Initiation Of Detonation Wave Research Articles

Study on coupling characteristics of supersonic inlet and pulse detonation combustor

Coupling model for two-dimensional mixed-compression supersonic inlet with Mach number of 2.5 at design point and pulse detonation combustor was established, and three working schemes were designed to investigate multi cycle working process by using unsteady numerical simulation with chemical reaction. The results show that the following two measurements can both restrain the back-propagating compression wave and broaden the stability margin of the inlet and increase the frequency, one of which is the pressure relief at the outlet of the combustor, the other is valve at the inlet of the combustor. Nevertheless, the former will lose thrust, while the latter can greatly increase thrust. Meanwhile, the valve will reflect the compression wave in the production; increase the turbulence in the combustor, and make the gas entrained into the diffuser section of the inlet at the moment of opening the valve. However, the reflected compression wave in the hot production will not affect the velocity and shape of the detonation wave. Furthermore, in the period of detonation wave initiation and propagation, the blockage ratio of physical obstructions at the inlet of the combustor should be expanded as much as possible. At the same time, the flow at the outlet of the inlet should not be blocked to increase the flow resistance.

Computational fluid dynamics simulation of detonation wave propagation in modified pulse detonation combustor

In this paper effect of Schelkin spiral material on thermal load and detonation combustion wave propagation in pulse detonation combustor has been simulated. As detonation combustion is supersonic combustion process and energy release rate is very high. In this regards present researches are focusing on flame acceleration process to reduce the DDT run up length. Hence the Schelkin spiral is inserted in detonation tube, which creates a bluff body and enhanced the turbulence of flame propagation. During simulation three turbulence models are used to carry out the reliable and repeatable detonation wave in pulse detonation combustor near thin boundary layer of helical shape Shchelkin spiral. The computational fluid dynamics (CFD) simulation has been performed using Ansys fluent platform. The Large Eddy Simulation (LES), detached eddy simulation with realizable k-ε turbulence model and detached eddy simulation with SST k-ω turbulence model are used for reacting flow simulation. From this simulation the LES turbulence model shows better turbulence initiation of detonation wave with velocity magnitude of 3040 m/s in detonation tube compared to other two turbulence models. This velocity is higher than C-J velocity of 1800 m/s. Further computational result shows that deflagration to detonation transition take place at several waves traveling region, in presence of Shchelkin spiral in detonation tube.

Temperature Distribution Analysis of Pulse Detonation Engines

In pulse detonation engines (PDE), combustion temperatures can rise as high as 3000 K across the detonation wave. The continuous exposure to such elevated temperature may risk the integrity of the structural components of the engines. In order to be able to estimate the heat load accurately. Hence, numerical and experimental studies of the temperature distribution on a pulse detonation engine model was conducted to quantify the heat load. Navier-Stokes conservation equations with viscosity and chemical reaction for deflagration-to-detonation transition (DDT) in detonation engines were solved through computational fluid dynamics. Reactive flow field of premixed mixtures (propane-oxygen) was modeled for detonation process. In the simulation, short-term detonation combustion (ms) and long-term wall heating process(s) are carried out together. Both single detonation and multiple continuous detonations were simulated and tested, and the simulation results are consistent with the experimental results. The results show that there is a correlation between heat flux and detonation wave structure and the instantaneous maximum heat flux appears in the detonation wave region of the detonation tube wall. The distribution of transient heat flux in time and space is very uneven, and the difference between transient heat flux and average heat flux is large. The position of detonation wave formation is the turning point of PDE wall temperature, and the temperature at the front end of the turning point is lower than that at the back end. The results show that the fresh mixtures have cooling effect on the detonation tube wall, which leads to the increase of the inner wall temperature with oscillation and the continuous increase of the outside wall temperature. The maximum wall temperature and the speed of temperature rise are positively correlated with detonation frequency. The results also show that the heat transfer coefficient of detonation tube has an effect on the initiation of detonation wave. When the heat transfer coefficient is large, detonation wave can not initiate in the studied engine. The focus of thermal protection is different between single detonation and multiple continuous detonations. Heat management of the detonation engines highlights an important part on the engine construction.

