Applied Science, Faculty of
Mechanical Engineering, Department of
DSpace
UBCV
Becker, Isaac
Master of Applied Science - MASc
University of British Columbia
Global climate change drives research and implementation of low-carbon fuels. Engine combustion imaging offers insights to fuel performance and can be conducted early in the fuel development cycle due to relatively low consumption rates compared to those required for steady-state emissions testing. A flexible fueling system is used, implementing a hydraulic media separator for direct injection of up to 260 mL alternative fuel samples at pressures up to 1200 bar into a 2.0L, single-cylinder, optically accessible diesel engine. Optical engine studies provide understanding of injection spray phenomena, ignition delays, heat release rates, and soot propensity with qualitative analysis of reaction zone structure and propagation using high-speed imaging of natural luminosity and OH*-chemiluminescence. A local, three-colour pyrometry probe enables measurement of in-cylinder soot concentration and temperature. Two operating conditions were chosen to investigate various phenomena. The first operating condition is a low load single fuel injection that allows for consideration of injection and ignition behaviour in the mixing controlled combustion regime. The second operating condition uses a pilot and main fuel injection and is representative of a medium load condition using modern diesel injection strategies. Six fuels are characterized: diesel and n-heptane, reference fuels; canola and soybean methyl ester, commercial biodiesels; and graphene-oxide (GO) doped diesel and a blend of upgraded bio-oil (UBO) from fast pyrolysis of pine biomass with diesel, novel fuels. Fuel properties were measured using ASTM standards for energy content, viscosity, elemental analysis, and moisture content. The UBO diesel blend demonstrates a 7% reduction in ignition delay and 25% reduction in in-cylinder soot concentration relative to neat diesel. The addition of 10ppm GO to diesel did not affect fuel performance.
Optical engine characterization of reference and novelfuels using a small-volume fuel systembyIsaac BeckerBS, California Polytechnic State University, 2018A THESIS SUBMITTED IN PARTIAL FULFILLMENTOF THE REQUIREMENTS FOR THE DEGREE OFMaster of Applied ScienceinTHE FACULTY OF GRADUATE AND POSTDOCTORATESTUDIES(Mechanical Engineering)The University of British Columbia(Vancouver)December 2022© Isaac Becker, 2022The following individuals certify that they have read, and recommend to the Fac-ulty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled:Optical engine characterization of reference and novel fuels using asmall-volume fuel systemsubmitted by Isaac Becker in partial fulfillment of the requirements for the degreeof Master of Applied Science in Mechanical Engineering.Examining Committee:Patrick Kirchen, Professor, Mechanical Engineering, UBCSupervisorSteve Rogak, Professor, Mechanical Engineering, UBCSupervisory Committee MemberNaoko Ellis, Professor, Chemical and Biological Engineering, UBCSupervisory Committee MemberiiAbstractGlobal climate change drives research and implementation of low-carbon fuels.Engine combustion imaging offers insights to fuel performance and can be con-ducted early in the fuel development cycle due to relatively low consumption ratescompared to those required for steady-state emissions testing. A flexible fuelingsystem is used, implementing a hydraulic media separator for direct injection of upto 260 mL alternative fuel samples at pressures up to 1200 bar into a 2.0L, single-cylinder, optically accessible diesel engine. Optical engine studies provide un-derstanding of injection spray phenomena, ignition delays, heat release rates, andsoot propensity with qualitative analysis of reaction zone structure and propagationusing high-speed imaging of natural luminosity and OH*-chemiluminescence. Alocal, three-colour pyrometry probe enables measurement of in-cylinder soot con-centration and temperature. Two operating conditions were chosen to investigatevarious phenomena. The first operating condition is a low load single fuel injectionthat allows for consideration of injection and ignition behaviour in the mixing con-trolled combustion regime. The second operating condition uses a pilot and mainfuel injection and is representative of a medium load condition using modern dieselinjection strategies. Six fuels are characterized: diesel and n-heptane, reference fu-els; canola and soybean methyl ester, commercial biodiesels; and graphene-oxide(GO) doped diesel and a blend of upgraded bio-oil (UBO) from fast pyrolysis ofpine biomass with diesel, novel fuels. Fuel properties were measured using ASTMstandards for energy content, viscosity, elemental analysis, and moisture content.The UBO diesel blend demonstrates a 7% reduction in ignition delay and 25% re-duction in in-cylinder soot concentration relative to neat diesel. The addition of10ppm GO to diesel did not affect fuel performance.iiiLay SummaryNew low-carbon fuels are needed for the transportation sector to reduce air pollu-tion and slow the pace of climate change. Fuel performance in engines must beunderstood before alternative fuels can be widely used. Since new fuels are pro-duced on small scales, innovative methods are needed to measure fuel performancein engines, which typically require a lot of fuel to operate. A low-volume, high-pressure fuel system has been added to a diesel engine with a window for cameraaccess to study the performance of two new fuels. One of the new fuels is a blendof diesel with a ”bio-oil” derived from wood. The other fuel is a mixture of dieselwith graphene oxide nanoparticles. The behaviour of new fuels is compared to thatof reference fuels like plain diesel. The bio-oil fuel produces 25% less soot thandiesel. The graphene oxide fuel shows no performance differences from diesel.ivPrefaceThis dissertation is an original intellectual product of the author, Isaac Becker. Ideveloped research questions, conducted the experimental measurement campaign,and wrote this document under the guidance of my supervisor, Dr. Patrick Kirchen,with the motivation of studying combustion of wood fast pyrolysis oils from a col-laborative international research grant provided by the Korea Institute of Scienceand Technology.Design and development of the research engine facility was done by Dr. JeremyRochussen, Dr. Mahdiar Khosravi, and Jeff Yeo. The addition of a third wave-length to the pyrometry probe was performed by Nicolas Jaeger. The aforemen-tioned researchers developed most of the data post-processing scripts, which I builtupon to perform the analysis for this work. A preliminary design for the me-dia separator was produced by Sahand Sohirad based on the design of a similarfuel system in Dr. Bruno Schneider’s Laboratorium fuer Aerothermochemie undVerbrennungssysteme at ETH Zurich. Initial identification of suitable operatingconditions was performed by Dr. Jeremy Rochussen.UBC Ethics Board approval was not required.vTable of ContentsAbstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iiiLay Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ivPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vTable of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viList of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ixList of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xList of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvList of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviAcknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Motivation & Background . . . . . . . . . . . . . . . . . . . . . 11.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.3 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Literature Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.1 Fast Pyrolysis of Lignocellulosic Biomass . . . . . . . . . . . . . 52.2 Optical Investigations in CI Engines . . . . . . . . . . . . . . . . 72.3 Literature Gap . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10vi3 Media Separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.1 Design Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 123.2 Design Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.2.1 Commissioning and Installation . . . . . . . . . . . . . . 173.3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.3.1 Fueling . . . . . . . . . . . . . . . . . . . . . . . . . . . 193.3.2 Test Procedure . . . . . . . . . . . . . . . . . . . . . . . 193.3.3 Fuel Flow Rate Measurement . . . . . . . . . . . . . . . 203.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 Experimental Facility . . . . . . . . . . . . . . . . . . . . . . . . . . 234.1 Fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.1.1 Fuel Selection . . . . . . . . . . . . . . . . . . . . . . . 234.1.2 Chemical Characterization . . . . . . . . . . . . . . . . . 254.2 Optical Engine Facility . . . . . . . . . . . . . . . . . . . . . . . 284.2.1 Instrumentation and Data Acquisition . . . . . . . . . . . 304.2.2 OH*-Chemiluminescence Theory . . . . . . . . . . . . . 324.2.3 Three-Colour Pyrometry Probe . . . . . . . . . . . . . . . 324.3 Engine Operating Conditions . . . . . . . . . . . . . . . . . . . . 344.4 Experimental Campaign . . . . . . . . . . . . . . . . . . . . . . 374.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395 Injection Spray Behaviour of Alternative Fuels . . . . . . . . . . . . 415.1 Image Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 425.2 Liquid Length Results and Discussion . . . . . . . . . . . . . . . 445.3 Spray Cone Angle Results and Discussion . . . . . . . . . . . . . 485.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516 Combustion Behaviour of Alternative Fuels . . . . . . . . . . . . . . 536.1 Fuel Consumption, Equivalence Ratio, and Indicated Efficiency . 536.2 Ignition Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586.3 Combustion Images, Phasing, and Soot Phenomena . . . . . . . . 616.3.1 Single Injection . . . . . . . . . . . . . . . . . . . . . . . 626.3.2 Pilot + Main Injection . . . . . . . . . . . . . . . . . . . 63vii6.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727.1 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77A Media Separator Design Calculations . . . . . . . . . . . . . . . . . 86B Media Separator Commissioning . . . . . . . . . . . . . . . . . . . . 88C Media Separator Assembly . . . . . . . . . . . . . . . . . . . . . . . 90viiiList of TablesTable 4.1 Fuel properties . . . . . . . . . . . . . . . . . . . . . . . . . . 26Table 4.2 Fuel elemental content . . . . . . . . . . . . . . . . . . . . . . 27Table 4.3 Volatility: 90% Distillation Temperature . . . . . . . . . . . . 27Table 4.4 Ricardo Proteus Optical Engine Parameters . . . . . . . . . . . 30Table 4.5 Thermal management system parameters . . . . . . . . . . . . 36Table 4.6 Optical test operating parameters . . . . . . . . . . . . . . . . 36Table 4.7 Experimental campaign single injection condition camera settings 37Table 4.8 Experimental campaign pilot + main condition camera settings 38Table 5.1 Segmentation parameters used for liquid spray image binarization 43Table 6.1 Stoichiometric Air-Fuel Ratios . . . . . . . . . . . . . . . . . 55Table 6.2 Key Injection and Combustion Metrics . . . . . . . . . . . . . 71ixList of FiguresFigure 2.1 A conceptual model of direct injected diesel combustion de-rived from laser-sheet imaging during the mixing controlledburn, i.e., before the end of injection. Adapted from Dec, 1997.[1]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Figure 2.2 Images of Mie scattered light from liquid fuel droplets demon-strating the effect of air density on liquid length, i.e., the pene-tration distance of the liquid phase of fuel sprays relative to theinjector orifice. Liquid length demonstrates the extent to whichvapor phase fuel can mix with air. Adapted from Siebers, 1998.[2] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 3.1 Section view of media separator. . . . . . . . . . . . . . . . . 13Figure 3.2 Fuel system P&ID. . . . . . . . . . . . . . . . . . . . . . . . 14Figure 3.3 Open gland design for the driven end-cap rod seal. The two-part rod seal uses an elastomeric o-ring to provide a load-ing force onto the inner PTFE ring, which has improved wearresistance against sliding friction. A spacer and externally-threaded nut simplify the installation and replacement of therod seal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Figure 3.4 Cart housing MS and common rail with connections to CP3pump and injector. . . . . . . . . . . . . . . . . . . . . . . . 18Figure 3.5 Raw data from the string potentiometer undergoes LOWESSsmoothing with 20% span to produce a signal that is easier todifferentiate for volumetric flow measurement. . . . . . . . . 20xFigure 3.6 Volumetric flow rates are obtained from the time derivative ofthe string pot position signal multiplied by the cross-sectionalarea of the driven volume of the MS cylinder. Thick red linesrepresent mean values for each region with thin lines repre-senting ±2 standard deviations. . . . . . . . . . . . . . . . . . 21Figure 4.1 Weight and weight loss rates for the considered fuels. . . . . . 28Figure 4.2 Optical engine P&ID. . . . . . . . . . . . . . . . . . . . . . . 31Figure 4.3 Spectral absorption coefficient of water vapour with a minorabsorption feature centered around 900nm. . . . . . . . . . . 34Figure 4.4 Location of pyrometry probe in combustion chamber. Two jetsstraddle the direct field of view of the probe, which is exposedto soot upon circulation and combustion of the fuel. . . . . . . 35Figure 4.5 Angle of jets with respect to horizontal from the beginning(left) and end (right) of experimentation. Care was taken toensure repeatable installation of the fuel injector when it wasremoved for engine maintenance. . . . . . . . . . . . . . . . 35Figure 4.6 HRR from the single injection condition demonstrating the ef-fects of the valve timing adjustment that was made to stop thepiston from impacting on the intake valve. . . . . . . . . . . . 39Figure 5.1 An overview of the image segmentation script for liquid lengthcalculation. Moving from left to right: the jets are extractedfrom the raw image using background image subtraction; gammaadjustment and morphological operations are applied; a binaryimage is produced and measured against the linear masks alongthe jet axes; the jet length is overlaid on the raw image for com-parison. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Figure 5.2 Definitions for liquid length and spray angle. Spray cone an-gles are evaluated over the yellow region for each frame andaveraged. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44xiFigure 5.3 Fuels exhibit comparable liquid length growth rates until reach-ing their respective maxima, which has inverse correlation tovolatility. e.g., highly volatile n-heptane has a 56% shortermax liquid length than diesel. . . . . . . . . . . . . . . . . . 45Figure 5.4 Liquid length rates of change highlight differences betweenfuels due to wide ranges of volatility. The zero-crossing in-dicates the point at which maximum liquid length is reached,which occurs earlier for n-heptane due to its high volatility andaccordingly short liquid length. . . . . . . . . . . . . . . . . 46Figure 5.5 CME and SME both exhibit piston bowl wall wetting due totheir liquid lengths extending to the edge of the field of view.Cylinder wall wetting is known to reduce combustion efficiencyand increase emissions of hydrocarbons and soot, though theeffects of piston wall wetting are not thoroughly documented. 47Figure 5.6 Maximum liquid length versus volatility. . . . . . . . . . . . 48Figure 5.7 Maximum liquid length versus viscosity. . . . . . . . . . . . . 49Figure 5.8 Crank-angle resolved spray cone angles. The highly volatilen-heptane has a significantly smaller spray cone angle than thediesels and biodiesels. . . . . . . . . . . . . . . . . . . . . . 50Figure 5.9 Spray cone angle versus volatility. . . . . . . . . . . . . . . . 51Figure 5.10 Spray cone angle versus viscosity. . . . . . . . . . . . . . . . 51Figure 6.1 Fuel consumption rates on a mass and energy basis for both op-erating conditions. Whiskers represent ±2 standard deviations,which are used in lieu of standard error due to the relativelyhigh measurement uncertainty of the string potentiometer. . . 54Figure 6.2 Global equivalence ratios from both operating conditions. Dieseland SME show a 15.9% difference in equivalence ratio result-ing from differences in fuel and air mass consumed. . . . . . . 55Figure 6.3 Engine load as defined by GIMEP. . . . . . . . . . . . . . . . 56Figure 6.4 Indicated efficiencies for both operating conditions. . . . . . . 58xiiFigure 6.5 HRR for the single injection operating condition illustrate dif-ferences in ignition timing and peak intensity when fuels com-bust in the premixed regime. Pressure waves from premixedcombustion result in intense HRR ”ringing” after the initial peak. 59Figure 6.6 Normalized IHRR and integrated OH*-CL signal for the singleinjection operating condition. The ignition delay is definedas the time elapsed between CSOI (-6 CAD) and 5% of peakintegral heat released or OH*-CL. Consistent trends hold forboth analyses with n-heptane exhibiting shortest ignition delayand both neat and GO diesel exhibiting the longest. . . . . . . 60Figure 6.7 Ignition delays determined from IHRR and integral OH*-CLanalysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Figure 6.8 Frame-by-frame OH*-CL images during ignition progressingfrom top to bottom. Frames are not CAD-synced across fuels,i.e., the first frame of diesel occurs at 4 CAD aTDC while thefirst frame of n-heptane ignition is at 3 CAD aTDC. . . . . . . 63Figure 6.9 Ensemble averaged OH*-CL images during ignition progress-ing from top to bottom. Frames are not CAD-synced across fu-els, i.e., the first frame of diesel occurs at 4 CAD aTDC whilethe first frame of n-heptane ignition is at 3 CAD aTDC. Igni-tion kernels for biodiesels are observed in the jet axis regionscloser to the injector compared to neat and GO diesel, whichappear to ignite along the piston bowl wall. UBO diesel andn-heptane exhibit some ignition and combustion in the jet axisregions, but less than the biodiesels. . . . . . . . . . . . . . . 