Effects of Fuel Absorbed in Oil Film on Unburnt Hydrocarbon Emissions from Spark Ignition Engines : Numerical Model of Dynamic Process of Fuel Absorption and Desorption

Absorption and desorption of fuel by motor oil that coats the cylinder side wall with a thin oil film is thought to be one of the important sources of unburnt hydrocarbon emissions from spark ignition engines. A simplistic model which describes the dynamic process of fuel absorption and desorption in the thin oil film has been developed. Calculated results show that the rate of the absorption and desorption process is comparable to the engine motion, and the amount of unburnt fuel emitted from the oil film depends on the position of the oil film, rotating speed, diffusion coefficient, oil layer thickness, existing cycles of the oil layer and initial fuel concentration in the motor oil. It is also demonstrated that the synthetic model which is the sequential connection of the four models, i.e., the fuel diffusion through the oil layer, the cylinder pressure, the ring gas pressure and the oil layer thickness, is useful in estimating the dynamic process in the engine given its specifications and operating conditions.