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This study focuses on the time history of the concentration of unburnt HC in an exhaust system of spark ignition engine. A mathematical model which can estimate gas temperature, and degree of oxidation in an exhaust system for given engine specifications and operating conditions is developed. This model is confirmed by experiment in which instantaneous HC concentrations are measured by using a fast sampling valve, and measurement of HC emissions in an exhaust pipe of a methane fueled engine.

In both spark ignition engines and diesel engines, exhaust gas recirculation system (EGR) is well known as an effective technique to reduce nitrogen oxides emissions. However, wear of piston rings and cylinder liners are sharply increased by EGR. It is widely considered that sulfur oxides contained in exhaust gas strongly relate to wear. In order to clarify the pure effect of sulfur oxides on piston ring wear, we experimented by adding sulfur dioxide positively to induction air. Furthermore, we compared the measured amount of wear with the amount of sulfur dioxide absorbed into a lubricating oil film, which was estimated by a numerical model. Consequently, it is confirmed that sulfur dioxide absorbed into a lubricating oil film played an important role on piston ring wear.

Unreacted fuel in ring crevice volumes is a significant source of hydrocarbon emissions from spark ignition engines. If the ring crevice is designed with a wider clearance into which the flame will propagate, the unreacted fuel can be reduced. In this paper, the conditions of flame propagation into the ring crevice are investigated by using ionization probes imbedded in the moving piston of a four-stroke spark ignition engine. It is found that the flame propagates into the ring crevice if the quenching distance when the flame reaches the crevice is narrower than the piston top land clearance.