Optical studies in a firing stratified-charge G-DI engine

This thesis describes investigations into fuel spray interactions within the cylinder of a prototype, direct injection, spark ignition engine. The literature review discussed the future of the automobile and its possible prime movers. It concluded that gasoline direct injection (G-DI) engines have the potential to meet increasingly stringent emissions regulations except for their excessive unburnt hydrocarbon emissions. Further studies are necessary to understand the causes and to investigate possible methods of reduction. A prototype cylinder head was supplied by Jaguar Cars Ltd. and a cylinder block and piston were designed and manufactured to provide optical access to study the fuel spray interactions. The design featured a piston with a deep bowl, three versions of which were made. One was non-optical (for benchmark testing), the second had a thin quartz slice to allow sheet illumination, while the third had a quartz disc set in the base of the bowl. The most suitable optical methods for the investigation were assessed. Mie scattering and Laser Induced Fluorescence (LIF) were chosen for their ability to show fuel in liquid and vapour form and their compatibility with an existing laser unit. The Mie tests were performed using pump gasoline with the engine firing. The main variables were injection timing, engine temperature and optical access through the piston. The LIF tests used the firing engine, but a three-component hydrocarbon fuel replaced gasoline. The fuel components were chosen to represent the evaporative behaviour of gasoline, but not to fluoresce. A dopant in known concentration was added to provide the fluorescence. Images were recorded using a charge-coupled device camera. Extensive image post-processing was performed to correct for background illumination, window fouling and light- sheet intensity variation. Finally, a comparison was made between the Mie and the LIF images, also taking into account corresponding ambient air fuel spray images