Numerical investigation of pre-detonator in rotating detonation engine

Pre-detonators are commonly used in rotating detonation engine (RDE) experiments. Current experimental studies focus on the performance of pre-detonator while ignoring the influence of pre-detonator on the flow field. In numerical simulations one-dimensional detonation wave is usually used to ignite the fresh gas in RDE. This is a simplification of the pre-detonator used in practical hotfire tests. But the coupling between the pre-detonator and the combustor is ignored. The aim of the present study is to study the influence of pre-detonator on the flow field in the RDE. A model of RDE with a pre-detonator is built, in which three-dimensional numerical simulations fueled with hydrogen/air is performed. The influence of pre-detonator on the combustor in different stages is studied. After initiation, detonation wave from the pre-detonator forms two counter-rotating detonation waves. The tangential installation of pre-detonator fails in directional initiation of detonation wave. The coupling effect is shown as the reflection and expulsion of shock wave. Detonation wave or oblique shock wave in the combustion chamber enters the pre-detonator and turns into shock wave before colliding with the end and re-entering the combustion chamber. Under some circumstances, the reflected shock wave will initiate a detonation wave and affect the wave structure in the combustion chamber. In the stable stage, the reflected shock wave has no effect on the flow field. However, periodic collision of reflected shock wave with detonation wave at the junction causes ablation in long-time experiments. Increasing the axial distance between pre-detonator and injection wall is expected to be a solution for the ablation problem.

Comparison of Air-Breathing Engines with Slow and Detonation Combustion

The ramjets of different schemes with slow and detonation combustion are compared. Steady and unsteady processes in these engines are described by simple models of gasdynamics and thermodynamics, detonation waves, air deceleration in air intakes, and combustion product acceleration in supersonic sections of nozzles. Within the framework of these models, at a fixed adiabatic exponent the characteristics of any engine depend on two parameters, namely, the flight Mach number and the dimensionless combustion heat of the combustible mixture. The comparison performed for all actual values of these parameters, together with an analysis of thermodynamic cycles and one-dimensional time-dependent calculations (for the engines with combustion in traveling detonation waves), confirmed the importance of taking the unsteady processes in combustors into account. The comparison made in this study is actual, due to frequent claims about a possible considerable increase in the thrust characteristics on replacement of ramjets with slow combustion under a constant pressure by engines with combustion in pulsed or rotating detonation waves (pulse-detonation engines (PDE) or rotating detonation engines (RDE)). Usually, these assertions are made on the basis of the comparison of the thermal efficiencies and specific thrusts and impulses calculated according to these values. In the case of unsteady flow in the combustor, the recalculation of the thrusts and impulses according to the thermal efficiency overestimates their values. The validity of this statement for multichambered PDEs is confirmed by time-dependent calculations. In the case of instantaneous opening and closing of the entrance into the detonation chambers and an instantaneous, without energy expenditures, detonation wave initiation, the PDE thrust is less than the ramjet thrust, starting from small supersonic flight Mach numbers. Analogous calculations for the RDEs are unjustified due to the passage into a rotating noninertial coordinate system.

Effect of arc obstacles blockage ratio on detonation characteristics of hydrogen-air

In this paper, the influence of maximum blockage ratio of arc obstacles on hydrogen-air detonation characteristics is simulated and analyzed by using OpenFoam package. The results show that the arc obstacles can effectively reduce the deflagration-to-detonation transition distance and the optimal maximum blockage ratio is 0.7. As the maximum blockage ratio increases, the flame acceleration and initiation of detonation wave show 3 different regimes: (1) For small maximum blockage ratio, the flame is affected by Squish flow, resulting the velocity differences between the flame near the wall and in the center of the tube, and the tulip flame formation. The tulip flame will generate two local explosion points and the explosion points develop and merge to initiate detonation. (2) For intermediate maximum blockage ratio, under the interaction of the reflected shock wave and the obstacles, the flame is a narrow fingertip shape. The initiation of detonation wave is engendered by the development and fusion of multiple hot spots. (3) For large maximum blockage ratio, the flame is also a narrow fingertip-shaped. The detonation wave is initiated by the coupling of the flame front with the leading shock wave at the throat of the obstacle.

