S. K. Abramov

Breakup of steady-state detonation in hydrogen-air mixtures under the action of propane admixtures

Minor amounts of propane effectively inhibit the detonation of hydrogen-air mixtures at atmospheric pressure. Controlled variation of the amount of the admixture provides means to break up the steady-state detonation wave at a preset distance from the place of its origination and to regulate its velocity in a certain range. This is possible due to the branched chain character of the combustion reaction in the detonation mode. Propane is not inferior to propylene in the effectiveness of action on detonation and, owing to its low cost and higher availability, is preferable as a means of preventing the explosion and detonation of hydrogen-air mixtures.

Effect of olefin + carbon dioxide admixtures on the ignition of methane-air mixtures

Experimental data are reported on the kinetics and mechanism of methane-air combustion in a closed space at atmospheric pressure and on the effects of inhibitor admixtures and inert gases. Ignition arises and develops as a result of a chain avalanche occurring in the mixture, and self-heating is significant only in developing chain combustion. Admixtures containing propene or isobutene and carbon dioxide (5% olefin + 20% CO2) efficiently prevent the ignition and combustion of methane-air mixtures of any composition.

Chemical control of combustion and detonation in carbon oxide and hydrogen mixtures with air

The paper presents data on the control of combustion and detonation in CO and H2 mixtures with air by small additives. The dependence of the kinetics of combustion and detonation characteristics on the initial mixture composition observed experimentally is in agreement with the predictions of theory taking into account the special features of reaction chains of the combustion of carbon monoxide in the presence of hydrogen-containing impurities. Works ignoring the chain character of the combustion of H2 and CO are critically reviewed.

Specific features of the combustion of hydrogen-oxygen mixtures near the lower concentration flammability limit

The combustion of hydrogen-air mixtures near the lower composition flammability limit in cylindrical reactors of various diameters is studied. The speed of flame propagation in the horizontal direction is lower than that in the upward direction. Chromatographic analysis showed that, during the combustion of these mixtures, hydrogen is consumed only partially. That the flame propagates despite a low adiabatic temperature can be explained by the formation of the well-known cellular structure.

Synergism in combustion processes

The effect of CF3H, CF4, and N2 on the ignition of methane–air mixtures has been investigated. The effect of trifluoromethane is due to its being involved in reaction chain termination. A nonadditive effect of trifluoromethane and nitrogen on the concentration limits of ignition and flame propagation in methane–air mixtures has been predicted and revealed. The synergistic effect arises from the exponential dependence of the rate of the chain process on the concentrations of the initial components.

Rules governing flame propagation in fuel-deficient hydrogen-air mixtures in cylindrical reactors

The special features of flame propagation in hydrogen-air mixtures with low hydrogen contents in horizontal cylindrical reactors with different diameters were studied. The dependences of the lower concentration limit of flame propagation and flame propagation velocity on the diameter of reactors and the chemical properties of the surface were determined. The character of the dependence of the flame cellular structure on mixture composition and reactor diameter was studied.

Difference in the Mechanisms of the Inhibition of Hydrogen Combustion in the Deflagration and Detonation Modes

It is shown that, in the process of inhibition of hydrogen combustion by hydrocarbons, intermediate products that play a key role are not only traditionally considered olefins, but also oxygen-containing compounds, such as alcohols, ketones, and the like. The role of the products of incomplete oxidation of inhibitors manifests itself primarily at high temperatures.

The role of molecular-kinetic and thermal factors in inhibition of steady detonation

It was experimentally shown that the reaction of the combustion of hydrogen–air mixtures in a detonation wave virtually completely (with an accuracy of 1%) occurs by a branched-chain mechanism; it is this mechanism that determines the characteristics of the detonation wave.

The important role of reactions between atoms and radicals in flame propagation in cylinder reactors

Results from studying features of the combustion of hydrogen in narrow cylinder reactors with diameters of <5.0 cm are presented. It is determined that the lower concentration limit of flame propagation in a reactor with a diameter of 1.1 cm is higher than 9% H2. The dependence of the principles of combustion on the method of initiation is studied. Mathematical simulations are performed that prove the impossibility of describing the combustion of hydrogen-deficient mixtures without assuming the cell structure of a flame. It is experimentally determined that increasing the termination of chains during the propagation of a flame results in its attenuation. It is noted that in addition to conductive heat abstraction, the recombination of atoms and radicals on the surface of the reactor plays an important role. It is concluded that these heterogeneous reactions representing the termination of reaction chains also result in the removal of recombination energy by the reactor’s walls.

Role of changes in the molar mass and heat capacity of the combustible mixture in the inhibition of hydrogen-air detonation

773 Gas phase combustion processes are known to occur via a branched chain mechanism not only at pressures that are tens of times lower than atmospheric pressure, contrary to what was thought earlier (see, e.g., [1–4]), but also at higher pressures that are important for practice (see, e.g., [4–6]). This makes it possible to prevent detonation and to break up the det onation wave in hydrogen–air mixtures by adding small amounts of lower hydrocarbons (see, e.g., [6, 7]). The molecules of these compounds react rapidly with reactive intermediates—atoms and radicals—to yield low activity products. As a consequence, addi tional chain termination takes place and combustion is prevented or suppressed. For example, under the action of 2.45–2.50% propane, the steady state deto nation wave in a 33% Н2 + air mixture splits into a decaying shock wave and a flame front progressively lagging behind the shock wave [7].