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This thesis describes the development and application of an electric discharge for regenerating gelcast ceramic foam diesel particulate filters (DPF) for effective and efficient reduction of particulate matter (PM) emissions from diesel fuelled IC engines. The combustion in diesel compression ignition engines generates a number of unwanted by-products including PM. The PM from diesel engines is believed to be potentially carcinogenic when inhaled into the lungs and, therefore, needs to be controlled. Emission legislation has made it increasingly difficult for engineers to reduce PM emissions whilst meeting NOx targets by combustion optimisation alone, leading to the requirement for exhaust gas aftertreatment, most notably exhaust gas filtration. Filtration and regeneration (filter cleaning) technology must be robust, filter high amounts of PM, be compact, energy efficient and cost effective. A large number of published solutions do not meet all of these criteria. This research has developed a compact, efficient, robust and cost effective solution: The Autoselective regeneration of gelcast ceramic foam DPFs. Gelcast ceramic foam geometry can be optimised on a microscopic and macroscopic scale with a large number of material characteristics. This thesis develops and applies new methodology for rapid optimisation of gelcast ceramic foam DPFs. The optimum foam geometry is found to be highly application-dependent. Filters with >95% filtration efficiency and a low filtration volume have been demonstrated, although are limited in their PM mass holding capacity. It was found that filters with higher PM mass holding capacity require larger pore sizes and filtration volume. Design maps were produced to allow rapid optimisation of gel cast ceramic foams with a novel methodology that can be applied to all forms of deep bed filtration, saving both time and cost in future filter development. Investigation and optimisation of Autoselective regeneration demonstrated that the regeneration system is most effective when the electric discharge is active within the filter volume. Using modelling and novel methods for measuring heat flux from electrical discharges, thermal optimisation of the heat flows in the system were achieved. Rig tests increased the robustness of the regeneration system and developed profiled mesh electrodes to maximise the effective regeneration volume. An engine test programme demonstrated regeneration effectiveness of -12 g kW·1 h-I which is equivalent to -333 W for a typical 56 kW heavy duty diesel engine. Alternatives such as fuel burners and electrical resistance heaters typically consume between I and 5 kW of fuel energy for filter regeneration. Multiple electrode prototypes are presented and evaluated for efficient and effective on-engine and on-vehicle PM control.

This thesis describes a digital signal processing analysis of diesel engine idle vibration in automobiles, and an analysis of the human subjective response to the idle vibration which occurs at the steering wheel. In order to quantify the variations in the diesel idle vibration that can be introduced by the engine technology, the vehicle, and the fuel type, a set of acceleration time histories were measured at the engine block and at the steering wheel for two automobiles equipped with 4-cylinder engines which had different injection systems and which operated under different fuel conditions. A combination of time domain, frequency domain and time-frequency wavelet-based analysis were used. Both the continuous wavelet transform and the discrete orthogonal wavelet transform were applied to the steering wheel acceleration time histories in order to analyse the statistical variation in terms of both instantaneous variations, and the cycle-to-cycle variations which occur across complete thermodynamic engine cycles. The combination of orthogonal wavelet transform and time-varying auto-covariance analysis, performed across a complete engine thermodynamic cycle, was identified as the most sensitive method for describing the statistical variation in diesel idle vibration. The second-order engine harmonic H2 was found to account for most of the vibrational energy at the steering wheel when at idle. Amplitude modulation of the second-order engine harmonic H2 by the half-order engine harmonic H112 has been identified as the main characteristic of the steering wheel signature of automobiles at idle. The steering wheel idle vibration produced by different engines and different fuel conditions have therefore been described in terms of the amplitude modulation depth "mil that characterises the idle waveform. Four psychophysical response tests, determined by the combination of two test protocols and two semantic descriptors, were performed. A model of the growth in the human subjective response to diesel idle vibration has been proposed in which the response scale is a function of the modulation depth parameter "mil. The model is defined over two regions of modulation depth. For values of "m" less than 0.2, humans have been found to be unable to distinguish variations in idle modulation. For values of "m" greater than 0.2, the human response grows as a power function with respect to modulation depth. Based on the current findings, suggestions for future research are also provided.

An experimental investigation of the effects of fuel composition on the ignition delay and heat release characteristics of a light duty, automotive compression ignition engine has been carried out. The ignition delay is defined as the period between the start of the main fuel injection event and the start of combustion (SOC). The research has covered a range of fuel types and blends to maximise the effects of composition on the ignition delay and heat release. The fuels used were diesel, gasoline and FAME (Fatty Acid Methyl Esters) produced from rapeseed oil, coconut oil and waste cooking oil. All the engine test studies were carried out using a 2.4 litre displacement, direct injection Ford Puma engine, at test conditions representing low load, mid load and high load at 2000rpm, with EGR rates of up to 35%. Single equation, semi-empirical ignition delay models based upon the Arrhenius equation were studied and developed to fit the experimental ignition delay data, and thus incorporate fuel composition effects. Fuel composition is shown to affect the duration of the ignition delay, but after the start of combustion the heat release characteristics, for a given energy supplied in fuel, proved to be relatively insensitive to fuel composition effects. The premixed fraction is shown to be directly proportional to the ignition delay. The ignition delay of biodiesel fuel is up to 15% shorter than diesel while a gasoline blend of 50% gasoline/50% diesel lengthens the ignition delay by up to 30% with respect to diesel. These differences in the ignition delay affect the engine thermal efficiency by up to 2% due to combustion phasing effects. Gasoline fuel blended up to 80% (by volume) with diesel was combusted successfully, resembling PCCI (Premixed Charged Compression Ignition) combustion regimes, while biodiesel fuel types RME (Rapeseed Methyl Esters), CME (Coconut Methyl Esters) and WCO (Waste Cooking Oil Methyl Esters) all showed differences in heat release characteristics due to ignition delay differences. Calibration changes are necessary to compensate for the fuel composition effects on the ignition delay and subsequent combustion characteristics. An engine specific, single equation ignition delay model was developed that successfully described the experimental ignition delay data over the fuel range of fuel composition: rID = 4.32p-l.02/'P-O.2exp (:;) where EA = A.Kevric University of Nottingham , ' )t8186 . Based upon the analysis of combustion characteristics of the experimental CN+ZS) data, the initial form of a universal ignition delay model was developed, composing of a physical delay portion and a chemical delay portion. A.

