Detonation Cellular Structure Research Articles

The effect of porous non-metallic balls on detonation propagation in hydrogen–oxygen mixtures

In this study, the influence of porous non-metallic balls on the dynamics of detonation propagation in hydrogen–oxygen mixtures is studied in stainless steel tubes with square cross-sections. The effect of the length and thickness of the balls is considered in detail. Four pressure transducers are used to record the detonation time-of-arrival, and the average velocity of detonation propagation is calculate. The smoked foil technique is performed to register the detonation cellular structures. The results indicate that increasing the filling length and thickness of the balls leads to a significant increase in velocity loss, critical pressure, and re-initiation distance during detonation propagation. Two propagation modes are observed near the critical pressure. In sub-critical mode, the detonation wave is attenuated and failed eventually, propagating to the end of the tube in the form of a low-speed deflagration wave. In super-critical mode, the detonation propagation can be promoted by inducing a vertical transverse wave generated by the detonation wave passing through a group of small balls. It is worth noting that the increase in filling thickness of the small balls leads to a greater velocity loss compared to the increase in filling length. However, an increase in the filling length will cause the detonation wave to undergo a longer and more sustained weakening process as it passes through the small balls, thereby resulting in a longer re-initiation distance and a lower average velocity over a short distance after re-initiation. By increasing the filling length of the small balls to 312 mm, the transition of the detonation wave from multi-head detonation to double-head detonation can be observed, and then successfully turns into stable detonation. However, when filling double-layer small balls, even in super-critical conditions, the attenuated detonation wave cannot achieve re-initiation over a short distance.

The failure and re-initiation of quasi-detonations in stoichiometric acetylene-oxygen mixtures diluted by nitrogen

In this study, the failure and re-initiation of quasi-detonations are investigated systematically in stoichiometric acetylene-oxygen mixtures diluted by nitrogen, and the nitrogen dilution range of 10–45 % is considered. Photodiodes are introduced to obtain the average velocity by recording the detonation time-of-arrival. The smoked foil technique is performed to register the detonation cellular structures, and a high-speed schlieren system is used to observe the propagation processes. Three propagation modes are defined based on nine repeated experiments, i.e., Go, No-go and Critical regimes. For the “go” regime, the exiting detonation all successfully evolves into a spherical detonation in nine repetitions of the experiments. For the “no-go” case, the detonation all fails upon exit and becomes a deflagration. The case between the Go and No-go is called as the critical mode. Near the limits, the critical pressure of successful evolution into a spherical detonation is obtained, and the data indicates that the critical pressure is approximately independent of the wall roughness. But the critical pressure can increase obviously by introducing the nitrogen dilution. The cell sizes for quasi-detonations are measured, and the ratio of the critical tube diameter (dc) to the cell size (λ) is considered to quantify the critical criterion of detonation re-initiation. Note that the previous criterion of dc/λ ≥ 13 about normal detonation re-initiation cannot be applied to the quasi-detonation, and the re-initiation condition for quasi-detonations can be nearly quantified as dc/λ ≥ 8. The results are consistent with those obtained in our previous study (Xuxu Sun et al., Combustion and Flame, 112280). Corresponding to the normal detonation in a smooth tube, the critical value of dc/λ is always lower for quasi-detonations, which indicates a favorable effect on the detonation transmission is verified.

BYCFoam: An Improved Solver for Rotating Detonation Engines Based on OpenFOAM

A rotating detonation engine (RDE) is a highly promising detonation-based propulsion system and has been widely researched in recent decades. In this study, BYCFoam, the latest gaseous version of the BYRFoam family, is developed specifically for RDE simulations. It is based on the standard compressible flow solver rhoCentralFoam in OpenFOAM and incorporates several enhancements: improved reconstruction variables and flux schemes; detailed chemistry and transport properties; the utilization of an adaptive mesh refinement (AMR) and dynamic load balancing (DLB). A series of comprehensive numerical tests are conducted, including the shock-tube problem, shock-wave diffraction, homogeneous ignition delay, premixed flame, planar detonation, detonation cellular structure and rotating detonation combustor (RDC). The results demonstrate that BYCFoam can accurately and efficiently simulate the deflagration and detonation processes. This solver enhances the capability of the BYRFoam family for the in-depth exploration of RDE in future research.

