Deflagration Process Research Articles

Visualization Study of Methane Deflagration Characteristics in Variable Diameter Pipelines Based on Schlieren Technique

ABSTRACT The phenomenon of pipe diameter change often exists in urban natural gas pipelines. To study the impact of pipe diameter variation on the propagation characteristics of combustible gas deflagration and provide theoretical basis for the prevention and emergency treatment of gas pipeline explosion accidents, this work uses a self-developed circular explosion pipe test bench with a length of 12 m and an inner diameter of 90 mm to study the methane deflagration characteristics in variable diameter pipelines. Under four experimental conditions of variable cross-sectional area ratio (VR) of 1.0, 0.6, 0.4, and 0.2, the schlieren images of the deflagration process of methane/air premixed gas with a methane concentration of 9.5% were captured by a high-speed camera. Combined with the traditional pressure and flame signal point source information, the research results show that the existence of variable diameter pipelines can change the flame structure and shape, causing the flame front to transform into a tulip flame in advance. The flame propagation speed under different experimental conditions is: VR = 0.4 > VR = 0.2 > VR = 0.6. The influence of the variable diameter pipeline on flame velocity depends on the suppression effect of the reflected wave generated by the cross-section area of the variable diameter pipe and the coupling effect of the reduced aperture area of the variable diameter section on the flame acceleration effect. When the reflected wave acts on the flame front, the flame propagation speed decreases, and in severe cases, it will cause flame stagnation and backfire.

Flame instability and heat transfer effect during deflagration of premixed hydrogen in tunnel

In the process of hydrogen deflagration, thermal diffusion and fluid dynamics instability lead to the instability of premixed flames. With the enhancement of instability, the behavior of the flame front becomes unstable, leading to an increase in flame surface area and flame speed. This study used the three-dimensional full-speed CFD code GASFLOW-MPI to perform numerical simulations of tunnel model deflagration experiments based on the compressible Navier-Stokes equations. The turbulent combustion model used in the study takes into account the effects of thermal diffusion instability, fluid dynamics instability, and local turbulent disturbances. This paper quantitatively calculates the thermal diffusion and fluid dynamics instability to explore their effects on developing tunnel premixed hydrogen deflagration flames. Based on the effective Lewis number of the unburned premixed gas of the flame front and the ratio of thermal expansion to the flame thickness, the interaction behavior between them is analyzed. Additionally, this paper explores in depth the influence of heat transfer boundary conditions on the propagation of flame instability. Results show that the calculation results of the combustion model considering heat transfer effects are highly consistent with the experimental values, demonstrating the importance of heat loss in the overpressure peak and pressure decay process. During the deflagration process, thermal radiation plays a leading role, while heat convection makes the main contribution to heat loss during pressure decay. As the flame evolves, the destabilizing effect of fluid dynamics instability first increases and then decreases, while the stabilizing effect of thermal diffusion instability gradually weakens and transitions to a destabilizing effect, with both effects mutually reinforcing each other. Heat transfer effects delay mixing hydrogen-premixed gases with fresh air, slowing the transition of thermal diffusion instability from stability to instability, weakening the destabilizing effect of fluid dynamics instability, and thereby delaying the evolution process from competition to promotion between the two.

Numerical simulation study on the effect of ignition position on premixed hydrogen deflagration characteristics in tunnels

To analyze the influence of different ignition positions on the propagation of deflagration characteristics and the disaster mechanism in the hydrogen deflagration process in the tunnel, this study compares and verifies the experimental data of tunnel model deflagration based on the CFD code GASFLOW-MPI. A combustion velocity model based on the accelerated separation effect is used, and the effect of heat transfer on the consequences of deflagration is considered. The propagation laws of pressure waves, fluid velocity and temperature in the tunnel are analyzed, and it is found that the changing trends of shock waves and fluid velocity in the tunnel are consistent, but completely opposite in the tunnel outside. The effects of different ignition positions on the hydrogen deflagration characteristics are compared and analyzed. The results show that when ignition occurs at different heights of the center of the premixed region, the impact on the deflagration characteristics is relatively small, while when ignition occurs at different horizontal distances in the premixed region, the impact on the deflagration characteristics is relatively large; the peak overpressure of side ignition is far lower than the case where ignition occurs in the center of the premixed region, but the maximum flow velocity is much higher than the center ignition. The impact on temperature is the smallest. In general, in areas close to the hydrogen/air premixed zone, side ignition results in more severe consequences, whereas in areas far from the premixed zone and outside the tunnel, central ignition leads to more severe consequences. This study provides theoretical support for understanding the disaster-causing mechanisms of hydrogen/air premixed gas deflagration in tunnels under different ignition positions.

