Experimental and numerical study on the ignition delay times of methane/propane mixtures diluted in carbon dioxide. (1st July 2023)

• Record Type: Journal Article
• Authors: Xia, Wenxiang; Zou, Chun; Yuan, Yi; Fu, Rui; Liu, Jiacheng; Peng, Chao
• Is Part Of: Fuel. Volume 343(2023)
• Publication Date: 2023-07-01
• Subjects: Oxy-fuel combustion -- CH4/C3H8 mixture -- Ignition delay time -- Chemical kinetics; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2023.127991
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: The ignition delay times of CH4 /C3 H8 mixtures in ratios from 90/10% to 70/30% diluted in CO2 were measured at pressures of 1.75 and 10 atm. The addition of propane promotes the ignition significantly in the C3 H8 proportion range from 0 to 30% in both cases of CO2 and N2, but has slight effects on the ignition with the C3 H8 proportion more than 30%. The fast increase of the methyl radicals in the initial stage is through C3 H8 (+M) ⇔C2 H5 + CH3 (+M) owing to the easier breaking of C-C bonds in propane, which enhances CH3 + HO2 ⇔OH + CH3 O, consequently promoting the ignition. The effects of CO2 on the promoting influence of C3 H8 addition are slight. H + O2 (+M) ⇔HO2 (+M) suppresses the ignition at the fuel-lean condition but promotes the ignition in stoichiometric and fuel-rich conditions at 10 atm. 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 /C3 H8 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 C3 H8 proportion range from 0 to 30% in both cases of CO2 and N2, but has slight effects on the ignition with the C3 H8 proportion more than 30%. The effects of CO2 on the promoting effects of C3 H8 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 C3 H8 addition and the equivalence ratio on the ignition delay of CH4 /C3 H8 mixtures was also analyzed in detail.