A Model of Quench Layer Entrainment During Blowdown and Exhaust of the Cylinder of an Internal Combustion Engine

An aerodynamic model of the entrainment of the head wall quench layer during blowdown and exhaust of an internal combustion engine has been developed. The model may be used to calculate the time resolved concentration and mass flowrate of hydrocarbons (HC) in the exhaust, from a knowledge of engine geometry and operating conditions. It predicts that the area A_s from which HC are swept will be proportional to the cube root of the ratio of the quench layer thickness δ_q to the thickness of the viscous boundary layer δ_v. Since the mass of HC emitted is proportional to the product of the HC density ρ_HC, the area A_s and the thickness δ_q, the HC emissions will be proportional to the product ρ_HC δ_q^4/3 and this is the most important factor determining the emissions.

The model also predicts that the time dependence of the HC mass flowrate will depend relatively strongly on the pressure ratio p₄/p_e across the exhaust valve when it opens: in an unthrottled engine virtually all the head wall HC exit during blowdown; in a heavily throttled engine the HC are emitted more or less uniformily during the exhaust stroke.

It is expected that the model will be useful both for interpreting experimental measurements of HC emissions and for predicting HC emissions from practical engines. Comparisons of the results obtained to date with the available experimental data shows good agreement.