The relative contributions of self-heating and chain branching to the kinetics of hydrogen oxidation outside the ignition region close to the third limit

It is shown that, in hydrogen-oxygen mixtures, under the conditions when the rate of reaction chain termination is higher than the rate of chain branching, the characteristic reaction time is hundreds of seconds even in the immediate vicinity of the third ignition limit. The self-heating of the mixtures therefore does not exceed several degrees and, contrary to the accepted views, cannot result in thermal combustion. Ignition observed in the third limit region is caused by a higher rate of chain branching compared with chain termination; that is, it is a chain reaction. Self-heating only becomes substantial during the development of chain combustion.