Self-sustained, high-frequency detonation wave generation in a semi-bounded channel

Combustion dynamics in a linear, semi-bounded channel were studied to characterize injection, mixing, and ignition processes in a two dimensional analogue of a rotating detonation wave combustor. The linear channel was developed to operate using natural gas and oxygen and to provide large optical accessibility in support of high-fidelity diagnostics at thermal power density levels representative of rotating detonation wave combustors over a broad range of flow conditions. Measurements of pressure and heat release were performed using an array of high-frequency dynamic pressure probes and OH*-chemiluminescence, respectively. Self-sustained, periodic generation of detonation waves was observed. These traveling combustion waves were initiated from low amplitude deflagrative fronts and steepened as they traveled through the combustion channel. The sensitivity of this instability to changes in acoustic boundary conditions was explored to determine the origin of the high-amplitude dynamics. The change in acoustic boundary at the end-wall affected the transverse acoustic mode frequency as expected, but had no effect on the detonation wave initiation. The detonation wave dynamics were found to be correlated with resonant frequencies in the propellant manifolds. It was determined that the frequency of the self-sustained chamber dynamics depends on which manifold has the strongest injection pressure ratio. OH*-chemiluminescence and pressure measurements indicate that the observed transition to detonation is linked to the auto-ignition of the reactants and that the auto-ignition event is coupled with the fluctuation in reactant mass flow associated with the manifold dynamics.

Numerical Study of Detonation Wave Propagation in the Variable Cross-Section Channel Using Unstructured Computational Grids

The work is dedicated to the numerical study of detonation wave initiation and propagation in the variable cross-section axisymmetric channel filled with the model hydrogen-air mixture. The channel models the large-scale device for the utilization of worn-out tires. Mathematical model is based on two-dimensional axisymmetric Euler equations supplemented by global chemical kinetics model. The finite volume computational algorithm of the second approximation order for the calculation of two-dimensional flows with detonation waves on fully unstructured grids with triangular cells is developed. Three geometrical configurations of the channel are investigated, each with its own degree of the divergence of the conical part of the channel from the point of view of the pressure from the detonation wave on the end wall of the channel. The problem in consideration relates to the problem of waste recycling in the devices based on the detonation combustion of the fuel.

Volumetric initiation of gaseous detonation by radiant heating of suspended microparticles

The concept of detonation wave initiation in the local volume of a fuel–gas mixture containing suspended chemically neutral microparticles heated by radiant energy from an external source is proposed. Mechanisms of initiation of the combustion and detonation waves in a region of accumulation of the radiation- heated microparticles have been studied by numerical simulation methods. Criteria that determine geometric dimensions of a region of the two-phase medium, which are necessary for the initiation of detonation waves, are formulated.

非一様な水素－空気予混合気体におけるデトネーション波の開始

非一様な水素－空気予混合気体におけるデトネーション波の開始

Review on Recent Advances in Pulse Detonation Engines

Pulse detonation engines (PDEs) are new exciting propulsion technologies for future propulsion applications. The operating cycles of PDE consist of fuel-air mixture, combustion, blowdown, and purging. The combustion process in pulse detonation engine is the most important phenomenon as it produces reliable and repeatable detonation waves. The detonation wave initiation in detonation tube in practical system is a combination of multistage combustion phenomena. Detonation combustion causes rapid burning of fuel-air mixture, which is a thousand times faster than deflagration mode of combustion process. PDE utilizes repetitive detonation wave to produce propulsion thrust. In the present paper, detailed review of various experimental studies and computational analysis addressing the detonation mode of combustion in pulse detonation engines are discussed. The effect of different parameters on the improvement of propulsion performance of pulse detonation engine has been presented in detail in this research paper. It is observed that the design of detonation wave flow path in detonation tube, ejectors at exit section of detonation tube, and operating parameters such as Mach numbers are mainly responsible for improving the propulsion performance of PDE. In the present review work, further scope of research in this area has also been suggested.

