s w i l l be discussed further, the b a c k g r o u n d m i x t u r e w a s too lean to support c o m b u s t i o n o n its o w n . C o n s e q u e n t l y , it was expected that D I injected after i g n i t i o n w o u l d not b u r n . Indeed, n o n P S C trials at the operating c o n d i t i o n s o f F i g u r e 4.14 p r o d u c e d o n l y m i s f i r e , therefore data was not collected.  4.2.2  Discussion  B y c o m p a r i s o n w i t h m o t o r e d engine data, it was clear that the P S C s y s t e m , operating i n the absence o f any other fuel source, failed to produce evidence o f c o m b u s t i o n . F i g u r e 4.15 shows that the t w o averaged pressure traces are i d e n t i c a l , t h o u g h the instrument is coarse at this scale.  51  17  1*  /  ¥ 3 OO. U fc  V  1 6  15  Motored  O  2.6g/hPSC  ^ Representative Error B a r  C-  O o  o o o o  0  o  14 -I  O  o  o o o  0  -15  15  Crank Postion ( C A D A T D C )  Figure 4.15  I n - C y l i n d e r Pressure Trace C o m p a r i s o n : M o t o r e d and w i t h P S C  T h e composite heat release profiles i n F i g u r e 4.16 are s i m i l a r ; both i n d i c a t i n g the same loss to heat transfer t h r o u g h the c o m b u s t i o n chamber w a l l s .  Figure 4.16  N e t H e a t Release Rate C o m p a r i s o n : M o t o r e d and w i t h P S C  A l t h o u g h the same P S C settings p r o d u c e d a significant result i n the lean b u r n case o f section 2.3, there is no evidence to suggest that the P S C p i l o t charge is i g n i t i n g w h e n surrounded b y air. G i v e n this result, it is not s u r p r i s i n g that P S C failed to produce a significant result  when  c o m p a r e d to c o n v e n t i o n a l spark i g n i t i o n d u r i n g the direct injection t i m i n g sweeps.  W h e n P S C is injected into pure air, it is l i k e l y that the concentration gradients are i n i t i a l l y quite h i g h , since the o v e r a l l transition must span the concentration range between zero and  100%  natural gas. W h e n P S C is injected into a dilute air-fuel m i x t u r e , the gradients are l i k e l y to be less severe since the o v e r a l l concentration range is narrower.  In b o t h cases, a c o m p l e x and h i g h l y  transient v o l u m e o f c o m b u s t i b l e chemistry w i l l result, h o w e v e r this r e g i o n w i l l be larger i n the case o f a w e a k l y f u e l l e d b u l k m i x t u r e , and more l i k e l y to bridge between the i g n i t i o n source and combustible mixture.  W h e n a v e r y w e a k (X, ~ 1.7), p r e - m i x e d b u l k charge was inducted, n o heat w a s released f r o m spark i g n i t i o n alone. Y e t e v i d e n c e o f c o m b u s t i o n w a s detected w h e n the P S C charge was added. T h i s is evident i n F i g u r e s 4.17 a n d 4.18, w h i c h s h o w the pressure traces and heat release profiles from the t w o cases.  53  -15  0  15  Crank Position ( C A D A T D C )  Figure 4.17 In-Cylinder Pressure Trace Comparison: With and Without PSC  X 1.69 Without P S C  O  /  \  X.1.69 W i t h 28 g/h P S C  3 Qi  •.  . . . . 'UAA^JIHS  ft.i  (U  <Z) CvS  <D O  Pi  •s  X -60  -40  -20  0  20  40  60  80  100  120  Crank Position ( C A D A T D C ) Figure 4.18 Net Heat Release Rate Comparison: Weak Mixture With and Without PSC  It is not clear to what extent the heat released in the PSC case was from pilot fuel or the surrounding bulk charge; it is likely a mixture of both. It appears, however, that this initial combustion does not propagate through the ultra-lean mixture. This inference is supported by the  54  h i g h exhaust levels o f unburned hydrocarbons and the discrepancy between the heat e v o l v e d from c o m b u s t i o n and the fuel energy entering the c o m b u s t i o n chamber ( T a b l e 4-1). T h i s suggests the presence o f a l i m i t e d c o m b u s t i o n event that extinguishes or continues to b u r n w i t h o u t propagating through the m i x t u r e .  T a b l e 4-1 Partial C o m b u s t i o n : W e a k M i x t u r e w i t h P S C Total Hydrocarbons  > 10,000 p p m - w e t  N e t Integrated Heat Release  41 ( J / c y c l e )  Heat Contribution o f P S C  23 ( J / c y c l e )  Heat Contribution o f Premixed Fuel  555 ( J / c y c l e )  T o t a l Inducted H e a t E n e r g y  578 ( J / c y c l e )  T h e initial c o m b u s t i o n p r o d u c e d w h e n P S C is c o m b i n e d w i t h a dilute m i x t u r e seems able to act as a pilot charge, p r o v i d i n g reliable i g n i t i o n to the directly injected fuel. Inspection o f the B S F C data, s h o w n this t i m e i n c o m p a r i s o n to the t i m i n g sweeps ( F i g u r e 4.19), indicates that reliable c o m b u s t i o n w a s o c c u r r i n g at direct injection t i m i n g s that were far later than w a s possible d u r i n g the t i m i n g sweeps.  