Detonation Wave Research Articles

Research on the Combustion Mode and Thrust Performance of Rotating Detonation Scrarmjet Engines

Decades of research in hypersonic science and engineering have shown that scramjet engines are the preferred choice for powering hypersonic vehicles. In these engines, oblique shock combustion and rotating detonation combustion are two common combustion modes. This article primarily focuses on the numerical simulation and theoretical analysis of these two combustion modes. The research indicates that as the combustible mixture injected into the combustion chamber increases, the combustion mode transitions from deflagration combustion to self-sustaining detonation combustion and then to forced detonation combustion to maintain stable combustion in the chamber. Under self-sustaining detonation combustion mode, as the amount of combustible mixture injected into the chamber increases, the number of detonation waves gradually increases from one to multiple and the angle between the detonation waves and the inflow changes from acute to right angles. In the forced detonation combustion mode, the minimum shock wave intensity required to initiate detonation combustion can be obtained by drawing a tangent from the Rayleigh line. The structure generating oblique shock waves in the combustion chamber needs to match the shock wave intensity. In the detonation combustion mode, both the exit total temperature and specific impulse of the combustion chamber increase with the increase in Mach number at the inlet, while the pressure ratio decreases. This article provides a reference for the design of the combustion chamber in supersonic combustion ramjet engines.

Experimental study on rotating detonation wave discontinuous propagation process of high-temperature ethylene-rich gas

The combination of air turbine rocket (ATR) and rotating detonation engine (RDE) is a promising form of combined power, and it is of great significance to study the propagation characteristics of rotating detonation waves (RDW) using rich combustion gas as fuel. Owing to the complex composition of the rich combustion gas, RDWs are prone to unstable propagation. In this study, the discontinuous propagation state of quenching and re-initiation of an ethylene-rich gas RDW was experimentally investigated. It was found that the back pressure of RDWs blocked the air injection process and influenced the mixing effect and filling height of the propellant, resulting in decoupling of the RDW. An increase in the gas temperature would shorten the formation time of the RDW and avoid its discontinuous propagation state. The re-initiation process was similar to the auto-initiation process which the combustible mixture generated an RDW through a deflagration-to-detonation process (DDT). The designed experiment verified this analysis. Increasing the air injection pressure and gas temperature can improve the propagation stability of the RDW and reduce the frequency of the quenching and re-initiation process.

Impact of Intermediate Species in Simulating Oblique Detonation with Pre-Vaporized N-Decane/air Mixtures Substituting for Kerosene/Air Mixtures

ABSTRACT A renewed two-step n-decane mechanism is presented to improve reliable and robust simulation results, substituting for kerosene. This mechanism demonstrates that effective control of ignition delay time and heat release, based on the Chapman – Jouguet condition, enables successful simulation of oblique detonation waves. Chain reactions influence the overall reaction heat and explosion temperature, especially in simplified mechanisms with few steps. Therefore, carbon monoxide (CO) generation is crucial for balancing the overall reaction heat and reducing species sensitivity to pressure, a factor previously not discussed in simplified models. The computational time for solving detailed chemical kinetics increases exponentially with species count, driving the pursuit for further reduction in kinetic mechanism size. The sensitive interaction between density and temperature during the fuel/air mixture explosion process affects initiation zone formation and cellular structure. Analyzing the distribution of CO can provide insights into structural details. The study considers applying the Rankine – Hugoniot curve to confirm detonation speeds, temperatures, and kinetic energy changes induced by chemical reactions.

A dynamic droplet breakup model for Eulerian-Lagrangian simulation of liquid-fueled detonation

