气门参数对汽油机可控自燃燃烧控制作用的数值模拟

Simulation of Control Effect of Valve Parameters on CAI Combustion in a Gasoline Engine

通过可变气门机构使部分燃烧废气保留在缸内,是实现汽油机可控自燃(controlled auto-ignition,CAI)燃烧的切实可行的办法,然而多参数可调气门机构增加了控制的复杂程度.为此,利用一维循环模拟软件在Simulink环境中建立了带有进、排气门升程及定时均可控的四变量气门执行机构(4-variable valve actuating system,4VVAS)的汽油机仿真试验平台,探讨了气门各参数对循环热废气及CAI燃烧过程的控制作用及控制敏感性.研究结果表明,其他参数相同时,排气门定时对汽油机CAI燃烧的影响主要体现在缸内废气残留量及废气温度的大小,而进气门定时主要通过影响进气回流和有效压缩比来影响燃烧过程;存在一个最佳位置没有进气回流,能够取得最大负荷.在当量比燃烧时,排气门参数对发动机负荷和着火时刻的控制最为直接和有效,是汽油机CAI燃烧的重要控制参数.

One practical and adequate approach to achieve controlled auto-ignition （CAI） combustion in the gasoline engine is trapping hot burned gas via variable valve actuation, but the control methods will become complex with various adjusted valve parameters. A virtual gasoline engine model equipped with a 4-variable valve actuating system （4VVAS） was established by employing I-D gas dynamic engine simulation programmer, GT-Power and commercial software, Simulink. Using this model, the control effect of valve parameters on CAI combustion was investigated and sensitivity analysis was carried out to obtain the key control parameters to these factors. Results show that, the effect of exhaust valve timing on the CAI combustion mainly depends on the residual gas fraction and its temperature control with other control parameters identical, while the intake valve timing can alter the intake backflow and effective compression ratio and there exists optimum timing to achieve maximum load without intake backflow. With stoichiometric mixture, the exhaust valve is the most direct and effective control parameter on load and ignition timing in a CAI gasoline engine.