On the Nature of superadiabatic temperatures in the flames of rich NH3/O2/H2/N2 mixtures
V. A. Bunev
Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
Keywords: hydrogen, ammonia, superadiabatic temperatures, autoignition
Abstract
The phenomenon of superadiabatic temperatures (SAFT) in flames of rich ammonia and hydrogen mixtures with air was studied using numerical methods. It was shown that the superadiabatic temperatures in these flames are due to the fact that unreacted ammonia remains in the flame front by the time the oxygen is completely consumed and the water concentration reaches its maximum value. Its dissociation in the post-flame zone leads to a decrease in temperature, an increase in the hydrogen and nitrogen concentrations, and, correspondingly, a decrease in the water concentration due to the increase in the number of moles. The somewhat preferential oxidation of ammonia compared to hydrogen in the flame front temperature range from the initial to the maximum value also contributes to the SAFT level.
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