64Figure 6.10 Heat release rates for the pilot + main injection operating con-dition. Differences in pilot ignition behaviour do not affectmain combustion timing. . . . . . . . . . . . . . . . . . . . . 65Figure 6.11 Heat release rates and pyrometry data for the pilot + main in-jection operating condition. Diesel and GO diesel exhibit thehighest soot cloud density of the fuels tested. . . . . . . . . . 66xiiiFigure 6.12 Single cycle OH*-CL images of flame development for themain fuel injection. Note the absence of strong OH*-chemiluminescencein the lift-off region for the diesel and blended diesels com-pared to the injector-attached signal in the biodiesel and n-heptane images. . . . . . . . . . . . . . . . . . . . . . . . . . 67Figure 6.13 Single cycle OH*-CL images of mid- and late-cycle combus-tion for the main fuel injection. . . . . . . . . . . . . . . . . . 68Figure 6.14 Ensemble averaged NL images of flame development for themain fuel injection. . . . . . . . . . . . . . . . . . . . . . . . 69Figure B.1 MS rod seal in the prototype end-cap upon installation (left)and after catastrophic failure (right). . . . . . . . . . . . . . . 88Figure C.1 Tapered tool for stretching PTFE rings onto MS piston. . . . . 90xivList of Symbolsc Speed of lighth Planck constantI Radiant intensityk Boltzmann constantKL Optical densityLl Liquid lengthncomp Polytropic exponent of compressionp PressureR2 Coefficient of determinationt Binarization thresholdT TemperatureT90 90% distillation temperatureV Volumeα Spray cone angleγ Contrastε Emissivityθ Crank angleλ Wavelengthν Kinematic viscosityτ Ignition delayφ Equivalence ratioxvList of AbbreviationsaTDC After top dead centerASOI After start of injectionASTM American Society for Testing and MaterialsCA Crank angleCAD Crank angle degreeCI Compression ignitionCME Canola methyl esterCO Carbon monoxideCO2 Carbon dioxideCOD Combination of dataCOI Combination of interpretationsCOV Coefficient of variabilityCSOI Commanded start of injectionGHG Greenhouse gasGIMEP Gross indicated mean effective pressureGO Graphene oxideHHV Higher heating valueHRR Heat release rateIHRR Integrated heat release rateIRO Intensified relay opticLHV Lower heating valueLOWESS Locally weighted scatterplot smoothingLVDT Linear variable differential transformerMS Media separatorxviNBPF Narrow bandpass filterNBR Nitrile rubberNL Natural luminosityNOx Oxides of nitrogenOH*-CL Hydroxyl radical chemiluminescenceP& ID Piping and instrumentation diagramPM Particulate matterPTFE PolytetrafluoroethyleneRPM Revolutions per minuteRSD Relative standard deviationSME Soybean methyl esterSOI Start of injectionTDC Top dead centerTGA Thermogravimetric analysisUBO Upgraded bio-oilUHC Unburned hydrocarbonsUV UltravioletWHSC World harmonized stationary cycleWHTC World harmonized transient cyclexviiAcknowledgmentsThis project could not have been completed without the overwhelming generosityof those who have supported me during the last three years.I would like to extend my deepest gratitude to my supervisor, Dr. PatrickKirchen, for all of the assistance he provided that is difficult to accurately quantify.His patience, encouragement, wisdom, and dad jokes form the foundation uponwhich this work is built.Thank you to Sahand Sohirad, Bruno Schneider, Kim Sheldon, and all of thetechnicians in the UBC MECH Machine Shop for their help in bringing the mediaseparator into existence.Additional tremendous thanks are owed to Kristie Henriksen for all of the as-sistance with procuring the expensive, high-tech toys I had the pleasure of playingwith for this project. Her contagious smile never failed to ease my worries when Iwas facing hardships in the lab.Thank you to my labmates who I had the pleasure of working with—Jeremy,Mike, Pooyan, Matt, Troy, Nick, Mark, Gibson, Anton, Mack, Brennan, and Ste-fan. All of the technical support and camaraderie have had a tremendous impacton my time at UBC.Thank you to my friends who have provided an abundance of support and levitywhen I desperately needed it.Thank you to my family who always rooted for me from afar in the midstof uncertain times and seemingly impossible cross-border travel. I have been sodeeply nourished by the time we’ve spent together since being able to reunite. Igive you all my love.xviiiTo Debbie, David, Kenny, and Emmy.xixChapter 1Introduction1.1 Motivation & BackgroundAnthropogenic climate change is one of the preeminent sociotechnical issues ofthe contemporary era. Novel approaches are required to reduce greenhouse gas(GHG) emissions to mitigate some of the most adverse effects of climate change.The Canadian government’s Clean Fuel Regulation represents a policy instrumentto combat climate change by mandating a 15% reduction in the carbon intensityof liquid fuels, i.e., gasoline and diesel, relative to 2016 levels by 2030 [3]. Ablend of low-carbon fuels must be integrated into the liquid fuel mix for diesel tomeet the requisite reduction in carbon intensity, which is currently 84.08 gramsof CO2 equivalent per MJ of fuel energy (gCO2e/MJ) in British Columbia anddecreasing every year [4]. Biodiesels have shown some promise at reducing GHGemissions relative to petroleum diesel for heavy-duty compression ignition (CI) en-gines—specifically, canola methyl ester (CME) and soy methyl ester (SME) havereported carbon intensities of 0.46 gCO2e/MJ and 3.49 gCO2e/MJ, respectively,suggesting strong potential to reduce the carbon intensity of diesel when blendedin modest amounts [5, 6]. The production of these biodiesels is dependent uponfirst-generation feedstocks, i.e., food crops, which drives direct competition withfood supply chains [7]. Given the high impact of biodiesels produced from first-generation feedstocks on food supply, first-generation biodiesels have limited abil-ity to penetrate the diesel mix.1A mixture of novel, low-carbon fuels produced from second-generation feed-stocks, i.e., non-food crops and waste biomass, will help meet mandated reductionsin liquid fuel carbon intensity while minimizing competition with food production.Each year, the forestry sector in British Columbia produces approximately 4.6 mil-lion metric tons of wood biomass that is not commercially viable and is burnedin slash piles as part of forest maintenance practices [8]. While the charcoal pro-duced by slash pile burning has benefits for future vegetative growth due to itssoil amending properties [9], slash pile burning contributes to reduced air qualityand forest residues may find increased utility and economic value if recovered andprocessed into marketable products. Bio-oil is a product of the fast pyrolysis ofwood biomass that has potential use as a low-carbon liquid fuel when producedfrom forest residues. Fast pyrolysis is a rapid thermochemical decomposition ofbiomass at temperatures around 500°C that produces solid char and pyrolytic va-pors, which can be condensed to form bio-oil. Crude bio-oil has several propertiesthat make it undesirable as a liquid fuel, namely its low energy density relative topetroleum fuels, high acid content, moisture content, and tendency to polymerizeat high temperatures, resulting in poor combustion quality [10, 11]. Despite un-certainty surrounding economic viability and exergetic efficiency, upgraded bio-oilmay find some utility as a fuel for use in compression ignition (i.e., diesel) engines.Optical engine studies can assess the feasibility of engine applications for novelfuels while providing spatial information about combustion that is impossible todirectly observe through conventional thermodynamic engine experiments. Thepressing need for a variety of renewable, low-carbon fuels motivates a desire tounderstand fuel performance in terms of both engine exhaust emissions and in-cylinder behaviour, which is a precursor to exhaust emissions and can be stud-ied through high-speed imaging of injection sprays and OH*-chemiluminescencefrom combustion. Optical engine operation provides a combination of thermo-dynamic and optical data including in-cylinder pressure, heat release rates, in-jection phenomena such as liquid and vapor lengths to assess fuel-air mixing,soot concentration and temperature, and images of natural luminosity and OH*-chemiluminescence of combustion, which help to understand spatial dependenceof emission formation as well as ignition and combustion behaviour.Increased fuel system flexibility may be required to carry out engine combus-2tion characterization of novel fuels with varied chemical compositions given thewide range of fuels under investigation for engine applicability such as bio-oilsfrom fast pyroylsis, ammonia, and myriad others. Drop-in fuels, i.e., alternativefuels that can be directly used in existing engines without the need for hardware up-grades, are a desirable outcome of the fuel development process. However, manyfuels pose material compatibility concerns early in development before fuel pro-duction and upgrading can performed on larger scales, thus motivating a need fora robust, high-pressure fuel system to aid in characterizing engine performance ofhighly varied novel fuels.In addition to material compatibility concerns, high pressure diesel systemsused in contemporary engines typically have capacities on the order of 10’s of litreswhile the production of novel fuels require significant time and capital investmentsto yield sample volumes on the order of single litres. Since the production andupgrading processes for bio-oils from fast pyrolysis currently result in extremelylimited sample volumes, engine combustion characterization is constrained to op-erating conditions with low rates of fuel consumption and/or blending with otherfuels to increase total sample volume. Optically accessible engines are often op-erated using skip-firing fuel injection strategies to reduce wear on and fouling ofthe transparent ceramic materials used for optical access, which has positive impli-cations for characterizing fuels with limited yields [12]. Still, a novel approach isneeded to supply small volume fuel samples with varied chemical compositions athigh injection pressures for diesel engine relevant conditions.1.2 ObjectivesThe primary objective of this work is to conduct a comparative assessment of novelfuel performance in a diesel engine to gauge the viability of novel fuels for engineapplications and provide a suite of thermodynamic and optical data for understand-ing exhaust emissions and developing combustion models. Specific objectives areas follows:1. Develop experimental methodology for comparative assessment of in-cylinderinjection, combustion, and emission formation behaviour across a range ofnovel and reference fuels and operating conditions.32. Identify links between in-cylinder behaviour and fuel properties.3. Produce high-fidelity images for fuel injection and combustion model devel-opment and validation.1.3 ApproachThis thesis introduces the experimental approach to addressing the defined objec-tives including the development of a robust fuel system, a discussion of fuel proper-ties, and the development of a methodology to characterize fuel performance rela-tive to reference fuels and the measured properties. Chapter 2 describes the state ofthe art for low-carbon liquid fuel implementation in diesel engines with a glimpseat several limited efforts to characterize novel fuel performance. Chapter 3 detailsthe design and implementation of a low volume fuel system for high-pressure di-rect injection of liquid fuels into optically accessible CI engine. The optical engineexperimental facility is described in Chapter 4 along with discussion of the theoret-ical background for several of the optical measurements used. The fuels selectedfor the experimental measurement campaign are described and characterized us-ing chemical analysis techniques. Chapter 5 investigates the in-cylinder injectionphenomena of novel and reference fuels using externally illuminated high speedimaging. Combustion performance is assessed in Chapter 6 using heat release rate(HRR), local multi-colour pyrometry, and high speed imaging of natural luminos-ity (NL) and OH*-chemiluminescence. Chapter 7 contains concluding remarksand offers suggestions for further inquiries into comparative optical engine studiesof novel fuels.4Chapter 2Literature ReviewThis chapter examines the state of literature on using fast pyrolysis of biomassas a means of producing liquid fuel from waste feedstocks. Efforts to upgradebio-oil and characterize combustion performance are discussed, primarily from thestandpoint of exhaust emissions, which are indeed an important area of focus fornovel fuel characterization. An overview of engine combustion imaging literatureis presented, detailing the motivations to understand in-cylinder fuel performanceto supplement studies in conventional engines focused on thermodynamic perfor-mance and exhaust emissions. The chapter concludes with a discussion of the gapsin the literature that this study seeks to address.2.1 Fast Pyrolysis of Lignocellulosic BiomassFast pyrolysis has demonstrated potential to produce low-carbon fuels from wastelignocellulosic biomass; however, the yield and physical properties of crude bio-oildepend on a variety of input factors. Bio-oil yield can vary significantly depend-ing on feedstock composition, with substantial yield reductions documented formodest increases in moisture and ash content as well as the ratio of herbaceous towoody biomass [13–15]. Operating parameters of the pyrolysis reactor, e.g., tem-perature and biomass residence time, also contribute to different yields of bio-oilversus the solid char and non-condensing gaseous products [16, 17]. Bio-oil yieldsas low as 31% of input biomass have been observed for uniform softwood pellets in5500°C reactors [18]. While there is not a clear estimate of the ratio of herbaceousbiomass to wood in BC’s forest residues, the logging practice of leaving tree topsand branches in slash piles likely contributes to a more varied biomass stream, sug-gesting potential for lower bio-oil yields relative to the more uniform wood pelletfeedstocks used in some existing bio-oil production facilities [8].In addition to the challenges with bio-oil yield consistency, bio-oils often havephysical and chemical properties that make them undesirable as liquid fuels intheir unprocessed state, including low energy content, high viscosity, high acidcontent, high water content, immiscibility with petroleum fuels, and chemical in-stability due to the presence of oxygenates [19, 20]. Attempts to combust crudebio-oil (including blends of crude bio-oil with other fuels and additives) in variousconfigurations have demonstrated accelerated wear on fuel system components in-cluding pumps, fuel delivery lines, and injectors [21–24]. In addition to these fuelhandling challenges and the increased rates of specific fuel consumption inher-ent with utilizing less energy-dense fuels, the aforementioned combustion studiesreport mixed results in terms of exhaust emissions. A review by Mueller et al doc-uments relatively consistent findings of reduced NOx at the expense of increasedCO emissions, likely attributed to lower flame temperatures resulting in less com-plete combustion [21]. While this is finding is supported in some publications [23],others report increases in both NOx and CO emissions [22, 25].Efforts have been made to improve bio-oil quality through the introduction ofcatalysts to the fast pyrolysis process and through other upgrading routes, thoughoccasionally at great financial and energetic cost to production. Hydrodeoxygena-tion has been suggested as one means of upgrading bio-oil by reducing waterand oxygenate content to facilitate incorporation with petroleum fuel infrastructure[17, 26, 27]. However, the consumption of hydrogen during hydrodeoxygenationhas been acknowledged to result in high costs and poor energy efficiency [27, 28].Implementing catalysts in the pyrolysis reactor has been demonstrated to producehigher quality bio-oil at lower energy costs than hydrodeoxygenation [29]. still,the high cost and rapid degradation of catalysts points towards the need for fur-ther innovation before upgraded bio-oil can be economically feasible. Combustionstudies of upgraded bio-oil suggest that further improvements to production andupgrading processes are needed to attain similar thermal efficiencies to conven-6tional petroleum fuels while maintaining reductions to emissions of GHGs andpollutants, in line with carbon intensity reduction targets [10, 18, 19].Investigations in the literature have documented important findings about theengine performance of upgraded bio-oil and blends of bio-oil with conventionalCI fuels from a thermodynamic and exhaust emissions perspective; however, thein-cylinder injection, combustion, and emission formation mechanisms remain tobe studied.2.2 Optical Investigations in CI EnginesOptically accessible engines have been employed to expand understanding of in-cylinder injection, combustion, and emissions formation processes for conven-tional and alternative CI fuels such as diesel and biodiesels. The use of in-cylinderpressure transducers provides a link between optical and thermodynamic enginestudies to compare heat release rates and assess the extent to which trends ob-served in imaging studies hold for combustion in conventional engine operation.While conventional engine studies offer important insights to thermodynamic per-formance and exhaust emissions that are difficult to obtain in optical studies, op-tical engines provide information about the in-cylinder processes that cause thethermodynamic performance and exhaust emissions that are observed in purelythermodynamic studies.Dec’s conceptual model of diesel combustion using laser-sheet imaging in anoptical engine stands as a prime example of the knowledge about fundamentalcombustion behaviour that is afforded by the use of advanced optical diagnostics[1]. Figure 2.1 demonstrates the conceptual model of a diesel flame in the ab-sence of cylinder air and wall interactions. Fundamental understanding of emis-sion formation can be utilized by engine and injector manufacturers to optimizedesign and operation for maximal thermal efficiency