Hydrocarbon Emissions from an Annular Crevice: Effects of Spark/Insert Position, Equivalence Ratio and Pressure

Abstract

The hydrocarbon emission (HC) from a crevice formed in the gap between a cylindrical insert and the reactor wall (similar to the piston top/bore geometry in a reciprocating engine) was determined in a combustion bomb under quiescent conditions for propane-air mixtures at four fuel-air equivalence ratios (1.0,0.9,0.82 and 0.71), initial pressures between 75 kPa and 600 kPa, several spark locations and two insert positions (edge and central location). The experiments were performed by removing product gas samples from the reactor with or without the insert in place during combustion and analyzing the samples by gas chromatography. The HC emission arose from the fuel-air mixture stored in the crevice and was related to the 2-plate quenching distance. For the centrally-mounted insert, the emission varied continuously as pressure and equivalence ratio were changed and did not instantly change when the quench distance equalled the gap spacing. For the edge-mounted insert, the emission varied significantly with spark location, with the higher HC emission occurring when the spark was located at the contact point of the insert with the reactor.