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Lifted multi-jet flames of hydrogen and steam-diluted oxygen are studied using direct numerical simulations (DNS). The DNSs have been carried out for laminar and turbulent flame configurations. The simulation data are analyzed to investigate the flame and flame-base structures and the flame-base propagation in a configuration akin to a gas turbine with multiple fuel jets. The laminar flames have a tribrachial structure, although lean premixed and diffusi on flame branches collide downstream owing to preferential diffusion. The turbulent multi-jet flames have a single connected base region, whereas the laminar flames have separate bases, each of which is associated with the corresponding fuel jet. Although turbulent multi-jet flames have substantially different flame-base characteristics from laminar multi-jet flames (and conventional single-jet lifted flames), the propagation speed is similar for both conditions. The results suggest that the well-known flame-base stabilization theory can be straightforwardly applied to the multi-jet configuration, despite the turbulent flame structure's unconventional features. [ABSTRACT FROM AUTHOR]

In order to seek a better inhibitor to suppress the explosion of lycopodium powder, this paper used Hartmann experimental system and 20 L spherical explosion experimental system to conduct the flame propagation and explosion pressure suppression experiments of lycopodium powder explosion, respectively, to study the suppression effect of lycopodium powder explosion under the conditions of adding different proportions of montmorillonite powder and hydroxy modified montmorillonite powder, combined with the FTIR curves before and after the explosion of lycopodium powder as well as the reaction involving it and inhibitors, the inhibition mechanism of montmorillonite powder and hydroxy- montmorillonite powder on the explosion of lycopodium powder was analyzed. The experimental results show that: with the increase of the addition ratio of the two inhibitor powder, the flame brightness becomes darker, the flame propagation speed gradually decreases, and the maximum explosion pressure and the maximum explosion pressure change rate gradually decreases. By the analysis of inhibition mechanism: montmorillonite powder blocks and absorbs thermal radiation and has basically no chemical inhibition effect whose inhibition effect is relatively weak; hydroxy-montmorillonite powder in addition to the basic physical inhibition with montmorillonite powder, but also decomposition at high temperatures to generate a large number of hydroxyl radicals, the radicals generated can make the reaction of the explosion in the reverse direction, and nearly can block the explosion chain reaction continues, playing a key role in chemical inhibition. Research results show that: montmorillonite powder and hydroxyl modified montmorillonite powder on lycopodium powder explosion have a certain inhibition effect, and modified hydroxyl montmorillonite powder than montmorillonite powder on the lycopodium powder explosion inhibition effect is better. [ABSTRACT FROM AUTHOR]

To further investigate the propagation characteristics of shock waves and flame waves in H‐type tunnel gas explosions, numerical simulation studies were conducted on a dual‐source gas explosion model using Fluent software. Three distinct operational conditions were designed and modeled, leading to the following outcomes. The shock wave flow field parameters from dual sources (with equal source energy) are symmetrically distributed in the H‐type tunnel, with high pressure and low flow velocity in the connecting roadway between the two shock waves. Under different conditions, the pressure is generally higher in closed tunnels (fully closed greater than semi‐closed) and lower in open tunnels. The largest overpressure in non‐explosion areas occurs at the closed ends and in the connecting roadway, while the areas bearing the greatest impulse are the shock wave reflection zones and pressure coupling regions. In closed conditions, the flame wave first moves forward and then propagates backward after the explosion, influenced by reflected waves and pressure differences between the ends and the tunnel. In open conditions, the pressure in the flame zone is lower than at both ends, inhibiting the forward propagation of the flame wave. [ABSTRACT FROM AUTHOR]

To study the flame propagating characteristic and its coupling effect with other parameters in the LPG pipeline, a typical pipeline model with two equal‐length branches perpendicular to each other is designed for experiment and simulation. Then, gas explosion scenarios are experimentally tested and numerically simulated, which is followed by the analysis of flame shape changing with time and peak temperature changing with space. Results show that when passing through the bifurcation, flame propagates to vertical branch B in a sharp knife shape affected by the strong vortex, reflected airflow, and compressed pressure wave in the pipeline with a diameter of 0.125 m. At the monitoring point that is 0.4 m away from the bifurcation point, the peak temperature of the vertical branch B is 57.87% bigger than that of the horizontal branch C, and its arrival time is 80% longer than that of the horizontal branch C, due to the existence of flame in vertical branch B. What's more, in both branches, the coupling results between peak temperature and peak velocity agree very well with the growth function, while the coupling results between peak temperature and peak pressure agree well with the decay function, providing aids to the optimal layout design of industrial pipeline branches as well as to the explosion suppression measures. [ABSTRACT FROM AUTHOR]

This paper is devoted to the numerical analysis of the spontaneous acceleration of a slow flame in a semi-closed channel. In particular, the flow development in the channel ahead of the propagating flame is analyzed. The applied detailed numerical model allows the clear observation of all features intrinsic to the reacting flow evolution in the channel, including the formation of perturbations on the scale of the boundary layer and their further development. In all considered cases, perturbations of the boundary layer emerge in the early stages of flame acceleration and decay afterward. The flow stabilizes more rapidly in a narrow channel, where the velocity profile is close to the Poiseuille profile. At the same time, the compression waves generated in the reaction zone travel along the channel. The interaction between compression waves in the area of combustion products can lead to the formation of shock waves. The effect of shock waves on the flow in the fresh mixture causes an increase in the flame area and a corresponding flame acceleration. In addition, shock waves trigger boundary-layer instability in wide channels. The perturbations of the boundary layer grow and evolve into vortexes, while further vortex–flame interaction leads to significant flame acceleration. [ABSTRACT FROM AUTHOR]

Porous media combustion greatly improves the combustion of low calorific value gas (LCG), and appropriate heat control contributes to optimizing the flame evolution. To obtain the dynamic characteristics of lean‐rich combustion, an enhanced heat‐recirculating burner is built by embedding the cylindrical rod with high thermal conductivity. The temperature distribution and gas products are investigated under different rod parameters and operating conditions. The results indicate that the reduction of the equivalence ratio and inlet velocity are both beneficial for the upstream propagation of rich‐methane flame, which has an opposite trend to lean combustion. Regardless of the direction in which the rich‐methane flame propagates, the flame propagates the fastest as the diameter of the cylindrical rod is 8 mm. When the 8–120 cylindrical rod is embedded in the burner, the downstream propagation time is shortened by 73.40%. The appropriate embedment of the cylindrical rods in porous media not only accelerates the rich‐methane flame propagation but also promotes the conversion of methane to syngas. Moreover, the decrease in pellet diameter is also conducive to increasing syngas production. The above conclusions provide theoretical support for the efficient and clean utilization of LCG in the porous media. [ABSTRACT FROM AUTHOR]

Abstract To further investigate the propagation characteristics of shock waves and flame waves in H‐type tunnel gas explosions, numerical simulation studies were conducted on a dual‐source gas explosion model using Fluent software. Three distinct operational conditions were designed and modeled, leading to the following outcomes. The shock wave flow field parameters from dual sources (with equal source energy) are symmetrically distributed in the H‐type tunnel, with high pressure and low flow velocity in the connecting roadway between the two shock waves. Under different conditions, the pressure is generally higher in closed tunnels (fully closed greater than semi‐closed) and lower in open tunnels. The largest overpressure in non‐explosion areas occurs at the closed ends and in the connecting roadway, while the areas bearing the greatest impulse are the shock wave reflection zones and pressure coupling regions. In closed conditions, the flame wave first moves forward and then propagates backward after the explosion, influenced by reflected waves and pressure differences between the ends and the tunnel. In open conditions, the pressure in the flame zone is lower than at both ends, inhibiting the forward propagation of the flame wave.