55  900  O 0° T i m i n g Sweep O 8° T i m i n g Sweep A Pilot Charge Study  600 —'  u  CQ 300  0 -90  -80  -70  -60  -50  -40  -30  -20  -10  0  10  20  30  D I S O I T i m i n g Relative to Ignition ( C A After Ignition) Figure 4.19 B S F C C o m p a r i s o n : P i l o t C h a r g e S t u d y W i t h T i m i n g S w e e p s  In t i m i n g sweep cases that e x h i b i t s i m i l a r B S F C to the p i l o t charge study, a m i x i n g interval o f at least 70 C A D w a s required before i g n i t i o n . T h i s was f o l l o w e d b y the b e g i n n i n g o f heat release a p p r o x i m a t e l y 19 C A D later.  T a b l e 4-2 shows average values o f i g n i t i o n delay for certain  operating c o n d i t i o n s selected f r o m F i g u r e 4.19.  A l l those f r o m the p i l o t charge study  are  i n c l u d e d , as w e l l as t i m i n g sweep c o n d i t i o n s w i t h a B S F C o f 350 g / k W h or less. In the case o f the p i l o t charge study, substantial heat release lags direct injection b y a s i m i l a r interval as i g n i t i o n delay i n the t i m i n g sweeps.  In both cases, this interval is s m a l l c o m p a r e d to the  timescales  required for adequate m i x i n g i n early D I . T h e prompt a r r i v a l o f heat release i n p i l o t charge study cases indicates that the late D I charge w a s b u r n i n g i n a h i g h l y stratified manner.  56  T a b l e 4-2 A v e r a g e B S F C and I g n i t i o n D e l a y T i m i n g Sweeps  P i l o t C h a r g e Study 325  325  B S F C (g/kWh) 0 - 1 0 % net H e a t Release D u r a t i o n  19  ( C A D after D I ) 0-10%) net H e a t Release D u r a t i o n ( C A D after Ignition)  22  T h e stable c o m b u s t i o n and absence o f misfire f o u n d i n the p i l o t charge study partially validates the concept o f c o m b i n i n g stratified charge w i t h p i l o t i g n i t i o n . H o w e v e r , g i v e n the o v e r l y r i c h g l o b a l m i x t u r e inherent i n this approach, h i g h levels o f unburned h y d r o c a r b o n s and r e l a t i v e l y poor fuel efficiency are inevitable.  Therefore this data does not support c o n c l u s i o n s on the  effectiveness o f P S C i g n i t i o n to i m p r o v e fuel usage i n a stratified charge engine.  4.3  SUMMARY  T h e experimental e v i d e n c e that P S C doesn't produce an ignitable p i l o t charge w h e n injected into air provides a n e x p l a n a t i o n for the l a c k o f c o m b u s t i o n at late direct i n j e c t i o n t i m i n g s . W i t h o u t a pilot charge, i g n i t i o n w o u l d depend o n spark i g n i t i o n alone.  S p a r k discharge produces a v e r y  s m a l l i o n i z e d v o l u m e between the electrodes, w h i c h i n this case, w e r e s l i g h t l y recessed into the c y l i n d e r head. Y e t this e n e r g i z e d r e g i o n w o u l d need to intersect the fuel j e t ' s n a r r o w and h i g h l y transient m a r g i n o f c o m b u s t i b l e mixture at the correct time.  C o n s i d e r i n g the v a r i a b i l i t y o f the  j e t ' s surface, and the size o f the affected v o l u m e p r o d u c e d b y spark discharge, it seems u n l i k e l y that c o m b u s t i o n w o u l d o c c u r r e l i a b l y f r o m spark discharge alone.  In the early D I t i m i n g sweeps, the P S C charge was injected into an air-fuel m i x t u r e c o m p o s e d o f v a r y i n g levels o f heterogeneity.  T h i s is a substantially different c o n d i t i o n than injecting P S C into  air, so it is not e x p e r i m e n t a l l y clear whether or not P S C p r o d u c e d a p i l o t charge under these  57  conditions; however the lack of differentiation between PSC and unaided spark ignition suggest that it did not.  58  5. CONCLUSIONS AND RECOMMENDATIONS The  P a r t i a l l y Stratified C h a r g e concept has p r e v i o u s l y been s h o w n to i m p r o v e c o m b u s t i o n  initiation and stability i n a lean fuelled, homogeneous charge engine.  It w a s hypothesised that  P S C w o u l d also i m p r o v e fuel usage i n a d i r e c t l y injected, stratified charge engine. T h e s p e c i f i c objective o f this research w a s to m o d i f y a research engine to support spark i g n i t e d c o m b u s t i o n o f a directly injected stratified charge.  It was expected that, i f successfully i m p l e m e n t e d , this  c o m b u s t i o n s y s t e m w o u l d produce h i g h levels o f unburned h y d r o c a r b o n s , as is characteristic o f external i g n i t i o n source stratified charge engines.  T h i s is l a r g e l y due to inconsistent i g n i t i o n o f  the fuel charge, p o o r c o m b u s t i o n propagation and o v e r - m i x i n g at the fuel charge boundaries.  It  was hypothesised that the h i g h i g n i t i o n energy offered b y the P S C s y s t e m w o u l d result i n reduced hydrocarbon emissions.  5.1  CONCLUSIONS  A single c y l i n d e r research engine, p r e v i o u s l y equipped w i t h the P S C system, w a s m o d i f i e d to accommodate a natural gas direct injector.  