V. V. Zamashchikov

Limits of Flame Propagation in a Narrow Channel with Gas Filtration

A model of gas–flame propagation in a narrow gap between two plates is proposed. Apart from the conventional regime, this model describes the regime of low velocities. A typical feature of the low–velocity regime is the fact that the flame propagates together with the heat wave in the plates generated by the flame. It is shown that the limits of flame propagation in the low–velocity regime are wider than the limits in the classical theory. Dependences of the flame–propagationvelocity and the critical Peclet number on the fresh–gas velocity are obtained. For Peclet numbers lower than the critical value defined by the classical theory, the flame may exist only within a certain range of velocities of the fresh mixture counterflow. A possible reason for the existence of the upper and lower limits of flame propagation relative to the flow velocity of the fresh mixture is discussed.

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.

Estimation of the Efficiency of Inhibitors Acting on Combustion of Gases

A method for estimating the efficiency of inhibitors acting on the processes of propagation of gas flames is proposed. The method is based on the assumption of independence of the chemical and thermophysical contributions of the action of the additive to the combustion process. It is shown that the simplest characteristic of the combustible mixture, which allows one to use the method proposed, is the rich or lean flammability limit. Three parameters are needed for a complete description of the action of the inhibitor: the depth of inhibition, the amount of the additive necessary for saturation of the chemical action, and the thermophysical parameter. Based on the analysis of the data in the literature, it is shown that all three parameters depend on the composition of the combustible gas mixture with a third component added to it.

Combustion of a liquid fuel in a rectangular channel

The possibility of flame spread over the surface of a liquid fuel (n-butanol) in two-phase flow with a gaseous oxidizer in a narrow rectangular channel is demonstrated. The results of a detailed experimental study of combustion in this system are given. Dependences of the flame propagation speed on the initial temperature and oxidizer and fuel flow rates are obtained.

Rotating Gas Flames

The so‐called spinning propagation of flames of premixed combustible gas mixtures has been achieved. Continuous rotation of one, two, and three hot spots has been observed.

Gas combustion in a narrow tube

A simplified model of flame propagation over a single capillary in the low-velocity regime is proposed. The model is based on the concept that the main features of flame propagation in the low-velocity regime are determined by the heat flux along the tube wall from the combustion products to the fresh mixture. Qualitative agreement with experimental results is obtained.

EXPERIMENTAL INVESTIGATION OF GAS COMBUSTION REGULARITIES IN NARROW TUBES

Combustion wave propagation in flowing combustible gas has been studied experimentally in tubes with inner diameters larger and smaller than the critical diameters. Combustion wave velocity has been shown to depend on the material of the tube walls, the tube inner diameter, the mixture composition, and the gas flow rate. In a tube which has an inner diameter larger than the critical diameter, two flame-propagation regimes exist.

Diffusion flame in an electric field with a variable spatial configuration

The influence of an electric field whose intensity vector rotates around the flame axis on the shape of the diffusion flame of propane is experimentally studied. Application of spectrozonal registration makes it possible to obtain information about the radiation intensity distribution at wavelengths of intermediate reaction products (OH, CH, and C2). Different positions of the peak intensity of the own radiation of the flame at different wavelengths testify to the influence of such an electric field on the mixing processes, namely, mixing is more intense than that in the regime without application of the electric field. This feature may turn out to be useful for increasing the efficiency of combustion of gaseous hydrocarbon fuels.

Laminar propane-air flame in a weak electric field

Three mechanisms of the electric field influence on combustion of gases are considered: ohmic heating, effect of chemical reactions on the kinetics, and ionic wind, which is the most important factor. Experimental data presented in the paper testify to a local action of the electric field directly on the zone of chemical reactions, which leads to deformation of the flame front.

Velocity and temperature fields in the combustion of rotating gas in a closed vessel

Nonsteady flame propagation in a closed vessel generates a complex velocity and temperature distribution in the fresh gas and its combustion products. In rotating the flow of the gas, additional forces such as inertial and Coriolis appear, leading to significant rearrangement of the flow and, in particular, to the appearance of an angular velocity distribution over the vessel radius. This paper attempts to elucidate mathematically the thermodynamic and gas dynamic features of this rotational flow in a closed vessel. The model is tested against experimental data for a methane-air mixture.