Study On Diesel Jet Controlled Compression Ignition Phase Of Diesel/Gasoline Premixed Charge

Low-temperature premixed compression ignition mode,which breaks through the trade?off between economy and emission performance of traditional engine combustion modes,can simultaneously reduce the fuel consumption,NOX and soot emissions.However,the ignition timing control,load extension and high THC and CO emissions severely limit the practical application of the premixed compression ignition mode.An innovative combustion mode named dual-direct injection diesel Jet Controlled diesel/gasoline premixed charge Compression Ignition(JCCI)mode was proposed in this research to robustly control the ignition timing,promote the practical use of the premixed compression ignition mode and achieve the unification of mixture formation,combustion mode and fuel in traditional engines.In this JCCI mode,the premixed charge is ignited by a small quantity of jet-injection diesel,which gives a robust control on the ignition timing.The stratification of the premixed charge controlled by the direct pre-injection parameters and the retarded ignition timing can be used to reduce the maximum pressure rise rate(MPRR),extending to the full engine load operation.In addition,the blends of diesel and other fuels such as gasoline are used as the pre-injection fuels,which improves the premixed charge reactivity.Combined with the control of premixed charge distribution,THC and CO emissions can be reduced effectively.The combustion and emission characteristics of JCCI mode were investigated on a principled engine,which was developed based on the 186FA diesel engine in conjunction with the relative measurement and control program.The experimental results showed that the ignition timing was controlled by the diesel jet-injection timing robustly at four engine loads.The second combustion stage was controlled by the premixed charge preparation process independently through the adjustment of the pre-injection parameters.The stratified premixed charge prepared with double pre-injection strategy reduced MPRR by over 60%.JCCI mode was extended to the full load operation with double pre-injection strategy and retarded diesel jet-injection timing.Compared to conventional diesel combustion(CDC)mode,the break specific fuel consumption(BSFC),soot emissions and NO,emissions were reduced by 4.3%,75.3%and 16.3%,respectively.Independent two-stage combustion process in JCCI mode has been found from the engine experimental results.A three-dimensional(3D)simulation by CONVERGE was conducted to analyze the in-cylinder working process of the JCCI mode.Simulation results showed that the spontaneous combustion of the jet-injection diesel,entraining some surrounding premixed charge,led to the first stage of high-temperature combustion,which is named as the jet fuel spontaneous combustion stage.Along with the first combustion stage,in-cylinder pressure and temperature increased rapidly,and the remaining premixed charge ignited independent of the first combustion stage region,led to the second high-temperature combustion stage,named as pre-mixture combustion stage.NO.emissions were rarely produced in the second combustion stage and THC emissions were mainly located in the crevice region.From the research of the engine experiment and 3D simulation,the second combustion stage and THC emissions were directly affected by the premixed charge preparation process.The spray visualization and engine experiments were carried out to investigate the effect of direct pre-injection blended fuels on the spray characteristics and JCCI mode performance.Spray visualization showed that low pre-injection pressure and late pre-injection timing are advantageous to reduce the blended fuels spray penetration distance and improve the wall-wet issues.The kerosene with lower viscosity and surface tension promoted the breakup and evaporation process.Engine experimental results showed that the pre-injection fuels with 15%mass fraction kerosene instead of diesel shortened the combustion duration and increased the indicated thermal efficiency,and THC and CO emissions were reduced obviously at higher engine loads.