Detonation Propagation Velocity Research Articles

Observation of Oblique Laser-Supported Detonation Wave Propagating in Atmospheric Air

Elucidation of the propagation velocity of a laser-supported detonation (LSD) wave and its propagation mechanism is necessary for various engineering applications. This study was conducted to observe an oblique laser-supported detonation wave off the laser axis. The relation between the local laser intensity and detonation-wave propagation velocity was investigated. For this purpose, the time-space distribution of the laser intensity was measured precisely. The change of the LSD wavefront shape was visualized using an ultrahigh-speed camera. The relation between the local laser intensity and the propagation velocity of the oblique LSD wave measured off the laser axis was found to be identical to the relation between the local laser intensity and the detonation propagation velocity at the laser axis.

Effect of Porous Wall on Detonation Propagation Velocity in Hydrogen-Oxygen Mixtures

ABSTRACT In this paper, the effect of flexible and rigid porous wall on the detonation propagation velocity in hydrogen-oxygen mixtures is investigated systematically. The roles of hydrogen concentration, initial pressure, porous wall geometry and porosity are considered in detail. Pressure sensors are used to record the time-of-arrival of the detonation wave, and the average velocity of the detonation wave can be obtained. The results indicate that the detonation propagation limit in a tube filled with porous materials is shorter than the value obtained in a smooth tube, and the velocity deficits increase obviously with the increase of the porosity and thickness. In the detonation limit, the velocity of detonation wave decreases firstly and then rises after passing through the absorption wall, which is due to the reflection of the shock wave on the surface of the wall. The reaction rate is increased quickly by introducing the local disturbance in the reaction zone, compensating the adverse effects of the porous wall. Compared with changing porosity, increasing thickness has a more significant effect on detonation attenuation. This phenomenon can be due to the excessive bending of the wave front and the heat loss increases.

Effects of Ozone Addition on Multi-Wave Modes of Hydrogen–Air Rotating Detonations

Ozone addition presents a promising approach for optimizing and regulating both combustion and ignition mechanisms. In Rotating Detonation Engines (RDEs), investigating the impact of ozone addition is particularly important due to the fact of their unique operating conditions and potential for improved efficiency. This study explores the influence of ozone concentration, total temperature, and equivalent ratio on the combustion characteristics of a hydrogen–air mixture infused with ozone. Utilizing the mixture as a propellant, the combustion chamber of a continuous rotating detonation engine is replicated through an array of injection ports, with numerical simulations conducted to analyze the detonation wave combustion mode. Our results show that an increase in total temperature leads to an increase in the number of detonation waves. Incorporating a minor quantity of ozone can facilitate the ignition process for the detonation wave. Increasing the ozone content can result in the conversion from a single-wave to dual-wave or multi-wave mode, providing a more stable combustion interface. A low ozone concentration acts as an auxiliary ignition agent and can significantly shorten the induction time. As the total temperature increases, the detonation propagation velocity and the peak heat release rate both decrease concurrently, which leads to a decline in the exit total pressure and an augmentation in the specific impulse. Employing ozone exerts a minimal impact on the detonation propagation and the overall propulsion performance. The requirement for ozone-assisted initiation differs noticeably between rich and lean combustion.

The propagation characteristics of particle-laden two-phase detonation waves in pyrolysis mixtures of C(s)/H2/CO/CH4/O2/N2

