A Global Reaction Model for the HCCI Combustion Process

This paper presents a new global reaction model to simulate the Homogeneous Charge Compression Ignition (HCCI) combustion process. The model utilizes seven equations and seven active species. The model includes five reactions that represent degenerate chain branching in the low temperature region, including chain propagation, termination and branching reactions and the reaction of HOOH at the second stage ignition. Two reactions govern the high temperature oxidation, to allow formation and prediction of CO, CO₂, and H₂O. Thermodynamic parameters were introduced through the enthalpy of formation of each species. We were able to select the rate parameters of the global model to correctly predict the autoignition delay time at constant density for n-heptane and iso-octane, including the effect of equivalence ratio. Keeping the same reactions and rate parameters, 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 - PRF 20, equivalence ratio - 0.4 and 0.5, and volumetric efficiency - 71% and 89%. The simulations are in good agreement with the experimental data for this initial set of runs using PRF 20, including temperature, pressure, ignition delay, combustion duration, and heat release.