PARTICLE MATTER EMISSION CONTROL AND RELATED ISSUES FOR DIESEL ENGINES by Jun Zhang A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Mechanical Engineering The University of Birmingham November 2010 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties.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 The particulate matter is probably one of the most critical issues of the diesel engine emissions. After years of research, people begin to understand it further, with respect to its impact on the environment and human health, its formation mechanism inside and outside the diesel engine, and most importantly, the methods to control its formation. This study has focused on the particulate matter emission control in diesel engines. It started with the application of two closely coupled Diesel Particle Filters (DPFs), consisting of an assistant DPF and a main standard honeycomb DPF, to replace the standard Diesel Oxidation Catalyst (DOC) + DPF system, commonly applied on diesel engines these days. This new after-treatment system showed a great potential to be adopted in the future, not only for the tighter emission regulations but also for the great cost reduction of the total after- treatment system by the reduction of the main DPF‘s size and weight and more options of other cheaper materials. The back pressure problem revealed in the experiment was then studied through a one dimensional model simulation and its influence to the engine performance was discussed. Fuel injection parameters which are related with the engine performance and emissions were also investigated in the study. After careful calibrations, a single injection induced Partially Charge Compression Ignition (PCCI) combustion was achieved, in which mode, NOx and smoke emissions were reduced by more than 80% compared with using the normal multiple injections. Following that, the non-volatile particulate emissions under the pilot injection‘s impacts were studied and the key parameters of the pilot control such as fuel quantity and 1 injection timing were examined. The particulate number concentrations and size distributions were investigated under different engine operation conditions and the results illustrated how a pilot injection alongside a main injection could influence particulates and what these effects were closely related to. The research continued with the investigation of bio-fuels on the particle emission reduction, when 10% alternative diesel fuel blends (Rapeseed Methyl Ester (RME) and Gas- to-Liquid (GTL)) were used. They indicated that without any modification to the engine, adding selected alternative fuels, even at a low percentage, could result in a noticeable reduction of the particle numbers, both in the total and the non-volatile parts; however, the number of nucleation mode particles could increase in certain cases. It was also revealed that the engine suffered very high numbers of the nucleation mode particulates during warming up. 2 ACKNOWLEDGEMENTS I would like to thank my supervisor Professor Hongming Xu for his guidance and encouragement throughout all my study. I thank my associate supervisor Professor Miroslaw Lech Wyszynski and also Dr Athanasios Tsolakis for their helpful suggestions. I would also like to express my gratitude to Thomas Gardiner from Jaguar Land Rover (JLR) for his technical support towards the research project, Sathaporn Chupeng for his kind help during my first year of study, Haiwen Song and Phil Price from Ford Motor Company Limited and Roger Cracknell from Shell Global Solutions UK for their technical advice. I acknowledge Dr Guohong Tian, Dr Mingshan Wei, and Dr Shaohua Zhong for their great help during my study, Dr Rizalman Mamat for his valuable discussions during my Wave model development, Dr Hanshan Dong from the Department of Materials and Metallurgy for his kind supply of the furnace for the DPF regeneration. A special thank goes to my friends and colleagues in the FPS group: Yanfei Li, Haiying Li, Fan Zhang, He Ma, Xuesong Wu, Paul Rounce, Ritchie Daniel, Nik Rosli Abdullah for their great support to my study as well as my social life. 3 I wish to dedicate this thesis to my families and friends for their love and great supports along the way 4 TABLE OF CONTENTS CHAPTER 1 INTRODUCTION…………………………………………………….…...26 1.1 Background…………………………………………………………….…...26 1.1.1 Diesel Engine Combustion………………….…................................27 1.1.2 Diesel Engine Emissions………………….