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The effects of changes in engine geometry on the breathing and combustion processes in a spark ignition engine have been investigated. It has been shown that a survey of engine geometry can readily illustrate design limitations in three areas : Fluid dynamic, Mechanical and Thermodynamic, and so reduce the extent of investigation available to the designer. The induction performance has been analysed mathematically and comparisons made with experimental work. The results indicate that an assessment of the effect of changes of geometry can be made using empirical relationships without complex mathematics. An attempt has been made to relate the turbulent to laminar flame speed ratio to the engine's physical parameters. These results compare well with previously published work by other workers.

Spark ignition engines are a significant source of air pollution. Emissions are most severe in the period after the engine has been started from cold. This is because fuel enrichment is needed to ensure reliable combustion in the cold cylinder. The problem is compounded by the exhaust treatment catalyst not reaching operating temperature until some minutes after starting. As the majority of car usage is for short journeys, engines spend much of their time in this high emission operating regime. One route to reducing emissions is to improve mixture preparation. This is Particularly effective after a cold start as less enrichment is required to ensure combustion. The aim of this project has been to evaluate a Vortex'Amplifier as a route to improving mixture preparation. The vortex amplifier is a no moving parts fluidic control device. It regulates a large volume supply flow by imparting swirl to it with a small volume control flow. The control flow vortex creates a region of highly turbulent flow at the device outlet which possesses the potential to atomise a fuel spray. The VA has been tested experimentally. The sprays produced by the vortex amplifier were measured by a laser diffraction technique. Numerical analysis has also been undertaken to determine the motion of droplets within the vortex chamber and the potential of the flow to disrupt a fuel spray. The vortex amplifier has been found to be a highly effective atomiser. It produces sprays with a Sauter mean diameter approximately half the size of the best current technology. However the spray impacts on the walls of any pipework downstream of the VA due to the high tangential velocities in the flow exiting the VA. This problem currently precludes engine us'e, but suggestions for improving the situation are contained in the recommendations for future work.

The experimental and theoretical investigation of the effect of swirl on the fuel-air mixing process in direct-injection diesel engines is described. The experimental work involved the further development of an existing hydraulic analogue technique which enables excellent flow visualisation. This was followed by the design and construction of a novel high-swirl combustion bomb which reproduces engine conditions under fine control. This experimental apparatus includes facilities for high-speed cine photography and a micro-computer based data acquisition and control system providing flexible software control of the fuel injection equipment and data sampling rates of up to 70 kHz. Typical non-combusting and combusting results are presented. Theoretical models of fuel-air mixing are reviewed. The phenomenological jet-mixing model developed and presented is based on an existing continuum mechanics approach and is solved by an integral method. The model includes momentum, heat and mass transfer and simulates jet cross-section distortion and the non-similarity of property profiles. It is intended that this model will form the basis of a proposed multi-zone combustion model.

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