Shock-flame Interaction Research Articles

Deflagration-to-detonation transition and detonation propagation in supersonic flows with hydrogen injection and downstream ignition

This study investigates the mechanisms of flame acceleration and deflagration-to-detonation transition (DDT) in supersonic flows using transverse hydrogen injection and downstream ignition. Utilizing the graphics processing unit accelerated adaptive mesh refinement approach, we examine the influence of downstream ignition jet pressure on DDT through high-resolution computational simulations. Our results indicate that the transverse injection of hydrogen into the supersonic mainstream generates strong turbulence and numerous vortices due to Kelvin–Helmholtz instability, enhancing fuel mixing efficiency along the flow but deviating from the ideal premixed state. Following the injection of the downstream ignition jet into the supersonic main flow, initial flame acceleration is less effective than in the premixed state due to the non-uniformity of the incoming flow. However, within the boundary layer, the flame remains stable, and the intense turbulence fosters shock–flame interactions. The convergence of multiple compression waves into a shock wave facilitates energy deposition, coupling with the flame to trigger local detonation via the reactive gradient mechanism. The detonation wave exhibits complex wavefront structures, including vertical and oblique fronts induced by boundary layer interactions. Ignition jet pressure significantly impacts the DDT process and detonation wave characteristics, reducing ignition time and affecting the detonation temperature, pressure, and propagation speed. This study provides valuable insights into the dynamics of flame acceleration and DDT in supersonic flows with non-uniform fuel distribution and downstream jet ignition. The findings highlight the critical role of ignition jet pressure in optimizing ignition and detonation processes, offering new perspectives for achieving low-energy, rapid detonation initiation within the tube.

Three-dimensional shock–flame interactions: effect of wall friction

Multi-dimensional numerical simulations were performed to study the interactions between shock wave and premixed flame. The three-dimensional (3D) fully-compressible, reactive Navier–Stokes equations were solved using a high-order numerical method on a dynamically adapting mesh. The effect of wall friction on the shock–flame interaction was examined by varying wall boundary condition on sidewall. The simulations agree with previous experiment in terms of flame perturbation and flame evolution. The results show two effects of wall friction on flame–shock interaction: (1) flame stretching and (2) damping of local flame perturbation very close to the no-slip wall. The stretch effect leads to non-uniform development of the perturbated flame and consequently a significantly higher growth rate in both global flame perturbation and averaged pressure in the no-slip case compared to the free-slip case. By contrast, the damping effect locally moderates the flame perturbation in close proximity to the no-slip wall because less vorticity is deposited on this part of flame during shock–flame interaction. Quantitative analysis of vortex dynamics suggests that vorticity generation that is produced by baroclinic torque and enhanced by the dilation term during shock–flame interaction causes a growth of flame perturbation via Richtmyer–Meshkov instability. Nevertheless, the vorticity generation is greatly weakened in close proximity to the no-slip wall by the viscous torque and viscous dissipation terms due to friction.

Numerical study on the deflagration to detonation transition promoted by transverse jet

To reveal the mechanism of deflagration to detonation transition promoted by transverse jet, the flame acceleration and detonation initiation process of H2/Air under transverse jet was numerically investigated. According to the flame propagation characteristics and the main factors that promote flame acceleration in different periods, the process of deflagration to detonation transition was divided into four stages: initial flame development stage, turbulence-flame interaction stage, shock-flame interaction stage, detonation initiation stage. The flame acceleration process of each stage was analyzed in detail. The results indicated that the curling and stretching effect of the transverse jet and vortexes on the flame can effectively increase the flame velocity. The flame would constantly produce compression waves during acceleration. The transverse wave formed by the superposition of the compression waves would be reflected multiple times between the walls and act on the flame front, which is critical for flame acceleration. In addition, the positive feedback between the leading shock wave and the flame was also important for the continuous increase of flame velocity.