In this paper, numerical simulations are carried out to study the propagation characteristics of detonation waves in carbon particle-laden two-phase pyrolysis mixtures consisting of C(s)/H2/CO/CH4/O2/N2. The results show that the hydrodynamic thickness of the detonation waves changes non-monotonically with the carbon particle mass loading ratio and particle diameter. Both the aerodynamic relaxation time and heterogeneous reaction time increase drastically by enlarging the carbon particles. Small particles with the diameter of less than 1 μm gather and then react near the detonation front, which significantly enhances the propagation velocity of the detonation waves. Under such conditions, the aerodynamic relaxation time scale is smaller than the detonation wave characteristic time scale, which causes both the velocities and temperatures of gas and particles to reach the maximum values at the detonation front. However, such effects diminish gradually as the particles enlarge in size. The investigations show that 50 μm-sized particles have almost no effect on the detonation wave, for which the aerodynamic relaxation and heterogeneous reaction time scales are considerably larger than the detonation wave characteristic time scale. The propagation velocity of the detonation wave in the presence of 50 μm-sized particles is close to the value of the gaseous case. The results also show that increasing the particle mass loading ratio induces nonlinear changes in the detonation propagation velocity, due to changes in the global equivalence ratio of the two-phase mixtures.

Numerical simulation of detonation wave propagation through a rigid permeable barrier

The results of calculation of the detonation propagation in a porous medium for hydrogen-air mixture are presented. The porous medium was specified explicitly and consisted of sets of individual obstacles in the form of solid walls or the sets of finite-size plates. Various modes of detonation propagation depending on obstacle parameters are obtained: propagation in a cellular mode, stationary propagation with destruction of the cellular structure of the detonation front, propagation of a monotonically attenuating detonation wave with destruction of the cellular structure of the front. The possibility of reducing the detonation propagation velocity by replacing solid plates with finite-size ones was shown. The effect of the geometrical parameters of the plates and the step of it installation on the degree of detonation attenuation was estimated. It was determined that an increase in the number of plates leads to a stronger attenuation of the detonation.

Single-head detonation propagation in a partially obstructed channel

Recent experiments have revealed the propagation of a sustained single-head detonation propagation through an obstructed channel. In this study, new experiments and analysis of the complex three-dimensional behaviour of such a single-headed wave in stoichiometric hydrogen-oxygen mixtures is presented. An optically accessible channel of square cross-section containing obstacles with 50% area blockage was used in conjunction with soot-foils and dual-axis high-speed schlieren imaging to study the phenomenon over an initial pressure range of 17 kPa to 24 kPa. Detailed analysis of the wave reveals a transverse asymmetry generated by detonation diffraction whereby a transverse detonation propagates in a zig-zag fashion down the channel reflecting off opposite channel sidewalls. Analysis of the single triple-point trajectory reveals a detonation propagation velocity between 1.4 and 0.5VCJ, with the transverse detonation propagating at a constant 0.9VCJ until reflection on the channel sidewall. The trajectory of the triple-point is undisturbed by the presence of obstacles. In the vicinity of the triple-point, flow analysis indicates prompt ignition (<1 μs induction time) of the gas mixture behind the Mach-stem and transverse waves, confirming the presence of detention waves within the structure. The role of the obstacle in the propagation mechanism is to weaken the Mach-stem detonation through diffraction to generate a separation in the shock and flame, through which the transverse detonation propagates.

Numerical simulation of shock and detonation waves in bubbly liquids

A well-posed mathematical model of nonisothermal, two-phase, two-velocity flow of a bubbly medium with chemically inert liquid and chemically inert or active gas bubbles is proposed. The model is based on the two-phase Euler equations with the introduction of an additional pressure at the gas-bubble surface, which ensures the well-posedness of the Cauchy problem for a system of governing equations, and the Rayleigh–Plesset equation for radial pulsation of gas bubbles allowing solutions of the soliton type that are realized in experiments to be obtained. The model is validated by comparing calculations of detonation wave propagation with experimental data in water or an aqueous solution of glycerin with bubbles of acetylene–oxygen mixture or with bubbles of argon–hydrogen–oxygen mixture for a volume gas content of 1–6%. The model is shown to provide satisfactory results for the detonation propagation velocity and detonation pressure profiles.

