Flame Propagation Velocity Research Articles

Investigation into the ignition sensitivity and detonation kinetics of Al/RDX energetic dust

Given the prevalence of Al/RDX energetic dust in industrial production, this study investigates their ignition safety and explosion hazards using Hartmann tubes and 20 L spherical explosion containers. The minimum ignition energy (MIE) increases from 20 mJ to 55 mJ as RDX content increases, indicating that adding RDX enlarges the effective particle size of the dust, thereby reducing its ignition sensitivity. A logistic regression model was used to develop a fitting equation for ignition probability, correlating dust concentration and ignition energy. The flame propagation velocity and explosion pressure of the energetic dust initially increase and then decrease with increasing RDX content. Optimal combustion characteristics were observed at 20 % RDX, with the maximum flame propagation velocity of 101 m s−1. However, the peak flame temperature decreases with increasing RDX content. The maximum explosion pressure and maximum explosion index at 1.77 MPa and 186.99 MPa m s−1 respectively, at 40 % RDX content. These findings highlight that 20 % RDX content yields the best combustion characteristics, while 40 % RDX content offers the maximum explosive potential, providing valuable insights for enhancing safety measures in industrial applications involving energetic dusts.

Suppression characteristics and mechanisms of solid inhibitors on sawdust explosions in dust transportation systems

The explosion characteristics of pine sawdust mixed with typical inhibitors (calcium carbonate, calcium phosphate, ammonium phosphate) were investigated under different inerting ratios in a vertical flame propagation device. Different analytical analyses by TG-DTG-DSC and FTIR analysis were also coupled to understand the physical and chemical mechanisms of the treated samples. The results show that the flame propagation velocity and the peak pressure decreased by more than 50% for an inerting ratio of 60 wt%.This work clarifies the suppression characteristics and mechanism of different inhibitors in the flame propagation of biomass dust and yields some insights into the prevention and mitigation of biomass dust explosions in industrial applications.

Impact of molybdenum disulfide diffused coir fiber on the physical, mechanical, thermal, and vibrational characteristics of polyester composites

AbstractThis research focuses on comparing the properties of molybdenum disulfide (MoS2) diffused coir fiber polyester composites (MCF‐PCs) with neat coir fiber polyester composites (NCF‐PCs) and exploring its applications in various industrial sectors such as automotive, construction and manufacturing, where mechanical strength and fire resistance are critical factors. The study aims to investigate the physical, mechanical, thermal degradation, fire performance, and vibration properties of these composites. Compression molding was used to develop composites with different coir fiber loadings (10%, 20%, and 30% by weight). MoS2 nanoparticles diffused on the fiber surface significantly improved mechanical characteristics, thermal stability, and fiber‐matrix compatibility. The findings indicate better crystallinity and physical properties in MCF‐PCs compared to NCF‐PCs. Morphological observations confirmed improved fiber‐matrix compatibility in MoS2‐diffused fiber composites with polyester. The MCF‐PC with 20% loading exhibited the highest tensile (28 ± 1.24 MPa), flexural (50 ± 0.50 MPa), and impact (15 ± 1.01 kJ/m2) strength. The flame retardancy of the composites was evaluated using a horizontal combustion test apparatus. In addition, MCF‐PCs exhibited better flame retardancy as evidenced by lower flame propagation velocity (9 ± 0.20 mm/min) and increased ignition time (13 ± 0.29 Sec). The MCF‐PC with 20% loading shows maximum natural frequencies of 77 ± 4.1 Hz.Highlights This study investigated MoS2‐diffused coir fiber‐reinforced polyester composites. Fiber‐matrix adhesion can be improved with modified fiber‐reinforced composites. The MoS2 diffusion on fibers improved the physical and mechanical properties of polyester composites. The MoS2 diffusion on fibers enhanced the thermal and vibrational characteristics of polyester composites. MoS2‐diffused natural fiber composites offer considerable research potential.