This study proposes a dynamic model to reflect the physical image of the droplet breakup process in two-phase detonation flows. This breakup model is implemented in a two-phase detonation solver developed based on an open-source computational fluid dynamic platform, OpenFOAM, and compared with three prevalent models (TAB, PilchErdman, and ReitzKH-RT model) under different droplet diameters (30–70 μm) in one- and two-dimensional detonation problems. The simulating results show that the present breakup model well predicts experimentally determined detonation parameters such as detonation velocities and post-wave temperature. In addition, the present model has the advantage of being free of the KH breakup time parameter, which the ReitzKH-RT model needs to fit the experimental data. The one-dimensional detonation simulations indicate that different breakup models slightly impact the detonation wave velocity because the droplet breakup process does not significantly affect the total heat release as long as it is sufficiently fast to sustain the detonation. However, the two-dimensional detonation simulations show that the breakup model and the droplet initial diameter significantly affect the detonation cell size due to the different droplet distributions predicted by various models. The breakup length, which is the distance from the shock wave to the location at which sufficiently small child droplets appear, affects the chemical reaction zone thickness and then the detonation cell size. A longer breakup length will result in a larger detonation cell size.

Numerical simulations and theoretical analysis of the forward shock wave in a non-premixed air-breathing rotating detonation combustor

The forward shock wave induced by the detonation wave propagates in the inlet and restrains the air from being injected into the rotating detonation engine, and the stable continuous propagation of the detonation wave is affected. Numerical simulation and theoretical derivation of air flow velocity and detonation wave height were carried out in a rotating detonation combustor. The influence of the forward shock wave on air flow velocity and air flow velocity on detonation wave height was analyzed. A non-premixed air-breathing rotating detonation combustor was numerically simulated with the two-dimensional Navier–Stokes equations and a kerosene/air reaction model based on the RYrhoCentralFoam solver. Analytical equations were derived and validated to calculate the air flow velocity across the forward shock wave and the height of the detonation wave. The results show that the air flow velocity across the forward shock wave is inversely proportional to the detonation wave velocity, incoming flow temperature, and pressure ratio at the forward shock wave. In addition, the angle of the forward shock wave is inversely proportional to the velocity of the detonation wave and incoming flow and is proportional to the incoming flow temperature and the pressure ratio. The forward shock wave leads to a blocked zone of injection in the combustor, as the inflow velocity decreases or even reverses across the shock wave. As a result, the forward shock wave induced by the detonation wave restrains the recovery of the reactant fill zone, which has an influence on the height of the detonation wave.

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.

A theoretical method for oblique and curved detonation waves

In this paper, a theoretical solution method for the post-wave parameters of detonation is proposed and developed with a series of analyses and applications. Based on Newton's method, the objective function for shock-coupled chemical reactions is constructed along with its derivative. Two verification examples demonstrate that the method can calculate accurate post-wave parameters quickly and is suitable for single-step and detailed mechanistic chemical reactions. In addition, the method provides sensitivities between various aerodynamic parameters to offer a fresh perspective for detonation, polar analysis with sensitivity is built as a result. Moreover, the method can predict the transition pattern of the detonation, and the validity is supported by the comparison of different examples. Rather than being limited to oblique detonation, the post-wave parameters of the curved detonation can also be calculated correctly, which indicates the excellent applicability of the method. This method can also be applied to the thermodynamic efficiency of detonation combustion and its sensitivity, which demonstrates the unique advantages of this method. Furthermore, the method can be rewritten as a solution for wedge angle under the given wave angle by changing the independent variable. This solution is validated by the simulation results, which implies that the method can be used as a simple inverse design method in oblique detonation engines. In general, the proposed method is an effective theoretical solution, analytical tool, and inverse design method for detonation.

Verification and characteristics of continuous rotating detonation waves in a novel rounded-rectangle hollow combustor

A noncircular cross-sectioned combustor holds the potential to facilitate the flexible design of continuous rotating detonation (CRD) engines, meeting the demands of airframe/engine integration. In this study, we propose and validate a novel rounded-rectangle hollow combustor comprising arc and straight segments. We conduct experimental and numerical investigations into the detailed propagation and combustion characteristics of the CRD wave in this combustor. The results demonstrate that a single hydrogen–air CRD wave can be achieved and sustained over a wide equivalence ratio (ER) range. As the ER increases from 0.71 to 1.25, the CRD wave's propagation velocity escalates from 1837.1 to 2190.8 m/s, with a substantial decrease in the relative standard deviation from 9.76% to 0.85%. The curvature variation along the combustor circumference influences the local propagation velocity, combustion intensity, shock wave strength, and shock wave system. Specifically, the constraints imposed by the arc segment significantly enhance combustion intensity and amplify shock wave strength. This is evident through a higher heat release rate fraction (fHRR), increased pressure peaks, and elevated propagation velocity. At the straight segment, the shock wave system comprises the CRD wave, leading, and trailing diffracted shock waves. However, the constraint from the arc segment leads to the formation of an additional reflected shock wave, altering the shock wave system to include the CRD wave, the reflected shock wave, and the leading diffracted shock wave. Thus, this study advances our understanding of CRD characteristics in noncircular cross-sectioned combustors, providing insight to the design theory for CRD engine combustors.

