Influence of the Mixture Formation on the Lubrication Oil Emission of Combustion Engines

Partly competing objectives, as low fuel consumption, low friction, long oil maintenance rate, and at the same time lowest exhaust emissions have to be fulfilled. Diminishing resources, continuously reduced development periods, and shortened product cycles yield detailed knowledge about oil consumption mechanisms in combustion engines to be essential. There are different ways for the lubricating oil to enter the combustion chamber: for example as blow-by gas, leakage past valve stem seals, piston rings (reverse blow-by) and evaporation from the cylinder liner wall and the combustion chamber. For a further reduction of oil consumption the investigation of these mechanisms has become more and more important. In this paper the influence of the mixture formation and the resulting fuel content in the cylinder liner wall film on the lubricant oil emission was examined. The oil emission behavior was investigated in a single cylinder spark ignition engine under different mixture formation conditions with Direct Injection (DI) and with Port Fuel Injection (PFI). The oil film thickness and the fuel content in the film were observed using the Light Induced Fluorescence (LIF) technique. The light accessed the cylinder liner through a silica glass window at significant locations which were determined by CFD-simulation. Moreover in-cylinder experiments have been carried out to measure the composition of the oil film and the hydrocarbon emissions by online mass spectrometry. Further numerical simulation results and fundamental laboratory experiments contributed to a more detailed understanding of the interrelation between mixture formation and oil emission.