A Skeletal Chemical Kinetic Model for the HCCI Combustion Process

ABSTRACT In Homogeneous Charge Compression Ignition (HCCI) engines, fuel oxidation chemistry determines the auto-ignition timing, the heat release, the reaction intermediates, and the ultimate products of combustion. Therefore a model that correctly simulates fuel oxidation at these conditions would be a useful design tool. Detailed models of hydrocarbon fuel oxidation, consisting of hundreds of chemical species and thousands of reactions, when coupled with engine transport process models, require tremendous computational resources. A way to lessen the burden is to use a “skeletal” reaction model, containing only tens of species and reactions. This paper reports an initial effort to extend our skeletal chemical kinetic model of pre-ignition through the entire HCCI combustion process. The model was developed from our existing preignition model, which has 29 reactions and 20 active species, to yield a new model with 69 reactions and 45 active species. The model combines the chemistry of the low, intermediate, and high temperature regions. All of the chemical reaction rate parameters come from published data. Simulations were compared with measured and calculated data from our engine operating at the following conditions: speed – 750 RPM, inlet temperature - 393 K to 453 K, fuel - 20 PRF, and equivalence ratio - 0.4 and 0.5. The simulations are generally in good agreement with the experimental data including temperature, pressure, ignition delay, and heat release. This demonstrates that the model has potential for predicting the behavior of HCCI engines, and may provide a way to include non-trivial chemistry in multi-zone CFD simulations.