Detonation Transition Process Research Articles

Spherically expanding flame simulations using Cantera coupled to an unsteady Lagrangian formulation

A Lagrangian-based one-dimensional approach has been applied, using Cantera libraries, to study the dynamics of spherically expanding flames. Detailed reaction models have been employed to examine spherical flame propagation in hydrogen-air mixtures. In the first part, our approach was validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that significant discrepancies were observed for the Markstein number, especially for rich mixtures. This suggests that even application of detailed reaction models can lead to inaccurate prediction of the stability of rich flames, which can be detrimental to the prediction of flame acceleration and the deflagration to detonation transition process. In the second part, a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths, it was found that at high stretch rates, the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rates. This induces faster rates of chemical heat release and active radical production which results in higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths, for which slower flame propagation was observed at high stretch rates compared to low stretch rates.

The effects of flame generated turbulence for turbulent-induced deflagration to detonation transition

The turbulent deflagration to detonation transition (DDT) process occurs when a subsonic flame interacts with intense turbulence resulting in spontaneous acceleration and the onset of DDT. The mechanisms that govern the spontaneous ignition are deduced intricately in numerical simulations. This work experimentally explores the conditions that are known precursors to detonation initiation. More specifically, the experiment presented investigates the role of flame-generated compression as a cycle that continuously amplifies until a hotspot forms on the flame front and ignites. The study quantifies the compression comparatively against other flame regimes through ultra-high speed pressure measurements while qualitatively detailing flame generated compression through density gradients via schlieren imaging. Additionally, flow field measurements are quantified throughout the flow using simultaneous particle image velocimetry (PIV) and OH* chemiluminescence. The turbulence fluctuations and flame speeds are extracted from these measurements to identify the reactant conditions where flame-generated compression begins. Collectively, these simultaneous high-speed measurements provide detailed insight into the flame and flow field characteristics where the runaway process occurs. This work ultimately documents direct flow field measurements to extract the contribution of flame-generated turbulence on the turbulent deflagration to detonation transition process.

Investigation of Multicomponent Diffusion in Numerical Simulation on H2-O2 Detonation Transition Process

A numerical calculation method for detonation transition process using an experimental-scale grid was proposed in this study. This method consists of multicomponent diffusion model. Detonation transition experiments were conducted to investigate the usefulness of the proposed method. A detonation was generated in rectangular tube with a square cross section of 30 mm per side. The tube was filled with an oxyhydrogen mixture with an initial pressure of 100 kPa, and an equivalent ratio of 1.0. The time history of the flame front position was obtained by observation with a high-speed camera. The time history of flame front position by the proposed numerical method were compared with one by the experimental results. As a result, the results obtained by the proposed numerical model are in good agreement with the experimental results. It was also found that the effect of thermal diffusion can be neglected in the simulation of the detonation transition process.

Effect of operating parameters on application based performance analysis of PDC: A recent review

Pulse detonation engines (PDEs) are advanced propulsion device for next generation of propulsion systems. The PDE combustion processes are filling of fuel-oxidizer, combustion reaction, blow down and purging. In conventional engine deflagration combustion takes places, which propagation speed is less (Ma < 1) rather than detonation combustion process. But detonation combustion process in pulse detonation engine takes place and its flame propagation speed is much higher than sonic (Ma = 1) velocity. So researchers are focusing on PDE combustion process and different propulsion performances enhancement process. Deflagration to detonation transition process takes placed inside the combustor due to effect of different operation conditions and combustor geometry. Further NOx emission mitigation techniques from Pulse detonation combustor (PDC) are big drawback to reduce the pollution. In these regards review studies on recent advances techniques on flame acceleration, NOx formation and propulsion performance have been indicated to increase the performance of the system. Further state of arts of application indicates that pulse detonation engine can be used for green manufacturing process, surface coating and pharmaceutical product manufacturing.

