On the Nature of the Synergistic Effect in Flames of Methane and Formaldehyde Mixtures with Air
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On the Nature of the Synergistic Effect in Flames of Methane and Formaldehyde Mixtures with Air V. M. Shvartsberga and V. A. Buneva
UDC 536.461.536.462
Published in Fizika Goreniya i Vzryva, Vol. 56, No. 4, pp. 93–103, July–August, 2020. Original article submitted August 7, 2019; revision submitted September 30, 2019; accepted for publication November 6, 2019.
Abstract: This paper deals with the nature of the synergistic effect in flames of methane and formaldehyde mixtures with air. Combustion of mixtures of different fuels is of great practical and fundamental interest. It has been found that the addition of formaldehyde to a rich methane/air flame at a constant concentration of methane first reduces the flame speed and then begins to increase it. The synergism mechanism in this case is due to the predominant and complete consumption of formaldehyde due to its higher reactivity and its negative impact on the rate of methane consumption. The predominant combustion of one of the fuels leads to the existence of two spatially separated heat release zones in the flame. In the first zone, heat release is mainly due to the oxidation of formaldehyde and formyl radical, and in the second zone, it is due to the recombination of methyl radicals. An analysis of the flame speed sensitivity has shown that the key reactions affecting the flame speed are the stages of formation of radicals (mainly hydroxyl) or products that lead to their formation. Reactions that make the main contribution to the heat release generally do not affect the flame speed. It has been found that the interaction of two fuels CH4 and CH2 O in a mixture with air leads to a marked increase in the superadiabatic temperature effect. Keywords: methane, formaldehyde, synergism, flammability limits, numerical modeling, selective oxidation. DOI: 10.1134/S0010508220040097
INTRODUCTION The study of the combustion of multifuel combustible mixtures is very important since fuels which are multispecies mixtures (natural gas, traditional and alternative motor fuels, syngas, etc.) are the most widely used in practice. Most studies have focused on mixtures of hydrocarbons with hydrogen or biofuels, whose purpose is to improve combustion performance and reduce the content of pollutants in combustion products. In addition to the practical importance of such studies, they are of fundamental interest because the mutual effect of fuels during combustion has been studied insufficiently, a
Voevodsky Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia; [email protected].
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and the mechanism of the mutual effect of fuels on the chemistry and kinetics of oxidation of each species is of considerable interest. An analysis of the literature shows that formaldehyde combustion has been studied far less than the combustion of methane and other hydrocarbons and oxygenates. Of greatest interest for combustion chemistry are experimental and numerical studies [1, 2] of the formaldehyde flame structure. The high-temperature oxidati
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