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. High energy spark ignition which produces a large sized flame kernel helps increase combustion flame speed. The above changes all help to achieve a stable lean combustion.