Detonation Propagation Research Articles

Numerical simulation of detonation propagation and extinction in two-phase gas-droplet ammonia fuel

Numerical simulations of detonation propagation and extinction in ammonia droplet-laden premixed ammonia–oxygen gas are performed in a 2-D planar channel. The sustained propagation and ultimate quenching of detonation with perturbations from ammonia droplets are observed under lower and larger values of initial droplet number density (Nd,0) and diameter (d0), respectively. The detonation always quenches under d0=15μm. The detonation propagation/extinction behaviour and cell structure are dependent on both d0 and Nd,0. The positive correlations between droplet volume fraction, inter-phase mass, momentum, and energy transfers and d0 are more nonlinear than their counterparts of Nd,0. The post-Mach stem region experiences higher-intensity detonative combustion and thus droplet evaporative, accelerative, and heating effects than the post-incident wave region. During the detonation extinction process, the detonation wave degenerates into detonative spots which then decouple into shock and reaction fronts; gaseous pressure, heat release rate, and nitric oxide volume fraction peaks decline.

The effect of porous non-metallic balls on detonation propagation in hydrogen–oxygen mixtures

In this study, the influence of porous non-metallic balls on the dynamics of detonation propagation in hydrogen–oxygen mixtures is studied in stainless steel tubes with square cross-sections. The effect of the length and thickness of the balls is considered in detail. Four pressure transducers are used to record the detonation time-of-arrival, and the average velocity of detonation propagation is calculate. The smoked foil technique is performed to register the detonation cellular structures. The results indicate that increasing the filling length and thickness of the balls leads to a significant increase in velocity loss, critical pressure, and re-initiation distance during detonation propagation. Two propagation modes are observed near the critical pressure. In sub-critical mode, the detonation wave is attenuated and failed eventually, propagating to the end of the tube in the form of a low-speed deflagration wave. In super-critical mode, the detonation propagation can be promoted by inducing a vertical transverse wave generated by the detonation wave passing through a group of small balls. It is worth noting that the increase in filling thickness of the small balls leads to a greater velocity loss compared to the increase in filling length. However, an increase in the filling length will cause the detonation wave to undergo a longer and more sustained weakening process as it passes through the small balls, thereby resulting in a longer re-initiation distance and a lower average velocity over a short distance after re-initiation. By increasing the filling length of the small balls to 312 mm, the transition of the detonation wave from multi-head detonation to double-head detonation can be observed, and then successfully turns into stable detonation. However, when filling double-layer small balls, even in super-critical conditions, the attenuated detonation wave cannot achieve re-initiation over a short distance.

Deflagration-to-detonation transition and detonation propagation in supersonic flows with hydrogen injection and downstream ignition

This study investigates the mechanisms of flame acceleration and deflagration-to-detonation transition (DDT) in supersonic flows using transverse hydrogen injection and downstream ignition. Utilizing the graphics processing unit accelerated adaptive mesh refinement approach, we examine the influence of downstream ignition jet pressure on DDT through high-resolution computational simulations. Our results indicate that the transverse injection of hydrogen into the supersonic mainstream generates strong turbulence and numerous vortices due to Kelvin–Helmholtz instability, enhancing fuel mixing efficiency along the flow but deviating from the ideal premixed state. Following the injection of the downstream ignition jet into the supersonic main flow, initial flame acceleration is less effective than in the premixed state due to the non-uniformity of the incoming flow. However, within the boundary layer, the flame remains stable, and the intense turbulence fosters shock–flame interactions. The convergence of multiple compression waves into a shock wave facilitates energy deposition, coupling with the flame to trigger local detonation via the reactive gradient mechanism. The detonation wave exhibits complex wavefront structures, including vertical and oblique fronts induced by boundary layer interactions. Ignition jet pressure significantly impacts the DDT process and detonation wave characteristics, reducing ignition time and affecting the detonation temperature, pressure, and propagation speed. This study provides valuable insights into the dynamics of flame acceleration and DDT in supersonic flows with non-uniform fuel distribution and downstream jet ignition. The findings highlight the critical role of ignition jet pressure in optimizing ignition and detonation processes, offering new perspectives for achieving low-energy, rapid detonation initiation within the tube.