Study on flame propagation characteristic and mechanism of polypropylene dust explosion

Polypropylene dust explosion poses a significant threat to the safe production of synthetic resin. To elucidate the flame propagation mechanism of polypropylene dust explosions, the flame propagation characteristics of polypropylene dust were experimentally studied. The minimum explosible concentration (MEC) for polypropylene particles with diameter < 75 μm, 75–100 μm, and 100–212 μm was 50 g/m3,100 g/m3,150 g/m3, respectively. Obvious fluctuations were observed in the flame propagation velocity of small particles, with smaller particles exhibiting more pronounced fluctuations, primarily caused by thermal feedback between the particles in the preheating zone and the reaction zone. While for large particles, the flame temperature exhibited multiple peaks, resulted from the discrete flame floating in front of the flame. The combustion process of polypropylene dust comprised the diffusion combustion of large particles and the gas-phase combustion of combustible gases pyrolyzed by small particles.

The effects of different equivalence ratios and initial pressures on the explosion of methane/air premixed gas in closed space

Methane/air is a widely used fuel. The effects of equivalent ratio (0.8–1.2) and initial pressure (1.0 atm–1.2 atm) on the flame propagation process and explosion overpressure of methane/air premixed gas were studied using a high-speed camera and pressure sensor in a rectangular closed container. Four flame modes in the late propagation stage are distinguished according to the different modes of secondary cup movement. The flame propagation velocity and structure evolution are analyzed by defining the characteristic times. The relationship between the flame structure evolution and the growth of flame propagation velocity and explosion overpressure is revealed. The results show that, in lean combustion, the maximum flame propagation velocity increases with initial pressure increase, and the explosion overpressure fluctuates more significantly. However, the opposite is true with fuel-rich combustion. The interaction between pressure waves and flame fronts can enhance the growth of explosion overpressure in fuel-rich combustion but can inhibit the growth in lean combustion. This work can provide more data support and reference for the application prospect and safe application of methane.

Study on backfire characteristics of port fuel injection single-cylinder hydrogen internal combustion engine

Hydrogen energy is one of the most promising sources of carbon neutrality from well to wheel. Among various applications of hydrogen energy, hydrogen internal combustion engines serve as the critical technical pathway. Nevertheless, several challenges persist, primarily related to abnormal combustion resulting from excessive flame propagation velocity. Of these challenges, backfire emerges as the most recurrent and pressing issue to be resolved in the port fuel-injected hydrogen internal combustion engine (PFI-H2ICE). In order to delve into the characteristics and mechanisms of backfire, this study concentrates on a critical internal parameter, namely the start of injection (SOI), and comprehensively assesses the backfire occurrences under varying lambda and engine speed conditions. Experimental findings reveal that SOI encompasses one of the pivotal factors influencing backfire. Backfire predominantly arises within two ranges of SOI conditions: the region before −430 degCA ATDC (Zone I) and the stretch between −360 degCA ATDC and − 280 degCA ATDC (Zone II). In the process of employing EGR to depress the effects of backfire on subsequent tests, it was incidentally found that the Universal Exhaust Gas Oxygen Sensor (UEGO) installed on the intake manifold for executing EGR rate calculations acted as a hotspot (with temperatures exceeding 100 °C). This not only intensified the backfire strength and the scope in Zone I but also caused the most severe backfire events to occur after −270 degCA ATDC (in Zone III). Despite this, the EGR strategy still demonstrated a significant backfire suppression effect, only exhibiting almost no influence on backfire caused by hotspots within the intake manifold. With an escalation in engine speed, the intensity of backfire diminishes, and the range of backfire occurrence decreases accordingly. By exercising control over SOI within the operating range from -430degCA to -360degCA ATDC (Zone A), the risk of backfire can be dramatically reduced, thereby achieving nearly backfire-free operation. Detailed analysis of cylinder pressure indicates that backfire may also give rise to other abnormal combustions, such as misfire, pre-ignition, and knock, in subsequent cycles. Moreover, this effect amplifies in tandem with an increase in mixture concentration. A certain degree of mutual promotion among diverse abnormal combustions is also observed. This study furnishes the most direct and practical foundation for internal and external strategies in the realm of backfire control.