A series o f direct i n j e c t i o n t i m i n g sweeps were  conducted to characterize the response o f fuel efficiency to the t i m e i n t e r v a l a l l o w e d for fuel-air m i x i n g p r i o r to i g n i t i o n .  F o l l o w i n g the t i m i n g sweeps, several trials were c o n d u c t e d i n w h i c h  direct injection and P S C were c o m b i n e d i n the presence o f a v e r y dilute h o m o g e n o u s b u l k charge. The f o l l o w i n g c o n c l u s i o n s are extracted from the resulting data:  1.  T h e e x p e r i m e n t a l engine c o n f i g u r a t i o n was not able to support stratified operation t h r o u g h late direct injection.  T h e best B S F C was o b s e r v e d at the most advanced  injection t i m i n g s , i n w h i c h the interval available for the fuel charge and s u r r o u n d i n g air to m i x w a s m a x i m i z e d .  E f f i c i e n c y degraded r a p i d l y w h e n this interval was  reduced b e l o w a m i n i m u m threshold.  59  2.  The minimum mixing interval was influenced by the angle at which the fuel jet entered the combustion chamber. The onset of severe performance degradation in the eight degree case occurred at a mixing interval approximately 10 crank angle degrees longer than when the jet was aimed directly at the spark plug electrodes. A 16° case was attempted, but failed to produce reliable combustion even at the most advanced timings.  3.  The PSC system exhibited no significant improvement in terms of BSFC, when compared to unaided spark ignition. Data collected during the early direct injection timing sweeps revealed that PSC ignition offered no systematic advantage in terms of BSFC, misfire rates, or the unburned hydrocarbon content of exhaust.  4.  The PSC system did not produce an ignitable pilot charge when, prior to PSC injection, the engine's combustion chamber contained only air. Currently, the PSC system has been shown to produce combustion only when injected into a dilute homogenous mixture.  5.  When the presence of an ignitable pilot charge was assured, the jet-guided stratified charge, created by late direct injection, ignited reliably and produced stable engine operation.  5.2 RECOMMENDATIONS  FOR FUTURE WORK  The reliable stratified charge combustion, produced when the presence of an ignitable pilot charge was assured, supports the conceptual validity of combining late direct injection with pilot ignition.  Future work on this concept is warranted; and efforts should focus on the reliable  establishment of an ignitable pilot charge, such that it can subsequently ignite a directly injected bulk charge. To this end, the following work is recommended in support of further developing the PSC concept:  60  1.  T h e P S C fuel jet d e v e l o p m e n t is currently not w e l l understood. vigorously combustion  It is not k n o w n h o w  it m i x e s w i t h the s u r r o u n d i n g m i x t u r e , nor is it clear to what chamber  b u l k m o t i o n carries it a w a y  from  the  electrodes.  A  extent better  understanding o f the P S C s y s t e m ' s in-situ f l u i d d y n a m i c s m a y e x p l a i n the pilot charge's failure to ignite w h e n injected into air; and m a y produce r e c o m m e n d a t i o n s for r e m e d y i n g this.  2.  T h e effectiveness o f P S C appears to be h i g h l y sensitive to g e o m e t r i c aspects o f the fuel path t h r o u g h the spark p l u g b o d y . A n e w P S C spark p l u g was b u i l t for this study. It had s e e m i n g l y m i n o r v a r i a t i o n , a i m e d at i m p r o v i n g its reach into the c o m b u s t i o n chamber, as c o m p a r e d to a p l u g recently used b y R e y n o l d s (2004).  This new plug was initially  installed d u r i n g the lean b u r n v e r i f i c a t i o n study p r e v i o u s l y d i s c u s s e d i n 2.3. N o n e o f the benefits that P S C had e x h i b i t e d w h e n p r e v i o u s l y a p p l i e d to the lean b u r n case were apparent w h e n the n e w p l u g was i n use.  It w a s n ' t u n t i l the o r i g i n a l p l u g w a s replaced,  that P S C s h o w e d the p o s i t i v e result reported i n 2.3. T h e p r e v i o u s l y v a l i d a t e d p l u g was used throughout a l l subsequent experiments reported i n this thesis; the reasons for its superior performance are not understood and warrant further i n v e s t i g a t i o n .  3.  T h e P S C system w o u l d benefit from a more precise means o f m e t e r i n g fuel f l o w .  As  m e n t i o n e d i n section 2.3, the current s y s t e m ' s v a g u e l y d e f i n e d end o f injection m a y result i n a r e s u m p t i o n o f fuel f l o w as c o m b u s t i o n c h a m b e r pressure drops d u r i n g the b l o w down.  T h i s w o u l d cause increased levels o f unburned h y d r o c a r b o n s and reduce fuel  efficiency.  U s e o f a purpose-built gaseous fuel injector m a y offer a m o r e clearly defined  end o f injection, as w e l l as an o v e r a l l i m p r o v e m e n t i n t i m i n g promptness and metering precision.  