Numerical modelling of an impact resistance analysis of EN C45 steel pipe buried beneath the ground surface loaded with a detonation wave generated by an explosion of a cubic TNT charge

Numerical modelling of an impact resistance analysis of EN C45 steel pipe buried beneath the ground surface loaded with a detonation wave generated by an explosion of a cubic TNT charge

A systematic study of carbon clustering dynamics for explosives

ABSTRACT The carbon clustering mechanism of insensitive explosive is investigated by molecular dynamics. We find that the free carbon gas aggregates to form flexible chain, and the chain changes to graphite-phase particle. A set of thermodynamic properties for carbon clusters are calculated, and five clustering mechanisms are investigated, including the nucleation, deposition, sublimation, diffusion and phase transition effects. We use chemical reaction model to describe the free carbon aggregation, use diffusion/impaction model to describe the deposition/growing process, use heterogeneous equilibrium condition to evaluate the sublimation rate, use Shaw's model to describe the Smoluchowski coagulation and use Arrhenius model to describe the phase transition rate. Based on the microscopic properties, the detonation wave of explosive is simulated by finite difference method. A set of detonation properties are calculated, and the meso-structure of slow reaction zone is obtained.

Study on detonation characteristics of pulverized coal and evolution law of detonation residue

This study explores the detonation characteristics and compositional changes of pulverized coal, focusing on its use in Rotary Detonation Wave (RDW) technologies. While pulverized coal has shown high fuel efficiency in RDW settings, transitioning from theory to practical detonation engineering presents substantial scientific and technical hurdles. A key issue is the reprocessing of detonation byproducts for in-situ coal mine gob filling, a topic that has received little attention. Utilizing advanced methods like X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), this paper investigates the micro-morphology, composition, and aromatic structures of gas–solid products pre and post-detonation at the Tashan Coal Mine's 2305 working face. Results indicate that coal dust from the underground mining face has enhanced detonation characteristics, with the addition of coal powder fuel extending the gas detonation limits. This benefits economic aspects by reducing reliance on gas fuel and lowering detonation fuel costs. The highest recorded detonation wave velocity was 2450 m/s, 14.8% greater than that of coal dust from external sources, suggesting more effective energy release and pressure gain. Furthermore, the study links detonation combustion intensity to coal's aromatic properties, noting a post-detonation aromaticity index (I) of 0.4941. This indicates an improvement in the aromatic structure under high-temperature conditions, vital for coal's reactivity and energy efficiency in RDW applications. This research not only deepens the understanding of coal dust combustion mechanisms but also advances clean coal utilization and deep coal fluidization mining, addressing significant RDW technological challenges.

The diffraction and re-initiation characteristics of gaseous detonations with an irregular cellular structure