Effect of initial pressure on hydrogen/propane/air flames in a closed duct

To investigate the flame propagation characteristics and chemical kinetics of premixed propane/hydrogen/air mixtures at elevated pressure, a series of experiments on propane/hydrogen/air mixtures with varying initial pressures (P0 = 100–300 kPa) and equivalence ratios (φ = 0.6–1.4) at a hydrogen fraction of 0.6 and an ambient temperature of 298 K were carried out in a closed duct with an aspect ratio of 15. The chemical kinetics of the elementary reaction were analyzed numerically. The results revealed that the combustion-induced rapid phase transition (cRPT) occurred in the premixed C3H8/H2/air flames. Both the combustion pressure and flame propagation velocity increase with initial pressure except at P0 = 300 kPa, where the flame propagation velocity decreases. Moreover, the linear dependence between the laminar burning velocity and peak mole fraction [H + O + OH]max was found by the effect of initial pressure on the peak mole fraction (H, O, OH). The explosion pressure Prea and the maximum rate of production of free radical H/O show excellent correlations. The maximum rate of pressure rise can be predicted by the maximum heat release rate (HHR). These results provide essential data on elevated-pressure duct accidents and have important implications for explosion prevention.

Effects of methane concentration on flame propagation mechanisms and dynamic characteristics of methane/coal dust explosions

The study explores the flame propagation and explosion dynamic behavior of gas/powder two-phase compound explosions, taking methane and coal dust mixture as the research object. The influence of different methane concentrations on the compound explosion characteristics was researched. The vertical pipeline, high-speed camera, ion current probe, and pressure sensor be used to test the propagation behaviors, microstructure characteristics, and explosion dynamics of compound explosion flames. The function of methane concentration on the propagation behaviors, combustion reaction zone thickness, flame temperature, propagation velocity, and explosion pressure of compound flame was revealed, and the propagation mechanisms of gas/powder compound explosion flames were explained. The experimental research discovered that the compound flame of methane/coal dust explosion presents a white luminous zone with uniform distribution and appears to have an approximate homogeneous combustion state. The explosion dynamics parameters all showed a trend of first increased and then decreased as the methane concentration increased, but the reaction zone thickness of the combustion first reduced and then increased. In addition, the dominant position of homogeneous or heterogeneous combustion in the combustion reaction zone will also switch with the change in methane concentration. The compound flame is similar to premixed gas combustion under optimal methane concentration, the combustion zone thickness (δ) and preheating zone thickness (β) are the smallest, and the compound explosion shows powerful performance. In addition, the flame propagation mechanisms of methane/coal dust compound explosion were elucidated based on the theory of heat.

Insight into energy release characteristics of TiH2 dust explosion through ignition experiments and molecular dynamic simulations

TiH2 is an efficient hydrogen storage material with high energy density and relatively stable chemical quality, which is commonly used in metal sponge production, hydrogen storage, battery technology, rocket propellants, etc. In this study, TiH2 dust explosion is systematically investigated by integrating ignition experiments with reactive force field molecular dynamics simulation. Findings show that when the TiH2 dust concentration is 750 g·m−3, both the explosion pressure and explosion pressure rise rate reach their maximum values under airtight and venting conditions. There are three stages in the whole combustion process: the combustion development stage, the stable combustion stage, and the decay stage. The flame length (L) and flame propagation velocity (v) grow with the increase of dust concentration. TiH2 dust explosion with different concentrations in macroscopic tests is approximated by simulating the combustion behaviors of the TiH2 system with different densities. The combustion reaction rate of TiH2 grows with an increase in system density, and the simulation results are consistent with experimental findings.