3D Effects of detonation re-initiation after diffraction at a back-facing step

Detonation diffraction at a backward facing step and subsequent re-initiation at the bottom wall at near critical detonation transmission conditions is studied in a square 7.6 cm channel. The experimental techniques used for this purpose include ultra high-speed schlieren video from the side and the top views. Direct photography is also performed in the top view configuration with a soot foil placed at the bottom wall after the step. The process of detonation re-initiation is studied for 2H2+O2+2Ar and CH4+2O2 mixtures that are characterized by a very regular and irregular detonation cellular structure, respectively. For both mixtures detonation re-initiation begins at discrete points where the descending transverse reflect from the bottom wall; the spacing of re-initiation points matches the wave number, suggesting the three-dimensional interaction of descending and lateral transverse waves on the reflecting wall trigger detonation re-initiation. The subsequent growth of these re-initiation kernels differs between mixtures. For regular cell mixtures, the detonation evolution is gradual and follows the lateral transverse wave along the bottom wall; whereas for irregular cell mixtures, explosive of hot spots grow independently of the lateral transverse waves. The observed initiation processes underscore the critical role of three-dimensional effects for both regular and irregular cell mixtures. The abrupt detonation initiation observed for methane-oxygen can be attributed to the high effective activation energy, i.e., high reaction rate temperature sensitivity.

A hybrid lattice Boltzmann method for gaseous detonations

This article is dedicated to the construction of a robust and accurate numerical scheme based on the lattice Boltzmann method (LBM) for simulations of gaseous detonations. This objective is achieved through careful construction of a fully conservative hybrid lattice Boltzmann scheme tailored for multi-species reactive flows. The core concept is to retain LBM low dissipation properties for acoustic and vortical modes by using the collide and stream algorithm for the particle distribution function, while transporting entropic and species modes via a specifically designed finite-volume scheme. The proposed method is first evaluated on common academic cases, demonstrating its ability to accurately simulate multi-species compressible and reactive flows with discontinuities: the convection of inert species, a Sod shock tube with two ideal gases and a steady one-dimensional inviscid detonation wave. Subsequently, the potential of this novel approach is demonstrated in one- and two-dimensional inviscid unsteady gaseous detonations, highlighting its ability to accurately recover detonation structures and associated instabilities for high activation energies. To the authors' knowledge, this study is the first successful simulation of detonation cellular structures capitalizing on the LBM collide and stream algorithm.

DetonationFoam: An open-source solver for simulation of gaseous detonation based on OpenFOAM

Detonation has promising applications in advanced propulsion systems, and numerical simulation is widely used to gain insights into the complex interaction between the hydrodynamic flow and chemical reactions involved in detonation. In this work, detonationFoam, an open-source solver for accurate and efficient simulation of compressible reactive flow and detonation are developed based on OpenFOAM. detonationFoam can simulate compressible, multi-component, reactive flow and it can accurately evaluate the detailed transport coefficients using the mixture-averaged transport model. Compared to rhoCentralFoam, the improved HLLC-P approximate Riemann solver is used in detonationFoam and it helps to accurately resolve shock waves appearing in detonation. Besides, the adaptive mesh refinement and dynamic load balancing algorithms are used in detonationFoam, which greatly improves the computational efficiency. Validation tests including homogenous ignition, unsteady diffusion, shock tube problem, premixed flame, planar detonation, double Mach reflection, detonation cellular structure and oblique detonation wave are conducted. These tests demonstrate that detonationFoam can be used to accurately and efficiently to simulate the compressible, multi-component reactive flow and detonation processes. Program summaryProgram Title: detonationFoamCPC Library link to program files:https://doi.org/10.17632/x45zh4nz28.1Developer's repository link:https://github.com/JieSun-pku/detonationFoamLicensing provisions: GPLv3Programming language: C++Nature of problem: Gaseous detonation involves different length scales and complicated chemistry. To accurately and efficiently simulate the gaseous detonation, adaptive mesh refinement needs to be conducted and detailed chemistry should be considered. Besides, the severe load imbalance caused by the chemical source term evaluation may greatly reduce the computation efficiency.Solution method: An open-source solver, detonationFoam is developed based on OpenFOAM. The species equations considering detailed chemistry are solved in detonationFoam and thereby detonation in a compressible, multi-component, reactive flow can be simulated. The adaptive mesh refinement technique and the dynamic load balancing algorithm are incorporated into detonationFoam. It is demonstrated that detonationFoam can accurately and efficiently simulate gaseous detonation.

