On CFD-Analysis of Heat Transfer of a Heavy-Duty Diesel Engine

Abstract: In this work, a heavy-duty diesel engine was studied by employing CFD simulations on a closed volume engine segment. These simulations were used to evaluate both the effects from certain parameters on the wall heat transfer, and to examine how reduction of heat transfer would effect the engine performance and emission levels. In the first study, an initial investigation concerning the in- cylinder heat transfer was performed. This included a simple parameter study, performed to estimate the contribution of each parameter on the in-cylinder engine heat transfer. The parameter study revealed that most of the parameters selected do in-fact significantly affect the in-cylinder heat transfer. However, the effects on the indicated mean effective pressure, or indicated power output are different. Changing the amount of EGR and the swirl number did not show any dramatic effects on the indicated power output, while the injection duration showed much more dynamic effects on the indicated power output. In the second study, an investigation was made on the same heavy duty diesel engine, using both conventional diesel combustion mode and a partially premixed combustion (PPC) mode. Both combustion modes were validated using experimental data, before various heat flux boundary conditions were applied. These conditions were used to evaluate the engine response in terms of engine performance and emission levels for the different levels of heat rejection. The engine performance was measured in terms of specific fuel consumption and estimated power output, while the calculated net soot and accumulated NOx mass fractions were used for comparing the emission levels. The results showed improved efficiency for both combustion types, but only the PPC combustion mode managed that without increasing the production of NOx emissions severely. It was also noticed that the emission levels, for the baseline cases, were much lower for the PPC combustion mode than for the diesel combustion mode.