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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.

Mixture formation technology for a fuel injection system has been investigated. The effects of spray droplet diameter on engine performance were clarified. The combustion light Intensity was measured with a spark plug integrated combustion flame sensor. When sequential injection is used for better responsiveness in fuel injection systems, engine performance may be reduced through increased HC emissions. Reducing the diameter of the spray droplets and preventing fuel from adhering to the intake manifold walls promote vaporization, reduce fuel concentration on the cylinder wall, decrease HC emissions, improve cold start ability, and give good idling performance.