Research on the initiation and wavefront evolution of diverging cylindrical detonations of acetylene and oxygen mixtures

The present study focuses on fundamental research about the transition from a planar detonation to a cylindrical detonation and the propagation of the diverging cylindrical detonation. We aim to figure out the mechanism of the transition and propagation of the diverging cylindrical detonation by analyzing the cellular pattern and critical initial pressure. The findings highlight that the successful detonation in a cylindrical chamber via transition through a straight channel is predominantly influenced by diffraction at the corners and the successive continuous reflections between the front and rear walls. Depending on the initial pressure, the initiation modes exhibit characteristics of subcritical, critical, and supercritical three-stage processes. Sustained propagation of cylindrical detonations necessitates increasing the number of cells to match the growth rate in the front region. Experimental investigations reveal two distinct modes of cell number increase: mild and violent. In the case of the former, cell number increase predominantly occurs on a scale of two to three times the characteristic cell size of the Chapman-Jouguet detonation. In contrast, a decaying Mach stem undergoes twisting and evolves into local kinks, leading to the development of new triple-wave points. The latter mode typically occurs near the limit, where cell increase primarily arises from randomly occurring local explosions, and operates on a scale of ten times the characteristic cell size or the chamber diameter. In addition, a numerical study of two-dimensional fundamental problems abstracted from the experiment is conducted to help interpret experimental results and reveal more about the physics of the problem.

Laboratory systems for detonation research

Decarbonizing global energy systems is among the most pertinent challenges in the climate crisis. Tightly tied to the economic prosperity of a nation and responsible for more than 75% of global emissions, decarbonization of the energy sector will require well-developed solutions. The emergence of detonation engines can reduce emissions in aviation and gas-fired power generation, with theoretical efficiencies 40% lower than conventional engines. These efficiencies have yet to be realized in practice, due to our lack of understanding of detonation propagation and its instabilities. This project aimed to develop the laboratory systems required to study detonations. To this end, a long rectangular channel was manufactured and outfitted with a gas handling system to inject a mixture, an ignition system, pressure transducers to capture the propagation characteristics, and an optical system enabling Schlieren photography. The gas handling system uses sonic nozzles, thus flow rate is a linear function of upstream line pressure. Each line contains a pressure transducer, microcontroller to process signals, LCD for pressure readout, and a regulator for adjustment of the line pressure. The ignition system uses an ignition box that steps up a 12 V supply to 400 V, an ignition coil raising the voltage to 15-40 kV, and a spark plug to ignite the mixture. Ignition, pressure transducer signal acquisition, and Schlieren photography are all synchronized using a NI-6356 DAQ with LabVIEW. The DAQs analog input ports receive readings from the pressure transducers along the channel, the timing of which and known distance between transducers allows for velocity calculations. The schlieren system utilizes the digital output channels to synchronize camera shutter with an LED driver, and parabolic mirrors, positioned to optimize schlieren imaging. The LED driver requires greater current than produced by the DAQ thus a current amplifier circuit is used to bridge the DAQ and driver.

Safety of using hydrogen: Suppression of detonation in hydrogen-air mixtures

Safety of using hydrogen as fuel in aerospace applications is closely connected with hydrogen explosion safety during its transportation and stockpiling at launch places. In this paper, preventing the detonation propagation in the mixtures of hydrogen with air due to accidental hydrogen releases is studied in numerical experiments. Another fuel - hydrocarbon propylene – is studied as an optional inhibitor to be added in a small volume quantity to hydrogen-air mixture. The dependence of detonation wave cellular structure on the content of inhibitor is studied for different fuel-air ratios. The results make it possible determining the content of inhibitor sufficient for preventing the detonation onset or destroying the existing detonation wave.

Evaluating the effect of ignition energy on gaseous hydrogen–oxygen detonations

The effect of ignition energy on the cellular structure of hydrogen-oxygen and hydrogen-oxygen-argon detonations was investigated experimentally over a range of initial conditions. The increase in ignition energy resulted in increased detonation propagation velocities, leading to overdriven detonations for most of the reactive mixtures. The detonation cell width decreased for mixtures subjected to higher ignition energy. A substantial reduction in the detonation cell width was observed for mixtures at a lower initial pressure. The coefficient of variation of the measured detonation cell width decreased with ignition energy, indicating greater regularity and uniformity in cellular structure. The observed reduction in the cell width can be attributed to the propagation of an overdriven detonation in the reactive mixtures due to high ignition energy.

Development of Node-centered finite-volume diffusion method on triangle mesh for detonation propagation simulation in insensitive high explosives

This study presents a numerical simulation of detonation waves in insensitive high explosives (IHE). A direct numerical simulation (DNS) method of detonation waves propagation was developed. It solves two-dimensional reactive Euler equations by using a semi-discrete node-centered finite-volume (NCFV) scheme on triangle mesh. Employing ZND model analytical solution as the initial condition, the upper and lower boundary conditions were designed as local sonic equilibrium conditions. The DNS method was validated using steady detonation wave propagation experimental results for tri-amino-tri-nitro-benzene (TATB) based explosives. The two-dimensional steady detonation propagation of the circular arc experiments was completed using a non-embedded technique (electric and optical fibre probe velocimetry). The comparison results demonstrate that the numerical method can provide a good prediction of the pseudo-steady-state detonation wave front propagation and the angular speed.

