Experimental and modeling study of ignition delay times of natural gas with CO2 dilution

Pressurized oxy-fuel combustion has attracted considerable attention as an efficient technology with lower emissions. Natural gas, which primarily consists of methane, ethane, and propane, is a widely used fossil fuel owing to its safety and low cost. The auto-ignition of 90 %methane/9 %ethane/1 %propane mixture diluted in CO2 or N2 were investigated using a shock tube at temperatures of 1280-1645 K, pressures of 2 and 10 bar, and equivalence ratios of 0.5-2.0 in this study. An updated model named OXY-NG can accurately predict the ignition delay times, species yields, and laminar flame speeds of natural gas mixtures in oxy-fuel and air combustion modes. The ignition delay times increased as the equivalence ratios increased related to the recombination of CH3 radicals at 2 bar but decreased as the equivalence ratios increased owing to reactions involving HO2 at 250 bar. The diluent CO2 has inhibitory effects on ignition compared with N2, and these effects were minor under high pressure and fuel-rich conditions when diluted in CO2. The effects on natural gas mixture ignition owing to chemical and physical properties of CO2 are discussed in detail.