COMBUSTION AND EMISSIONS OF A DIRECT INJECTION GASOLINE ENGINE USING BIOFUELS by Chongming Wang A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY The University of Birmingham School of Mechanical Engineering Sep/2014 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. ABSTRACT This thesis exams the combustion characteristics and emissions of bioethanol and two other novel biofuel candidates, 2-methlyfuran (MF) and 2,5-dimethylfuran (DMF) in a spray- guided GDI engine. The impact of fuels, injector pressure and fouled injectors on PM emissions, and oxidation of soot produced from GDI engines are also investigated. Biofuels are one part of the solutions for the renewable energy supply and emission reduction. Research interests cover detailed combustion characteristics and emissions, especially particulate matter (PM) emissions. Gasoline is used as the benchmark fuel. A spray-guided single-cylinder direct-injection (DISI) engine is used in this thesis. A Horiba MEXA-7100DEGR Gas Analyser is used to measure gaseous emissions such as hydrocarbon (HC), nitrogen oxide (NOx) and carbon monoxide (CO). Aldehyde emissions and key HCs have been investigated using the High Performance Liquid Chromatography (HPLC) and Gas Chromatography Mass Spectrum (GC-MS) techniques. A Scanning Mobility Particle Sizer (SPMS) is used to measure the particle size distributions. A Thermo-gravimetric analyser (TGA) is applied in the study of the PM composition and soot oxidation process. The combustion of DMF and MF in DISI engines demonstrates better knock resistance properties and faster burning rates compared to those of gasoline. DMF and MF have much lower fuel consumptions than ethanol due to their higher energy density. The combustion of DMF and MF produces much lower hydrocarbon (HC) and PM emissions than those of gasoline. However because of much higher combustion temperatures, their NOx emissions are significantly higher than those of gasoline, when fuel-optimized spark timings are used. This issue can be solved by either retarding ignition timing at the price of fuel consumption penalties, i or by using exhaust gas recirculation (EGR) which is more efficient and has a less negative impact on fuel economy, if it is optimized. DMF and MF produce much lower aldehyde emissions compared with gasoline and ethanol. The majority of HCs in the exhaust are unburned fuel. Toluene and benzene are detected in the exhaust; however their concentrations are relatively low. Since biofuels such as bioethanol have oxygen in their molecule, PM emissions from ethanol are lower than those from gasoline, giving it good potential in PM emission reduction. Therefore, the impact of fuels (ethanol and gasoline) on PM emissions from a GDI engine under various injection pressure and injector fouling has been studied. Particles are classified into nucleated and accumulated particles, a distinction not made by most other researchers. Results show that PM emissions vary to fuels, injection pressure, and injector fouling. Ethanol produces less PM mass emission compared to gasoline. Unlike gasoline, PM emissions from the DISI engine fuelled with ethanol are not sensitive to injection pressure. This thesis highlights the significant negative impact of fouled injectors on PM emissions when using gasoline as the fuel, and it also highlights how ethanol is able to keep PM emissions low from fouled injectors. A trade-off between particle number (PN) and PM mass emissions is observed when using ethanol. Further work has been done to investigate PM composition and soot oxidation of PM produced in a GDI engine fuelled with DMF, ethanol and gasoline. This is one of the few investigations focusing on the PM oxidation characteristics from a GDI engine. It is found that even under rich combustion and later injection timing operating conditions, soot only accounts for a small fraction (<30%) of PM mass whilst volatility components are the main contributors. Soot produced from the combustion of oxygenated fuels such as DMF and ethanol is more easily oxidized than gasoline soot due to their unique capsule type oxidation mode, smaller primary, and agglomerated particles. ii ACKNOWLEDGEMENTS This thesis would be impossible without the support of the following individuals in my PhD. I‘d like to give the sincerest gratitude to Prof. Hongming Xu for providing invaluable guidance in my PhD program. I also like to thank Prof. Miroslaw L. Wyszynski, Dr. Thanos Tsolakis for giving me useful comments in my 9, 18 and 30 month reviews; I gratefully thank the University of Birmingham for providing scholarship, supporting my PhD. Thanks go to my friends for their supporting in my daily life. I‘d like to give my special gratitude to Dr. Ritchie Daniel, Dr. Jose Martin Herreros and Mr. Thomas Lattimore for the friendship and technical support. I am grateful to our colleagues from Jaguar & Land Rover, Adam Weall, and Shell, Jens, Krueger-Venus for their support in publishing of one review paper. I also thank Shell Global Solutions UK, for the supply of fuels. Chongming Wang Sep/2014 iii I wish to dedicate this thesis To my father, Jiansheng Wang To my mother, Yuezhen Shen To my fiancé, To my sister, And friends iv CONTENTS ABSTRACT ........................................................................................................................................ i ACKNOWLEDGEMENTS ............................................................................................................. iii CONTENTS ........................................................................................................................................v LIST OF FIGURES ........................................................................................................................ viii LIST OF TABLES .......................................................................................................................... xiii LIST OF NOTATIONS ................................................................................................................. xiv LIST OF PUBLICATION ........................................................................................................... xviii CONFERENCE PRESENTATION ................................................................................................xx CHAPTER 1 ........................................................................................................................................1 1 INTRODUCTION ...................................................................................................................1 1.1 Overview ............................................................................................................................1 1.2 Objectives and Approaches ................................................................................................3 1.3 Research Outline ................................................................................................................4 1.4 Thesis Outline ....................................................................................................................5 CHAPTER 2 ........................................................................................................................................8 2 LITERATURE REVIEW .......................................................................................................8 2.1 GDI Engines .......................................................................................................................8 2.2 Gasoline in SI Engines .....................................................................................................10 2.3 Bio-ethanol, DMF and MF ...............................................................................................13 2.4 Emissions in SI Engines ...................................................................................................27 2.5 GDI Injector Deposits ......................................................................................................36 2.6 Summary ..........................................................................................................................44 CHAPTER 3 ......................................................................................................................................46 3 EXPERIMENTAL SETUP ...................................................................................................46 3.1 Engine and Instrument .....................................................................................................46 3.2 Single Cylinder Research Engine .....................................................................................48 3.3 Combustion System .........................................................................................................49 3.4 Intake and Exhaust System ..............................................................................................50 v 3.5 Fuel