Formation Of Detonation Wave Research Articles

Formation of detonation waves in channels and interaction of the waves with penetrable screens

Two-dimensional channel flows with shock waves resulting from the detonation of a combustible gas mixture are considered. Conditions for detonation and the parameters of the shock waves are determined. The feasibility of reducing the shock wave intensity and loads on the structure by mounting a set of mesh screens in the channel is investigated. The numerical computation of detonation initiation in an air-hydrogen mixture and subsequent passage of shock waves through the mesh screens is carried out. Basic quantitative characteristics of shock wave reduction depending on the mesh screen penetrability and mutual arrangement of variously penetrable screens are obtained.

Formation of a detonation wave in the thermal decomposition of acetylene

The formation of a condensation detonation wave has been experimentally observed in the shock-induced thermal decomposition of acetylene. The stable detonation wave in the 20% C2H2 + 80% Ar mixture has been obtained at an initial pressure behind the shock wave of no less than 30 atm. The main kinetic characteristics of the pyrolysis of acetylene—the period of the induction of condensation and the growth rate constant of condensed particles—have been determined. The correlation of various stages of the process with the heat release in the condensation has been analyzed. It has been shown that the period of the particle growth induction is not accompanied by noticeable heat release. The subsequent condensation stages characterized by significant heat release occur very rapidly (faster than 10−5 s) in the so-called explosive condensation. The analysis of the results indicates that the reactions leading to the growth of large polyhydrocarbon molecules, which precede the formation of condensed carbon particles, constitute the limiting stage of the process, which determines the possibility of the formation of the condensation detonation wave in acetylene. An increase in the pressure is accompanied by the sharp narrowing of the induction region and the transition of the process to the condensation detonation wave.

Formation of the preheated zone ahead of a propagating flame and the mechanism underlying the deflagration-to-detonation transition

The Letter presents analytical, numerical and experimental studies of the mechanism underlying the deflagration-to-detonation transition (DDT). Insight into how, when, and where DDT occurs is obtained by analyzing analytically and by means of multidimensional numerical simulations dynamics of a flame accelerating in a tube with no-slip walls. It is shown that the deflagration-to-detonation transition exhibits three separate stages of evolution corroborating majority experimental observations. During the first stage flame accelerates and generates shocks far ahead of the flame front. During the second stage the flame slows down, shocks are formed in the immediate proximity of the flame front and the preheated zone ahead of the flame front is created. The third stage is self-restructuring of the steep temperature profile within the flame, formation of a reactivity gradient and the actual formation of the detonation wave itself. The mechanism for the detonation wave formation, given an appropriate formation of the preheated zone, seems to be universal and involves a reactivity gradient formed from the initially steep flame temperature profile in the presence of the preheated zone. The developed theory and numerical simulations are found to be well consistent with extensive experiments of the DDT in hydrogen–oxygen and ethylene–oxygen mixtures in tubes with smooth and rough walls.

Study of detonation initiation in hydrogen/air flow

While extensive studies have been conducted concerning the formation of detonation waves in various combustible gaseous mixtures under static conditions since the 1950s, there is very little experimental work on simple flowing systems. In this study, experiments on the deflagration to detonation transition (DDT) of a hydrogen–air flow system were carried out to see the effects of tube diameter, equivalence ratio, and flow types in a premixed and non-premixed flow. Tube diameters used were 25, 50, and 100 mm. The premixed experiments show that the larger tube diameter provides a wider range in run-up distance, reduction of L DDT/D (ratio of the run-up distance, L DDT to tube diameter), and expansion of the detonable concentration limit by spreading the cell width. The result of the non-premixed experiments show that similar values of the run-up distance to the premixed experiments are obtained at an equivalence ratio of about 1.0, however, fluctuations of DDT occur near the DDT concentration limit. Under laminar flow conditions at a Reynolds number of less than 2,300, the difference between the two systems could not be observed. However, when the Reynolds number increases towards turbulent conditions, the DDT run-up distance decreases compared to that of static flow conditions.