Enhancement of continuously rotating detonation in hydrogen and oxygen-enriched air

The enhancement of continuously rotating detonation in oxygen-enriched air was demonstrated in an annular rotating detonation combustor (RDC) under a diffusive supply of hydrogen and an oxidizer. Experimental tests were performed to reveal the effects of oxygen volume fraction, mass flow rate, and equivalent ratio on the propagation of continuously rotating detonation wave (CRDW). It is observed that an increase in the air mass flow rate from 25 g/s to 225 g/s causes an increase in the propagation velocity of the stable CRDW in the RDC. For an oxygen volume fraction up to 35%, the difference between the propagation velocity of detonation and the theoretical Chapman–Jouguet value is less than 5%. Under the chemical stoichiometric ratio condition for air, the CRDW is stabilized when the air mass flow rate reaches 185 g/s. However, stabilized CRDW is observed even when the air flow rate is only 45 g/s under the presence of 30% or 35% oxygen. Increase in the oxygen volume fraction leads to an extension of the rich/lean limit for generating a stable CRDW. This study aims to provide guidance for the modulation of continuously rotating detonation.

Detonation velocity behavior and scaling analysis for ethylene-nitrous oxide mixture

In this study, a detailed experimental investigation of the detonation propagation velocity behavior of stoichiometric ethylene-nitrous oxide in narrow channels is conducted. The experimental results in 4mm (inner diameter) round tube indicate the detonation experiences three propagation modes with the decreasing of initial pressure (p0), i.e., steady mode (p0>40kPa), unstable mode (40–27kPa) and decay mode (p0<27kPa), it is confirmed that below pc=27kPa the failure of detonation occurs. The maximum of the velocity deficit at the critical pressure is 35% VCJ. However, only steady and decay detonation modes are observed in 14mm round tube, and the critical pressure for the detonation limits is 15kPa, at which the maximum velocity deficit is 15% VCJ. In 36mm round tube, there are steady and decay modes can be found, the critical pressure for detonation limits is 5.2kPa, its corresponding maximum velocity deficit is 12% VCJ. The results indicate that with the decreasing initial pressure and tube diameter, boundary layer displacement thickness increases and causes more losses through the flow divergence and hence the increasing of velocity deficits. A linear relationship is obtained between the normalized detonation average velocity and (p0·d)−1 by scaling analysis. It suggests the normalized velocity and dimensionless parameter of length scale, i.e., ratio of tube diameter and ZND induction zone length (d/ΔI) collapse to a single exponential curve.

On the detonation propagation behavior in hydrogen-oxygen mixture under the effect of spiral obstacles

Detonation propagation velocity behavior and cellular structure of stoichiometric hydrogen-oxygen mixture in spiral obstacles with four roughness (ξ = 0.133, 0.231, 0.4, 0.625) are systematically examined, at the conditions outside-, near- and within the propagation limits. The experimental results indicate that, at p0 = 10 kPa (outside the limits), spirals with roughness smaller than 0.4 facilitate the initiation of detonation, but ξ = 0.625 spiral causes the detonation quench earlier than that in smooth tube without spiral, and suggests it has prohibiting effect on the detonation propagation. At p0 = 12 kPa (near the detonation limits), spirals with ξ = 0.133 and 0.231 extend the detonation limits and therefore they have the facilitating effect on the detonation propagation, but this positive effect is not obvious in the spiral with larger roughness (i.e., ξ = 0.4 and 0.625). As the initial pressure is higher than 15 kPa, under such condition detonations are well within the limits, the dual effects of promoting and prohibiting of the spiral on the detonation propagation are more obvious, which are confirmed by the cellular structures obtained from smoked foil. The ZND induction zone length (ΔI) analysis confirms ΔI is shorter at higher initial pressure, under this condition detonation is more sensitive and easier to survive from failure as it enters into the spiral section.

