Vadim N. Kurdyumov

A new mode of flame propagation from a wall in a mixture below the flammability limit is described. We consider a simple chemistry model in which the reaction rate vanishes for temperatures below some critical cutoff value. Two models for flame initiation by the wall are considered. The first model assumes heat release by the wall over a finite time, after which it becomes adiabatic. The second model assumes that the wall temperature changes according to a given law. Unlike the standard flame propagation mode, in which the flame propagates at a constant velocity through the unburned mixture, and which is not possible under the considered conditions, in the new mode the flame moves at a speed inversely proportional to the square root of time. It is found that the value of the fuel Lewis number, italic Le Le $\textit{Le}$ , is determinant: the new mode of propagation exists only if italic Le less than 1 Le < 1 $\textit{Le}\lt 1$ . The influence of thermal expansion on the existence of this new propagation regime is investigated. It is interesting to note that the flame structure resembles the classical Stefan solution for phase-transition front propagation. However, the fundamental difference is that in the classical phase-transition front propagation problem the Lewis number is infinite, in our nomenclature, while the new flame propagation regime arises at italic Le less than 1 Le < 1 $\textit{Le}\lt 1$ .