Abstract: Based on a 1.4 L tumble-intake-port gasoline engine, the refluent exhaust gas stratified distribution status and combustion performance improvement with different control parameters of the exhaust valve secondary open were studied using 3D computational software FIRE,and the simulated regularities were verified by optical measurement. The simulation results show that refluent exhaust gas forms basically homogeneous distribution in the combustion chamber with exhaust valve secondary open earlier at intake stroke.While,the exhaust gas forms evident stratified distribution with fresh charge after the formation of intake swirl at later intake stroke.Longer exhaust secondary open duration leads to higher EGR rate and weaker tumble intensity,which is able to reduce over-rotated exhaust gas.Refluent exhaust could not take full use of the fresh charge flow with higher exhaust valve secondary open lift,so the gas is easily diffused to the center of combustion chamber.Refluent gas could reduce the adverse effect of EGR on combustion from the aspects of EGR stratified distribution and thermal effect.Regardless of the knock possibility,stratified exhaust gas temperature at 850 Kelvin condition,the cylinder pressure peak is 51.4% higher and the heat release peak is 91.4% higher than that at 298 Kelvin condition with the same exhaust valve secondary open duration 70~180 °CA ATDC and max lift of 5 mm. meanwhile, the cylinder pressure peak and heat release peak of stratified exhaust gas at 298 Kelvin condition are 79.8% and 147% higher respectively than that in EGR homogenous distribution case with the same gas mass.

Key words: dynamic mechanical engineering, tumble intake port, exhaust gas backflow, exhaust gas stratification, combustion improvement