Theory of Burning Velocity. I. Temperature and Free Radical Concentrations Near the Flame Front, Relative Importance of Heat Conduction and Diffusion

Abstract

A previous paper having suggested that hydrogen atoms play an important part in combustion, an investigation is made of the relative importance of heat conduction and diffusion in establishing concentrations of hydrogen atoms near the flame front. To do this, differential equations are set up for heat transfer and for material transport. These equations are solved for two typical mixtures, one containing moist carbon monoxide, the other containing hydrogen. It is shown that the temperature falls rapidly as the distance from the flame front increases, and that the local thermal equilibrium concentration of hydrogen atoms, being a negative exponential of that temperature, falls more rapidly still. On the other hand, the local non‐equilibrium concentration of hydrogen atoms, which is caused by diffusion from the flame front into unburnt gas, falls only slowly with distance. It is thus concluded that diffusion plays a more important role than heat transfer.