基于多组分蒸发模型的汽油机冷起动数值模拟

Application of Multi-Component Fuel Vaporization Model to Simulation of Cold Starting in PFI Engine

建立了汽油多组分油膜蒸发模型,并运用该模型对进气道喷射式汽油机冷起动首循环的气流运动、喷雾过程、油膜形成和发展过程、混合气形成过程及缸内燃烧进行了三维数值模拟,详细解析了油滴和油膜中每种组分的蒸发规律,给出了每种组分的浓度分布。模拟结果表明:冷起动时轻组分的蒸发主导首循环混合气的形成质量,中、重组分的蒸发情况仅起辅助作用;汽油的轻组分越多,燃料蒸发量越大,有利于形成稳定可靠的可燃混合气,改善缸内燃烧过程,提高起动稳定性;计算所得的缸压曲线与试验结果吻合良好,说明开发的多组分汽油蒸发模型具有较高的模拟精度。

An evaporation model for multi-component wall film was developed.Based on it the three-dimension numerical simulation on air flow,fuel spray,wall film behavior,mixture formation and combustion of the first cycle during cold starting in an actual PFI engine were conducted.The evaporation of each component in droplet and wall film was analyzed individually and the concentration distribution of each component was also obtained.Numerical simulation results show that the mixture formation quality during cold starting is dominated by the evaporation process of the light component.The middle and weight components have only a little contribution.The more the light component in the gasoline,the more the fuel evaporation fraction,and the more beneficial to formation of stable combustible mixture,consequently,engine combustion and starting stability are improved.The calculated cylinder pressure curves agree with the measured,thus proving the developed multi-component evaporation model for wall film has good accuracy.