Numerical Simulations of DDT Limits in Hydrogen-Air Mixtures in Obstacle Laden Channel

The main aim of this study was to perform numerical simulations of deflagration to detonation transition process (DDT) in hydrogen–air mixtures and assess the capabilities of freeware open-source ddtFoam code to simulate and capture DDT limits. The numerical geometry was based on the real 0.08 × 0.11 × 4 m (H × W × L), rectangular cross-section detonation channel previously used to experimentally investigate DDT limits in obstacle-filled channel. The constant blockage ratio (BR) equal to 0.5 was kept for three obstacle spacing configurations: S = H, 2H, 3H. The results showed that hydrogen concentration limits for successful DDT from simulations are close to the experimental values, however, the simulated DDT limits range is wider than the experimental one and depends on the obstacles spacing. The numerical results were analyzed by means of propagation velocities, overpressures, and run-up distances. The best match between numerical and experimental DDT limits was observed for obstacles spacing L = 3H and the lowest match for spacing L = H. The comparison between experimental and numerical results points at the possible application of ddtFoam in geometry with a relatively low level of congestion. This work results proved that simulations in such geometry provide numerical flame acceleration velocity profiles, run-up distance, and recorded overpressures very close to experimentally measured.

The effects of Zn2+ and ClO4− in the excellent primary explosive Zn(CHZ)3(ClO4)2

AbstractMetal carbohydrazide perchlorates (M(CHZ)3(ClO4)2, simplified as MCP, M = alkali earth metals, Mn, Fe, Co, Ni, Cu, Zn, and Cd) are a series of stable and high‐energetic compounds, in which ZnCP as an environment‐friendly and high energetic primary explosive has been applied broadly in recent 10 years. Based on the traditional viewpoints, the cleavage of Zn‐N coordinative bond initializes the decomposition, where the perchlorate is only an oxidizing agent in ZnCP. However, by applying CPMD method, we prove the decomposition is not only from the cleavage of coordinative bond, but also with the synergetic homolysis of the Cl‐O bond of perchlorate. We find the relationship between the explosive performance and the centre metal in ZnCP. The electronic structure suggests Zn2+ is a stabilizer in the complex under the ambient condition. But in the decomposition, Zn2+ is a catalyst and an anion‐carrier in the explosion. For ZnCP, the initial process of the decomposition proceeds as the synergetic oxygen transferring mechanism, but it is a stepwise ring‐opening mechanism in the deflagration to detonation transition process. The total explosion pathways of ZnCP are descripted in our simulation.

Experimental research into the influence of two­spark ignition on the deflagration to detonation transition process in a detonation tube

The paper reports a study into the initiation of detonation in pulse detonation engines. The chosen direction to resolve this issue is the use of detonation tubes with multifocal ignition. We applied two spark discharges as a source of ignition, which ignited synchronously. The spark discharges were ignited at a distance, which provided for the intensive gas-dynamic interaction between the discharges. The interaction implied a collision between shock waves generated by the spark discharges. As a result, the growth in temperature of gas was ensured in the region between spark intervals, due to a collision between the oncoming shock waves.The influence of dual spark ignition on the time and length of the section where deflagration transfers into detonation along a detonation tube was studied by comparing the transition parameters for cases of single-spark and dual spark ignition all other conditions for research being equal. The study involved a detonation tube with a length of 2.3 m and an inner diameter of 22 mm. Spark plugs were located at the closed end of the tube. We applied a stoichiometric mixture of propane with oxygen, diluted with nitrogen by 50 % at the initial pressure in the mixture equal to 50 kPa. To register the time of propagation of the flame front and to measure the process rate, the tube was equipped with 22 ionization sensors. Distance between the sources of ignition was 6 mm. Length of the discharge interval at each source of ignition was 2.5 mm. Sources of ignition in the form of spark plugs were connected to high-voltage units with a total discharge energy of 3.3 J.The results of our study helped establish a reduction in the distance of deflagration to detonation transition by 1.6…2 times, and in the time of transition ‒ from 3.9 ms to 1.2 ms for the case of the transition from single-spark to dual spark ignition.The results obtained could be used when designing ignition systems for pulse detonation engines.

