Modeling in-cylinder heat transfer for a single cylinder HCCI engine

In-cylinder heat transfer processes have a direct effect on autoignition timing, burn rate and in-cylinder pressure in homogeneous charge compression ignition (HCCI) engines. Because of the complexity of the system, development of HCCI engine models that accurately reproduce in-cylinder pressure measurements (i.e. pressure rise rate and maximum pressure) requires an empirical treatment of the in-cylinder heat transfer. The purpose of this paper is to evaluate the performance of Woschni and Hohenberg heat transfer correlations by comparing GT-Power engine model predictions with measured in-cylinder pressure data from a single cylinder HCCI engine. Analysis was performed by generating a single zone GT-Power model of a modified John Deere DI 2.4L four-cylinder engine, which was previously converted by the authors to operate in HCCI port injection mode. The HCCI engine was operated at an equivalence ratio of 0.33 and a fuel mixture of 40% iso-octane and 60% n-heptane by volume. The combustion chemistry was modeled using a reduced Primary Reference Fuel (PRF) mechanism from Ra and Reitz with 41 species and 130 reactions. Results from the GT-Power engine model, which included the effects of in-cylinder heat transfer, were compared against the experimental engine data and a 0-D CHEMKIN model using the same chemical kinetic mechanism. The modeling results underscore the importance of the in-cylinder heat transfer model for accurate predictions of in-cylinder pressure history.