while targeting reductions inemissions. While the highly advanced optical diagnostics leveraged in Dec’s workare not available for this study, the optical diagnostics employed herein can stillprovide helpful insights regarding comparative understandings of how in-cylinderprocesses change with fuel composition.Images of Mie scattering of light are commonly used to characterize the liquid7Figure 2.1: A conceptual model of direct injected diesel combustion derivedfrom laser-sheet imaging during the mixing controlled burn, i.e., beforethe end of injection. Adapted from Dec, 1997. [1].portion of fuel injection sprays to understand rates of fuel-air mixing based on in-jector and engine design as well as fuel properties. A foundational work by Siebersinvestigated the liquid phase penetration length of diesel fuel sprays in an opticallyaccessible, constant volume combustion chamber [2]. Siebers identified correla-tions between liquid length and gas temperature/density, fuel temperature/density,and fuel volatility, with additional important findings that liquid length was inde-pendent of injection pressure and that less volatile components in multi-componentfuels tend to dominate in determining liquid length. Other works using diesel directinjection into optical engines have supported the correlations identified betweenthe property of volatility and independence upon injection pressure [30–32]. Otherstudies that have examined biodiesel sprays in optical engines have provided sup-port for the correlation between volatility and liquid length [33, 34]. Gaps in theliterature exist for examination of the spray phenomena of multi-component novelfuels to assess whether volatility can act as a strong predictor of liquid length, and8Figure 2.2: Images of Mie scattered light from liquid fuel droplets demon-strating the effect of air density on liquid length, i.e., the penetrationdistance of the liquid phase of fuel sprays relative to the injector ori-fice. Liquid length demonstrates the extent to which vapor phase fuelcan mix with air. Adapted from Siebers, 1998. [2]whether presence of lower volatility components dominates over liquid length.OH*-chemiluminescence imaging provides spatial information about the loca-tion, propagation, and relative intensity of reaction zones, which enables qualita-tive discussion of fuel-air mixing and combustion. For premixed combustion ofhydrocarbon fuels, OH*-chemiluminescence acts as an indicator of reaction zonelocation and can be used to quantify ignition delays while providing spatial infor-mation about differences in ignition kernel location. OH*-chemiluminescence hasbeen used to characterize mixing-controlled combustion of diesel and low-carbonalternative fuels to identify regions of high-temperature reactions (i.e., flame fronts)and soot oxidation as well as to measure ignition, heat release rate, lift-off length,and reaction zone growth rates in an array of studies conducted in droplet burners,swirl furnaces, constant volume chambers, and optical engines [1, 1, 32, 35–39].Comparative combustion studies of alternative fuels begin to establish under-9standings of differences in behaviour relative to conventional diesel. In a studyby Jeon et al, an endoscopic CCD camera was used to characterize the tempera-ture and soot distribution of soy biodiesel relative to diesel [40]. The study foundbiodiesel to have lower soot emissions despite higher initial soot formation, higherflame temperature, and higher brake specific NOx emissions relative to diesel, ex-panding upon understanding of the in-cylinder combustion behaviours that resultin different exhaust emissions profiles for biodiesel. The limited visualization ca-pabilities of an endoscopic camera preclude observations for combustion throughthe entire combustion chamber, but they are compatible for use with toroidal pistonbowl geometry, which more closely represents the fuel-air mixing that is observedin contemporary diesel engines. Pastor et al examined the effects of injector ge-ometry on injection and combustion using schlieren and OH*-chemiluminescenceimaging of diesel and alternative fuels including hydrotreated vegetable oil andoxymethylene ethers [41]. While the study presents important findings on the rela-tive sensitivity of fuel performance (e.g., liquid length, vapor penetration, ignitiondelay, and soot propensity) to injector nozzle geometry, the experimental combus-tion apparatus was a constant volume pressure vessel, thus limiting the applicabil-ity of results when understandings of in-cylinder behaviour are desired. Mancar-uso et al have conducted optical engine characterizations of rapeseed methyl esterbiodiesel using diesel and n-heptane as reference fuels [33, 34, 42]. The biodieselhas demonstrated increased liquid length, decreased in-cylinder soot concentration,increased ignition delay, and increased exhaust NOx emissions relative to diesel.The various diagnostics enabled through engine optical access can be com-bined to further develop understanding of the links between in-cylinder processes,thermodynamic performance, and exhaust emissions. The aforementioned worksdemonstrate the capabilities of optical diagnostics to create knowledge surroundingdifferences in injection and combustion behaviour that occur when using alterna-tive fuels compared to conventional diesel.2.3 Literature GapBio-oils from fast pyrolysis of waste biomass are one example of an alternativefuel from low-carbon feedstocks that may assist in decreasing the carbon intensity10of liquid fuels to mitigate climate change. Despite undesirable fuel properties inthe raw state, upgrading bio-oils holds some promise at improving fuel quality foraddition to the liquid fuel mix. Combustion of upgraded bio-oils has been studiedto some extent in CI engines, though in-cylinder behaviour is poorly understood.This work seeks to apply optical engine characterization methods to upgraded bio-oils to understand in-cylinder performance relative to reference and commercialfuels such as diesel and biodiesels. Still, an innovative approach is required toenable the direct injection of upgraded bio-oil fuels, which typically have smallsample volumes available for characterization due to time consuming, low yieldupgrading processes.11Chapter 3Media SeparatorA media separator (MS) was developed to enable high-pressure direct injectionof small sample volumes of alternative fuels into an optical CI engine using adiesel common rail fuel system. This chapter includes discussion of MS designobjectives, specifications, commissioning, and operational considerations for theexperimental campaign.3.1 Design OverviewImplementation of a robust, small volume fuel system is motivated by the pri-mary objective to perform experimental engine characterization of alternative fuelsranging from commercially available biofuels to novel fuels produced from wastebiomass feedstocks. Objectives for the flexible fueling system are as follows:1. Integrate with existing high pressure diesel supply system infrastructure.2. Operate safely at working pressures up to 1200 bar.3. Handle a broad range of fuels with varying material compatibility concernsincluding high acid content.4. Contain sufficient fuel for optical engine operation while anticipating smallyields of novel fuel samples.125. Isolate alternative fuel samples from contamination by diesel or other sub-stances.6. Be robust and portable for integration with different engines and fuel sys-tems.The MS design is based on a hydraulic cylinder in order to fulfill the opera-tional objectives while keeping the system simple and robust. Similar designs havebeen successfully demonstrated in other engine works [43] [44]. A labeled sectionview of the MS is shown in Figure 3.1. High pressure diesel enters the “driving”side of the MS where it pressurizes the test fuel on the “driven” side of the freepiston, which has two reciprocating hydraulic seals to separate driving and drivenfuels. The competing constraints of low sample volumes, the need for sufficientBB SECTION B-BSCALE 1 : 2.25Connection to injector Driven volume Driving volumeConnection to common railPistonPiston rodDriven end-capDriving end-capCylinderA AB B2211Sheet 1 of 2Media Separator AssemblymmUnits5/8/22DateCheckedByDrawn By Isaac BeckerFigure 3.1: Section view of media separator.fuel to run consecutive tests between refills, and the need for the system to be rel-atively portable resulted in the decision to design the MS with a fairly small fuelcapacity compared to conventional fuel systems, which handle 10’s of litres of fuel.Cylinder dimensions were selected to ensure safe operation at high pressure whilemeeting the volumetric requirements and taking into account the total weight ofthe system, which was a concern for installation and portability.The MS uses a free piston that is not intended for actuation of mechanicalcomponents. The piston rod is instead implemented to provide a reduction in pistonsurface area for the driven volume. The reduction in surface area on the driven sideof the piston corresponds to an 8% increase in pressure relative to the driving side.In the event of seal failure or fluid movement across the piston seals, the higher13pressure of the driven fuel reduces the likelihood of contamination by the drivingfuel.Diesel, the driving fuel, is supplied by a Bosch CP3 pump and common rail ca-pable of maximum working pressures of 2000 bar. A maximum operating pressureof 1200 bar was selected for the MS, comparable to medium-high load injectionpressures for contemporary diesel direct injection systems. If the MS were to havea maximum working pressure of 2000 bar, the cylinder wall thickness would needto be significantly larger, thus greatly increasing the system dimensions and weightat the expense of the desire to keep the MS relatively portable.Figure 3.2: Fuel system P&ID.The MS is integrated into the existing common rail diesel system as shown inFigure 3.2 to minimize the impact on existing infrastructure. By implementing theMS downstream of the common rail, the high fuel pressure delivery capabilities ofthe existing diesel system are preserved while minimizing the number of critical14components exposed to potentially incompatible fuels. Since it is inevitable thatthe direct injector will be subjected to the driven fuel at high pressures for enginecharacterization, additional Bosch CRI2.2 injectors were obtained in anticipationof nozzle blockage or corrosion.3.2 Design DetailsThe MS was designed to have a 260 mL capacity (including high pressure fuel linesconnecting to the injector) to minimize required sample volume and enable testinga wider range of novel fuels, which often have limited yields while production takesplace at the lab scale. Small fuel volumes are suitable for conducting tests while theengine facility is in its optical configuration due to the skip-firing injection strategythat is used to preserve the quartz window in the bowditch piston. See sectionChapter 4 for further discussion of the engine facility and operation.Seal glands designs are based on the geometric requirements specified in theseal manufacturer catalogs, with additional consideration given to improve installa-tion and maintenance. The gland for the rod seal inside the driven end-cap utilizes aspacer and threaded nut to make seal installation simple while maintaining sealingquality. An assembly drawing demonstrating this seal gland design is presentedin Figure 3.3. Early design iterations of the MS end-cap seal gland neglected toconsider installation, and as such there was degraded sealing performance due tothe significant deformation required to install the seal in the gland. Easier seal ac-cess also improves maintenance and cleaning of seal glands between MS rebuilds.The seals on the piston are external, and thus easier to install without extensiveconsideration of gland design.Seal materials and geometries were selected based on material compatibilitywith the fuels slated for characterization and seal manufacturer recommendationsfor performance under high pressures. O-rings are used for sealing between thecylinder and end-caps since this interface is static during MS operation. Two-partseals are used at interfaces between surfaces with relative motion, i.e., the piston/-cylinder interface and the piston-rod/end-cap interface. An elastomeric o-ring isused to provide a preload on a PTFE ring, which acts as the sealing surface at thereciprocating interface due to its lower coefficient of kinetic friction than the o-15AABSECTION A-ADETAIL BSCALE 5 : 1Rod SealNutSpacerA AB B2211Figure 3.3: Open gland design for the driven end-cap rod seal. The two-partrod seal uses an elastomeric o-ring to provide a loading force onto theinner PTFE ring, which has improved wear resistance against slidingfriction. A spacer and externally-threaded nut simplify the installationand replacement of the rod seal.ring. Viton (FKM) and perfluoroelastomer (FFKM) were selected for all o-rings(static seals and elastomeric preloaders for reciprocating seals) due to their supe-rior compatibility with a broad range of alternative fuels when compared to NBR,which is conventionally used in hydraulic cylinders. Viton is suitable for use withfuels including diesel, biodiesels, and n-heptane. FFKM has better chemical resis-tance to acids, such as those typically found in pinewood bio-oil. The Viton ringswere cut to have square cross-sections for relatively even application of pressureon the PTFE sealing surfaces compared to round o-rings. Due to the high tool-ing costs that would be required to cut the FFKM rings into square cross-sections,conventional circular cross-section o-rings were selected for the FFKM seals. Car-bon infused PTFE was chosen over the bronze infused PTFE rings typically usedin hydraulic cylinders because it has less propensity for wear and superior sealing16performance at pressures in the desired operating range of the MS.The cylinder, end-caps, and piston are machined from cold rolled steel (C1144)for broad material compatibility and high yield strength. The cylinder wall dimen-sions were selected using a 1.4 factor of safety above the yield strength at maximumworking pressures of 1200 bar when considering rupture failure of a thick walledpressure vessel. A safety factor of 1.5 over yield strength at 1200 bar was usedwhen considering shearing failure of threaded components, i.e., end-caps, piston,and piston rod.3.2.1 Commissioning and InstallationAfter completing the design and fabrication, additional work went into the instal-lation, commissioning, and maintenance of the MS, with the intent of ensuringoperational safety and repeatable testing of fuels.A portable cart was built to house the MS along with the common rail and otherfittings, lines, and valves used for integration into the existing diesel fuel system. Aphoto of the MS as it is mounted in the cart is shown in Figure 3.4. Small ellipticalplates loosely resting between the exterior of the end-caps and cylinder are usedwith large eye bolts to facilitate lifting the MS with an engine crane, as it weighsapproximately 25 kg fully assembled. Referring back to Figure 3.2, two-way andthree-way switching ball valves are used to enable high pressure diesel from thecommon rail to bypass the MS, which allows for direct injection of diesel. Theswitching valves are also used to direct fuel flow when performing initial fillingof both sides of the MS with diesel for preliminary pressure testing. Simultaneousfilling with diesel and bleeding of air pockets is performed by running the CP3pump at a relatively low speed (e.g., 500 rpm, 1/3 of full speed operation) fortwo full piston strokes. Stainless steel reservoirs containing 20 µm fuel filters areconnected to tees directly above the MS and adjacent to the common rail to allowair pockets that may have been trapped in the MS during filling to rise to local highpoints for ease of bleeding.Upon assembly, the MS is mounted vertically and tees are placed directly abovefuel lines attached to both end-cap fuel ports to aid with bleeding pockets of air,which are highly compressible and can cause catastrophic damage by ejecting17Figure 3.4: Cart housing MS and common rail with connections to CP3 pumpand injector.heavy components during the rapid expansion of air in the event of componentfailures or leaks.After any disassembly of the MS system, the MS undergoes several rounds ofdiesel pressure testing at 800 bar, which was determined to be the desired injectionpressure for the experimental campaign. The control system did not require tuningto reach stable rail pressures of 740±5 bar, corresponding to 800 bar on the drivenside when factoring in the pressure amplification provided by the piston rod. Thediesel rail pressure is set to 740 bar for a cumulative runtime of 2 hours to confirmthere is no evidence of fuel leakage. Since experiments on the optical engine arecompleted within two minutes of runtime, the sealing performance of the MS isdeemed sufficient for proceeding to on-engine fuel injection testing with the MS.3.3 OperationThis section discusses the operational considerations for the MS as it was used inthis experimental campaign.183.3.1 FuelingA repeatable procedure is used for filling the MS with fuel from stainless steelreservoirs containing in-line filters to eliminate the risk of solid particles enteringthe MS and injector. First, any fuel remaining in the driven side of the MS ispurged from the system by connecting an empty filling tank and running the CP3pump at a low speed (sim500 rpm) to provide enough pressure to overcome theresistance from the reciprocating seals to move the MS piston. The filling tanksare drained of spent fuel and flushed with methanol prior to filling with the desiredfuel sample. Fuel is drawn into the MS by manually depressing the piston rod untilthe driven side is full. The tank is left connected to the MS while the CP3 pump isagain allowed to run at low speed to bleed any air bubbles that may have enteredthe drive side of the MS during draining and filling. The piston is again depresseduntil the driven side is full. A pressure test is conducted for at least 10 minutes atthe operating pressure of 800 bar (driven side pressure; 740 bar rail pressure) toconfirm the seals