Influence of longitudinal obstacle spacing on the deflagration-to-detonation transition through a bank of obstacles in a hydrogen-air mixture

Flame acceleration and deflagration-to-detonation transition (DDT) in a channel containing an array of staggered cylindrical obstacles and a stoichiometric hydrogen-air mixture were studied by solving the fully-compressible reactive Navier-Stokes equations using a high-order numerical algorithm and adaptive mesh refinement. Four different longitudinal spacings (ls) of the neighboring obstacle rows (i.e., ls = 15.28, 19.1, 25.4, and 38.2 mm, corresponding to 1.2, 1.5, 2 and 3 times of obstacle diameter, respectively) were used to examine the effect of obstacle spacing on flame acceleration and DDT. The results show that the main mechanisms of flame acceleration and transition to detonation in all the cases studied are consistent. While the flame acceleration is caused by the growth of flame surface area in the initial stage, it is governed by shock-flame interactions in the later stage when shock waves are generated. The focusing of strong shocks at flame front is responsible for the initiation of detonation. It was found that the flame propagation speed and the DDT run-up distance and time are highly dependent on ls. Specifically, the flame acceleration declines as ls increases, since a larger ls leads to less disturbance of flow by obstacles per unit channel length. For detonation initiation, both the run-up distance and time increase with the increase of ls. It is interesting to note that the DDT distance and time increase significantly as ls increases from 19.1 mm to 25.4 mm. This is related to the slowdown of the increase rate of energy release over a period before DDT occurs under large ls condition, because every time the flame passes over an obstacle row the shock-flame interaction is delayed and numerous isolated pockets of unburned gas material are formed.

Flame acceleration and transition to detonation in a pre-/main-chamber combustion system

Numerical simulations are performed to study the mechanism of deflagration to detonation transition (DDT) in a pre-/main-chamber combustion system with a stoichiometric ethylene–oxygen mixture. A Godunov algorithm, fifth-order in space, and third-order in time, is used to solve the fully compressible Navier–Stokes equations on a dynamically adapting mesh. A single-step, calibrated chemical diffusive model described by Arrhenius kinetics is used for energy release and conservation between the fuel and the product. The two-dimensional simulation shows that a laminar flame grows in the pre-chamber and then develops into a jet flame as it passes through the orifice. A strong shock forms immediately ahead of the flame, reflecting off the walls and interacting with the flame front. The shock–flame interactions are crucial for the development of flame instabilities, which trigger the subsequent flame development. The DDT arises due to a shock-focusing mechanism, where multiple shocks collide at the flame front. A chemical explosive mode analysis (CEMA) criterion is developed to study the DDT ignition mode. Preliminary one-dimensional computations for a laminar propagating flame, a fast flame deflagration, and a Chapman–Jouguet detonation are conducted to demonstrate the validity of CEMA on the chemical-diffusive model, as well as to determine the proper conditioning value for CEMA diagnostic. The two-dimensional analysis with CEMA indicates that the DDT initiated by the shock-focusing mechanism can form a strong thermal expansion region at the flame front that features large positive eigenvalues for the chemical explosive mode and dominance of the local autoignition mode. Thus, the CEMA criterion proposed in this study provides a robust diagnostic for identifying autoignition-supported DDT, of which the emergence of excessive local autoignition mode is found to be a precursor. The effect of grid size, initial temperature, and orifice size are then evaluated, and results show that although the close-chamber DDT is highly stochastic, the detonation initiation mechanism remains robust.

