OXIDATION OF THE PISTON CREVICE HYDROCARBON DURING THE EXPANSION PROCESS IN A SPARK-IGNITION ENGINE

Engine-out HC emissions were measured in SI engine experiments in whic h the piston topland crevice size was changed systematically. For a wa rmed-up engine, the HC emissions were found to be modestly sensitive t o the piston crevice size-a 10% change in size results in approximatel y a 2% change in HC emissions. This low sensitivity is explained in te rms of a crevice HC diffusion/oxidation model in the expansion process . When the piston crevice is sufficiently small, however, the model sh ows that the HC emissions have a one-to-one correspondence with the cr evice size.