Simulation of HC-Emissions from SI-Engines - A Parametric Study

Earlier modelling of SI engine HC-emissions indicated that the absorption/desorption of fuel HC in the oil film played a rather important role for the engine-out HC-emissions. However, recent experimental results seem to indicate that this mechanism does not play a major role. Therefore, we updated a previous model in order to obtain a better understanding of the absorption/desorption phenomenon. The upgraded absorption/desorption model has been combined with the MIT ring/liner lubrication model and applied to a single cylinder engine with known lubrication characteristics. The calculations have been carried out for steady-state and warm-up conditions. Compared to earlier results we found that due to an essentially smaller oil film thickness calculated by the lubrication model the absorption/desorption process exhibits a much faster response than previously estimated. The main statement is that the oil film on the cylinder liner is fully penetrated by the absorption /desorption process for warmed-up conditions in the case of ideal lubrication. The importance of this work is that the in-cylinder HC-emissions originating from this HC-emission source are proportional to the total volume of oil contained on the combustion chamber surfaces. This result stresses the importance of further increased oil control for SI-engines. However, the contribution to engine-out HC-emissions is smaller than previously thought due to increased postoxidation of the hydrocarbons emitted from this source.