Effect of shock-flame interactions on initial damage characteristics in highway tunnel under hazmat tanker truck accident

Hazardous materials road transportation (HMRT) accidents are the main hazards of highway tunnels, and the damage evolution process subject to catastrophic consequences have gained significance due to increasing accidental events. This study presents the scene reconstruction referenced with actual case of methanol tanker truck explosion in highway tunnel and integrates it with effecting parameters such as location, causation, consequence, time series data, tunnel structure, hazmat properties, emergency. In this work, the damage characteristics caused by tanker truck explosion are discussed by comparing with different traffic situations inside the highway tunnel. The results indicate the strength of shock wave is enhanced as the traffic flow grows, especially in the ceiling and ground of tunnel, the peak overpressures are significantly higher than that in other areas. With the increasing of the traffic vehicles in tunnel, the process of the explosion overpressure changing in tunnel can be categorized in five stages. This study presents the predictive model relating with explosion specific impulse, which can be better presented in impulse changes in tunnel with the minimum degree of fitting is 0.9139. By comparison between different traffic situations in tunnel, it reveals the formation of precursor shock wave enhances the flame propagation, and the accelerated flame in turn strengthens the overpressure, indicating the underlying damage mechanism. This study contributes to better understanding multi-factor damage mechanism of HMRT accident in highway tunnel, and further optimizing HRMT accident detections and emergency plans.

Flame Acceleration and DDT in a Channel with Continuous Triangular Obstacles: Effect of Blockage Ratio

ABSTRACT Experiments were conducted in a stoichiometric hydrogen-oxygen mixture at initial pressure of 1 atm to study the flame acceleration and deflagration-to-detonation transition (DDT) in a 20 mm high channel equipped with continuous triangular obstacles. Effect of blockage ratio (br) was explored by considering different obstacle heights of 0, 1 mm, 3 mm, 5 mm, and 7 mm, corresponding to br = 0, 0.1, 0.3, 0.5, and 0.7, respectively. High-speed schlieren photography and OH* chemiluminescence recording were used to visualize the processes. Results show that blockage ratio has a significant effect on the scales and velocities of the vortices generated in the gaps between neighboring obstacles and consequently on the subsequent flame-vortex interactions. Higher br leads to faster flame acceleration via stronger flame-vortex interactions. The intricate shock-flame interactions cause successive local explosions in the br = 0.3, 0.5, and 0.7 cases, creating conditions for DDT. An eventual choking regime occurs in the br = 0.7 case due to energy losses by continuous diffractions at the obstacle vertices. It was found that the onset of DDT is triggered when the critical height of the unobstructed passage is approximately greater than three detonation cell sizes. The mechanism of DDT changes as the br decreases. One important feature observed is that the br = 0.1 case has the shortest DDT distance. In addition, the final flame speed (~740 m/s, 1.4 times unburned sound speed) before DDT for br = 0.1 is significantly smaller than those (~1300 m/s, 2.4 times unburned sound speed) for br ≥ 0.3. The reason is that the low obstacles retain the characteristics of the obstacle, while mimicking the wall roughness, resulting in both shock compression of unburned gas and viscous heating in the boundary layer ahead of the flame front. The combined effects promote the occurrence of DDT for the case with br = 0.1.

Topologies of flow and combustion in shock–flame interactions

Topologies of flow and combustion in shock–flame interactions

Numerical investigation on reacting shock-bubble interaction at a low Mach limit

We investigate the deflagration combustion in the reacting shock-bubble interaction at M = 1.34 using a novel adaptive mesh refinement combustion solver with comprehensive H2/O2 chemistry. The numerical results are compared with an experiment by Haehn et al [1]. The Richtmyer-Meshkov instability dominates the shock-bubble interaction, and the shock focusing in the heavy bubble induces ignition. By following the initial experimental setup published by Haehn et al [1]. and adopting the axisymmetric assumption, we successfully reproduce most of the flow features observed in the experiment both qualitatively and quantitatively, including the bubble morphology evolution and the corresponding chemiluminescence images. The fuel consumption rate is nonmonotonic because of unsteady flame propagation, and it also depends on interfacial instabilities. The deflagration waves increase transverse bubble diameter, mildly decrease the total vorticity, and promote mixing by more than 150% because of the thermal effects. The mixing promotion is approximately 88% related to the diffusivity and 12% related to other mechanisms after ignition. A new shock focusing mechanism is observed due to the secondary refracted shock. During shock focusing, Mach reflection occurs and transits from the bifurcated type to the single type. This transition causes two ignitions: the first occurs in the spiral hot spot entrained by the jet vortex, and the second arises from the hot spot caused by the triple point collision. After the second ignition, the newborn flame is a deflagration at the beginning but is unstable and tends to transit to a detonation as a consequence of shock-flame interactions. Nevertheless, the deflagration-to-detonation transition fails, and the stable combustion mode is deflagration.

