Structure Of Detonation Wave Research Articles

Deflagration-to-Detonation (DDT) Characteristics and Detonation Wave Structure of Flake Aluminum Powder/Air Mixture

Deflagration-to-Detonation (DDT) Characteristics and Detonation Wave Structure of Flake Aluminum Powder/Air Mixture

REALIZATION OF CONTINIOUSLY ROTATING DETONATION FOR SYNGAS-AIR MIXTURES

Numerical simulation of continuously rotating detonations (CRD) of stoichiometric two-fuel mixture with air has been carried out for the cylindrical annular detonation chamber (DC) of the rocket-type engine. Thesyngas (1 - α)óO + αH2, a binary mixture of hydrogen H2 and carbon monoxide CO, is taken as a fuel. The global flow structure in the DC and the detailed structure of the transverse detonation wave (TDW) front in thecontinuously rotating regime have been studied. Integral characteristics of the detonation process - the distribution of average values of static and total pressure along the length of the DC - and the value of specific impulse on the DC exit have been obtained. The regions of existence of stable CRD regime in coordinates “stagnation pressure pm - stagnation temperature Tm” in the injection manifold (receiver) have been determined. The minimal values of the DC length and radius for CRD for some regions at the pm-Tm plane have been found.

Three-dimensional simulation of a rotating detonation engine in ammonia/hydrogen mixtures and oxygen-enriched air

Rotating detonation using ammonia as fuel may be a potential carbon free combustion technology for gas turbine. The detonation wave structure and flow field of a rotating detonation annular combustor are investigated by three-dimensional simulation with detailed chemistry of ammonia/hydrogen-air. The detonation properties, propagation mode, combustor performance and emission characteristics are studied by varying the equivalence ratios and hydrogen concentrations. Both the increases of the combustor pressure and the hydrogen concentration promote the chemical reaction rate of the ammonia burn and the detonation wave velocity gradually increases with increasing hydrogen proportion based on one-dimensional simulation. A stable single-rotating waves resulting in ammonia/hydrogen combustor are observed for a wide range of equivalent ratios only when the hydrogen concentration is at least 0.2. The steady run of the single rotating detonation had an optimal cycle efficiency when the hydrogen concentration is increased to a critical value of 0.3. NOx emissions are more dependent on equivalent ratios than hydrogen concentration in equivalence ratios ranging from 0.70 to 1.40.

Statistical analysis of detonation wave structure

Hydrocarbon fueled detonations are imaged in a narrow channel with simultaneous schlieren and broadband chemiluminescence at 5 MHz. Mixtures of stoichiometric methane and oxygen are diluted with various levels of nitrogen and argon to alter the detonation stability. Ethane is added in controlled amounts to methane, oxygen, nitrogen mixtures to simulate the effects of high-order hydrocarbons present in natural gas. Sixteen unique mixtures are characterized by performing statistical analysis on data extracted from the images. The leading shock front of the schlieren images is detected and the normal velocity is calculated at all points along the front. Probability distribution functions of the lead shock speed are generated for all cases and the moments of distribution are computed. A strong correlation is found between mixture instability parameters and the variance and skewness of the probability distribution; mixtures with greater instability have larger skewness and variance. This suggests a quantitative alternative to soot foil analysis for experimentally characterizing the extent of detonation instability. The schlieren and chemiluminescence images are used to define an effective chemical length scale as the distance between the shock front and maximum intensity location along the chemiluminescence front. Joint probability distribution functions of shock speed and chemical length scale enable statistical characterization of coupling between the leading shock and following reaction zone. For more stable, argon dilute mixtures, it is found that the joint distributions follow the trend of the quasi-steady reaction zone. For unstable, nitrogen diluted mixtures, the distribution only follows the quasi-steady solution during high-speed portions of the front. The addition of ethane is shown to have a stabilizing effect on the detonation, consistent with computed instability parameters.

