EXPERIMENTAL STUDY OF THE IMPACT OF PORT AND DIRECT FUEL INJECTION STRATEGIES ON THE EFFICIENCY, PERFORMANCE AND EMISSIONS OF A DOWNSIZED GDI ENGINE A thesis submitted for the degree of Doctor of Philosophy by Reza Golzari Department of Mechanical and, Aerospace Engineering College of Engineering, Design and Physical Sciences Brunel University London United Kingdom November 2018 Abstract In recent years after the introduction of gasoline direct injection (GDI) engines, gasoline engine downsizing has been widely adopted to reduce fleet CO2 emissions of passenger cars. These engines are typically boosted direct injection gasoline engines equipped with variable valve timing systems for both intake and exhaust valves. Fuel consumption reduction in these downsized engines is achieved by operating more at higher brake mean effective pressure (BMEP) area of the engine map in order to reduce pumping losses and through reducing cylinder numbers to decrease total friction losses. However, the degree of downsizing and compression ratio (CR) of these engines are constrained by thermal stresses and knocking combustion as well as the low speed pre-ignition phenomena. In addition, combustion efficiency and emissions in these GDI engines can be improved further by better in-cylinder mixture preparation (in terms of homogeneity and temperature). To overcome these limitations, technologies such as dual injection systems, cooled external exhaust gas recalculation (EGR), Atkinson and Miller cycle, variable compression ratio (VCR) and water injection have been found to be highly effective in improving the combustion processes and reducing pollutant emissions. The present work investigates the impact of port and in-cylinder fuel injection strategies as well as intake port injection of water on boosted downsized GDI engine combustion, efficiency and emissions. A single cylinder direct injection gasoline engine and its testing facilities were used for extensive engine experiments. Various PFI / DI injection strategies were tested, and the results compared to the baseline PFI only and DI only strategies. Intake port injection of i water also was investigated at different water/fuel ratios and with gasoline with three different research octane numbers (RON). The experiments were performed at several steady state points to determine the optimal strategy for improved engine fuel economy in real applications. The results show that PFI / late DI and early DI / late DI strategies can reduce the net indicated specific fuel consumption (NISFC) significantly by a maximum of 9% at low speed / mid-high load compared to the baseline due to the reduction of end of compression temperature and therefore advancement in knock limited spark timing. Smoke emissions were also lower under PFI / late DI, PFI / early DI, and PFI only operations compared to early DI / late DI, and DI only operations due to the improvement in mixture preparation. In addition, the results showed that PFI / late DI and early DI / late DI extend the lean limit from 1.5 to 1.7 at 1000 rpm / 8.83 bar net indicated mean effective pressure (NIMEP) due to a more advanced combustion phasing and shorter combustion duration compared to the baseline PFI only and DI only operations. Water injection results show net indicated efficiency improved significantly by a maximum of around 5% at medium load and around 15% at high load when increasing the injected water mass. Improvement in efficiency was mainly due to the increased heat capacity of charge (higher specific heats of water and increased in-cylinder mass) and the cooling effect of the injected water evaporation which reduced the in-cylinder pressure and temperature. Thus, knock sensitivity was reduced and more advance spark timings could be used which shifted the combustion phasing closer to the optimum point. However, increasing the water ratio further (more than 1 at medium load and more than 1.5 at high load) deteriorated the combustion efficiency, prolonged the flame development angle ii and combustion duration, and caused a reduction in the net integrated area of the P-V diagram. Comparison of fuels of different RON also reveals that water injection can virtually increase the RON of fuel, therefore makes it possible to run on a low octane number fuel and achieve higher efficiency by adjusting the water mass. In terms of other, harmful, non-CO2 emissions, water injection was effective in reducing the NOx (by a maximum of around 60%) and particle emissions significantly but increased the HC emissions as the water/fuel ratio increased. In addition, water injection also reduced the exhaust gas temperature by around 80 °C and 180 °C at medium and high loads, respectively. iii Acknowledgment I would firstly like to express my thanks and upmost respect to my supervisor, Professor