Experimental Study On The Influence Of DI Fuel Characteristics On PPCI Engine Performance

Currently, high efficiency and low emission combustionin engine isone of the targets pursued by engine experts. Due to the diffusioncombustion mode, it is hard to achieve the low smoke and NOx emissionssimultaneously in traditional engine. PPCI(Partially PremixedCompression Ignition) is a new combustion mode, which have the potentialto achieve the goal of high efficiency and low emissions.Based on a single compression ignition cylinder, CNG premixed tubeis added. The combustion characteristics and emissions of PPCI engine areinvestigated in which liquid fuels are injected directly into the cylinderwhile the CNG is premixed with air. Later, the effect of EGR on theperformance of PPCI engine is researched.The research on performance of the diesel/CNG PPCI engine showthat:(1)With the increase of premixed CNG, combustion phase is delayed,the maximum pressure in cylinder decrease, gas mean temperaturedecrease. The equivalent fuel consumption can reach low level withreasonable CNG ratio.(2)Compared to the original engine, diesel/CNGPPCI engine have a better performance of equivalent fuel consumption athigh load, NOxand smoke emissions decrease, CO and unburned HCemission increase.(3)With the increase of EGR, maximum pressuredecrease, combustion phase is delayed, the peak of heat release increasesmoothly. CO emissions increase, unburned HC and smoke emissions keepunchanged, NOxemission decrease sharply. The research on performance of the biodiesel/CNG PPCI engine showthat:(1)Compared to Diesel/CNG PPCI engine, the combustioncharacteristics is almost same.(2)The equivalent fuel consumption is lowerwhen the RCNGis low. CO, NOxand smoke emissions are lower, unburnedHC is higher.(3)The effect of the EGR on biodiesel/CNG PPCI engine isalmost same. The only difference is smoke emission decrease more sharplywith the increase of EGR.The research on performance of the DME/CNG PPCI engine showthat:(1)Compared to the original diesel engine, engine fueled with DMEcan only reach40%of its full load and have a better emission performance.(2)Compared with the other two PPCI engine, DME/CNG PPCI engine canachieve a lower emissions performance.(3)The effect of the EGR onDME/CNG PPCI engine is almost same.The combined results show that stable combustion progress of PPCIengine can be achieved by choosing the pilot fuel properly. The fuel withhigher oxygen percentage and higher octance number can be used to reduceCO, NOxand smoke emissions. Moreover, such fuels have the potential toavoid smoke emission and the benefit to adopt higher EGR ratio which isused to reduce NOxemissons.