It was shown that at 298 K and 100–300 Torr, the flame front of a well-mixed dilute methane–oxygen mixture, propagating to the ends of hollow cylindrical and conical obstacles, does not form a vortex shedding behind them; however, under the same conditions, this instability occurs when hot products flow behind the obstacles.

The patterns of catalytic ignition of deuterium–air mixtures above the surface of metallic rhodium at pressures of 1–2 atm and temperatures of 20–250°C using hyperspectrometers in the range of 400–1650 nm and high-speed filming have been established. It is established that the catalytic ignition of deuterium–air mixtures in the studied temperature range is observed at a deuterium content of more than 12

It was found that the reactivity of a hydrocarbon during oxidation catalyzed by a noble metal begins to play a significant role with an increase in the number of carbon atoms in its molecule. Thus, the process of hydrocarbon mass transfer to (or on) the catalyst surface determines the oxidation rate.

— In experiments on the ignition of the stoichiometric mixture of hydrogen and oxygen over strips of palladium and platinum foil at a total pressure of up to 200 Torr and initial temperature up to 300°C, the temperature of the foils during ignition was measured using an infrared camera and data on temperature dependence of metal resistivity. The temperature of the ignition initiated at 40 Torr over a heated palladium foil was shown to be ~100°C lower than that over a platinum foil. Even the minimal measured foil temperature (623°C) is sufficient to ignite the explosive mixture, implying that the influence of a catalytic reaction of hydrogen oxidation over the noble metals is insignificant in the case of initiated ignition. The presence of water vapor was found to prevent ignition. In the case of thermal ignition, it was found out that at a pressure of up to 180 Torr and 288°C the catalytic activity of the palladium foil is significantly higher than that of the platinum foil. The palladium foil activity is manifested in the competition of two processes: the emergence of local ignition centers on the foil, from which a combustion wave propagates, and a dark catalytic reaction of transformation of the explosive mixture into water.

The values of the ignition temperature are experimentally determined and the effective activation energies of the limits of catalytic ignition of mixtures ((40–70

Экспериментально определены значения температуры воспламенения и оценены эффективные энергии активации пределов каталитического воспламенения смесей ((40÷70%)H 2 + (60÷30%)CH 4 ) стех + + воздух над металлическим родием при давлении 1.7 атм в температурном интервале 20–300 °C. Над поверхностью родия, обработанной воспламенениями, температура каталитического воспламенения смеси 70% H 2 + 30% CH 4 + воздух составляет 62 °C, что указывает на возможность использования родия для существенного снижения температуры воспламенения топлив на основе водородно-метановых смесей. Экспериментально обнаружен критический характер осуществления объемной реакции: объемный процесс происходит при [H 2 ] = 45%, но отсутствует при концентрациях водорода ≤40%. Если [H 2 ] ≤ 40%, происходит только медленная поверхностная каталитическая реакция. Это явление проиллюстрировано посредством качественного расчета. Установлено, что эффективные энергии активации как верхнего, так и нижнего пределов каталитического воспламенения стехиометрических смесей H 2 + CH 4 в диапазоне линейности равны примерно (2.5 ± 0.6) ккал/моль. Это означает, что ключевые реакции, ответственные за возникновение верхнего и нижнего пределов каталитического воспламенения, одинаковы. Показано, что при катализе родиевым катализатором процесс развития цепи, скорее всего, имеет гетерогенную природу, поскольку эффективная энергия активации составляет менее 3 ккал/моль.

The specific features of the ignition of premixed stoichiometric n-pentane–air mixtures are studied in the region of the negative temperature coefficient (NTC) of the reaction rate in a static fast puffing reactor in the presence of metallic platinum and palladium. It is shown that thermoacoustic oscillations occur in the NTC region in the absence of noble metals. However, in the presence of a platinum catalyst, which reacts with oxygen at the flame temperature and generates catalytic centers that propagate into the volume by convection/diffusion, thermoacoustic ignition modes disappear. In other words, the catalytic surface of platinum eliminates a certain stage of the kinetic mechanism: probably, the stage of inhibition after the appearance of a cold flame, while the NTC phenomenon disappears. In the presence of a palladium catalytic surface that does not generate catalytic centers propagating into the volume, the NTC phenomenon is observed. The discovered patterns should be taken into account when numerically simulating this phenomenon in the presence of a platinum surface; i.e., an acceptable chemical mechanism should describe thermoacoustic oscillations in the NTC region; and exclusion of a certain stage of the kinetic mechanism (probably of a surface nature) should cause the disappearance of the NTC reaction regime in the presence of a platinum catalyst. The stage should include a surface reaction of an active combustion intermediate on the platinum surface. In this reaction, the more active intermediates are formed from the less active product.

