Effects of Propane on the Flammability Limits and Chemical Kinetics of Methane–Air Explosions

ABSTRACT

This work presents a comprehensive account of how adding C₃H₈ impacts the possibility of explosion for CH₄–air mixtures. A series of experiments was carried out to determine the upper and lower flammability limits (UFL and LFL, respectively), and the explosive risk value for different mixtures of CH₄ and C₃H₈. The critical oxygen concentration, the concentrations of CH₄ and N₂ at the point where the LFL and UFL merge, and the CH₄ explosive triangle were obtained for nitrogen-diluted mixtures. In addition, we used a detailed mechanism (GRI-Mech3.0) in the CHEMKIN software package to acquire the impacts of adding C₃H₈ on the chemical kinetics of the explosion of CH₄. The flammable limits of CH₄ decrease linearly with the addition of C₃H₈ while the flammable range increases slightly. The explosive risk value for CH₄ in air increases greatly upon adding C₃H₈ following a parabolic relationship. Nitrogen dilution noticeably decreases the UFL and slightly increases the LFL, ultimately resulting in these points merging. The concentration of CH₄ and nitrogen at this merging point varies linearly when the C₃H₈ concentration is varied between 0% and 2.0%. The addition of C₃H₈ also expands and shifts leftwards and downwards CH₄’s explosive triangle. Numerical analysis reveals that the maximum temperature and pressure during the explosion, and the formation rates of CO and NO_x, noticeably increase after adding C₃H₈. Sensitivity coefficients of key dominant reactions show that overall more •H, •O, and •OH are consumed when C₃H₈ is added. Furthermore, the time between ignition and maximum pressure (the burning time) is evidently shortened by the addition of C₃H₈, which also shortens the explosion duration.

KEYWORDS:

• Methane explosion
• flammable limit
• limiting parameters
• explosive triangle
• reaction kinetics
• sensitivity analysis

Acknowledgments

This work was supported by the National Key Research and Development Program of China (Project Nos. 2017YFC0804702 & 2016YFC0800100), the National Natural Science Foundation of China (Grant Nos. 51674193 & 51504190), the Fundamental Research Project for Natural Science of Shaanxi (Grant Nos. 2017JM5068 & 2018JM5152) and the Foundation of Shaanxi Educational Committee (Grant No. 17JK0487).

Meanwhile, we appreciate Ms. Ronghua Lv who has helped us a lot with English language.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51674193 & 51504190];National Key Research and Development Program of China [2017YFC0804702 & 2016YFC0800100];Foundation of Shaanxi Educational Committee [17JK0487];Fundamental Research Project for Natural Science of Shaanxi [2017JM5068 & 2018JM5152];