Effect of injection dynamics on detonation wave propagation in a linear detonation combustor

The effect of reactant injection and mixing on detonation wave propagation is studied in a self-excited, optically-accessible linear detonation combustor operated with natural gas and oxygen. Fuel injection and mixing processes are captured with 100 kHz planar laser induced fluorescence (PLIF) measurements of acetone tracer injected into the fuel stream. Measurements are acquired at multiple orthogonal planes downstream of the reactant injection site to investigate the three-dimensional mixing field in the chamber. The fuel distribution field is correlated with simultaneously acquired OH* chemiluminescence measurements that provide a qualitative indication of heat release in the combustor. These measurements are used to provide quantitative information of the fuel injector recovery process and its impact on detonation wave structure across a range of equivalence ratios. While significant differences in the detonation wavefront are observed with change in equivalence ratio, the characterization of the fuel refill process into the chamber after the passage of the detonation wave highlights some key generalizable features. The time available for fuel recovery is consistently between 12 – 19% of the detonation wave period across an equivalence ratio range of 0.83 – 1.48. A linear correlation between injector recovery times and the ratio of the average detonation wave pressure amplitude relative to the pressure drop across the fuel injector is observed. Instantaneous and phase-averaged measurements of acetone-PLIF with the time-coincident OH* chemiluminescence images provide qualitative information of wave structure and injection dynamics along with quantification of fuel injector recovery, a key metric that drives combustor operation and performance. These measurements significantly enhance the ability to obtain detailed information on the intra- and inter-cycle spatiotemporal evolution of the reactant refill process and its coupled effects on the detonation wave structure and propagation.

Effects of wedge-angle change on the evolution of oblique detonation wave structure

Compared to pulse detonation engine and rotating detonation engine, oblique detonation engine has the advantage of higher flight Mach number. However, it is still challenging to achieve stabilized oblique detonation wave for a broad range of flight conditions. To control oblique detonation wave, this study focuses on the oblique detonation wave structure evolution induced by changing the wedge angle. Transient two-dimensional simulations are conducted for wedge-stabilized oblique detonation wave in a stoichiometric hydrogen/air mixture. The detailed chemistry of hydrogen combustion is considered, and the thermal states of the reactants are determined by the specified flight altitude and the Mach number. The angle change between inflow and wedge can be achieved in two ways: inflow-angle change with fixed wedge angle and wedge-angle change with fixed inflow direction. Results indicate that no new autoignition zone exists in the transient wave evolution caused by wedge-angle change, which is different from that of inflow-angle change observed in previous studies. For the wedge-angle change process, the effects of wedge-angle change rate on transient oblique detonation wave structure evolution are further assessed. It is found that the transient oblique detonation wave structure is more sensitive to the wedge-rotation angular velocity for increasing wedge angle (controlled by the thermodynamic properties of the mixture) than that for decreasing wedge angle (controlled by the shock wave dynamic). For the quasi-steady triple-wave structure during wedge-angle decreasing process, a normal detonation wave occurs and becomes dominant in the wave structure evolution, whose formation mechanism is analyzed by the polar curve theory.

A chemical reaction insight of shock initiation criterion

Shock initiation criteria are essential to the shock initiation process and applications in modern pyrotechnics. The most commonly used shock initiation criteria are Walker and James criterion, which can very well describe the threshold data of the impactor with sufficient size. However, the criteria were also found not to provide a good fit to the data of thin, curve, or small flyers. By comparing the wave structure of the shock process with the stable detonation wave structure, a shock initiation criterion is developed based on the concept of the chemical reactions during the impact, focusing more on the properties of the explosives. Furthermore, a desktop micro-flyer initiating system was designed for the initiation of the thin metal flyer. The obtained data and classical historical data were analyzed with the proposed criterion, producing an excellent fit, with R2 values greater than 0.96. Compared to the existing criteria, the proposed criterion can weaken the influence of the interfacial properties of the impact and collapse the threshold velocity data with different impactor types to a single curve. The shock sensitivities of various explosives are also discussed based on the criterion. A denser impactor or the incorporation of impurities may contribute to the generation of the hot spot during the impact, leading to an increase in the sensitivity. The proposed criterion provides insight into the development of the shock initiation criteria and may help to understand the mechanism of shock initiations.

