Gaseous Detonation Research Articles

Lagrangian characterization of induction and reaction timescales in a cellular gaseous detonation

A Lagrangian approach was proposed to analyze induction and reaction times in the cellular gaseous detonation. Two-dimensional simulations in an argon-diluted and non-diluted hydrogen-based mixtures were performed with detailed chemistry, along particle trajectories. The distribution of the induction and reaction times inside the cell was significantly different between the Eulerian and the Lagrangian perspectives, the latter showing non-monotonic behavior. Preferential thermodynamic paths laid along the Rankine–Hugoniot curve and behind transverse waves (TW). All particles were ignited within half and one cell cycle for the diluted and non-diluted mixture, respectively. The ignition mechanisms were not only one-dimensional, but also multi-dimensional, with ignition behind the TW being the most important, and collision of TW and triple points being secondary. A new topology inside the cell could be drawn, from the intersection of the ignition front with TW. TW appeared as phase waves in the (x,t) diagram. Comparison of H2O mass fraction between local and equilibrium values indicated that a local chemical disequilibrium remained (superequilibrium), due to TW. Equating the mean sonic plane with thermochemical equilibrium in the non-diluted case is not completely accurate. Furthermore, the characteristic time scales for chemical and hydrodynamic phenomena were compared. The diffusive phenomenon did not make any contribution in the mixtures tested. In comparison with the Zel'dovich–von Neumann–Döring model, a shorter average induction time was found in the non-diluted mixture, which is not in line with the results from previous Favre approaches. The average reaction time was also shorter in both mixtures.

Metal Powder Production by Atomization of Free-Falling Melt Streams Using Pulsed Gaseous Shock and Detonation Waves

A new method of producing metal powders for additive manufacturing by the atomization of free-falling melt streams using pulsed cross-flow gaseous shock or detonation waves is proposed. The method allows the control of shock/detonation wave intensity (from Mach number 4 to about 7), as well as the composition and temperature of the detonation products by choosing proper fuels and oxidizers. The method is implemented in laboratory and industrial setups and preliminarily tested for melts of three materials, namely zinc, aluminum alloy AlMg5, and stainless steel AISI 304, possessing significantly different properties in terms of density, surface tension, and viscosity. Pulsed shock and detonation waves used for the atomization of free-falling melt streams are generated by the pulsed detonation gun (PDG) operating on the stoichiometric mixture of liquid hydrocarbon fuel and gaseous oxygen. The analysis of solidified particles and particle size distribution in the powder is studied by sifting on sieves, optical microscopy, laser diffraction wet dispersion method (WDM), and atomic force microscopy (AFM). The operation process is visualized by a video camera. The minimal size of the powders obtained by the method is shown to be as low as 0.1 to 1 μm, while the maximum size of particles exceeds 400–800 μm. The latter is explained by the deficit of energy in the shock-induced cross-flow for the complete atomization of the melt stream, in particular dense and thick (8 mm) streams of the stainless-steel melt. The mass share of particles with a fraction of 0–10 μm can be at least 20%. The shape of the particles of the finest fractions (0–30 and 30–70 μm) is close to spherical (zinc, aluminum) or perfectly spherical (stainless steel). The shape of particles of coarser fractions (70–140 μm and larger) is more irregular. Zinc and aluminum powders contain agglomerates in the form of particles with fine satellites. The content of agglomerates in stainless-steel powders is very low. In general, the preliminary experiments show that the proposed method for the production of finely dispersed metal powders demonstrates potential in terms of powder characteristics.

