缸内直喷汽油机喷雾、混合气形成和燃烧过程的三维数值模拟

Three-Dimensional Numerical Simulation of Spray,Mixed Gas Formation and Combustion Process for Gasoline Direct Injection Engine

建立了带进排气道的缸内直喷(GDI)汽油机三维数值模型,并对喷雾模型和燃烧模型进行了实验标定,进而模拟了GDI发动机化学当量比条件下均质混合气和分层混合气两种模式从进气-喷雾-混合气形成-燃烧的全过程.模拟结果表明,GDI发动机高压多孔喷嘴喷雾雾化明显,贯穿距离较长,进气过程中缸内形成强滚流促进燃油蒸发和油气混合;进气冲程单次喷射可在缸内点火之前形成较为均匀的混合气,进气和压缩冲程中进行两次喷射可在缸内点火之前形成火花塞附近较浓、周围较稀的分层混合气;在化学当量比条件下适当采用分层混合气燃烧,与均质混合气相比可以降低燃烧速度,从而减小最大爆发压力和压力升高率.计算结果有助于深入理解GDI发动机的工作过程,并为后续研究GDI燃烧控制策略提供了模拟计算平台.

A three-dimensional moving mesh with intake and exhaust ports used for a gasoline direct injection （GDI） engine was established. The spray and combustion models were validated via visualization in a combustion bomb and pressure measurement in a GDI engine, respectively. The processes of intake, spray, mixed gas formation and combustion of homogenous stoichiometric and stratified stoichiometric mixture were simulated and analyzed. The simulation results show that the high-pressure multi-hole injector has the spray characteristics of rapid atomization and long penetration. The mixture was formed due to the interaction of the spray and the tumble during the intake process. The homogenous mixture was formed before ignited in-cylinder with single-stage injection, and the stratified mixture was formed before ignited in-cylinder with two-stage injection. When stoichiometric mixture was stratified, flame propagation slowed down, peak pressure and pressure accelerating rate decreased. The results provide better understanding of the GDI engine working process and set up a simulation platform for combustion optimization of the GDI engine.