Abstract To study the flame propagating characteristic and its coupling effect with other parameters in the LPG pipeline, a typical pipeline model with two equal‐length branches perpendicular to each other is designed for experiment and simulation. Then, gas explosion scenarios are experimentally tested and numerically simulated, which is followed by the analysis of flame shape changing with time and peak temperature changing with space. Results show that when passing through the bifurcation, flame propagates to vertical branch B in a sharp knife shape affected by the strong vortex, reflected airflow, and compressed pressure wave in the pipeline with a diameter of 0.125 m. At the monitoring point that is 0.4 m away from the bifurcation point, the peak temperature of the vertical branch B is 57.87% bigger than that of the horizontal branch C, and its arrival time is 80% longer than that of the horizontal branch C, due to the existence of flame in vertical branch B. What's more, in both branches, the coupling results between peak temperature and peak velocity agree very well with the growth function, while the coupling results between peak temperature and peak pressure agree well with the decay function, providing aids to the optimal layout design of industrial pipeline branches as well as to the explosion suppression measures.

The increasing demand for sustainable and renewable energy sources has prompted extensive research into alternative biomass fuels, particularly in regions like Nigeria, where traditional wood-based fuels are prevalent. A comprehensive experimental analysis of briquettes derived from various wood sources found in Nigeria aims to assess their combustion characteristics and potential as a viable alternative to traditional fuels. The selected wood species include indigenous varieties known for their abundance and accessibility. This study examines the physical and thermal properties of briquettes made from six wood types commonly found in Nigeria: Ayo, Obobo, Obeche, Araba, Afara, and Eku. From the experiment study, the flame propagation rate, afterglow time of the briquettes, calorific value, and heat combustion value 0.72 to 0.73, 408 to 415 sec, 18,745 to 34,857 kJ/kg, and 17079 to 20012 kJ/Kg respectively. The experimental analysis of the briquettes showed that their physical and thermal properties varied, with notable differences in calorific value and propagation rate. The data suggests that the composition and density of wood play a significant role in determining the efficiency and performance of the briquettes. This research addresses the technical aspects of briquette combustion and emphasizes the potential socio-economic and environmental benefits of adopting such alternative fuels. This study's outcomes can guide future initiatives in the quest for cleaner and more sustainable energy practices in Nigeria, aligning with global efforts to mitigate the impact of traditional biomass consumption on the environment and public health.

Gas explosions mostly occur in turbulent environments in practical situations. Meanwhile, the current research on the explosion characteristics of hydrogen-doped natural gas is mostly methane/hydrogen mixed fuel, ignoring the influence of other components of natural gas on the explosion characteristics of the actual situation. Therefore, the effects of different jet intensities (P jet), hydrogen-doping ratios (X H2) and equivalence ratios (φ) on the explosion characteristics of multi-component natural gas/hydrogen mixed fuel are experimentally investigated in cylindrical tanks of 30 L. Additionally, it extensively explored the dual influence of jet disturbance and gas inerting effect on the flame propagation characteristics of multi-component natural gas/hydrogen mixed fuel. With the increase of P jet , both P max and (d p/ d t) max initially increase and then decrease, while τ continuously decreases. When P jet = 0.4 MPa, the promotion effect on P max and (d p/ d t) max is most significant. The lifting of X H2 leads to a gradual increase in P max and decreasing τ. (d p/ d t) max exhibits a trend of initially increasing and then decreasing with the elevation of X H2 , reaching its maximum at X H2 = 40%. The introduction of jet flow significantly reduces the promotion or inhibition effect on explosions of high hydrogen blending ratio mixtures. Furthermore, the introduction of jet flow is more effective in promoting the explosive performance of multi-component natural gas/hydrogen mixed fuel with high equivalence ratios and low hydrogen doping ratios under rich fuel conditions. This study can provide a key reference for the explosion hazard assessment during the practical application of natural gas/hydrogen mixed fuel. • Hydrogen-doped natural gas is used in explosion experiments collected in real environments. • A gas jet disturbance experimental platform has been established. • The flame propagation characteristics under turbulent conditions have been summarized. • The promotion effect on the explosion is most significant when the jet intensity reaches 0.4 MPa. [ABSTRACT FROM AUTHOR]

This experimental study investigated the influence of different turbine guide vane parameters on the ignition limit and light-round processes in a triple-dome combustor. It was found that for the triple-dome combustor, the minimum fuel/air ratios at the ignition limit all show a trend of initial decrease followed by subsequent increase with the growth of incoming air mass flow rate. The ignition fuel/air ratio decreases with the increase in turbine blockage ratio, and the optimal scheme is achieved with a blockage ratio of 0.8. Under the condition where the incoming air mass flow rate is 0.089 kg/s, the light-round time decreases with the increase in fuel/air ratio, and the light-round time of the combustor without guide vanes is shorter than that of the other schemes. With the increase in incoming air mass flow rate, the light-round time of the schemes with guide vanes is shortened. Under the same incoming air mass flow rate and fuel/air ratio, the increase in the blockage ratio will lead to an increase in the light-round time of the triple-dome combustor. [ABSTRACT FROM AUTHOR]

Gas explosion accidents can easily lead to large-scale casualties and economic losses, significantly impeding the urban development. The purpose of this study was to comprehensively review and investigate a significant gas fuel explosion accident in Yinchuan City, China, and to conduct an in-depth discussion on process traceability, failure risk, hazard prevention, and urban development related to the accident. The research found that the accidental failure of double-valve liquefied petroleum gas cylinders and human error were identified as the direct causes of gas leakage. The numerical results indicated that the progression of the accident disaster was chaotic and highly destructive. The maximum explosion overpressure of 92 kPa resulted in severe shock-wave damage to personnel, leading to the complete destruction and collapse of the 0.2 m thick solid brick wall and obstructing the stairway for escape. The rapid change in temperature and oxygen levels caused by the explosion led to the risk of burns and asphyxiation for personnel at the scene. By utilizing the system safety theory, a gas leakage accident control structure system was developed. This system comprised four key levels: the local government, gas management department, gas company, and individual user. The tragedy of 31 deaths was ultimately caused by a serious lack of safety constraints on the behavior of the lower level by the higher level. The research conclusions are of great significance for preventing clean fuel explosion accidents and ensuring sustainable urban development, especially in the face of the negative impact of accidents. [ABSTRACT FROM AUTHOR]

