Reactions in the H2O2 system not involving HO2 or

Reactions in the H2/O2 system are part of the main chain-branching processes of ignition or maintaining high-temperature combustion of hydrocarbon fuels. Due to their pervasive importance, these reactions have been investigated in detail by many workers using a variety of techniques. This leads to the unique situation that in some cases (e.g., determination of the 

Because of the relative simplicity of this system (8 species, at most about 40 relevant elementary steps), it is possible to give a complete picture of the reactions involved. Since complete reviews have been given by Baulch et al (1972), in this chapter only results published after 1972 are discussed, together with the recommendations given in this Leeds report. 

The reaction of H atoms with molecular oxygen is the basic chain-branching process in high-temperature combustion. About 80% of the O2 is consumed by this step in typical hydrocarbon-air stoichiometric flames at atmospheric 

The scatter of the data for H + O2 OH + O given in the Leeds report (Baulch et a/., 1972) is considerable, corresponding to a factor of about 6 at flame temperatures. Because of this scatter, it was impossible to decide whether there is non-Arrhenius behavior of the temperature dependence of the reaction under consideration (as is clearly the case for O -f H2 and OH -1- H2, see below and Chapter 3). New measurements done after 1972 improve this situation (Fig. 5). Especially, the expression given by Schott (1973) results from direct and sensitive measurements. Extrapolation of his expression to lower temperatures, however, leads to incompatibilities with reliable data. The recommendation given by Dixon-Lewis (1983) provides a close match to these data. The higher values given by the Leeds expression at flame temperatures are supported by some indirect but reliable flame modeling studies. 

Since this reaction is the reverse of H + O2 OH -h O, it distinctly inhibits high-temperature combustion, and there is a moderate sensitivity of flame propagation to its rate coefficient (Fig. 4). Measurements are available only below 425 K. However, it is reasonable to assume zero activation energy for this exothermic radical-radical reaction. This leads to a temperature-independent rate coefficient of 1.8 x 10 cm /mol s (Fig. 6), in agreement with the Leeds report low-temperature recommendation (2 X 10 cm /mol s) and, roughly, with the rate coefficient determined from the reverse reaction and the equilibrium constant. 

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