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Spray characteristics of injectors depend on, among other factors, not only the level of turbulence upstream of the nozzle plate, but also on whether cavitation arises. "Bulk" cavitation, by which we mean cavitation which arises far from walls and thus far from streamline curvature associated with salient points on a wall, has not been investigated thoroughly experimentally and moreover it is quite challenging to predict by means of computational fluid dynamics. Information about the effect of the injector geometry on the formation of bulk cavitation and quantitative measurements of the flow field that promotes this phenomenon in gasoline injectors does not exist and this forms the background to this work. Evolution of bulk cavitation was visualized in two gasoline multi-hole injectors by means of a fast camera.

A high-swirl, low Compression Ratio (CR), optically accessed engine that was able to produce a stratified charge was used to investigate the differences in HCCI combustion and in the propagation of the autoignition front between a non-stratified and a stratified charge. Furthermore the relevance of charge stratifying an engine using variable injection timing with large temperature inhomogeneities was investigated. The CHEMKIN code and a detailed reaction mechanism were used to simulate the fuel chemistry of ignition and combustion in a low CR engine. The aim of the simulation was to quantify the effect of initial mixture temperature, Ti and A/F ratio on cool flame and main ignition timing and to evaluate the possibility of charge stratifying our engine.