Detonation In Channels Research Articles

Control of a Detonation Wave in a Channel with Obstacles Using Preliminary Gas Mixture Preparation

Using the detailed kinetic mechanism of chemical interaction, the effect of preliminary preparation of the stoichiometric hydrogen-air mixture (dissociation of a part of molecular hydrogen and oxygen on atomic gases) on the detonation wave characteristics is investigated numerically with the aim to control detonation combustion in plane channels with obstacles. It is found that the above-mentioned partial initial dissociation can be used to prevent quenching of detonation in channels with both a single obstacle and multiple barriers. It is revealed that the mixture, obtained as a result of preparation, differs from the initial hydrogen-air mixture by the qualitatively different type of detonation re-initiation after interaction with obstacles.

Numerical Simulation of Multidimensional Modes of Gaseous Detonation

ABSTRACTProcesses observed in experiments with the initiation and propagation of divergent detonation in a narrow gap between plates was simulated. The detonation wave is formed in a round tube adjoined to one of the plates at a right angle. Complicated cellular structures of the 2D detonation have been obtained. The process of formation of 3D cellular detonation in channels of square, rectangular, circular, and elliptical cross sections was studied. The process of spontaneous formation of spin detonation in channels of circular cross section was considered. Calculations of the transition of spin detonation to the channel of larger or smaller diameter were conducted and conditions of self-sustained spin detonation were formulated. Detonation is initiated in a quiescent combustible mixture by an instantaneous homogeneous electric discharge in a finite-width zone near the flat closed end of the channel. All computations of 3D detonation were performed in a correct formulation for the entire channel of large length (1 m) rather than only in a certain zone moving together with the wave.

Shock transition to detonation in channels with obstacles

Multidimensional numerical simulations of an unconfined, homogeneous, chemically reactive gas were used to study interactions leading to deflagration-to-detonation transition (DDT). The configuration studied was a long rectangular channel with regularly spaced obstacles containing a stoichiometric mixture of ethylene and oxygen, initially at atmospheric conditions and ignited in a corner with a small flame. The compressible reactive Navier–Stokes equations were solved by a high-order numerical algorithm on a locally adapting mesh. The initial laminar flame develops into a turbulent flame with the creation of shocks, shock–flame interactions, shock–boundary layer interactions, and a host of fluid and chemical-fluid instabilities. The final result may be eventual deflagration-to-detonation transition (DDT). Here two types of simulations are described, one with DDT occurring in a gradient of reactivity, which is common in the channels with higher obstacles, and another in which DDT arises from energy focusing as shocks converge. For the latter case, the rate of energy deposition necessary to initiate a detonation in the unburned gas is analyzed using a control volume analysis.

Experimental and numerical investigation of propagation mechanism of gaseous detonations in channels with porous walls

In the present work the propagation of gaseous detonations in a channel with porous walls is investigated experimentally and numerically. The main goal of the study is to determine the role of diffusive turbulent mixing and transverse waves in controlling the detonation limits in channels with porous walls. Detonations in propane–oxygen and hydrogen–oxygen–argon mixtures, which are characterized by their irregular and regular cellular structures, are considered in the experimental and numerical investigations. Euler simulations are performed for parameters corresponding to both regular and irregular detonations. In the smooth wall region Schlieren photographs of hydrogen–oxygen–argon detonation show laminar reaction zones behind the main front. In addition, as the detonation propagates over the porous wall, due to the mass divergence into the damping section, the frontal wave curvature increases. The number of transverse waves decreases in the porous section which is caused by the attenuation of the detonation wave. In comparison to the stable argon diluted detonations, experiments for unstable propane–oxygen detonations illustrate lower wave curvature and high turbulence in the reaction zone in the porous section. The numerically obtained results for both regular and irregular detonations show that close to the porous wall the front curvature increases, a finding that is also observed in experiments. If the curvature extends to the whole channel width the detonation wave fails to propagate. Nevertheless, the numerical critical limit of W/λ for unstable detonations is found to be higher than that of stable detonations, which is in contradiction with the experimental results. This discrepancy can be explained by the effect of turbulent diffusive mixing in controlling the reaction rate in highly unstable detonations, which is not taken into account in the current numerical simulations.