still retain pressure with the newly filled alternative fuel.3.3.2 Test ProcedureA repeatable test procedure is followed for MS operation to eliminate the risk ofexceeding designed operating pressures. Safety thresholds are set in the LabViewvirtual instrument that is used to control and monitor the diesel rail pressure. Be-cause the control system initially overshoots pressure targets before stabilizing atthe desired set point, conservative safety thresholds are used: 875 bar for a highpressure alert and 975 bar for critical pressure shutdown, which correspond to 945bar and 1050 bar on the driven side of the MS due to the pressure amplificationresulting from the piston rod.Pressurizing the MS is done incrementally to ensure the system has time tosafely stabilize before reaching the desired fuel injection pressure. Once safetycontrols have been set in LabView, pressure to the driving side of the MS is sup-plied by turning on the CP3 pump at its rated speed of 1500 rpm, which bringsthe diesel rail pressure to 25 bar. The rail pressure is set to 550 bar to allow pres-sure to settle at an intermediate value, and then to 740 bar so the driven side hasa fuel pressure of 800 bar. The actual rail pressure fluctuates within ±5 bar of the19740 bar target, corresponding to fuel injection pressure fluctuations of ±6 bar, or0.7% of the desired pressure. Once the media separator is at pressure, no additionalalterations to the optical engine operating procedure are required.3.3.3 Fuel Flow Rate MeasurementA string potentiometer is used to monitor piston position throughout each test,which provides a test-averaged volumetric fuel consumption rate. Three rates ofpiston movement are typically observed: a “pre-test” rate when the rail pressure isat 740 bar but no fuel has been injected, a rate during the test while fuel is being in-jected, and a “post-test” rate after fuel injection has concluded but while the systemis still pressurized. The raw and smoothed data from the string potentiometer arepresented in Figure 3.5, which clearly demonstrates the three regions of fuel flowout of the MS. Piston movement during the pre- and post-test phases is caused byFigure 3.5: Raw data from the string potentiometer undergoes LOWESSsmoothing with 20% span to produce a signal that is easier to differ-entiate for volumetric flow measurement.steady flow through the low pressure return line of the fuel injector, which behaveslike a cracked needle valve. This fuel is collected in a spent fuel pail and disposedof. The raw data from the string potentiometer has a considerable amount of noiseand the DAQ used for monitoring this instrument has a relatively low temporal20resolution (sample rate = 100 Hz), both of which prevent direct measurement offuel injection events since injection durations used in this work are on the scaleof 0.7 to 2 ms. Sample rates of at least 2000 Hz would be required to resolveindividual injections of 0.5ms duration. In light of this, average fuel flow ratesare determined using the string potentiometer data. A locally weighted scatterplotsmoothing (LOWESS) algorithm is applied to the raw data with a 20% span to pro-duce the position line with substantially less noise than the raw data presented inFigure 3.5. The large ‘X’ data markers represent the three previously described re-gions of relatively constant flow rate, which are used for evaluation of test-averageflow rates.Figure 3.6: Volumetric flow rates are obtained from the time derivative of thestring pot position signal multiplied by the cross-sectional area of thedriven volume of the MS cylinder. Thick red lines represent mean valuesfor each region with thin lines representing ±2 standard deviations.The volumetric flow of fuel out of the media separator is calculated by differ-entiating the smoothed piston position with respect to time and multiplying by thecross sectional area of the driven volume of the MS. Figure 3.6 provides the vol-umetric fuel flow rate from the media separator with three regions demonstratingrelatively constant values. The average flow rate for each test is calculated from themain test flow rate subtracted by the mean of the pre- and post-test rates. Confi-21dence intervals are determined using ±2 standard deviations for each region. Whilethere appears to be some cyclical fluctuation in the flow rate while injection occurs,the period of these fluctuations is primarily a function of the span window chosenfor the LOWESS algorithm. The varied flow conditions resulting from skip-firingof the injector can not be directly observed in the volumetric flow rate with thelimited signal-to-noise ratio and temporal resolution of the string potentiometerdata.3.4 SummaryThe media separator is a novel contribution to the optical engine facility fuel sys-tem, enabling direct-injection of small samples of alternative fuels. The design ofthe MS satisfies the defined objectives including safe operation at working pres-sures up to 1200 bar, broad material compatibility, small fuel capacity, direct inte-gration with an existing diesel common rail system, and sufficient isolation of fuelsamples from contamination. Test-averaged fuel consumption rates are made pos-sible through the use of a string potentiometer attached to the MS piston rod. Theexperimental campaign conducted in this work was completed using fuel suppliedby the MS.22Chapter 4Experimental FacilityExperiments were conducted to assess injection dynamics and combustion charac-teristics for a range of reference and alternative fuels using a 2.0L, optically acces-sible, single-cylinder, CI research engine with fuel supplied by the media separator(See: Chapter 3). This chapter discusses the fuels considered and the results ofchemical and thermogravimetric analysis. A summary of the engine facility andmethodology is presented along with discussion of the theoretical grounding forthe pyrometry probe and OH*-chemiluminescence imaging. Further detailed dis-cussion of the design and commissioning of the facility is documented in previouspublications [12] [45].4.1 FuelsSix fuels are examined in this work to establish a baseline understanding of con-ventional CI fuel behaviour and to contribute new knowledge about the combustioncharacteristics of alternative fuels. This section describes the fuels selected anddiscusses fuel properties.4.1.1 Fuel SelectionThe fuels used in this experimental campaign have been grouped into three cat-egories: reference fuels, biodiesels, and novel fuels. Reference fuels (diesel andn-heptane) provide links to other direct-injected CI engine literature and act as a23benchmark for characterizing novel fuels. Biodiesels (canola and soybean methylesters) are increasingly used as a way of decarbonizing the heavy duty transportsector, which warrants further optical engine investigation of combustion perfor-mance. Two novel fuels (diesel with graphene oxide additive and a blend of up-graded pine bio-oil with diesel) represent potential avenues for next-generation fuelimplementation.The reference fuels selected are diesel and n-heptane. Diesel is used as a refer-ence due to the abundance of works characterizing diesel combustion. n-Heptaneis a monocomponent research fuel that is commonly used as a surrogate for dieselin simulation works due to validation of its chemical kinetic models [46] [47].Canola and soybean methyl esters (CME and SME, respectively) are the twobiodiesels selected for testing. These two fatty acid methyl ester biodiesels areproduced from the transesterification of vegetable oils and represent an alterna-tive to conventional diesel production from fossil fuels. Compared to diesel, SMEand CME demonstrate reduced emissions of soot and increased emissions of NOx[40, 48]. The oxygen content in biodiesels has been suggested to inhibit soot for-mation [49]. These biodiesels provide a benchmark for alternative fuel combustionsince they closely match the combustion performance of diesel, albeit with reducedsoot emissions and only marginally reduced energy per unit mass of fuel burned.A major drawback to the use of biodiesels is the amount of food crops requiredfor fuel production [50]. Biodiesels are chosen for this characterization due totheir commercial relevance as alternative fuels despite the evident supply chainconcerns.The two novel fuels selected for this work are a blend of upgraded pinewoodbio-oil with diesel at a 10:90 volume ratio and a diesel doped with 10ppm (byweight) graphene oxide nanoparticles. A sample of pine bio-oil underwent up-grading through transesterification and hydrodeoxygenation, though clogging ofthe catalyst used for hydrodeoxygenation resulted in reactor failure, resulting inextremely limited yields of the upgraded bio-oil. A total of 52 mL of upgradedbio-oil (UBO) was produced with two distinct, immiscible layers: about 22 mL ofhighly viscous liquid closely resembling the raw bio-oil and about 30 mL of a lessviscous and more buoyant layer similar in appearance to the biodiesels used in thiswork. The entire UBO sample was added to diesel at a 10:90 volume ratio using a24magnetic stir plate set to 500 RPM for 4 hours and allowed to settle for 24 hours.The viscous bottom layer present in the blended sample was removed prior to fil-tering and filling the MS. The blended sample was filtered through Grade 41 filterpaper to extract solid particles over 11 µm in diameter since the direct injector hashighly sensitive internal geometry that degrades in performance when exposed tosolids at high pressure.Graphene oxide has been examined in a handful of studies as a fuel additive todiesel-biodiesel blends with evidence of enhanced droplet atomization and reducedemissions of CO, CO2, NOx and unburned hydrocarbons (UHC) when comparedto neat diesel [38][51]. A sample of graphene oxide was provided with the intent ofperforming characterization of GO-doped diesel in a CI engine. As of the time thiswork was written, there has yet to be any documented research into the study ofblends consisting solely of diesel and GO in CI engines. The work by Mosadeghet al to study GO-doped diesel found a 7% increase in droplet burning rate atGO mass loadings of 0.001%. This mass loading was chosen to assess if any ofthe differences observed at the droplet scale would be present in combustion atengine-relevant conditions.4.1.2 Chemical CharacterizationFuel properties were determined using off-engine chemical analysis to provide po-tential causal reasons for differences in injection dynamics, ignition delays, energyreleased, and soot propensity observed in the engine experiments. The characteri-zation was conducted by Econotech Services Ltd. Moisture content was measuredusing Karl Fisher titration. Parr oxygen bomb calorimetry was used to determinehigher heating value (HHV). Lower heating value (LHV) is approximated usingthe HHV and water content based on an equation provided by the US Environmen-tal Protection Agency for determining LHV of biofuels [52]. A viscometer wasused to measure kinematic viscosity. Acid number was determined using ASTMD803/D465. The results of this analysis are presented in Table 4.1. The lowerheating value (LHV) is a measure of the energy density of a fuel. Moisture contentwas measured since most CI fuels typically have very low moisture by mass. Theraw pinewood bio-oil has a relatively high moisture content which may result in25Table 4.1: Fuel propertiesFuel LHV Moisture Viscosity Acid No.- [MJ/kg] [wt.%] [cSt@40C] [mg KOH/g]Diesel 42.0 0.01 3.4 0.017n-Heptane 44.5 0.04 0.6* <0.002CME 37.0 0.06 4.6 0.157SME 37.1 0.04 4.2 0.390Bio-oil 16.3 19.4 15.0 68.133GO Diesel 42.1 4.7** -*** 0.015UBO Diesel 42.2 4.8** -*** 0.085* Typical value, not measured** Uncertain origin*** Analysis not performed due to insufficient sample volumelonger ignition delays and combustion instability. Viscosity is anticipated to effectrates of fuel penetration during injection. The high acid number of bio-oil is well-documented and is a significant enough deterrent to engine operation to merit fur-ther upgrading (e.g., transesterification, hydrodeoxygenation)[23, 53, 54]. Giventhe 10:90 blend ratio for UBO to diesel, it is estimated that the UBO sample hasan acid number of 0.697 mg KOH/g, slightly higher than that of the biodiesels but2 orders of magnitude less than the raw bio-oil. Despite similarities in appearanceto crude oil, the raw bio-oil has few similarities to conventional CI fuels.Further fuel analysis was performed using automated flash combustion and gaschromatography to characterize the relative proportion of elements found in eachfuel. Oxygen content is of particular interest since it has been suggested to reduceemissions of soot, CO and unburned hydrocarbons for biodiesel combustion whencompared to neat diesel [55]. The oxygen content of diesel and n-heptane andthe nitrogen content of n-heptane were unable to be repeatably measured, becauseof relatively high volatility causing incompatibility with the experimental assays.Since diesel is the primary component of the GO diesel and UBO diesel samples,the presented oxygen results are of uncertain accuracy. While the raw bio-oil ishighly oxygenated, it also has much lower hydrocarbon content compared to theother fuels, which is consistent with it having a relatively low energy content, i.e.,LHV.26Table 4.2: Fuel elemental contentFuel C H O N[wt.%] [wt.%] [wt.%] [wt.%]Diesel 84.4 14.1 <0.1* <0.1n-Heptane 83.9 16.1 <0.1* <0.1*CME 76.9 13.3 11.0 <0.1SME 76.7 13.4 10.8 <0.1Bio-oil 44.8 7.4 41.0 0.127GO Diesel 85.6 13.1 1.1** <0.1UBO Diesel 84.9 13.1 1.2** <0.1* Assumed** Uncertain accuracyThermogravimetric analysis (TGA) of fuel samples contributes to understand-ing of fuel volatility, which has been demonstrated to affect the liquid penetrationof fuel sprays and potentially promote fuel-air mixing [30]. Analysis was con-ducted using a 10°C/min heating rate to a peak temperature of 500°C in a non-reacting N2 atmosphere. The weights and weight loss curves from TGA are com-piled in Figure 4.1. 90% distillation temperature, T90 is the temperature at which90% of sample mass loss has occurred, and it serves as a measure of volatility, i.e.,fuels with high T90 are less volatile than fuels with low T90. The mean 90% distil-lation temperature and relative standard deviation (RSD) expressed as a % of themean value are presented in Table 4.3. n-Heptane exhibits the highest volatilityTable 4.3: Volatility: 90% Distillation TemperatureFuel Diesel n-Heptane CME SME GO Diesel UBO DieselT90 [°C] 197 52 228 230 198 194RSD [±%] 2.6 11.9 1.5 2.2 3.4 1.0and the lowest T90, showing non-negligible mass loss rates at room temperature.The differences in weights and weight loss rates for each TGA test of n-heptaneare attributable to the evaporation of fuel during the stabilization of the TGA appa-ratus prior to the beginning of the heat profile. Diesel is less volatile than n-heptanebut more volatile than both biodiesels, having lost 90% of its mass at 197°C, wellbelow the T90 of either biodiesel. The GO and UBO diesels demonstrate simi-lar weight loss curves to neat diesel, with only minor differences in mean T90 for27Figure 4.1: Weight and weight loss rates for the considered fuels.across the triplicate tests. The variation within each set of T90 measurements for thediesel and novel fuels is greater than the variation between the means, suggestingthat GO, UBO, and neat diesel have consistent T90. Volatility is thus not affectedby the addition of 0.001% (wt.) GO or 10% (vol.) UBO to diesel. Despite comingfrom different feedstocks, CME and SME show similar distillation curves.The fuels characterized in this work represent a cross-section of practical, refer-ence, and novel liquid fuels for CI engines. The use of the media separator enablesfurther optical engine assessment of fuel performance.4.2 Optical Engine FacilityEngine experimentation for this work was conducted on a 2L, single-cylinder, op-tically accessible CI engine based on the Ricardo Proteus research engine. Theengine has two configurations for operation. Thermodynamic mode is a standardengine configuration using all metal components with a toroidal piston bowl ge-ometry, representative of piston bowls seen in modern, heavy duty, direct injecteddiesel engines to promote fuel-air mixing. Optical mode uses a Bowditch pistonin conjunction with a fused quartz window to render the combustion chamber op-28tically accessible. A metal puck can be used in lieu of the window to run testswithout using high speed cameras. The optical piston bowl has a cylindrical ge-ometry due to the installation of the window/puck. All tests for this experimentalcampaign were conducted with the engine in its optical configuration. Table 4.4contains parameters specific to the engine used in this work.Tests in the optical configuration are run using skip-firing of the fuel injectorin order to preserve the quartz window and reduce optical fouling. The skip-firingsequence consists of 15 cycles, where each cycle contains 2 crankshaft revolutions.Fuel injection occurs for three consecutive cycles in order to heat the combustionchamber and attain conditions that approximate steady-state engine operation [12].The data and images from testing are analyzed from the third fired cycle of eachskip-fired sequence since it has comparable cycle-to-cycle variability to steady-state thermodynamic operation. The remaining 12 cycles are non-fired, which al-lows the window to cool slightly while also reducing the total soot deposited ontothe window. Window fouling is of particular concern when taking into accountthe statistical analysis of the OH*-chemiluminescence signal, which is discussedfurther in Chapter 6.The skip-firing strategy precludes conventional measurements of exhaust emis-sions and fuel flowrates. Test average fuel flowrate measurements are obtained byusing a string potentiometer attached to the MS piston rod. Since the string poten-tiometer data was logged using a medium speed NI 9205 DAQ, it is not possibleto obtain cycle-specific fuel flowrates. An average rate of fuel consumption acrossthe duration of each test can be calculated instead.The Bowditch piston uses a custom fabricated piston liner that is intended torun without lubrication in order to avoid fouling of the quartz window. PTFE pistonrings