Large eddy simulation of a supersonic lifted hydrogen flame with sparse-Lagrangian multiple mapping conditioning approach

The Multiple Mapping Conditioning / Large Eddy Simulation (MMC-LES) approach is used to simulate a supersonic lifted hydrogen jet flame, which features shock-induced autoignition, shock-flame interaction, lifted flame stabilization, and finite-rate chemistry effects. The shocks and expansion waves, shock-reaction interactions and overall flame characteristics are accurately reproduced by the model. Predictions are compared with the detailed experimental data for the mean axial velocity, mean and root-mean-square temperature, species mole fractions, and mixture fraction at various locations. The predicted and experimentally observed flame structures are compared through scatter plots of species mole fractions and temperature against mixture fraction. Unlike most past MMC-LES which has been applied to low-Mach flames, in this supersonic flame case pressure work and viscous heating are included in the stochastic FDF equations. Analysis indicates that the pressure work plays an important role in autoignition induction and flame stabilization, whereas viscous heating is only significant in shear layers (but still negligibly small compared to the pressure work). The evolutions of particle information subject to local gas dynamics are extracted through trajectory analysis on representative fuel and oxidizer particles. The particles intermittently enter the extinction region and may be deviated from the full burning or mixing lines under the effects of shocks, expansion waves and viscous heating. The chemical explosive mode analysis performed on the Lagrangian particles shows that temperature, the H and OH radicals contribute dominantly to CEM respectively in the central fuel jet, fuel-rich and fuel-lean sides. The pronounced particle Damköhler numbers first occur in the fuel jet / coflow shear layer, enhanced at the first shock intersection point and peak around the flame stabilization point.

Addressing the complex geometric effects on the three-dimensional transition to detonation in hydrocarbon-air mixtures using a parametrized level-set algorithm

A new level-set algorithm is developed that distinguishes the interior from the exterior of complex geometry by parameterizing the correlation between the stereolithography (STL) information and grid points in order to embody three-dimensional boundary interfaces in the Cartesian coordinate system. The method is applied to the flame and shock wave interactions in hydrocarbon fuel blends including the transition to a detonation in various three-dimensional geometric complexities for predicting the maximum chamber pressure. The locations of the strong shock-flame interactions and the onset of the hot spot initiation in the regions of the strongest interaction are investigated. Moreover, the study is intended for providing safety assessments of the pressure confinements that include bends, steps, and narrow channels connecting cavities by utilizing the present algorithm that can identify the triggering effects of the transition to detonation.

Cumulative energy effect in the shock-discontinuity interaction under real-gas conditions

A recently proposed technique for improving ignition timing is investigated for real-gas effects. A correction to the model describing the cumulative energy effect in the presence of the shock-discontinuity interaction was done by re-considering the Rankine–Hugoniot relations and the shock refraction equations. Non-dissociating gas in thermal equilibrium state, with excited translational, rotational, vibrational, and electronic degrees of freedom is considered. When applied to N2 gas at T = 3000 K, 11% density increase and 17% temperature and 7% pressure jump decrease were found, compared to that in ideal gas. The derived relations are largely built on experimental data thus avoiding the complexity of careful accounting for all real gas effects and still offering satisfactory precision levels. The main result is that in real gases the effect in the interaction can be stronger than that in an ideal gas. The findings can be of interest in design of efficient combustors for hypersonic systems, detonation, space and craft design, shock-flame interaction, in astrophysics, and fusion research.