• The flame propagation process of R152a under different RH conditions was recorded • The R152a reaction activation energy is reduced in O 2 and O 2 /H 2 O environments. • OH is the crucial active fragment that promotes the oxidation of R152a. • The combustion mechanism of R152a in humid air was revealed. 1,1-difluoroethane (R152a) is one of the most prospective low GWP refrigerants but may trigger fires and explosions once it leaks. Understanding the flame propagation process and combustion mechanisms at different relative humidity conditions is essential to use flammable refrigerants safely. In this study, a high-speed camera has recorded the flame propagation of R152a combustion near the flammability limit. Combining with macroscopic experimental phenomena, we revealed the effect of H 2 O on the microscopic mechanism of R152a combustion by using reactive force field molecular dynamics simulations with a reliable force field. The promotion effects of H 2 O on the oxidation of R152a were revealed from an atomistic perspective. The differences of oxidation intermediates and products in different environments were analyzed for the first time. The H 2 O/O 2 environment was the most potent promoter of R152a decomposition, followed by the O 2 and the pyrolysis environment. The O 2 /H 2 O environment reduced the apparent activation energy of R152a, significantly enhanced the consumption rate of R152a, and enriched the number of species. O 2 reacts with H 2 O or H to form OH to accelerate the reaction process. The H 2 O could provide more OH active fragments for the reaction. Moreover, it promotes the formation of HF and H 2, H 2 O + F→HF + OH, H 2 O + H→H 2 + HO. This study aims to provide a guiding theory for the safe application and disaster prevention of flammable refrigerants. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xihua University (Natural Science Edition) is the property of Xihua University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using the experimental and large eddy simulation (LES) methods, the impacts of equivalence ratio and adjacent obstacle blockage ratio on flame propagation, flame moving velocity, and explosion overpressure in a closed obstructed duct are investigated. The results indicate that the developed LES method is able to reproduce the tendency of flame propagation, flame moving velocity, and explosion overpressure of BR = 30%, 50%, 70% and BR = 70%, 50%, 30%. The early flame propagation and flame moving velocity are not affected by the first obstacle. As the explosion flame passes through the three obstacles, the flame acceleration and deceleration occur in sequence due to the decreasing cross-section and vortex-flame interaction, eventually forming three ascending peak flame moving velocity. The higher vorticity magnitude of BR = 70%, 50%, 30% and BR = 30%, 50%, 70% is mainly concentrated in the early stage and later stage of hydrogen explosion, which directly results in the fact that the flame acceleration and rise rate of explosion overpressure of BR = 70%, 50%, 30% is higher than that of BR = 30%, 50%, 70%. Additionally, the maximum value of flame moving velocity and explosion overpressure of BR = 30%, 50%, 70% is higher than that of BR = 70%, 50%, 30%. • Flame propagation and explosion overpressure are experimentally obtained. • LES method is established to predict flame propagation and explosion overpressure. • The velocity vectors and vorticity magnitude are analyzed. [ABSTRACT FROM AUTHOR]

The explosion characteristics of AlH 3 dust clouds with varying micron particle sizes are investigated in this paper. The explosion mechanism of AlH 3 dust clouds is initially explored. The results indicate that the activation energy for hydrogen evolution shows an increasing trend with the AlH 3 particle size, and both of these values are comparable to the 30 kJ/mol desorption energy of hydrogen from large AlH 3 clusters. Due to the rapid dehydrogenation rate and small-size residual aluminum core, fine AlH 3 particles exhibit a continuous gas-phase flame and fast propagation velocity. With increasing particle size, the lower dehydrogenation rate, reduced specific surface area, and higher volume heat capacity contribute to a higher level of incomplete reaction. Consequently, large micro-sized AlH 3 particles display a discrete flame, slower flame velocity, and lower explosion pressure. The flame delamination phenomenon is not observed in our experiments on AlH 3 dust clouds. [Display omitted] • The explosion characteristics of AlH 3 dust with different particle sizes are studied. • The phenomenon of flame delamination is not observed in the AlH 3 dust clouds. • The activation energy for H 2 release increases with particle size, similar to large AlH 3 clusters' desorption energy. • The explosion mechanism of AlH 3 dust with different particle size is revealed. [ABSTRACT FROM AUTHOR]

A possible way to introduce hydrogen into the energy matrix would be to enrich traditional fuels like natural gas and propane with hydrogen. Therefore, the study of the flame propagation behavior of these hydrogen enriched fuels becomes important to future industrial applications. In the present work the aim was to experimentally study the effect of hydrogen enrichment of propane and natural gas. However, in order to achieve more generality, the studied mixtures were characterized through the Lewis (Le), Zeldovich (Ze) and the reaction Damköler (Da°) numbers. A total of six mixtures were considered, in which the Ze varied from 4.94 to 8.45, the Le varied from 0.71 to 1.36 and the Da° varied from 14.56 to 36.11. In addition, the obtained results were compared to previous work to assess the effect of the experimental boundary conditions on the flame propagation velocity. The experimental results show that, for mixtures with similar Le numbers, the lower the Ze number the higher the flame propagation velocity. The maximum propagation velocities obtained in the first propagation section of the module are between 18.60 m/s and 57.11 m/s. Therefore, these flames can be considered as weakly accelerating flames. Moreover, the maximum flame propagation velocities showed a good correlation with the product Le × Ze. Regarding the presence of the flame arrester housing without an arrester element, it was observed that it causes an increase in flame propagation velocity. However, when compared to a previous work in which a flame arrester element was inside the housing, the velocity was higher for the present work. • Hydrogen enrichment of mixtures containing propane and gas natural were considered in this study. • The influence of the Lewis and Zeldovich numbers was investigated. • The flame propagation velocity was investigated in terms of these dimensionless numbers. • The results show that lower Zeldovich numbers promote higher propagation velocities for similar Lewis numbers. • Through comparison with published results the effect of experimental boundary conditions was assessed. [ABSTRACT FROM AUTHOR]

Until recently, it was attempted to explain the flame propagation without considering the chain nature of combustion, but the contradictions between theory and experiments failed to be explained. The difference in the roles of reaction chains and self-heating was not considered, as well as the role of heterogeneous chain termination. These issues are addressed in this chapter. Greater uncertainty in the quantitative interpretation of gas combustion is due to the limited information on heterogeneous reactions of active particles and the nonstationary state of the surface. Under these limitations, the propagation of flame of the 4H2 + O2 mixture was simulated. To reduce the role of the nonstationary state of the surface, conditions for the limiting role of diffusion of H atoms to the walls were chosen. A method for solving differential equations and conditions for replacing the Laplace operator with an averaging rate constant for the chemisorption of atomic hydrogen are described. The flat flame approximation is used. The flame characteristics for their comparison with the results of experiments conducted with the participation of the author were obtained. Experimental results showing the strong dependence of all characteristics of flame propagation on the changing properties of the surface are presented. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As an ideal energy source, hydrogen is highly susceptible to spontaneous ignition once leaked, which is an urgent issue that needs to be addressed. Based on the shock tube model, this paper investigates flame propagation under various pressures, tube lengths, and diameters by employing the LES approach and a detailed hydrogen/air combustion mechanism. The results indicate that within the tube, the ignition kernels gradually evolve into tulip flames when specific conditions are satisfied. As pressure and tube length increase, the likelihood of forming a complete flame rises significantly; with the increase of tube diameter, the flame front is flatter and the flame intensity is more uniformly distributed. Furthermore, this paper develops a model to predict the formation of a complete flame: Pb/Pa=570.64(L/D)−0.6. Outside the tube, once the intact flame passes out of the tube and evolves into a jet flame, structures such as flame envelopes and jet vortices will appear. Higher release pressures make it more difficult for the flame to propagate steadily, whereas increasing tube length and diameter promotes combustion and sustains the flame outside the tube.

