AN EXPERIMENTAL INVESTIGATION OF LEAN-BURN DUAL-FUEL COMBUSTION IN A HEAVY DUTY DIESEL ENGINE A thesis submitted for the degree of Doctor of Philosophy by Ian Alexander May Department of Mechanical, Aerospace and Civil Engineering College of Engineering, Design and Physical Sciences Brunel University London May 2018 II Abstract Natural gas is currently an attractive substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. This is primarily attributed to its cost effectiveness, but also its ability to reduce the amount of CO2 and harmful engine pollutants emitted into the atmosphere. Lean-burn dual-fuel engines substitute natural gas in place of diesel but typically suffer from high engine-out methane (CH4) emissions, particularly under low load operation. In response to this issue, this work set out to improve upon the efficiency and emissions of a lean-burn dual-fuel combustion system in an HD diesel/natural gas engine. Thermodynamic experimental engine testing was performed at various steady- state operating points in order to identify the most effective methods and technologies for improving emissions and efficiency. Low Temperature Combustion (LTC) along with several valvetrain and injection strategies were evaluated for benefits, with special attention paid to low load operating conditions. LTC was proven to be a useful method for decreasing methane emissions while simultaneously improving engine efficiency. The benefits of LTC were a function of load with the greatest advantages experienced under medium load operation. Additionally, the low load strategies tested were determined to be effective techniques for reducing methane emissions and could possibly extend the dual- fuel operating regime to lighter load conditions. Overall, no operating condition tested throughout the engine map resulted in a brake engine-out methane emissions level of less than 0.5 g/kWh at gas substitutions greater than approximately 75%. It is suggested that the limits of this particular lean-burn dual-fuel design were reached, and that it would likely require improvements to either the combustion system or exhaust after-treatment if Euro VI emissions levels for methane were to be achieved. Keywords: Lean-burn dual fuel combustion; natural gas and diesel; low temperature combustion; Miller cycle; low carbon fuel; methane emissions . III List of contents Publications and awards related to this research ................................................ VI List of illustrations .............................................................................................. VII List of tables ...................................................................................................... XVI Acknowledgements .......................................................................................... XVII Notation ............................................................................................................ XIX Chapter One Introduction .................................................................................1 1.1 Preface .......................................................................................................1 1.2 Research Objectives ...................................................................................3 1.3 Thesis Outline .............................................................................................3 Chapter Two Literature Review ........................................................................5 2.1 Introduction .................................................................................................5 2.2 The Diesel Engine ......................................................................................5 2.2.1 History and Background .......................................................................6 2.2.2 Evolution of Diesel Engine Technology .............................................. 10 2.2.3 Diesel Engine Operation .................................................................... 15 2.3 Role of Natural Gas .................................................................................. 25 2.3.1 Natural Gas as a Fuel ........................................................................ 25 2.3.2 Current Utilisation of Natural Gas....................................................... 28 2.4 Improvement of Lean Burn Dual-Fuel Natural Gas Engines ..................... 30 2.4.1 Low Temperature Combustion ........................................................... 31 2.4.2 Low Load Operation ........................................................................... 34 2.5 Summary .................................................................................................. 36 Chapter Three Experimental Methodology ....................................................... 37 3.1 Introduction ............................................................................................... 37 3.2 Experimental Setup .................................................................................. 37 3.2.1 Engine Specification ........................................................................... 38 3.2.2 Valvetrain ........................................................................................... 43 3.2.3 Fuel Systems ..................................................................................... 45 3.2.4 Data Acquisition and Control .............................................................. 47 3.2.5 Dynamometer .................................................................................... 51 3.2.6 Emissions Measurement .................................................................... 52 3.3 Data Analysis ............................................................................................ 54 IV 3.3.1 Heat Release Analysis ....................................................................... 55 3.3.2 Overall Engine Parameters ................................................................ 57 3.3.3 Engine-Out Emission Analysis ........................................................... 59 3.4 Summary .................................................................................................. 64 Chapter Four Engine and Fuel Injector Validation .......................................... 65 4.1 Introduction ............................................................................................... 65 4.2 Motored Engine Tests ............................................................................... 65 4.3 Firing Engine Tests ................................................................................... 69 4.4 Combustion System Benchmarking .......................................................... 73 4.5 Diesel Fuel Injector Calibration ................................................................. 77 4.5.1 Experimental Setup and Methodology ............................................... 77 4.5.2 Injector Calibration and Injector Delay ............................................... 81 4.5.3 Common Rail Pressure Waves .......................................................... 84 4.6 Summary .................................................................................................. 86 Chapter Five Conventional and Premixed Dual-Fuel Combustion ................. 88 5.1 Introduction ............................................................................................... 88 5.2 Definition of Combustion Modes ............................................................... 88 5.3 Test Procedures ....................................................................................... 89 5.4 Diesel Combustion Baseline ..................................................................... 91 5.5 Conventional Dual-Fuel Combustion ........................................................ 98 5.5.1 Injection Timing and Rail Pressure Optimisation with Engine Load ... 99 5.5.2 Natural Gas Substitution .................................................................. 105 5.5.3 Engine Speed Sensitivity ................................................................. 112 5.6 Premixed Dual-Fuel Combustion ............................................................ 120 5.6.1 Low, Medium, and High Load Operation .......................................... 120 5.6.2 Conventional Dual-Fuel and Premixed Dual-Fuel Combustion ........ 135 5.7 Summary ................................................................................................ 143 Chapter Six Advanced Conventional and Premixed Dual-Fuel Operation ..... 145 6.1 Introduction ............................................................................................. 145 6.2 Methodology ........................................................................................... 145 6.3 Miller Cycle and Throttling ...................................................................... 146 6.3.1 Test Procedures ............................................................................... 146 6.3.2 Effective Compression Ratio Calculation ......................................... 148 6.3.3 Miller Cycle and Throttling ................................................................ 150 V 6.3.4 Miller Cycle at a Constant In-Cylinder Lambda ................................ 161 6.4 Internal Exhaust Gas Recirculation ......................................................... 168 6.4.1 Test Procedures ............................................................................... 168 6.4.2 Calculation of Residual Gas Fraction