Influence of thermal radiation on layered dust explosions

Multidimensional unsteady numerical simulations were carried out to explore the influence of thermal radiation on the propagation and structure of layered coal dust explosions. The simulation solved the reactive compressible Navier-Stokes equations coupled to an Eulerian kinetic-theory-based granular multiphase model. The radiation heat transfer is modeled by solving the radiation transfer equation using the third-order filtered spherical harmonics approximation. The radiation was assumed to be gray and all boundaries of the domain are black at 300 K. The reaction mechanism is based on global irreversible reactions for each physical process including devolatilization, char burning, moisture vaporization, and methane combustion. The governing equations were solved using a high-order Godunov method. Several simulation configurations were considered: layer volume fractions of 47% and 1%, channel lengths of 10 m and 40 m, and radiative and non-radiative cases. The results show that gray radiation has a significant influence on the propagation and structure of a layered dust explosion. However, radiation can have opposite effects on different scenarios. For example, radiation promotes the propagation of the dust flame when the layer volume fraction was 1% and in the short-channel cases where reflected shock-flame interactions are important. However, radiation enhances quenching for the 47% volume fraction dust layer in the longer channel.

Vortex dynamics and fractal structures in reactive and nonreactive Richtmyer–Meshkov instability

Hydrodynamic instabilities caused by shock-flame interactions are a fundamental challenge in the accurate prediction of explosion loads in the context of nuclear and process plant safety. To investigate the Richtmyer–Meshkov instability, a series of three-dimensional numerical simulations of shock-flame interactions are performed, including lean, stoichiometric, and nonreactive homogeneous H2/Air mixtures. The equivalence ratio has a strong influence on the achievable flame wrinkling and mixing, by impacting key physical parameters such as the heat release parameter, flame thickness, and reactivity. The reactivity is found to be a decisive factor in the evolution of the wrinkled flame brush, as it can cause burnout of the developing fresh gas cusps and wrinkled structures. The importance of reactivity is further emphasized by comparisons to a nonreactive case. Analysis of the enstrophy (energy equivalent of vorticity) transport terms shows that baroclinic torque is dominant during shock-flame interactions. After the shock interaction, the vortex stretching, dissipation, and dilatation terms gain in importance significantly. A power-law based modeling approach of the flame wrinkling is investigated by explicitly filtering the present simulation data. The values determined for the fractal dimension show a nonlinear dependency on the chosen equivalence ratio, whereas the inner cutoff scale is found to be approximately independent of the equivalence ratio for the investigated cases.

Enhanced DDT mechanism from shock-flame interactions in thin channels

We show experimentally and numerically that when a weak shock interacts with a finger flame in a narrow channel, an extremely efficient mechanism for deflagration to detonation transition occurs. This is demonstrated in a 19-mm-thick channel in hydrogen-air mixtures at pressures below 0.2 atm and weak shocks of Mach numbers 1.5 to 2. The mechanism relies primarily on the straining of the flame shape into an elongated alligator flame maintained by the anchoring mechanism of Gamezo in a bifurcated lambda shock due to boundary layers. The mechanism can increase the flame surface area by more than two orders of magnitude without any turbulence on the flame time scale. The resulting alligator-shaped flame is shown to saturate near the Chapman–Jouguet condition and further slowly accelerate until its burning velocity reaches the sound speed in the shocked unburned gas. At this state, the lead shock and further adiabatic compression of the gas in the induction zone gives rise to auto-ignition and very rapid transition to detonation through merging of numerous spontaneous flames from ignition spots. The entire acceleration can occur on a time scale comparable to the laminar flame time.