Numerical study of oblique detonation wave initiation in a stoichiometric hydrogen-air mixture

Two-dimensional, oblique detonations induced by a wedge are simulated using the reactive Euler equations with a detailed chemical reaction model. The focus of this study is on the oblique shock-to-detonation transition in a stoichiometric hydrogen-air mixture. A combustible, gas mixture at low pressure and high temperature, corresponding to the realistic, inflow conditions applied in oblique detonation wave engines, is presented in this study. At practical flight conditions, the present numerical results illustrate that oblique detonation initiation is achieved through a smooth transition from a curved shock, which differs from the abrupt transition depicted in the previous studies. The formation mechanism of this smooth transition is discussed and a quantitative analysis is carried out by defining a characteristic length for the initiation process. The dependence of the initiation length on different parameters including the wedge angle, flight Mach number, and inflow Mach number is discussed. Despite the hypothetical nature of the simulation configuration, the present numerical study uses parameters we deem relevant to practical conditions and provides important observations for which future investigations can benefit from in reaching toward a rigorous theory of the formation and self-sustenance of oblique detonation waves.

Ignition experiment with automotive spark on rotating detonation engine

An experimental study on rotating detonation engine with the slot-orifice impinging injection method was presented in this paper. Reactants were gaseous H2–Air mixtures and ignited by an automotive spark plug. The engine was initiated successfully and rotating detonation wave propagated continuously and steadily in the circumferential direction. Through the detailed analysis on the initiation and propagation process of rotating detonation wave, it was found that deflagration-to-detonation transition (DDT) was observed in the annular combustion chamber, and the DDT time exhibited an obvious randomness. For the operating conditions which the rotating detonation wave propagated stably, the fluctuation of the pressure spike of detonation wave was relatively small, and the detonation wave propagated continuously without interruption; for the operating conditions which the detonation wave was unstable, the fluctuation of pressure spike of detonation wave was relatively large, and the interruption occurred, which might result in the change of propagation direction of rotating detonation wave. And in some operating conditions, a new phenomenon that strong detonation and weak detonation occurred alternately was found. Besides, in order to obtain the success rate of rotating detonation wave initiation with automotive spark plug, repeatability experiments were carried out. The results show that the success rate was up to 94%.

Influence of quantum effects on the initiation of ignition and detonation

A theoretical analysis that allows one to quantify the quantum corrections to the rate constants of endothermic reactions associated with an increase in the high-energy tails of the momentum distribution functions at high pressures due to a manifestation of the uncertainty principle for the energy of the colliding particles at a high collision frequency is performed. The initiation of ignition of hydrogen-oxygen mixtures is investigated and special series of experiments on the initiation of detonation waves of condensation in carbon suboxide and acetylene at elevated pressures near the low-temperature limits have been carried out. The experimentally observed deviations in the Arrhenius dependences of the induction periods of the initiation of hydrogen ignition and detonation waves of condensation are shown to be well described by the proposed quantum corrections.

Critical energy of bubble detonation wave initiation by a wire explosion

Initiation of bubble detonation by a short shock wave generated by exploding a wire located in a chemically active bubbled medium is studied experimentally. Critical energies of detonation initiation are determined for different volume fractions of bubbles. It is demonstrated that this method of initiation transforms the compression wave to a detonation wave at a length of ≈0.3 m. In the case of a wire explosion in a gas-liquid medium, the critical energy of bubble detonation initiation can be reduced by more than two orders of magnitude, as compared with initiation by a gas detonation wave.

Initiation of detonation waves in channels of variable cross section filled with liquid with combustible gas bubbles

Special features are investigated of the initiation of detonation waves in chemically active bubble media located in channels of variable cross section. It is found that, depending on the initial volume content of combustible mixture, the detonation in convergent channels may proceed with the emergence of one or two detonation solitons. The possibility of the emergence of a stable detonation wave upon reflection from the channel bottom is demonstrated in channels with closed bottom. Also demonstrated is the possibility of initiation of detonation upon reflection of the wave from the region of “pure” liquid. Depending on the amplitude of initiating wave and of the initial volume content of bubbles, a map of solutions is constructed which illustrates the modes of the process of detonation in the considered channels.

