A Note on Unburned Hydrocarbon Emissions from Automotive Engines

Abstract

A careful treatment of an unsteady one-dimensional laminar model of the interaction of a propagating premixed fuel-lean flame with a cooled wall is undertaken. For the reciprocating-piston-type automotive-engine context of interest, expansional cooling of the power stroke, and thermal nonuniformhy in the burned gas owing to nonisobaric combustion, are included; nevertheless, nearly complete oxidation of residual near-wall hydrocarbons prior to blowdown is confirmed. Measurement of a significant peak at blowdown for hydrocarbon content of the cylinder exhaust under heavy-load operation, once explained in terms of head-wall-quench-layer content, now seems puzzling, and the alternative crevice-content explanation appears forced. Suggestions for further experimental and theoretical investigations concerning piston-crevice contributions to unburned-hydrocarbon emissions, and their reduction, are set forth.