Optimized global reaction mechanisms for H2, CO, CH4, and their mixtures

Abstract

Global reaction mechanisms (GRMs) are widely used in combustion engineering. However, it is difficult to find GRMs commonly available for various mixtures of H2, CO, and CH4 (with air), which are likely to be the primary fuels in the future. In this study, a series of GRMs were optimized to follow the results of the five detailed reaction mechanisms (GRI 3.0, USC II, San Diego, FFCM-1, CRECK) for the essential fuels (H2, CO, CH4) and their mixtures (at 300 K and 1 bar). At first, a 1-step GRM of H2+air (R1) and another of CO + air (R2), were optimized to reproduce their respective laminar burning velocities (LBVs). After that, an additional water-gas shift reaction (R3) was suggested to improve the prediction for the H2+CO + air mixture. Similarly, a 1-step GRM (M1) was developed for the fuel-lean mixtures of CH4+air, and a 2-step GRM (R1+M1) was proposed for the fuel-lean mixtures of H2+CH4+air. In the case of the mixture of H2+CO + CH4+air, an additional methane oxidation reaction (M1L) producing H2 and CO was suggested, and a 4-step GRM (R1+R2+R3+M1L) showed reliable results in the fuel-lean conditions. However, to get reliable LBVs over all equivalence ratios, two additional reactions (M2+M3) were proposed to reflect the endothermic reaction. Furthermore, the pre-exponential factor of the methane oxidation reaction (M1R) varied as a function of the hydrogen concentration in the fuel. Conclusively, acceptable LBVs could be obtained for the H2+CO + CH4+air mixtures in a moderate temperature range (300 K–600 K).