Influence of piston cooling jet and renewable fuel blends on particulate emissions in a gasoline engine

Abstract

Replacing a portion of the hydrocarbons in fossil fuels with renewable ones can lower net carbon dioxide (CO 2 ) emissions but may increase engine-out pollutants. Gasoline direct injection (GDI) engines emit particle number (PN) emissions due to fuel evaporation, mixing, and fuel composition issues. Piston cooling jets (PCJs) help reduce piston temperature but can decrease fuel evaporation. This study investigates PN emissions under PCJ-on and PCJ-off conditions at an indicated mean effective pressure (IMEP) of 9 bar, with varying start of injection (SOI) timing and fuel injection pressure (FIP). Images of combustion were captured to identify the sources of soot. Results indicate that the fuel film on the piston promotes pool fires and PN emissions under PCJ-on conditions. PCJ-off (hot piston) conditions showed ∼ 99 % and ∼ 35 % lower PN emissions than PCJ-on conditions at advanced and optimal SOI timing, respectively. Retarded SOI timing showed pool fires at the injector tip in both PCJ-on and PCJ-off cases. The effects of three gasoline blends (P, F1, F2) on PN emissions were investigated at 12–18 bar IMEP under hot piston conditions. Results indicate that all test fuels exhibited significant differences solely in particles with a mobility diameter of 10–100 nm. Particles with < 10 nm accounted for ∼ 80 % of the total PN at higher IMEPs. Particles with 10–23 nm accounted for 52–75 % of particles larger than 10 nm. Hydrocarbon (HC) and nitrogen oxide (NO) emissions decreased, while PN and CO 2 emissions increased with increasing engine load.