Environmental Engineering Reference
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FIGURE 8.1 Temperature and pressure dependence of the reaction rate of H + O 2 (+M) → HO 2 (+M)
for M = N 2 . Solid lines represent the values used in the mechanism proposed in Li et al. [2], and dashed
lines the recommendations of Troe [3]. Source : Reproduced with permission from Li et al. [2].
The parameters are clearly dependent on the specific third-body gas used.
Among the reactions, the H + OH + M reaction was found to be primarily
important only to laminar flame speed propagation predictions at high pres-
sure. The overall H 2 /O 2 reaction system is very sensitive to the key chain
branching reaction (H + O 2  = O + OH) and the important chain termination
reaction (H + O 2  + M = HO 2  + M). The branching ratio of the rate constants
of these two reactions depends strongly on temperature and pressure, and
results from an earlier and subsequently updated models are compared and
shown in Figure 8.2 [1, 2]. The agreement is excellent in the temperature
range of 800-900  K, where the value of rate constant used in the earlier
model by Mueller et al. was experimentally derived.
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