Numerical study on the effects of CO 2 /H 2 O dilution on the ignition delay time of methane

In this study, the effects of CO 2 /H 2 O dilution on the ignition delay time (IDT) of methane under different conditions were studied by the method of sensitivity analysis, mole fraction analysis and reaction path analysis. The predictions of six published kinetic models were first compared with experimental data from the literature; the kinetics of the model judged best were then analyzed in greater detail to investigate coupling effects of different ratios of CO 2 /H 2 O dilution, temperature, pressure, and equivalence ratios on the IDT of methane. Through this research, it was found that under high temperature conditions (1700–2000 K), the IDT increases with CO 2 /H 2 O ratios increasing. At the equivalence ratio of 2.0 and low to medium temperatures (1000–1700 K), the diluent gas at the ratio of CO 2 /H 2 O = 0.4/0.6 has the maximum suppression effect on methane ignition, and the inhibitory effect of diluted gas in the IDT can be enhanced by 4.9% compared with other cases. Through the path analysis, it was found that the reaction path under the condition of CO 2 /H 2 O = 0.4/0.6 is changed into the O radicals generation reactions and CH 3 consuming Reactions (R155, R106, and R158) comparing with the condition of CO 2 /H 2 O = 0.8/0.2. By providing insight into the factors affecting the IDT of methane under a wide variety of conditions, the present study extends our understanding of methane combustion and can be used to guide the development of a combined application of EGR and in‐cylinder water injection.