1995-02-01

In-Cylinder Charge Homogeneity During Cold-Start Studied with Fluorescent Tracers Simulating Different Fuel Distillation Temperatures 950106

High boiling point components of gasoline have been shown to have an adverse effect on engine-out hydrocarbon emissions for port fuel injected (PFI) engines. Fuel charge inhomogeneity and wall wetting contributes to the abnormally high hydrocarbon emissions associated with cold and warm engine starting. In this work, a series of aldehydes with varying molecular weight and boiling points were used as fluorescent tracers to study the effect of fuel volatility and engine operating conditions on the in-cylinder charge distribution. The tests were conducted in an optically accessible engine consisting of a production GM Quad-4 cylinder head and intake manifold, with an FEV systemmotor crankcase and “Bowditch” transparent piston. Planar laser induced fluorescence was used to study the in-cylinder fuel vapor distribution and to determine the presence of liquid droplets. The incident laser beam, from a tunable excimer laser operating at 308 nm, was formed into a horizontal sheet parallel to the piston surface. The fluorescence signals were detected through the transparent piston by a gated intensified charge-coupled device (CCD) detector. Iso-octane, which has a boiling point near the mean boiling point of a fully formulated gasoline, was doped with tracers to simulate various distillation components of gasoline (boiling point temperatures ranging from 49°C to 178°C).A variety of engine operating conditions were studied. Intake air temperature and engine coolant temperature were varied with the engine operated both with (fired) and with out (motored) spark ignition. Liquid fuel droplets are observed late in the compression stroke for some operating conditions and fuels. The distribution of liquid and vapor fuel for various engine operating conditions is discussed as a function of fuel boiling point.

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