To obtain the ignition performance of an integrated inclined combustor, we perform an experimental study on the ignition performance of an inclined combustor under various ignition positions, inlet flow rates, and fuel air ratios (FARs). The experimental results reveal the following. 1) During ignition at I1, the inclined combustor presents the best ignition performance. 2) The forward propagation process of flame along the swirler's inclined direction easily realizes flame propagation, whereas the backward flame propagation process in the swirler's inclined direction is difficult to achieve; forward and backward flame propagations exhibit evident differences. 3) The diffusion propagation of swirl flames at the ignition head is the main means swirl flames are generated at the nonignition head. 4) During the ignition process, the combustion intensity increases with the increase in FAR and decreases with the increase in inlet flow rate. 5) The successful ignition time decreases with the increase in inlet flow rate and FAR.

This work primarily focuses on a three-dimensional model of flame propagation and stable combustion in a scramjet chamber. The one-equation LES turbulence model is adopted to close the sub-grid-scale turbulent viscosity terms. The finite-rate combustion model, along with the Jachimowski detailed hydrogen reaction mechanism with eight components and nineteen steps, is used to analyze the flame propagation characteristics of hydrogen combustion in the scramjet combustion chamber. Initially, based on the combustion chamber model, the effect of different injection locations and equivalence ratios on flame kernel formation and the flame propagation process is analyzed. The relationship between different fuel injection conditions and the oxygen consumption rate of the combustion chamber, as well as the total pressure recovery coefficient changes, is investigated. The research focuses on changes in equivalence ratios and injection hole distributions, with injection holes arranged upstream, downstream, and inside of the cavity. The result indicated that when the injection holes were arranged downstream of the cavity, there was a phenomenon of flame backflow into the cavity, which was related to the size of the injection pressure. For this work, the pressure causing flame backflow was approximately 2 MPa. When the injection hole was arranged inside the cavity, the relative distance difference between the injection hole and the upper wall of the cavity led to the formation of two reaction zones in the combustion chamber. When the injection hole was arranged upstream of the cavity, different injection equivalence ratios affected the final stable position and structure of the flame. Therefore, the injection position, injection pressure, and injection equivalence ratio all had a certain impact on the flame kernel formation and flame propagation process. [ABSTRACT FROM AUTHOR]

The vented deflagration of hydrogen-air mixture is studied with the influence of hydrogen concentration. The pressure oscillation and flame propagation mechanism are investigated by analyzing the internal and external pressure histories and flame propagation images. The experimental results present that the pressure oscillation phenomenon has a great effect on the internal pressure peak. All of the internal pressure curves present the remarkable pressure oscillation. The pressure oscillation curve is processed by the fast Fourier transform(FFT) method. The internal pressure peaks of origin curves are higher than the results of the FFT filter curves, especially the fuel-rich conditions. The internal pressure peak of origin curve increases with the increase of the hydrogen concentration(c (H 2)) approximatively, but the filtered internal pressure peak increases first and then decreases as c (H 2). The duration of the external pressure rise is significantly shorter than the internal results. The external pressure curves have one or two pressure peaks. The external pressure histories just have one peak as c (H 2) ranging from 15 vol% to 25 vol%. But the external pressure histories turn out to two peaks as c (H 2) is more than 30 vol%. It can be found that the duration of the internal pressure history increases monotonically with the decrease of c (H 2). The duration of external flame propagation is contrary to the duration of internal pressure history in the change rule. The duration of external flame propagation increases with the increase of c (H 2). The external explosion phenomenon can be found as c (H 2) is higher than 30 vol%. And the backdraft phenomenon in external flame propagation process can be found as c (H 2) is higher than 40 vol%. • The pressure oscillation phenomenon has a significant impact on the internal overpressure peak. • The duration of the external pressure rise is significantly shorter than the internal results. • The external explosion phenomenon can be found as c (H 2) is higher than 30 vol%. • The backdraft phenomenon can be found as c (H 2) is higher than 40 vol%. [ABSTRACT FROM AUTHOR]

Nano aluminum powder effectively enhances reactivity, thereby improving energy-containing materials' performance. To investigate micro-nano self-assembled aluminum powders' energy output and their application in composite explosives, we tested the heat of combustion and ignition characteristics (ignition delay, ignition energy, flame propagation speed) using oxygen bomb calorimetry and Hartmann tube. Results showed that the combustion heat decreased with increasing nano aluminum powder content. The addition of nano aluminum powders substantially decreased ignition delay and energy, enhancing the combustion rate and reactivity of aluminum powder dust. The ranking of reactivity among the five aluminum powders was as follows: μ@n-Al-10 % > μ@n-Al-5% > μ/n-Al-10 % > μ/n-Al-5% > μAl. Assessing explosives containing various aluminum powders showed that the self-assembled 5 % content sample had the highest heat of detonation at 8490 kJ/kg. Mechanical sensitivity increased with higher nano aluminum powder content, with explosives containing 5 % nano content exhibiting the highest safety performance.

To understand the explosion characteristics of methane-lignite coal dust mixtures and the spatiotemporal evolution of the early flame flow field, explosion pressure, OH* emission spectra, and early flame schlieren images were captured in a 60L constant volume combustion bomb. Schlieren image velocimetry was used to obtain the instantaneous velocity distribution of the methane-coal dust flame front. The results indicate that adding coal dust causes a nonlinear increase in explosion pressure, particularly at low methane concentrations. At a 5 % methane concentration, adding coal dust can increase the maximum explosion pressure by up to 39 % (190 kPa). The trend of the OH* emission spectra corresponds with the maximum explosion pressure. A slight increase in coal dust significantly enhances the OH* emission spectra, especially at lower concentrations, potentially increasing it by nearly five times. However, at higher coal dust concentrations, the OH* emission spectra are significantly reduced. Additionally, within the considered concentration range (≤58.14 g/m³), larger turbulent integral length scales in initial conditions consistently result in the fastest flame acceleration. These findings provide experimental evidence for further exploration of the explosion mechanisms of methane-coal dust mixtures and the development of chemical reaction kinetic models.

