Effects of engine restart strategy on particle number emissions from a hybrid electric vehicle equipped with a gasoline direct injection engine

Abstract

Hybrid electric vehicle (HEV) tend to emit large amount of gaseous and particle emissions right after engine restart (ER). In this study, on-board particulate number (PN) measurement test and chassis dynamometer tests were conducted to analyze the effects of the ER combustion strategy on the gaseous and particle emission characteristics of a gasoline direct injection (GDI) HEV. The on-board PN measurement tests were conducted to examine the effect of a parameter sweep such as injection pressure, end of injection (EOI), spark timing of ER. It was measured by the pegasor particle sensor (PPS)-M, a device that measures the number of particles with a size from 23 nm to 25 μm, and the ES-582.1 module that can acquire electronic control unit (ECU) data. In the chassis dynamometer test, particle emissions, gaseous emissions and fuel economy of the reference case and the Combination Case 2 were compared and analyzed in the worldwide harmonized light vehicles test cycles (WLTC) mode test using Horiba, MEXA-ONE and MEXA-2000 solid particle counting system (SPCS). Reference case refers to a control strategy that does not touch anything in the vehicle's basic control strategy, and Combination Case 2 is the largest PN reduction case combined by calibrating the parameters. On-board PN measurement tests show that in reference case, ER PN accounted for about 70% of the total PN. Compared to the reference case, the sum of ER PN averages tended to decrease with higher injection pressure, advanced EOI, and retarded spark timing. The results of Combination Case 2 indicate that the sum of ER PN averages decreased by 88.7% compared to the reference case. In the WLTC mode test, THC, CO emissions and fuel economy were almost the same, and NOx was reduced by 85.6%. In both PPS and SPCS, the sum of ER PN average ratios decreased by 20%.