Temporal and Cyclic Fluctuation of Fuel Vapor Concentration in a Spark Ignition Engine

Laser Rayleigh scattering was applied for the remote, nonintrusive measurements of fuel vapor concentration in the combustion chamber of an automotive SI engine with the multipoint fuel injection. The fuel was simulated by Freon-12, which was injected intermittently or continuously into the flow of dust-free dry air through an intake port. The measurements were made of the time histories of instantaneous fuel vapor concentration at a location in the vicinity of a spark plug in the combustion chamber of the engine motored at 650 rpm for various air fuel ratios, fuel injection durations and fuel injection timings. The measured results were analyzed to derive an ensemble-averaged mean concentration, a cyclic variation of the temporal mean concentration and a temporal concentration fluctuation in a specific cycle. The steady flow test rig was also provided to obtain the spatial distribution of the temporal mean concentration and the concentration fluctuation around a spark plug and intake valves during the intake stroke.