Impact of test cycle on mass, number and particle size distribution of particulates emitted from gasoline direct injection vehicles

Abstract

This paper presents an investigation of emissions from gasoline direct injection (GDI) vehicles and analyzed the characteristics of emitted particulate matter (PM), the emission factors of particulate number (PN) and size distribution properties, including four test cycles: the new European driving cycle (NEDC), the worldwide harmonized light vehicle test cycle (WLTC), the USA federal test procedure-75 (FTP-75) and the China light-duty vehicle test cycle (CLTC). The results reveal that for China VI standard GDI vehicle, compared with CLTC, which is the newest test cycle according to realistic road conditions in China, the aforesaid evaluation indexes of FTP-75 and WLTC are basically higher due to their higher acceleration and deceleration ratio. Compared with hot start, a cold start followed by warming-up process has a significant impact on PN emissions over all test cycles and different test cycles show diverse sensitivity to the change of start-up conditions. The particles with a diameter of 5.6–23 nm (sub-23 nm) account for 43.1–57.7% of the total PN emission quantity for China V standard GDI vehicle, which is about 5–15% higher than that of theoretical assumptions. Different piecewise speed segments exhibited different impacts on PN characteristics when acceleration and deceleration reveal greater influence. Gasoline particulate filter (GPF) could effectively capture full-size particulates including fine particles as sub-23 nm particles, which is verified over FTP-75 and CLTC, while sub-23 nm PN emission is still at a high level over WLTC for its ultrahigh speed segment. There could have been an underestimation of the real particle number emitted from GDI vehicle while the emission of solid sub-23 nm particles was excluded under current emission regulations.