Les réactions en chai'nes et les propriétés des mélanges inflammables de méthane et d'air

Abstract

Abstract1. A chain reaction mechanism is proposed for the inflammation of CH4, the individual branching reaction requiring an activation energy of about 40 kcalories. This value is deduced from the experimental data on the lag on ignition according to the chain reaction theory of Semenoff.2. Assuming that for a slow propagating flame (as in CH4 — air mixtures) the speed depends on the reaction rate rather than on physical factors as conductivity and heat capacity, a very simple expression for the “fundamental speed” of flames can be found. It allows to predict the fundamental speed changes in function of the initial temperature and in function of the addition of inert gases.3. Factors which modify the ignition temperature are considered; their action is explained qualitatively in terms of the same theory.4. Conditions for no propagation of the flame are considered in relation with the protections devices against firedamp explosions.Plate protection devices and wire gauzes are effective because the desappearance of the active centres on the walls prior to the branching reaction rather than because their cooling effect.Foreign ignition sources (sparks and hot wires) may be uneffective in certain circumstances which can be predicted. The important feature is that the small volume, primarily heated above the ignition temperature, must be so small so as to give to the active centres a sufficiently small branching probability.