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This thesis is concerned with the potential applications for in-cylinder ionisation probes for the feedback control of spark ignition engines. Such sensors are shown to yield useful qualitative information about the combustion process. Two different implementations of an in-cylinder ionisation probe are investigated - both types are demonstrated to have potential for specific control applications. The first implementation is a <i>Flame front sensor</i> - here an ionisation probe is used to determine the time of flame arrival at a position remote from the spark plug. This parameter is typically subject to a high degree of cyclic variability, but is generally sensitive to variables which affect the flame speed such as air/fuel ratio, turbulence characteristics etc. The flame arrival time is shown to be useful as an indicator of relative cylinder to cylinder variations. The general signal characteristics were determined for a range of engine conditions and a system for the real-time, feedback control of a fuel injection system was developed and demonstrated. Results showed that, with the controller implemented on a four cylinder engine, the lean misfire limit could be extended to higher air/fuel ratios and the brake specific fuel consumption was improved. The second implementation of a <i>Post-flame ionisation sensor</i> -- the residual ionisation in the burnt gases behind a flame front is used to provide a signal which is sensitive to cylinder temperature and pressure. The central electrode of the spark plug is conveniently located to produce such a signal -- providing precautions are taken to protect the signal circuitry from the high voltage ignition spark. The signal characteristics of the spark plug ionisation probe were evaluated. Applications of the signal to the feedback control of ignition timing and/or fuelling, based on the estimation of peak cylinder pressure arrival and knock intensity, are demonstrated.

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The objective of this thesis is to develop and validate a model of soot formation which is capable of being applied to a computational fluid dynamic (CFD) simulation of gas turbine combustion. The work follows previous research by Moss and Co-workers (Moss et al.1987, Syed 1990, Stewart et al.1991) The concept of the study is to generate a detailed set of experimental data in turbulent flames of kerosine in which the complicating factors of gas turbine combustion - that is 3D geometry and droplet combustion - are removed. This allows more confidence in the computational simulation of the flames and therefore more insight into the soot formation process. There are two components to the work: the experimental and theoretical studies. The first involves the compilation of an experimental dataset of key variables in ethylene and vaporised kerosine jet flames at elevated pressure, the second with the simulation of two of the experimentally studied flames using CFD methods. The main achievement of the study is the generation of a formidable and detailed experimental database for flames at a variety of pressures and conditions. The unexpected finding is the extremely large conversion of carbon to soot found in the flames even at low pressure. This results in high radiant heat losses and measurement difficulties. From the data, it is possible to assess the pressure dependence of soot growth in kerosine flames. Although, at the higher pressures, high soot levels created uncertainties in the measurements, in absolute terms growth rate is shown to be independent of pressure up to 6atm pressure. Above this it increases significantly. The soot model of Moss et al.1988 - originally developed in laminar e~hylene flames - was shown to give excellent agreement in turbulent situations. However, owing to the large radiant heat loss and soot levels, its application to the kerosine flames was more problematic since the assumptions that soot is a perturbation to the gaseous field and that temperature may be accurately described by a single perturbed flamelet were no longer valid. Further models to deal with such situations are proposed and tested. Aside from the obvious relevance of this study to the field of gas turbine combustion, the large radiant heat loss and high soot levels observed in the flames studied here imply a further significance for the study of fire hazards. That a laboratory scale flame maybe made to behave in a similar manner to a much larger pool fire flame is a very useful finding.

This study seeks to advance present modelling capabilities in respect of soot and thermal radiation emission from fires. Such developments are crucial to the improved estimate of the hazard potential of accidental fires. Radiation calculation requires the prediction of temperature and the concentrations of all radiatively important species. In hydrocarbon combustion, the key species are carbon dioxide, water vapour, carbon monoxide and particulate soot. In large hydrocarbon fires the latter is usually the dominant radiator. The detailed prediction of the gaseous species in turbulent combustion has previously been shown to be successfully achieved using laminar flamelet modelling in the fast chemistry limit. Soot, however, is governed by relatively slow formation processes which as yet remain poorly understood. The present study proposes a model for soot formation in turbulent non-premixed combustion which aims to address both the slow chemistry and turbulence interaction. In order to circumvent uncertainties in soot formation processes the model relies on empiricism, through the experimental investigation of a sooting laminar diffusion flame. The soot formation model is used to predict soot levels in a jet diffusion flame. Subsequent comparison with experimental data suggests the satisfactory performance of the model, but highlights soot oxidation to be a more significant problem. This stems from uncertainties associated both with instantaneous soot oxidation rate and the highly intermittent nature of this process in turbulent non-premixed flames. The soot formation model is also applied to the prediction of soot levels in a simulated buoyant methane fire, which supplement temperature and gaseous species predictions using a flamelet approach. Detailed predictions of spectrally resolved radiative intensity are then performed and compared with similarly detailed experimental data. The encouraging agreement with experiment allows the assessment of the effect of turbulence-radiation interaction. This is shown to be particularly important in buoyancy-driven fires and is most evident for the luminous radiation. This arises from the soot which is largely confined to narrow sheets that typically lie close to peak temperature zones. A strategy in which more representative soot-temperature correlations may be realised is also described.

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