Methane/air explosion is one of the common hazards in process and mining industries. In this study, the methane explosion propagation is studied, and two-dimensional configuration is considered. The gas phase equations are solved using an OpenFOAM code for compressible reacting flow, EXiFOAM. The effects of the low blockage ratio (LBR) obstacles are investigated. The results show that the flame propagation speed, flame structure, shock wave propagation, and gas flow are considerably affected by LBR obstacles. Specifically, the flame propagation speed first increases and then decreases. As the initial pressure increases, the flame propagation speed gradually increases. The maximum speed is up to 500 m/s, when the initial pressure is 1.5 MPa. If the flame propagation is prevented, resulting in the flame deformation. Moreover, the flame disruptive phenomenon is captured due to the reflected waves. In front of the obstacle, the cellular structures of the high-pressure distribution are formed. Note that the tiny cellular structures are produced in the wake of the leading shock. Furthermore, a high-speed flow region and two low-speed flow regions are produced around the LBR obstacles. It is found that as the initial pressure increases, the explosion pressure is larger, while the temperature change is not obvious. These research findings have implications for enhancing safety production in coal mines.

The safety implications of aluminum powder and petroleum ether have garnered significant attention as two typical materials in the production process of energetic materials. To investigate the effect of the common solvent petroleum ether on the ignition and explosion characteristics of aluminum powder, ignition energy, flame propagation characteristics, and explosion pressure of three aluminum powder sizes and their mixtures with petroleum ether through a Hartmann tube test device and a 20 L spherical explosion vessel test system. Findings show that the ignition energy of aluminum powder initially decreases and then increases with the increase of petroleum ether content. At the petroleum ether concentration of 5.5 % and 11 %, the minimum ignition energies of the mixed systems of Al-Flake, Al-T4, and Al-T2 are 1–20 mJ, 5–30 mJ, 450–485 mJ, and 1–20 mJ, 5–25 mJ, 440–480 mJ, respectively. Lower than the minimum ignition energy of the original sample (1–30 mJ, 10–40 mJ, 470–510 mJ), indicating that the aluminum powder dust containing low concentration solvent (5.5%, 11 %) is more sensitive to an electric spark. The ignition energy of the mixed system is rather increased when the content of petroleum ether is further increased to 16.5 %. On the contrary, the probability of ignition and the electric spark sensitivity are decreased. With the addition of petroleum ether to Al-Flake and Al-T4, the flame propagation speed slightly decreases and the phase duration lengthens. The flame propagation characteristics and combustion state of Al-T2 with large particles remained largely unchanged after the addition of petroleum ether. During the 20 L spherical explosion vessel test, the maximum explosion pressure and explosion index of the mixed samples initially increase and then decrease with the increase in petroleum ether concentration. A small quantity of petroleum ether intensifies the reaction intensity of aluminum dust. At an aluminum powder dust concentration of 250 g m-3, the explosion pressure and explosion index of Al-Flake and Al-T4 peak at a petroleum ether content of 5.5 %, while Al-T2 reaches its peak at 11 %.

Nitrous oxide and fuel blends propellant as one of the substitutes for highly toxic hydrazine are under investigation. This study investigated the flame structure and dynamics of stoichiometric nitrous oxide and propane mixture (N2O/C3H8) by using polymethyl methacrylate (PMMA) tubes of varying inner diameters (5, 10, 15, and 50 mm) and a consistent length (1400 mm). The influence of tube diameter on flame acceleration was analyzed. The results reveal that within the 50-mm diameter tube, the flame propagation speed increased as the flame front moved forward in the tube, achieving a maximum speed of 532 m/s. In the tubes with 5-, 10-, and 15-mm diameters, all three stages—deflagration, transition to detonation, and detonation attenuation—were observed. Notably, the flame acceleration rate and maximum propagation velocity increased with the tube diameter, with the maximum velocities in the 5-, 10-, and 15-mm tubes being 1900, 2060, and 2140 m/s, respectively. The oxidation pathways of C3H8 reacting with N2O were studied using the B3LYP/6–31++G** method based on density functional theory. Thus, the study could determine changes in the configurations of reactants, intermediates, transition states, and products; the characteristics of the potential energy associated with the reaction pathways; and the reaction laws and thermodynamic parameters.

[Objective] Compared with conventional gas fuel, hydrogen is more susceptible to explosion. Meanwhile, the existence of obstacles notably stimulates hydrogen combustion and accelerates flame propagation, causing more serious consequences of accidents. To reduce destructive damage caused by hydrogen combustion under obstacle conditions, it is particularly important to reveal the influences of different obstacle conditions on the characteristics of flame propagation of hydrogen. [Methods] Based on large eddy simulation, the hydrogen/air combustion and explosion processes under different obstacle shapes and blockage rate conditions were numerically simulated.Focus was given to the research on different flame propagation velocities caused by different obstacle shapes and the sensitivity to blockage rate changes. [Results] Under low blockage rate, grid-type obstacles had a stronger destructive effect on the regular flow field at the flame front than single-side obstacles, and as the number of voids in grid-type obstacles increased, their destructive effect on the flow field motion further intensified, making it difficult for the flame front to recover to a regular state. When the blockage rate went up, the difference of the shapes of obstacles became insignificant in causing damage to the regular flow field, and the flame front was continuously distorted under all obstacle conditions. As the blockage rate continued to increase, single-side obstacles brought higher peak flame propagation velocity than grid-type obstacles. At the same blockage rate, the mechanism of flame acceleration by grid-type obstacles can be changed by adjusting the single void area to enhance the acceleration effect. [Conclusion] The shape and blockage rate of obstacles are the key factors influencing the state of flame front behind obstacles.The single-side obstacle is more sensitive to the blockage rate,while the grid-type obstacle has higher acceleration potential.The research results provide basic reference data for the prevention and control of hydrogen fire accidents and serve as a reference for the design of hydrogen power systems.

This paper is devoted to the numerical analysis of the spontaneous acceleration of a slow flame in a semi-closed channel. In particular, the flow development in the channel ahead of the propagating flame is analyzed. The applied detailed numerical model allows the clear observation of all features intrinsic to the reacting flow evolution in the channel, including the formation of perturbations on the scale of the boundary layer and their further development. In all considered cases, perturbations of the boundary layer emerge in the early stages of flame acceleration and decay afterward. The flow stabilizes more rapidly in a narrow channel, where the velocity profile is close to the Poiseuille profile. At the same time, the compression waves generated in the reaction zone travel along the channel. The interaction between compression waves in the area of combustion products can lead to the formation of shock waves. The effect of shock waves on the flow in the fresh mixture causes an increase in the flame area and a corresponding flame acceleration. In addition, shock waves trigger boundary-layer instability in wide channels. The perturbations of the boundary layer grow and evolve into vortexes, while further vortex–flame interaction leads to significant flame acceleration.