Study on the influencing factors of gas-liquid two-phase explosions of hybrid methane/isoprene on the basis of bush fires

To evaluate the explosion hazard of hybrid isoprene/biogas in a primary forest environment, a 20 L spherical explosion vessel combining with a colorimetric thermometry was used to study the explosion parameters, flame structures and temperature distributions of hybrid isoprene/methane at different methane content and initial temperatures. Furthermore, the relationships between the explosion gas products and explosibility of hybrid isoprene/methane were analyzed. Experimental results showed that when the mass concentration of isoprene was 272.4 g m−3, the explosion pressure, the pressure rising rate, and the average combustion temperature reached their peak values of 0.89 MPa, 63.9 MPa s−1 and 2216 K, respectively. When the mass concentration was fixed at 272.4 g m−3, the explosibility of hybrid isoprene/methane initially enhanced and then decreased with the increasing methane volume fraction, and got the maximum values at 5 vol% methane. It was worth noting that the explosibility of hybrid methane/isoprene weakened continuously as the initial temperature increased, and it exhibited a stronger explosion power at a lower temperature. The research results would be helpful for understanding the deflagration processes and mechanisms of bush fires under various conditions, providing scientific basis for the formulation of its prevention and control measures.

Effect of Temperatures on Flame Propagation of Diethyl Ether Spray Explosion

ABSTRACT The study aims to identify the flame propagation in the diethyl ether (DEE) spray explosion through mathematical analysis by processing the gray-level histogram of the flame images. Different ambient and material temperatures’ effect on flame propagation and structure was investigated using a high-speed camera in a 20-L explosion vessel. The results showed that the overall duration could be divided into combustion and deflagration processes. With the ambient temperature increased, the combustion duration showed a trend of first decreasing, then increasing, and then decreasing again. The combustion zone first increased and then decreased. The explosion duration showed an overall decreasing trend. The explosion duration was longer than the combustion duration, ranging from 152.75 to 307 ms. The overall combustion and explosion duration trend was consistent with the explosion duration. When the ambient temperature was 308.15 K, the combustion duration reached its minimum value of 13.25 ms, and the equivalent radius of the combustion zone reached its maximum value of 52.89 mm. With the increase in material temperature, both the combustion and explosion durations showed a trend of first decreasing and then increasing, with combustion durations ranging from 12.42 to 16.25 ms and explosion durations ranging from 106 to 117.5 ms, respectively. When the material temperature was 308.15 K, the combustion zone expansion rate reached its maximum value of 10.20 m/s, and the explosion zone expansion rate reached its maximum value of 13.36 m/s. The effect of ambient temperature on the development of combustion zone is greater than that of material temperature, which is mainly reflected in the obvious change of equivalent radius.

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

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

A grain-scale modeling on the surface burning and agglomeration of the metalized solid propellants

This study delves into the dynamic behavior of reactive grains within metalized propellants during surface deflagration. Our grain-scale simulations account for both fast and slow deflagration processes involving two distinct metal fuels, namely zirconium and magnesium, with potassium perchlorate (KClO4) as the common oxidizer. Our primary goal is to develop a model and numerical technique capable of replicating the surface reactions observed in experiments. To achieve this, we utilize the compressible Navier–Stokes equations, incorporating the Arrhenius rate law and Johnson-Cook stress model. We pay particular attention to the melt layer, where surface burning occurs in an open atmosphere, and we develop a mechanism to describe the interaction between reactive grains and exhaust gases. We differentiate between two limiting scenarios: convective burning, where unreacted particles experience high-speed compression waves leading to reduced thermal diffusion within the cold reactant, and diffusive burning, characterized by insufficient pressure from particles undergoing both reaction and deformation to erode the burning surface. This results in pronounced agglomeration and the formation of gaseous metal oxides above the melt layer. The results shed light on critical factors influencing surface combustion, including the thermal softening of reactive particles, the time required for particle agglomerations, and tangential forces at multi-element interfaces within the grain-scale simulation domain.