Numerical simulation and growth mechanism of TiO2 prepared by gaseous detonation

Numerical simulation and growth mechanism of TiO2 prepared by gaseous detonation

Analysis and comparative study on the detonation performance of different heavy metal azides through theoretical calculations

Abstract In this paper, the detonation performance of different types of heavy metal azides is analyzed and compared using the detonation thermodynamic calculation method. Using the Virial-Peng-Long (VPL) equation of state (EOS) which based on the theoretical values of the 2-5th order virial coefficients of the Exponential-6 (Exp-6) potential to describe the high temperature and high pressure thermodynamic state of the gaseous detonation product N2, and the trinomial EOS Wu-Chen-Peng (WCP) which based on the universal Debye temperature specific volume function was used to describe the thermodynamic relations of the corresponding condensed metal product. Based on the VPL EOS and WCP EOS, the detonation velocity, detonation C-J (Chapmann-Jouguet) pressure and isentropic expansion P-V relations of detonation products for four kinds of metal azides: lead azide, silver azide, cuprous azide, and cupric azide, were obtained at different densities through detonation thermodynamic calculations. The detonation performance of different metal azides was compared and evaluated by combining detonation heat and gaseous product content. The reaults show that cupric azide has relatively better detonation velocity and work capacity, especially suitable for initiation by driving flyer. Lead azide and silver azide have higher detonation C-J pressure which are suitable to direct initiation.

Fragment Velocity Distribution of Controlled Fragmentation Warhead Under Eccentric Point Initiation

Abstract Three-Point eccentric initiation is one of the most common technologies of directional warhead for enhancing fragment lethality against targets. The fragment velocity distribution is a significant concern in warhead design. However, there is as yet no reasonable theory for predicting the fragment velocity distribution of a specific enhanced shell under three-point eccentric initiation; existing approaches are either limited to single or double-point eccentric initiation scenarios or ignore the effects of detonation gas leakage on fragment acceleration. In this paper, through theoretical analysis and numerical simulations, a new model was established to study the fragment velocity distribution of warhead shells under the combined effects of gas leakage and three-point eccentric initiation. Firstly, an equation for detonation velocity gain of explosives under three-point eccentric initiation was developed by numerical simulations, where the shells were set to be free from disintegration and gas leakage. Secondly, the fracture strain or radius of controlled fragmentation warhead was solved by the disintegration model established in our previous work. Then the equations for detonation velocity gain and the fracture strain were associated with a proposed gas-leakage equation in which the gas expansion was assumed to be locally isentropic. Finally, theoretical analysis was conducted by solving the associated equations. Grooved cylindrical shell was explosively expanded to disintegrate to verify the proposed model. Theoretical predictions of the fragment velocity distribution showed good agreement with experimental results, indicating that the model was suitable for predicting the fragment velocity distribution of an explosively-driven metal grooved cylinders under three-point eccentric initiation. Besides, this study provides an insight into the differences of fragment velocity enhancement among single point initiation, double point initiation and three point initiation.

Investigation on the suitability of conventional film hole under pulsed detonation incoming flow conditions

As a novel and efficient engine, the pulse detonation engine will increasingly demand advanced cooling technology. Film cooling, widely utilized in conventional aero engines, is also anticipated to be employed in pulse detonation engines. However, further investigation is required to assess the suitability of conventional film holes for pulse detonation engines. This study determines the cooling characteristics of a plate with a single film hole in a pulse detonation engine operating at a frequency of 30Hz through numerical calculations. The types of film holes considered include cylindrical, fan-shaped, laid-back, laid-back fan-shaped, and converging-slot holes, all of which have a diameter of 1 mm and an inclination angle of 30°. The single pulse detonation period is divided into stages: initiation and detonation wave propagation, gas exhaust, and refilling. During the initiation and detonation wave propagation stage, the film hole exhibits a significant backflow phenomenon, with the magnitude of gas backflow positively correlated with the outlet area of the film hole. Notably, the converging-slot hole experiences the least amount of gas backflow, with an exit area 33 % smaller than that of cylindrical holes and a corresponding 18 % reduction in backflow enthalpy. Throughout the initiation and detonation wave propagation stage, the backflow gas carries an enthalpy ranging from 0.43 J to 0.63 J into each individual film hole. In the gas exhaust stage, the blowing ratio increases over time as the mainstream pressure decreases, leading to a rapid decline in the film cooling effectiveness of the cylindrical and laid-back holes. The converging-slot holes have the largest film covering area, thus exhibiting the highest film cooling effectiveness, which is 53 % higher than that of the cylindrical hole. In the refilling stage, the mainstream temperature reaches the same level as the secondary flow temperature, rendering the consideration of the cooling characteristics of the film hole unnecessary. Under the conditions of this study, the converging-slot hole is found to be most suitable for cooling the pulse detonation engine.

