Improvement of H2/O2 chemical kinetic mechanism for high pressure combustion

Abstract

An updated H2/O2 kinetic mechanism was proposed by incorporating carefully selected reaction rate coefficient and great progress in radical chain mechanisms, in which the uncertainties of rate coefficient were discussed. The performance of the current mechanism was compared to other H2 mechanism and validated against a wide range kinetic targets, including oxidation, decomposition in shock waves, ignition, flame speed and flame structure. Results show that the current mechanism obtains an overall improvement of performance, especially for the flame speed. By using the updated binary diffusion coefficient from ab initio calculations and the chemically termolecular reactions, the current mechanism presents better agreement with the new experimental flame speed at atmospheric pressure and obtains the improved performance with respect to the negative pressure dependence of high-pressure H2 flame. Furthermore, the flame speed predictions are strongly sensitive to the H2O third body efficiency in the H2 mechanism, affecting the water-contained H2 flame. The modeling results of rapid compression machine ignition show that present mechanism can more accurately predicts the ignition delay under engine-like conditions. However, all three mechanisms cannot accurately reproduce the negative pressure dependence behavior of mass burning rate in high-pressure H2 flame, which may be attributed to the fact that the important reaction O + OH(+M) = HO2(+M) that significantly affects lean high-pressure H2 flame is not included in current mechanism. Consequently, continuous works should be emphasized on the reactions that are important but neglected in H2 mechanism. All these not only develop an improved H2 reaction mechanism for high-pressure combustion, but also point out the direction for refining the H2 mechanism.