A gas explosion experimental system based on a piece of 15 m-long and 9I8O semi-closed wide open steel pipe was constructed. An explosion experimental study on straight pipelines and pipeline structures with different angles (45°, 90°, and 135°) was conducted. Research results demonstrated that before the turn, flame propagation speed and flame sustaining time in different pipeline structures were consistent. With the increase of the distance away from the ignition source, the flame propagation velocity increases and the flame sustaining time decreases; at the turning point, the flame velocity suddenly decreases and the flame duration increases obviously. Meanwhile, the peak value of overpressure on the lateral wall of the turning corner is greater than that on the inner wall. Among the three different angles, the peak value of overpressure on the lateral wall of 135° bend is the highest. Different pipeline structures have great influence on gas explosion overpressure and flame propagation speed. These research conclusions provide theoretical references for gas explosion resistance in coal mines. [ABSTRACT FROM AUTHOR]

Aluminum hydride (AlH 3) dust is a high-capacity hydrogen storage material but is prone to explosion. In this paper, explosion characteristics and flame propagation behavior of AlH 3 dust are investigated. The results indicate that the exposure of bare aluminum and the increase of specific surface area lead to the maximum explosion pressure of AlH 3 dust being 4 times higher than that of Al dust. The enhancement of heat transfer by hydrogen combustion causes a higher combustion rate, leading to a higher maximum explosion pressure rise rate and flame propagation velocity of AlH 3 dust. The thermo-diffusive instabilities and the evolution of hydrogen result in a pulsation flame propagation velocity of AlH 3 dust. Combining the explosion temperature calculated by NASA CEA with the explosion residues analysis, the explosion mechanism of AlH 3 dust is further revealed. The break of the oxide film and the combustion of hydrogen result in a different explosion mechanism. • The explosion characteristics and flame propagation behavior of AlH 3 dust are investigated. • The hydrogen evolution characteristic is studied by the comparison of Al dust. • The explosion mechanism of AlH 3 dust is revealed. [ABSTRACT FROM AUTHOR]

Nowadays we are gradually transitioning from fossil to renewable energy in our energy consumption, but the green electricity, represented by solar and wind power, is highly fluctuating and difficult to use efficiently. Hydrogen production from electrolysis of water is currently an important pathway to consume green electricity, yet hydrogen still faces difficulties in large – scale long – term storage. Subsequently, a new pathway for the efficient use of renewable energy has been proposed: powering by renewable energy – preparing metal by electrolysis – heating by metal combustion. Metals are easy to store, and transport and its market is large. This makes it possible to realize the large – scale long – term storage of fluctuating renewable energy. In this new technical route, metal combustion is a crucial element. This work reviews the combustion models of iron and aluminum as fuels, and discusses their combustion characteristics under different particle sizes and microgravity conditions, as well as the flame propagation process. We hope that our work will benefit the development of this field. [ABSTRACT FROM AUTHOR]

In this paper, we present a mathematical approach for studying the changes in pressure and temperature variables in flames. This conception extends beyond the traditional second-order Laplacian diffusion model by considering the p-Laplacian operator and a bi-stable reaction term, thereby providing a more generalized framework for flame diffusion analysis. Given the structure of our equations, we provide the boundedness and uniqueness of the solutions in a weak sense from both analytical and numerical approaches. We further reformulate the governing equations in the context of traveling wave solutions, applying singular geometric perturbation theory to derive the analytical expressions of these profiles. This theoretical development is complemented by numerical assessments, which not only validate our theoretical predictions, but also optimize the traveling wave speed to minimize the error between numerical and analytical solutions. Additionally, we explore self-similar structured solutions. The paper then concludes with a perspective on future research, with emphasis being placed on the need for experimental validation in laboratory settings. Such empirical studies could test the robustness of our model and allow for refinement based on actual measurements, thereby broadening the applicability and accuracy of our findings in practical scenarios. [ABSTRACT FROM AUTHOR]

Aluminum hydride (AlH 3) is an excellent hydrogen storage material, whereas hydrogen is easily released because of the low-temperature dehydrogenation characteristic. Therefore, the explosion mechanism of AlH 3 dust is explored by comparison with the Al/H 2 mixture. The findings indicate that since the residual aluminum after hydrogen evolution combusts more completely, AlH 3 has a higher explosion pressure value than Al/H 2 mixture. However, the explosion pressure rise rate and average flame propagation velocity of AlH 3 dust are lower than those of Al/H 2 mixture. It is attributed to the initial free hydrogen state and initial higher hydrogen concentration of Al/H 2 mixture. The key radicals that generate main explosion residues Al 2 O 3 are AlO and O. AlH 3 (+M) ≤> AlH + H 2 (+M) has the greatest sensitivity on the formation of O and AlO. Hydrogen combustion expedites the phase transition process of aluminum dust, while their competition for oxygen is not conducive to the formation of Al 2 O 3. • The explosion characteristics of AlH 3 dust are analyzed by comparison with the Al/H 2 mixture. • The initial state and content of hydrogen lead to different explosion processes. • The explosion mechanism of AlH 3 dust is revealed by reaction kinetics simulation. [ABSTRACT FROM AUTHOR]

In this paper, we studied the effects of transverse concentration gradients on methane explosion characteristics using a fully-transparent pipeline and finally came to the following conclusions. The peak explosion overpressure changed in a waveform of "M" along different measuring points, but a set of non-equivalent concentration gradients maximized this peak value. Higher methane concentrations in the Q2 region could cause the secondary peak overpressure near the both ends of the pipe. In this process, the flame outside the pipe tends to form a near-spherical shape. However, at lower methane concentrations in the Q2 region, the secondary peak overpressure was only detected near the outlet. Its occurrence at different sites may relate to the turbulence effect heightened by concentration gradients. Besides, under the same gradient, the smallest propagation speed was measured on the right of the ignition source when the flame propagated fastest on the left, which was attributed to different inhibiting effects of reflected waves on flame propagation. • There exists a set of non-equivalent concentrations to maximize the explosion overpressure peak. • The spatial evolution law of gas explosion overpressure in pipeline with concentration gradient was revealed. • The formation mechanism of slope flame and secondary overpressure peak were described. [ABSTRACT FROM AUTHOR]

A 20L spherical device and a schlieren system were used to study the suppression effect of CF 3 I on the hydrogen explosion pressure and flame characteristics. The results show that CF 3 I can promote and inhibit the pressure parameters of hydrogen under lean fuel, but only inhibit the pressure parameters of hydrogen under equivalence ratios and rich fuel. Such as, φ = 0.6, adding 10 % CF 3 I, the maximum explosion pressure increased by 8.8 %. φ = 1, adding 5 % CF 3 I, the maximum explosion pressure decreased by 25 %. Different from the explosion pressure, the laminar burning velocity of hydrogen with different equivalence ratio decreases gradually with the increase of CF 3 I concentration. Numerical simulation was used to reveal the mechanism of CF 3 I inhibiting hydrogen. The results show that the concentration of active free radicals(H, O, OH) decreases with the increase of trifluoroiodomethane concentration. Further analysis on the rate of production and sensitivity of H free radicals found that R822 and R839 are the main generation reactions of H free radicals in the fluorine- and iodine-containing elemental reactions, and R1397, R1396, R1391 and R859 are the main consumption of H free radicals reaction. The elementary reaction with the greatest inhibitory effect on H free radicals is R1391, and the elementary reaction with the greatest promoting effect is R850. • CF 3 I has two effects of promoting and suppressing hydrogen explosion pressure. • Analysis of the effect of suppressant on hydrodynamic instability. • CF 3 I has inhibitory effect on laminar burning velocity of hydrogen. • The kinetic mechanism of CF 3 I suppressing hydrogen explosion was analyzed. [ABSTRACT FROM AUTHOR]