must be used in lieu of the conventional steel rings that can be used whenthe piston liner is lubricated. The PTFE piston rings wear down at much fasterrates than typical steel piston rings, resulting in degraded sealing performance andlowered polytropic exponent of compression, ncomp, which is given aspcyl ∗V ncompcyl = constant (4.1)where pcyl is measured by an in-cylinder pressure transducer and Vcyl is calculated29Table 4.4: Ricardo Proteus Optical Engine ParametersDisplaced Volume 1998ccStroke 152mmBore 130mmConnecting Rod 275mmCompression Ratio 13.25:1Speed Limit 1200rpmMaximum Cylinder Pressure 110barNumber of Valves 2Optical Piston Bowl Shape Cylindrical (80mm diam.)Diesel Pump Bosch CP3Diesel Direct Injector Bosch CRI2.2, 7-hole, 148° inc. anglefrom the piston position according to the measured crankshaft angle. EvaluatingEquation 4.1 over the duration of the compression stroke gives a near-constantpolytropic exponent, ncomp ≈ 1.34. Piston rings have been replaced after repeattests demonstrate that ncomp ≤ 1.33.4.2.1 Instrumentation and Data AcquisitionThe section will detail the instrumentation used for data measurement. A partialP&ID of the engine in its optical configuration with relevant instrumentation is pre-sented in Figure 4.2. A Kistler 6125C pressure transducer provides measurementof pcyl , the in-cylinder pressure for heat release rate analysis. A Kistler 4005BA5Fpressure transducer in the intake manifold is used to record the manifold absolutepressure and to index the in-cylinder pressure. A BEI H25 optical encoder recordsthe position of the crankshaft to the nearest 1/4 crank angle degree. A WavetekCT238 current probe measures the injector current signal to verify that the pro-grammed injection sequence is being sent at the correct time and duration.Two high-speed cameras record images of natural luminosity (NL) in the broad-band visible light spectrum and OH*-chemiluminescence (OH*-CL) at 310 nm.OH*-CL imaging is performed using a dichroic beamsplitter to reflect only the UVlight to a Photron SA1.1 FASTCAM equipped with a CERCO 100 mm f/ 2.8 UVlens for improved optical performance with UV light. A 310 nm narrow bandpassfilter (NBPF) is mounted on the lens to ensure only OH*-CL is imaged. A LaVi-30Figure 4.2: Optical engine P&ID.sion Intensified Relay Optic (IRO) amplifies the incident OH*-CL signal so it canbe recorded using a standard high speed camera sensor. An external LED illumi-nates the combustion chamber for injection spray imaging, which uses droplet lightscattering to identify liquid length penetration rates [56]. Additionally, a Nikon200mm f/4 Macro lens is used for the injection spray imaging to enhance the sizeof the jets for improved clarity and jet edge detection. The NL combustion imagesprovide qualitative information about the temperature and concentration of the in-candescent fuel-soot mixture. OH*-CL images can be used to quantify ignitiondelay and reaction zone location and growth rates. A neutral density filter wasadded to the NL camera to compensate for high incandescence when combustingliquid fuels.314.2.2 OH*-Chemiluminescence TheoryChemiluminescence is the emission of light that occurs when atoms or moleculesthat have reached excited energy states due to chemical reactions relaxing intothe ground energy state, releasing a photon. For the combustion of hydrocarbons,hydroxyl (OH*) radicals produce chemiluminescence as photons of wavelengthpredominantly centered around 310 nm [35]. OH* is observed as short-lived,electronically-excited intermediates in several reactions observed during combus-tion, one of which is provided in Equation 4.2 [57].CH +O2 −→ OH∗+CO (4.2)This work utilizes OH*-CL imaging to characterize ignition kernel locations andignition delays, as well as providing qualitative commentary on reaction zone struc-tures and differences in propagation.4.2.3 Three-Colour Pyrometry ProbeA local, three-colour pyrometry probe is used to measure soot cloud temperatureand optical density (KL). Details about the design of the prototypical two-colourpyrometry probe used in past works in this experimental facility can be found in[45] and [58]. The principles of multi-colour pyrometry and modifications to theprobe are described in this section.Planck’s law is the fundamental equation used to characterize the intensityof radiation of a black body at a given temperature and wavelength, which pro-vides the basis for pyrometric measurements of soot temperature and concentra-tion. Equation 4.3 gives the expression of Planck’s law,Ib,λ (λ ,T ) =2hc2λ 51ehcλkT −1(4.3)where Ib,λ (λ ,T ) is the blackbody radiation at a given wavelength λ and temper-ature T, h is the Planck constant, c is the speed of light, and k is the Boltzmannconstant. Given that soot is a gray body, i.e., it does not exhibit ideal radiation atall wavelengths, its radiation is given by Equation 4.432Iλ (λ ,T ) = ελ Ib,λ (λ ,T ) (4.4)where ελ is the spectral emissivity at a given wavelength λ and is <1 by definition.This monochromatic emissivity is given by Hottel and Broughton in Equation 4.5,ελ = 1− e−KLλα (4.5)where K is a wavelength-independent extinction coefficient per unit length of emis-sive medium, L is the path length through the emissive medium, and α is an em-pirically determined constant over a limited range of wavelengths [59]. Hotteland Broughton determined α to equal 1.39 for the visible light spectrum, whichis taken as the accepted value for this work. Considered together, the product KLhas been demonstrated to closely correlate to soot concentration [60, 61]. The graybody spectral radiation intensity given in Equation 4.4 is restated in Equation 4.6in terms of the equivalent blackbody emission at an apparent temperature, Ta.Iλ (λ ,T ) = Ib,λ (λ ,Ta) (4.6)Combining Equation 4.3-Equation 4.6, the measured radiative intensity at twowavelengths can be equated to give1− e C2λ1T −1eC2λ1Ta,1 −1λα1 =1− e C2λ2T −1eC2λ2Ta,2 −1λα2 (4.7)where C2 = hc/k. Equation 4.7 can be solved numerically for the actual soot cloudtemperature, T. Temperature can then be used to calculate the soot cloud concen-tration, KL using Equation 4.8.KL =−λα ln(1− eC2λ ( 1Ta− 1T ))(4.8)For this work, a third wavelength was added to the pyrometry probe for in-creased confidence in measured temperatures and soot concentrations. A trifur-cated fiber optic cable was used in conjunction with three narrow bandpass filtersat 700 nm, 800 nm, and 880 nm to measure the radiant light intensity of the soot33cloud. The addition of the 880 nm light measurement allows for three wavelengthpair combinations, which has improves the robustness of probe calibration relativeto the use of a single wavelength pair by allowing for cross-validation of pyromet-ric data. The 880 nm wavelength was selected to maximize the distance betweenmeasured wavelengths in the visible spectrum while avoiding uncertainty from aradiation absorption feature caused by water vapour around 900 nm as seen inFigure 4.3. Only wavelengths in the visible light range were considered becausedifferent values for α are recommended for wavelengths in the infrared and ultra-violet bands, which would introduce unwanted uncertainty [59, 62].Figure 4.3: Spectral absorption coefficient of water vapour with a minor ab-sorption feature centered around 900nm.The location of the pyrometry probe within the combustion chamber can beseen in Figure 4.4. The fuel spray axes depend upon the orientation of the injectorwithin the engine block, which was kept constant within 5°for the duration of theexperimental campaign, as demonstrated in Figure 4.5. Although the jet does notdirectly cross the probe tip, the circulation of fuel and air around the cylinder wallcauses soot to form in the field of view of the probe.4.3 Engine Operating ConditionsSeveral relevant operating conditions were defined with measures taken to ensurerepeatability. Given the short, skip-fired nature of the tests, the coolant, intake air,and oil all required preheating to simulate steady-state engine operation. At the34Figure 4.4: Location of pyrometry probe in combustion chamber. Two jetsstraddle the direct field of view of the probe, which is exposed to sootupon circulation and combustion of the fuel.Figure 4.5: Angle of jets with respect to horizontal from the beginning (left)and end (right) of experimentation. Care was taken to ensure repeatableinstallation of the fuel injector when it was removed for engine mainte-nance.beginning of each day of testing, the engine’s thermal management systems wereheated to temperatures listed in Table 4.5 for approximately an hour to establishrepeatable engine conditions.Two engine operating conditions were selected for characterization: a low loadcondition with a single fuel injection per cycle and a medium load condition withpilot and main fuel injection. Descriptions of the two operating conditions are35Table 4.5: Thermal management system parametersSystem Set Temperature [°C] Test Temperature [°C]Oil 70 70±10Coolant 85 85±5Intake Air 55 55±2presented in Table 4.6.Table 4.6: Optical test operating parametersParameters Operating ConditionsDescription Pilot + Main Injection Single InjectionPilot start of injection (PSOI) -20 CAD aTDC -Pilot pulse width (PPW) 0.45 ms -Main start of injection (MSOI) -6 CAD aTDC -6 CAD aTDCMain pulse width (MPW) 2.0 ms 0.7 msGross indicated mean 6.58 bar 1.98 bareffective pressure (GIMEP)Fuel injection pressure 800 barIntake air pressure 1.07 barIntake air temperature 55 CEngine speed 1000 rpmThe pilot + main injection condition is representative of a standard fuel injec-tion scheme used in contemporary diesel direct injection systems. A small massof pilot fuel is injected shortly before the main injection near TDC and combustsin the premixed phase to heat the cylinder and shift most of the combustion of themain fuel injection to the mixing-controlled phase. The pyrometry probe is usedto measure integrated soot concentration and temperature for this operating condi-tion since the mixing-controlled combustion produces sufficient soot to generate ameasurable pyrometry signal.The single injection operating condition allows for thermodynamic and opti-cal measurement of the ignition delay of each fuel based on HRR and OH*-CL,respectively. Fuel injection concludes well before ignition is observed, suggestingthat ignition timing is not directly influenced by injection, which increases con-fidence that different ignition delays are caused primarily by differences in fuelcomposition. The pyrometry probe can not be used for this condition because the36premixed combustion of a small fuel mass results in negligible soot formation.The single injection condition is operated using externally illuminated fuel injec-tion spray imaging to measure the liquid length and spray cone angle of the liquiddroplets. Fuel jet penetration is expected to change with the volatility of each fuelbased on correlations observed in the literature [2, 31]. Spray cone angle has beensuggested to increase with fuel viscosity [63].Injection duration was held constant for all fuels despite differences in LHVbecause of insufficient fuel sample volume for iterative refinement of injection du-ration to maintain constant mass/energy. Altering injection duration is commonlyseen in literature as a means of compensating for differences in energy density[64, 65]. Data from the MS string potentiometer is used to measure volumetricfuel consumption rates, which are converted into mass flow rates using fuel den-sity. The rates of fuel consumption are used to justify the extent to which con-clusions are dependent upon fuel content rather than differences in total energy orequivalence ratio.4.4 Experimental CampaignThis section details the experimental campaign conducted for this work, includinginformation about camera settings, valve timing adjustments, and repeat measure-ments. Testing began with diesel using the metal puck to establish the expectedpeak pressures, GIMEPS, and camera signal intensities for both operating condi-tions.Table 4.7: Experimental campaign single injection condition camera settingsCamera Photron Nova Fastcam Photron SA1.1 FastcamSubject Injection Spray NL OH*-CLExposure 23 µs 4 µs 61.7 µsFramerate 40,000 fps 15,000 fps 15,000 fpsAperture f/5.6 f/16 f/8IRO Gate - - 28.5 µsIRO Gain - - 70%Filter - - 310 nm NBPFFrames per trigger 150 150 150Lens focal length 200 mm 105 mm 100 mmCamera settings were chosen to minimize the number of frames with large37regions of sensor saturation for the natural luminosity imaging and to avoid anysensor saturation for the OH*-chemiluminescence camera. Performance of theintensified relay optic (IRO) degrades with prolonged high-intensity incident light,hence the avoidance of sensor saturation for OH*-CL imaging. Settings for thesingle injection and pilot + main operating conditions are presented in Table 4.7and Table 4.8, respectively.Table 4.8: Experimental campaign pilot + main condition camera settingsCamera Photron Nova Fastcam Photron SA1.1 FastcamSubject Natural Luminosity OH*-ChemiluminescenceExposure 1.7 µs 61.7 µsFramerate 15,000 fps 15,000 fpsAperture f/16 f/8IRO Gate - 28 µsIRO Gain - 70%Filter 1.0 ND 310 nm NBPFFrames per trigger 150 150Lens focal length 105 mm 100 mmDuring the experimental campaign, intake and exhaust valve timing drifted by6.5 CAD. The advanced intake valve actuation during the gas exchange strokescaused interference between the intake valve and piston crown around TDC. Thechange in intake air charge dynamics may be responsible for some of the observeddifferences in ignition delay behaviour, as suggested in Figure 4.6 by the 1 CADadvance in ignition timing for n-heptane after the valve timing was retarded by 6.5CAD. In light of the different valve timing, testing was repeated for diesel, SME,and n-heptane to ensure consistency of control conditions across fuels. CME wastested with only the advanced valve timing since there was no remaining fuel for re-peat testing after the valve timing was reset. Testing for GO diesel and UBO dieseltook place after the valve timing change. The advanced HRR does not intuitivelyalign with the retarded intake valve closing, which should theoretically result inan lower effective compression ratio and thus lower air pressure and temperatureat SOI. It is possible that the valve and piston interference during the advancedvalve timing was causing incomplete closing of the intake valve, thus decreasingthe effective compression ratio before the valve timing was reset.38Figure 4.6: HRR from the single injection condition demonstrating the ef-fects of the valve timing adjustment that was made to stop the pistonfrom impacting on the intake valve.4.5 SummaryA suite of six fuels was selected for optical engine characterization: two referencefuels (diesel and n-heptane), two biodiesels (CME and SME), and two novel fuels(GO diesel and UBO diesel). Analysis of fuel properties showed that the conven-tional CI fuels have comparable properties to one another, whereas the raw bio-oilhas much lower LHV and higher moisture, viscosity, and acid number. The novelfuels show predominantly similar properties to diesel due to the large mass contri-bution of diesel to both blended fuels. The biodiesels contain significant oxygencontent relative to diesel. Results of oxygen analysis for the novel fuels have ques-tionable accuracy. n-Heptane shows the highest volatility of all fuels, with dieseland the novel fuels being intermediate and the biodiesels being least volatile.Relevant portions of the engine facility and instrumentation were described.39Two engine operating conditions were selected: a medium load, pilot + main in-jection condition and a low load, single injection condition. The pilot + maincondition is used to identify differences between HRR and soot formation, and thesingle injection is chosen to elucidate injection and ignition behaviour.40Chapter 5Injection Spray Behaviour ofAlternative FuelsHigh speed imaging of fuel injection is used to characterize injection behaviourssuch as liquid length and spray cone angle to understand the influence of fuel prop-erties on fuel-air mixing and ignition delay. This chapter describes the image pro-cessing script developed in MATLAB and presents analysis of the injection sprayliquid lengths and cone angles resulting from image segmentation. The effects offuel properties on spray cone angle and liquid length maxima are assessed.Previous works have used high speed imaging to investigate fuel injection be-haviour both in optical engines [30, 31, 33, 66] and constant volume pressure ves-sels at engine-relevant conditions [63, 67–69]. There is good agreement amongstthese references on the existence of inverse correlations between maximum liquidlength and volatility as well as in-cylinder air charge temperature and pressure, i.e.,shorter liquid lengths are observed for more volatile fuels and warmer in-cylinderair. Characterization is typically performed using diesel, gasoline, or monocompo-nent surrogate fuels, with a handful focused on novel and alternative fuels includingfatty acid methyl esters [33, 63, 66], and plain canola oil [69].Understanding how liquid lengths and spray cone angles change when fuelproperties are varied contributes to efforts to optimize CI engine design and opera-tion for alternative fuel combustion. Injection spray data is also useful for validat-ing numerical models of alternative fuel combustion in CI engines. Liquid lengths41provide information about fuel evaporation and potential instances of piston bowlwetting and cylinder wall wetting, which has been demonstrated to reduce combus-tion efficiency, increase emissions, and degrade lubricant performance [68]. Coneangle has been observed to vary with fuel properties such as viscosity, density, andvolatility as well as with injector orifice diameter and typically shows and inversecorrelation to liquid length [30, 63, 69].5.1 Image AnalysisAn image segmentation script was developed in MATLAB to evaluate injectionspray liquid lengths from externally illuminated images. Figure 5.1 demonstrateskey steps of the segmentation process, which is described in greater detail here. Thefirst frame in a cycle shows the illuminated engine fire deck and injector tip priorto fuel injection and is