Modeling the amplitude growth of Richtmyer–Meshkov instability in shock–flame interactions

This paper discusses the shock–flame interactions and the aspects associated with it, including the types of interactions, role of interactions in turbulent flames, high pressure generation during interactions, initial pressure effects on interactions, equivalence ratio effects on turbulent interactions, and the Richtmyer–Meshkov instability (RMI). In particular, the theory of RMI and the models associated with its amplitude growth with time have been discussed. Then, a new analytical model, Al-Thehabey model, is presented based on the impulsive acceleration of Richtmyer, not the gravitational acceleration. This model predicts the amplitude growth of the interface perturbation in terms of Atwood number (A), wave number of the perturbation (k), interface velocity (uc), and time (t). This new model’s prediction of the amplitude growth of the RMI is tested on six different combinations of fluids at different interface velocities. The results of the new model are compared with the results of four other existing analytical models and the new model’s performance fared very well. In addition, the new model’s performance has been compared with the experimental results from a shock wave incident on CO2–air, at Mach number, M = 3.08, interface velocity, u = 699.1 m/s, Atwood number, A = 0.206, and wavelength, λ = 990.0 × 10−6 m. The new model showed much closer results with the experimental ones than all other models used in the evaluation. The advantage of this new model is that it is capable of predicting the amplitude growth for both linear, at the early stages of the instability, and non-linear later regimes of the instability. In addition, it covers a larger time-domain than both the Alon et al. and the Sadot et al. models.

Numerical study of premixed flame dynamics in a closed tube: Effect of wall boundary condition

Numerical simulations were conducted to study the dynamics of premixed flames propagating in a closed tube by solving the fully compressible reactive Navier–Stokes equations using a high-order numerical method on a dynamically adapting grid. A simplified chemical-diffusive model was used to describe the reactions and energy release in a stoichiometric hydrogen-air mixture. The influence of wall boundary condition on the flame dynamics was explored by considering three different types of condition on the walls: adiabatic no-slip, adiabatic free-slip, and isothermal. The calculations show that the wall boundary condition has a significant effect on the generation and amplification of pressure waves and consequently on the flame dynamics. In the early stages of flame propagation, the flame behaves in a similar manner for different boundary conditions, that is, the flame develops a tulip shape that further evolves into a distorted tulip flame (DTF) through Rayleigh-Taylor instability arising from acoustic-flame interaction. Significant differences, however, arise after DTF formation in the late stages, especially when the primary acoustic wave is amplified to form a shock wave in the adiabatic free-slip and isothermal cases. The shock-flame interactions facilitate the formation of a series of increasingly corrugated flames by triggering the Richtmyer–Meshkov instabilities. The way how the lateral flame fronts touch the tube sidewalls to generate the primary acoustics and the heat conduction through the tube sidewalls play an important role in the generation and amplification of the pressure waves.

Effect of the plasma location on the deflagration-to-detonation transition of a hydrogen–air flame enhanced by nanosecond repetitively pulsed discharges

This work presents a method for using nanosecond repetitively pulsed (NRP) plasma discharges for accelerating a propagating flame such that the deflagration-to-detonation transition occurs. A strategy is developed for bringing the location of the plasma near the tube wall and, thus, reducing the presence of the electrodes in the combustion tube as well as presenting a configuration in which cooling of the electrodes is viable for practical applications. Time-of-flight measurements were used in combination with energy deposition measurements and high-speed OH*-chemiluminescence imagery to investigate the flame acceleration process. For stoichiometric hydrogen–air flames, successful transition to detonation was achieved by applying a burst of 110 pulses at 100 kHz, with energies as low as 10 mJ per pulse. This was also achieved when plasma discharges were applied in the vicinity of the wall. Two enhancement mechanisms for flame acceleration were identified. The essential role of shock–flame interaction was established as being the main mechanism for flame acceleration when the discharges are located near the wall. This work presents an effective alternative that allows for NRP discharges to be applied near the wall while successfully maintaining a promising success rate for detonation transition.

