Abstract
A combustion concept was proposed to reduce unburnt THC from gasoline direct injection engines during cold-start. (1) The retarded ignition control with the split injection, the 1st injection timing is the later period of compression stroke and the 2nd one is the early period of expansion stroke was able to heat the exhaust gas up more than 700 deg.C at 20 seconds after the engine start. (2) Combustion stability at retarded ignition was improved exceedingly by using the fuel-spray directed under the spark plug and the step-shaped piston. The fuel injected at the 1st injection timing was guided around the spark plug so stable stratified mixture was generated until the retarded spark timing. (3) There was no penalty at full load conditions with the proposed combustion concept, because required step height on the piston for the concept was considerably low so mixture distribution at full load condition was not affected by the piston geometry.