1D study of the detonation phenomenon and its influence on the interior ballistics of the combustion light gas gun

Abstract One-dimensional simulations with a detailed hydrogen-oxygen reaction mechanism have been performed to investigate detonation phenomenon in a combustion light gas gun (CLGG). Convection fluxes of the Navier-Stokes equations are solved using the WAF (weighted average flux) scheme HLLC Riemann solver. A high resolution fifth-order WENO scheme for the variable extrapolation at the volume interface and a fourth-order Runge-Kutta scheme for the time advancement are used. Validation tests of the stoichiometric hydrogen-oxygen deflagration to detonation transition process shows good agreement between the computed results and the analytical and documented solutions, demonstrating the reliability on the detonation simulation of the current scheme. Simulation results of the interior ballistic process of the CLGG show that the flame propagation experiences three distinct stages. The blast detonation wave causes a high-pressure shock and hazardous oscillations in the chamber and makes the projectile accelerate with fluctuations, but has only a small improvement to the muzzle velocity.

Numerical Calculation on Detonation Transition Process in a Channel with Obstacles

Numerical Calculation on Detonation Transition Process in a Channel with Obstacles

Numerical study of hydrogen–oxygen flame acceleration and deflagration to detonation transition in combustion light gas gun

A large eddy model with detailed chemical reaction mechanism is developed to investigate the interior ballistic process of the combustion light gas gun (CLGG). Flame acceleration and deflagration to detonation transition process with high initial pressure and low initial temperature hydrogen–oxygen mixture in CLGG is numerically studied. Simulation results indicate that the hydrogen–oxygen flame propagation experiences an exponential acceleration stage, a nearly uniform propagation stage and a fast reacceleration stage. Detonation can be triggered through two different mechanisms, which are the amplification between the overlapped shock wave at flame surface, and the elevated flame velocity and shock strength caused by local explosions. Reflected shock waves play an important role in the suppression of the flame propagation when the flame front is close to the chamber throat, leading to a deceleration of the deflagration flame.

凸形の火炎と平面衝撃波の干渉によるデトネーション遷移過程

凸形の火炎と平面衝撃波の干渉によるデトネーション遷移過程

Numerical study of nonequilibrium plasma assisted detonation initiation in detonation tube

Nonequilibrium plasma has shown great merits in ignition and combustion nowadays, which should be especially useful for hypersonic propulsion. A coaxial electrodes configuration was established to investigate the effect of alternating current (AC) dielectric barrier discharge nonequilibrium plasma on the detonation initiation process in a hydrogen-oxygen mixture. A discharge simulation-combustion simulation loosely coupled method was used to simulate plasma assisted detonation initiation. First, the dielectric barrier discharge in the hydrogen-oxygen mixture driven by an AC voltage was simulated, which takes 17 kinds of particles (including positively charged particles, negatively charged particles, and neutral particles) and 47 reactions into account. The temporal and spatial characteristics of the discharge products were obtained. Then, the discharge products were incorporated into the combustion model of a detonation combustor as the initial conditions for the later detonation initiation simulation. Results showed that the number density distributions of plasma species are different in space and time, and develop highly nonuniformly from high voltage electrode to grounded electrode at certain times. All the active species reach their highest concentration at approximately 0.6T (T denotes a discharge cycle). Compared with the no plasma case, the differences of flowfield shape mainly appear in the early stage of the deflagration to detonation transition process. None of the sub-processes (including the very slow combustion, deflagration, over-driven detonation, detonation decay, and propagation of a self-sustained stable detonation wave) have been removed by the plasma. After the formation of a C-J detonation wave, the whole flowfield remains unchanged. With the help of plasma, the deflagration to detonation transition (DDT) time and distance are reduced by about 11.6% and 12.9%, respectively, which should be attributed to the active particles effect of nonequilibrium plasma and the local turbulent enhancing effect by the spatial characteristics of discharge. In addition, as the duration of forming a shock wave in the combustor is shortened by approximately 8.1%, it can be inferred that the plasma accelerates the DDT process more significantly before the flow becomes supersonic.

Numerical simulation of deflagration to detonation transition in granular HMX explosives under thermal ignition

To study the deflagration to detonation transition process in granular explosive under thermal ignition condition, the conductive burning is introduced into the classical model. The novel space–time conservation element and solution element method is applied to solve the mathematical governing equations. The transition process in granular HMX bed which is packed to 85 % of theoretical maximum density is simulated. The development of conductive burning, convective burning and detonation is analyzed. In the early stage, the combustion propagates slowly. It moves no more than 0.2 mm within 8.16 ms. After onset of convective burning, it takes only 20 μs to form a steady detonation with the velocity of 8165 m s−1. The time to detonation increases with the decrease in particle diameter.

