Experimental Study On Combustion And Control Of Gasoline HCCI Engine Base On Fuel Design And Injection Management

Homogeneous Charge Compression Ignition(HCCI)technology has great potential to reduce fuel consumption and emissions significantly,which has attracted more and more attention.HCCI has challenges on load expansion,combustion control,etc.,which limits the application of HCCI technology.Recently researches mainly focus on how to solve these problems of HCCI implementation on engineering application.In the thesis,technology combination of combustion control,dual fuel injection and coordination with hybrid system are used to optimize HCCI engine combustion and expand load operation range for the HCCI engine implementation on vehicle.First a 4-cylinder HCCI engine test bench based on Optimized Kinetic Process(OKP)is set up.Engine control system is developed for HCCI engine.Mode transition between SI combustion mode and HCCI combustion mode is realized based on OKP heat management system control.Experimental results show that,steady mode transition process of HCCI engine is realized with thermal management system and torque control strategy.Mode transition temperature threshold can be reduced and mode transition time can be shorten with inceasing compression ratio.When compression ratio is 13,mode transition time is about 5 minutes and intake air temperature threshold is about 170℃.while compression ratio is 15,mode transition time is about 3.5 minutes and intake air temperature threshold is about 105℃.In order to improve mode transition response,a new approach of n-heptane and gasoline real time control is implemented to realize HCCI engine mode transition.The experiments result shows,fast transition between SI and HCCI through real time control of n-heptane and gasoline injection quantity can be realised.There are one or two misfire combustion cycle during the process.Through the fuel quantity cycle by cycle control method,the fluctuation of engine torque and speed can be improved.In the thesis,the effects of fuel proportion,VVT and other important factors on HCCI combustion are experimental investigated.The experiments result shows,dual fuel proportion range for HCCI combustion is different on different engine operation points.The optimal dual fuel proportion rate is moved on different engine operation points.Dual fuel HCCI combustion can run stably even engine coolant temperature has a big fluctuation.Variable Valve Timing(VVT)can adjust air flow significantly,which can be used for HCCI low load expansion.Dual fuel mode HCCI combustion can reduce HC,CO and NOx emission significantly.To expand dual fuel HCCI combustion operation range further,the effect of air pressure and EGR on HCCI combustion are investigated.The experiment result shows,intake air boost can expand HCCI operating area on high load,and reducing intake air pressure can improve combustion stability on low load.EGR can improve combustion stability on high load.EGR has different effect on HCCI combustion with different dual fuel proportion.With the combination of intake air boost and EGR,dual fuel HCCI engine can reach 70% of original engine working load,which shows a wider operation range with OKP HCCI engine.A series hybrid system based on OKP HCCI engine is set up on test bench to investigate HCCI engine implementation on vehicle.The experiments result shows,a series hybrid system with HCCI engine shows fuel consumption 5.56L/100 km in NEDC cycle test,which has 11.75% reduction vs normal SI hybrid system.It can reduce 22% fuel consumption vs original vehicle.The combination of hybrid system and HCCI engine shows big potential on fuel economy and emissions improvement.