Numerical Study of Formation of a Detonation Wave in a Supersonic Flow over a Wedge by an H2-O2 Mixture with Nonequilibrium Excitation of Molecular Vibrations of Reagents

Specific features of formation of an oblique detonation wave in a supersonic hydrogen-oxygen mixture flow over a plane wedge are analyzed. Preliminary excitation of molecular vibrations of H2 is shown to lead to a noticeable (severalfold) decrease in the induction-zone length and the distance at which the detonation wave is formed. These effects are manifested even if H2 molecules are excited in a narrow region in the vicinity of the flow centerline. The reason for these effects is intensification of chain reactions in the H2-O2 (air) mixture owing to the presence of vibrationally excited hydrogen molecules in the flow.

Influence of Reactive Particles on The Formation of a One-Dimensional Detonation Wave

ABSTRACT A model is proposed which demonstrates the influence of reactive particles on the formation of a detonation wave in a combustible two-phase system. Detailed kinetics was used to describe the gas phase processes whereas two different models for the description of the heterogeneous gas-solid reactions were introduced to describe the combustion. The governing equations, formulated for two interacting continua, were solved numerically using state of the art flux-difference splitting methods and implicit time integration. The shock and detonation waves were resolved correctly by employing a dynamically moving grid. Results obtained indicate the formation of detonation wave with a double-head structure.

Thermonuclear detonations in collapsing white dwarf stars

Collapsing white dwarf stars (or degenerate cores) may occur in binary systems, in the formation of Type I supernovae or in the formation of pulsars. These collapsing configurations may explode their nuclear fuel (12C or16O) by the detonation wave mechanism. A combination of analytical and numerical models is used to investigate the formation of detonation waves. The tentative conclusion is that a detonation wave will form which will lead to the ignition of esentially all the fuel in such a collapsing star. This potentially explosive configuration will be strongly affected, however, by rapid beta processes which occur in the detonated matter and which should cause a fraction of the stellar mass to collapse toward a neutron star state. The nature and effect of such beta processes, which have not yet been incorporated in the dynamical calculations, are discussed.

Formation of detonation waves in flowing hydrogen-oxygen and methane-oxygen mixtures.

Detonation induction distances were determined in a 9-mm (i.d.) detonation tube at an initial pressure of 1 atm at ambient temperature for hydrogen-oxygen mixtures flowing at initial velocities ranging from 0-100 m/sec, and for methane-oxygen mixtures flowing at velocities from 0-30 m/sec. Some experiments with hydrogen-oxygen mixtures were conducted at 5 atm initial pressure. The induction distances for hydrogen-oxygen mixtures decrease linearly with the logarithm of the Reynolds number based on the initial linear gas velocity. Results show that the induction distance of the detonation wave propagating upstream is shorter than that of the wave propagating downstream. Induction distances in methane-oxygen mixtures were essentially constant over the range of flow velocities employed. Certain observations seem to indicate that higher turbulence levels in the initial gas flow cause an effective decrease in the quenching diameter.

Supersonic flow of a combustible gas mixture past a sphere

In recent years considerable interest has developed in the problems of steady-state supersonic flow of a mixture of gases about bodies with the formation of detonation waves and slow combustion fronts. This is due in particular to the problem of fuel combustion in a supersonic air stream.

Formation of Gaseous Detonation Waves. A Comparison of the Knallgas-Steam and Heavy Knallgas-Heavy Water Mixtures.

Data for the formation of detonation waves in the heavy knallgas-heavy water system at 100 deg C utilizing spark ignition (360 millijoules) in a 1-in. ID reactor of 13-foot length are presented. Formation of detonation in this system differs markedly from the knallgas-steam system at comparable conditions. These differences cannot be accounted for by the relative reaction rates of deuterium and oxygen as compared to hydrogen and oxygen. The data seem to indicate that heavy water acts not only as a diluent but as a more active inhibitor than steam. (N.W.R.)

Formation of detonation wave during combustion of gas in combustion tube

Formation of detonation wave during combustion of gas in combustion tube