Experimental Study on Effects of Different Factors on Continuous Detonation of Superfine Lignite: Particle Size and Fuel Equivalent Ratio

ABSTRACT The Rotating Detonation Engine (RDE) is garnering attention for its high thermal cycle efficiency. In order to explore the detonation evolution of lignite/gas/oxygen gas-solid two-phase fuel in RDE, self-developed RDE(L:1000 mm) was used to study the detonation characteristics of lignite dust with ultra-fine particle size in methane/oxygen atmosphere, and the effects of ultra-fine particle size and equivalent ratio on detonation characteristics were explored, achieving stable propagation of rodtating detonation waves (RDW) with durations between 0.611 and 0.684s. The results indicate that the introduction of lignite dust significantly enhances the detonation effects compared to pure methane fuel. An increase in the overall equivalence ratio boosts the propagation velocity of RDW in methane-solid fuels, while a larger lignite dust particle size slows it down. Among ultrafine lignite powder sizes, a 1 μm particle size achieved the highest detonation wave speed. In terms of RDW propulsion, the impact of particle size and methane-solid fuel equivalence ratio on thrust mirrors their effect on detonation wave velocity. At a global equivalence ratio (GER) of 1.8, the specific impulse under different particle sizes was about 0.6 times that at a GER of 1.0, suggesting that an excess of fuel can reduce detonation effectiveness. The optimal specific impulse results were obtained with a lignite powder addition rate of 6 g/s, particle size of 1 μm, and GER of 1.0, reaching 4.6 kN·s·kg−1. The research results reveal the detonation process and detonation propagation law of lignite in methane/oxygen, especially for the future application of lignite in detonation energy release engineering.

Experimental investigation on detonation characteristics of boron-rich gelled propellant in static premixed combustible gases

A detonation in multiphase air-kerosene-boron mixtures is studied experimentally and the initiation and propagation characteristics of multiphase pulse detonation are emphasized. The boron-rich kerosene gelled propellants are taken as the fuel to analyze its detonation characteristics in static premixed combustible gases. The factors affecting detonation initiation including component, atomization, and ignition method of propellant are elucidated respectively. Considering atomization, evaporation and combustion, a small molecular organic compound is employed to fabricate metallized gelled propellants enriched with substantial boron particles. The dynamic atomization of gelled propellant with varying boron content is imaged by means of visual observation devices, and the ejecting parameters are optimized properly from actual initiation conditions. A flame jet by hot turbulent jet is applied to amplify the ignition energy of deflagration to detonation transition in boron-rich gelled propellant, which has not been seen ever. Results show that the ignition energy is positively correlated with initial pressure formed by combustible gas products. The multiphase detonation wave of boron-rich gelled propellant is successfully induced by premixed H2/O2 mixtures, and its detonation propagation characteristic is closely associated with the increase of initial pressure of premixed gas and mass mixing ratio of working medium. The pressure peak and propagation velocity of detonation wave show a considerable improvement with increasing initial pressure of premixed combustible gas and mass mixing ratio, and the highest values can reach up to 8.65 MPa and 2750 m/s respectively.

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.

Air-breathing rotating detonation engine supplied with liquid kerosene: propulsive performance and combustion stability

Experimental results are presented for a rotating detonation engine supplied with liquid kerosene and preheated air without liquid or gaseous additions to the propellant mixture. Various combustion modes for the generic combustor geometry design were observed—from deflagration, through pulsed combustion and high-frequency instabilities, to stable detonation propagation. Attention was paid to detonation stability (if present), its characteristics, and the propulsive performance of the combustor with a focus on specific thrust and pressure gain through thrust and outlet total pressure measurement. These parameters measured for the observed modes were compared. The stability of the detonation combustion proved not to be critical to achieve high performance of the combustion chamber. For example, high performance was achieved for combustion modes with high-frequency instabilities.