Hua Zhao, for giving me the vital guidance and support in the last four years and the opportunity to work in one of the most renowned engine research groups in the UK (Centre for Advanced Powertrain and Fuels Research). I am deeply grateful to the assistance and technical support of the technicians Andy Selway and Eamon Wyse. Their commitment and perfectionism were simply exceptional. I would like to extend my special thanks to Justin Mape, Tony Cains, Jonathan Hall and Dr Mike Basset from Mahle Powertrain, and Dr John Williams from BP Technology Centre for giving me advice and support on many occasions. To all my friends and colleagues, you not only helped me in my studies but were also valuable companies and a source of motivation. Finally, and perhaps the most important, is the love and support of my family and my girlfriend which greatly helped me and kept me motivated during my PhD and all the years of my education. Without this support, I could not have coped, I owe you so much. iv Nomenclature Abbreviations ABDC After Bottom Dead Centre AFR Air Fuel Ratio APV Alternatively-Powered Vehicles ATDC After Top Dead Centre BBDC Before Bottom Dead Centre BDC Bottom Dead Centre BLD Borderline Detonation BMEP Brake Mean Effective Pressure BSFC Brake Specific Fuel Consumption BTDC Before Top Dead Centre BTDCF Before Top Dead Centre Firing BTDCNF Before Top Dead Centre Non-firing CA Crank Angle CA10 Crank Angle at 10% Mass Fraction of Mixture Burned CA50 Crank Angle at 50% Mass Fraction of Mixture Burned CA90 Crank Angle at 90% Mass Fraction of Mixture Burned CAD Crank Angle Degrees CAFE Corporate Average Fuel Economy CAI Controlled Autoignition CFD Computational Fluid Dynamics CI Compression Ignition v COV Coefficient of Variation CR Compression Ratio DAQ Data Acquisition DI Direct Injection eBoost Electrical Boosting ECU Electronic Control Unit ECV Electrically-Chargeable Vehicles EGR Exhaust Gas Recirculation EMOP Exhaust Maximum Opening Point EMS Engine Management System EOI End of Injection EOI2 End of Second Injection EPA Environmental Protection Agency EVC Exhaust Valve Closing FID Flame Ionization Detector GDI Gasoline Direct Injection GIMEP Gross indicated Mean Effective Pressure HCCI Homogeneous Charge Compression Ignition HEV Hybrid Electric Vehicle ICE Internal Combustion Engine IEffg Gross Indicated Fuel Conversion Efficiency IEffn Net Indicated Fuel Conversion Efficiency IEffp Pumping Indicated Fuel Conversion Efficiency IMEP Indicated Mean Effective Pressure IMOP Intake Maximum Opening Point ISFC Indicated Specific Fuel Consumption vi IVC Intake Valve Closing IVO Intake Valve Opening KI Knock Intensity LIVC Late Intake Valve Closing LIVO Late Intake Valve Open LSPI Low Speed Pre-ignition MBT Minimum spark advance for Best Torque MFB Mass Fraction burn NA Naturally Aspirated NEDC New European Driving Cycle NI National Instruments NIMEP Net Indicated Mean Effective Pressure NISFC Net Indicated Specific Fuel Consumption NOx Nitrogen Oxides PFI Port Fuel Injection PID Proportional Integral Derivative PM Particulate Matter PMEP Pumping Mean Effective Pressure PN Particulate Number PRT Platinum Resistance Thermometer RON Research Octane Number rpm revolutions per minute SI Spark Ignition SOI Start Of Injection TDC Top Dead Centre UEGO Universal Exhaust Gas Oxygen vii ULG Unleaded Gasoline US United States VVA Variable Valve Actuation VVT Variable Valve Timing WOT Wide Open Throttle Symbols M Molecular weight n Polytropic exponent/specific heat ratio RON Research octane number p In-cylinder pressure, pressure pf Pressure feedback pn Predicted pressure Δp Change in pressure ΔT Temperature difference V Volume Chemical Abbreviations CO Carbon Monoxide CO2 Carbon dioxide H Hydrogen atom N Nitrogen atom N2 Nitrogen NO Nitric oxide NO2 Nitrogen dioxide O Oxygen atom O2 Oxygen viii THC Total hydrocarbons ix Contents Abstract .............................................................................................................. i Acknowledgment .................................................................................................. iv Nomenclature........................................................................................................ v Abbreviations ..................................................................................................... v Symbols .......................................................................................................... viii Chemical Abbreviations .................................................................................. viii List of figures...................................................................................................... xvi List of tables ....................................................................................................