PFI汽油机油气混合过程三维瞬态数值模拟

Three dimensional transient simulation of air-fuel mixture process in PFI gasoline engine

以KIVA程序作为三维瞬态模拟软件,对进气道喷油式汽油机(PFI汽油机)采用闭阀喷射模式在3500r/min全负荷工况以及800 r/min怠速工况下单个工作循环内的油气混合过程进行了计算研究.计算表明两工况有着相似的燃油蒸气浓度分布状况,并且点火前时刻两工况下缸内的混合气浓度分布都比较均匀,空燃比的变化范围不大.计算还表明,800 r/min怠速工况下的燃油蒸发状况明显劣于3500 r/min全负荷工况,该工况下气道内不仅存在附壁油膜,而且部分油膜不能在本循环完全蒸发,致使点火时刻缸内的燃油蒸气浓度明显低于3500 r/min工况下的燃油蒸气浓度.

Three dimensional transient simulation is an effective way to explore liquid fuel distribution and fuel evaporation condition in the air fuel mixtue process. Using KIVA as the simulation tool, this paper simulates the air fuel mixture process in a single engine working cycle of PFI gasoline engine under 3 500 r/min full load condition and 800 r/min idle condition with the closed-valve injection mode. The results show that both of the two working conditions have similar fuel vapor distribution. However, under 800 r/min idle condition there is less fuel evaporation, there existing wall films in the port and parts of the film cannot evaporate totally, which finally results a less fuel vapor concentration in the cylinder before ignition.