M. F. Ivanov

Self-ignition of a fuel gas upon pulsed efflux into an oxidative medium

It is demonstrated that hydrogen can exhibit self-ignition when a starting shock wave, on which the temperature increases above the stagnation temperature, appears in front of a cold expanding gas jet. This heating leads to the ignition of the hydrogen-air mixture formed at the contact surface. The results of numerical simulations show that, at a gas pressure in the vessel on the order of 300–600 bar, the intensity of a shock wave formed in air is sufficient to produce self-ignition of the hydrogen-air mixture formed behind the front of the jet of compressed hydrogen.

On a possible mechanism of the formation of large-scale disturbances in Jupiter’s atmosphere as a result of the falling of fragments of Comet Schoemaker-Levy 9

A mechanism explaining the sizes and structure of large-scale disturbances produced in Jupiter’s atmosphere by the impact of the fragments of Comet Shoemaker-Levy is proposed.

The Shock-Wave Mechanism of Spontaneous Ignition of Hydrogen under Conditions of Sudden Efflux from Reservoir at High Pressure

Analysis is made of the conditions of spontaneous ignition of hydrogen as a result of emergence of a starting shock wave in air before an expanding cold flow of gas. The rise of temperature behind the shock wave causes ignition of the mixture of combustible gas with air, which forms on the contact surface. The condition for spontaneous ignition is the sufficient time of residence of mixture at high temperature for mixing and ignition. The calculations of spontaneous ignition of hydrogen jet are based on a model which takes into account the gasdynamic transport of viscous gas, the kinetics of oxidation of hydrogen, multicomponent diffusion, and thermal conductivity. The range of pressures is determined in a reservoir, during whose depressurization the shock wave forming in air exhibits intensity sufficient for igniting the hydrogen-air mixture behind the front of propagating jet of compressed hydrogen. Results of analysis are given of the dependence of conditions of ignition on the pressure of hydrogen in the reservoir, on the size of the outlet opening, and on the initial temperature of hydrogen and air.

Influence of an Acoustic Field on Flame Development and Transition to Detonation

The work is devoted to experimental and numerical study of flame interaction with acoustic waves in closed and semiclosed pipes filled with preliminarily mixed gaseous mixtures. We analyze the influence of eigenfield (generated by the flame itself) and external acoustic field on the flame dynamics. We show that acoustic field affects the combustion process at all stages. The effect increases with any increase in the energy of initiation of combustion. At later stages of flame development, acoustic waves can initiate the transition to detonation or prevent it. Thus, it is possible to control the combustion modes using external acoustic field.

Mechanisms of development of superhigh pressures under conditions of propagation of explosion waves in conical cavities

In this study, numerical simulation methods are used for investigating the processes of propagation in a conical cavity (conical target) of weak shock waves caused by the blast of a microcharge in combustible mixture outside of the cone volume. A more general question is considered: how do the parameters of the medium at the cone vertex depend on whether it was a neutral gas (air) or combustible mixture (hydrogen-air) that filled the cone initially? Comparison is made of the maximal attainable pressures in the cases where the cone is filled with a combustible mixture and in the cases where the cone contains a neutral gas (air). The leading physical factors are identified and substantiated, which provide for attaining extremely high pressures in narrowing volumes. The problem under consideration is of applied importance from the standpoint of predicting the development of emergencies caused by the propagation of explosion waves in volumes filled with combustible gas.

Generation of high pressures during the shock wave–flame interaction

The interaction of a flame with shock waves generated by external sources is investigated using numerical simulation methods. It is shown that the effect of shock waves with various intensities on the combustion front in a closed volume (channel) leads to qualitatively different scenarios of the further development of combustion. Situations when the process development results in the generation of sufficiently high pressures, which exceed many times the pressures in the incident shock wave, are singled out individually. In this case, maximum high pressures occur as a result of thedeflagration-to-detonation transition (DDT). The detailed analysis of the dynamics of DDT, which is developed by various scenarios, showed that the most general mechanism of the transition is the localization of the pressure peak in the reaction zone. The well-known scenario of transition to detonation by the mechanism of the formation of “hot spots” ahead of the flame is observed in a relatively narrow range of initial conditions. The development of detonation in such a mode leads to generation of still higher pressures, which exceed the pressure in DDT, and the probability of the realization of this scenario rises with the decrease of mixtures reactivity.

A numerical modeling of the acceleration of a flame by an additional energy input ahead of its front

The acceleration of a flame after an additional energy input ahead of its front was simulated using numerical methods. The combustion of a hydrogen-air mixture in a semiopen channel was considered. The calculations were performed within the framework of a two-dimensional hydrodynamic model of premixed flames, with consideration given to heat transfer, multicomponent diffusion, and chemical kinetics. It was demonstrated that, when the interaction of the flame front with the near-wall boundary layer is taken into account, even a moderate energy input could substantially promote the development of the Landau-Darrieus instability and, possibly, deflagration to detonation transition.

Effect of the composition of the combustible mixture on the development of flame front instability

Numerical simulations are used to study the effect of the chemical composition of the combustible mixture on the development of the hydrodynamic instability of the flame front, its acceleration, and the possibility of transition to the detonation regime. The combustion of hydrogen-containing mixtures in confined spaces (channels) was considered. Calculations were performed within the framework of a two-dimensional hydrodynamic model for the combustion of premixed mixtures with account of viscosity, heat conduction, multicomponent diffusion, and chemical kinetics. It was demonstrated that the presence of an inert component and the deviation of the mixture composition from stoichiometry caused not only a quantitative but also a qualitative change in the character of burning of gaseous combustible mixtures.