灰分沉积特性对汽油机颗粒捕集器再生性能影响研究

Effect of ash deposition characteristics on regeneration performance of gasoline particulate filter

基于某直喷式汽油机进行发动机后处理台架试验,研究不同灰分量汽油机颗粒捕集器(GPF)对发动机转矩影响和GPF前后端压差对比。利用三维计算流体动力学软件(CFD)建立GPF压降模型和再生模型,分析不同灰分分布系数和灰分量对GPF再生性能的影响。结果表明:灰分沉积质量与GPF压差呈正相关关系,在高转速工况下,灰分累积会降低发动机转矩影响其动力性;灰分全部分布于壁面,即灰分分布系数s=1时,会提高再生压降,降低再生性能,灰分累积过多会增加GPF再生压降,适量的灰分累积有利于提高再生峰值温度,促进碳烟再生氧化。

Gasoline direct injection(GDI)engine is widely used on light vehicles thanks to its excellent power performance and high fuel economy.Due to its direct injection of oil into the cylinder,however,the uneven distribution of the mixture and unnecessary particles can be easily caused,especially in the cold start stage.The particulate matter(PM)and particulate number(PN)emissions are significantly higher than those of port fuel injection(PFI)engines.As particulate matter can often be damaging to both environment and human bodies,the original emission of GDI engine hardly meets the PN limit requirements of the national phase VI motor vehicle pollutant emission standards on new vehicles,200000 km durability and real vehicle operating conditions.Thus,it is imperative to install an effective after-treatment device to markedly reduce the emissions of particulate matter.Traditional in-cylinder purification and three-way catalyst(TWC)technologies can barely meet the requirements of emission regulations.Currently,to install a gasoline particulate filter(GPF)to capture particulate matter and control the emission of particulate matter through regeneration is widely considered the most effective measure.However,GPF tends to leave metal and inorganic components,which are collectively referred to as ash and cannot be easily removed during the regeneration process.The ash mainly derives from the consumption and combustion of lubricating oil,the friction debris in the engine cylinder and the catalyst coating of the TWC.However,excessive ash deposition in GPF undermines the capturing and regeneration effect of GPF.So far,studies have been primarily focused on the micro-morphology of particulate matter inside GPF,the capturing performance of GPF,the arrangement mode of GPF,or the variation characteristics of GPF performance obtained through vehicle WLTC cycle test.Little research has been done on the regeneration performance of GPF with different ash characteristics.Therefore,based on a GDI engine after-treatment bench test,this paper investigates the influence of GPF with different ash components on engine torque and the pressure difference between the front and rear ends of GPF.The pressure drop model and regeneration model of GPF is built by 3D computational fluid dynamics(CFD)software,and the impact of different ash distribution coefficients and ash components on the regeneration performance of GPF is analyzed.The results show that a positive correlation exists between ash deposition mass and GPF pressure.At a high rotational speed,ash accumulation reduces engine torque and undermines engine power performance.When a large amount of ash is deposited at the end of GPF(the ash distribution coefficient s<0.5),the regeneration performs better,the regeneration pressure drops and residual soot load is lower.When all ash is distributed on the wall,the ash distribution coefficient s=1 increases,the regeneration pressure drops and the regeneration performance gets poorer.Excessive ash accumulation increases the regeneration pressure drop of GPF.An appropriate amount of ash accumulation is conducive to increasing the regeneration peak temperature and promoting the regeneration oxidation of soot.This paper analyzes the impact of GPF with different ash deposition characteristics on engine performance and GPF regeneration performance by bench test and CFD numerical simulation.It is both theoretically and practically significant for exploring the optimal GPF regeneration conditions and improving regeneration strategies and subsequent application of GPF.