Experimental and numerical study on the ignition delay times of methane/propane mixtures diluted in carbon dioxide

Abstract

Pressurized oxy-fuel combustion has gained great interest owing to its low emission and high efficiency. Methane and propane are important composition of natural gas, which is a clean fossil fuel and widely utilized for combustion applications including gas turbines. In this work, the auto-ignition properties of CH4/C3H8 mixtures in ratios from 90/10% to 70/30% diluted in CO2 were measured at pressures of 1.75 and 10 atm; equivalence ratios of 0.5, 1.0, and 2.0; and temperatures in the range of 1240–1520 K in a shock tube. Four key reactions in the Oxymech 2.0 model were updated and the modified model shows reasonable performance in both the ignition delay time and the laminar flame speed predictions in O2/N2 and O2/CO2 atmospheres. Two kinetic models (NUIG 1.0 and AramcoMech 3.0) were evaluated by present data and the laminar flame speed from the literature. The results of the experiment and calculation show that the addition of propane promotes the ignition significantly in the C3H8 proportion range from 0 to 30% in both cases of CO2 and N2, but has slight effects on the ignition with the C3H8 proportion more than 30%. The effects of CO2 on the promoting effects of C3H8 addition are slight. The ignition delay times increase with the equivalence ratio at 1.75 atm but no statistical difference is observed between the measured data of different equivalence ratios at 10 atm. The influence of C3H8 addition and the equivalence ratio on the ignition delay of CH4/C3H8 mixtures was also analyzed in detail.