Construction of Al@PTFE composites with excellent ignition and combustion properties through mechanical and thermal activation

Fluorine-based aluminum thermite have excellent ignition and combustion properties. Nonetheless, its combustion kinetics and energy release are hindered by slow mass diffusion and incomplete reactions. Therefore, this study successfully prepared an Al@PTFE composite with a core-shell structure, utilizing mechanical activation and sintering techniques, to enhance combustion properties and energy release rate. SEM, XRD, FTIR and XPS characterization results demonstrate the unique core-shell structure of the samples and the homogeneous distribution of elements on the surface. In comparison to the physical mixture, the Al@PTFE composite exhibits significantly higher values for Pmax (2.19 times), Pmax/Δt (11.30 times), and flame propagation velocity (4.5 times). Furthermore, the combustion duration required to reach the maximum flame height was reduced by 131.75 ms. The adsorption, decomposition and reaction processes of PTFE on the surface of aluminum particles were demonstrated based on RMD simulations. The promotion mechanism of PTFE on combustion in aluminum particles was elucidated.

A study of the effect of hydrogen on methane deflagration characteristics in a square confined space

Macroscopic and microscopic explosion kinetic properties of H2/CH4/air mixtures are investigated. The explosion characteristics of CH4/air mixtures with different hydrogen blending ratios(0–25%) are investigated experimentally. It is found that the increase of hydrogen blending ratios has almost no effect on the peak overpressure of the methane gas explosion, but the rate of maximum pressure rise, the explosion index and the flame propagation velocity increase significantly. The effect of hydrogen blending ratios on the chemical kinetics of CH4-air mixtures is analyzed based on the CHEMKIN software. The concentration of key radicals, which play a major role in the reaction, does not change much as the hydrogen blending ratio increases. A prediction model of explosion overpressure in a square confined space is established using the segmentation method, and it is verified that the relative errors between the model calculation results and experimental results are less than 10%.

Features of the Mechanism of Gas-phase Ignition of Wood Biomass Particles

ABSTRACT Use of woody biomass instead of coal as fuel for thermal power plants (TPP) is considered a promising direction for reducing emissions of anthropogenic substances during the operation of coal-fired thermal power plants. But the process of replacing coal with wood in the thermal power industry is happening very slowly due to objective reasons. The main one is the deposition of particles that have not fully passed the pyrolysis stage (in this case, a layer of substance in a resinous state is retained in the wood particle) on heating surfaces (for example, superheaters) and a decrease in the efficiency of using the heat of combustion of fuel as a result of contamination of the heating surfaces. Therefore, when developing technologies for burning dispersed wood in the furnaces of boiler units, reliable experimental data are required on the characteristic times of ignition and combustion of woody biomass particles, taking into account the time of transition from local (focal) gas-phase ignition to the combustion of volatiles in the entire vicinity of the particle (tsf). The article presents the results of experimental studies of flame propagation processes in the small vicinity of a particle during the ignition period. The experiments made it possible to establish that the flame propagation velocity in the small vicinity of the particle significantly depends on the ambient temperature. It is shown that under conditions of low-temperature heating (air temperature Tg = 873 K), the propagation velocity of the combustion (flame) is minimal. An increase in Tg values (from 873 K to 1273 K) leads to a significant (4–5 times) increase in the time of complete flame coverage of the particle. According to the results of the experiments, two heating modes were identified: high-temperature and low-temperature with a conditional interface Tg = 873 K. At Tg = 873 K, the characteristic particle size of wood biomass has no significant effect on the characteristics and conditions of flame propagation in a small vicinity of the particle. An increase in the ambient temperature (up to 1273 K) leads to an increase in the influence of particle size on the characteristics and conditions of flame propagation. A hypothesis describing the process of flame propagation has been developed.

Influence of Side Duct Position and Venting Position on the Explosion and Combustion Characteristics of Premixed Methane/Air

In order to explore the influence of the side duct position and venting position on the premixed combustion and explosion characteristics of methane/air, a premixed combustion and explosion experiment of methane/air and a simulation of an explosion of the same size were carried out in a tube with an internal size of 2000 mm × 110 mm × 110 mm. The results showed that the side duct could change the flame structure and accelerate the flame inside the tube. The maximum increase ratio of the flame propagation speed was 106.1%. The side duct had a certain venting effect on the explosion pressure. For different position cases, when the venting film was placed over the bottom section, the maximum overpressure first decreased and then increased. When the venting film was placed over the middle section and the top section, the maximum overpressure first increased and then decreased, and the change trend of the top section was stronger. Turbulence mostly occurred inside the side duct when the venting film of the side duct ruptured. There is no linear relationship between the maximum flame propagation velocity within the tube and the maximum turbulent kinetic energy inside the side duct. The two had a relationship that could be fitted to the Gauss function; the correlation coefficient R2 was 0.836, and the minimum value was at (4767.72, 17.918), suggesting that the side duct had the best venting effect on the flame inside the duct at this maximum turbulent kinetic energy. The analysis results of the influence of the location of the vent on the maximum flame propagation velocity inside the tube are helpful for optimizing the layout design of the underground space, reducing the combustion efficiency, and ensuring the safety of the process.