Two-dimensional numerical simulations were performed in this study to look at the diffraction and subsequent evolution of an irregular structure detonation in a stoichiometric hydrogen-air mixture, propagating from a small-width pre-detonator (width d) into a larger-width testing channel (width D). By varying the ratio D/d from 1.1 to 5.5, three kinds of propagation modes and the corresponding dynamics of the irregular structure detonation waves are elucidated. The numerical results show that, for an irregular structure detonation wave, the D/d range from 1.0 to 1.1 corresponds to the supercritical mode, the critical mode for D/d ranging from 1.2 to 5.0, and a D/d larger than 5.0 results in the subcritical mode. Compared to the equivalent numerical study for regular structure detonations, the critical width ratios for the supercritical mode and the critical mode are found different for irregular structure detonation. Detonation waves with an irregular structure are more likely to change from the supercritical mode to the critical mode. In the critical mode, the re-initiation process of an irregular structure detonation could originate in two ways, i.e., the Mach reflection of the diffracting lead shock LS to form the main triple point TP1 or self-sustained triple points (the TP2∼TP4) from the diffracting cellular detonation front. On the other hand, the re-initiation process of a regular structure detonation could result solely from the Mach reflection of the LS to form the TP1. By defining the distance between the backward-facing step and the explosion bubble HS formed by the collision of the new triple points as the characteristic distance L (mm), it is shown that the irregular structure detonation requires a longer characteristic distance L than the regular structure detonation to generate the HS at the centerline. The findings of this study offer potential avenues for optimizing pre-detonator and combustion chamber configurations in detonation engines.

Limit Cycle Oscillating Detonation Wave Behavior Analysis Within a Rotating Detonation Engine

Limit cycle oscillation (LCO) detonation wave behaviors are presented and analyzed for test times exceeding 20 s in a water-cooled rotating detonation engine (RDE). LCO detonation waves exhibit cyclic acceleration and deceleration, resulting in oscillating wave spacing at unique process conditions. In previous RDE studies, similar behaviors have been studied as microsecond-scale instabilities leading to ascending or descending modal transitions. In the current work, however, LCO waves are considered a persistent wave mode, occupying unique portions of the operational envelope adjacent to those of their equally spaced counterparts. These occurrences of LCO waves are repeatable, enduring behaviors. A method to generate shifted contour surfaces specifically intended to extract and analyze wave spacing variation through time, termed limit cycle oscillation visualization (LCOV) surfaces, is presented. LCOV surfaces transform data into the reference frame of a primary traveling wave and are used to analyze quasi-steady, short-timescale, and transitional LCO modes. Results are leveraged to understand the relationship between fill height, wave strength, local wave acceleration, and subsequent LCO wave spacing for individual wave sets. Quasi-steady LCO waves display wave spacing oscillations between equal spacing values associated with ±1 wave across runs exceeding 18 s.

Micro-jetting and Transverse Waves in Oblique Detonations

We present a highly-resolved 2D numerical simulation of a wedge-induced Oblique Detonation Wave (ODW) using a 9-species 21-reaction chemical kinetic mechanism for a stoichiometric H2-air mixture. Adaptive Mesh Refinement (AMR) is leveraged to obtain a resolution close to the continuum limit at the finest level (Δxfinest=0.78μm=20λ, where λ is the mean-free path of the fuel–air mixture), which spans the ODW front and its transverse waves. The simulation is performed for a sufficiently large domain, enabling us to unveil the multi-zonal structure of the ODW. We capture, for the first time, the onset of microscopic hypersonic jets (micro-jets) far downstream of the wedge tip associated with cellular structures resembling those of a multi-headed Normal Detonation Wave (NDW). In contrast, the upstream “cell-like” structure (christened as “pseudo-cellular” hence) are found to be devoid of these micro-jets with a morphology similar to that of single-headed NDWs, such as spinning/zig-zag detonations in tubes/2D channels, respectively. A detailed investigation into the transverse-shock structure downstream reveals that a colliding pair of transverse waves lead to the micro-jetting phenomenon. The absence of one of the pair of transverse waves in the upstream region results in the observed pseudo-cellular structures. The origin of these transverse waves in an ODW, unclear in previous literature, is shown to arise from coalescing and strengthening of Compression Waves (CWs) that are produced from two distinct mechanisms. During the “early” phase of the ODW stabilization, CWs are formed as a result of local blast events. In the subsequent “middle” phase, these are formed as a result of the shear-layer instabilities coupling with the local shock structure, leading to the so-called left-running transverse waves (LRTWs) upstream and the right-running transverse waves (RRTWs) downstream. The identified mechanisms offer a plausible explanation on why ODWs exhibit a multi-zonal morphology.Novelty and Significance StatementThe present study is one of the very few studies in the Oblique Detonation Wave (ODW) literature that includes multi-step chemistry while solving for the compressible reacting Navier-Stokes equations on a large simulation domain revealing the multi-zonal structure of the ODW. Furthermore, the resolution employed for the study approaches the continuum limit, making it on-par with the current state-of-the-art for ODW simulation. For the first time, this study has demonstrated the existence of microscopic hypersonic jets (micro-jets) far downstream of the wedge tip in a wedge-induced ODW and a method to isolate them in numerical simulations, leading to insights on the broader micro-jetting phenomenon in detonations. The existence of a cell-like (which we term as “pseudo-cellular”) region bearing similarity with that of single-headed spinning detonations is also noted due to the absence of a transverse wave family upstream. The exact physical mechanisms leading to the formation of transverse waves in ODW are also investigated, which were previously ambiguous in the literature.

