In this study, the effects of CO2/H2O 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 CO2/H2O 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 CO2/H2O ratios increasing. At the equivalence ratio of 2.0 and low to medium temperatures (1000–1700 K), the diluent gas at the ratio of CO2/H2O = 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 CO2/H2O = 0.4/0.6 is changed into the O radicals generation reactions and CH3 consuming Reactions (R155, R106, and R158) comparing with the condition of CO2/H2O = 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.

A model coupling Reynolds-averaged Navier-Stokes (RANS) method and linearized Navier-Stokes equations (LNSEs) was established in order to investigate the acoustic excitation and attenuation effect from a coupling perspective of time–space–frequency under various flow velocities and mass fractions of methane. Results show that the energy distribution of acoustic modes under high-frequency acoustic excitation is more uniform. The amplitude of the acoustic oscillation at a multiple coupling physical field is 10,000 times higher than that at simple flow field. The case when [Formula: see text] = 0.8 owns the largest percentage of energy conversion from fundamental to high-frequency signals, the largest percentage of transmitted waves from the combustion chamber system to outside and the strongest non-linear effect. When [Formula: see text] rises, the amplitude of oscillations at points and the attenuation effect of high-frequency signals along the axial are enhanced. At the case of Uin = 15 m/s, the amplitude of harmonics is reduced by 18% compared with other cases, while the proportion of the high-frequency harmonic increases, proving the non-linearity cannot be neglected in this case. As velocity rises, the energy conversion from fundamental to high-frequency signals enhances; while closer to the outlet position, the more complex the oscillation signal is. Model-shapes analysis shows that a case of [Formula: see text] = 0.8 owns the largest amplitude of the second harmonic at downstream of the burner, while the amplitude of the harmonics rapidly increases at Uin = 15 m/s at the end of the burner, which further indicates that the energy conversion of low-frequency signals to high-frequency signals occurs mainly in the middle and downstream regions.

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