61  4.  S h o u l d efforts to i m p r o v e the i g n i t a b i l i t y o f the P S C p i l o t charge prove successful, late D I c o m b i n e d w i t h P S C s h o u l d be further e x p l o r e d . T h i s s h o u l d i n c l u d e variations i n the D I strategy s u c h as d i f f e r i n g injector angles, m u l t i p l e o r i f i c e injection and  multiple  injection pulses.  62  REFERENCES Abata D (1987). A review of the stratified charge engine concept. In R. L. Evans (Ed.) "Automotive Engine Alternatives" New York, New York: Plenum Press, pp.37-82, Arcoumanis C, Hull D R, Whitelaw J H (1994). An Approach to Charge Stratification in LeanBurn, Spark-Ignition Engines. SAE Technical Paper Series. 941878. Bowker A H, Lieberman G J (1972). "Engineering Statistics" 2nd Ed. Englewood Cliffs, New Jersey: Prentice-Hall, Inc. pp 296. ISBN: 0-13-279455-1 BP p.I.c. (2005). "BP Statistical Review of World Energy - June 2005" (electronic resource URL:http://www.bp.com/liveassets/bp internet/globalbp/globalbp uk english/reports and publi cations/statistical_energy_review_2006/STAGING/local_assets/downloads/pdf/statistical_review _of_world_energy_ful l_report_2005.pdf Brown G (2003). "Performance of a Partially Stratified-Charge Gasoline Engine" University of British Columbia, Canada, M.A.Sc dissertation. Dale J D, Checkel M D, Smy P R (1997). Application of High Energy Ignition Systems to Engines. Progress in Energy and Combustion Science, Vol. 23. pp. 379-398, 1997  Etrema Products Inc. (2006). "Terfenol-D Data Sheet" (electronic resource URL: http://www.etrema-usa.com/products/terfenolA)  Webmaster: Global Reach Internet Productions,  Accessible as of March 2007. Evans R L (2000). "Control Method for Spark-Ignition Engines" United States Patent No: 6,032,640, Issued March 7, 2000 Ferguson C R (1986). "Internal Combustion Engines - Applied Thermosciences" 2 Ed. USA: nd  John Wiley & Sons, Inc. ISBN: 978-0-471-35617-2 Fraily M , Norton P, Clark N N and Lyons D W (2000). An Evaluation of Natural Gas versus Diesel in Medium-Duty Buses. SAE Technical Paper Series. 200-01-2822. Germane G J, Wood C G, Hess C C (1983). Lean combustion in spark-ignited internal combustion engines - a review. SAE Technical Paper Series. 831694. Goto Y, Sato Y (2001). Combustion improvement and exhaust emissions characteristics in a direct injection natural gas engine by throttling and exhaust gas recirculation. From "Direct Injection SI Engine Technology 2001" (SP-1584) Warrendale, Pennsylvania, USA: S A E International. ISBN 0-7680-0731 -3 Goudie D, Dunn M , Munshi S R, Lyford-Pike E, Wright J, Duggal, V , Frailey M (2004). Development of a Compression Ignition Heavy Duty Pilot-Ignited Natural Gas Fuelled Engine for Low Nox Emissions. SAE Technical Paper Series. 2004-01-2954  63  Green R K, Zavier C C (1992). Charge Stratification in a Spark Ignition Engine Proc. Instn Mech Engrs, Vol. 206 Part A , pp 59-64. Gupta M , Bell S R (1994). An Investigation of Lean Combustion in a Natural Gas Fuelled Spark Ignited Engine. ASME - Natural Gas and Alternative Fuels for Engines ICE-Vol. 21 1993.  Heywood J B (1988). "Internal Combustion Engine Fundamentals" New York: McGraw-Hill. ISBN 0-07-100499-8. Hill P G, Ouellette P (1999). Transient Turbulent Gaseous Fuel Jets for Diesel Engines. Journal of Fluids Engineering, Vol. 121, pp 93-101  Holman J P (2000). "Experimental Methods for Engineers" 7 Ed. New York: McGraw-Hill, Inc. th  ISBN 0073660558 Huang Z, Shiga S, Ueda T, Nakamura H, Ishima T, Obokata T, Tsue M , Kono, M (2002). Combustion Characteristics of Natural-Gas Direct-Injection timings, Proc. Instn Mech. Engrs, Vol. 217 Part D, pp 393-401 Iaconis J-L (2003). "An Investigation of Methane Autoignition Behaviour Under Diesel EngineRelevant Conditions" University of British Columbia, Canada, M.A.Sc dissertation. Kubesh J T (2002). Development of a Throtteless Natural Gas Engine - Final Report. NREL/SR540-31141, National Renewable Energy Laboratory. Lahbabi F Z, Boree J, Nuglisch H J, and Charnay G (1993). Analysis of Starting and Steady Turbulent Jets by Imaging Processing. Techniques Proceedings of the 1993 ASME  Winter Annual  Meeting, ASME-FED-Vol. 172, pp. 315-321. Reynolds C (2001). "Performance of a Partially Stratified-Charge Natural Gas Engine" University of British Columbia, Canada, M.A.Sc dissertation. Reynolds C, Evans R L (2004) The Low NOX Potential of Partially Stratified-Charge Combustion in a Natural Gas Engine. Combustion Institute / Canadian Section, Spring Technical Meeting, Kingston, Ontario, Canada, May 9-12, 2004 Ricardo p.l.c. (2005). Hydra web-page (electronic resource URL: http://www.ricardo.com/engineeringservices/engine.aspx?page=hydra) accessible as of March 2007 Rood E P, Demetri P T (1991). Journal of Fluids Engineering Policy on Reporting Uncertainties in Experimental Measurements & Results. Journal of Fluids Engineering, September 1991 Editorial on Experimental Uncertainty. Society of