Abstract
The European legislation will bring a restriction on the particle number emission for gasoline direct injection spark ignition engines. Liquid fuel films attached on wall surfaces are presumed to cause the soot emissions during the cold startup period. In this study, soot formation originated in combustion of liquid fuel films was investigated by using a 3D engine simulation. Calculations were performed for Rapid Compression and Expansion Machine model having a bore of 80. 3mm, a stroke of 95.0mm and a compression ratio of 10.5. Results show that liquid fuel films remained until the end of expansion stroke without evaporating when the wall temperature was low, even with the passage of flame. In contrast, liquid fuel films evaporated quickly and the fuel diffused into the cylinder when the wall temperature was sufficiently high. From the above, it was revealed that liquid fuel films have a large influence on the soot generation at an intermediate temperature during the cold startup period. Emission factors of liquid fuel films and soot can be expressed as a function of the wall temperature.