Numerical investigation of pre-flawed FGM tubes repaired with different composite jackets under sequential gaseous detonation loading

Investigation on the structural response of pre-flawed functionally graded material (FGM) cylindrical tubes submitted to sequential detonation loading is the main contribution of this study. Analyses are made for repaired and unrepaired tubes using three different composite patch (CP) geometric shapes: full cylindrical, semi-cylindrical, and circular. The effect of non-homogeneous FGM materials (ceramic-to-aluminum, aluminum-to-ceramic, and steel-to-ceramic) and CPs on the stress field in the tube is studied using three-dimensional finite element (FE) models. The FE analyses are conducted for two distinct categories of detonation loading: low- and high-pressure detonations. This approach helps to enhance the understanding of how material gradation influences stress distribution and damage assessment in tubes subjected to these specific loading conditions. The FE analyses revealed that both forward and reflective waves coming from detonation load significantly contribute to crack propagation by elevating stresses near crack tips. The application of CPs, made of boron/epoxy material, effectively mitigated stress concentrations across all FGMs, with full cylindrical CPs providing the best results. Delamination was observed in CPs with two composite layers under high-pressure loading, particularly in aluminum-to-ceramic FGM.

Numerical Study of Powder Particle Flight Behavior during Gas Detonation Spraying Process

Numerical Study of Powder Particle Flight Behavior during Gas Detonation Spraying Process

Preparation of Fe@C nanoparticles via hydrogen-oxygen explosion

In order to study the growth process of Fe@C nanoparticles prepared by gas explosion method, experiments and numerical simulations of hydrogen-oxygen explosion were carried out. The influence of hydrogen concentration on the propagation of explosion wave, the variation of detonation parameters and the growth of Fe@C nanoparticles were analyzed. The results show that the hydrogen-oxygen explosion in a closed tube includes the propagation stage and the attenuation stage of the explosion wave, and they are greatly affected by the hydrogen concentration. When the hydrogen concentration increases from 66.7 vol% to 80 vol%, the detonation wave in the propagation stage will be replaced by a deflagration wave. The peak values of velocity, pressure, and temperature in the explosion process generally show a decreasing trend, and the attenuation speed in the attenuation stage gradually slows down after the explosion reaction. The morphology of Fe@C nanoparticles prepared by the hydrogen-oxygen explosion is closely related to the propagation and attenuation of explosion waves, and it can be controlled by adjusting the hydrogen concentration. When the hydrogen concentration in H2–O2 mixture gas is 66.7 vol%, the explosion reaction forms a severe temperature and pressure environment, and the deflagration wave in attenuation stage decays rapidly, as a result, the Fe@C nanoparticles were obtained. As the hydrogen concentration reaches 80 vol%, the velocity and attenuation speed of the deflagration wave in attenuation stage slows down, which prolongs the high-temperature time within the unit interval, and creates a relatively mild temperature and pressure environment for the growth of CNTs. Then the Fe@C nanoparticles with a large number of CNTs were prepared. This study provides a reference for the study of controlled preparation of Fe@C nanoparticles by gaseous detonation method.

Experimental and numerical study on critical oxygen concentration for shale gas detonation induced by oxygen-enriched combustion

