The chain character of the third self-ignition limit of hydrogen-oxygen mixtures and flame propagation at atmospheric pressure

Initiation of chain and thermal explosions by the reactor surface. Criterion for the participation of branching chains in a thermal explosion

“…A comparison of the conclusions of [1,20] with those of [15][16][17][18][19] reveals serious contradictions, and we shall analyze them.…”

“…Therefore, the explanation [17] of thermal explosion at atmospheric pressure by chain branching without specification of the particular reaction cannot be recognized plausible since it is in contradiction to the basic propositions of CBP theory [1]. Fundamental papers [1,20,21] outline the main direction for a noncontradictory explanation of thermal explosion -the formation and decomposition of hydrogen peroxide on the reactor wall, which, unfortunately, was ignored in [15][16][17][18][19]. (Here and below, by a plausible explanation is meant an explanation that relates to the research subject and is consistent to the basic propositions of the classical Semenov and Hinshelwood theory of CBPs, whose solid formulations are based on a large body of experimental findings.…”

“…According to [1], this reaction cannot be responsible for the occurrence of a chain ignition limit because it is a chain continuation rather than branching or loss reaction. Instead of reaction (5), Azatyan et al [15][16][17][18][19] could indicate a particular chain of reactions with increasing number of valences which can occur without the participation of heat. However, according to our analysis, such a chain is likely absent in the well-known hydrogen combustion mechanism [1,3].…”

“…In [15][16][17][18][19], the hypothesis of explosion initiation at the third limit by branching chains was revived but the branching channel was not indicated. A comparison of the conclusions of [1,20] with those of [15][16][17][18][19] reveals serious contradictions, and we shall analyze them.…”

“…These varied "constants," except for k 0 from [15][16][17][18][19], were one to four orders of magnitude larger than the gas-phase reaction rate constants measured by the shock wave method without the influence of the surface [11]. Thus, for example, in [4,10], the ignition of an oxyhydrogen gas was described quantitatively using the "heterogeneous constant" k 0 = 0.7 · 10 −18 cm 3 /(molecule · sec), which was four orders magnitude larger than the "gas-phase constant" k 0 ≈ 10 −22 cm 3 /(molecule · sec).…”