Prediction of Pre-ignition Reactivity and Ignition Delay for HCCI Using a Reduced Chemical Kinetic Model 2001-01-1025

Homogeneous Charge Compression Ignition (HCCI) engines have the possibility of low NOx and particulate emissions and high fuel efficiencies. In HCCI the oxidation chemistry determines the auto-ignition timing, the heat release rate, the reaction intermediates, and the ultimate products of combustion. This paper reports an initial effort to apply our reduced chemical kinetic model to HCCI processes. The model was developed to study the pre-ignition characteristics (pre-ignition heat release and start of ignition) of primary reference fuels (PRF) and includes 29 reactions and 20 active species. The only modifications to the model were to make the proscribed adjustments to the fuel specific rate constants, and to enhance the H2O2 decomposition rate to agree with 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, fuels - 20 PRF, 50 PRF and 20 PRF with alkenes and aromatics, and equivalence ratio - 0.4 and 0.5. The simulations are in good agreement with the experimental data including temperature, pressure, ignition delay, and preignition heat release. This demonstrates the model has potential for use in predicting the behavior of HCCI engines. From both the experiments and the reduced kinetic model, the results show that for 20 PRF the first-stage ignition begins at 707 K, the second-stage ignition temperature is 910-924 K, and significant reaction occurs during the preignition process resulting in pre-ignition heat release of about 7%-10% of the potential heat release. The second-stage ignition time varies with inlet temperature, equivalence ratio, engine load and octane number. When the engine is run with a volumetric efficiency of 71% at 750 RPM, inlet temperature 423 K, equivalence ratio 0.4 and 20 PRF, the duration from the first to second-stage ignition is 25 CAD.