Automotive Engineers. (1999). Stoichiometric Air-Fuel Ratios of Automotive Fuels SAE J1829 Dec97. from "SAE Handbook". Warrendale, PA. U.S.A.: Society of Automotive Engineers, Inc.  64  Turner J W G, Pearson R J, Kenchington S A (2004). Concepts for Improved Fuel Economy from Gasoline Engines. International Journal of Engine Research, IMechE 2005, vol. 6, DOI:  10.1243/146808705X7419, pp 137-157, 2005 U.S. Department of Energy (a) - Energy Efficiency and Renewable Resources (2005). "Properties of Fuels" (electronic resource URL:  http://www.eere.energy.gov/afdc/pdfs/fueltable.pdf)  U.S. Department of Energy (b) - Energy Efficiency and Renewable Resources (2006). "Clean Cities Alternative Fuel Price Report - October 2006" (electronic resource URL: http://www.eere.energy.gov/afdc/resources/pricereport/pdfs/afpr_oct_06.pdf),  Contact: Michael  D. Laughlin, New West Technologies, L L C , 4351 Garden City Drive, Suite 600, Landover, M D 20785. Accessible as of March 2007. White F M (1994). "Fluid Mechanics" 3 Ed . McGraw-Hill, ch 9, ISBN 0-07-113765-3. rd  Wilcox D C (2003). "Basic Fluid Mechanics" 2  nd  Ed. California, USA: D C W Industries, Inc. pp  631-639, ISBN 1-928729-03-7 Williams D (2006). B.A.Sc University of Toronto, 2003. M . A . S c Candidate, U B C 20032006. personal communication. Zhao F , Harrington D L , Chi M (2002). "Automotive Gasoline Direct-Injection Engines" Warrendale, Pennsylvania, U S A : S A E International. ISBN: 0-7680-0882-4  65  APPENDIX A: DESIGN  DOCUMENTATION  DIHEAD MODIFICATION:  GEOMETRIC  REPRESENTATION  The solid model pictured in Figure A . l below was constructed in Pro/Engineer version 2000i  2  This model served as the basis for the design study in which room for the J43 fuel injector was found within the head's internal geometry.  Information was gathered from the original design  drawings, as well as measurements taken from the sand casting patterns.  Figure A . l Aluminium SI Cylinder Head Solid Model  66  DI HEAD MODIFICA TION: STA TIC STRESS ANAL YSIS Figure A.2 below shows the output of a geometric element analysis (GEA) performed using Pro/Mechanica version 2000i . The purpose of this analysis was to estimate the stresses in the 2  fire-deck due to the axial pre-load necessary to seal the injector penetration against combustion pressure.  Pictured below is the copper combustion seal (see Figure A.3, sheets 3 and 6)  transferring load to the aluminium fire-deck. The pre-load (see Appendix B) is applied normally to the upward facing surface of the combustion seal. The model includes the combustion seal and fire deck assembled as separate pieces. The clipping shown below is for presentation purposes and was not present in the geometry analysed. The fire deck material, 365 aluminium, has a yield stress of approximately 165 MPa. The results were deemed acceptable, as the majority of stresses fall below 130MPa. The apparent high stress "hot-spots", if not due to the analysis technique, could be expected to yield slightly until a new lower stress equilibrium was reached.  Figure A.2 GEA Analysis of Stress Due to Combustion Seal Pre-Load  67  DI HEAD MODIFICA TION: FABRICA TION PROCESS DRA WINGS (Begin next page)  NOTES . FOR QUESTIONS AND ADDITIONAL INFORMATION: PtEA.SE CONTACT DAVID SOHBT AT UBC ISO*) B72-0I9I, dg.rbyftneek.ubf.ca . FABRICATION INCLUDES TRIAL RUN ON SPARE HEAD (TO BE INSPECTED WHEN COMPLETE). AS * £ L L AS FINAL MODIFICATION OF OPERATIONAL READ (ALUMINIUM HEADS PROVIOED BY UBC)  RICARDO RESEARCH ENGINE ALUMINUM HEAD DIRECT INJECTION  GENERAL  ASSEMBLY  MODIFICATIONS  C<!§X MECHANICAL ENG)NEERIHG DEPARTMENT THE UNIVERSITY OF BRITISH COLUMBIA HEAD MODIFICATION - PROCESS DRAWING GENERAL ASSEKBLT  NOTES I.  VERIFT AS-BUILT DIMENSION FOR USE WITH ADDED MATERIAL PART (SEE SHEET 2)  • I ; I JCIIIIDEI IftAD IMKWIMB Bl OTHCK31i J »|"JJ l  i ITCH : an. < K i c t i f i i c n I  BILL  Of  m r t m i MATER IAL  | HECHAHICAL ENGINEERING DEPARTMENT I  THC UNIVERSITY OF BRITISH COLUMBIA HEAD BREAK-IN CUT DETAIL  «EV ISIOMS  NOT E S  REVISION-I NOTFS: COMBUSTION SEAL HEIGHT REDUCED  INJECTOR MOUNTING FLANGE 1018 STEEL I REQUIRED  0IT.I  •25 \  0!.2S'J- 4  r^TbTtM'TL'TK I—^  V  T T t S t /  I I I IT.  iCONBUSTIOt S(»l i tNJECTDt (MUMTING FUKE fADOEG NATtlUL PART • OEKIIHIW BILL  i CWPER STECL - ALUMN I UM lUIElUL  OF MATERIAL  MECHANICAL ENGINEERING DEPARTMENT ADDED MATERIAL ALUMINUM 606 I I REQUIRED  COMBUSTION SEAL CI 1000 COPPER I REQUIRED  THE UNIVERSITY OF BRITISH COLUMBIA  HEVISIONS  WELD SHALL FORM A WATER-TIGHT SEAL AROUND ADDED MATERIAL COMPONENT  BILL  OF M A T E R I A L  HECHANICAL ENGINEERING DEPARTMErli THE U N I V E R S I T Y  OF B R I T I S H COLUMBIA  HEAD MODi AT'O HEAD/ADDED MATERIAL WELD DETAIL  wevisiONS  NOTES i.  b a s i c dimensions are f o r p r a c t i c e head o n l t . for f i n a l fabrication, v e r i f y d i m e n s i o n s t o match e x i s t i n g hole p a t t e r n WIRE INSERT IS P R A C T I C E HEAD;  NOT N E C E S S A R Y FOR D R I L L 08 THRU O N L Y  FOR F I N A L F A B R I C A T I O N . W I R E WILL REQUIRE SHORTENING F R O M 8 TO - 5  REV I S I Q N - 1  INSERT  notes:  AMBIGUOUS ANGULAR D I M E N S I O N S REMOVED FROM I N J E C T O R P E N E T R A T I O N A X I S . U S E B A S I C D I M E N S I O N S OF T R U E - L E N G T H V I E W ( S H E E T 6 ) , AND P O I N T - 0 AS R E F E R E N C E .  ,0* ^  ji  I i •  j  inan.H MM-CO L I till  ustn  n i l B I L L O F MATER I AL  ;M M r t m t L •  MECHAN JCAL £NGIN[[RING OEPARFMENT | !  THE  UNIVERSITY  OF B R I T I S H COLUMBIA  I H E A D MODIFICAT I ON - PROCESS DRAW I iPENETRATJON DET At L. - ORT HC^RjAPH IC V J E W S NG  |  H £ * D B .1 I( " K I .«  I " * **" "" 04/U/It  PISTON CROWN DETAILS  3,188£,£93 r  0.407  Dimensions in Inches Figure A.4 Geometry: Piston # 476P by Federal Mogul for Ford Fiesta (1978-80)  APPENDIX B: SAMPLE CALCULATIONS COMBUSTION SEAL  PRE-LOAD  The following MathCad worksheet calculates the pre-load required to seal the direct injector's fire-deck penetration against combustion pressures.  The pre-load is calculated at standard  temperature conditions and accounts for expected thermal expansion as the engine is brought to operating temperature.  The tensile side of the load path includes a substantial aluminium  component, whereas all other components are steel; consequently the "cold" condition represents the maximum stress, due to the de-tensioning effect that aluminium's greater thermal expansion plays in the load path when the engine is warm.  Pmax := 6000000Pa Area:=—Dia 4  Dia := 9.2mm . m Area = 6.648 x 10 £  £  A  -  5  O  Est := 200- 10 -Pa 9  2  m  Angle from Datum A:  Faxial := Pmax-Area  9 := 63deg  Faxial = 398.857 N  Thermal elongation of head/bolt combination M6xlbolts  a  s  t  .  1  1  7  =  '  1  AT := 100-K  0  L c M 6 := 9 3 m m  K 8thM6 := a s t - A T L c M 6 8thM6= 1.088 x 10" m 4  a A l :=  2  4  1  0  K  —  L c A l := 102-mm  8thAl := a A l A T L c A l 8thAl= 2.448 x 1 0  _ 4  m  Continued...  76  Total thermal elongation of head/bolt combination: Sth := 8thM6 + SthAl 8th = 3.536 x 10" m 4  Thermal elongation of Injector LcJ43 := 183-mm 5thJ43 := ocst-ATLcJ43 8thJ43 = 2.141 x 10" m 4  Relative elongation of head/bolt combo: 8r:= 8 t h - 8thJ43 8r= 1.395 x 1 0 " m 4  Bolt Pre-load to take up relative elongation: _  a := or-  Est LcM6  a = 3 x 10 Pa 8  PSC MAXIMUM BACK PRESSURE FOR CHOKE FLOW The following is a MathCad program which accepts reservoir pressure as input and calculates the maximum back pressure that will allow frictionally choked flow at the end of the PSC flow path. bar := 100000-Pa Reservoir Pressure (Po)Po := I5bar k := 1.32  To := 300K  D := .0225-in  L := 20cm  A:=  ^2  speed := 2000- —— min  Rm := 518  n 4  2  pol := s K 2  ung:=1.34.10- -^ m  D  6  l  VoD  4  Reo= 4.487 x 10  D  2.625 x 10  Vo := 109 — s  - 3  durationtime:=  Maguess := 0.1  ss  — s  9.799  Given f-L  duration := 50-deg  P°  2  f-L D  angVel = 209.44 Hz  Po Rm-To  u = 1.388 x 10  u :=  5  Reo:  e := 0.0015mm angVel := speed-360 deg  f := .028  2 1 - Maguess 2 k-Maguess  k+ 1  +  2-k  In •  2 (k + l)-lvlaguess 2 2 + (k - 1 )• Maguess  duration angVel  durationtime = 4.167 x 10  s  Mai := MinErr(Maguess) = (0.242) Tl guess := 500-K Given To Tlguess  = i +  h  2  L  .  M  a  i  2  Tl :~ MinErr(Tlguess) = (297.213K) Tl := T l al := (k-Rm-Tl)  VI := M a l a !  0.5  al •= 450.802-  Tl = 297.213 K  VI = 109.131 — s  Continued...  78  p i guess:=  1-—-  m Given 1  ITT = 1 +-.(k- l ) M a l  1 7 0 1  p i guess  2  2  pi := MinErr(plguess) =  9.375 ^ -  m pi = 9.375 ^Sm"  mdot:= p i - A - V I  mdot = 2.624 x 1 0 ~ - ^ 4  s  minj = mdot-durationtime speed . . avgmdot := ——minj  - 6  minj = 1.094 x 10  :  2  P  I  •-  kg —  avgmdot = 6 5 . 6 1 2 —  (k-1)  1+-(k- l)Mal  h r  2  2  PI = 1.443 x 1 0 P a 6  PI Pstar :=  k+ Mai  1  , .. . . . . ,2 2 + (k - l ) M a l  Pstar = 3.259 bar  P1 = 14.434 bar  Po = 15 bar  k 1 2 Postar := Pstar- 1 + — ( k - 1)-Mal 2  ( k  Prjequired :=  P r j e q u i r e d = 1.845 2  -  1 }  < "> k  l  k+ 1 Min_outlet_i3ressure_tbr_choke  Postar Prjequired  Min_outlet_pressure_for_choke = 1.836 bar  5 Postar = 3.387 x 10  DIMASS  FLOW  AND  ORIFICE  SIZE  CALCULATION  The following is a MathCad program which accepts reservoir pressure as input and calculates the mass flux through the DI orifice for a given injection interval. This was used iteratively to solve for the orifice size. Initial •Assumptions  kp=3 ;s:=;2GO0  Vs - -163.30111 3; Vc: 56.13cm :  To:=310K  Pi:=0:97-aun ev  R:=8.31451<  pule.  kng := 1.32! faim 1 A.  mole- K.  0 73 •Mfu8ls=-ra-38mole  M a i r - 137.3552  niojg  Rmetlsine :=|5183  kg-K  AFRst:^ 1 6 . 6 9 ^ mokss. air st:  moles_fuel_sl := molar AFRsIs  moles air st moles ^ftiel slJ  Mair  Mfuel  moles air st = 121.5 lmol;  moles fuel st = 57.537mol  molar tA:FRsi.=j2. U2 :  L  mqlar_.AFR:- mnlflr_AFRst»X  Mole fraction fuel  Pcrit:. 2.5x lO^Pa  minPcritQV erPo :=  moles . 