TY - JOUR A1 - Xie, Y. A1 - Lv, N. A1 - Wang, X. A1 - Wu, Dejian A1 - Wang, S. T1 - Thermal and fire characteristics of hydrogen jet flames in the tunnel at longitudinal ventilation strategies N2 - Hydrogen leakage of vehicles in the tunnel is a great threat to the safety operation of the tunnel and longitudinal ventilation strategies have always been utilized to control the fire and smoke movement of rail transit, electric and fossil-fueled vehicles in the engineering field. It is in doubt whether the longitudinal ventilation strategy could still help to reduce the jet fire hazard of transportation with H2 power in the tunnel, considering the rapid development of the hydrogen energy. In present work, a numerical research on effects of longitudinal ventilation strategies on hydrogen jet flames in the tunnel is conducted. The results illustrate that longitudinal ventilation could affect the flame characteristics of jet flames greatly in the tunnel. The critical ventilation velocity increases firstly with the increase of hydrogen leakage rates and then changes little after a critical value. The predicted theoretical model of pool fires could well predict the critical ventilation velocity for hydrogen jet fires. With the increase of longitudinal ventilation velocity, maximum ceiling temperatures are decreased greatly. According to the heat releases, jet speeds and ventilation velocities, three kinds of flame bending characteristics of hydrogen jet fire could be observed due to different effects of the inertial force. At last, the stable thermal stratification could also be destroyed by large ventilation velocities but the corresponding ventilation velocity is far larger than the critical ventilation one. With the increase of longitudinal ventilation velocities, the height of thermal layer is reduced firstly and then maintained at a constant value. KW - Hydrogen leakage KW - Tunnel KW - Jet flame KW - Longitudinal ventilation PY - 2021 DO - https://doi.org/10.1016/j.fuel.2021.121659 SN - 0016-2361 VL - 306 SP - 1 EP - 12 PB - Elsevier Ltd. AN - OPUS4-55054 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, S. A1 - Cai, Y. A1 - Guo, H. A1 - Wu, Dejian A1 - Xie, Y. T1 - Effect of fuel concentration, inert gas dilutions, inert gas–water mist twin fluid medium dilutions, and end boundary condition on overpressure transients of premixed fuel vapor explosion N2 - A series of experiments were conducted in a 10L closed and vented tube with L/D = 10.0, and effects of initial fuel volume concentration, inert gas dilutions (diluted by N2 and CO2), inert gas–water mist twin fluid medium dilutions (diluted by N2-H2O twin fluid medium, CO2-H2O twin fluid medium) and end boundary conditions on overpressure transients of hydrocarbon fuel–air mixtures explosion were revealed. Results show that the overpressure-time profiles consistent with the dynamic evolution law of ‘approximately zero-1st overpressure rising stage-2nd overpressure rising stage-descending stage’, and ‘rate of overpressure rise-time’ curves exhibit the characteristics of multi-stages and multi-peaks, such as (dp/dt)(1,max), (dp/dt)(1,min), (dp/dt)(2,max) and (dp/dt)(2,min). Specifically, as the fuel volume concentration increased, both the maximum overpressures (pmax), and the maximum rates of overpressure rise ((dp/dt)(1,max) and (dp/dt)(2,max)) show a variation trend of increasing firstly and then decreasing, while the corresponding times (tmax, θ(1,max) , θ(2,max)) show a total different variation trend. Moreover, when YCH is lower than 1.88%, the value of (dp/dt)(1,max) is greater than (dp/dt)(2,max), while the value of (dp/dt)(1,max) was less than (dp/dt)(2,max), and when YCH was higher than 1.88%. The addition of N2 and CO2 can obviously inhibit the explosion intensity of hydrocarbon fuel, and the inhibition effect of CO2 is better than that of N2. Due to the synergy inhibition effect of the inert gas and ultrafine water mist, all the values of pmax, (dp/dt)(1,max) and (dp/dt)(2,max) diluted by inert gas-ultrafine water mist twin fluid medium were smaller than those diluted by sole inert gases. In addition, there are significant differences in the overpressure-time and the rate of overpressure rise-time profiles between closed and end venting explosions. The values of maximum overpressure and the rates of overpressure rise of the closed explosion were higher than those of the venting explosion, but the minimum rate of overpressure rise is a smaller one. KW - Premixed fuel vapour KW - Overpressure transients KW - Inert gas KW - Diluent additions KW - Twin fluid medium