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As part of an ongoing investigation, the influence of In Cylinder Pressure (ICP) and fuel injection pressure on the soot formation processes in a diesel fuel spray were studied. The work was performed using a rapid compression machine at ambient conditions representative of a modern High Speed Direct Injection diesel engine, and with fuel injection more representative of full load. Future tests will aim to consider the effects of pilot injections and EGR rates. The qualitative soot concentration was determined using the Laser Induced Incandescence (LII) technique both spatially and temporally at a range of test conditions. Peak soot concentration values were determined, from which a good correlation between soot concentration and injection pressure was observed. The peak soot concentration was found to correlate well with the velocity of the injected fuel jet.

As part of an ongoing investigation, the influence of in-cylinder charge density, and injector nozzle geometry on the behaviour of diesel sprays were examined using high-speed imaging. Both liquid and vapour penetration profiles were investigated in operating conditions representative of a modern turbocharged after-cooled HSDI diesel engine. These conditions were achieved in an optical rapid compression machine fitted with a common rail fuel injection system. Differences in spray liquid and vapour penetrations were observed for different nozzle geometries and in-cylinder conditions over a range of injection fuelling representative of those in a typical engine map. Investigation into the differences in spray structure formed by multi-hole and single-hole injections were also undertaken.

Laser Doppler velocimetry, phase Doppler anemometry and Mie scattering were applied to a single-cylinder, four-valve, spark-ignition gasoline research engine equipped with a fully transparent liner and piston, to obtain information about the tumble flow and the droplet size and velocity distributions during induction and compression, for lean air/fuel mixture ratios of 17.5 and 24 and with closed-valve and open-valve fuel injection. The mixture distribution obtained with the two injection strategies was correlated with flame images, pressure analysis and exhaust emissions which confirmed the advantages of combining open-valve injection with tumble to allow stable and efficient engine operation at an air/fuel ratio of 24 through charge stratification and faster flame growth.