Ignition delay time measurements and kinetic modeling of CH4 initiated by CH3NO2

Ignition delay times for methane/nitromethane binary fuels with oxygen diluted in Ar (CH4/CH3NO2/O-2/Ar mixtures) are measured with a heated shock tube behind the reflected shock wave at 995-1962 K and 4-18 atm for different equivalence ratios (0.5, 1.0, and 2.0). Blending ratios for CH3NO2 are varied (0, 0.1, 0.2, 0.5, and 1) to investigate the promotion of CH3NO2 on CH4 during the ignition process. OH* emission histories at a sidewall are used to determine the measured ignition delay times of the binary fuels mixture. Correlations for the measured ignition delay times are obtained using multiple linear regression as a function of pressure, temperature, blending ratio, and equivalence ratio. Experimental results show that a small addition of CH3NO2 dramatically reduces the ignition delay times of CH4, and induces a weak two-stage ignition. Three literature mechanisms are examined and compared with the measured ignition delay times for CH4/CH3NO2 binary fuels mixtures, and the mechanism from Mathieu et al. is updated and validated against the experimental data. In this mechanism, the rate constants for some important reactions are theoretically determined by quantum chemical calculation. In addition, sensitivity analysis and reaction pathway analysis as well as rate of production are carried out to further elucidate the promotion of CH3NO2 on ignition of the CH4.