Uuburned Hydrocarbons Emission Source from Engines

A UHC emission source analysis was done for a lean burn natural gas-fired engine. The possible sources were chosen as wall quenching, crevices, too slow turbulent burning velocities, and flame quenching by excessive turbulence. By making each source analysis for each possible source, it was discussed qualitatively what the major source is, while engine geometry (crevice volume), equivalence ratio, and ignition timing were varied. It was confirmed that (1)flame quenching must have occurred in practical engines, (2)the amount of UHC by flame quenching is very successfully explained by Karlovitz number (Ka) and it is linearly correlated to Ka, (3) the magnitude of Ka at which flames quench obtained from the experiments exactly coincides with the author's classification at which flame starts to be quenched, (4)UHC from crevices is a major source at higher equivalence ratio, but UHC by flame quenching suddenly increases at lower equivalence ratio, and it becomes a major source, (5)the dependence of UHC from crevices on the equivalence ratio is very weak, but the dependence of equivalence ratio on flame quenching is very strong.