taken as a “tare” image. The fuel spray is isolated fromthe frame undergoing segmentation as the sole feature of interest by subtractingthe image from the background tare image. The resulting subtracted image showsdroplet sprays with the background removed. The droplet spray directly in front ofthe injector tip is lost in the background subtraction as a consequence of the injectortip being darker than the surrounding regions of interest. The subtracted imageundergoes a gamma adjustment to increase contrast. Morphological opening andclosing operations are performed on the image to improve segmentation continuityand reduce noise. The image undergoes binary segmentation into regions of jet andbackground using global thresholding. The binary image is then compared againstline masks in the jet axial directions to determine the pixel length of each dropletspray region.Two approaches to segmentation are available with the 15 cycles of injectionspray images collected: combination of data (COD) and combination of interpre-tations (COI) [70]. In COI analysis, each cycle of fuel injection undergoes imagesegmentation independent of other cycles. COI analysis affords straightforwardquantification of cycle-to-cycle liquid length variability by evaluating standarddeviations. Images are ensemble-averaged for COD analysis, causing the liquiddroplets in the core of fuel sprays to be clearly defined with slight reductions inclarity at the edges due to cycle-to-cycle variations in jet geometry. COI analysis42Figure 5.1: An overview of the image segmentation script for liquid lengthcalculation. Moving from left to right: the jets are extracted from theraw image using background image subtraction; gamma adjustment andmorphological operations are applied; a binary image is produced andmeasured against the linear masks along the jet axes; the jet length isoverlaid on the raw image for comparison.is preferred over COD since it enables direct computation of injection variability.COI results of injection spray image segmentation are presented herein.The same input settings were used for consistent segmentation across tests, aspresented in Table 5.1. Settings were determined heuristically through repeatedsegmentation and comparison of results. The global threshold, tb, used for imagebinarization depends on the value of γ since the image contrast adjustment affectspixel brightness for the subtracted droplet spray image. The pair of values for γand tb used in this analysis provide a reliable means of identifying droplet sprayregions with the exception of the region immediately in front of the injector tip.Two structuring elements with different diameters were used for morphologicaloperations to eliminate features imprinted onto the droplet spray from backgroundsubtraction i.e., the circular gap between injector sleeve and fire deck surface.Table 5.1: Segmentation parameters used for liquid spray image binarizationParameter Description Valueγ contrast adjustment 0.92tb global binarization threshold 0.077ta small area rejection threshold 0.145%Dcl structuring element diameter for closing 3 pxDop structuring element diameter for opening 7 pxSpray cone angles are measured using two points orthogonal to the jet axis andthe defined injector orifice point. In each frame, angles are calculated for all points43between 1/2 and 1/3 of the maximum liquid length, as shown in Figure 5.2. Theangles are averaged, resulting in a single cone angle per image.Figure 5.2: Definitions for liquid length and spray angle. Spray cone anglesare evaluated over the yellow region for each frame and averaged.5.2 Liquid Length Results and DiscussionDuring injection, fuels demonstrate different behaviours in the liquid phase thatcan be classified using four regimes: mechanical injector delay, jet growth, quasi-steady maximum liquid length, and post-injection droplet evaporation. The firstthree phases of fuel injection are discussed in this section. Liquid lengths and theirderivatives are presented in Figure 5.3 and Figure 5.4, where dotted and solid linesindicate results of individual cycles and average results of COI analysis, respec-tively.The mechanical injector delay is a function of fuel injection pressure and theinjector itself, with virtually no variation observed for all fuels tested. Delayedactuation of the injector needle results in an apparent start of injection (SOI) afterthe commanded start of injection (CSOI). Apparent SOI is defined as the crankangle corresponding to the first frame in which fuel can be observed exiting the44Figure 5.3: Fuels exhibit comparable liquid length growth rates until reach-ing their respective maxima, which has inverse correlation to volatility.e.g., highly volatile n-heptane has a 56% shorter max liquid length thandiesel.injector orifices. The mechanical delay phase occurs between -6 CAD (CSOI) and-2.5 CAD (apparent SOI) or 0.59 ms after CSOI for all fuels except CME, whichhas apparent start of injection at -2.3 CAD or 0.62 ms after CSOI. While CMEhas the lowest volatility of the fuels considered, SME has a comparable volatilityand has an apparent start of injection comparable to the more volatile diesels andn-heptane. The delayed apparent start of injection for CME may be the result ofexperimental uncertainty rather than fuel properties.The liquid length growth phase occurs between apparent start of injection andthe point at which maximum liquid length has been reached, dLdt = 0. Injection pres-sure is held at 800±5 bar for all tests, resulting in consistent liquid length growthrates from -3 CAD to -2 CAD before liquid length development is affected by dif-ferences in volatility. The growth phase lasts for different amounts of time becausevolatility affects maximum liquid length. Highly volatile n-heptane exhibits liq-uid length growth between -2.5 CAD and -1.3 CAD. Diesel and GO diesel exhibit45Figure 5.4: Liquid length rates of change highlight differences between fuelsdue to wide ranges of volatility. The zero-crossing indicates the pointat which maximum liquid length is reached, which occurs earlier for n-heptane due to its high volatility and accordingly short liquid length.liquid length growth between -2.5 CAD and 0.5 CAD. SME and CME, the leastvolatile fuels, exhibit liquid length growth until 2 CAD, which is the end of injec-tion. Both of these fuels exhibit some wetting of the piston bowl, which can beseen in Figure 5.5 where both fuels exhibit liquid lengths reaching the edge of thefield of view.The maximum liquid lengths follow the same inverse correlation with fuelvolatility that is seen in the literature. Diesel and GO diesel show similar maxi-mum liquid lengths: 34.6±0.2 mm and 34.9±0.4 mm, respectively, indicating thatthe 0.001 wt.% GO loading has no significant effect on volatility or maximumliquid length. CME and SME have maximum liquid lengths of 36.7±0.2 mm and38.5±0.1 mm, respectively. These are 6% and 11% longer maximum liquid lengthsthan diesel, which is likely caused by both biodiesels being less volatile than diesel.n-Heptane has a max liquid length of 14.8±0.1 mm, 57% shorter than that of diesel,which is consistent with the high volatility of n-heptane. Diesel, n-heptane, and GO46Figure 5.5: CME and SME both exhibit piston bowl wall wetting due to theirliquid lengths extending to the edge of the field of view. Cylinder wallwetting is known to reduce combustion efficiency and increase emis-sions of hydrocarbons and soot, though the effects of piston wall wet-ting are not thoroughly documented.diesel reach their maximum liquid lengths and then exhibit a decline in length fol-lowed by a relatively steady plateau during quasi-steady injection. The biodieselsreach their maximum liquid lengths at 2 CAD, right at the end of the quasi-steadyinjection phase.Fuels show different droplet evaporation behaviour after end of injection (EOI)at 2 CAD, likely due to differences in volatility. While the highly volatile n-heptaneshows a 60% smaller rate of liquid length decrease than diesel after EOI, this maybe attributed to it having a 57% shorter liquid length than diesel to begin with,i.e., there is less liquid n-heptane evaporating after EOI. CME shows a more pro-nounced delay in evaporation relative to the other fuels for an unknown reason.Diesel, GO diesel and SME all exhibit similar timing for their peak rate of liquidlength decay at 3 CAD, though GO diesel exhibits a 20% reduction in decay raterelative to diesel. This reduction is the only significant departure between the in-jection behaviour of neat and GO diesel, which may be attributed to experimentaland segmentation uncertainty.The maximum liquid lengths are compared to 90% distillation temperature andkinematic viscosity at 40°C for evaluation of potential correlations between the47Figure 5.6: Maximum liquid length versus volatility.injection phenomenon and fuel properties. Figure 5.6 presents maximum liquidlengths plotted against volatility (i.e., T90) with a linear fit and coefficient of de-termination included. Vertical whiskers represent ±2 standard deviations due tocycle-to-cycle variability. Since R2 = 0.98, a strong linear correlation is suggestedbetween maximum liquid length and volatility, which is supported in the literature[56]. UBO diesel and GO diesel are omitted in the plot of liquid length versusviscosity presented in Figure 5.7 because the kinematic viscosities of these twofuels were unable to be characterized due to limited sample volume for analy-sis. A linear correlation has been calculated using the remaining fuels, which hasR2 = 0.96, suggesting decent correlation, albeit weaker than that between liquidlength and volatility. Both correlations are limited by piston bowl wall wettingthat was observed for both biodiesels, causing hard limit on max LL for CME andSME.5.3 Spray Cone Angle Results and DiscussionSpray cone angles are measured to identify correlations with fuel properties suchas volatility and viscosity and investigate whether fuel-air mixing can be improved48Figure 5.7: Maximum liquid length versus viscosity.by considering the interplay of spray angle with injector nozzle and piston bowldesigns. The measured angles can be used to validate numerical simulations foroptimizing CI engine design and operation. Measured angles are presented in Fig-ure 5.8. A consistent trend across fuels can be seen in the initial period of rapidgrowth, reaching a maximum angle, and then settling to a quasi-steady angle forthe remainder of injection. The highly volatile n-heptane has a smaller spray coneangle than all other fuels. Despite differences in fuel properties between the dieselsand biodiesels, they exhibit no clear correlation to any individual property.The relatively low viscosity and high volatility of n-heptane may cause it tohave a smaller spray cone angle than diesel, biodiesels and novel fuels. Diesel,CME, and SME have viscosities of 3.4 cSt, 4.6 cSt, and 4.2 cSt at 40C, respectively.The viscosities of UBO diesel and GO diesel were not able to be measured due tolimited sample volume. While the viscosity of n-heptane could not be measured, itis documented to have a viscosity of approximately 0.35 cSt at 40°C [71]. Undernon-evaporating conditions, decreasing viscosity has been suggested to increasethe spray cone angle; however, the reverse trend was observed for evaporatingconditions [30].49Figure 5.8: Crank-angle resolved spray cone angles. The highly volatile n-heptane has a significantly smaller spray cone angle than the dieselsand biodiesels.The mean cone angles are plotted versus viscosity and volatility (i.e., T90) toassess whether correlations may exist between the liquid phase phenomenon andfuel properties. Figure 5.9 compares mean cone angle, α with T90. Whiskersrepresent ±2 standard deviations, which are relatively large due to high cycle-to-cycle variability and potential difficulties with accurately determining cone anglewith the image segmentation script used. While the coefficient of determinationis 0.84 based on the mean angle values, the large confidence intervals bring intoquestion the true validity of this correlation. Similarly, the cone angle is plottedagainst viscosity in Figure 5.10, with UBO and GO diesels again omitted due touncertainty about kinematic viscosity. The correlation between angle and viscosityhas R2 = 0.85, but again there is enough variation in the cone angle measurementsto call to question the validity of this correlation.50Figure 5.9: Spray cone angle versus volatility.Figure 5.10: Spray cone angle versus viscosity.5.4 SummaryLiquid droplets in the fuel jet core scatter incident light, producing a visible spraythat can be characterized using image segmentation techniques. Liquid lengthgrowth rates are dominated by fuel injection pressure and in-cylinder air pressure,resulting in comparable behaviour before fuels reach their respective maximum51liquid lengths.The results of this work support the inverse correlation between liquid lengthand fuel volatility that has been previously documented, with R2 = 0.98 for thelinear correlation. Liquid length and viscosity shows a degree of linear correlation(R2 = 0.96), the fit includes a limited range of fuels due to the inability to charac-terize the viscosity of UBO and GO diesels. The correlations between measuredproperties and cone angle likely have limited validity due to large variations inangle measurements.The following are novel findings of this injection spray characterization. n-Heptane has a smaller injection spray cone angle than more viscous and less volatilediesels and biodiesels. UBO diesel demonstrates a comparable spray cone angleto and marginally smaller liquid length than diesel. Addition of 0.001 wt.% GOto diesel has no effect on bulk fuel properties and thus no effect on liquid lengthor spray cone angle relative to neat diesel. Additional alternative fuel characteri-zation is required to improve confidence in the reported correlations between fuelproperties and fuel spray liquid phase phenomena.52Chapter 6Combustion Behaviour ofAlternative FuelsIn-cylinder combustion processes of six fuels are characterized in this chapter.Consistency of engine operation is assessed using fuel consumption rates, equiva-lence ratios, and engine load via gross indicated mean effective pressure (GIMEP).Gross indicated efficiency is discussed. This chapter investigates the effects of fuelcomposition on ignition delay, heat release rates (HRR), combustion phasing, andsoot propensity with additional qualitative discussion of OH*-chemiluminescence(OH*-CL) and natural luminosity (NL) images. A summary table is presented con-taining key injection and combustion metrics with mean values ±2 standard errors,i.e., standard deviation divided by√N where N is the number of measurements.6.1 Fuel Consumption, Equivalence Ratio, and IndicatedEfficiencyFuel consumption rates are consistent on a volumetric and mass basis for the fu-els and operating conditions tested. Consistent injection parameters (i.e., pressure,timing, duration) were used for fuels with varying properties such as density, lowerheating value, and viscosity, which can result in differing volume and mass flowrates and total fuel energy consumed. See Figure 6.1 for comparison of the cycle-averaged fuel injection rates on a mass and energy basis with whiskers representing53±2 standard deviations. The maximum difference between mean energy consumedfor the pilot + main (UBO diesel and SME) and single injection (diesel and CME)are 19.1% and 38.9%, respectively. The coefficient of variability (COV) of energyinjected for the UBO diesel and SME pilot and main conditions is 19.0% and 8.7%,respectively, suggesting that differences between mean values only marginally ex-ceed variation within each measurement. The diesel and CME single injectionsexhibit coefficient of variability of energy injected of 25% and 24%, respectively.While the difference between mean energy injected is larger than the variation,there is still considerable uncertainty in the measurements. The string potentiome-ter that was used to measure the volumetric fuel flow rate proved to have limitedaccuracy for evaluating test-averaged fuel mass and energy consumption due to alow temporal resolution and low signal-to-noise ratio.Figure 6.1: Fuel consumption rates on a mass and energy basis for both op-erating conditions. Whiskers represent ±2 standard deviations, whichare used in lieu of standard error due to the relatively high measurementuncertainty of the string potentiometer.The global equivalence ratio, φ , is the stoichiometric air-fuel ratio for oxida-tion divided by the actual air-fuel ratio. The equivalence ratio calculation is givenin Equation 6.1 [72]. The actual air and fuel masses are measured from a massflow sensor in the intake manifold and the string potentiometer attached to the me-dia separator piston. The stoichiometric air-fuel ratio is evaluated by balancing thestoichiometric oxidation reaction, Equation 6.2, where x,y, and z represent elemen-tal mass fractions obtained from chemical analysis and a,b, and c are coefficients54required to balance the reaction. The stoichiometric air-fuel ratios are presented inTable 6.1, where the more highly oxygenated fuels require less mass of air to attainstoichiometric combustion.