An extremely lean burning engine has been expected to improve fuel consumption rate of engines. To achieve this, stable combustion should be realized for a wide range of operating conditions at air-fuel ratio over 40.0. In direct injection gasoline engines, cyclic variations of combustion derive from some main factors such as those of air flows and spray motions. In this report, we examine the influence of cyclic variations of "Air flows" and "Spray motions" on combustion instabilities, while

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... her variation factors are fixed for each cycle of engine, by using our simulation model. The cyclic variations of stratified-charge turbulent combustion in direct injection gasoline engine can be simulated during ten continuous cycles based on the multi-level formation for the stochastic compressible Navier-Stokes equation and also a spray model. Computational results agree with cycle-averaged experimental data fairly well, while the cyclic variations computed are comparable to experimental ones reported by the other research group. Consequently, the present computational model will reveal an essential factor which generates the cyclic variations and will offer us an effective way to control combustion instabilities on very lean burning conditions.