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• Burst pressure has a significant effect on the hazard of hydrogen explosion venting. • The damage area of the venting flame increases with the increase of burst pressure. • Mastering dynamic evolution is the effective means of achieving explosion protection. • Mastering explosion protection mechanisms is essential for the hydrogen development. A series of experiments are carried out to investigate the effect of burst pressure on hydrogen explosion venting in a 20 L square vessel. Pressure buildup and flame evolution are recorded using piezoelectric pressure transducers, high speed camera, high speed infrared camera and schlieren system. The results show that both the maximum explosion pressure (P max) inside and outside the vessel increase with the increasing burst pressure, and the P max in the external space decreases rapidly with the increase of the distance from the vent port. Compared to the burst pressure of 0 kPa, the P max inside the vessel and at 1200 mm increased by 79.1 % and 153.6 %, respectively, when the burst pressure was 325 kPa. The venting flame surface during the propagation is smoother with the increasing burst pressure, the width and area of the flame also increases. There is little effect of burst pressure on the maximum flame propagation distance (L max), but with the increase of burst pressure, the flame propagation time is shortened and the average propagation velocity is increased. The venting flame propagation time is shortened from 5.0 ms to 3.5 ms with the burst pressure increases from 0 kPa to 325 kPa. The high temperature zone of venting flame is mainly distributed in the flame front, while the maximum flame temperature (T max) gradually increases with the increase of burst pressure. The increase in burst pressure results in an increase in the turbulence intensity inside the vessel and an advance in the time to stabilization inside the vessel. Furthermore, the moment at which flow backflow occurs at the vent port is advanced from 16.5 ms to 8.5 ms with the increase in burst pressure. [ABSTRACT FROM AUTHOR]

Hydrogen explosions happen occasionally, resulting in heavy casualties and huge property losses. Explosion venting as an effective method of explosion protection need to be further studied. In this work, the influence of hydrogen concentration (20%–60%) on the explosion venting was investigated. It was indicated that the maximum explosion pressure (P max) inside the vessel and in the vent pipe first increased and then decreased with the increase of hydrogen concentration. The P max in the vent pipe was always much larger than that inside the vessel. However, the P max outside the vessel increased gradually with increasing hydrogen concentration. The propagation characteristic and the temperature field distribution of the explosion venting flame were also analyzed. There was no obvious venting flame for 20% hydrogen concentration, because of the exhaustion of hydrogen inside the vessel. The change of the concentration affected the occurrence of secondary explosion, which affected the flame morphology, propagation velocity and flame temperature field distribution. The maximum temperatures were 1164 °C and 1207 °C for 50% and 60% hydrogen concentrations. Furthermore, changes of hydrogen concentration resulted in changes of the explosion intensity inside the vessel, thus affecting the flow field microstructure inside the vessel and near vent port. The stronger the explosion intensity, the more unstable the flow field microstructure and the shorter the time required to reach stability inside the vessel. • The influence of hydrogen concentration on the explosion venting was investigated. • P max externally increased with increasing concentration, unlike inside the vessel. • Flame propagation velocity and temperature distribution were analyzed intensively. • Second explosion affected the flame characteristics at high hydrogen concentration. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Synergy effect of resistance/inhibition on protection of gas explosion was studied. • Correspondence between explosion parameter during success and failure was clarified. • Effects of mist amount and syngas concentration on explosion parameter were grasped. • Critical value of synergy effect for complete inhibition of explosion was proposed. • Effective engineering guidance was proposed and its synergy mechanism was revealed. [ABSTRACT FROM AUTHOR]

• Venting characteristics of gas/dust hybrid explosions was researched by experiment. • Relationship between the venting flame propagation and pressure rise was clarified. • Propagation characteristics of venting flame and its change mechanism were studied. • Distribution and variation of venting flame temperature field were analyzed deeply. • Physical model of gas/dust two-phase explosion venting process was established. This research focused on the venting characteristics and influence factor of methane and coal dust mixture explosions. The corresponding relationship between the venting parameters was analyzed and the effect of methane concentration was obtained. Results indicate that the venting flame propagation and pressure rise of vessel interior and exterior presented the clear corresponding relationship. The venting flame underwent the evolution process of "mushroom", "spherical" and "strip" structures. At 6% methane concentration, the venting flame was longest and its propagation velocity was fastest. During the extinguishing stage, the flame exhibited an obvious oscillation. The venting flame appeared a secondary venting phenomenon at 6% and 8% methane concentrations, and the phenomenon was more evidently at 8% methane concentration. The pressure at the venting pipe was the greatest and its change was also most significant, even appeared a larger negative value. Compared with the vessel interior, the pressure of vessel exterior was continuously decreased as the venting distance increased. The venting pressure was the greatest at 6% methane concentration, followed by 8% methane concentration. The pressures of four points at 4% methane concentration were respectively reduced by 25.0%, 34.9%, 43.8% and 81.8%. The corresponding flame temperature also presented the same change trend. Besides, the venting flame image showed a good correspondence with the temperature field distribution and the highest temperature appeared in the center of spherical flame. The secondary venting resulted in the recurrence of high temperature flame at the venting port (500℃-650℃) and was affected by the methane concentration inside the vessel. [ABSTRACT FROM AUTHOR]