Propagation instabilities of the oblique detonation wave in partially prevaporized n-heptane sprays

Two-dimensional oblique detonation wave (ODW) propagations in partially prevaporized n-heptane sprays are numerically simulated with a skeletal chemical mechanism. The influences of the droplet diameter and total equivalence on oblique detonation are considered. The initiation length is found to increase first and then decrease with increasing initial droplet diameter, and the effect of droplet size is maximized when the initial droplet diameter is approximately $10\ \mathrm {\mu } {\rm m}$ . As the initial droplet diameter varies, unsteady and steady ODWs are observed. In the cases of unsteady ODWs, temperature gradients and non-uniform distributions of the reactant mixture due to droplet evaporation lead to formation of unsteady detonation propagation, therefore leading to fluctuations in the initiation length. The fluctuations in initiation length decrease as the pre-evaporation gas equivalence ratio increases for the unsteady cases. The results further suggest that the relationship between the evaporation layer thickness along the streamline and the corresponding theoretical initiation length can be used to identify an unsteady or steady ODW in cases with large droplets that evaporate behind an oblique shock wave or ODW under the effects of different initial droplet diameters.

Computational and Experimental Study of Detonation Propagation in TATB-Based Cylindrical Charges

Computational and Experimental Study of Detonation Propagation in TATB-Based Cylindrical Charges

Near-limit detonation in long spiral tube: An improved experimental methodology and frequency analysis

In the present work, near-limit detonations in near stoichiometric propane-oxygen mixtures were investigated using a long spiral tube facility. Compared to previous studies, our improvements in the tube length, framing rate and resolution, image processing methods for distortion correction and detonation front detection, allow for a significant increase of the amount and quality of data obtained. As the initial pressure was decreased, stable, stuttering, and galloping regimes of detonation propagation were successively observed. The use of wavelet transform made it possible for the first time to visualize the change of the intrinsic frequency of the oscillation of the detonation front velocity during the highly unstable propagation in the stuttering and galloping regimes. The failure/re-initiation cycles produce the highest power density at frequencies in the range of 500–1000 Hz. In the stuttering regime, additional velocity fluctuations were observed in the range 2000–12000 Hz during the re-initiation events. In the galloping regime, velocity fluctuations took place during the low-velocity periods, with characteristic frequencies in the range of 2000–2500 Hz. The dynamics of the failure and re-initiation events were characterized in terms of induction length normalized wavelength. It was shown that in the stuttering regime, the detonation failure events occur after a quite random length, whereas the detonation re-initiation events appear to occur after a rather constant length. In the galloping regime, less variability was observed, and failure and re-initiation events occur at a rather well defined frequency.Novelty and Significance Statement1. Improved experimental facility and techniques to study near-limit detonations in long spiral tube2. First application of wavelet transform to study near-limit detonations3. Detailed study of the frequency of failure and re-initiation events in the stuttering and galloping regimes

The Mechanism of Resonant Amplification of One-Dimensional Detonation Propagating in a Non-Uniform Mixture

The propagation of detonation waves (i.e., supersonic combustion waves) in non-uniform gaseous mixtures has become a matter of interest over the past several years due to the development of rotating detonation engines. It was shown in a number of recent theoretical studies of one-dimensional pulsating detonation that perturbation of the parameters in front of the detonation wave can lead to a resonant amplification of intrinsic pulsations for a certain range of perturbation wavelengths. This work is dedicated to the clarification of the mechanism of this effect. One-dimensional reactive Euler equations with single-step Arrhenius kinetics were solved. Detonation propagation in a gas with sine waves in density was simulated in a shock-attached frame of reference. We carried out a series of simulations, varying the wavelength of the disturbances. We obtained a non-linear dependence of the amplitude of these pulsations on the wavelength of disturbances with resonant amplification for a certain range of wavelengths. The gain in velocity was about 25% of the Chapman–Jouguet velocity of the stable detonation wave. The effect is explained using the characteristic analysis in the x-t diagram. For the resonant case, we correlated the pulsation period with the time it takes for the C+ and C− characteristics to travel through the effective reaction zone. A similar pulsation mechanism is realized when a detonation wave propagates in a homogeneous medium.

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.

A high-order simulation method for compressible multiphase flows with condensed-phase explosive detonation in underwater explosions

This study introduces an efficient method designed for the simulation of compressible multiphase flows associated with explosive detonation, primarily in the context of underwater explosions. The proposed approach integrates three core components: the compressible Euler equations, the level-set equation, and the program burn model. Spatial terms of the compressible Euler equations undergo discretization using a fifth-order accuracy weighted essentially non-oscillation reconstruction, while the third-order total variation diminishing Runge–Kutta scheme manages the temporal terms. The level-set method ensures accurate tracking of the multiphase interface. To detail the transition from solid, non-reactive explosives to gaseous detonation products in the condensed charge's detonation reaction zone, the program burn model based on Zeldovich, von Neumann, Doering theory. The efficacy and accuracy of the incorporated program burn model and the multiphase interface capture method are employed through four benchmark tests, exhibiting excellent agreement with previously published data from alternative numerical methods or commercial software. In conclusion, applying the proposed method to four distinct engineering scenarios facilitates a comprehensive understanding of the inherent dynamics associated with detonation and shock wave generation and propagation.

