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The influences of injector nozzle geometry, injection pressure and ambient air conditions on a diesel fuel spray were examined using back-lighting techniques. Both stills and high speed imaging techniques were used. Operating conditions representative of a modern turbocharged aftercooled HSDI diesel engine were achieved in an optical rapid compression machine fitted with a common rail fuel injector. Qualitative differences in spray structure were observed between tests performed with short and long injection periods. Changes in the flow structure within the nozzle could be the source of this effect. The temporal liquid penetration lengths were derived from the high-speed images. Comparisons were made between different nozzle geometries and different injection pressures. Differences were observed between VCO (Valve Covers Orifice) and mini-sac nozzles, with the mini-sac nozzles showing a higher rate of penetration under the same conditions.

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.

The temperature of fuel injectors can affect the flow inside nozzles and the subsequent spray and liquid films on the injector tips. These processes are known to impact fuel mixing, combustion and the formation of deposits that can cause engines to go off calibration. However, there is a lack of experimental data for the transient evolution of nozzle temperature throughout engine cycles and the effect of operating conditions on injector tip temperature. Although some measurements of engine surface temperature exist, they have relatively low temporal resolutions and cannot be applied to production injectors due to the requirement for a specialist coating which can interfere with the orifice geometry. To address this knowledge gap, we have developed a high-speed infrared imaging approach to measure the temperature of the nozzle surface inside an optical diesel engine.

For efficiency, the majority of modern diesel engines implement multiple injection strategies, increasing the frequency of transient injection phases and thus, end of injection (EOI) events. Recent advances in diagnostic techniques have identified several EOI phenomena pertinent to nozzle surface wetting as a precursor for deposit formation and a potential contributor towards pollutant emissions. To investigate the underlying processes, highspeed optical measurements at the microscopic scale were performed inside a motored diesel engine under low load/idling conditions. Visualisation of the injector nozzle surface and near nozzle region permitted an indepth analysis of the post-injection phenomena and the behaviour of fuel films on the nozzle surface when the engine is not fired. Inspection of the high-speed video data enabled an interpretation of the fluid dynamics leading to surface wetting, elucidating the mechanisms of deposition and spreading.