Shock-Induced Ignition of Methane, Ethane, and Methane/Ethane Mixtures Sensitized by NO2

Ignition delay times of stoichiometric CH4/NO2/O2/Ar, C2H6/NO2/O2/Ar, and CH4/C2H6/NO2/O2/Ar mixtures are measured with a shock tube, to investigate the role of NO2 in ignition of methane, ethane, and natural gas (CH4:C2H6 = 9:1). All measurements are carried out at 1016-1981 K and 5-16 atm. Different NO2 concentrations (0%, 25%, 50% and 75% of fuel molar concentrations) are explored. The addition of NO2 promotes considerably the ignition of methane and natural gas, but moderately for ethane. In addition, the promoting effect is temperature-dependent. Four assembled models are examined against the present measurements, and an updated kinetic model is proposed and validated in comparison with the experimental data. The current model is chosen for sensitivity and reaction pathway analyses, which reveal the role of NO2 in ignition of methane, ethane, and natural gas.