To improve the shortcomings of Shchelkin spiral in enhancing overpressure utilizing oxygen-enriched combustion-induced detonation (OEC-DET) has seldom been touched upon. Systematic experiments and simulations have been conducted to reveal the kinetic mechanism and critical conditions of OEC-DET. Longmaxi (LMX) and Cambrian (HWX) shale gases with 4 % and 20 % nitrogen content were selected as fuels. Explosion overpressure histories of 0.8, 1.0 and 1.2 equivalence ratio fuels at different oxygen concentrations were tested in a 90 L multiphase fuel detonation tube. Temperature sensitivity coefficients of combustion reactions were then supplemented by kinetic simulations. OEC-DET was demonstrated to be a manifestation of pressure wave development promoted by liquid–gas phase transition of H2O produced by OEC. One underlying mechanism is that the increase in oxygen concentration enhances the temperature sensitivity and H2O production rate, thus favoring the occurrence of OEC-DET. The critical oxygen concentration (COC) of OEC-DET in shale gas has been determined to be around 25 %–30 % herein. The lower the nitrogen content and equivalence ratio, the lower the COC. Both the explosion overpressure and pressure rise rate exhibit segmented linear and exponential growth with the increase of COC, and particularly the growth trend becomes accelerated after OEC-DET. Two COC prediction equations have thus been derived with an accuracy exceeding 90 % and these shed light on the thermal engineering such as in-situ methane deflagration fracturing.

The universal gaseous detonation dynamics

The present communication proposes a new scaling approach to unify the dynamics of gaseous detonations subject to wall losses in both the narrow channels and small tubes, by compiling the published experimental data of detonations in 23 different mixtures with a very large range of cellular instabilities. A kinetic induction length Δi,loss can be determined from the detonation velocity deficit and detailed chemistry. In order to take into account the sensitivity of the latter length to post-shock temperature fluctuations (through the reduced activation energy θ), which is a partial and indirect marker of the cellular structure, and to bring out energetics (through the Chapman–Jouguet detonation Mach number MCJ), an effective kinetic length of Δi,loss(MCJ4/θ3) was built and has been shown to collapse the different detonation dynamics of various gaseous mixtures, subjected to wall losses, into a single universal curve for detonation velocity deficits.Novelty and Significance: Scaling analysis of large sets of published data of gaseous detonation experiments in narrow channels and small tubes has been made for 23 different mixtures with varied cellular instabilities and activation energies. The universal dynamics of gaseous detonations subject to wall losses in different mixtures has been achieved, for the first time, by adopting an effective kinetic length by taking into account the effect of both the activation energy and the energetics.

Secondary-explosion modification study on gaseous detonation synthesis of Fe@C nanoparticles

To enhance the graphitization degree of Fe@C nanoparticles synthesized via gaseous detonation, this study employed ferrocene as the precursor and hydrogen–oxygen mixed gas as the explosion source to investigate the effects of secondary-explosion on the phase composition, morphology, and magnetic properties of carbon-encapsulated iron nanoparticles. The results show that after the secondary-explosion, the phase composition of Fe@C nanoparticles changes significantly, with partial oxidation of iron carbide/iron to FeO. The morphology remains largely unchanged, with particle sizes between 20–40 nm, but the crystallinity of both the metal core and carbon layer improves markedly, and lattice fringes become more distinct. The saturation magnetization(Ms) and residual magnetization(Mr) of Fe@C nanoparticles decrease by 56.7 % and 69 %, respectively, while the coercivity force shows little change.

Numerical investigation on the interaction characteristics between the gaseous detonation wave and the water droplet

In this paper, the interaction characteristics between the gaseous detonation and the water droplet are numerically investigated, utilizing a modified compressible two-phase flow model coupling with detailed hydrogen-oxygen chemistry. Firstly, an analysis is conducted on the propagation behaviors of the cellular detonation obstructed by the droplet. It is found that the cellular detonation undergoes reflection, diffraction, local extinction, and re-ignition upon the obstruction, and these behaviors vary with the droplet relative positioning with multi-dimensional structures of the cellular detonation, particularly in terms of the extinction degree caused by the diffraction and the relative positioning of the re-ignition region. Further, the droplet deformation characteristics are detailly analyzed. It has been revealed that the deformation behavior of the shocked droplet under planar detonation is consistent with that under high-speed airflow. However, for the droplet shocked by the cellular detonation, several windward surface pits are induced due to impaction from transverse shocks and direct hitting of the triple-point. The emergence of these pits notably precedes the onset of surface instabilities caused by high-speed airflow erosion. Further investigation has revealed that post-detonation flow, through the entrainment effect of the central pit, progressively penetrates and segregates the droplet into upper and lower segments, and this penetrating effect heavily depends on the droplet relative positioning. Moreover, the side pit, whose presence is significantly determined by whether there is direct impaction of the triple-point on the droplet windward side, is crucial for the deformation around the droplet equator and the subsequent shedding of smaller droplets.

