Effect of an inter-ring crevice on unburned hydrocarbon emissions in a spark-ignition engine

The effect of the inter-ring crevice, the volume between the top and the se cond piston rings, on unburned hydrocarbon (UHC) emission was experimentall y investigated. The ultimate goal of this study was to reduce the level of UHC emission by minimizing the effect of the inter-ring crevice. For this p urpose, the unburned mixture trapped in the inter-ring crevice was extracte d to the crankcase during the late period of expansion and the early period of the exhaust stroke through the engraved grooves on the lower part of th e cylinder wall. The extraction of the mixture resulted in significant redu ctions in UHC emission by 23 per cent at maximum over a range of speeds (12 50-3500 r/min) and loads (185-556 kPa, b.m.e.p.), without any losses of eff iciency and power. This experimental study has confirmed the importance of the inter-ring crevice on UHC emission in a spark-ignition (SI) engine.