Study on the influence of ignition position on the deflagration characteristics of oil mist in ship cabins

ABSTRACT In order to study the effect of ignition position on the deflagration characteristics of oil mist in ship cabins, a self-constructed simulated cabin experimental platform was created to conduct experiments on the effect of ignition position on oil mist deflagration characteristics. The results indicate that the deflagration process of oil mist under various conditions can be divided into four stages, they are respectively deflagration, turbulent combustion, flame stretch and self-extinguishing. The peak velocity of flame propagation decreases with the increasing of the distance between the ignition position and the nozzle. When the distance increases from 13 cm to 83 cm, the peak velocity decreases by 6 m/s with a reduction of 57.14%. The peak temperature inside the cabin decreases with the increasing of the distance between the ignition position and the nozzle. When the distance increases from 13 cm to 83 cm, the peak temperature decreases by 118.2°C with a reduction of 13.94%. The pressure distribution inside the cabin after ignition increases first and then decreases. As the distance between the ignition position and the nozzle increases, the peak pressure at various positions also increases, and the maximum peak pressure is located at 110 cm in the cabin. At the ignition position of 83 cm, the peak pressure reaches the maximum value of 1.603 MPa, which increases by 0.858 MPa (115.17%) compared with the ignition position of 13 cm.

Experimental study on deflagration characteristics of non-uniform oil mist in an enclosed chamber

The deflagration characteristics of oil mist in the marine enclosed chamber are studied. The results show that oil mist deflagration in a non-uniform enclosed chamber is a violent process. When the nozzle size is 1.0 mm, the maximum oil mist deflagration overpressure in the chamber can reach 0.945 MPa. Increasing the nozzle size strengthens the deflagration intensity of oil mist. As the nozzle size increases, the oil mist deflagration flame propagation velocity, peak deflagration overpressure, and gas temperature increase. In addition, the oil mist deflagration process is facilitated by the increase in injection pressure. The maximum flame propagation velocity and maximum deflagration overpressure gradually improve with the increase in injection pressure. This is mainly because the increase in injection pressure leads to better atomization of oil mist droplets, increasing surface area of the oil mist, and the increase in oil mist concentration, which makes the intensity of oil mist deflagration in the enclosed chamber more intense. Nozzle size on the intensity of oil mist deflagration is more influential than the injection pressure.

Fluorinated graphene-containing Al/CuBi2O4 nanothermites for a transient destruction process of microchip

Countless valuable or private information is stored in electronic devices, thus the research in improving the security-grade for electronic systems has flourished in the digital age. In this work, a novel ternary nanthermite is assembled by the prepared double-based metal oxide (CuBi2O4), commercial Al and fluorinated graphene. Owing to the combining features of both CuO and Bi2O3, these formulations exhibit a higher energy release and pressure output. Besides, the introduction of fluorinated graphene further enhances the pressure release. Therefore, the thermite system containing 5 wt% fluorinated graphene displays violent deflagration process, which can perform a reliable destruction behavior for the simulative microchip in 4 ms with only 20 mg. To sum up, this study will offer a new insight for the protection of digital information.

