As a part of the effort to comply with increasingly stringent emission standards, engine manufacturers strive to minimize engine oil consumption. This requires the advancement of the understanding of the characteristics, sources, and driving mechanisms of oil consumption. This paper presents a combined theoretical and experimental approach to separate and quantify different oil consumption sources in a production spark ignition engine at different speed and load conditions.
A sulfur tracer method was used to measure the dependence of oil consumption on engine operating speed and load. Liquid oil distribution on the piston was studied using a Laser-Induced-Fluorescence (LIF) technique. In addition, important in-cylinder parameters for oil transport and oil consumption, such as liner temperatures and land pressures, were measured.
Engine test data and modeling results were combined to separate and quantify the contributions of oil entrained in the blowby gas flow, oil evaporation, and oil flow past piston and valve guides into the combustion chamber. The results show that the contribution of each consumption source varies with engine operating conditions. At low load, oil flowing into the combustion chamber was found to be the major consumption source (90 percent), while the contributions of oil evaporation and of blowby entrainment became more significant with increasing engine load. The variation of engine speed at full load increased the contribution of all three oil consumption sources. However, the relative importance of each source did not vary significantly with engine speed. The major contributions were from the oil transport (40 to 50 percent) and oil evaporation (30 to 40 percent).