Investigation of EGR Effect on Combustion and PM Emissions in a DISI Engine

Exhaust gas recirculation (EGR) is a well known technique for suppressing knock and reducing nitrous oxide (NOx) emissions in spark-ignition engines, and this technique is now receiving more attention because of the negative effect of EGR on engine particulate emissions. This paper investigates the effect of EGR on engine combustion (in-cylinder pressure and temperature, mass fraction burned (MFB), knock limited maximum brake torque (KLMBT) spark timing, net indicated specific fuel consumption (ISFCnet), exhaust gas temperature) and emissions (NOx, unburned hydrocarbon (HC), particulate matter (PM)) in a direct injection spark ignition (DISI) engine. The tests were carried out in a single-cylinder DISI research engine with engine loads between 5.5 and 8.5 bar indicated mean effective pressure (IMEP) and various EGR ratios of up to 13%. The results show that by adding 12% EGR, the KLMBT spark timing could be advanced by 8 crank angle degrees (CAD) which resulted in a 4.1% fuel consumption reduction at 7.0 bar IMEP. EGR addition generally increased the accumulation mode particles and reduced the nucleation mode particles.