Numerical Analysis on Detonation Wave and Combustion Efficiency of Pulse Detonation Combustor With U-Shape Combustor

Abstract The research work is carried out for deflagration and detonation combustion processes at different equivalence ratios of hydrogen–air mixtures in a pulse detonation combustor (PDC). Furthermore, the U-shape channel curvature radius and thickness effect on detonation wave propagation are also investigated. This numerical simulation has been done using a SIMPLE algorithm with the finite volume discretization method and laminar finite rate chemistry for volumetric reaction in the Ansys Fluent platform. The numerical result shows that the U-bend radius of R = 3.5 cm can enhance the faster deflagration-to-detonation transition. So far, the fully developed detonation wave was found near the curvature area of the detonation tube having a width of W = 8 cm. This enhanced detonation wave velocity reaches 2775 m/s, which is higher than the C-J detonation velocity. Furthermore, the entropy generation has been analyzed in two modes of the combustion process. The entropy generation number of 0.76 and 0.7 is obtained from the deflagration and detonation combustion processes. However, the entropy production rate is less in the detonation combustion process, but thermal entropy generation is more in the deflagration combustion process with a magnitude of 3.5 kJ/kg K for an equivalence ratio of φ = 1.5. A combustion efficiency of 78% is found in the detonation combustion process, which is comparatively higher than the deflagration process.

Numerical analysis of the distribution of combustion products from methane explosions in a full-scale tunnel using all-speed CFD code GASFLOW-MPI

ABSTRACT Methane explosions are among the main hazards in coal mines. Shock waves from methane explosions can cause damage near the explosion site, and combustion products can spread along the tunnel to locations far from the explosion source and endanger the lives and health of personnel. Therefore, the study of the propagation patterns of methane explosion shock waves and the distribution of high-temperature combustion products in tunnels. has significance for emergency decision-making in the event of methane explosions in a mine. This study uses the 3D Computational Fluid Dynamics (CFD) program GASFLOW-MPI, which models the one-step methane combustion mechanism with the addition of a heat transfer model. The methane explosion process is simulated and reproduced at the Lake Lynn Experimental Mine (LLEM) to analyze the process of gas deflagration. The results reveal that the overpressure in the tunnel after the methane explosion oscillates and decays with time. Gaseous products of the explosion “expand and compress” and flow back and forth in accordance with the oscillation of overpressure. The maximum expansion ratio of the CO2 concentration isosurfaces of 0.5% in the heat transfer simulation is 6.21, whereas the volume expansion ratio is 3.78 once the flow field stabilizes. The distribution of combustion products along the alleyway exhibits a Gaussian decay trend. The range of gaseous product distribution and temperature fields in the adiabatic tunnel is significantly higher than that in the heat transfer simulations, thus indicating that heat loss significantly influences the temperature characteristics and distribution pattern of combustion products in the full-scale tunnel.

Comparative study on methane/air deflagration with hydrogen and ethane additions: Investigation from macro and micro perspectives

Natural gas usually contains a small amount of hydrogen and ethane in addition to methane, which would pose a threat to the safety of natural gas production and utilization by affecting its explosion risk. In order to reveal the effect mechanism of hydrogen and ethane on methane deflagration, the deflagration behaviors of methane-hydrogen/ethane-air mixtures([CH4]=7.0, 9.5, 11.0 vol. %; [H2]=0–2.0 vol. %; [C2H6]=0–2.0 vol. %) at normal temperature and pressure are compared and analyzed from macro and micro perspectives. The results indicate that the deflagration pressure and the spectral intensity of free radicals (H* and OH*) show different change trends depending on equivalent state of the system with adding hydrogen or ethane to methane/air mixtures. There is a parabolic relationship between the average rising rates of deflagration pressure (VP) and spectral intensity (VI) and they are positively correlated. The contribution of H* to deflagration pressure gradually decreases while the promotion of OH* to it increases with the volume fraction of methane changing from 7.0 % to 11.0 %. Besides, the top 10 most significant elementary reactions were obtained in the methane deflagration process with adding hydrogen and ethane. Hydrogen promotes methane deflagration by reacting with OH and O, while ethane contributes to it by reacting with OH and CH3.