…...................................27 1.1.3 Overview of the Diesel Engine Emission Regulation and Controls..29 1.1.4 The Diesel Engine After-treatment System ……………………..…31 1.1.5 New Fuels and Their Blends ………………….…………….……...32 1.1.6 New Fuel Injection and Combustion Strategies ………..…….….....33 1.2 Objectives and Approaches…………………....….………………………...34 1.3 Thesis Outline……………………………………………………………....34 CHAPTER 2 LITERATURE REVIEW……………………………………...………….36 2.1 Engine Emission Toxicity and Regulations ………….…….........................36 2.1.1 The Toxicity of the Engine Emissions ………………………..........37 2.1.2 Global Automotive Emission Regulations……………………….....38 2.2 Particulates…………………………….……………………….....………...39 2.2.1 The Mechanism of Engine Particulate Formation ……………........41 2.2.2 Particulate Measurement …………………….…….…….…….…...43 2.2.3 Diesel Engine Particulates …………………….…….......................45 2.3 Diesel Particulate Filter (DPF).………………………….….........................47 2.3.1 DPF Regeneration …………………………….……………………48 2.3.2 New DPF Configuration and Materials ……………………….…...49 2.4 New Injection Strategies for Diesel Engines …………..……….…….……51 5 2.4.1 Multiple Injection Strategies ………………………………………52 2.4.2 Exhaust Gas Recirculation (EGR)……….………………..………..53 2.4.3 LTC, HCCI and PCCI Combustion……….………………..………54 2.5 Alternative Fuels for Diesel Engines …………..……….………...………..56 2.5.1 Biodiesel …………………………………….……………………...56 2.5.2 Gas to Liquid (GTL) Diesel ……….………………..……………...59 2.5.3 Combined Alternative Fuels with New Injection Strategies ……….61 2.6 Summary…………….……………………………………………………...62 CHAPTER 3 RESEACH METHODOLOGY..………………………………………....63 3.1 Engine and Instrumentation……….…………….………………………….64 3.1.1 Engine….…………………………………………………………...64 3.1.2 Engine Start and Control System …………………………..............65 3.1.3 Dynamometer…………………………….………............................68 3.1.4 Dynamometer Control System ……………………………….…….70 3.1.5 In-cylinder Pressure Data Acquisition ………………………….….74 3.1.6 Temperature and Pressure Measurement …………………………..77 3.1.7 The Fuel and the Fuelling System ………….....................................79 3.1.8 Cooling System …………………..………………………………...80 3.2 Exhaust Measurement……………..…………….………………………….81 3.2.1 Engine Exhaust Gas Emissions ……………….……………………81 3.2.2 Engine Smoke Emissions …..............................................................82 3.2.3 Engine Emission Particulate Number Size Distribution ….………..83 3.2.4 Diluter ……………….……………………………………………..85 3.2.5 Scanning Electron Microscope (SEM)……………………………..87 6 3.3 DPF Regeneration……………………………………..................................88 3.3.1 Furnace ……………….…………………………………………….88 3.3.2 Arvin Meritor Vaporizer ……………….…………………………..88 3.4 One Dimensional Engine Model …………………………………………...90 3.4.1 Woschini Model ……………….…………………………………...90 3.4.2 Diesel Wiebe Model ……………….……………………………….92 3.5 Experimental Data Uncertainties Analysis …………….…………………..94 3.6 Summary…………….……………………………………………………...95 CHAPTER 4 APPLICATION OF TWO CLOSELY COUPLED DPFS AS THE DIESEL ENGINE AFTER-TREATMENT SYSTEM …………………96 4.1 Problems and Possible Solutions to the Current After-treatment System….96 4.1.1 Cost and Installation………………………..….……….......................97 4.1.2 Concept of Solutions to the Problems ………………..….…………..98 4.1.3 Research objective………………..….………………………………98 4.2 Engine Test Modes and Procedures……..….………………………………98 4.3 Pressure Drop along the Two Different After-treatment Systems………...101 4.3.1 Transient test A………………………………………….……..….101 4.3.2 Transient test B………………………………………….……..….104 4.3.3 Steady State Test………………………………………….……….106 4.4 Emissions along the Two Different After-treatment Systems…………….107 4.4.1 Gaseous Emissions………………………………….……………..107 4.4.2 Smoke Emissions………………………………………….………108 4.4.3 PM Characteristics…………………………….…………………..109 4.5 Impact of the Exhaust Back Pressure on the Engine Performance ……….112 7 4.5.1 One Dimensional Diesel Engine Model Set up …………………..112 4.5.2 Model Validation………………………………….………………115 4.5.3 Model Application………………………………….……………..116 4.6 Summary…………….…………………………………………………….119 CHAPTER 5 PM CHARACTERISTICS WITH SINGLE INJECTIONS…………..122 5.1 Fuel Injection Impact on the Engine Performance and Emissions………..122 5.1.1 Fuel Injection Parameters……………….…………………………123 5.1.2 Engine Test Modes……………….………………………………..124 5.1.3 Main Injection Timing……………………….……………………124 5.1.4 EGR………………………………………………………………..127 5.1.5 Injection Pressure………………………………………………….129 5.2 Single Injections VS Multiple Injections………………………………….131 5.3 PCCI Combustion with Single Injections ………………………………...137