Kinetic analysis of the effect of propylene additive on ignition and combustion of hydrogen-air mixtures

The results of kinetic analysis are presented taking into account the rates of chemical reactions and heat release when solving problems of spontaneous ignition and laminar combustion of hydrogen-air reactions with a 1% addition of propylene. The solution was obtained using computer modeling. It has been shown that the addition of propylene to hydrogen-air mixtures significantly slows down the course of chemical reactions due to the recombination of atomic hydrogen during spontaneous combustion in the entire range of initial temperatures from 800 to 1400 K, as well as during the propagation of laminar combustion waves in rich and stoichiometric mixtures. However, propylene is a flammable substance, and during its decomposition and oxidation, heat is released, which increases the rate of temperature increase. As a consequence, under certain conditions, in particular at an initial temperature of 800 K, with the reduced rates of chemical reactions of hydrogen oxidation, as well as in the case of lean mixtures, the addition of propylene leads not to an increase, but to a decrease in the ignition delay, and to a significant increase in the temperature and speed of propagation of the combustion wave. Additional data were obtained on the important role played in laminar flames of hydrogen-air mixtures by reactions involving the HO2 radical: the branching reaction HO2+H => OH+OH and the trimolecular reaction H+O2(+M) => HO2(+M), as well as the maximum concentration of the HO2 radical. These reactions proceed at high rates in the low temperature area due to the participation of atomic hydrogen diffusing from the high temperature area of the flame and provide a significant contribution to the release of heat. The maximum concentration of the HO2 radical is achieved at the temperature that presumably corresponds to the “leading zone” of combustion. When propylene is added, the change in the maximum concentration of the radical correlates with the change in the velocity of normal combustion.