To research the influence of inert gases on the explosion behaviors of LPG/air mixtures, LPG explosion tests suppressed by CO2 and N2 were conducted in a spherical chamber and the chemical reaction kinetic properties were analyzed. The results show that CO2 has a better inhibitory effect than N2, especially when the added amount is small. With the increasing volume fraction of inert gases, the LPG explosion flame propagation speed continuously decreases, and the phenomenon of flame uplift and wrinkling deformation occurs. The explosion pressure of LPG/CO2(N2)/air mixture and the average flame propagation speed in the initial stage follow an exponential function with an offset. The laminar flame structure of 4% LPG is similar to its mixtures with N2 and CO2. After adding inert gases, the maximum temperature of the LPG laminar flame decreases significantly, and the flame thickness increases. The key elementary reactions affecting the N2(CO2)/LPG/air explosions are given. The research results have important implications for suppression of LPG explosions. [ABSTRACT FROM AUTHOR]

Accidental crankcase explosions in marine diesel engines are presumably caused by the inflammation of lubricating oil in air followed by flame propagation and pressure buildup. This manuscript deals with the numerical simulation of internal unvented and vented crankcase explosions of lubricating oil mist using the 3D CFD approach for two-phase turbulent reactive flow with finite-rate turbulent/molecular mixing and chemistry. The lubricating oil mist was treated as either monodispersed with a droplet size of 60 μm or polydispersed with a trimodal droplet size distribution (10 μ m (10 wt%), 250 μ m (10 wt%), and 500 μ m (80 wt%)). The mist was partly pre-evaporated with pre-evaporation degrees of 60%, 70%, and 80%. As an example, a typical low-speed two-stroke six-cylinder marine diesel engine was considered. Four possible accidental ignition sites were considered in different linked segments of the crankcase, namely the leakage of hot blow-by gases through the faulty stuffing box, a hot spot on the crankpin bearing, electrostatic discharge in the open space at the A-frame, and a hot spot on the main bearing. Calculations show that the most important parameter affecting the dynamics of crankcase explosion is the pre-evaporation degree of the oil mist, whereas the oil droplet size distribution plays a minor role. The most severe unvented explosion was caused by the hot spot ignition of the oil mist on the main bearing and flame breaking through the windows connecting the crankcase segments. The predicted maximum rate of pressure rise in the crankcase attained 0.6–0.7 bar/s, whereas the apparent turbulent burning velocity attained 7–8 m/s. The rate of heat release attained a value of 13 MW. Explosion venting caused the rate of pressure rise to decrease and become negative. However, vent opening does not lead to an immediate pressure drop in the crankcase: the pressure keeps growing for a certain time and attains a maximum value that can be a factor of 2 higher than the vent opening pressure. [ABSTRACT FROM AUTHOR]

In the current work, the combustion of NH3/H2/air blends is experimentally investigated in a constant-volume combustion chamber in terms of two different ignition modes: spark ignition (SI) mode and turbulent jet ignition (TJI) mode with ammonia and hydrogen fueled in the pre-chamber. The results show that for the SI mode, the burning rate and propagation of premixed NH3/air flames are significantly accelerated by a hydrogen addition of only 3% (v/v). A cellular structure is observed and becomes more intense with the increasing hydrogen volume fraction. For the TJI mode, the hot jet generation and turbulent flame development of ammonia inside the main chamber are captured optically for the first time. The combustion process inside the main chamber can be categorized into three phases for both the TJI-ammonia and TJI-hydrogen modes. The cold jet that mainly contains the unburned fuel and air is observed under the TJI-hydrogen mode. The hot jet produced by the pre-chamber can effectively promote the ignition initiation and hence flame propagation in the main chamber. An accelerated burn rate of ammonia is obtained, and the TJI-hydrogen mode makes a stronger promoting impact on the combustion of the main chamber. Significantly, compared with SIhydrogen mode, the TJI-hydrogen mode can bring a considerable promoting effect to ammonia combustion with significantly lower hydrogen consumption. [ABSTRACT FROM AUTHOR]

This experimental study investigated the influence of different turbine guide vane parameters on the ignition limit and light-round processes in a triple-dome combustor. It was found that for the triple-dome combustor, the minimum fuel/air ratios at the ignition limit all show a trend of initial decrease followed by subsequent increase with the growth of incoming air mass flow rate. The ignition fuel/air ratio decreases with the increase in turbine blockage ratio, and the optimal scheme is achieved with a blockage ratio of 0.8. Under the condition where the incoming air mass flow rate is 0.089 kg/s, the light-round time decreases with the increase in fuel/air ratio, and the light-round time of the combustor without guide vanes is shorter than that of the other schemes. With the increase in incoming air mass flow rate, the light-round time of the schemes with guide vanes is shortened. Under the same incoming air mass flow rate and fuel/air ratio, the increase in the blockage ratio will lead to an increase in the light-round time of the triple-dome combustor.

Gas explosion accidents can easily lead to large-scale casualties and economic losses, significantly impeding the urban development. The purpose of this study was to comprehensively review and investigate a significant gas fuel explosion accident in Yinchuan City, China, and to conduct an in-depth discussion on process traceability, failure risk, hazard prevention, and urban development related to the accident. The research found that the accidental failure of double-valve liquefied petroleum gas cylinders and human error were identified as the direct causes of gas leakage. The numerical results indicated that the progression of the accident disaster was chaotic and highly destructive. The maximum explosion overpressure of 92 kPa resulted in severe shock-wave damage to personnel, leading to the complete destruction and collapse of the 0.2 m thick solid brick wall and obstructing the stairway for escape. The rapid change in temperature and oxygen levels caused by the explosion led to the risk of burns and asphyxiation for personnel at the scene. By utilizing the system safety theory, a gas leakage accident control structure system was developed. This system comprised four key levels: the local government, gas management department, gas company, and individual user. The tragedy of 31 deaths was ultimately caused by a serious lack of safety constraints on the behavior of the lower level by the higher level. The research conclusions are of great significance for preventing clean fuel explosion accidents and ensuring sustainable urban development, especially in the face of the negative impact of accidents.

