Simulation Study On Influence Of EGR Distirbution；to Methanol Engine

Faced with the shortage of oil resources and environmental degradation, engine workersare seeking effective measures to enhance engine’s power and reduce fuel consumption, andon the other hand are actively seeking alternative fuel. The oxygenated fuel---methanol hasalready got human’s attention and deeply exploration whether as additive blended withconventional fuels or as fuel burnt in internal combustion engine. Based on this, this paperinvestigated the application of exhaust gas recirculation (EGR) on a high compression ratiomethanol engine, and studied different EGR distribution in cylinder how to effect the engineperformance using CFD software. The following are the main contents of the paper:1. Set up simulation platform.Generate dynamic mesh of the intake port and chamber, select the correlativemathematical models and initial conditions using AVL FIRE software. And verify thecorrectness of the model.2. Research on effect of homogeneous EGR to methanol engine.(1) Pumping loss during intake process decreases with the increase of EGR rate, and themore the cycle fuel injection is, the more obvious EGR controls pumping loss. The throttle isopended entirely when load is70%and EGR rate is30%, so the pumping loss is reduced tothe lowest. The purpose of using EGR to control pumping loss is achieved.(2)30%EGR rate is a turning point. When EGR rate is below30%, peak of pressure incylinder and heat release rate is growing with the increasing of EGR rate, and peak phase isslightly delayed. But if EGR rate is higher than30%, the peak will drop fast and phase isdelayed a lot. The combustion is deteriorated by too much EGR. The accumulated heatrelease at TDC gets lower with EGR rate increasing, but it has little effect to the maximumheat release. Besides, with EGR rate increasing, combustion duration gets longer, and theignition time is delayed. Influence from EGR becomes weak when cycle fuel injectionincreases.(3) Raising EGR temperature can make up the deterioration on combustion for excessive EGR gas. It will help get good engine performance to advance the ignition timingat higher EGR rate and delay the ignition timing at lower EGR rate.3. Research on effect of stratified EGR to methanol engine.(1) It can keep EGR and fresh charge separated in the cylinder of a two valve methanolengine by adding helical partition in the intake port. The results show that if EGR pressure isequal or lower than fresh charge pressure EGR stratification is not ideal.(2) Keepping fresh charge pressure is80kPa, if only turning EGR pressure up, averageEGR rate in cylinder increases but stratified gradient is less than5%. If at the same timeshortening EGR inlet time, EGR stratification will get well in cylinder. And stratifiedgradient will increase too. For example, when EGR pressure is130kPa stopped at the430°CA, average EGR rate is up to40%with53%highest EGR rate and23%lowest EGR.Besides, it discovered that EGR temperature has little effect on the EGR stratification.(3) Analysis the difference on engine combustion between the homogeneous EGR andstratified EGR. The result shows that when EGR is stratified in cylinder the pumping lossduring intake process is lower than homogeneous EGR. And many combustion parameterssuch as the peak of mean pressure in cylinder, rate of heat release and combustion durationetc shows that stratified EGR optimizes the combustion of homogeneous EGR.