GCI Low-load Combustion Stability Research Based On Fully Variable Valve Actuation

In order to deal with energy security problems and increasingly stringent fuel consumption regulations,Gasoline Compression Ignition(GCI)has been taken seriously and developed.GCI is developed by HCCI,which not only has high efficiency and low NO_x and PM emissions as HCCI,but also has good controllability to combustion phase.However,it remains combustion instability problems in low loads,which is one of the obstacles of restricting the development and application of GCI.Internal Exhaust Gas Recirculation(EGR)has obvious influence on GCI combustion stability in low loads.Fully variable valve actuation has the advantages to realize Negative Valve Overlap(NVO),which allows internal EGR rate adjust in a wide range.Therefore,firstly a kind of Electro-Hydraulic Fully Variable Valve Actuation(EHVVA)is developed.LMS AMESim is used to build simulation platform of this system,and study the effect of system parameters on the valve performance,thus choosing reasonable system parameters.In addition,one-way throttle valve is adopted to improve buffering performance of valve motions,and the throttling parameters is optimized by genetic algorithm,the optimized final speed in closing process can be decreased to 0.07m/s.Then EHVVA test platform was built,and equipped with the engine for performance experiment.It turns out that experimental result is consistent with simulation result,which means the validity of simulation design.The system hydraulic pressure leads to valve lift change linearly,which is an effective way to valve lift adjustment.Solenoid valve signal inputs lead to valve timing change linearly,which can be used as valve timing adjusting.On the basis of regulation,the hydraulic pressure and solenoid valve input signal is calibrated for NVO at an engine speed of 1500r/min.Finally,based on NVO,the research about GCI low-load combustion stability is conducted based on different internal EGR rates and injection strategies.Single injection and double injection is used for GCI combustion performance experiment at first.The result show that compared with internal EGR rate,the injection timing has smaller effect on GCI combustion cyclic variation(COV-IMEP)by using double injection.However,the injection timing is equally important to internal EGR rate by using single injection when it comes to the influence to combustion cyclic variation,but the equivalent ratio has little effect.Futhermore,the GCI low-load combustion stability was studied under the condition of lean combustion with single injecton.It turns out that with the increase of the internal EGR rate,in order to realize stable GCI combustion,the equivalent ratio should be decreased and the injection timing should be advanced.At last when COV-IMEP is decreased to 4.37%,IMEP is extended to1.78bar under the condition of internal EGR rate 20%?equivalent ratio 3 and injection timing 22°CA BTDC.In summary,lower internal EGR rate is proper for charge and temperature uniformity adjustment,which contributes to GCI low-load stable combustion over a wider variation range of equivalent ratio and injection timing.