Spin gas combustion in a narrow slot

Combustion in a gap between two thin circular plates with point injection of the gas in the center is experimentally examined. The existence of several combustion regimes is demonstrated. Unstable pulsed combustion is observed in the case of high flow rates. As the flow rate decreases, a transition to spin combustion occurs under certain conditions. If the distance between the plates is sufficiently small, the so-called excess-enthalpy flame can be realized in an expanding gas flow. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 23–26, May–June, 2006.     

Specific features of combustion in a variable-section narrow channel with a periodically changing gas flow

Results of numerical and theoretical research of flame behavior in a periodically changing gas flow during combustion in a variable-section narrow channel are presented. The influence of the mean mass flow of the gas and amplitude and frequency of periodic oscillations of the flow on the mean position and temperature of the flame front is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 16–24, September–October, 2008.     

Flame stabilization in a planar microcombustor partially filled with anisotropic porous medium

Heat recirculation through the combustor walls is responsible in sustaining flames in microcombustors. Incorporating porous medium into microcombustors helps further enhance heat recirculation via the solid matrix. However, the problem of anisotropy arises when the pore size is comparable to the characteristic length of microcombustors. To quantitatively address the problem, an experimental study on the flame stability limits of premixed H₂/air in a planar microcombustor partially filled with porous medium is undertaken. Three folding schemes, namely, parallel sheets, streamwise flow passage, and streamwise flow blocking, are employed to realize the anisotropic properties. By varying the width (W) and position (L_out) of the porous medium, the effects of folding schemes on the critical flashback (Ф₂), and breaking‐through (Ф₃) conditions are examined. The experimental results indicate that the disturbance to flow velocity in the transverse direction mainly influences Ф₂, while Ф₃ is greatly affected by the blocking normal to the flow direction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 153–160, 2018     

Effect of modulations of opposed gas flow velocity on flame spread rate over a liquid surface

The effect of modulations of the velocity of the gas flow incident on the flame on the average flame velocity over a shallow liquid is studied. It is shown that the average flame velocity depends on the modulation frequency. If the modulation frequency is higher than the flame oscillation eigenfrequency, then, upon the imposition of the modulation, the flame velocity first increases and then gradually returns to the initial value. At frequencies close to the flame oscillation eigenfrequency, the average flame velocity is constant but is higher than the initial value. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 1, pp. 11–17, January–February, 2009.     

纺粘非织造窄狭缝牵伸器喷射流场的研究与分析

建立了纺粘窄狭缝牵伸器喷射流场的理论模型,采用有限差分法对该模型求解,采用SIMPLE算法求解速度和压力耦合,用交错网格解决速度和压力的锯齿状分布问题,差分格式为二阶迎风格式,使用交替方向的逐线TDMA方法求得差分方程。数值计算得到了气流速度在x方向上的分量,与实验结果吻合较好。通过对几种纺粘牵伸器喷嘴的喷射流场进行了数值模拟,给出了相应的流场矢量图,显示了该研究在对纺粘设备进行计算机辅助设计方面的应用前景。     

Surface Effect on Branching Chain Reactions In Filtration Combustion of Gases

The existence of lean and rich concentration limits of the low-velocity regime of flame propagation was shown experimentally under filtration of a combustible gas mixture in narrow tubes. The values of the limits depend on the inner diameter of the tube. Experiments with an inhibitor affecting the concentration limits of combustion-wave propagation in tubes in a low-velocity regime showed that branching chain reactions occur in the filtration combustion wave and the concentrations of active centers thus exceed the equilibrium values. In the low-velocity regime, the surface of the narrow quartz tube slightly decreases the role of active centers in combustion-wave propagation.     

Estimates of efficiency of a small-size thermoelectric channel in terms of conversion of heat produced by gas combustion to electric power

Stationary regimes of combustion in an energy-conversion system are studied, and its efficiency is estimated. This system is a channel with thermoelectric converters embedded into the channel walls and with combustion of premixed gases inside the channel. For the maximum efficiency of energy conversion in a small-size device to be reached, the properties of thermoelectric materials, the device geometry, and other parameters have to be correlated with the internal structure of the flame. In particular, the efficiency of energy conversion in a small-size device can be higher than that in a similar large-size device, and the maximum efficiency is reached near the flammability limits. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 15–22, July–August, 2007.     