Explosion Safety Aspects of Shock Wave-Induced Condensation in Fuel-Rich Gaseous Mixtures

The possibility of fuel vapor condensation in shock waves in fuel-rich cyclohexane-oxygen gaseous mixtures is shown. The influence of fuel vapor condensation on shock waves parameters and explosion behavior of corresponding mixtures is analyzed. It is shown, that condensation process led to the increase of pressure and temperature and can essentially change the chemical composition of the gas. For example, the molar fraction of the oxidizer can increase in a few times. This possibility should be taken into account in modeling of shock waves propagation and detonation wave initiation in corresponding gaseous mixtures. For example, the mixtures, which have an initial gas composition above the upper flammability limit, can, nevertheless, explode. It can happen, if the chemical composition of the gas starts to be inside the flammability range owing to fuel vapor condensation. The rate of the condensation process is estimated. According to estimations, this process can be fast enough to significantly change the chemical composition of the gas and shift it into the flammable range during the compression phase of blast waves, generated by explosions of typical fuel-vapor clouds.

Rayleigh–Benard convection in a chemical equilibrium gas (simulation of surface detonation wave initiation)

The problem of the Rayleigh–Benard convection for a chemical equilibrium gas is solved numerically. The gas is assumed to be incompressible, and the layer boundaries are assumed to be flat, isothermal, and free from shear stress. The Boussinesq model with the coefficient at the buoyancy term depending on the transverse coordinate is used. The resultant nonlinear system of equations is solved by a previously developed numerical method based on the spectral representation of vorticity and temperature fields. According to the idea of splitting, analytical formulas are first used to take into account the linear increase in disturbances, and then the nonlinear convective transfer is calculated by the finite-difference method. Various convection modes are obtained: stationary, periodic, quasi-periodic, and stochastic convection. The model of convection of a chemical equilibrium gas, presented here, can be useful for the understanding of the transition of a cellular combustion of surface systems into an explosion (initiation of surface detonation) and for the calculation of operating regimes of chemical reactors.

The Limits of Applicability of Usual Kinetic Relations to the Detonation Waves Chemistry. Homogeneous Explosives

The report presented contains the brief description of some of the macrokinetic dependencies in field of detonation of homogeneous, preferably liquid, explosives. Chemical kinetics data and mechanisms of the detonation reactions of pure nitrocompounds at different initial temperature, and the mixtures of them with sulfuric acid are obtained. The data from both groups of measurements for TNT virtually coincide with results of kinetic calculations at which the frequency of spin-pulsating subsurface waves in lean TNT/RDX mixture was used as a source of macrokinetic information. A.N.Dremin theory of failure diameter, usually used for kinetic calculations, is supplemented in three directions. (1) Velocity of the dark wave, one of the most significant elements of the theory, is connected with energy of activation and in this way it is defined independently as an inherent part of the extinguishment process. (2) The gas bubbles formation and growth in the compressed reactive substance in the dark zone are included into consideration as important moments of the detonation wave initiation. (3) The new phenomenon, that has been observed in some of the modern molecular modeling investigations: separation and collection in groups of particles of different mass in shock and detonation waves, was applied in order to explain the strong influence of additives on detonation ability of nitromethane.

Simulation of ignition and combustion wave propagation in enclosed C 2H 6/O 2/N 2 mixtures

The dynamics of one-dimensional C2H6/Air combustion waves originating from hot-spot ignition was studied numerically by solving the corresponding conservation equations for mass, species, energy and momentum. The model included a detailed reaction mechanism and a multispecies transport model. The numerical solution was based on the method of lines and on a dynamic adaptive grid technique. Due to the stiffness of the resulting differential equations, a BDF-code was used to integrate the system. In this work, hot-spot ignition was studied for a reaction system under high pressure and high temperature conditions. The results show that hot-spot ignition can cause different combustion phenomena depending on the shape of the temperature nonuniformity. A supersonic combustion wave was observed when the velocity of the temperature-gradient based autoignition wave was much higher than the velocity of pressure waves. Detonation wave initiation was the result when an interaction between ignition process and pressure wave was possible. Ordinary flame propagation occurred, when the mixture outside the hot-spot was far away from autoignition.