0 2 . - molr AKR  .mcmJIZi* molar_AFR-3 76  mihPcritbvcrPo  total moles := moles 02 + moles N 2 4 1  1  minPosonic = 4.611 x 10 Pa  xfiiel ;=: /total_moles:  Pi := 5  min_sonic_PR :  1 minPcritova-Po;  mill sotric PR = 1.845  Po: 3000090psi  xftiel - 0.032 xfuel-Pi-Vs nfuel :=;.ev.-To-R  From, Hill and Oulett (1999) losses in injector correspontto 1 0 % stag pressure loss Po  nfucl = 4.139* 10  Pcrit  minP.6s;6mc :='•  mol  Nfuel .-nfuel;— 2'  • R-T6 po i-y-Mfuel'  v - 7.222/. 1 m po - 125.521  in fuel avg — NfuelMiuet mfueljwg - 0.432— hr  pent  3  3 m.  r-  Vcritr-  2-kng-RineUiaiio- To kng  4  1  Continued:  80  Iterates to find orifice size based on desired mass flux over specified injection interval Tfuel:=293-K  Cycte:=360 Period:= s  Period = 30x ]0"  3 s  Cycle  ATcrank Jingle = 83.333x 10  AT_inj:= Inj_durationATcrank_angle  lnj_duration := 13.7  fucl_delivery _t ime Jfract ion :=  mfuel inst :=  ATcrank_angle :=  AT_inj  AT_inj = 1.142x 10  6  s  s  fuel_delivery_time_fractton = 0.019  Period-2  mfuel_avg fuel_deHveryjime_fraaion  mfuel_injectioi. := mfuel_instAT_inj  mfuel inst = 6.301-^sec mfueHnjectibn = 7.194mg  mfueLinst-Y (RmethaneTfuelj 1  Acrit:  0  Acrit = 0.197mm  khgr-l kng-1  >/kng-  kng + 1  •Po  Dinj:  4-Acrit  Dinj= 0.5 mm  81  APPENDIX C: ENGINE OPERATING PROCEDURES Ricardo Hydra Engine (NG) Operating Procedure Alternative Fuels Laboratory, UBC Mechanical Engineering The following is the start-up procedure for the Ricardo Hydro single-cylinder research engine in the U B C Alternative Fuels Laboratory. Please follow these steps carefully to avoid equipment damage or injury to personnel.  Note: Steps preceded by the DI superscript are particular to the Natural Gas Direct Injection System. If the injector is not installed these steps are omitted. If the DI injector is installed, these steps must be followed regardless of whether or not DI will be used in current trials.  Initial checks and engine warm-up: 1. Turn on ventilation in test cell (main fan - switch outside door - and fume hood). 2. Turn on emissions bench to allow sufficient warm-up (see separate procedure). 3. Check engine oil and coolant levels, and check around the engine for leaks. 4. Check that guards are on flywheel and timing belt. 5. Crank engine by hand once or twice (to ensure there has been no leak into the combustion chamber). 6. Check that there is no condensation in the exhaust (briefly open valves: engine out, muffler drain and horizontal run). Ensure all drains are closed before engine start. 7. Turn on engine cooling water (open tap fully). 8. Start pressure transducer cooling pump. 9. Turn on ignition/injection driver box (test-cell - by DAQ). 10. If the natural gas direct injector will be used, plug in the power supply first, then plug injector driver into power supply. (Not mandatory if injector will not be used) 11. Turn on thyristor drive unit in the test cell. (Main breaker on cell wall should be left on). 12. Turn on oil and water pumps/heaters. 13. Ensure that back pressure valve control box is powered and that valve is plugged in. 14. While oil and water are heating, calibrate emissions bench (see separate procedure).  82  Starting the engine software: 15. Turn on the control room.computer (password = "Ricardo"). 16. Open  Dynoclient and select file to save data to (in D:\ drive). The file name should have  the following format: <date>_<user>_<speed>_<throttle%>_<test description>.csv, for example:  "031121_CR_2000rpm_100%_homogeneous_lean_limit_noPSC.csv".  (Note: If not acquiring data, open "junkdynodata.csv".) 17. Open  Pressureclient.  18. Open VNC„ (password = "Riccardo"). Run 19. Open/run  Timing Controller.  Ric_Emissions_Runtime for monitoring, calculated values. (Start Menu,  "Programs", "Windows NT Explorer", D:\...)  Starting the Engine: 20. Reset emergency stop buttons (one on post by engine, one on control panel). 21. Open the two green N G valves in test cell, and the N G valve in the control room. 22.  0 1  Turn on high-pressure supply at the test cell outer wall gas panel, and ensure that the  supply pressure is between 2000 and 3000 psi - do not operate  this panel without  prior instruction. 23.  0 1  Ensure that in-cell high-pressure supply valve is fully open, and vent valve on test cell  outer wall is fully closed. 24. Turn on ignition switch (control panel). 25. Check oil temperature is greater than 60 ° C 26. Check (control panel): •  Speed setting is at 3.0 (1500 rpm)  •  Throttle setting is at 5 0 %  •  Fuel setting is at 2.2  27. Make a note of the following in the Ricardo Logbook: •  Date  •  Engine hours  •  Speed and Load  •  Operator Comment (test description) and initials  28. Press "reset" then immediately press green "start" button. (  Dl  listen for pneumatic high-  pressure supply cut-off valve to energize upon pressing "reset". Do not proceed if valve does not energize.)  83  Firing the Engine: (Engine firing is always started at 1500rpm, 50% Throttle, Lambda 1.0 and MBT Spark)  29. In. Timing Controller set spark timing to -23 deg, ("duration" should be set to 1.0 deg). Turn on ignition. 