Simultaneous 100-kHz acetone planar laser-induced fluorescence and OH* chemiluminescence in a linear non-premixed detonation channel

Reactant mixing and combustion are investigated in an optically accessible, self-excited linear detonation combustor. The mixing field is captured using 100 kHz planar laser-induced fluorescence (PLIF) imaging of acetone as a tracer in the fuel supply, while 100 kHz chemiluminescence imaging of excited-state hydroxyl (OH*) radicals simultaneously resolves the evolution of the detonation wave. Time sequences are acquired over multiple detonation cycles in each test, with acetone-PLIF images collected along multiple orthogonal planes to reveal the complex three-dimensional topography of the fuel distribution. The instantaneous and phase-averaged acetone-PLIF images enable measurement of key fuel injection characteristics, such as the injector recovery time, fuel jet velocity, and refill height for a range of operating conditions. Instantaneous and phase-averaged measurements of acetone-PLIF with the time-coincident OH* chemiluminescence images also reveal a number of key features, such as fuel stratification and weak detonation in the injector near field, incomplete combustion and deflagration behind the detonation wave, vitiation and deflagration of reactants ahead of the detonation wave, and fuel and oxidizer recovery time mismatch. These measurements significantly enhance the ability to obtain detailed information on the intracycle and intercycle spatiotemporal evolution of the reactant refill process and its coupled effects on the detonation wave structure and propagation.

Formation of multiple detonation waves in rotating detonation engines with inhomogeneous methane/oxygen mixtures under different equivalence ratios

The performance of rotating detonation engines is strongly affected by the multiple detonation waves that occur, although the reason for their formation has not yet been fully explained. In this paper, two-dimensional unfolded rotating detonation waves are simulated to investigate the effects of the equivalence ratios on the number of detonation waves. The compressible reactive Navier–Stokes equations with a detailed CH4/O2 chemistry model are solved using third-order hybrid weighted essentially non-oscillatory/centered-difference numerical methods on a structured adaptive mesh. Compared with the typical two-dimensional rotating detonation wave structures in the homogeneous environment, the flow field is more unstable in the more realistic inhomogeneous environment. As the detonation propagates, coupling, decoupling, and further coupling occur due to the discontinuity of the detonation wave. The fuel mixing is enhanced by the flow field behind the wave, and the accumulation of fuel and the generation of local hot spots lead to the formation of multiple detonation propagation modes. As the equivalence ratio increases in the inhomogeneous environment, the number of detonation waves gradually increases. The intensity of the detonation waves, height of reactants, and heat release are particularly high when the equivalence ratio is close to 1.0. Moreover, equivalence ratios in the range 0.8–1.4 have little effect on the average thrust, but multiple detonation waves can be used to stabilize the thrust in the combustion chamber.

On the effects of reactant stratification and wall curvature in non-premixed rotating detonation combustors

