Analysis of Hydrocarbon Emissions From Conventional Spark-Ignition Engines

Abstract

The quench layer on the cylinder wall of a spark-ignition engine is modeled for the case where a tangential or swirl velocity exists. Both asymptotic and numerical methods of solution are used, The usual two-layer structure is employed for the turbulent boundary layer and Crocco's integral is used to relate the temperature and velocity fields. The quench layer is defined as the region in which the temperature is less than an ignition temperature. In the first analysis only quenching is considered, and it is shown that the resulting concentration of hydrocarbons is much too high compared to experimental results. Next, the model is extended to allow diffusion, and it is shown that in one stroke time the majority of the mass of unburned mixture in the original quench layer has diffused out and burned. Finally, two means of replenishing the unburned mixture in the quench layer. consisting of the desorbing of fuel from the oil film and outgassing from the first ring crevice, are included in the model. Calculations are carried out using parameters associated with a typical production engine. Variations of unburned HC in the exhaust with several important engine parameters are presented. In each case, the trends of the calculated data agree with those found experimentally.