Experimental study on characteristics of flame propagation and pressure development evolution during methane-air explosion in different pipeline structures

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.

Experimental research on the synergy effect of resistance/inhibition on the syngas explosion

This experimental research focused on the combined effect of wire mesh and spray mist on the syngas explosion. The difference between flame propagation and pressure rise under success and failure conditions was analyzed, and the influence rule and mechanism of spray condition were determined. Results indicate that the synergistic effect was related to the spray condition and was affected by mist parameters. Nozzle type and spray pressure could change the mist parameters, thus affecting the inhibition effect of mist on explosion. Compared with failure condition, the pressure history of lower end only presented an acceleration process under success condition, and the pressures at both ends were evidently decreased. As the nozzle type increased, the mist parameter was increased. Flame propagation velocity and explosion intensity of upper end were reduced. Especially, the dwell time of flame inside the wire mesh was prolonged. As the spray pressure increased, the comprehensive effect of changes in mist parameters resulted in a change process of failure - success - failure. The velocity history and explosion intensity showed a trend of decreasing first and then increasing. Temperature history also exhibited the same variation regular. Apart from the energy weakening and wall effect of wire mesh on flame and compression wave, the flame front would form four structures affected by water mist: the laminar flame, small-scale weakly turbulent flame, large-scale weakly turbulent flame, and large-scale strong turbulent flame after contacting with mist. The change of mist parameters could cause varying degrees of disturbance and pulsation intensities on flame front, thereby affecting the physical and chemical effects of mist on flame. The inhibitory effect of wire mesh could be enhanced on the syngas explosion after adding mist, and was affect by the comprehensive effect of mist parameters.

Study on the synergy inhibition of ultrafine water mist and metal wire mesh on the syngas explosion

Synergy inhibition of wire mesh and spray mist on syngas explosion was researched. The correspondence between the explosion parameters under success and failure conditions were analyzed, and its influence regular and inhibition mechanism were revealed. An evident difference appeared in the correspondence at different synergy results. Compared with the failure, the pressure of lower end only experienced an acceleration rise under the success condition although the propagation velocity of flame was slightly increased as it approached wire mesh. Corresponding pressure was also reduced. After passing through wire mesh, flame propagation was evidently accelerated due to the turbulence disturbance caused by wire mesh despite the strong endothermic effect of mist. The corresponding explosion reaction rate was also increased. Pressures of two ends did not appear obvious change under the success condition, but the pressure of upper end was evidently reduced compared with the failure. Due to the combined effect of wire mesh disturbance and mist heat absorption, the velocity history showed a change of increasing firstly and then decreasing as the spray time increased after passing through wire mesh. The synergy inhibition was attributed to the combined physical and chemical effects, and was related to the syngas concentration and spray amount.

Application of microencapsulated fibrous carrier inhibitors in suppressing flake aluminum dust explosion: Performance and mechanism