The optimization of non-premixed rotating detonation combustors (RDCs) requires improved understanding of the coupled effects of reactant stratification, fluid property gradients, and complex shock-wave interactions on the detonation wave structure within annular geometries. In the current work, simultaneous orthogonal views of chemiluminescence and hydroxyl planar laser-induced fluorescence (PLIF) are utilized to establish the existence of a dual-wave system characterized by leading and trailing detonation waves that are closely coupled by the local flow physics. These features are persistent over a wide range of mass flow rates and are consistent with prior observations of non-premixed rotating detonations in annular geometries. The detailed instantaneous time sequences are compared with a 3D reactive unsteady Reynolds averaged Navier-Stokes (URANS) simulation to more clearly elucidate the in-situ combustion dynamics and the sensitivity to reactant inlet conditions. It is found that the dual-wave system results from unburned reactants that survive the leading detonation wave in the injector near field and are consumed within a trailing azimuthal reflected-shock combustion (ARSC) zone. By contrast, the injector far field is characterized by rapid mixing due to a sudden drop to subsonic conditions, and the bifurcated detonation wave structure collapses into a stronger, single-wave detonation front with higher overall pressure ratio as compared with the dual-wave system. While each RDC will have different inflow, mixing, and combustion characteristics, the underlying interactions between the stratified reactants and azimuthal wave dynamics identified through the combination of advanced MHz-rate diagnostics and 3D numerical simulations have important implications for the study of detonation wave stability, mode transition, and combustion efficiency in non-premixed annular RDCs.

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.

Thermal detonation wave in liquid lead – water mixture

It was developed the model of thermal detonation in a mixture of continuous liquid lead and dispersed steam/water particles. Stationary equations of mass, impulse and energy conservations laws for multiphase continuum are applied to describe internal structure of thermal detonation wave. They are supplemented by closing relations describing interfacial friction, heat transfer, and fragmentation. Conditions at leading shock wave and at Chapman-Jouguet plane are used as boundary conditions.

Reaction zone structure and detonation parameters of nitromethane/polymethylmethacrylate and its mixture with microballoons

In the present work, the detonation wave structure and detonation parameters for nitromethane (NM) and its mixtures with polymethylmethacrylate (PMMA) and glass microballoons (GMB) were studied by a velocity interferometer system for any reflector laser interferometer. The PMMA concentration varied from 2% to 4%. It is shown that PMMA additives lead to a change in the reaction zone structure, which can be observed as an appearance of a cellular instability of the detonation front. The detonation parameters of the mixture up to 3% PMMA are close to those of pure nitromethane and reduced when 4% PMMA is added. The addition of 2% GMB to the NM/PMMA mixture leads to the formation of a detonation front with a characteristic size of heterogeneities on the order of GMB diameter. In this case, the detonation parameters are reduced, and the values of the detonation velocity decrease by about 10% compared to NM/PMMA mixtures.

Mach reflection of a H2-O2-Ar detonation wave on the rough wedge based on soot track measurements

Gaseous detonation wave reflection on the rough wedge was experimentally investigated by soot track measurements. Various wedge angles, step numbers and initial pressures were taken into account. The results show that the Mach reflection can form on the rough surface due to the three-dimensional structure of the cellular detonation wave or the pseudo triple-point configuration. The wedge angle is still a significant parameter to affect the Mach stem height and the triple-point trajectory. The Mach stem on the rough surface is weaker and the triple-point is easily deflected due to the triple-point disappearance from the Mach stem. The wedge with smaller step number leads to the triple-point trajectory starting in the downstream region, instead of its starting from the wedge apex. As the step number increases, the Mach stem height on the rough wedge gradually approaches the one on the smooth wedge. The initial pressure has a more significant effect on the Mach reflection on the rough surface compared to that on the smooth surface. Moreover, the Mach reflection on the rough wedge keeps localized self-similarity, and satisfies the frozen limit in the near field and the equilibrium limit in the far field. The critical wedge angle of the transition from regular reflection to Mach reflection is dependent on the step number.

Detonation in bubble media: the effect of initial pressure

The influence of parameters of mono- and polydisperse, one- and multicomponent bubble media on the conditions of initiation, structure, propagation velocity, and pressure of detonation waves is experimentally investigated. It is established that the variation of initial pressure of bubble medium is an efficient method to control the parameters of waves of “bubble” detonation.