Reticulated effectiveness assessment of polyurethane form in the melting process with deflagration method

The flexible polyurethane foam (FPUF) is widely used in the impact damping, noise insulation and other fields because of its good mechanical properties and porous structure. Unlike the previous methods, deflagration method can effectively remove partial original membrane while preserving skeleton structure, and is an environmentally friendly treatment process, representing an efficient and simple operation technology. Combustible premixed gas (CPG) is vital for deflagration process and can determine the reticulated effectiveness of polyurethane foam. The research purpose of this paper is to study the effect of the combustible premixed gas (CPG) parameters (the inflation coefficient, gas type and gas concentration) on the open porosity index of the polyurethane film through modeling and simulation methods. Based on the established mode, the paper uses the standard k-ε model coupling with the melting-solidification model based on the enthalpy-porosity method. The numerical simulation results demonstrate good agreement with the experimental data. The external surface center temperature (ESCT) is probably not constant but increases with the inflation coefficient. The analysis demonstrates that inflation coefficient significantly affects the concentration of CPG. Since the calorific value of combustible gas is limiting, a suitable union of inflation coefficient and concentration would provide better utilization of the method. Combustible gas with high calorific value were able to achieve an average open porosity promotion 0.275 within the inflation coefficient rage from 1 to 5. The approach adopted allows to provide heoretical basis for the efficient and standardized production of flexible polyurethane foam.

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

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

The effect of hydrogen addition on methane/air explosion characteristics in a 20-L spherical device

The addition of hydrogen to methane changes its deflagration characteristics and increases the combustion rate. However, studies on the effect of hydrogen on methane deflagration remain insufficient. Therefore, based on the CFD code GASFLOW-MPI, a four-step combustion-mechanism model was established for methane/hydrogen mixtures. The deflagration characteristics of a premixed combustible gas in a 20-L spherical device was numerically simulated using a methane/hydrogen/air equivalence ratio of 1 and hydrogen addition in the range of 0–50%; subsequently. The results were compared with experimental data. The four-step methane/hydrogen combustion-mechanism could effectively reproduce the methane/hydrogen deflagration process on considering the heat losses. With an increase in hydrogen addition, the laminar burning velocity increases, and the deflagration duration reduces. It decreases the explosion heat loss and increased the maximum deflagration pressure. Under adiabatic simulation, the maximum deflagration pressure decreased with an increase in hydrogen addition, in contrast with the experimental results. This indicates that the heat-loss effect of the methane/hydrogen/air-mixture deflagration process should not be ignored. Moreover, the heat loss during the methane/hydrogen/air-mixture deflagration was mainly caused by thermal radiation. Thus, the influence of the thermal-radiation and convective heat-transfer mechanisms should be considered in the numerical simulations of methane/hydrogen/air-mixture deflagration.

Engineering in-plane π-conjugated structures in ultrathin g-C3N4 nanosheets for enhanced photocatalytic reduction performance

In this study, an energetic materials (EM) deflagration process coupled with a gas-shocking exfoliation strategy was proposed for the in-situ introduction of a π-electron-conjugated structure into ultrathin g-C3N4 nanosheets. The optimal 2C-CNS sample was endowed with a porous-ultrathin-nanosheets morphology (3–4 nm thickness), larger exposed surface area (144.1 m2/g), and significant pore volume (0.51 cm3/g). Using urotropin-deflagration and gas-shocking-driven processes, the precursors were dissociated and copolymerized in an aqueous solution into g-C3N4 nanosheets chemically modified with conjugated carbon moieties. Most importantly, an expanded π-electron conjugated system was successfully constructed between the carbon moieties that interacted with the ultrathin g-C3N4 (2C-CNS), which endowed its with a faster electron-hole separation efficiency and enhanced visible-light harvesting ability. The H2 evolution rate and Cr6+ reduction efficiency for 2C-CNS reached 2360 μmol h−1 g−1 for k = 0.0301 min−1, which was almost 25.8/23 times higher than that of bulk g-C3N4 (Bu-CN, 91.2 μmol h−1 g−1, k = 0.0013 min−1). Also, 2C-CNS showed 2.8/2.4 times higher performance than the g-C3N4 ultrathin nanosheets without a carbon-section modification (0C-CNS, 853 μmol h−1 g−1, k = 0.0125 min−1).