Flake aluminum powder (FAl), due to its larger specific surface area and higher reactivity, posing a potential threat to the process safety of involved enterprises. To mitigate the explosion caused during the production of FAl, a green composite inhibitor, Sep@CS@PA-Na, was successfully prepared in the aqueous phase using microencapsulation technology with sepiolite (Sep), chitosan (CS), and sodium phytate (PA-Na) as raw materials. The suppression of FAl explosions in a vertical combustion duct system by inhibitors with different inerting ratios (α) was investigated. The results showed that after adding Sep@CS@PA-Na with an α of 0.75, the maximum flame propagation velocity (Vmax), the average flame velocity (Vavg), and the velocity of the flame reaching the pipeline top (Vtop) decreased by 79.6%, 75.1%, and 86.2%, respectively, and the reduction of the maximum flame front pressure (Pmax) and the maximum flame pressure rise rate ((dP/dt)max) were 90.4% and 89.8%, respectively, and the peak temperature (Tp) dropped to 505°C. Combined with TG-DSC and explosion product analysis, Sep@CS@PA-Na possessed both gas-phase reaction and surface reaction suppression functions, which were mainly reflected in the dilution effect, quenching effect, and barrier effect. This work will provide technical support for the emergency prevention and control of energetic metal dust explosions.

Experimental Observation of Flame Propagation Behavior of Hydrogen Enriched Flames Upstream of a Flame Arrester Housing with Parallel Plates as the Arrester Element

ABSTRACT The phenomenon of flame propagation in closed and semi-open ducts that have no obstacles is of interest due to the need to include alternative fuels into the energetic matrix. Tulip flames can develop under these configurations. Therefore, the behavior of flame propagation upstream of a flame arrester housing is relevant to assess the challenges of flame quenching under this configuration. The objective of this article is to investigate the effect of the effective Lewis (Leeff ) number, Zeldovich (Ze) number and initial pressure (p i ) on the flame propagation behavior upstream of a flame arrester housing with parallel plates as the flame arrester element. The Leeff and Ze numbers were varied between 0.60 and 1.36 and between 4.19 and 8.77 respectively. In addition, the initial pressure was varied from 40 kPa to 80 kPa. The mixtures considered involved natural gas, hydrogen, helium and air, which were stoichiometric in all cases. It was observed that the tulip flame developed in all cases, but with different positions of the tulip flame formation. This is important for the development and testing of flame arresters as the inlet velocity and pressure are influenced by this phenomenon. The maximum flame propagation velocities (V max ) and the maximum pressure ratios (p max /p i ) were also determined. It was found that V max decreased for higher values of the product Leeff ⨯Ze for all mixtures and initial pressures. Similarly, p max /p i decreased with increasing Le eff ⨯Ze for the initial pressures of 40 kPa and 60 kPa. A slightly different behavior was observed for pmax/pi at 80 kPa, which did not decrease significantly with higher Leeff ⨯Ze. Therefore, the flames were characterized by weak acceleration and moderate pressure ratios.

The influence of pipeline deposited dust on the explosion propagation of dust collector

An explosion experiment involving corn starch was conducted using a small tank directly connected to the pipeline. The objective was to investigate how the mass and location of deposited dust in the pipeline affect the explosion pressure and flame propagation characteristics of the dust cloud. The results revealed that when the container was at the optimum dust explosion concentration, as the mass of deposited dust increased, the maximum explosion pressure of both the container and pipeline increased and then decreased. Additionally, the maximum flame propagation velocity and flame propagation length gradually decreased as deposited mass increased. Furthermore, as the distance between the location of deposited dust in the pipeline and the container increased, the maximum explosion pressure increased and then decreased. Similarly, the maximum flame propagation velocity demonstrated a similar trend, whereas the flame propagation length gradually increased. In conclusion, the study's findings offer a theoretical foundation for scientifically assessing and effectively preventing and controlling explosion disasters in dust removal systems.

Combustion Of Methane With Microdroplets Of Water In A Weak Electric Field

The effect of a weak electric field on the flame of a Bunsen burner, including the case of an aerosol consisting of water microdroplets in an air-methane mixture has been studied in detail. The propagation velocities of the laminar flame have been determined. If the stabilization area (burner edge) and the flame tip are excluded from consideration, the average propagation velocity of a laminar flame in the absence of an electric field is constant. For a stoichiometric mixture of methane with air and aerosol combustion, it is equal to Su≈0.35 and 0.3 m/s, respectively. When an electric field is applied, there is a common trend for cases of combustion of methane and a gas-droplet mixture, i.e., maintaining the flame front propagation velocity from the anode side and increasing by about 8-10% from the cathode side.