Multi-Dimensional Numerical Simulation For The Scavenging And Injection Processes In A Two-Stroke DISI Engine

Two-stroke gasoline engine has a feature of high power density capable of beingmade compact and simple, but has defects such as bad fuel economy and highhydrocarbon emission due to mixture short-circuiting and poor combustion at lightloads, which limit its application. Direct fuel injection into the combustion chamberoffers one of the most promising solutions for the short-circuiting problem whilecharge stratification is a suitable solution for combustion irregularities at light loads.Multi-dimensional numerical simulation is made to analyze the characteristics ofthe scavenging and injection processes in a two-stroke DISI (direct injection sparkignition) engine. The result shows that to get charge stratification at light loads, lateinjections are advantageous when proper injector position and injection direction areselected, but to ensure homogeneous combustion at heavy loads, injection advanceshould be as high as possible, with the limit that excessive advances give rise to lossof fuel from the exhaust port. The computation results also indicate that injectionpressure is a very important parameter. It decides the droplet size distribution andspray penetration, which control the final charge structure present in the combustionchamber at the instant of spark kernel initiation. So a little low injection pressure isnecessary to decrease the mean penetration velocity and thereby avoid a detrimentalwall film formation on the crevices of the combustion chamber, on the other hand, atheavy loads, high injection pressure is beneficial to the evaporation of spray dropletsand the achievement of homogeneous mixture.