China 6 EGR gasoline vehicles without a GPF may struggle to meet the potential SPN10 limit

Particles larger than 10 nm from engine exhaust are gaining global concerns. In light of this, to investigate how EGR affects gasoline vehicle SPN10 (solid particles larger than 10 nm) emissions, seven gasoline vehicles (hybrid or conventional) were studied experimentally. The results revealed that EGR vehicles risk failing the current limit (6 * 10¹¹ #/km) more than those without EGR if the cut-off size was tightened from 23 nm to 10 nm. More specifically, during the WLTC test, EGR increased the SPN10 emission factors by 2 ∼ 3 times depending on vehicle powertrains (conventional or hybrid). Notably, SPN10 emissions increased significantly when EGR was actively engaged but showed a decrease when the EGR rate remained constant. EGR and the enriched fuel-air mixture are the critical reasons for the increased SPN10.