Evaluation of detonation characteristics of aluminum/JP-10/air mixtures at stoichiometric concentrations

In order to investigate the heterogeneous detonation characteristics of aluminum particles/JP-10/air mixtures, the gas–solid two phase flow and detonation models were established using the discrete phase model (DPM) and turbulent combustion model, and detonation properties of the aluminum particles/JP-10/air mixtures were simulated. At stoichiometric concentrations of the solid particle–gas mixtures, and four different mass ratios (100% aluminum particles/air, 60% aluminum particles/40% gaseous JP-10/air, 40% aluminum particles/60% gaseous JP-10/air, 100% gaseous JP-10/air), results reveal that obvious reaction relaxation phenomenon exists in aluminum particles detonation process, however, addition of gaseous JP-10 to aluminum particles obviously contributes to higher steady detonation propagation velocity and extended reaction zone width. Furthermore, 60% aluminum particles/40% JP-10/air mixture achieves the highest detonation velocity up to 2128m/s, detonation pressure of 3.7MPa, efficiently enhanced reaction zone width of 0.369m, and the reaction times of JP-10/air and aluminum particles/air of 2.07μs and 5.65μs, respectively.

Detonation velocity deficits of H2/O2/Ar mixture in round tube and annular channels

In this study, a series of experiments have been carried out to determine the detonation velocity deficits of 2H2–O2 and 2H2–O2–3Ar mixtures in narrow gaps. Those gaps include a 36 mm inner round tube and three annular channels gaps (w = 2 mm, 4.5 mm and 7 mm, w is the gap of annular channel). Photodiodes and shock pins are employed to measure the time of arrival of the detonation wave. Smoked foils are used to record the cellular detonation structure. Experimental results indicate that for those detonations in 2H2–O2 and 2H2–O2–3Ar mixtures within the limits, the detonation propagates at a relatively steady velocity with small deficit, as the limits are approached by progressively reducing the initial pressure, the velocity gradually decreases and the failure of detonation occurs as the initial pressure below a critical value. In the 36 mm diameter round tube, the critical pressures for successful propagation detonation in 2H2–O2 and 2H2–O2–3Ar mixtures are 13 kPa and 11 kPa respectively, and the maximum velocity deficits for above mixtures are 9% and 5%. By introducing a more accurate method that calculate the intermediate parameters (i.e., detonation cell size, reaction zone thickness) for Fay's model, a modified theoretical model to predict the detonation velocity deficits in different geometries is proposed. By comparing with the experimental results, it confirms the theoretical model is suitable for experimental data with reasonable accuracy in most cases. Due to the theoretical model does not consider the boundary condition, which is fairly prominent in very narrow gap (e.g., 2 mm annular channel), therefore, larger discrepancy between the experiment and theoretical prediction can be observed in the case of small gap. Both experimental and theoretical results indicate velocity deficit increases as detonation transmits from round tube to annular channel, which is due to the heat and momentum losses from wall reduces the propagation velocity of detonation.

Utilizing unsteady curved detonation analysis and detailed kinetics to study the direct initiation of detonation in H 2–O 2 and H 2–Air mixtures

In the present paper, utilizing a detailed chemical kinetics, the simplified unsteady reactive Euler equations are solved in the reaction zone of a curved detonation, to derive the relation between detonation propagation velocity ( D) with its acceleration ( D ˙ ) and front curvature ( κ), that is the so called D ˙ − D − κ relation. Then, this relation is used for tracking the detonation front and to study the onset of a self sustained near CJ detonation. The reaction-zone history is studied to understand the events that happen during the onset of a detonation in Hydrogen/Oxygen mixtures. It is observed that the relative movement of the location of the peak of the thermicity function with respect to the front, and its absolute value, are two parameters that determine the physics of the onset. Utilizing the D ˙ − D − κ relation based on the detailed chemical kinetics, the critical initiation energy is calculated for the H 2–O 2 and H 2–Air mixtures. Although, the previous studies by single step kinetics [A. R. Kasimov, PhD Thesis, Univ. of Illinois at Urbana-Champaign] and the present results both predict the critical initiation energy with acceptable accuracy, however, the present work makes a better prediction of the equivalence ratio at which the H 2–O 2 mixture experiences its minimum critical energy. Also the present predictions are more accurate for the lean H 2–O 2 and H 2–Air mixtures. Using the present method, the effect of initial pressure on the critical initiation energy of H 2–O 2 mixture is well predicted compared to empirical results.