Multi-front detonation structure in two-fuel mixtures – numerical modelling

A numerical simulation of a two-dimensional (2D) structure of the detonation wave (DW) in a two-fuel gaseous mixtures with air mixture at normal initial condition has been conducted. This study is based on a two-stage generalised model of detonation kinetics for a mixtures of two fuels first proposed by us. The computations have been performed in a wide range of channel height. The changes in the 2D front structure of the self-sustaining DW on variations of the height of the channel have been studied. From the analysis of the flow structure and the number of primary transverse waves in channel, the dominant sizes of the detonation cell for studied mixture have been determine. Numerical data on the detonation cell sizes have been carefully analyzed and compared with available experimental data.

Structure of Detonation Waves in Mixtures of Tetranitromethane with Nitrobenzene and Methanol

Experimental studies of the structure of detonation waves in mixtures of tetranitromethane with methanol and nitrobenzene have been performed. Particle velocity profiles at the arrival of detonation waves at the interface with a water window were measured by a laser interferometer. It has been shown that the flow pattern in the reaction zone changes sharply at a concentration of diluents in the vicinity of stoichiometry, resulting in a decrease in the amplitude of the von Neumann spike up to its complete disappearance. The detonation waves are stable to the formation of a cellular structure of the front over almost the entire concentration range, except in the range near the limiting values. At the same time, the amplitude values of particle velocity show poor reproducibility from experiment to experiment performed under the same conditions. The obtained experimental dependences of detonation velocity on the concentrations of methanol and nitrobenzene are in good agreement with thermodynamic calculations.

Detonation properties of solution of hydrazine nitrate/water

In our work, the study of detonation wave structure was performed by VISAR laser interferometer for a hydrazine nitrate/H2O (HN/water) solution and pressed HN with maximum density of 1.68 g/cm3. The range of water concentration in which the HN/water solution detonated at a room temperature was found to be 25 - 36 wt.%. For the HN/water solution, the detonation velocity decreases linearly with increasing water concentration whereas for pressed HN, the dependence of detonation velocity on initial density is not monotonic, but has a characteristic “s”-shape. It was shown that the particle velocity profiles in pressed HN are smoother than in the HN/water solution. This means that detonation waves in the liquid HN are unstable, and the characteristic amplitude size of inhomogeneities is about 400 µm. Optical registration of the detonation wave propagation in the HN/water solution was done by two different high speed optical recording techniques. A very poor glow of the detonation front in the visible part of the spectrum and its instability were observed. This may be due to the low temperature in the detonation waves in the water solution of HN.

Influence of viscous boundary layer on initiation zone structure of two-dimensional oblique detonation wave

The influence of the viscous boundary layer on the oblique detonation wave structure has been simulated and analyzed by solving the two-dimensional Navier–Stokes equations containing the hydrogen/air elementary reaction model. It is found that the effect of the viscous boundary layer can be neglected in the smooth transition initiation structure, but not in the abrupt transition initiation structure. The interaction of the lateral shock wave and the viscous boundary layer results in the formation of a high-temperature recirculation zone near the wall of the initiation zone, a novel structure that does not appear in inviscid formulations. Within this structure, the chemical reaction is triggered to occur in advance, eventually leading to the equilibrium initiation position relocating upstream compared with the inviscid case. Nevertheless, the viscous boundary layer has a limited impact on the main flow region downstream of the oblique detonation. The shock wave structures and pressure distributions at various Mach numbers are obtained computationally and analyzed in detail.

Numerical study on the shock/combustion interaction of oblique detonation waves

To determine the shock/combustion interaction structure of a wedge-induced oblique detonation wave, high-order numerical simulations solving the two-dimensional reactive Euler equations embedded with a two-step chemical kinetic model have been performed. In this study, various dimensionless heat release amounts ranging from 40.0 to 52.5 are selected to investigate the flow configuration. The computational results show that four types of typical shock/combustion interactions, namely, Type VI, I, V and IV (following the classification of shock/shock interaction proposed by Edney), can be observed. The detailed structures and characteristics of the interaction types are presented and shown to be different than the classic shock/shock interaction. Additional insight into the transition principles of different shock/combustion interactions is illustrated through shock polar analysis.