Formation of spin detonation in channels of circular cross section

Formation of spin detonation in channels of circular cross section

3D cellular detonation in cylindrical channels

Gas detonation is a complex multidimensional process. In nature, the multidimensionality of detona� tion manifests itself in the cellular structure and in the spin. The cellular and spin detonations are formed due to instability of the burning zone behind the head shock wave, due to which small perturbations increase, and periodic spatial flows arise with trans� verse waves in the flow behind the head shock and with breaks of its front [1–4]. Previously, various authors investigated mainly numerically the formation of the 2D cellular detonation in the channels. In this case, the triple points in the spots of breaks of the 2D deto�

Initiation and propagation of multidimensional detonation waves

Three-dimensional detonation in channels of different cross sections and spinning detonation in channels of circular cross sections are numerically studied. A possibility of galloping detonation in a supersonic flow of a mixture with a variable fuel concentration over a plane channel width is discussed. Conditions of detonation formation under the action of moving boundaries of the flow region due to rotation of an elliptical cylinder and in a variable-size square chamber are obtained. Formation of three-dimensional detonation in a supersonic flow in a helical channel of elliptical cross section and in a variable-size square channel is calculated.

Parametric investigation of the propagation of detonation in narrow channels filled with a propane-butane-oxygen mixture

In this article, the propagation of the detonation of a propane-butane mixture with oxygen is investigated in a channel of constant cross section with a diameter smaller than the critical one for detonation propagation. The ignition of the mixture is performed in a precombustion chamber. The entering of the flame front into the narrow channel causes the development of detonation in the channel. In this work the profiles of the pressure at the entry into the channel and the average velocities of propagation of the flame front for different sections of the channel are presented. The values of the velocity correspond to the values of the Chapman-Jouguet velocity. In this work various scenarios of the propagation of detonation depending on the size of the precombustion chamber have been investigated.

Approximate Calculation of Overdriven Gaseous Detonation in Convergent Channels

A simple quasi-one-dimensional model is presented to describe the propagation of gaseous detonation in a channel with variable cross-section. This model is applicable for the approximate analytical calculations of the degree overdrive of detonation wave in the transition of detonation from a broad to a narrow tube, and estimating the values of gasdynamic parameters at the detonation front

Hydrogen-oxygen flame acceleration and transition to detonation in channels with no-slip walls for a detailed chemical reaction model

The features of flame acceleration in channels with wall friction and the deflagration to detonation transition (DDT) are investigated theoretically and using high resolution numerical simulations of two-dimensional reactive Navier-Stokes equations, including the effects of viscosity, thermal conduction, molecular diffusion, and a detailed chemical reaction mechanism for hydrogen-oxygen gaseous mixture. It is shown that in a wide channel, from the beginning, the flame velocity increases exponentially for a short time and then flame acceleration decreases, ending up with the abrupt increase of the combustion wave velocity and the actual transition to detonation. In a thin channel with a width smaller than the critical value, the exponential increase of the flame velocity is not bounded and ends up with the transition to detonation. The transition to detonation occurs due to the pressure pulse, which is formed at the tip of the accelerating flame. The amplitude of the pressure pulse grows exponentially due to a positive feedback coupling between the pressure pulse and the heat released in the reaction. Finally, large amplitude pressure pulse steepens into a strong shock coupled with the reaction zone forming the overdriven detonation. The evolution from a temperature gradient to a detonation via the Zeldovich gradient mechanism and its applicability to the deflagration-to-detonation transition is investigated for combustible materials whose chemistry is governed by chain-branching kinetics. The results of the high resolution simulations are fully consistent with experimental observations of the flame acceleration and DDT.

On the mechanism of weakening and breaking of gas detonation in channels with acoustically absorbing walls

The physical mechanisms of the weakening of detonation waves in channels with acoustically absorbing and, particularly, porous walls are analyzed on the basis of experimental data available. The effect of weakening (and breaking) of a multifront detonation wave due to the inelastic properties of the channel walls was numerically investigated within the framework of a simplified mathematical model for propagation of two-dimensional gas detonation. The role of different physical mechanisms in the narrowing of the domain of near-critical detonation regimes observed experimentally is determined. A criterion for effectiveness of the influence of the acoustic properties of the wall on the detonation wave is formulated.

Near-limiting detonation in channels with porous walls

The propagation of detonation is studied in channels with walls whose acoustic resistance varies over a factor of 4000. Noticeable weakening of detonation waves is observed in near-critical regions. Optimum dimensions for coatings of porous materials to quench near-limiting detonation are determined.