30. Check fuel control is set to "flow" (switch 1) then turn on (switch 2). Engine should fire. (Note that fuel flow output on DAQ should be 0.8 kg/h - this corresponds to lambda 1.0). 31. After one minute of firing, turn on AFRecorder (lambda sensor): •  Press "sys", "6" (says 'enable'), "ENT", "1" (says 'measure').  32. Wait until oil temperature is approx. 90 °C and coolant temperature is approx 95 °C before beginning to acquire data. Important Note: If testing for a long time, may need to recalibrate the emissions bench, as the calibration of the instruments drifts with changing temperature. Recommended Practice: Before proceeding with the test, run the engine at the above "standard" conditions for at least 20 mins, and acquire data at this point (for repeatability). The emissions bench can be calibrated during this time.  Acquiring Data: 33. Set test point. Note that when running very lean, the lambda based on mass flows is more accurate than lambda from the AFRecorder, (i.e. use Ric_Emissions_Runtime by pressing "Send data to Excel" button in Dynoclient). 34. In the paper "Test Sheet", record details of test point for future reference. 35. Record Pressure data (must be done for every test point). The file name should have the following format: <date>_<tesW>_<speed>_<throttle%>_<spark>_<Lambda>_<PSCdetails>_pr.csv, for example: "031121_t05_2000rpm_50%_S23 _L1.0_noPSC_pr.csv".  36. Record Performance data: In Dynoclient, update: •  Test number  •  Spark timing  •  PSC details (if running with PSC)  Then click "Log data to File" and wait (approx. 2 mins.) 37. Set next test point and repeat data acquisition.  84  38. When testing isfinished,return the engine to the start-up settings (1500rpm, 50% throttle, lambda 1.0).  Shutting down the engine: 39. Turn off the NG supply at the flow-meter. 40. Turn off ignition (Timing  Controller on computer.  41. Allow engine to motor briefly, until exhaust temperature drops below 130°C. 42. Press red "dyno" stop button. Engine will come to a complete stop. 43. Turn off ignition switch on control panel 44. Turn off oil/water heaters (but not the pumps). 45. About two minutes after firing stops, disable AFRecorder. •  Press "sys", "6" (says 'enable'), "ENT", "1" (says 'measure').  •  Display should now read 'Sensor Disabled'  46. Close all three NG valves on NG lines. 47.  D l  Turn off high-pressure supply at the test cell outer wall gas panel.  48. Turn off switch on ignition/injection box in test cell. 49. If plugged in, unplug natural gas direct injector power supply and driver box (order doesn't matter). 50. When engine has cooled (after at least fifteen minutes): •  Turn off oil and water pumps.  •  Turn off the thyristor drive breaker.  •  Turn off cooling water tap and unplug pressure transducer cooling pump  •  Shut down emissions bench.  •  Stop all software and shut down control room computer.  51. When testing is complete and engine shut down, stop the Dynoclient - this closes the file you have been saving performance data to. (if you wish to continue monitoring engine conditions  during  the  cool-down  stage,  start  Dynoclient  again  and use  "junkdynodata.csv"). 52. Comment on any important issues in the Ricardo Logbook, record engine hours and running time.  85  EMERGENCY SHUT DOWN: Hit red "STOP" button in Test cell or on Control Panel. Ignition and dyno are disabled and the engine will come to a complete stop. Note that fuel does not shut off automatically, nor are there gas detectors in the cell connected to the ESD. (These issues are addressed in the new C E R C cells).  Do not use the emergency stop button unless necessary.  86  APPENDIX D: F U E L COMPOSITION Table D - l BC Natural Gas Composition Lower Heating Molecular Mass of Component Value of Component Compound (kg/kmol) (kJ/kg) 50030 16.043 0.914326657 91.43 Methane (CH4) 47511 30.070 0.066023333 6.60 Ethane (C2H6) 46333 44.097 0.32 0.003216667 Propane (C3H8) 45560 0.000703333 58.123 0.07 i-Butane(C4H10) 45719 58.123 0.00047 0.05 n-Butane (C4H10) 45249 0.00022 72.150 0.02 i-Pentane (C5H12) 45345 72.150 0.02 0.00016 n-Pentane (C5H12) 45052 72.150 0 neo-Pentane 45103 86.177 0.00005 Hexane (C6H14) 0.01 44921 100.204 0.00 0 Heptane (C7H16) 44783 114.231 0.00 0 Octane (C8H18) 0 44.010 0.00397 0.40 Carbon Dioxide (C02) 28.013 0 0.010926667 1.09 Nitrogen (N2) Based on BC Natural Gas as measured on Micro at GC Westport Innovations Inc, Oct, 2005 Mole % in Fuel  Moles in Fuel  Table D-2 Mixture Properties Molecular Mass of Fuel (kg/kmol): 17.38 Hydrogen/Carbon Ratio (mol/mol): 3.839 Oxygen/Carbon Ratio (mol/mol): 0.007 Nitrogen/Carbon Ratio (mol/mol): 0.020 Upper Heat Value (kJ/kg): 53489 Lower Heating Value (kJ/kg): 48302 Simple Air/Fuel Ratio by mass (kg/kg): 16.50 SAE Air/Fuel Ratio by mass (kg/kg): 16.69 SAE Air/Fuel Ratio by mass H/C only (kg/kg): 17.06 SAE Air/Fuel ratios based on J1829 SAE recommended Practice  87  

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