DEFORMATION OF A TWO-DIMENSIONAL TRACE PATTERN OF A DETONATION FLOW WITH A “CONTINUOUS” CHANGE IN THE WIDTH OF A FLAT CHANNEL

A numerical study of two-dimensional cellular detonation of a hydrogen-air mixture in channels of various widths was carried out and data were obtained on the process of formation of a cellular structure, on the number, shape, and size of cells depending on the channel width. Based on the results of calculations, a classification of two-dimensional cellular detonation structures was carried out. The study was carried out at the facilities of the JSCC RAS. The flow model of a multicomponent reacting mixture was implemented using a customized opensource solver of the OpenFoam framework based on the Kurganov–Tadmor scheme.

Formation and Evolution of Cellular Structures in Wedge-Induced Oblique Detonations

Numerical simulation of an oblique detonation induced by a wedge is performed to investigate the formation and evolution of the oblique cellular detonation structure and the quantitative comparison of the cellular structure of a normal and an oblique detonation. The compressible reactive Euler equations are solved using the seventh-order WENO scheme on an adaptive mesh based on the open source program Adaptive Mesh Refinement in Object-oriented C++ (AMROC). The numerical results show that there are two sets of transverse waves, the left-running transverse waves (LRTW) and the right-running transverse waves (RRTW), which form the oblique cellular detonation structure. Although both sets of transverse waves are convected downstream, they propagate at almost the same relative velocity in the opposite direction. The LRTWs start in the transition zone because of the detonation instability. However, the RRTWs form due to the interaction between the deformed detonation front and the reflected shock wave from the wedge. For the same degree of overdrive, numerical simulations reveal that the characteristic cell size of an oblique detonation is almost the same as that of a normal detonation.

Influences of a small obstacle on the sidewall upon a detonation cellular structure

Influences of a small obstacle on the sidewall upon a detonation cellular structure

Isolating gasdynamic and chemical effects on the detonation cellular structure: A combined experimental and computational study

The dependence of detonation cell regularity on mixture gasdynamic and chemical kinetic properties are investigated through hydrogen-oxygen detonations with different diluent and ozone addition. A total of seven mixtures are specifically designed such that the post-shock specific heat ratio γVN, representing the gasdynamic effect, and the effective activation energy ϵi, representing the chemistry effect, can be varied independently among these mixtures. Both experiments and two-dimensional (2D) Navier-Stokes simulations are performed. For the ranges of γVN and ϵi considered, γVN is found to moderately affect cell regularity. For mixtures of relatively large γVN (≥1.3), detonation cells become slightly irregular with decreasing γVN. A clear increase in cell irregularity is found when γVN is small (<1.3). In contrast, the impact of ϵi on cell regularity is more notable: mixtures of large ϵi produce significantly more irregular cells, corresponding to frequent appearances of transverse detonation structures that dominate the global burning behavior. Finally, ozone is qualitatively and quantitatively shown to regulate the detonation structures in both simulations and experiments tested in this study, and results suggest that trace additives that alter the ϵi of a mixture can likely be used to tune the mixture for a desired regularity.

Time-resolved imaging of the cellular structure of methane and natural gas detonations

Time-resolved imaging of the cellular structure of methane and natural gas detonations

Experimental Research on Detonation Cell Size of a Purified Biogas-Oxygen Mixture

Interest in alternative and renewable energy sources has risen significantly in recent years. Biogas is a prime example of a promising, alternative fuel that might be a possible replacement for fossil fuels. It is a mixture consisting mainly of CH4 and CO2 with various additions. Biogas is easily storable and as such is a more reliable and stable source of energy than solar and wind sources, which suffer from unreliability due to their dependence on weather conditions. In this paper, the authors report experimental results of detonation of a biogas-oxygen mixture. The composition of the biogas was 70% CH4 + 30% CO2 and the experiments were carried out for a range of equivalence ratios (Φ = 0.5 ÷ 1.5) and initial pressures (0.6 ÷ 1.6 bar). The aim of the research was to analyze the cellular structure of detonation. The soot foil technique was used to determine the width of the detonation cells (λ). The conducted experiments and subsequent analysis of the detonation cell size confirm that both the increase in the initial pressure of the mixture or move away from stoichiometric (Φ = 1) composition is accompanied by a decrease in the width of the detonation cell. The authors also argue that due to the unstable cellular structure of the detonation, it is insufficient to report only the average cell size. Instead, the researchers propose more detailed statistical description assured values.