Numerical investigation of detonation initiation in a modeled rotating detonation engine

In experimental studies, single-wave mode and two counter-rotating wave mode are often observed in rotating detonation combustors. To investigate the mechanism behind different propagation modes, high-resolution numerical simulations of two-dimensional detonation in hydrogen/air mixtures are conducted by solving the reactive Navier–Stokes equations with a detailed chemical mechanism. The numerical results show that the occurrence of the dual-wave detonation propagation mode is positively influenced by an increase in both the channel width and the initial pressure. The dual-wave modes are observed when increasing the channel width, and it is found that the dual-wave modes are caused by increasing the residual premixed gas height near the inner wall. When increasing the initial pressure, the initial peak detonation heat release increases, which leads to the increase in the hot spot intensity formed, and it is found that the dual-wave modes are mainly caused by the interactions between the initial detonation wave and the inner wall. However, the initial equivalent ratio appears to have a relatively minor impact on the detonation propagation mode due to a relatively narrow range variation of physical properties. The peak heat release rate exerts a greater influence on the change of the propagation mode than the induction time does through a wider range test on rotating detonation engines' working condition. Moreover, the velocities and the cell sizes of detonation waves propagating in different directions with different channel widths are also analyzed, revealing that the characteristics of the detonation waves propagating in different directions are nearly the same.

Numerical study on the reinitiation mechanism of detonation propagating through double slits in a planar channel

In this study, numerical simulations were performed to investigate the reinitiation of diffracted detonation waves through a double-slit-plate. A planar detonation wave was set to propagate through a channel of a height of 50 mm filled with the stoichiometric mixture of hydrogen and oxygen at 20 kPa. Several slit-plates with different slit widths and slit spacing were considered to explore the effects of slit geometry on reinitiation and its underlying mechanisms. For this, two-dimensional multi-species reactive Navier–Stokes equations were solved using a finite volume solver. The results revealed that upon diffraction, the detonation waves become decoupled and subsequently exhibit one of three distinct phenomena depending on the specific slit geometry. These phenomena include reinitiation by shock–shock interaction (RSSI), reinitiation by shock-wall interaction (RSWI), and complete suppression. It was found that a residual transverse wave is crucial in generating a detonation kernel. In cases where this residual transverse wave is absent, the detonation kernel fails to develop. As a result, only complete suppression of the detonation wave was observed. The narrow slit widths effectively suppress residual transverse waves through the steep expansion that occurs as the detonation front passes through the slit. Moreover, larger slit spacing resulted in further expansion of the shock front before the collision, due to the increased time delay for the shock waves to intersect. As a result, it was found that a larger slit spacing is unfavorable for the formation of a detonation kernel. Yet, in this regard, it is important to note that the onset of RSSI was not guaranteed even with a detonation kernel. Rather, the onset of RSSI was highly dependent on the curvature of the main detonation trajectory. RSSI was inhibited in cases where the forward propagating detonation wave experienced significant expansion due to the large curvature of the main detonation wave trajectory. Smaller slit spacing was found to be particularly unfavorable for RSSI as they exhibit more divergent curves. Overall, this study illustrates that the reinitiation mechanisms of detonation show two different pathways in the transition to detonation from decoupled shock waves and reaction fronts upon diffraction propagating through double slit configurations, and enhances understanding of RSSI by providing insights into the complex interplay between slit geometry, detonation kernel formation, and curvature of detonation wave based on highly-resolved numerical simulations using detailed chemistry. The findings from this study have implications towards the design and optimization of systems involving detonation propagation and suppression.Novelty and significanceThis study focuses on the reinitiation mechanism of detonation propagating through double slits in a planar channel. Specifically, this numerical study aims to understand the critical behaviors that occur when the slit width and the cell width of the detonation are comparable, based on the previously reported experiment. Reinitiation by shock–shock interaction which had previously been limited in understanding was explained in detail and the effects of slit geometry were examined. It is worth noting that there is a lack of in-depth explanations in the literature regarding the double slit configuration with various dimensions of slit-plates. Moreover, this investigation deals with smaller scales of slit width compared to the well-known critical length scale of a planar channel which is about ten times of cell width. As a result, the findings of this study offer further insights for optimizing the design of detonation arrestors.