瓦斯爆炸过程中火焰传播的实验与数值模拟研究

为了研究矿井瓦斯爆炸火焰发展过程中结构与参数的动态变化特征,建立小尺寸管道气体爆炸实验平台,结合高速纹影摄影技术,探测了不同浓度的甲烷-空气预混气体火焰在管道内传播的结构变化特性,并得出速度变化特征曲线。同时建立相应的数学模型和物理模型,通过模拟实验研究管道内气体爆炸反应过程中火焰传播速度变化过程,计算图像和实验图像走向趋向一致。     

壳体厚度对传爆药慢速烤燃响应的研究

针对传爆药在制造、存贮、运输及实战环境中可能会遭受意外的热刺激,本文通过壳体厚度对传爆药慢速烤燃响应特性的影响的实验研究,来检测弹药对意外刺激的敏感程度和发生反应时的剧烈程度,并对实验结果进行了分析。实验以钝化RDX为主装药,以45#钢为壳体,利用自行设计的慢速烤燃试验系统对其进行试验。结果表明：在相同装药条件下,随着壳体厚度的增加,单位时间内传热量减少,体系升温速率减慢,炸药的烤燃时间随之增加,热爆炸延滞期增长;同时,随着壳体厚度的增加传爆药发生慢速烤燃反应的温度升高,热敏感程度降低,热安定性也随之提高。另外,在相同装药条件下,壳体厚度对慢速烤燃响应的剧烈性也有很大得影响。烤燃反应的剧烈程度随着壳体厚度的增大而减小。     

Inerting characteristics of ultrafine Mg(OH)2 on starch dust explosion flame propagation

Experiments on the flame propagation of starch dust explosion with the participation of ultrafine Mg(OH)₂ in a vertical duct were conducted to reveal the inerting evolution of explosion processes. Combining the dynamic behaviors of flame propagation, the formation law of gaseous combustion products, and the heat dissipation features of solid inert particles, the inerting mechanism of explosion flame propagation is discussed. Results indicate that the ultrafine of Mg(OH)₂ powders can cause the agglomeration of suspended dust clouds, which makes the flame combustion reaction zone fragmented and forms multiple small flame regions. The flame reaction zone presents non-homogeneous insufficient combustion, which leads to the obstruction of the explosion flame propagation process and the obvious pulsation propagation phenomenon. As the proportion of ultrafine Mg(OH)₂ increases, flame speed, flame luminescence intensity, flame temperature and deflagration pressure all show different degrees of inerting behavior. The addition of ultrafine Mg(OH)₂ not only causes partial inerting on the explosion flame, but also the heat dissipation of solid inert particles affects the acceleration of its propagation. The explosion flame propagation is inhibited by the synergistic effect of inert gas-solid phase, which attenuates the risk of starch explosion. The gas-solid synergistic inerting mechanism of starch explosion flame propagation by ultrafine Mg(OH)₂ is further revealed.     

A simple design method of dust explosion venting size at elevated static activation pressure

To develop the application of explosion venting technology in high-pressure vessels, a new model for the design of dust explosion venting size was presented, which took the physicochemical phenomenon deriving from the elevation of the static activation pressure into account. Firstly, for confined pressure rise, the wall quenching effect originating from the dust flame thickness was considered by adopting the three-zone model. Secondly, for the venting pressure rise, the energy loss due to the discharge of high-energy burnt mixture (quantified as the specific surface area loss of the flame) was taken into account and the induced turbulence factor was introduced. Thirdly, for the venting pressure drop, a dynamic pressure relief capability evaluation model which takes into account the flame morphology evolution (tear-shaped flame) and the proportion of discharged mixture (relative volume ratio) at elevated activation pressure was proposed. The predicted maximum reduced pressure and venting size were checked against the PMMA explosion experiments and a more great performance was obtained compared with standards.     

Making hybrid mixture explosions a common case

Explosions of gas-dust hybrid mixtures have long been considered as particular cases encountered in specific industrial contexts. However, it should be reminded that during the explosion of an organic powder, the presence of a hybrid mixture composed of the dust itself and its pyrolysis gases is compulsory. On these premises, an experimental study to determine the role of cellulose pyrolysis products (gaseous, condensable and solid) on the global phenomenon is presented. Hybrid mixture explosion tests were exploited to carry out the investigation. The G-G furnace and the 20 L sphere were employed. Several experimental strategies were chosen to demonstrate the impact of pyrolysis reaction on the explosion of organic powders: i) the fuel equivalence ratio of the reactive mixture (case 1), or ii) the mass of reactants (case 2) were respectively kept constant, iii) the effects of water vapor, char and tar were tested. They were next compared to identify the most suitable one. The two first experimental approaches lead to significantly different results: only case 2 keeps the maximum explosion pressure almost constant, but maximum rate of pressure rises and deflagration index greatly decrease when the pyrolysis gases concentration decreases, which highlights the importance of the pyrolysis reaction on the explosion kinetics. It should also be stressed that the maximum explosion severity is not obtained for the pure gases but when a small dust content is added. The same evolution is observed when a small amount of char is introduced to pyrolysis gases, which underlines the influence of the radiative transfer. Adding small amounts of tar to cellulose tends to increase its explosion severity. However, this impact is less than that generated by the addition of pyrolysis gases.     

