ISSN 0023-1584, Kinetics and Catalysis, 2009, Vol. 50, No. 2, pp. 156–161. © Pleiades Publishing, Ltd., 2009. Original Russian Text © O.P. Korobeinichev, A.G. Shmakov, I.V. Rybitskaya, T.A. Bol’shova, A.A. Chernov, D.A. Knyaz’kov, A.A. Konnov, 2009, published in Kinetika i Kataliz, 2009, Vol. 50, No. 2, pp. 170–175. 156 The mechanism and chemistry of the combustion and ignition of hydrogen/oxygen mixtures have been the subject of detailed studies for many years. One of the causes of this interest is that the combustion and ignition of these mixtures provide glowing examples of branched chain reactions, which were discovered by N.N. Semenov and were investigated in detail by his followers [1–6]. Numerous modiﬁcations of the kinetic mechanism of hydrogen ignition and combustion have been suggested to date [1–16], and they have proved convincingly that the reactions proceed via a chain mechanism. However, the authors of a recent publica- tion [17] deny the branched chain character of hydro- gen ignition and combustion at near-atmospheric pres- sures. The advances in the understanding of the mech- anisms of chemical reactions in ﬂames have been made by comparing experimental data (propagation rate, ignition delay, ﬂame structure, etc.) collected over the widest possible ranges of conditions (pressure temper- ature, the initial composition of the reaction mixture) with the results of numerical calculations for the trial mechanisms. The determining role in branched chain processes is played by reactions involving active species, namely, atoms and free radicals. Therefore, the most important and most complicated problem is to measure their con- centrations and to record their concentration proﬁles in the ﬂame. Molecular-beam sampling mass spectrome- try (MBSMS) with soft electron-impact ionization is among the most efﬁcient methods used for this purpose. Eltenton [14] and, later, Foner and Hudson [15] were the ﬁrst to apply this method to the detection of atoms and radicals in rareﬁed ﬂames. MBSMS, which is the most universal method from the standpoint of simulta- neous measurement of the concentrations of all com- pounds in the ﬂame, including atoms and free radicals, is widely used in the study of the ﬂame structure, including for hydrogen–oxygen mixtures. Most of the studies of the structure of these ﬂames deal with subat- mospheric pressures [16, 18–20] because of the difﬁ- culties in the use of the MBSMS method at P = 1 atm. Nevertheless, there have been several studies on the structure of hydrogen/oxygen ﬂames at atmospheric pressure and above [21–23]. These studies provided concentration proﬁles only for stable compounds in rich [21, 22] and stoichiometric [23] ﬂames. For detailed and comprehensive veriﬁcation of the kinetic mechanism of the chemical reactions involved in hydrogen combustion at 1 atm, it is necessary to have concentration distribution data for the active species H and OH • in these ﬂames. Here, we report a development in testing a soft electron-impact ionization MBSMS technique for ﬂame structure studies (primarily for measuring the H and OH • concentrations and concen- tration proﬁles) at atmospheric pressure and the appli- cation of this technique to “atmospheric” H 2 /O 2 /N 2 ﬂames having different stoichiometries. A comparison between the results of this experiment and the results of simulation for mechanisms known from the literature would make it clear whether these mechanisms are valid. EXPERIMENTAL In order to perform experiments under conditions close to the adiabatic conditions of free ﬂame propaga- tion, we used a technique ensuring heat ﬂux balance (HFB) on the burner [24, 25]. The burner was a tube 35 cm in height on which a copper disc 24 mm in diam- eter and 3 mm in thickness was mounted. The disc had Kinetics and Mechanism of Chemical Reactions in the H 2 /O 2 /N 2 Flame at Atmospheric Pressure O. P. Korobeinichev, A. G. Shmakov, I. V. Rybitskaya, T. A. Bol’shova, A. A. Chernov, D. A. Knyaz’kov, and A. A. Konnov e-mail: korobein@kinetics.nsc.ru Received March 26, 2008; in ﬁnal form, April 24, 2008 Abstract—The kinetics and mechanism of chemical reactions in the H 2 /O 2 /N 2 ﬂame were studied experimen- tally and by simulating the structure of premixed laminar ﬂat atmospheric H 2 /O 2 /N 2 ﬂames of different initial compositions. The concentration proﬁles for stable compounds (H 2 , O 2 , and H 2 O), H atoms, and OH • radicals in ﬂames were measured by molecular-beam sampling mass spectrometry using soft electron-impact ioniza- tion. The experimental data thus obtained are in good agreement with the results of simulations in terms of three familiar kinetic mechanisms, suggesting that these mechanisms are applicable to the description of the ﬂame structure in hydrogen–oxygen mixtures at atmospheric pressure. DOI: 10.1134/S0023158409020025