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Meeting future exhaust emission and fuel consumption standards for passenger cars will require refinements in how the combustion process is carried out in spark ignition engines. Improvements must be made in the fuel injection device, intake air system, and ignition device based on careful studies of the engine combustion process. Lean burn is preferable to decrease fuel consumption under a road load cruising condition. To achieve stable combustion in a lean air fuel ratio, the in -cylinder air flow must be optimized. Vortex flow in the vertical direction is produced by auxiliary air passages which are located beside the intake air port. The fuel injector has a two-direction spray for the two intake valves. The spray flows into the cylinder uniformly through these two intake valves. Due to effects of air flow from the auxiliary air passages and the two-direction fuel spray, the in -cylinder mixture concentrates around the spark plug.

A thermodynamic analysis of mixture formation in cylinders that takes into account mixture inhomogeneity and the wall film is presented. Conditions for obtaining low hydrocarbon emission are clarified analytically as a function of the fuel mass of the wall film and inhomogeneity of the mixture. Optimum processes for atomizing and vaporizing fuel are presented to reduce the inhomogeneity and the fuel mass of the film.

Meeting future exhaust emission and fuel consumption standards for passenger cars will require refinements in how the combustion process is carried out in spark ignition engines. A direct injection system reduces fuel consumption under road load cruising conditions, and stratified charge of the air-fuel mixture is particularly effective for lean combustion. This paper describes an approach to improve combustion stability for direct fuel injection gasoline engines. Effects of spray characteristics (spray pattern and diameter) and air flow motion on the combustion stability were investigated. Spray patterns were observed by the laser sheet scattering method and 3-dimensional laser doppler velocimetry. Mixture behavior in the combustion chamber was observed by the laser-induced fluorescence method using an excimer laser and single cylinder optical engine. It was found that the spray pattern for a pressurized condition affects the combustion stability and smoke generation.