Numerical simulation of two-dimensional detonation propagation in partially pre-vaporized n-heptane sprays

In this paper, two dimensional detonation propagation in partially prevaporized n-heptane sprays is studied by using Eulerian/Lagrangian methods. The effects of droplet preevaporation on the detonation propagation are investigated. The general features and detailed structures of two-phase detonations are well captured with the present numerical methods. The results show that the detonation propagation speed and detonation structures are significantly affected by the preevaporated gas equivalence ratio. The numerical soot foils are used to characterize the influence of preevaporated gas equivalence ratio on the detonation propagation. Regular detonation cellular structures are observed for large preevaporated gas equivalence ratios, but when decreasing the preevaporated gas equivalence ratio, the detonation cellular structures become much more unstable and the average cell width also increases. It is also found that the preevaporated gas equivalence ratio has little effects on the volume averaged heat release when the detonation propagates stably. Moreover, the results also suggest that the detonation can propagate in the two-phase heptane and air mixture without preevaporation, but the detonation would be first quenched and then re-ignited when the preevaporated gas equivalence ratio is small or equal to zero.

Detonation propagation through a nonuniform layer of hydrogen-oxygen in a narrow channel

Experiments were carried out to study detonation propagation through a nonuniform layer of stoichiometric hydrogen-oxygen in a narrow channel. Premixed stoichiometric hydrogen-oxygen was injected through a series of 1.3 mm diameter, 4.8 mm spaced holes into a 7 mm wide optically accessible channel initially filled with an inert gas. A Chapman-Jouguet detonation wave was transmitted into the test section from a pre-detonator of equal height. The height of the layer was varied by changing the time of hydrogen-oxygen injection relative to the arrival-time of the detonation wave. Schlieren photography was used to record the progression of the detonation wave. Soot foils mounted to the back window, were used to record the detonation cellular structure and visualization of the soot incandescence provided tracking of the reaction zone. With the channel initially filled with argon, detonation propagation was only possible when the layer height accommodated at least 8–11 detonation cells. Detonation propagation was not possible when the channel initially contained nitrogen, or carbon dioxide, indicating strong mixing with the injected premixed hydrogen-oxygen. Numerical simulations confirmed the strong mixing between the injected premixed hydrogen-oxygen with the prefilled inert gas. The simplified mixing condition, i.e., injection of premixed hydrogen-oxygen, provides a unique data set for numerical code validation and verification for a linear RDE geometry.

A chemical-diffusive model for simulating detonative combustion with constrained detonation cell sizes

This paper presents a way that improves the use of the chemical-diffusive model (CDM) in a fluid dynamics code to simulate the multidimensional structure of propagating gaseous detonation waves. In the CDM, a set of critical parameters is calibrated and used in a reaction rate that converts fuel to product. The parameters are currently chosen to reproduce properties of a one-dimensional standard laminar flame and the Zel’dovich-Neumann-Döring (ZND) detonation when a reaction is incorporated in the compressible Navier-Stokes equations. The ability of the CDM to compute cellular structure of stoichiometric hydrogen-air detonations is compared to results obtained using a detailed chemistry model and experimental measurements. Both the CDM and the detailed chemical model produce very similar detonation cells in terms of shape and size, but these cells are smaller than experimental values by a factor of two to three. In a new approach, the CDM is calibrated using experimental detonation cell data. A relation between the effective activation energy and the ratio of the detonation cell size to the ZND half-reaction distance is used to incorporate known properties of detonation and detonation cells in the CDM optimization procedure. Numerical simulations using the new CDM parameters reproduce detonation cells of the same size and shape as experimental measurement.