Flame spread over a liquid surface in a channel of finite section under oncoming air-flow conditions

The propagation of a combustion wave over a shallow hot liquid (n-butanol) blown over by an air flow was studied experimentally. The flame spread was accompanied by pulsations, whose amplitude depended on the oncoming gas velocity. Dependences of the average flame speed on temperature and oncoming gas velocity were obtained. The average speed was found to be independent of the liquid depth ahead of the flame within the experimental error. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 29–34, January–February, 2008.     

Hybrid autowaves in filtration combustion of gases in a catalytic fixed bed

A mathematical model of autowave processes in a heterogeneous medium with chemical reactions in the gas phase and on the catalyst is constructed. The coefficients of heat and mass transfer between the phases and the thermal conductivity of the solid phase are determined from the current values of system parameters. The model describes three types of autowaves: waves due to filtration combustion of gases in the low-velocity regime, waves due to a catalytic reaction, and hybrid waves. The behavior of phase trajectories of the dynamic system is studied by methods of qualitative and numerical analysis, and an effective technique is developed for searching for a physically grounded autowave solution of the problem. The laws of propagation of autowaves due to filtration combustion of gases and hybrid autowaves are numerically examined, and the effect of system parameters on the basic technological characteristics of autowave processes is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 3–13, March–April, 2008.     

矩形双通道间脉动的非单值性试验研究

矩形平行通道流动不稳定性问题是影响紧凑装置安全运行的重要因素之一。文中在中国核动力研究设计院热工试验回路上进行了矩形双通道管间脉动试验。通过对各种热工水力参数和单通道加热的试验研究,得出结论:在低压低质量流速下,随着进口过冷度的增加,界限含汽质量分数先增加、后减小;随着系统压力的升高,质量流速脉动周期先变短、后变长;在低质量流速下,单通道加热时产生管间脉动的界限热流密度比双通道均匀加热情况下的高,在较高质量流速下,单通道加热时的界限热流密度比双通道均匀加热情况下的低。     

Numerical predictions of flow patterns due to natural convection in a vertical slot

Natural convection in rectangular slots has vital applications in cooling of nuclear reactor insulation, chemical vapor deposition, insulation of double pane windows, environmental processes, and phase change processes. Flow patterns arising out of density differences depend on height to width ratio (aspect ratio (AR)) and temperature difference. These flow patterns have a significant effect on rate of heat transfer. Hence flow patterns in a slender vertical slot with large height to width ratio (AR=20) have been numerically studied for four fluids (mercury, air, and water and silicon oil) of varying Prandtl numbers. The circulation cell formation and merging has been seen as a quasi-periodic behavior for water and silicon oil at various Rayleigh numbers. The genesis of formation of circulation cells due to the pressure differentials (as a result of thermal gradients) has been satisfactorily explained for mercury, air, and water and silicon oil and a criterion for the same has been developed for the range of Prandtl number between 0.71 and 7 on the basis of numerical predictions.     

Specific Features of the Mechanism of Flame Propagation in Rich Hydrogen–Propane–Air Mixtures

Propagation of a planar laminar flame in rich homogeneous propane–air and hydrogen–propane–air mixtures is numerically studied. It is shown that the maximum burning temperature is higher than the thermodynamically equilibrium value and is reached when chemical and physical processes have not been yet completed. The degree of superadiabaticity depends on the ratio of hydrogen and propane concentrations. Superadiabaticity in rich hydrogen–propane–air mixtures, in addition to the inhibiting action of propane, determines the deviation from Le Chatelier's principle for flammability limits in these mixtures.     

Liquid–gas flow patterns in a narrow electrochemical channel

The flow in a narrow (3 mm wide) vertical gap of an electrochemical cell with gas evolution at one electrode is modeled by means of the two-phase Euler–Euler model. The results indicate that at certain conditions an unsteady type of flow with vortices and recirculation regions can occur. Such flow pattern has been observed experimentally, but not reported in previous modeling studies. Further analysis establishes that the presence of a sufficient amount of small (∼10 μm) bubbles is the main factor causing this type of flow at high current densities.     

Filtration Combustion of an Energetic Material in a Cocurrent Flow of Its Combustion Products. Critical Combustion Conditions

The paper reports results of a numerical calculation using the threetemperature model developed previously by the authors. In addition to the temperature difference between the gas and the solid phase (skeleton), the model approximately takes into account the temperature distribution in skeleton elements. It is shown that quenching is possible (after burnout of part of the charge) with variation in a number of input parameters: the thermal conductivity of the charge, the ignition temperature, the weight of the igniter, the initial temperature, the porosity of the charge, and the local rate of its decomposition.     

