Improvement in modeling NH3/CH4 combustion based on the effects of the H-abstraction reactions and disproportionation reactions

Abstract

The H-abstraction reactions and disproportionation reactions play very important roles in the NH3/CH4 combustion model. The rate coefficient of the H-abstraction reaction, CH2O + NH2 = HCO + NH3 (R1430), theoretically calculated by Li & Lü was multiplied by 100 in the works of Dai et al. to better match the experiment, which was repeatedly adopted in the subsequent NH3/CH4 kinetic models. Moreover, the disproportionation reaction, HCO + NH2 = CO + NH3 (R1449), is not considered in the current existing NH3/CH4 kinetic models. In this work, the NH3-CH4 model is proposed including the C1-C2 sub-model, NH3 sub-model, and cross-reactions between nitrogen-containing species and hydrocarbon species including R1430 with the rate coefficient of Li & Lü, and R1449. The NH3-CH4 model was extensively validated by the SPs, IDTs, and LFSs of NH3/CH4 mixtures from the literature. The effects of the H-abstraction reaction and disproportionation reactions on the profiles of CH2O, IDTs, and LFSs of NH3/CH4 are closely studied by the sensitivity analysis and the rate of production (ROP) analysis using the NH3-CH4 model, and the effects of R1430 and R1449 are discussed by the comparison among the NH3-CH4 model, KAUST model and KAUST model with original rate constants. R1430 inhibits the CH2O formation. Multiplying the rate constant of R1430 by 100 in the KAUST model significantly deteriorates the prediction of CH2O. R1449 has significant inhibiting effects on LFSs due to reducing the H production in the pathway HCO→CO in the NH3-CH4 model. The rate constant of R1430 had to be artificially enhanced to predict well LFSs of NH3/CH4 mixtures in the KAUST model due to the absence of R1449. R1430 has significant promoting effects on IDTs, and the disproportionation reactions have a negligible influence.