MECHANISM OF INHIBITION OF HYDROGEN-AIR FLAMES BY HYDROGEN BROMIDE AND ITS RELEVANCE TO THE GENERAL PROBLEM OF FLAME INHIBITION

The structures and properties of a 60% hydrogen-40% air flame, both uninhibited and inhibited by the addition of 4% HBr to the unburnt gas, were computed using a reaction mechanism and rate coefficients previously proposed by Dixon-Lewis and Simpson [6]. Both flames were at atmospheric pressure, with Tu = 298°K. From the results of the calculation, the approaches of several of the flame reactions H+HBr⇌Br+H2Br+HBr⇌H+Br2OH+H2⇌H2O+HH+O2⇌OH+OO+H2⇌OH+O towards partial equilibrium was examined. Reaction (R23) was found to be more or less equilibrated over virtually the whole of the reaction zone, whereas reaction (R24) was always far from partial equilibrium. An interesting feature of the inhibited flame is that the first intimation of the reaction zone encountered by the incoming gas is the appearance of bromine atoms (and some molecular bromine), which arrive at the unburnt end of the flame by upstream diffusion. As a result of the investigation, certain essential features of a chemical inhibition mechanism for flames are proposed. © 1979.