O'Donoghue, Shane T. C.; (2002) A study of fuel spray structure and its relationship to emissions and performance of a gasoline direct injection engine. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The research reported in this thesis is one of three linked investigations aimed at improving the understanding of the flow and fuel/air mixing processes that occur within direct injection gasoline engines through the application of both experimentation and modelling techniques. The components of work covered by this thesis are an investigation into the structure of fuel sprays from four different high-pressure swirl injectors, and a subsequent investigation of how two of them perform in a single-cylinder direct injection gasoline engine. The fuel injectors were initially tested on a rig in the UCL fuel systems test facility. Two different experiments were carried out to obtain a significant amount of information about each of the injectors' sprays under various conditions. High-speed photography using a copper vapour laser for illumination was employed to capture details of the spray structures, as well as penetration rates and cone angles. In a separate series of tests, droplet sizes were obtained using a Malvern particle sizer. A tomographic technique was developed in an attempt to deconvolve the spray structure. A statistical design of experiment approach was used because of the large number of variables to be investigated during the engine testing. Two designs of injectors were tested in two positions for two different fuel pressures. For each arrangement, a Central Composite Rotatable Design of experiment was employed for four variables at five levels. The variables were inlet valve timing, fuel injection timing, ignition timing and air/fuel ratio. The results of these tests were modelled by regression analysis using quadratic functions, which included the possibility of interactions between pairs of variables. The measured engine responses were unbumt hydrocarbons (HC) emissions, oxides of nitrogen emissions (NOx), brake specific fuel consumption (BSFC) and exhaust gas temperature. The results from the engine and injector testing suggest that there is a strong, yet complex interaction between the fuel spray structure and the engine performance.

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