Study on the preparation of novel NiB/Hβ-Al2O3 micro-mesoporous suppressant and its inhibition mechanism of coal dust explosion flame

Coal dust explosion is one of the serious accidents in the coal industry. It is of great significance to study the flame suppression of coal dust explosions. In this paper, a novel active component NiB with amorphous structure for explosion suppression was synthesized by the chemical reduction method. Furthermore, the novel explosion suppressant NiB/Hβ-Al₂O₃ was prepared through the kneading method by loading novel amorphous NiB nanoparticles on Hβ-Al₂O₃ with the micro-mesoporous structure as the carrier. The morphology and structure of NiB/Hβ-Al₂O₃ were characterized by XRD, BET, SEM, and FTIR, which showed that the NiB/Hβ-Al₂O₃ has proper pore structure and NiB nanoparticles are uniformly distributed as active components for explosion suppression in suppressant. Hartmann tube was used to evaluate the inhibition of coal dust deflagration. The results showed that the flame propagation distance and velocity decreased with the increase of the explosion suppressant. When the addition of explosion suppressant was 30 wt%, the explosion of coal dust was suppressed effectively. Furthermore, combing with the analysis results of the products after coal dust deflagration, the physical and chemical inhibition mechanism of the novel NiB/Hβ-Al₂O₃ explosion suppressant on coal dust deflagration was put forward.     

The influence of melt composition,liquidus temperature and solidus temperature on vapour explosions in melt droplet impingement experiments

For the investigation of vapour explosions, droplet impingement experiments were performed with the binary system Pb–Sn and the pseudo-binary system PbS–Cu₂S. The experiments were performed with a melt at 600 °C (Pb–Sn) or 700 °C (PbS–Cu₂S) and a water bath at ambient temperature and pressure. A hydrophone and a high-speed camera were used to study the interaction and from this data, the explosion probability and intensity were determined.The explosion probability had a single minimum around 70 wt% Sn, close to the eutectic composition. Moreover, the explosion probability increased approximately linearly with changing composition towards the pure melts, and was similar for pure tin and pure lead. On the other hand, the explosion intensity was comparable for tin and the eutectic alloy while clearly lower for lead. Almost all intermediate alloys had a reduced explosion intensity.Based on the variation in composition, the effects of the liquidus or solidus temperature and the liquidus-solidus gap on the explosion behaviour were also investigated. The explosion probability in both systems increased with increasing liquidus temperature. Also, the maximum explosion intensity in the Pb–Sn system increased with increasing liquidus temperature. Both could be related to easier triggering due to (partial) solidification. On the other hand, the explosion intensity was found to decrease with increasing gap between liquidus and solidus temperature, as was also found in literature. No significant trends for the explosion intensity were found for experiments with PbS–Cu₂S.     

Experimental study on CO2/CF3I suppression of methane-air explosion and flame propagation

To explore the inhibitory effects of CF₃I and CO₂ gas on the explosion pressure and flame propagation characteristics of 9.5% methane, a spherical 20 L experimental explosion device was used to study the effect of the gas explosion suppressants on the maximum explosion pressure, maximum explosion pressure rise rate and flame propagation speed of methane. The results indicated that with a gradual increase in the volume fraction of the gas explosion suppressant, the maximum explosion pressure of methane and maximum explosion pressure rise rate gradually decreased, and the time taken to reach the maximum explosion pressure and maximum explosion pressure rise rate was gradually delayed. At the same time, the flame propagation speed gradually decreased. Additionally, the time taken for the flame to reach the edge of the window and the time taken for a crack as well as a cellular structure to appear on the flame surface was gradually delayed. The fluid dynamics uncertainty was suppressed. The explosion pressure and flame propagation processes were markedly suppressed, but the flame buoyancy instability was gradually enhanced. By comparing the effects of the two gas explosion suppressants on the pressure and flame propagation characteristics, it was found that at the same volume fraction, trifluoroiodomethane was significantly better than carbon dioxide in suppressing the explosion of methane. By comparing the reduction rates of the characteristic methane explosion parameters at a volume fraction of 9.5%, it was observed that the inhibitory effect of 4% trifluoroiodomethane on the maximum explosion pressure was approximately 4.6 times that of the same amount of carbon dioxide, and the inhibitory effect of 4% trifluoroiodomethane on the maximum explosion pressure rise rate and flame propagation speed was approximately 2.7 times that of the same amount of carbon dioxide. The addition of 0.5%–1.5% trifluoromethane to 4% and 8% carbon dioxide can improve the explosion suppression efficiency of carbon dioxide. This enhancing phenomenon is a comprehensive manifestation of the oxygen-decreasing effect of carbon dioxide and the trifluoroiodomethane-related endothermic effect and reduction in key free radicals.     

Explosion behavior of n-alkane/nitrous oxide mixtures

The explosion properties of alkane/nitrous oxide mixtures were investigated and were compared with those of the corresponding alkane/oxygen and alkane/air mixtures. The explosion properties were characterized by three parameters: the explosion limit, explosion pressure, and deflagration index. For the same alkane, the order of the lower explosion limits (LELs) of the mixtures was found to be alkane/oxygen ≈ alkane/air > alkane/nitrous oxide. In addition, the mixtures containing nitrous oxide tended to exhibit higher explosion pressures than the corresponding mixtures containing oxygen under fuel-lean conditions. The Burgess–Wheeler law was also observed to hold for the mixtures containing nitrous oxide.