φ =m f uel ∗ AF stoichmair(6.1)CxHyOz+a∗O2 −→ b∗CO2+ c∗H2O (6.2)Table 6.1: Stoichiometric Air-Fuel RatiosFuel Diesel n-Heptane CME SME GO Diesel UBO DieselA/Fstoich [-] 14.79 15.17 12.81 12.86 14.33 14.34The equivalence ratios for all fuels over both operating conditions are shownin Figure 6.2, with ±2 standard deviation interval using uncertainty propagationfrom signal noise in both air and fuel flow measurements. The maximum differ-Figure 6.2: Global equivalence ratios from both operating conditions. Dieseland SME show a 15.9% difference in equivalence ratio resulting fromdifferences in fuel and air mass consumed.ence in mean equivalence ratio for the single injection is seen between diesel and55SME, a 38.9% difference with COV in each measurement of 24.6% and 43.0%,respectively. For the pilot and main condition, UBO diesel and SME showed thelargest difference in mean equivalence ratio of 19.7%, with COV of 19.0% and8.7%, respectively. Similar to the rates of fuel injection, the differences betweenthe mean equivalence ratios are generally smaller than the variations, suggestingthat conclusions can not be drawn on the basis of differences in equivalence ratio.The need for improved fuel consumption rate measurement confidence is evidentin the equivalence ratios.Engine load is defined in this work using the gross indicated mean effec-tive pressure (GIMEP), which demonstrates modest differences between fuels dueto differences in energy content and combustion efficiency. Figure 6.3 containsGIMEP for both operating conditions for all fuels. The largest difference betweenFigure 6.3: Engine load as defined by GIMEP.mean GIMEPs for the single injection condition is seen between UBO diesel andn-Heptane, which have a 4.8% difference. The standard deviations of GIMEP forthe single injection condition for n-Heptane and UBO diesel are 5.0% and 4.1% ofthe respective means, suggesting that the difference in mean GIMEP between fuelsis mostly within the deviation of GIMEP for each fuel. For the pilot + main con-56dition, SME shows an 8.8% reduction in mean GIMEP relative to GO diesel, bothof which have respective COV of 1.2% and 2.2%, indicating that the differencebetween means exceeds the variability in GIMEP for each fuel.Gross indicated efficiency provides an understanding of the combustion effi-ciency of each fuel based on the amount of work produced in-cylinder and theenergy of fuel consumed. Equation 6.3 provides a definition for gross indicatedefficiency,ηi,g =Wi,gm f LHV(6.3)where m f is the mass of fuel consumed per cycle, LHV is the lower heating value orenergy density of fuel, and Wi,g is the gross indicated work, calculated by integrat-ing the in-cylinder pressure with respect to cylinder volume over the compressionand expansion strokes [72]. Indicated efficiencies are presented in Figure 6.4 alongwith whiskers representing propagation of measurement uncertainties of indicatedwork and fuel mass consumption rates. n-Heptane and UBO diesel represent thefuels with the highest and lowest indicated efficiency for the pilot and main condi-tion, with UBO diesel showing a 14.2% decrease in efficiency relative to n-heptane.For the single injection, diesel exhibits a 32.6% decrease in efficiency comparedto CME. COV ranges from 8.4% to 19.3% for the pilot and main efficiencies, andfrom 21.0% to 43.3% for the single injection, which does not indicate high confi-dence in identifying clear efficiency trends based on fuel content. Again, the highmeasurement uncertainty of the string potentiometer is the primary contribution tothe reported variability in indicated efficiency.Injection duration was held constant across fuels for each operating conditiondue to a desire for consistent fuel injection and a constraint of small fuel samplevolumes, which prohibited iterating on injection duration to match energy injectedacross fuels. As a result of the constant injection durations, the maximum differ-ence in mean energy injected was 19.1% between UBO diesel and SME for thepilot + main condition and 38.9% between diesel and CME for the single injec-tion condition. The maximum difference in mean engine loads are 8.8% and 4.8%for the pilot + main and single injection conditions, respectively. The maximumdifferences in mean equivalence ratios are 19.7% and 38.9% for the pilot + mainand single injections, respectively. The significant differences in mean fuel energy57Figure 6.4: Indicated efficiencies for both operating conditions.consumption and equivalence ratios are obfuscated by large COV owing to lowmeasurement accuracy of the string potentiometer. While some conclusions canbe drawn based on fuel composition causing differences in combustion behaviour,further study is required using a more accurate instrument for measuring fuel con-sumption rates and iteration on injection duration to try to match energy injectedand/or equivalence ratio.6.2 Ignition DelayThe single injection operating condition enables the consideration of differencesin ignition delay that arise in the partially premixed combustion regime. The HRRare shown in Figure 6.5 along with the injector signal, which is present from -5to -1 CAD aTDC. Chapter 5 demonstrated that injection for this operating condi-tion occurred between -2.5 CAD and 2.5 CAD aTDC due to delays between the58received signal and injector needle actuation. Differences in ignition delay can beobserved directly in the HRR, though integrated HRR (IHRR) analysis allows formore intuitive evaluation of ignition delay by considering the time between SOIand a consistent metric of combustion progress.Figure 6.5: HRR for the single injection operating condition illustrate differ-ences in ignition timing and peak intensity when fuels combust in thepremixed regime. Pressure waves from premixed combustion result inintense HRR ”ringing” after the initial peak.Ignition delay is determined using thermodynamic (HRR/IHRR) and optical(OH*-CL) analysis of the single injection operating condition where fuel combustsin the premixed regime. The thermodynamic ignition delay, τign,th, is defined inEquation 6.4 as the time elapsed between CSOI (-6 CAD) and 5% of IHRR. Opticalignition delay, τign,opt , uses the same computation but with a threshold of 5% ofpeak integrated OH*-CL signal instead of IHRR, since OH*-CL signal correlateswith HRR for premixed combustion. The OH*-CL images provide validation forignition delay trends despite the signal during ignition being less sensitive thanthe HRR. The reduced sensitivity of the OH*-CL signal results from the camerasettings being chosen to avoid sensor saturation at peak intensity. In addition tovalidating ignition delays, OH*-CL images also provide qualitative spatial data59about differences in ignition kernel location. Integrated OH*-CL and heat releaserates are presented in Figure 6.6. Trends for combustion timing are in agreementbetween the IHRR and integral OH*-CL.τign =(CA5−θCSOI)∗60∗1000RPM ∗360 [ms] (6.4)Figure 6.6: Normalized IHRR and integrated OH*-CL signal for the singleinjection operating condition. The ignition delay is defined as the timeelapsed between CSOI (-6 CAD) and 5% of peak integral heat releasedor OH*-CL. Consistent trends hold for both analyses with n-heptaneexhibiting shortest ignition delay and both neat and GO diesel exhibitingthe longest.Ignition delay is affected by fuel composition in both thermodynamic and op-tical analyses. The ignition delays determined from thermodynamic and opticalanalysis are presented in Figure 6.7, where n-heptane shows a 13.5% shorter ig-nition delay than diesel. The whiskers reflect ±2 standard deviations based on thecycle-specific ignition delays for the 15 cycles of combustion considered. UBOdiesel exhibits an ignition delay that is 7.0% shorter than diesel and a 5.2% COV,suggesting marginally increased variability in ignition delay relative to diesel, whichhas a 3.8% COV. This marginal increase in variability may have implications forlegacy engine applications of this novel fuel, since increased variability in ignition60timing can lead to greater combustion instability, especially at higher load (i.e.,longer injection duration) operating conditions. GO diesel shows no change in ig-nition delay relative to neat diesel when considering the confidence intervals com-puted from ±2 standard deviations in the measurement. A similar trend is observedin the optically determined ignition delays: n-heptane has the shortest τign,opt of1.89 ms ASOI and both diesel and GO diesel have τign,th = 2.25 ms ASOI. The shortignition delay of n-heptane may be partially caused by increased rates of vapor-airmixing due to the high volatility and relatively short liquid length observed duringinjection. The biodiesels show shorter ignition delays than neat diesel, suggestingthat the effects of fuel chemical composition on combustion chemistry dominateover the effects of vapor-air mixing since these fuels are less volatile than dieseland potentially less premixed prior to ignition. Since the upgraded bio-oil dieselhas comparable volatility to neat diesel and the biodiesels, oxygen content is likelyresponsible for the shorter ignition delay. The addition of 10 ppm GO to diesel hasno influence on ignition delay.Figure 6.7: Ignition delays determined from IHRR and integral OH*-CLanalysis.6.3 Combustion Images, Phasing, and Soot PhenomenaCombustion phenomena including HRR, combustion progress (CA10−50), and sootpropensity are considered in this section with qualitative discussion of NL andOH*-CL images. Discussion is separated into the single injection condition and61the pilot + main condition because they represent different combustion regimes,i.e., premixed and mixing-controlled combustion, respectively.6.3.1 Single InjectionThe single injection condition is a low load (∼2 bar, 1000 rpm) condition thatexhibits premixed combustion and is not representative of contemporary CI engineoperation, which typically uses multiple fuel injections to operate in the mixing-controlled combustion regime at higher loads. Legacy engines that are limited tosingle fuel injections utilize similar injection strategies, albeit at higher loads andthus longer injection durations. A relatively short injection duration was used forthis condition to avoid approaching the 110 bar maximum cylinder pressure forthe optical configuration. Referring back to Figure 6.5, combustion timing is theprimary difference between HRRs and is caused by differing fuel content. Ringingin the HRR is caused by pressure wave reflections within the combustion chamberresulting from spatial differences in ignition structure and reaction zone growth.Differences in ignition kernel locations between fuels are observed in the OH*-CL images as shown in Figure 6.8 and Figure 6.9. The images from Figure 6.8 givesome sense of the cycle-to cycle variability in ignition kernel location that is notcaptured in the ensemble averaged images shown in Figure 6.9. The images startin the top row and progress with time in each successive row, though the imagesstart at the respective start of ignition for each fuel to illustrate spatial differencesin ignition phenomena in a compact figure. Biodiesels and UBO diesel, whichhave shorter ignition delays and higher oxygen content than neat diesel, appearto predominantly begin ignition in the fuel jet region closer to the injector beforethe fuel-air mixture impinges upon the piston bowl walls. The reaction zone tendsto propagate toward the piston bowl walls where the remainder of fuel quicklycombusts. Delayed ignition of the fuel that has impinged upon the piston bowlmay be caused by heat losses from the fuel to the piston. Diesel and GO dieselexhibit ignition kernels around the piston bowl wall, which then propagate aroundthe bowl and inward toward the unburned fuel-air mixture remaining in the jet axisregions.62Figure 6.8: Frame-by-frame OH*-CL images during ignition progressingfrom top to bottom. Frames are not CAD-synced across fuels, i.e., thefirst frame of diesel occurs at 4 CAD aTDC while the first frame of n-heptane ignition is at 3 CAD aTDC.6.3.2 Pilot + Main InjectionThe pilot + main condition is representative of contemporary CI engine operationat medium-low load (∼6 bar, 1000 rpm), where differences in combustion phe-nomena are observed primarily in soot concentration, with slight differences inmean combustion timing. The mixing-controlled combustion of the main injectionresults in more consistent HRR across fuels compared to the premixed single injec-tion condition, where effects of ignition delay dominate. Soot formation is causedby incomplete combustion of fuel due to richer local equivalence ratios than thesingle injection condition.The mixing-controlled main injection exhibits comparable HRR for all fuels.The pilot + main HRR are presented in Figure 6.10 along with injection signals.While the premixed pilots observe ignition delays similar to those seen in the sin-gle injection condition, HRR timing is consistent for the main injection because63Figure 6.9: Ensemble averaged OH*-CL images during ignition progressingfrom top to bottom. Frames are not CAD-synced across fuels, i.e., thefirst frame of diesel occurs at 4 CAD aTDC while the first frame of n-heptane ignition is at 3 CAD aTDC. Ignition kernels for biodiesels areobserved in the jet axis regions closer to the injector compared to neatand GO diesel, which appear to ignite along the piston bowl wall. UBOdiesel and n-heptane exhibit some ignition and combustion in the jetaxis regions, but less than the biodiesels.it occurs in the turbulent, injection-driven, mixing-controlled combustion regime.A thermodynamic measure of combustion progress, CA10−50 is given as the crankangle degrees elapsed between 10% and 50% of total energy released during com-bustion. The CA10−50 timing is consistent within 0.13 ms across all fuels. UBOdiesel exhibits the longest CA10−50 of 1.48±0.02 ms, followed by neat and GOdiesel at 1.43±0.02 ms and 1.43±0.03 ms, n-heptane at 1.41±0.02 ms, CME at1.39±0.02 ms, and SME at 1.35±0.02 ms, where ±2 standard errors are presented.This results in a maximum difference in mean CA10−50 timing of 8.7% betweenSME and UBO diesel, which both have COV of 5.4% and 5.2%, respectively. Thedecreased rate of combustion for UBO diesel is consistent with findings from theliterature that show bio-oils to have longer burnout times compared to petroleum64Figure 6.10: Heat release rates for the pilot + main injection operating con-dition. Differences in pilot ignition behaviour do not affect main com-bustion timing.fuels [16].The primary differences in combustion phenomena for the pilot + main con-dition are seen in soot formation and oxidation due to differences in fuel compo-sition. HRR, IHRR, soot concentration (KL) and soot temperature are shown inFigure 6.11. Biodiesels and n-heptane show drastically reduced peak soot cloudoptical density relative to diesel. Graphene oxide doped diesel and neat dieselshow comparable peak KL values of 1.16±0.22 and 1.14±0.01, respectively. Theaddition of 0.001% graphene oxide to diesel has negligible effect on rates of in-cylinder soot formation and oxidation. The peak KL values for CME and SMEare 0.41±0.05 and 0.60±0.06, respectively, which are a 64% and 47% reductionrelative to diesel. The peak KL for UBO diesel is 0.85±0.11, a 25% reductionfrom neat diesel. The fuel-bound oxygen in biodiesels inhibits in-cylinder sootformation and promotes oxidation, consistent with findings that show reduced sootemissions of biodiesels relative to petroleum diesel [49, 73]. While it was hypoth-esized that oxygen content in the UBO diesel would play a role in reducing sootconcentration, the uncertainty of oxygen content in UBO diesel makes it difficultto understand whether this hypothesis is supported. Despite an uncertain cause,65the decrease in in-cylinder soot concentration relative to neat diesel implies thatUBO diesel may still reduce exhaust soot emissions, which has positive implica-tions for improving air quality and slowing climate change [74]. n-Heptane showsa peak KL value of 0.49±0.10, a 57% reduction relative to diesel. Soot productionis inhibited since n-heptane is aliphatic, i.e., there is no aromatic content.Figure 6.11: Heat release rates and pyrometry data for the pilot + main injec-tion operating condition. Diesel and GO diesel exhibit the highest sootcloud density of the fuels tested.In-cylinder soot cloud temperature represents a close approximation of theflame temperature, which has implications for thermal NOx formation. The peaksoot cloud temperature for diesel and GO diesel were 2386 K and 2372 K. CME66and SME have peak temperatures of 2330 K and 2313 K, respectively. The peaksoot cloud temperature of n-heptane was 2287 K, representing a maximum differ-ence in peak temperature of 4.1% across fuels. While the reduced flame tempera-tures of the biodiesels and n-heptane may reduce the thermal NOx that is formedduring combustion, other NOx formation mechanisms may contribute to the occa-sionally higher NOx emissions of biodiesels relative to neat diesel observed in theliterature [48, 73].Figure 6.12: Single cycle OH*-CL images of flame development for the mainfuel injection. Note the absence of strong OH*-chemiluminescence inthe lift-off region for the diesel and blended diesels compared to theinjector-attached signal in the biodiesel and n-heptane images.Images of OH*-CL are assessed qualitatively for the pilot + main operatingcondition since neither signal directly correlates with HRR or flame temperaturefor mixing-controlled combustion. OH*-CL images are presented in Figure 6.12and Figure 6.13 in 2 CAD increments from 0.8 to 16.9 CAD aTDC of a singlecycle. Of particular interest is the presence of injector-attached OH*-CL signal67for the biodiesels and n-heptane. Diesel and the two additive diesels show flamelift-off lengths, that is, regions of zero (or near zero) OH*-CL signal close to theinjector orifices. See the regions circled in red in Figure 6.12 for demonstration ofthe injector-attached OH*-chemiluminescence in the biodiesels and n-heptane andthe presence of a flame lift-off length for neat diesel and the diesel blends. Thelift-off length region may not be actively undergoing fuel oxidation, which is thesource of OH*-CL and signifies the location of the flame front. The oxygen contentand high volatility of the biodiesels and n-heptane, respectively, may be the reasonfor OH*-CL signal appearing immediately adjacent to the injector. Since the OH*-CL images are scaled to the same intensity range, the increased peak signal in theUBO diesel images is also of note, though its significance is not immediately clearsince it does not correspond to a higher peak HRR. Quantitative analysis of OH*-CL images is obfuscated by window fouling caused by soot that accumulates overthe test duration.Figure 6.13: Single cycle OH*-CL images of mid- and late-cycle combustionfor the main fuel injection.68Figure 6.14: Ensemble averaged NL images of flame development for themain fuel injection.Ensemble averaged NL images are provided for further qualitative discussionof soot temperature and concentration during mixing-controlled combustion. Im-ages from 0.8 to 8.8 CAD aTDC are presented in Figure 6.14. There is somecorrelation with flame temperature and soot