This thesis presents an investigation into a novel method of estimating the air-fuel ratio of a gasoline-fuelled spark-ignition internal combustion engine. The measurement of the air-fuel ratio is important for controlling an engine to reduce exhaust emissions. In production vehicles, the air-fuel ratio is measured using an exhaust gas analyser and the exhaust emissions are reduced by using electronically controlled three-way catalytic converters, which are expensive and subject to operationallimitations such as, requiring the engine to operate with a stoichiometric air-fuel ratio. A micro-processor based engine management system monitors the engine performance and controls various engine parameters - the fuel pulse width, ignition timing, exhaust gas re-circulation etc. - to maintain strict control of the engine and ensure optimum engine performance. In the USA and UK the engine management system is also responsible for performing on-board diagnostics and warns the driver of any problems such as misfire, knocking combustion and failure of the catalytic converter. The method of measuring the air-fuel ratio presented in this thesis, termed Spark Voltage Characterization (SVC), uses neural networks to analyse the time varying spark voltage waveform to estimate the air-fuel ratio. The spark plug is in direct contact with the combustion itself, thus making it is an excellent candidate for use as a combustion sensor. As it is already installed in the engine, no modifications are required to the engine block itself. The method uses few external components making it cheaper to implement. Preliminary investigations on this method showed that it was possible to estimate the air-fuel ratio by neural network analysis of the spark voltage waveform. As different engines are equipped with different types of ignition systems, it is important that the sensor is independent of the ignition system thus ensuring that it is able to operate with any type of ignition system. The work presented in this thesis includes: i) an extensive review of other methods of measuring the air-fuel ratio, noting the advantages and disadvantages of each method and how the SVC sensor overcome these disadvantages; ii) a description of the theoretical operation of the sensor; iii) investigation of the effects of various engine parameters on the performance of the sensor; iv) suggestions for further work to improve the sensor performance.

This thesis presents an experimental investigation of the near-nozzle region of the fuel spray issuing from a pressure-swirl injector commonly found in a direct injection spark ignition engine. Specifically, the effects of the back pressure and impinging air flows were investigated. In addition to this the effect of fuel pressure was investigated. The literature survey reveals only limited published work on the near-nozzle characteristics of fuel sprays, and the requirement for more detailed knowledge of the area to aid in the general understanding of the topic and the development of mathematical models. Two separate experimental test rigs were designed and built to carry out the testing, firstly a static pressure chamber to identify the effects of back pressure on the fuel spray, and secondly a steady state flow rig, to investigate the effects of an impinging air flow. The steady state air flow rig was designed to simulate the air flow from the inlet valves of a direct injection spark ignition engine cylinder head. A novel void fraction technique was utilised to quantify the fuel spray break up process. It was found that there was a correlation between the void fraction and the fuel spray break-up length. The results from this analysis were compared to mathematical models currently available in the literature. It was found that the models do not compare well with the experimental results. A modified mathematical model was therefore proposed by the author, which can be easily integrated into existing computational codes. It was shown that impinging air flows do not affect the primary fuel spray break-up process, however they do affect the secondary break-up of the fuel spray from ligaments into droplets. Impinging air flows also affect the general fuel spray shape, and will determine the location of the fuel spray within the cylinder far downstream of the injector.

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The cold start catalyst warm-up operation is seen as one of the most important modes in Direct Injection Spark Ignition (DISI) Engine operation. When the catalyst is cold the engine out emissions become the tailpipe out emissions, so it is vital for the catalyst to obtain its working temperature as quickly as possible. A very high exhaust temperature can be achieved with a very retarded ignition - the engine can be made to operate at no load with a close to wide open throttle. With a retarded ignition, a split injection strategy has been shown to improve combustion stability which is critical for the trade-off between tailpipe emissions and vehicle idle stability. The spray guided DISI engine has a multi- hole injector centrally located in the chamber with the spark plug. For catalyst heating operation, the first injection occurs during induction, which forms a relatively well mixed but lean mixture in the cylinder before ignition, and the second injection occurs close to a retarded ignition, which produces a stratified fuel rich mixture in the central region of the combustion chamber near the spark plug. Combustion initialization is found to be sensitive to spark plug protrusion and orientation, injector orientation and 2nd injection timing relative to ignition. High tension current and voltage measurements have been taken in order to characterize the effect of the 2nd injection timing on both the breakdown and the glow phase of the arc discharge. Both phases are shown to be influenced by the timing of the 2nd injection. The richer mixture causes the breakdown voltage to increases while the airflow entrained in the 2nd injection has been shown to stretch the spark and in the worst case extinguish it prematurely. In-cylinder spray imaging by Mie scattering has been taken with frame rates up to 6000 fps, with high speed video photography of chemiluminescence and soot thermal radiation. Tests have studied the effect of the spark plug orientation and injector orientation, with timing sweeps for the phasing of the second injection. The images show interaction of a fuel jet with the earth electrode, stretching of the arc, variable location for the start of combustion and significant cycle-by-cycle variations with the same operating point leading to normal combustion, slow combustion and misfiring cycles. Spectroscopic measurements have confirmed the presence of OH *, CH * and C2*; emissions lines, and their relative magnitude compared to soot radiation. Filtering for CH * has been used with a photo-multiplier tube. These signals show the arc discharge, the delay between the arc and the kernel growth and (depending on the timing of the 2nd injection) small kernels which do not subsequently fully develop and can cause misfiring cycles. Unburned hydrocarbon emissions have been measured with a fast-response FID, so that emissions can be related to: misfiring cycles, slow burning cycles (0 < GMEP <0.5), and normal cycles. These measurements show that only the misfiring cycles lead to significant unburnt hydrocarbon emissions. The misfire mechanism depends on the timing of the 2nd injection. When the 2nd injection ends at the spark, no kernel is seen for a misfiring cycle. However, a kernel is shown to grow in the lean background mixture indicating that the misfire mechanism, when the 2nd injection ends close to the spark, is that the local air/fuel ratio is too rich for the onset of combustion. However, when the 2nd injection is significantly retarded from the spark a different misfire mechanism is present. A small kernel is shown to exist between the spark and the arrival of the fuel from the 2nd injection. For the misfiring cycle, this kernel is extinguished early, possibly due to an interaction between the kernel and the 2nd injection.

This is a thesis that brings together work conducted over a thirty year period concerning the research, development and knowledge management of high perfonnance and low exhaust emission engines. The thesis includes nine published and refereed works that are discussed and appended. Internal combustion engines translate the chemical energy of a fuel into mechanical work by burning the fuel with air in a combustion chamber. It is demonstrated that this process can be improved beneficially with respect to power output, fuel economy and exhaust emissions, by efficient cylinder filling and the generation of enhanced charge motion characteristics at the point of ignition. The advantages of multivalve engines, particularly with 5-valves per cylinder, and the methods of producing and measunng good air flow and beneficial amounts of tumble or barrel swirl, are described. Two patents and three novel research techniques for air flow and air motion are presented and discussed. The combustion developments carried out by the author for competition and high-perfonnance road cars are presented as examples of the application of the theory and research.