Experimental investigation into effects of combustor structure on characteristics of rotating detonation of cracked kerosene gas

This study examines the influence of the structure of the combustor on the propagation of rotating detonation waves (RDWs) of cracked kerosene gas (CKG) by using oxygen-rich air, with mass fractions of oxygen of 36% and 48%, as the oxidant while maintaining stable values of the state parameters of CKG. The experimental results showed that the structure of the combustor played a key role in the initiation and stable propagation of CKG, and suitable values of its width and the width of its outlet promoted the stable self-sustained propagation of the RDWs. Combustors of 8 and 14 mm width failed to initiate with 36% oxygen-rich air and without blockage ratio. In the combustors of 20 and 26 mm width, as the blockage ratio increased, the modes of propagation of the RDW included a single stable RDW, intermittent single RDW, and four, six, and eight counter-rotating RDWs. With the further increase in the blockage ratio, the reflected shock wave at the end of the combustor was enhanced, resulting in an increase in the number of RDW wave heads. As a result, the height of the fresh fuel layer was decreased, the mixing time was decreased and led to a decrease in the RDW velocity. The increase in the width of the combustor was conducive to the radial and axial diffusion of fuel and oxidizer in the combustor, which led to an obvious increase in the propagation velocity of RDW. In the 26 mm width combustor, the maximum RDW velocity is 1769 m/s.

Analysis of coupling supersonic turbine stage with rotating detonation combustor under different turbine parameters

The rotating detonation gas turbine boasts several advantageous characteristics, including self-pressurization, minimal entropy increase, high thermal efficiency, and a high thrust-to-weight ratio. These features make it a promising candidate for the next generation of aerospace power devices. This study investigates the flow characteristics and performance attributes of the supersonic turbine stage coupled with a rotating detonation chamber based on different rotational speeds, blade ratio of rotor and stator, and hub radius, and uses DMD (Dynamic Mode Decomposition) to analyze the main modes of the supersonic turbine. The research identifies distinct wave modes in both the stator and rotor blades of the supersonic turbine. In the stator blades, the modes include waveless contact modes, opposite side λ-wave oblique shock wave modes, and derived modes from opposite side λ-wave oblique shock waves. In the rotor blades, the modes encompass non-separation modes (waveless modes, asymmetric dual λ-wave modes, oblique cut wave modes, and single-side λ-wave modes on the pressure surface), leading-edge stator excitation single separation bubble modes, saddle-type separation modes, and dual separation bubble modes. The efficiency and power of the supersonic turbine stage increase with the rotational speed. The turbine efficiency is highest when the blade ratio is 10:7. Under multi-wave mode conditions, detonation waves demonstrate adaptive self-regulation abilities, ultimately achieving equilibrium in speed, detonation wave height, and spacing. The dominant modes in the stator blades and combustion chamber are governed by detonation waves and slip lines, while in rotor blades, the primary mode is the flow-directional vortex mode governed by detonation waves and slip lines at a frequency lower than their propagation frequency. This research holds certain reference significance for understanding the internal flow characteristics of rotating detonation gas turbines, as well as discussing the patterns of efficiency, power, and load characteristics, thereby offering valuable insights for the practical application of rotating detonation gas turbines.

Improved method for prediction of detonation velocity for C−H−N−O based pure, mixed and aluminized explosives

AbstractAn improved method is presented for the prediction of detonation velocity of C−H−NO based pure, mixed, and aluminized explosives. The new empirical relation is based on calculated values of the heat of detonation and the number of moles of gaseous detonation products. A constant of the empirical relation has been found using regression analysis of 74 data points of pure and mixed explosives as well as 22 data points of aluminized explosives. The value of the constant is found to be 1.00 with R2 value of 0.96. Proposed empirical relation has been validated by comparing predicted values of detonation velocities with measured values for TNT, HMX/RDX‐TNT‐Al and HMX‐TNT based explosives. Experimental measurement of detonation velocity has been carried out using pin‐ionization method on cylindrical explosive charges of diameter 50 mm and height 150 mm. The predicted values of detonation velocities are in good agreement with measured values with a root mean square error of 1.28 %. The validation of the new relation has also been carried by comparing calculated values of detonation velocities using present and literature methods with reported experimental values.