formation since the primary contrib-utor to NL is soot incandescence, but quantitative analysis is not available for thebroadband visible spectrum imaging that was performed. Regions of light attenu-ation around the piston bowl circumference are caused by soot deposition over thespan of 15 cycles in the ensemble-averaged images. The reduced size and inten-sity of the attenuation regions in the CME, SME, and n-heptane images supportthe pyrometry data that show reduced soot concentrations. Since the reduction insoot concentration for the UBO diesel is not as significant as the highly oxygenatedbiodiesels and aliphatic n-heptane, differences between the ensemble averaged NLimages of neat and UBO diesel combustion are not as clear. An additional contribu-tion to reduced NL signal for n-heptane is the 57% reduction in soot concentrationand the 100°K reduction in soot temperature relative to diesel, causing less incan-descence overall.696.4 SummaryThe experimental methodology developed in this work shows some promise at en-abling comparative assessment of fuel performance in an optical CI engine. Fuelcomposition was observed to primarily influence ignition delay during premixedcombustion and soot propensity in mixing-controlled combustion, with combustionphasing remaining relatively unchanged for the pilot + main condition. Biodieselsdemonstrated reductions in peak KL values of 47-64% relative to diesel. UBOdiesel exhibited a 25% reduction in peak KL compared to diesel, while n-heptaneexhibited a 57% reduction in peak KL. All of the fuels considered here (GO dieselexcepted) demonstrate potential reductions in soot emissions, which is beneficialfor combating air pollution and climate change. Liquid length is suspected to af-fect fuel-air mixing enough to cause a shorter ignition delay for n-heptane. Theinfluence of fuel chemical content on shortening ignition delay dominates over liq-uid length for the biodiesels and upgraded bio-oil diesel, which have comparableor lower volatility than neat diesel. UBO diesel was shown to have a marginallyhigher variation in ignition delay than neat diesel, suggesting potential incompati-bility for legacy engines operating with single fuel injections since a varied ignitiondelay can result in further combustion instability. Spatial differences in ignitionkernel location were observed in the OH*-chemiluminescence images of the sin-gle injection condition. Biodiesels demonstrated a tendency to ignite in the jetaxis region closer to the injector than diesel and GO diesel, which primarily ig-nited around the perimeter of the piston bowl. UBO diesel and n-heptane showedsome ignition in-between the bowl perimeter and injector. Understanding wherefuels tend to ignite may have applications for engine manufacturers interested inaltering piston bowl and injector orifice designs in order to better control fuel-airmixing. The addition of 10 ppm graphene oxide to diesel did not have an effecton any of the observed metrics. While the string potentiometer attached to the MSpiston rod was able to provide coarse measurements of fuel consumption rates, thelow signal-to-noise ratio and temporal resolution of the potentiometer resulted insignificant measurement uncertainty, thus limiting confidence in observed differ-ences in equivalence ratio and indicated efficiency between fuels. Compiled keyresults of injection spray and combustion analysis are given in Table 6.2 where70mean values are presented with ±2 standard errors.Table 6.2: Key Injection and Combustion MetricsFuel Ll αl τign,th τign,opt KLmax[mm] [°] [ms ASOI] [ms ASOI] [-]Diesel 34.6±0.1 15.1±0.8 1.85±0.02 2.25±0.02 1.14±0.01CME 36.7±0.1 14.3±0.6 1.72±0.01 1.99±0.02 0.41±0.01SME 38.5±0.1 15.5±1.0 1.72±0.02 2.00±0.02 0.60±0.02n-Heptane 14.8±0.1 9.4±0.4 1.60±0.01 1.89±0.02 0.49±0.03GO Diesel 34.9±0.1 16.0±0.9 1.81±0.02 2.25±0.02 1.16±0.06UBO Diesel 35.8±0.1 15.3±0.7 1.72±0.02 2.12±0.03 0.85±0.0371Chapter 7ConclusionsThis study of injection and combustion phenomena for direct injected novel, com-mercial, and reference fuels contributes to the understanding of low-carbon fuelperformance in compression ignition engines and expands experimental character-ization techniques for new fuels. An optical engine experimental methodology wasdeveloped using a low-volume, high-pressure fuel system for the comparative as-sessment of injection spray liquid length, cone angle, ignition delay, combustionphasing, soot concentration and temperature with additional qualitative analysisof ignition kernel locations and flame structures, which are precursors to the ex-haust emissions that can be characterized in conventional thermodynamic enginestudies. A flexible, 260 mL capacity fuel system called the media separator (MS)was designed to enable direct injection of alternative fuel samples at high pressuresinto an optically accessible CI engine equipped with an in-cylinder pressure trans-ducer and local three-colour pyrometry probe. Two engine operating conditionswere identified for characterizing performance of reference fuels (i.e., diesel andn-heptane), commercially available biodiesels (i.e., canola and soybean methyl es-ters, CME and SME, respectively), and novel fuels (i.e., diesel doped with a 10ppm mass loading of graphene oxide (GO) and upgraded pinewood fast pyrolysisbio-oil (UBO) blended with diesel at a 10:90 volume ratio). A low-load singlefuel injection enables observation of ignition phenomena and premixed combus-tion, and a medium-load condition uses pilot and main fuel injection to representcontemporary CI engine operating strategies with emphasis on in-cylinder soot72concentration. Given the small volumes of novel fuels available for experimentalcharacterization, constant injection durations were used at each operating condi-tion for all fuels with an understanding that total fuel energy consumed would varydue to differences in LHV.Externally illuminated injection imaging was used to examine the liquid lengthand cone angle of fuel sprays, which may have implications for fuel-air mix-ing, ignition delay, and potential instances of cylinder wall wetting. A linearcorrelation was identified between liquid length and 90% distillation temperature(R2 = 98.2%) as well as with kinematic viscosity at 40°C (R2 = 95.7%), i.e., longerliquid lengths were observed for less volatile and more viscous fuels. Despite thehigh coefficients of determination for the linear correlations, the fuels consideredcomprise two clusters of data points with a gap in fuels with intermediate volatili-ties and viscosities, thus weakening confidence in the linearity of these correlations.The liquid lengths of CME and SME also limit the confidence in these correlationssince liquid droplets were observed to impinge upon the piston bowl walls, sug-gesting that larger maximum liquid lengths may be observed if the piston bowldiameter were increased. The observation of piston bowl wetting also suggeststhat cylinder wall wetting may occur for early-cycle injection of fuels with lowervolatility, which has negative implications for combustion efficiency, exhaust emis-sions, and lubricant performance [68]. Correlations between cone angle and fuelproperties were obfuscated by large frame-to-frame and cycle-to-cycle variabilityin cone angle.Differences in ignition behaviour are observed in the single injection operatingcondition, which has implications for legacy engines that have less flexibility forinjection parameters. Ignition delays are determined thermodynamically using athreshold of 5% of integrated heat released and optically using 5% of integratedOH*-chemiluminescence. n-Heptane shows a 13.6% shorter ignition delay thandiesel, which had the shortest and longest ignition delays, respectively. The rela-tively short liquid length of n-heptane supports the hypothesis of increased fuel-airmixing in the vapor phase resulting in shorter ignition delay. UBO diesel showsa 5.2% COV for ignition delay, which is a marginal increase in ignition variabil-ity relative to the 3.8% COV exhibited by diesel. Because of this slight increasein variability of ignition timing for UBO diesel, the fuel requires further exami-73nation under premixed combustion before implementation in legacy engines canbe recommended. Differences in combustion chemistry due to fuel compositionplay a dominant role in shortening ignition delay since UBO diesel and biodieselshave shorter ignition delays than neat diesel despite comparable or longer liquidlengths. No differences in ignition delay were observed for GO diesel relative toneat diesel, suggesting that GO doping must exceed 10ppm by mass for ignitionbehaviour to change. Qualitative differences are observed in both single-cycle andensemble averaged images of OH*-chemiluminescence: diesel and GO diesel ig-nite and combust primarily around the walls of the piston bowl, while biodieselsignite and combust mostly in the jet axis region closer to the injector orifice. Com-bustion of UBO diesel and n-heptane occurs partially in the jet axis region butalso around the bowl walls. The qualitative differences in reaction zone structuresupport the conclusion that premixed combustion is influenced by both changesin rates of fuel-air mixing from different physical properties as well as changes incombustion chemistry caused by varied chemical compositions and stoichiometricair-fuel ratios. The spatial differences in combustion have implications for pistonbowl and injector orifice design for the use of alternative fuels to promote fuel-airmixing and improve combustion efficiency.In-cylinder soot concentration is the primary difference observed in combus-tion behaviour between fuels in the pilot and main operating condition. The useof a short pilot fuel injection preheats the combustion chamber and reduces thetotal energy released during premixed combustion, which is highly variable andcauses greater changes in pressure than the mixing controlled combustion that oc-curs during main fuel injection. Peak in-cylinder soot concentration for UBO dieselwas reduced by 25% relative to neat diesel. Soot concentrations for oxygenatedSME, CME, and aliphatic n-heptane were reduced relative to diesel by 47%, 64%,and 57%, respectively. The addition of 10 ppm GO to diesel had no effect onsoot cloud optical density. Reductions in soot concentration reflect a combineddecrease in soot formation and increase in oxidation for the fuels with increasedoxygen content and decreased aromatic content relative to diesel, though the rela-tive contributions of changes in formation and oxidation are not quantified in thiswork. Other works have demonstrated correlations between exhaust emissions ofsoot with in-cylinder soot concentration [61].74The data collected at the operating conditions in this work act as a starting pointfor the development of a database of fuel injection and combustion behaviour thatcan be expanded with further engine characterization of other novel fuels. Thisdatabase will assist in validating numerical combustion models aimed at reducingGHG emissions from heavy-duty CI engines. Additional fuels can be consideredbecause of the broad material compatibility of the MS fuel system.The primary outcome of this work is the development of an experimental meth-odology utilizing an existing optical diesel engine and a novel, low-volume fuelsystem to assess combustion characteristics of fuels. The methodology has beenapplied here to several reference and alternative fuels to understand quantitativedifferences in injection, ignition, and combustion phenomena including soot for-mation and oxidation. Qualitative analysis of combustion images provides guid-ance for numerical modeling and may be useful for engine manufacturers interestedin altering piston bowl and injector geometries and operating strategies to increasecombustion efficiency and decrease GHG and pollutant emissions for alternativefuels.7.1 Future WorkIt is recommended to implement a higher fidelity technique to measure the po-sition of the MS piston rod to increase confidence in the fuel mass consumptionrates, global equivalence ratios, and indicated efficiencies. Confidence in reportedfuel consumption rates is limited in this work due to the relatively low temporalresolution (100 Hz) and signal-to-noise ratio of the MS string potentiometer. Alinear variable differential transformer (LVDT) may provide improved measure-ment frequency (1-10 kHz) and for measuring the displacement of the MS pistonrod. Challenges with using an LVDT include the high cost relative to string poten-tiometers, added considerations for mounting and alignment, and the requirementfor shielding from external magnetic interference.Steady-state operation in the thermodynamic configuration of the research en-gine is recommended for validation of the results from this study and examinationof exhaust emissions. Steady-state operation would offer increased confidence inthe observed metrics and provide new understanding of exhaust emissions, which75can not be easily measured with the skip-fired optical engine operation. This testingis heavily dependent upon scaling up novel fuel production as well as conductingmaterial compatibility testing with fuel system components. Testing was confinedto the optical configuration in part due to small sample sizes of novel fuels aswell as concerns over corrosion damage to fuel system infrastructure such as highpressure pumps and direct injectors with precision geometries. Previous workscharacterizing UBO diesel blends resulted in fuel pump failures due to corrosioncaused by high acid content in the bio-oil.Further optical engine tests with iteration on injection duration would deepenthe understanding of the effects of fuel mass and energy on the metrics investigatedin this work. The decision to hold injection duration constant for this study wasmotivated in part by the understanding that novel fuel sample volumes would belimited. Iterating tests to match fuel energy injected may increase confidence inthe conclusions drawn herein.To broaden the applicability of the data collected, further testing of alternativefuels should use operating conditions included in the World Harmonized Stationaryand Transient Cycles (WHSC and WHTC, respectively), two regulatory emissionstest cycles used for heavy-duty vehicles. The operating conditions selected forthis work were intended to represent a medium-load condition for contemporaryCI engines and a low-load condition for engines limited to single fuel injections.Using operating conditions that are part of the WHSC and WHTC would improvethe ease of validating results and comparing with outcomes from other works sincethese cycles are standardized and used internationally.Characterizing single injection operating conditions at higher loads (i.e., longerinjection durations) would improve the relevance to older engines with mechan-ically actuated injectors. 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The rodseal was observed to fail at low pressures (sim20 bar), causing a steady stream ofdiesel to leak out of the piston rod bore on the driven side end-cap. The MS wasthen disassembled to assess whether the rod seal had any visible damage. Upondisassembly, negligible signs of rod seal damage were observed.Figure B.1: MS rod seal in the prototype end-cap upon installation (left) andafter catastrophic failure (right).After replacing the rod seal, the diesel pressure testing was repeated. Similarbehavior was observed at around 20 bar, with diesel once again leaking out the88top of the end-cap. Per the recommendations of the seal manufacturer, the railpressure was set to 200 bar to see if the seal would seat at a higher pressure and stopleaking. The rail pressure fluctuated within 50 bar of the set point (from sim150bar to sim250 bar), and the piston rod was observed to oscillate up and down untilthe rod seal experienced a catastrophic failure by bursting. A loud pop was heardand a cloud of diesel droplets was observed emanating from the piston rod bore inthe driven end-cap.Analysis of the seal failure mode suggests that it was likely caused by a com-bination of damage incurred during installation, extrusion caused by high fluidpressures and large hole/shaft clearance, and insufficient bleeding of air pocketsprior to pressurizing. The installation of the rod seal in the prototype end-cap re-quired plastic deformation of the PTFE sealing ring (see Figure B.1), which likelycontributed to degraded sealing performance. The wide pressure fluctuation andpiston oscillation were most likely caused by an insufficient procedure for bleed-ing air pockets out of the media separator plumbing. Large volumes of air may havebeen compressed by orders of magnitude, causing the control system dynamics forthe common rail to change significantly from what was expected.89Appendix CMedia Separator AssemblyThe MS end-caps are tightened to 120 N-m using a torque wrench. This preloadspecification was selected to protect against the end-cap threads unseating due tothe maximum working pressure of 1200 bar. Anti-sieze compound was applied tothe end-cap threads prior to assembly to avoid galling. 20.50 13.20 45.00 46.50 11.00 41.00 37.00 AA 5.00 0.75 SECTION A-AA AB B2211Drawn ByCheckedByIsaac BeckerDate 2/8/21Units mm Piston Ring Tool w/ TabSheet 1 of 1Figure C.1: Tapered tool for stretching PTFE rings onto MS piston.Viton seals have a broad range of material compatibility, so they were installedfor diesel, CME, SME, and n-heptane testing. FFKM seals were used with the up-graded FPO because of the high acid number of the fuel, 68 mg KOH/kg. Since thecarbon-PTFE rings in the piston seals are difficult to evenly stretch for installation,a conical tapered ring stretching tool is used to facilitate piston seal installation(see Figure C.1). Once the inner diameter of the PTFE ring is wider than the pistondiameter, it can easily slide into position around the Viton o-rings. A 45 mm hoseclamp is used to tighten the PTFE ring back to the desired dimensions for adequate90sealing prior to installing the piston inside the cylinder.91
Thesis/Dissertation
eng
Mechanical Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Kirchen, Patrick
Optical engine characterization of reference and novel fuels using a small-volume fuel system
Text