Three-dimensional discrete element method to simulate the ignition and combustion of HMX explosives under hot spots

The key to the initiation of condensed explosives is the hot spot which is universally acknowledged. Different hot spots will be produced in explosive particles under different impacts, making quite a discrepancy in the combustion and deflagration processes. In this paper, the ignition and combustion behaviors of the cyclotetramethylene-tetranitramine (HMX) explosive particles under hot spots, and the effect of particle size on the ignition and combustion behavior are developed based on the three-dimensional discrete element method (3D-DEM). The simulation results emphasize that the number of hot spots in the explosive will have an important impact on the ignition and combustion of the explosive. The deflagration performance of the explosive may be inhibited when the number of hot spots generated is too large. In addition, the difference in particle size of explosives can also cause differences in ignition sensitivity and deflagration performance. It is believed that fine explosives are easier to ignite, which is consistent with the experimental observation. The simulation results also reveal a positive correlation between ignition sensitivity and deflagration performance. • The HMX with more hot spots may tend to burn rather than explode. • The HMX with small particle size is more sensitive and has better deflagration. • The apparent pressure of HMX under hot spots is negative at the beginning.

Experimental and Numerical Study on the Explosion Dynamics of the Non-Uniform Liquefied Petroleum Gas and Air Mixture in a Channel with Mixed Obstacles

Mixed obstacles have a great influence on the deflagration process of liquefied petroleum gas (LPG)-air premixed combustible gas with concentration gradient. The arrangement of mixed obstacles may further stimulate overpressure and flame propagation. In this work, based on experimental and numerical simulations, this paper analyzes the flame and overpressure, and mainly studies the coupling relationship among the explosion overpressure characteristics, the structure of flame and the speed of flame propagation. The result shows that when the rectangular obstacle is 100 mm away from the ignition source, not only the speed of flame is the fastest, but also the time required to reach the maximum over-pressure is the shortest. In this configuration, an elongated flame is formed between a rectangular obstacle and a flat obstacle, and an obvious backflow structure appears. In addition, the average growth rate of overpressure has a minimum value, reaching at −35 MPa/s. The existence of rectangular obstacles further stimulates the overpressure. When the rectangular obstacle is 400 mm away from the ignition source, the maximum overpressure value is the highest among the four configurations. Besides, the time when the maximum area of flame appears in the simulation is almost the same as the time when the maximum overpressure is obtained. In addition, the average growth rate of overpressure increases significantly after touching the rectangular obstacle, which coincides with the mutation time of the front tip of the flame, overpressure and area of flame after the flame encounters the rectangular obstacle. This research has an important theoretical guiding significance for preventing LPG leakage and explosion accidents in a long and narrow space.

Research on the effect of the vent area on the external deflagration process during the explosion vent

Explosion-vent area is an important parameter for pressure vessel explosion vent design, which is of great significance to the safe operation of pressure vessels. The phenomenon of external explosion occurs outside the vent when the pressure vessel vents. The impact of explosion vent area on the external explosion was researched by numerical simulation in this paper. The results show that the impact of the explosion vent area on the external explosion is relatively significant. The large vent area has a larger area of high pressure, higher pressure and higher fluid turbulence intensity outside the vessel, which leads to more powerful explosion intensity. The smaller vent area leads to weaker external explosion intensity, but leads to higher pressure values inside the vessel. Additionally, the pressure-relief process of vessel with smaller vent area tends to form a “jet fire” and the pressure-relief efficiency is low, in which process, the external flame’s shapes show a long strip. The pressure-relief form of vessel with larger vent area tends to “external explosion” and the process of pressure relief is quicker, in which process, the shape of the external flame showing a “spherical”. Gas from the vent, the under-expansion flow in high-pressure develops into sub-atmospheric in process of moving forward, which can be compressed by surrounding air to intensify the thermochemical reaction, thus prompting the occurrence of external explosions. The larger the venting area is, the quicker the dissipation of the high-pressure area appears. As a result of the external explosion, the Helmholtz oscillation appears inside vessels. Larger vent area leads to larger amplitude and higher frequency of Helmholtz oscillations, in which process, the duration of Helmholtz oscillations is longer.