The ignition temperatures and effective activation energies of mixtures of 5–40% H 2 –air over metallic Rh and stoichiometric mixtures (30–70% H 2 + 70–30% C 2 H 6 (and C 2 H 4 )) + air over metallic Rh and Pd are experimentally determined at pressures of 1 to 2 atm over the temperature range 20–300°C. It is shown that, for the investigated mixtures, metallic Rh is more effective than Pd, and the effective activation energies of ignition depend not only on the nature of the catalyst but also on the chemical nature of the hydrocarbon in the mixture. The data obtained indicate that catalytic ignition is initiated only by an exothermic surface reaction of hydrogen oxidation on the catalyst; the hydrocarbon on the surface is consumed in reactions involving intermediate products of hydrogen oxidation that do not lead to chain branching; and then combustion propagates into the volume. It is established that in an untreated reactor, the ignition temperature of the mixture of 70% H 2 + 30% methane with air above the surface of palladium at a pressure of 1.75 atm is 310°C; and above the surface of rhodium, 105°C. In a reactor treated with ignition, the ignition temperature of a mixture of 70% H 2 + 30% methane with air above the surface of palladium at a pressure of 1.75 atm is 270°C; and above the surface of rhodium, 62°C. The result obtained indicates the potential of using a rhodium catalyst to significantly lower the ignition temperature of fuels based on methane and hydrogen mixtures.

For the first time, vibrationally excited HF molecules (v = 2, 3) are observed with the use of hyperspectrometers in the VIS and NIR ranges in the products of the reactions of oxidation of hydrogen and methane in the presence of Difluorodichloromethane (CF2Cl2). The combustion of hydrogen and methane in air and oxygen at atmospheric and reduced pressure is initiated by a spark discharge. The propagation of the flame front is recorded using high-speed color filming. It is found that during the combustion of methane HF (v = 3) molecules are formed at the moment of reaching the maximum rate of the chemical transformation, i.e., reactions involving CF2Cl2 molecules compete directly with the development of reactive chains. It is also found that the concentration limit of the ignition of a premixed hydrogen-air mixture in the presence of Difluorodichloromethane at a pressure of 1 atm exceeds 10% CF2Cl2, while the concentration limit of the ignition of a premixed methane-air mixture is 1% CF2Cl2. This means that the active centers of the combustion of hydrogen and methane, which determine the development of combustion, have a different chemical nature. It is shown that the set of reactions involving Difluorodichloromethane molecules, leading to the formation of HF (v = 2, 3) during methane combustion, should include active centers of methane combustion.

In this paper, we report the results of studying the combustion characteristics of fuels containing a hydrogen–hydrocarbon (C 1 –C 6 , as in CH 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 , C 5 H 12 , and C 6 H 14 ) mixture with a fuel fraction of 0.6–1.2 in a mixture with air above the palladium surface at a total pressure of 1–2 atm. The propagation features of the flame front in mixed fuels are revealed, and the temperature dependences of the ignition limit over the palladium surface are determined. The observed separation of the CH and Na emission bands in time during the combustion of the 30% propane + 70% H 2 + air mixture (the fuel fraction in the mixture with air is unity) was established to be caused by the occurrence of hydrodynamic instability of the flame when it touches the end of a cylindrical reactor.

The ignition temperature of the 40% H2 + air mixture in the presence of metallic palladium (70°C, 1 atm) was found to be ~200°C lower than above the platinum surface (260°C, 1 atm). In addition, Pd initiated the ignition of (30–60% H2 + 70–40% CH4)stoich + air mixtures at temperatures below 350°C, while Pt foil did not initiate the burning of these mixtures up to 450°C. The effective activation energy of ignition over Pd was evaluated to be ~3.5 kcal/mol. It was found using a hyperspectral sensor that the system of emission bands of H2O* was absent in the range 570–650 nm in the presence of leucosapphire; a possible explanation of this phenomenon was given. An explanation was proposed for the appearance of an additional source of excited water molecules emitting in the range 900–970 nm.