Instability of Detonation Wave at Downstream of Aluminum Crimped Ribbon

Instability of Detonation Wave at Downstream of Aluminum Crimped Ribbon

Influence and comparison of cylindrical engineered defects on detonation waveshape in a rubberized RDX explosive

AbstractInhomogeneities within explosives affect the sensitivity and detonation waveshape of energetic materials. The influence of voids on explosive initiation has been well documented; however, the effects that voids between 0.1 mm and 10 mm have on a propagating detonation wave remains largely unexplored. The effect of single cylindrical voids on detonation waveshape and re‐initiation was examined here using manufactured voids in a rubberized 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) explosive. Two streak imaging techniques were fielded to investigate void influence. For the first, back‐surface streak imaging, the location of the void on the samples was changed and the resulting change in detonation waveshape at the downstream breakout was captured using a streak camera in cut‐back experiments. The results from this experiment showed the effects of an initial jet form for short cut‐back distances and as shock propagation progressed, the jet formation was absorbed by the unaffected portions of the wave front. The second method, top‐surface streak imaging, was used to investigate the re‐initiation/downstream propagation of the detonation front and the detonation velocity of the rubberized explosive. These experiments were compared to similar experimental results from machined voids in PBX 9501, an 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (HMX)‐based explosive, to investigate the interaction of a detonation wave with a 0.5 mm void for different explosives. The experiments were also compared to simulations using a multi‐dimensional and multi‐material hydrodynamic code. These results showed the influence that small features can have on detonation waveshaping and how explosive properties play a key role in that interaction.

Detonation properties and nitrogen oxide production in ammonia–hydrogen–air mixtures

Ammonia is a promising compound for chemical storage of renewable energy produced from non-continuous sources. However, the low reactivity of ammonia requires to use ammonia–hydrogen blends as a fuel for combustion applications. The present study corresponds to a first numerical assessment of the potential of ammonia–hydrogen–air mixtures as reactive mixtures for detonation engine applications. Both ideal and curved detonation models were employed to calculate the detonation properties, entropy production, and NOx production for mixtures with varying amounts of ammonia and hydrogen under a wide range of initial thermodynamics conditions. Interestingly, our calculations show that the entropy production and the amount of nitrogen oxides produced at the Chapman–Jouguet state respectively decreases and increases with the proportion of hydrogen in the ammonia–hydrogen blend. These aspects could have a great impact on engine efficiency and air pollution and should be considered with care. Our results also demonstrate that only mixtures with relatively low amounts of ammonia, i.e., XNH3 lower than 0.25 of the fuel blend, can be employed for detonation engine applications.

Research on the crack formation mechanism of shaped charge blasting and the new dual-shaped charge blasting technology

