Abstract
Liquid fuel films attached on wall surfaces are presumed to cause soot emissions during the cold startup period of gasoline direct injection spark ignition engines. In this study, soot formation originated in combustion of liquid fuel films was investigated by using a 3D simulation. Calculations were performed for a Rapid Compression and Expansion Machine model. Effects of physical properties and the composition of the fuel were examined. Results showed that a portion of liquid fuel films remained until the end of the expansion stroke without evaporating even with the passage of the flame under the cold startup condition. Emission factors of liquid fuel films and soot were lager for PRF095 (i-C_8H_<18> 83%, n-C_7H_<16> 4%, C_6H_5CH_3 13%) than those of PRF100 (i-C_8H_<18> 100%). PRF100-ND having evaporation properties same as n-C_<10>H_<22> and chemical kinetics same as i-C_8H_<18> was prepared numerically. Emission factors of PRF100-ND were larger for liquid fuel films and smaller for soot than other fuels under the cold startup condition.