Cavity flameholding subjected to an expansion fan in a rocket-based combined cycle combustor

The effect of expansion fan on cavity flameholding was investigated in a rocket-based combined cycle combustor fueled by ethylene. The inflow of the combustor was at a condition where the Mach number, stagnation temperature, and total pressure were 2.92, 1650 K, and 2.6 MPa, respectively. The global equivalence ratio was 0.25. A backward-facing step (BFS) was used to simulate a rocket that was shut down and create an expansion fan. The dimensionless distance between the BFS and the cavity (d/H) varied from 1.5 to 7.5, where d = 60–300 mm was the actual distance and H = 40 mm was the height of the combustor entrance. The result indicated that the cavity shear layer reattached at the cavity floor in the combustor with 2.5 ≤d/H≤ 3.5 because of the pressure gradient resulting from the expansion fan. The expansion fan also significantly decreased the static pressure in the cavity. As a consequence, the combustor with 2.5 ≤d/H≤ 3.5 failed in ignition. In the combustors with d/H = 4.0 and 6.0, the cavity flows were open-type. However, the ignition attempt failed because the expansion fan and the reattachment shock wave might worsen the local equivalence ratio in the cavity. Successful ignition and flame stabilization were achieved in the combustors with d/H = 1.5, 2.0, 4.5, and 7.5. Three combustion modes and three kinds of combustion oscillation were identified. In the combustor with d/H = 1.5, only a small part of the cavity was exposed to the expansion fan. The combustor operated in the cavity stabilized scramjet mode because the flame front was anchored at the cavity leading edge. The cavity shear layer impingement onto the cavity ramp lead to the combustion oscillation with a frequency ranging from 300 to 400 Hz. The combustion mode and combustion oscillation in the combustor with d/H = 2.0 were the same as their counterparts in the combustor with d/H = 1.5. Unsteady jet-wake stabilized scramjet mode was witnessed in the combustor with d/H = 4.5. In this combustor, the fuel jet and the front of the cavity were exposed to the expansion fan. The reattachment shock wave lifted the cavity shear layer. The combustion oscillation induced by shock-flame interaction showed a dominant frequency at 107.1 Hz. The expansion fan and the reattachment shock wave were upstream of the cavity in the combustor with d/H = 7.5. Both of them made the boundary layer more sensitive to adverse pressure gradient. The flame front was upstream of the cavity because the heat release resulting from vigorous chemical reaction choked the combustor and induced large-scale boundary layer separation. The combustor operated in ramjet mode. The unsteady shock train and thermal throat induced the combustion oscillation with a frequency of approximately 800 Hz.

Effect of Metal Foam Mesh on Flame Propagation of Biomass-Derived Gas in a Half-Open Duct.

The effect of metal foam mesh on flame propagation of biomass-derived gas in a half-open duct was studied. The explanations are based essentially on the experimental investigations of premixed biomass-derived gas explosions carried out in a rectangular half-open combustion chamber. The initial temperature T0 and pressure P0 were 300 K and 1.0 atm, respectively. The key parameters of explosive characteristics, such as flame propagation images and explosive overpressure, were analyzed by changing the porosity, the pore density of porous metal foams, and the gas components. The results show that the use of porous metal foam has a significant inhibitory effect on the gas explosion. Although the combustion structure of the flames is similar, the action of the porous metal foam during the experiment also shows the characteristics consistent with the obstacles. When the porosity of the porous foam is 97%, the flame can be stimulated to produce turbulence, and then the shock–flame interaction generated by the reflection of the lead shock wave can enhance the explosion propagation and promote the explosion escalation. However, with the increase of hole density, the existence of the porous metal foam by momentum loss and heat loss to curb the spread of the explosion not only hindered the flow of not flammable but also extracted energy from the expansion of the combustion products at the same time. This study also confirms that the biological hydrogen and methane component has a vital role in the flame, and a reasonable hydrogen and methane ratio can improve the flame burning to get more economic value.