The Effect of Friction Modelling on the Prediction of Turbocharged Diesel Engine Transient Operation

A detailed transient analysis simulation program developed has been used to study the effect of friction modelling on the prediction of turbocharged diesel engine operating under transient conditions. Friction modelling during the transient event is simulated using one of the following methods: a) the mean fmep (friction mean effective pressure) approach with friction torque remaining constant during the cycle, b) the method proposed by Rezeka and Henein where friction torque is explicitly modelled at each degree crank angle, and c) a simplified method which combines the simplicity of the mean fmep approach with the in-cycle variations of the explicit one. It is revealed, as shown in a series of detailed diagrams for various load changes, that the mean fmep approach underestimates engine speed droop up to 12% for the transient cases considered, whereas the simplified method gives results which come very close to the results of the explicit one based on the Rezeka-Henein model.