Optimization Study Of Combustion And Emission Characteristics For A Compression Ignition Engine Fueled By Gasoline/Hydrogenated Catalytic Biodiesel Blends

Gasoline compression combustion(GCI)engines have received more and more attention owing their higher thermal efficiency and lower harmful emissions.However,GCI engines fueled by pure gasoline with high volatile,high octane number and low reactivity are limited to poor combustion stability at low loads,start difficulties at low temperature and high pressure rise rate at high loads.The hydrogenation catalyzed biodiesel(HCB)prepared by hydrogenation decarboxylation has the advantages of low cost,good ignition performance,no oxygen and good stability.Therefore,this paper proposes to blend the highly reactivity second-generation HCB with gasoline to improve the problems of GCI engines under low load conditions.The main research contents of this article are as follows:(1)An experimental study of GCI engines fueled by gasoline/HCB blends under different load conditions was performed on a heavy-duty diesel engine.The results show that with the increase of HCB blended ratio,the ignition performance and combustion stability are significantly improved,and the maximum combustion pressure in the cylinder is effectively suppressed.In addition,it was found that the blended ratio of HCB should match the injection time(SOI)in order to obtain better engine performance and a wider operating range.In terms of emissions,with the increase in the blending ratio of HCB,the emissions of nitrogen oxides(NOx),carbon monoxide(CO)and unburned hydrocarbons(HC)can be significantly reduced,but the particulate emissions are slightly increased.(2)Based on the above test results,a numerical investigation of GCI combustion fueled by gasoline/HCB blends under low load conditions was performed on a heavy-duty diesel engine.The effects of HCB blended ratio,initial intake gas temperature and SOI on GCI engine performance were mainly studied.The results show that high-reactivity HCB initiates the combustion of low-reactivity gasoline,and the blended ratio of HCB,initial intake gas temperature and SOI have a great influence on the thermodynamic state of fuel/air mixture and engine performance.With the increase of HCB blended ratio,the engine noise,CO and HC emissions can be effectively suppressed,but when the intake gas temperature is too high,it will lead to an increase in NOx emissions,and when the intake gas temperature is too low,it will cause an increase in soot emissions.Delayed SOI can achieve more stable combustion and reduce CO emissions,but at the same time will increase NOx emissions.Overall,the optimal operating range of the GCI engine is mainly limited by engine noise.This problem can be improved by two-stage injection.In addition,the differences in combustion and emission performance under low load conditions between the GCI mode and the reactive control compression ignition(RCCI)mode are also discussed.The results show that,compared with GCI mode,RCCI mode has lower combustion noise.However,the RCCI engine is greatly affected by the initial intake temperature,and its fuel economy is worse than the GCI engine.(3)Coupling KIVA-3V program and non-dominated genetic algorithm(NSGA-?),a computational optimization was performed on a GCI engine fueled by gasoline/HCB blends under low load conditions.In addition,the influence weighting of multiple injection and engine operating parameters on GCI combustion under optimal operating conditions is discussed.The results show that the optimized G70H30(70% gasoline and 30% HCB)can reduce the demand for intake temperature and intake pressure and obtain the optimal operating conditions for efficient combustion with ultralow NOx and soot emissions.As the increase of HCB blended ratio,the diversity of engine operating parameters is getting better,which can effectively reduce the initial temperature requirement for optimal operating conditions.When the main injection occurs after the combustion caused by the pilot injection,the main injection reduces the heat release rate(HRR)by generating both concentration and temperature stratification in the reaction zone.At this time,the exhaust gas recirculation(EGR),time of pilot injection and main injection and pilot injection fraction play a leading role in engine performance;When the main injection occurs before the combustion caused by the pilot injection,the main injection mainly reduces HRR through concentration stratification.At this time,EGR,initial temperature and pilot injection ratio play a leading role in engine performance.