Flammability and Propagation Dynamics of Planar Freely Propagating Dimethyl Ether Premixed Flame

Flammability dynamics and physics play a crucial role in fire safety and combustion efficiency. This paper numerically studied the flammability dynamics of dimethyl ether/air freely propagating premixed flame over a broad range of equivalence ratios (ϕ). The results showed that the traditional flammability range should be redefined considering the impact of low-temperature chemistry. A physically stable warm-flame branch existed in the ultrarich region (ϕ = 7.58-12.59), which connected the hot and cool flame transition smoothly. However, in the lean region, the transition between hot and cool flames was completed by extinguishment or ignition. Sensitivity analysis was performed to reveal the governing chemical and diffusive processes for the flammability limits (FLs). In addition to the high-temperature reactions, low-temperature chemistry also played an important role in the lean hot-flame FL because of its double-flame structure. Heat conduction and fuel and oxygen diffusions were the most significant diffusive processes for the near-limit flame propagation. The near-limit flames had a diffusion-reaction structure, in which the flame front propagation was sustained by the heat conduction-induced ignition rather than the autoignition wave. The hot-flame extinction was induced by radiative extinguishment of the high-temperature propagating front embedded in the double-flame structure, and the cool-flame extinction was induced by excessive diffusive loss.