Foam metal as a promising application of explosion-proof and explosion-suppression materials, which itself has a complex three-dimensional pore structure, can be more effective in quenching gas and dust explosion flame in this research, a platform was created to experiment with dust deflagration using transparent quartz tubes and high-speed photography. The study focused on how copper foam affects flame propagation during deflagration of three kinds of dust: polyethylene, aluminum, and wheat. The results showed that copper foam hinders the flame front displacement and reduces fluctuations in flame propagation velocity when compared to deflagrations that do not have copper foam. However, placing copper foam too close to the ignition source can increase the magnitude of fluctuations in the early stages of the deflagration. When copper foam was placed 360 mm above the source of ignition, the 10PPI and 20PPI copper foam were able to decrease the flame of polyethylene dust and aluminum dust. As the porosity of the metal foam increases, the 30PPI copper foam can completely extinguish the flame of the three powders. The research also found that copper foam can divide the flame, quench the flame entering the copper foam, and block some of the burned and unburned powders, thereby reducing the energy of the deflagration and weakening the reaction. Comprehensively, to explore the inhibition effect of different parameters of copper foam against dust deflagration, which is of some significance for the study of fire and explosion control.

A gas explosion experimental system based on a piece of 15 m-long and φ180 semi-closed wide open steel pipe was constructed. An explosion experimental study on straight pipelines and pipeline structures with different angles (45°, 90°, and 135°) was conducted. Research results demonstrated that before the turn, flame propagation speed and flame sustaining time in different pipeline structures were consistent. With the increase of the distance away from the ignition source, the flame propagation velocity increases and the flame sustaining time decreases; at the turning point, the flame velocity suddenly decreases and the flame duration increases obviously. Meanwhile, the peak value of overpressure on the lateral wall of the turning corner is greater than that on the inner wall. Among the three different angles, the peak value of overpressure on the lateral wall of 135° bend is the highest. Different pipeline structures have great influence on gas explosion overpressure and flame propagation speed. These research conclusions provide theoretical references for gas explosion resistance in coal mines.

This work primarily focuses on a three-dimensional model of flame propagation and stable combustion in a scramjet chamber. The one-equation LES turbulence model is adopted to close the sub-grid-scale turbulent viscosity terms. The finite-rate combustion model, along with the Jachimowski detailed hydrogen reaction mechanism with eight components and nineteen steps, is used to analyze the flame propagation characteristics of hydrogen combustion in the scramjet combustion chamber. Initially, based on the combustion chamber model, the effect of different injection locations and equivalence ratios on flame kernel formation and the flame propagation process is analyzed. The relationship between different fuel injection conditions and the oxygen consumption rate of the combustion chamber, as well as the total pressure recovery coefficient changes, is investigated. The research focuses on changes in equivalence ratios and injection hole distributions, with injection holes arranged upstream, downstream, and inside of the cavity. The result indicated that when the injection holes were arranged downstream of the cavity, there was a phenomenon of flame backflow into the cavity, which was related to the size of the injection pressure. For this work, the pressure causing flame backflow was approximately 2 MPa. When the injection hole was arranged inside the cavity, the relative distance difference between the injection hole and the upper wall of the cavity led to the formation of two reaction zones in the combustion chamber. When the injection hole was arranged upstream of the cavity, different injection equivalence ratios affected the final stable position and structure of the flame. Therefore, the injection position, injection pressure, and injection equivalence ratio all had a certain impact on the flame kernel formation and flame propagation process.

In this paper, we present a mathematical approach for studying the changes in pressure and temperature variables in flames. This conception extends beyond the traditional second-order Laplacian diffusion model by considering the p-Laplacian operator and a bi-stable reaction term, thereby providing a more generalized framework for flame diffusion analysis. Given the structure of our equations, we provide the boundedness and uniqueness of the solutions in a weak sense from both analytical and numerical approaches. We further reformulate the governing equations in the context of traveling wave solutions, applying singular geometric perturbation theory to derive the analytical expressions of these profiles. This theoretical development is complemented by numerical assessments, which not only validate our theoretical predictions, but also optimize the traveling wave speed to minimize the error between numerical and analytical solutions. Additionally, we explore self-similar structured solutions. The paper then concludes with a perspective on future research, with emphasis being placed on the need for experimental validation in laboratory settings. Such empirical studies could test the robustness of our model and allow for refinement based on actual measurements, thereby broadening the applicability and accuracy of our findings in practical scenarios.

• Visualization of in-cylinder flow and flame using an optically accessible engine. • Characteristics of in-cylinder flow and flame in the catalyst-heating mode. • Effects of intake valve timing and duration on tumble and flame propagation speed. • Investigation of the amount of residual gas depending on exhaust valve timings. The effects of intake and exhaust valve timing and duration were investigated using an optically accessible multi-point injection engine under catalytic heating conditions. The target engine features a quartz cylinder and an extended piston with a quartz piston crown. To understand the effects of valve timing and duration on the in-cylinder flow, particle image velocimetry (PIV) was applied to visualize the in-cylinder flow. The acquired images were used to quantitatively evaluate the in-cylinder flow characteristics, and the effects of these flow characteristics on the flame propagation were analyzed through flame visualization experiments. The results indicate that when the intake valve timing was advanced by 20°, the average flow velocity was 59.5% higher, the tumble ratio was 72.2% greater, and the flame propagation velocity was also the fastest. The longest duration of 218° was advantageous for the intake valve duration, and the formation of a tumble flow pattern was important for fuel and air mixing. Finally, in the exhaust valve timing and duration experiment, the exhaust valve closing timing affected the amount of residual gas inside the cylinder. Therefore, the ratio of diffusion flames increased when the exhaust valve timing was advanced or retarded compared to the reference exhaust valve timing. [ABSTRACT FROM AUTHOR]

• Ignition and flame propagation of NH 3 /diesel dual fuel mode with high NH 3 energy ratio were studied. • The two combustion modes, multiple ignition and flame propagation, depend on the ammonia energy ratio. • Weakening the diesel mixing is beneficial for promoting the ignition of NH 3 /diesel dual fuel. Ammonia (NH 3) is considered as one of the most promising zero-carbon fuels for internal combustion engines. Based on diesel engine modification, The ammonia/diesel dual-fuel mode with port injection of ammonia and in-cylinder direct injection of diesel has been proven to be the most feasible strategy. In this paper, the effects of ignition and flame propagation of premixed ammonia ignited by direct-injected diesel were studied based on an optical rapid compression machine (RCM). The results show that the spray and distribution of diesel play the key role in the ignition and flame propagation of NH 3 /diesel dual fuels combustion. For total excess air ratio (λ T) of 1.0, the ignition delay of NH 3 /diesel with high energy ratio of ammonia (ER of 95 %) was much shorter than ER of 66 % which was mainly due to the low injection pressure of diesel. Under the same injection pressure, with the large nozzle diameter of diesel injector of 0.28 mm, the ignition delay of NH 3 /diesel will be shortened significantly. When the ER is low, the combustion process presents the characteristics similar to the multi-point compression combustion. When the ER rises to 83 %, the combustion process is mainly dominated by NH 3 premixed combustion, and diesel mainly plays the role of ignition. Reducing the background pressure and temperature to 4 MPa and 887 K, respectively, NH 3 is not able to be ignited by diesel. [ABSTRACT FROM AUTHOR]