Numerical Investigation On The PODE/Gasoline HPCC Combustion

The heat release rate and combustion phase can be controlled in Highly Premixed Charge Combustion(HPCC)by combining the in-cylinder direct injection of high reactivity fuel with port injection of low reactivity fuel.Ultra-low NO_x and soot emissions can also be achieved over a wide range of engine loads.However,one of the major issues of HPCC operation is that the high load extension is limited by the excessive pressure rise rate and high NO_x and soot emissions.PODE is a high reactivity fuel with high oxygen content,low heating value and no C-C bond.It can replace diesel as high reactivity fuel in HPCC mode and greatly reduce soot emission.Because of the low energy injection rate of PODE,the fuel injection duration can be significantly prolonged,and the heat release rate can be effectively reduced,which also provides potential approach for heavy load extension.Because it is difficult to observe the combustion heat release process of in-cylinder mixture in experimental study,so it is necessary to study the combustion process of PODE/gasoline HPCC by numerical simulation.Nevertheless,the influence of PODE,which is a new high reactivity and low energy density alternative fuel,on in-cylinder mixing,spontaneous ignition,combustion heat release and emissions of dual fuel HPCC is still unclear.Therefore,it is necessary to study PODE/gasoline HPCC mode by numerical simulation.Firstly,the combustion and emission characteristics of PODE/gasoline dual fuel HPCC under medium and high load were investigated and compared with diesel/gasoline dual fuel HPCC mode.The results show that,under medium load condition,when the combustion phase remains the same,the initial heat release region of PODE/gasoline HPCC distributes more widely in the cylinder and in the area with lower equivalence ratio than that of diesel/gasoline HPCC.Under heavy load condition,when direct injection fuel ratio remains the same,the initial heat release of PODE/gasoline HPCC is also concentrated in the lower equivalence ratio area.However,due to the longer duration of direct injection,PODE is injected continuously and combusts with gasoline at the same time.So,there is still heat release of high equivalence ratio in the follow-up.Compared with diesel/gasoline,combustion phase delays,and combustion duration is prolonged.Under medium and high load conditions,PODE instead of diesel as HPCC direct injection fuel can improve IMFP and reduce soot,CO and HC emissions while reducing pressure rise rate.On this basis,the effects of PODE direct injection time,premixed fuel ratio and EGR ratio on combustion process and emissions in PODE/gasoline HPCC mode under medium and high load conditions were studied respectively,and the optimal control strategy was obtained.The results show that under heavy load conditions,using in-cylinder late injection strategy and reducing premixed fuel ratio to 50%~60%can reduce the heat release rate and prolong the combustion duration.The peak pressure rise rate and in-cylinder peak pressure can be within the engine limits without adopting high EGR rate.At the same time,NO_x and soot emissions can meet the Euro VI standard.Medium load condition is the ideal operation condition.NO_x and soot emissions are very low,and the parameters can be flexibly changed without the limitation of pressure rise rate and emissions.Therefore,PODE as HPCC high active fuel can achieve extremely low soot emission under medium and high load conditions,meanwhile has the potential to expand to higher loads.