No description available.

The work described in this thesis was carried out to investigate the application of variable valve actuation (VVA) to light-duty diesel engines for use in passenger vehicles. The background to this was that there was little published on the subject and with advanced turbochargers, exhaust gas re-circulation systems and high pressure fuel injection systems reaching maturity it seemed likely that further enhancement of the air management in this type of engine, through VVA would receive greater interest. The first section of this thesis discusses the external pressures on engine manufacturers, from legislation and from the customer expectations, which could be expected to influence the adoption of VVA, while looking at the criteria on which they would assess a VVA system prior to adoption. Section two provides an overview of the effects of VVA and how they may be used to improve engine operation by highlighting the specific features of diesel engines, i.e. cold starting and compression ratio, part load fuel economy, full load torque and transient torque rise, that can be influenced by air management and what characteristics are required from the VVA system in order to provide improvements in these areas. Having identified the key features of a VVA system that would be suitable for use in light duty diesel engines section three presents a brief literature review and discusses the family of non-constant angular velocity VVA systems that were identified as having the correct characteristics and relative simplicity necessary for any system that might be made in high volume production. This section also provides a detailed analysis of one system of this type to highlight its behaviour and impact on valve train design. Software was written to model the selected mechanism and produce the valve lift characteristics for use in simulating the engine's behaviour. Section four provides an overview of engine simulation techniques and some detail of the model constructed for this investigation. It also discusses the additional code and methodologies required to model the turbine, compressor and combustion processes, which required special treatment, and presents data to compare the behaviour of the model with the baseline of known engine behaviour. Section five presents simulation results that show the following possible improvements: a) a 23% increase in torque, b) light part-load fuel economy improvements of 13% and c) transient rise to maximum torque times reduced from 2.3 seconds to 1.6 seconds. It also discusses the features of engine operation with VVA that provide the potential for these improvements in engine operation, quantifies the benefits that might be expected at a large number of operating conditions and discusses the interactions between the VVA and other systems such as the turbo-charger and EGR system. Section six presents conclusions which beside the enumeration of the potential benefits and description of the key effects of VVA, highlights the need for test data to verify the extent to which the benefits can be realised in real engines and suggests areas for future research.

Nowadays, the European automotive market is dominated by Diesel engines. Despite their high efficiency, these produce significant levels of pollutants. Among the various pollutants released, nitrogen oxides and soot are the main issues. Their formation is linked to the combustion process and attempts to reduce one often lead to an increase of the other. Laser diagnostics are among the best tools for experimental, non-intrusive studies inside combustion chambers for a better understanding of the complex combustion processes. Depending on the optical diagnostic, numerous combustion characteristics and processes can be investigated. The work presented here intends initially to develop a quantitative laser technique for characterising soot and, secondly, to further the knowledge on soot formation in Diesel engines by the application of this technique in an optical combustion chamber. Some of the main characteristics describing soot formation are the soot volume fraction, number density and particle sizes. Soot volume fraction is the major one as it is representative of the volume of soot produced. Planar characterisation of soot volume fraction, number density and particle size were achieved for the first time by simultaneous recording laser-induced incandescence (LII), laser scattering and two-colour time-resolved (2C-TiRe) LII signals. Qualitative planar distributions of particle diameter and soot volume fraction were derived from the image ratio of scattering and incandescence signals. 2C- TiRe LII technique allowed the simultaneous recording of the temporal LII signal for two different wavelengths in order to obtain quantitative values of the laser-heated particles temperature, soot volume fraction and particle size for a local or global part of the flame. These were used to recalibrate relative size and soot volume distributions. An initial development of the technique was performed on a laminar diffusion flame (Santoro burner) to validate its viability and performance. Equivalent temperature, soot volume fraction and particle diameter were determined throughout the flame. The results were found to be in good agreement with the ones published in the literature. The diagnostic was subsequently applied to an optical Diesel rapid compression machine, and further refinements were undertaken to cope with the higher soot concentration and lower LII signal. Tests were conducted for in-cylinder pressures ranging from 4 to 10 MPa, and injection pressures up to 160 MPa. A fixed injection timing and injected fuel quantity were used. Effects of in-cylinder pressure, fuel injection pressure and cetane number on soot formation and characteristics were observed. High injection pressure, cetane number and in-cylinder pressure caused a reduction of soot particle size and volume fraction but an increase of the soot particle density.