Investigation of rotating detonation gas turbine cycle with different combustor passage areas

Application of rotating detonation combustion can significantly enhance gas turbine performance, but the limited flow capacity caused by normally aspirated characteristic of rotating detonation combustor (RDC) severely constrains the operating range of gas turbine. In this paper, the detailed investigation was carried out for the influence of RDC passage area on cycle characteristic parameters for a 25MW single shaft gas turbine. The results demonstrated that changes of RDC passage area had a significant impact on operating range of rotating detonation gas turbine. As RDC passage area increased, operating range of gas turbine moved to the higher power, with the slight increases for cycle efficiency, cycle efficiency increment and net power increment compared to traditional gas turbine at identical net power. For the process when RDC passage area decreased from 0.0272 m2 to 0.0240 m2, the lower working limit of rotating detonation gas turbine decreased to 53.3 % of rated power, in which equivalence ratio of RDC replaced turbine efficiency as the greatest influence factor on cycle efficiency increment.

Characterization and Mechanism Elucidation of Nano-TiO2 Composites Prepared by Gaseous Detonation Method.

In this study, a series of nano-TiO2 composite materials, including nano-TiO2, nano-SnO2/TiO2, nano-SiO2/TiO2, and nano-Fe2O3/TiO2, were successfully synthesized via the gaseous detonation method. Comprehensive characterization of the synthesized samples was carried out through X-ray diffraction (XRD), transmission electron microscopy/high-resolution TEM (TEM/HRTEM), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), Brunauer-Emmett-Teller (BET) method, and Fourier transform infrared (FTIR) analysis, which unveiled the significant influence of precursor types on the microstructure of the composite materials. Specifically, the incorporation of Sn4+ promoted the transformation of TiO2 to the rutile phase, reducing particle sizes from 25 to 19 nm and increasing the specific surface area from 44 to 86 m2/g. In contrast, the introduction of SiO2 impeded the rutile phase formation, leading to a marked reduction in particle size to 14 nm and an enhancement of the specific surface area to 104 m2/g. Furthermore, the presence of Fe3+ promoted the formation of the rutile phase and enabled particle growth to 44 nm. These findings not only deepen the understanding of structural control in the synthesis of nano-TiO2 composite materials via the gaseous detonation method but also highlight the critical role of precursor selection in determining the properties of the resulting materials.

Numerical studies of the breakup of the water jet by a shock wave in the barrel of the fire extinguishing installation

This scientific paper delves into the numerical studies of the process of filling the barrel with water and the subsequent breakup of the water jet and water atomization in the barrel of the fire extinguishing installation. The numerical model of the process of water injection into the barrel with the subsequent breakup of water by a shock wave was substantiated. To simulate these processes, the ANSYS software was used. VOF (volume of fluid) method-based model was applied where it is assumed that there is no penetration of one medium into another. The solution is based on the surface tracking method applied to a fixed Eulerian grid. According to the results of the numerical study, it was established that the water injection time significantly exceeds the duration of the gas detonation cycle in the fire extinguishing installation. In particular, we found out that it takes 8 ms just to spread the water jet from one side of the barrel to the other. It was observed that a high quality of water atomization under the action of a high-speed gas flow including the water located along the barrel wall. We stated that it is unreasonable to use the pulse injection of water into the barrel in the designed fire extinguishing installation due to a high fregiency of the shock wave generation exceeding 23 Hz.

Development of detonation gas spraying technology of coatings in the E.O. Paton electric Welding Institute of the NASU (Overview)

Development of detonation gas spraying technology of coatings in the E.O. Paton electric Welding Institute of the NASU (Overview)