Real-world particle number emissions from hybrid electric vehicles with port fuel injection and dual injection (MPI-GDI) systems

Abstract

The particle number (PN) emissions in hybrid electric vehicles (HEVs) were analyzed, focusing on multipoint injection (MPI) and dual injection systems. Measurements were conducted under real driving conditions using a portable emission measurement system (PEMS). The MPI HEV showed higher PN emissions and more frequent engine restarts during the cold start phase, indicating the dual-injection system's greater effectiveness in reducing PN emissions. In the urban section after cold start, both vehicles exhibited PN spikes due to frequent engine restarts and combustion instability. During high-speed driving, PN emissions were more influenced by the fuel injection strategy than by engine restarts. The MPI HEV maintained lower emissions under fully warm conditions, promoting better mixture formation and combustion. In contrast, the dual-injection HEV likely operated in direct injection mode, increasing PN emissions due to limited mixture formation and potential fuel wall wetting. For both MPI and dual-injection HEVs, analysis of the PN contributions from engine restarts revealed that 70 % of total PN emissions occurred within 30 s after engine start. MPI HEVs recorded higher PN emissions in urban driving phases, with 90 % of total emissions occurring in this phase, of which 70 % was attributed to cold starts. In contrast, dual-injection HEVs emitted more PN emissions in rural and motorway sections, accounting for 74 % of their total PN emissions. These findings highlight the effects of injection type, driving conditions, and engine restarts on PN emissions in hybrid vehicles, supporting strategies to reduce emissions in real driving conditions.