連続した障害物を有する流路におけるデトネーション遷移過程（障害物の高さおよび間隔がDDT過程に及ぼす影響）

連続した障害物を有する流路におけるデトネーション遷移過程（障害物の高さおよび間隔がDDT過程に及ぼす影響）

Thrust measurement method verification and analytical studies on a liquid-fueled pulse detonation engine

In order to test the feasibility of a new thrust stand system based on impulse thrust measurement method, a liquid-fueled pulse detonation engine (PDE) is designed and built. Thrust performance of the engine is obtained by direct thrust measurement with a force transducer and indirect thrust measurement with an eddy current displacement sensor (ECDS). These two sets of thrust data are compared with each other to verify the accuracy of the thrust performance. Then thrust data measured by the new thrust stand system are compared with the verified thrust data to test its feasibility. The results indicate that thrust data from the force transducer and ECDS system are consistent with each other within the range of measurement error. Though the thrust data from the impulse thrust measurement system is a litter lower than that from the force transducer due to the axial momentum losses of the detonation jet, the impulse thrust measurement method is valid when applied to measure the averaged thrust of PDE. Analytical models of PDE are also discussed in this paper. The analytical thrust performance is higher than the experimental data due to ignoring the losses during the deflagration to detonation transition process. Effect of equivalence ratio on the engine thrust performance is investigated by utilizing the modified analytical model. Thrust reaches maximum at the equivalence ratio of about 1.1.

Study on the Mechanism of the Deflagration to Detonation Transition Process of Explosive

We present a numerical study of the mechanisms of the deflagration to detonation transition (DDT) process of explosives to assess its thermal stability. We treated the modeling system as a mixture of solid explosives and gaseous reaction products. We utilized a one-dimensional two-phase flow modeling approach with a space–time conservation element and solution element (CE/SE) method. Simulation results show that in the chemical reaction process a plug area of high density with relatively slow chemical reactions preceeds the new violent reactions and the consequent detonation. We found that steady detonation occurs at the regions where physical characteristics, such as pressure, density, temperature, and velocity, peak simultaneously. These simulation results agree well with high-temperature DDT tube experiments.

Effect of initial disturbance on the detonation front structure of a narrow duct

The effect of an initial disturbance on the detonation front structure in a narrow duct is studied by three-dimensional numerical simulation. The numerical method used includes a high-resolution fifth-order weighted essentially non-oscillatory scheme for spatial discretization, coupled with a third-order total variation diminishing Runge-Kutta time-stepping method. Two types of disturbances are used for the initial perturbation. One is a random disturbance which is imposed on the whole area of the detonation front, and the other is a symmetrical disturbance imposed within a band along the diagonal direction on the front. The results show that the two types of disturbances lead to different processes. For the random disturbance, the detonation front evolves into a stable spinning detonation. For the symmetrical diagonal disturbance, the detonation front displays a diagonal pattern at an early stage, but this pattern is unstable. It breaks down after a short while and it finally evolves into a spinning detonation. The spinning detonation structure ultimately formed due to the two types of disturbances is the same. This means that spinning detonation is the most stable mode for the simulated narrow duct. Therefore, in a narrow duct, triggering a spinning detonation can be an effective way to produce a stable detonation as well as to speed up the deflagration to detonation transition process.

Deflagration to detonation transition in aluminum dust–air mixture under weak ignition condition

Deflagration to detonation transition (DDT) in flake aluminum dust–air mixture was studied in a 199 mm inner diameter and 29.6 m long horizontal tube. 40 sets of dust dispersion system were used to disperse flake aluminum into the experimental tube. An electric spark of 40 J was used to ignite the aluminum–air mixture. Self-sustained detonation was observed and the characteristics of deflagration to detonation transition process were studied. Contributed to the transverse wave and cellular structure of detonation wave front in aluminum–air mixture, the propagation velocity of detonation wave ranges from 1480 m/s to 1820 m/s and the maximum overpressure oscillates between 40 and 102 bar. Single head spinning detonation wave in aluminum dust–air mixture was observed and the cell size was evaluated.