Propagation behavior of rotating detonation waves with premixed kerosene/air mixtures

The propagation of multiple detonation waves in the two-dimensional modeled rotating detonation combustor fueled by premixed kerosene/air mixtures is numerically investigated with a reduced two-step global chemical mechanism. Discrete fuel injection model is adopted to simulate the discontinuous distribution of reactants in Rotating Detonation Engine (RDE) experiments. A parameter inlet-area ratio (ψ) is proposed to obtain the reactants with different dispersion degree. This work focuses on the effect of discontinuous reactants on detonation cells and overall flow-field structure of rotating detonation waves. The results show that with full-area injection model (ψ=1.0), the reactants distribute continuously in triangular gas layers. Rotating detonation waves propagate stably with regular detonation cellular structure. When ψ is less than 1.0, the injection reactants are distributed in strips. At the position far away from the head-end wall of combustor, the fresh reactants and combustion products are mixing with each other which causes the deflagration zones in triangle gas layers. The reactants remaining after deflagration process in deflagration zones cannot support the propagation of detonation leading to the partially decouple of detonation front. The large area of deflagration zones distorts the flow-field structure and reduces the propulsion performance of combustor.

The influence of the equation of state on the cellular structure of gaseous detonations

The propagation of multidimensional gaseous detonations at elevated pressures was investigated numerically. Initial conditions at which deviations from ideal gas are expected (i.e., p0 &amp;gt; 2 MPa) were used to assess whether real gas effects influence their multi-cellular structure. The simplest equation of state that accounts for real gas effects was selected, Noble–Abel, and compared with the results obtained using perfect gas. Approximate and exact relationships are provided for the von-Neumann and Chapman–Jouguet states, as well as sound speeds, for both equations of state. Results show that real gas effects alter the multi-cellular structure of gaseous detonations at elevated pressures. Moreover, neglecting these effects renders a more irregular structure than that obtained when real gas effects are reinstated. The source of the perceived instabilities was identified as a Mach bifurcation due to jetting and their growth was related to a shear layer triple point interaction, giving birth to new triple points. The more unstable structure seems to arise from an effective change in the isentropic coefficient that is not included in the perfect gas formulation.

Velocity fluctuation and cellular structure of near-limit detonations in rough tubes

Detonation limits are characterized by a decrease in the propagation velocity, cellular structures to lower unstable modes and an increase in the velocity fluctuation of the detonation. The increase in the average velocity deficit as the limits are approached is not a sensitive change since the failure of the detonation can occur at a relatively small velocity deficit of the order of 20%. A more sensitive indication of the onset of detonation limits is the lowering of the unstable mode (i.e., towards single-headed spin) and the large longitudinal fluctuation of the detonation velocity. In this paper, recent results are reported for the aforementioned near-limit detonation characteristics for a number of detonable mixtures and tube diameters for both smooth and rough tubes. Mixtures include H2, C2H2, C3H8, CH4 fuels with both O2 or N2O as oxidizers. Tube diameters were 25.4 mm, 38.1 mm, 50.8 mm and 76.2 mm. To investigate the effect of wall roughness on the limits phenomena in tubes, wire spirals with different diameters were inserted into the different diameter test tubes. Regularly spaced photodiodes (IF-950C) along the tube were used for velocity measurements and smoked mylar foils were inserted into the tube for the measurement of the cellular structure. Results confirm that the cellular structure evolution towards the lower unstable modes follows well the observed increase in velocity fluctuation; the subsequent detonation failure defined by the absence of cells occurs also at high-velocity fluctuation and an abrupt increase in the average velocity deficit.

Viscous jetting and Mach stem bifurcation in shock reflections: experiments and simulations

Abstract

Effect of boundary layer losses on 2D detonation cellular structures

We evaluate the effect of boundary layer losses on two-dimensional H2/O2/Ar cellular detonations obtained in narrow channels. The experiments provide the details of the cellular structure and the detonation speed deficits from the ideal CJ speed. We model the effect of the boundary layer losses by incorporating the flow divergence in the third dimension due to the negative boundary layer displacement thickness, modeled using Mirels’ theory. The cellular structures obtained numerically with the resulting quasi-2D formulation of the reactive Euler equations with two-step chain-branching chemistry are found in excellent agreement with experiment, both in terms of cell dynamics and velocity deficits, provided the boundary layer constant of Mirels is modified by a factor of 2. A significant increase in the cell size is found with increasing velocity deficit. This is found to be very well captured by the induction zone increase in slower detonations due to the lower temperatures in the induction zone.