Radical recombination in near-stoichiometric and fuel-lean systems

3 Radical recombination in near-stoichiometric and fuel-lean systems 

They found the heat release rate to be proportional to the product [H] [O21 [H2O], and the dependence of H on pressure and mass flow to be also consistent with the removal of H by reaction (iv). Similar conclusions about the recombination were reached by Getzinger and Schott [181] from shock tube experiments, in which OH concentrations were measured and used to calculate total radical concentrations by means of the partial equilibrium assumption. 

The hypothesis that the HO2 formed in reaction (iv) is rapidly removed (thus preventing its re-dissociation) has recently been examined for flame systems by Dixon-Lewis et al. [182]. On the assumption of equilibration of the fast, bimolecular, electron spin conserving reactions (i), (ii) and (iii), it is possible to compute concentration profiles for all the chemical species in the recombination region of a wide variety of flame systems. The calculation requires knowledge of the rate coefficients 4, Sa and ki 7— 225 which control the rate of electron spin removal (recombination). The rate of recombination via HO2 is calculated as the difference 

Third order rate coefficients for H + O2 + M = HO2 + M from shock ignition of lean H2—O2—diluent mixtures 

Comparison of the computed profiles with experiment may in principle be used to establish values of some of the unknown rate coefficients. The radical pool in this computation includes molecular oxygen as a bi-radical. The validity of the partial equilibrium assumptions will be discussed in Sect. 5.4.4. 

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