Increasing the burning velocity of a low-pressure hydrogen-oxygen flame by the addition of trimethyl phosphate in terms of Zel’dovich’s chain mechanism of flame propagation

Abstract

The chain reaction mechanism and theoretical approach proposed by Zel’dovich for hydrogen flame propagation are used to describe the effect of increasing the burning velocity of a low-pressure hydrogen-oxygen flame by the addition of trimethyl phosphate (TMP), which induce a catalytic recombination of hydrogen atoms. The promotion of a stoichiometric hydrogen-oxygen flame at subatmospheric pressure by the addition of TMP at a low concentration (0.1–0.5%) is described using a model of the catalytic recombination of hydrogen atoms. The results of calculation using Zel’dovich’s theory with the proposed simplified kinetic model are in good agreement with simulation results for the complete kinetic mechanism. It is shown that increasing the recombination rate of hydrogen atoms in a catalytic reaction involving phosphorus-containing species increases the heat release rate and, hence, the flame burning velocity. A kinetic analysis was performed of the dependence of the ratio of the recombination and branching rates, the temperature at the maximum reaction rate, and the maximum mole fraction of hydrogen atoms on the pressure and additive concentration. The study confirmed Zel’dovich’s prediction that the recombination not only has the harmful effect of terminating chains, but it also has the beneficial effect of releasing heat.