Shaped charges are extensively utilized in various rock engineering fields for directional fracturing. Numerous scholars have conducted extensive research on this topic, yielding significant results and widespread application in engineering projects. Efforts have focused on improving the directional fracture effects and fully utilizing the energy generated by the explosion to enhance the directional blasting effects of shaped charges and minimize damage to the rock mass in areas not targeted by the shaped energy. This approach aims to preserve the integrity and stability of the rock mass in the areas unaffected by the directional fracture, thereby reducing damage to the surrounding rock. This study builds on the foundations of explosion mechanics. It incorporates a novel digital laser dynamic caustic line experiment system and pressure fields, and numerical analysis techniques. The research systematically analyzes the process of explosive action in shaped charges and proposes a new type of dual polymer charge. This novel charge is compared to traditional and common charges. The findings revealed that, compared to standard-shaped charges, the new dual-shaped charge achieves a more effective directional fracturing, The rock damage is less in the direction of non-gathering energy. Under the conditions of the same amount of explosive and the same decoupling coefficient, The crack propagation length of common charge is 1.34 times of the diameter of the gun hole, the crack propagation length of shaped charge is 10.17 times of the hole diameter, The crack propagation length of the new dual-charge is 19.67 times of the hole diameter. HIGHLIGHTS In this paper, a new type of dual-charge is proposed. The findings revealed that, compared to standard-shaped charges, the new dual-shaped charge achieves a more effective directional fracturing, The rock damage is less in the direction of non-gathering energy. Under the conditions of the same amount of explosive and the same decoupling coefficient, The crack propagation length of common charge is 1.34 times of the diameter of the gun hole, the crack propagation length of shaped charge is 10.17 times of the hole diameter, The crack propagation length of the new dual-charge is 19.67 times of the hole diameter. 1.Following the charge explosion, influenced by the shaped charge tube, the detonation wave and explosive gas alter, expanding outward in an approximate "elliptical" shape. The explosion stress field distribution is approximately "one"-shaped in the direction of energy concentration. The primary explosive crack expands along the direction of energy accumulation, while the secondary cracks predominantly distribute in the perpendicular direction. The seam width and the transmission coefficient (material) influence the condenser’s concentration effect. 2.Compared to ordinary charge blasting, shaped charge blasting exerts a pronounced guiding effect on the explosion stress field. The stress field primarily transfers along the direction of energy concentration, with the stress being markedly greater in this direction than in the direction of non-concentrated energy. In comparison, dual charge blasting undergoes two convergence effects, with longer durations and distances of convergent action. The stress field generated by dual-charge blasting is significantly greater than that of the shaped and common charges, offering enhanced effects. 3.Agglomeration length is a crucial factor in the agglomeration effect. Explosion energy directly transfers to the solid medium via the coalseam, minimizing explosion energy loss in the air medium and controlling the detonation wave shape and explosive gas flow in the energy accumulation direction, resembling "one." The dipolymer charge notably extends crack propagation length in the polymer direction and mitigates damage in the non-polymer direction.

CONTROL OF PARAMETERS AND STRUCTURE OF DETONATION WAVE IN A DUAL-FUEL METHANE-HYDROGEN MIXTURE

A generalized model of chemical kinetics of detonation combustion of stoichiometric dual-fuel methane-hydrogen mixture is proposed. It allows calculating the molar mass and internal energy of a mixture without calculating its detailed chemical composition. The model was verified within the framework of a numerical calculation of the cellular multifront structure of a detonation wave. The calculated size of the detonation cell, as well as the qualitative structure of detonation (irregularity of the cellular structure due to the formation of both primary and secondary transverse waves, and incomplete combustion of gas in the detonation wave) are in good agreement with experiment.

120 kHz mid-infrared TDLAS sensor for H2O concentration and temperature measurement in rotating detonation engine exhaust flows

Rotating detonation engines (RDEs) require advanced rapid combustion diagnostic techniques to better understand their complex detonation processes. A fast mid-infrared TDLAS sensor was proposed to simultaneously monitor H2O concentration and temperature at the outlet of an H2/air-fueled RDE annular combustor. An iterative parameter extraction method from transmitted laser intensity was proposed to extract the H2O concentration and temperature of the detonation waves. A measurement rate of 120 kHz enables high-speed and simultaneous quantification of detonation wave combustions. The results show that when RDE operates stably, the detonation frequency, average temperature, and average molar percentage of H2O concentration of the detonation waves are 4.631 kHz, 1572.8 K, and 0.335, respectively. The detonation frequency extracted from H2O concentration and temperature is highly consistent with that extracted from thermal radiation, and the relative frequency error is only 0.022 %. The time-resolved H2O concentration and temperature data measured by the sensor accurately capture the thermal dynamics of the transient detonation waves.