The flame resistance characteristics of wire mesh and its influence factor on syngas explosion were researched by experiment. Relationships between flame propagation and pressure rise at the flame resistance system two ends were clarified under different flame resistance results. And the effect of syngas concentration on explosion parameters was obtained and flame resistance mechanism was also revealed. Results indicate that the existence of wire mesh could indirectly affect pressure rise by affecting the flame propagation, and flame propagation and pressure rise presented a clear corresponding relationship. The wire mesh could play a better inhibiting role and reduce the explosion intensity, affecting by syngas concentration. As the flame resistance failed (c =30%), △ P max was effectively decreased from 0.81 MPa to 0.52 MPa above wire mesh and from 0.58 MPa to 0.39 MPa below wire mesh. And the reduction extent was more significant under flame resistance success (80.25% and 68.97%). With reduction of syngas concentration and increase of mesh layer, explosion parameters were evidently decreased. Especially the temperature above wire mesh did not present an increase trend and reach the ignition point of syngas under flame resistance success. The inhibition mechanism was mainly attributed to the combination of endothermic and wall effects. [ABSTRACT FROM AUTHOR]

• The temperature of H 2 jet flame with suppressants addition are analyzed. • Water mist containing DMMP exhibit good suppression effect on H 2 jet flame. • The influence of DMMP on lean CH 4 and lean H 2 flames is compared. • There is no combustion enhancement effect of DMMP on lean H 2 flame. This work investigates the suppression effect of water mist containing dimethyl methylphosphonate (DMMP) on H 2 jet flame. The flame appearances are analyzed and the flame temperature is recorded by a high-speed infrared camera. Results show that the suppression effect of water mist containing DMMP is better than that of pure water mist. To better understand the suppression effect of water mist containing DMMP, the burning velocity, heat production and free radicals are analyzed. Results indicate that suppressant could scavenge lots of free radicals to reduce the burning velocity in a wide range of equivalence ratios. Moreover, the influence of DMMP on lean CH 4 and H 2 flames is compared. Different with that of lean CH 4 flame, the combustion parameters of lean H 2 flame decline with DMMP addition. There is no combustion enhancement effect of DMMP on lean H 2 flame. Because of the higher combustion intensity of lean H 2 flame, the hydrocarbon in DMMP has little impact on the combustion. Furthermore, the reaction path of DMMP decomposition is analyzed. Results demonstrate that the rates of most phosphorus reactions in H 2 flame are larger than that in CH 4 flame. This work could provide foundation for improving the safety of hydrogen energy application. [ABSTRACT FROM AUTHOR]

• Inhibition characteristics of mist on gas/dust explosions was studied by experiment. • Pressure, flame temperature, propagation characteristics and products were analyzed. • Relationship between mixture explosion parameter under mist condition was clarified. • Effects of mist and methane concentrations on explosion inhibition were obtained. • Effective engineering suggestion was proposed and inhibition mechanism was reveale. Inhibition of water mist on the gas/dust two-phase explosions and its influence factor were studied inside the vessel. The effects of mist and methane concentrations on the pressure and its rise rate, flame propagation characteristics and its temperature were explored. Especially the explosion products were analyzed by the infrared spectroscopy. The weakening effect was revealed based on the corresponding relationship and changing rule of explosion parameters. As the flame developed and changed, the pressure rise showed the same correspondence. However, the corresponding moment was evidently prolonged compared with the case no mist. The mist could effectively inhibit the intensity of mixture explosions, causing a dark-irregular structure in the early stage and accelerating its extinction in the later stage. After the mist concentration increased, the explosion parameter was evidently reduced. As the methane concentration increased (4% ≤ c ≤ 10%), the explosion parameters appeared a trend of firstly rising and then reducing. As c = 6%, the explosion intensity was the greatest. After adding mist, the explosion parameter exhibited the same change regular. And the weakening effect of mist on the weaker flame was more outstanding and was constantly enhanced as the rise of mist concentration. Besides, the mist could effectively inhibit the pyrolysis and combustion reactions of macromolecular functional groups, further leading to evident increase in the functional group content inside the coal dust as the mist concentration increased. [ABSTRACT FROM AUTHOR]