Comparative evaluation of engine control strategy on regulated emissions and nano-particle characteristics of LPG direct injection (LPDI) vehicle during the cold start and the hot phases in the FTP-75 cycle

To evaluate the potential of a dedicated LPG direct injection (LPDI) vehicle, we investigated several engine control parameters that are closely related to the characteristics of mixture preparation and nano-particle emissions. Many researches have pointed out that any amount of particle emissions from GDI vehicles were made during the cold start and cold transient phase. Therefore, in the study, four types of engine control strategies for the LPDI vehicle were applied to evaluate particle number (PN) concentration and regulated emissions in the cold start phase and the hot start phase under the FTP-75 cycle. The reduction rate of the PN concentration with LPG application reached approximately over 99% less than that of the GDI vehicle. The PN level of LPDI vehicle applied various engine control parameters was decreased 60.3% less than that of the LPDI vehicle applied the double split injection (DSI). 73.5% of the total exhausted nanoparticles were emitted during the first acceleration period of phase 1 for the GDI vehicle, whereas those of LPDI vehicles were emitted were 51-78%. A bimodal particle size of 5<dp<100 nm was formed in the GDI vehicle, whereas a sub 23 nm nucleation mode was mainly formed in the LPDI vehicle. The regulated emissions of the LPDI vehicle showed better performance than the GDI vehicle. CO₂ emissions and fuel economy of the LPDI vehicle was decreased approximately 8-11% and 16-18% compared with those of the GDI vehicle.