LES model of large scale hydrogen–air planar detonations: Verification by the ZND theory

The large eddy simulation (LES) model of hydrogen–air detonation at very large scales, which doesn't require Arrhenius chemistry, is presented. The progress variable equation is applied for the first time to simulate propagation of a reaction front following and coupled with a leading shock. The gradient method, based on a product of pre-shock mixture density and detonation velocity, is employed as a source term in the progress variable equation. Chemical kinetics enters the combustion model only through its influence on the detonation velocity and modelling of detailed chemistry is omitted. The LES model is verified against theoretical solution by the Zel'dovich–von Neumann–Doring (ZND) theory for a case of planar 29.05% hydrogen–air detonation in elongated 3 × 3 × 100 m calculation domain. Thermodynamically calculated values of the specific heats ratio for burned mixture γ = 1.22 and the standard heat of combustion Δ H c = 3.2 MJ/kg are applied without any adjustment often applied in other models. Numerical simulation reproduced theoretical values of von Neumann spike, Chapman–Jouguet pressure, Taylor wave and detonation propagation velocity. There are no adjustable parameters in the model. Practically no grid sensitivity for the planar detonation wave is demonstrated by the LES model. Detonation velocity and pressures are shown to be nearly independent of the computational cell size in a wide range of cell sizes 0.1–1.0 m. Impulse depends to some extent on a cell size. Three-dimensional version of the LES model is under development to simulate pressure effects and identify design solutions, including mitigating techniques, for hydrogen safety engineering. There is no intention to use this oriented on large scale applications engineering LES model to reproduce fine structure of the detonation wave.

Detonation propagation characteristics of superposition explosive materials

In order to investigate detonation propagation characteristics of different charge patterns, the detonation velocities of superposition strip-shaped charges made up of a detonating cord and explosives were measured by a detonation velocity measuring instrument under conditions of different ignition. The experimental results and theoretical analysis show that the maximum detonation propagation velocity depends on the explosive materials with the maximum velocity among all the explosive materials. Using detonating cord in a superposition charge can shorten detonation propagation time and improve the efficiency of explosive energy. The measurement method of detonation propagation velocity and experimental results are presented and investigated.

A simple theory for the propagation of film detonations

Detonation propagation velocity through tubes with walls coated with thin fuel film, using turbulent boundary layer theory

Photography of the disturbance which propagates detonation to a charge of explosive

Detonation propagation velocity behavior and cellular structure of stoichiometric hydrogen-oxygen mixture in spiral obstacles with four roughness (ξ = 0.133, 0.231, 0.4, 0.625) are systematically examined, at the conditions outside-, near- and within the propagation limits. The experimental results indicate that, at p0 = 10 kPa (outside the limits), spirals with roughness smaller than 0.4 facilitate the initiation of detonation, but ξ = 0.625 spiral causes the detonation quench earlier than that in smooth tube without spiral, and suggests it has prohibiting effect on the detonation propagation. At p0 = 12 kPa (near the detonation limits), spirals with ξ = 0.133 and 0.231 extend the detonation limits and therefore they have the facilitating effect on the detonation propagation, but this positive effect is not obvious in the spiral with larger roughness (i.e., ξ = 0.4 and 0.625). As the initial pressure is higher than 15 kPa, under such condition detonations are well within the limits, the dual effects of promoting and prohibiting of the spiral on the detonation propagation are more obvious, which are confirmed by the cellular structures obtained from smoked foil. The ZND induction zone length (ΔI) analysis confirms ΔI is shorter at higher initial pressure, under this condition detonation is more sensitive and easier to survive from failure as it enters into the spiral section.