On the Nature of Superadiabatic Temperatures in Premixed Rich Hydrocarbon Flames

The propagation of flat laminar flames is studied numerically. It is shown that in rich homogeneous propane–air and methane–air mixtures, the maximum flame temperature exceeds the flame temperature in thermodynamic equilibrium. The degree of superadiabaticity depends on the concentration of the fuel mixed with air. It is shown that the superadiabaticity of rich flames is due to the diffusion of hydrogen from the reaction zone to the preheating zone and its preferential (compared to hydrocarbon) oxidation. The total enthalpy of the gas varies along the coordinate at the flame front and has a maximum.     

Filtration combustion of porous metallic samples in a gas diluted by an inert component

Filtration combustion of a porous layer with natural filtration of the oxidizer diluted by an inert component is studied. The problem of ignition of a porous layer by a heated surface permeable for the gas is solved, and the time of ignition is determined as a function of pressure in the reactor and initial porosity of the sample. Formation of an inert gas “plug” preventing chemical interaction is examined. It is shown that the mean depth of conversion of the condensed reagent in the porous layer depends on the sample length, porosity, pressure of the gas mixture, and concentration of the inert component. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 1, pp. 73–79, January–February, 2008.     

Splitting flames in a narrow channel with a temperature gradient in the walls

A possibility of simultaneous formation of two chemical reaction fronts during nonstationary combustion of a gas in a microchannel with a temperature gradient in the walls is demonstrated. Combustion in a straight tube and in a gap between two disks with radial fuel injection is considered. In both cases, the characteristic transverse size of the channel is smaller than the critical diameter determined for the ambient temperature, and gas combustion occurs in the region where the wall temperature is higher than the ambient temperature. A numerical study of flame repetitive extinction/ignition (FREI) demonstrated a possibility of simultaneous formation of two chemical reaction fronts in the hot region of the channel. One front corresponds to conventional flame propagating upstream from the hot to the cold part of the channel, and the other front moves in the downstream direction and decays as the fuel burns out. Based on this study, a new mechanism of ignition and incomplete combustion of the combustible mixture in microsystems is proposed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 12–19, March–April, 2008.     

Filtration combustion of a carbon-inert material system in the regime with superadiabatic heating

Superadiabatic regimes of combustion of carbon mixed with an inert solid with filtration of the steam-air mixture are studied theoretically and experimentally. The temperature in the combustion wave and the composition of gaseous products are obtained as functions of the fraction of carbon in the fuel and the amount of steam in the gaseous oxidant. In the examined range of the control parameters, the maximum temperature in the combustion wave is shown to depend only slightly on the fraction of carbon in the mixture and the amount of steam in the oxidant gas. Simulations of filtration combustion of carbon with allowance for the kinetics of its oxidation are in good agreement with experimental results. The calculated combustion temperature coincides with that measured in experiments. In calculating the composition of the gaseous products, coincidence with experimental data is observed only for particular compositions with the mass content of carbon under 60%. As the fraction of the fuel exceeds 60%, the yield of CO and H₂ increases in experiments, though such a behavior is not predicted by the theoretical analysis. Hypotheses on the reasons for the disagreement in results are put forward and experimentally checked. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 30–38, May–June, 2008.     

Hydrogen combustion in an axisymmetric duct with a supersonic air flow

Results of an experimental study of hydrogen combustion in a supersonic high-enthalpy air flow in axisymmetric ducts with constant and variable cross sections are described. Conditions of flow reconstruction due to heat addition in ducts of different geometry are considered. It is demonstrated that a gas-dynamic action ensures stable self-ignition and it becomes possible to control combustion in expanding ducts with special profiles. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 3–8, May–June, 2007.     

Model of Vapor—Air Gasification of a Solid Fuel in a Filtration Mode

A two-temperature mathematical model of steady filtration combustion of a solid fuel in open systems is proposed. Air or a mixture of air with water vapors is considered as a gaseous oxidizer. The model takes into account that the heat capacities of the phases depend on temperature and composition and that the reactor length is finite and allows obtaining the composition of gaseous combustion products. Calculated results on gasification of a mixture of carbon with an inert component are presented. It is demonstrated that thermodynamic calculations are important for obtaining the upper estimate of gasification efficiency. Even a sufficiently long reactor becomes “short” in the regime of transient combustion waves, which results in more intense entrainment of heat by combustion products and, as a consequence, in lower efficiency of the process. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 65–72, January–February, 2006.