Experimental and Numerical Study of the Effect of CO2 on the Ignition Delay Times of Methane under Different Pressures and Temperatures

Pressurized oxy-fuel combustion is regarded as a new generation of oxy-fuel technology. The ignition delay times of methane in an O-2/N-2 atmosphere (0.21O(2) + 0.79N(2)) and an O-2/CO2 atmosphere (0.21O(2) + 0.79CO(2)) were measured in a shock tube at a pressure of 0.8 atm, an equivalence ratio of 0.5, and within a temperature range of 1501-1847 K. The present experimental data and the experimental data of Hargis and Peterson at 1.75 and 10 atm were adopted to evaluate five representative chemical kinetic models. This paper studied the chemical effects (chaperon effects of CO2 and the effects of reactions containing CO2) and physical effects of CO2 on the ignition of methane at different pressures and temperatures in detail using a modified model. Artificial materials X and Y were employed to analyze the chemical and physical effects. The analysis showed that the physical effects of CO2 inhibit the ignition of methane and are not sensitive to the temperature. The chemical effects of CO2 vary greatly with the pressure and temperature. At 0.8 and 1.75 atm, the chemical effects of CO2 promote the ignition of methane at a high temperature while suppress the ignition of methane at a low temperature. The chaperon effects of CO2 promote the ignition of methane in O-2/CO2 atmospheres at a high temperature mainly because of HCO + M double left right arrow CO + H + M. The chaperon effects of CO2 suppress the ignition of methane at a low temperature because of 2CH(3) (+M) double left right arrow C2H6 (+M). The chemical effects of CO2 offset half of the physical effects of CO2 at a high temperature, and those two effects are great at a low temperature, which is the reason for the fact that the effect of CO2 is subtle at a high temperature and evident at a low temperature. At 10 atm, the chemical effects of CO2 suppress the ignition of methane at 1350-1700 K. The chaperon effects of CO2 suppress the ignition of methane mainly as a result of 2CH(3) (+M) double left right arrow C2H6 (+M) and are strengthened with the decrease of the temperature. The inhibition of reactions involving CO2 is mainly attributed to CO + OH double left right arrow CO2 + H and weakened with the decrease of the temperature; thus, the chemical effects of CO2 on the ignition are almost not sensitive to the temperature. The effects of CO2 have almost not change with the temperature at 10 atm.