Experimental evaluation of engine control strategy on the time resolved THC and nano-particle emission characteristics of liquid phase LPG direct injection (LPG-DI) engine during the cold start

This study investigates the time resolved total hydrocarbon (THC) and nano-particle emission characteristics of liquid phase LPG direct injection (LPG-DI) engines during the cold start and during fast-idle operation state. The fuel circuit for the direct injection of LPG fuel was converted from a returnless-type into a return-type system to evaluate the cold start performance of a dedicated LPG-DI engine. To improve the engine-out THC as well as nano-particle emissions and catalyst light-off behavior during the cold start phase, the effect of various spark timings and excess air ratio were investigated using a fast response THC analyzer, combustion analyzer, and differential mobility spectrometer (DMS). The combustion stability, cycle-to-cycle THC, light-off temperature (LOT) of the catalyst, and nano-particle emission characteristics were evaluated during the cold start and warm-up phase of the LPG-DI engine. The experimental results showed that the retarded spark timing after the top dead center (TDC) and lean operation have advantage to improve the time resolved THC, LOT, and combustion characteristics in the cold start condition. The cumulative THC reduction rate during 30 s was about 25-43% and the light-off times of the catalyst were shortened by 25-31 s as the retarded spark timing after TDC.