KW - Venting boundary condition PY - 2021 DO - https://doi.org/10.1016/j.fuel.2021.122083 SN - 0016-2361 VL - 309 SP - 1 EP - 16 PB - Elsevier Ltd. AN - OPUS4-55055 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Huang, P. A1 - Ye, S. A1 - Qin, L. A1 - Huang, Y. A1 - Yang, J. A1 - Yu, L. A1 - Wu, Dejian T1 - Experimental study on the maximum excess ceiling gas temperature generated by horizontal cable tray fires in urban utility tunnels N2 - Safety concerns on cable tray fires in urban utility tunnels, which may further trigger huge casualties, ceiling structure damages, power failures and other domino effects, attract increasing attention in recent years. Determining the maximum excess ceiling gas temperature (MECT) induced by cable tray fires in urban utility tunnels is crucial to evaluate the fire risks. A series of one-layer horizontal cable tray fire experiments to explore the MECT were carried out in a large-scale utility tunnel without mechanical ventilations. The number of cables on the tray was varied from 8 to 18 in the experiments. The experimental results showed that the cable tray fire burning could be divided into three distinct stages, including ignition, self-sustaining and decaying stages. In the self-sustaining combustion stage, the cable tray was found to burn relatively steady. The mean MECT was also investigated since it represents one of the main characteristics of the cable tray fire. By redefining two parameters (the heat release rate and the effective ceiling height) in three classical MECT models proposed originally based on pool-fire, these three models could be extended to be able to predict the mean MECT generated from the cable tray fire (solid combustible) within 20% deviations. Consequently, two novel models were respectively proposed to predict the mean MECT at the self-sustaining burning period and the instantaneous MECT of one-layer horizontal cable tray fire in utility tunnel, which would be useful in the field of fire protection engineering. KW - Urban utility tunnel KW - Cable tray fire KW - MECT KW - Heat release rate KW - Tunnel fire PY - 2021 DO - https://doi.org/10.1016/j.ijthermalsci.2021.107341 SN - 1290-0729 VL - 172, Part B SP - 1 EP - 10 PB - Elsevier Masson SAS AN - OPUS4-55056 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Guo, Y. A1 - Ren, K. A1 - Wei, A. A1 - Tao, C. A1 - Huang, W. A1 - Zhao, Peng A1 - Wu, Dejian T1 - Iron dust explosion characteristics with small amount of nano-sized Fe2O3 and Fe3O4 particles N2 - Iron powder, as one of the most abundant metal fuels that can be used as recyclable carriers of clean energy, is a promising alternative to fossil fuels in a future low-carbon economy. It may pose a potential explosion hazard during the process of processing, storage, transport, and reduction/oxidation (redox). The explosion characteristics of iron dust in air were undertaken via a 20 L spherical explosion chamber with an emphasis on minimum explosion concentration (MEC) of iron dust. The alternative method of combustion duration time (tc) was used to determine MEC and compared with the standardized over pressure method. Two kinds of nano-sized iron oxides (Fe2O3 and Fe3O4) were used as inertants to determine the inhibition effect of different oxidation products. The iron dust explosion products with various shapes and sizes were found to be able to grow up 4–6 times of the iron dust for the first time. Adding small amount of Fe2O3 or Fe3O4 could reduce the explosion severity and sensitivity of iron dust. The MEC data determined by both methods were comparable. The addition of 5 % oxide has obvious inhibition effect under 1500 g/m3 concentration. With the increase of oxide concentration to 10 %, the inerting effect increases, and the MEC of iron dust increases more than 3 times. The increase of dust concentration will weaken the inerting effect. When the concentration increases from 500 g/m3 to 3000 g/m3, the weakening effect of 10 % Fe2O3 on the explosion pressure decreases from 38.45 % to 2.24 %, and 10 % Fe3O4 decreases from 46.21 % to 10.63 %. Unlike coal, biomass or aluminum dusts, the iron dust explosion was found to have a unique secondary acceleration of pressure rise rate for the first time. These results provide a fundamental basis to mitigate the iron dust explosion via solid inerting method without adding extra elements. KW - Iron dust KW - Iron oxides KW - MEC KW - Combustion duration time KW - Explosion products KW - Pressure rise rate PY - 2022 DO - https://doi.org/10.1016/j.fuel.2022.124786 SN - 0016-2361 VL - 324, Part C SP - 1 EP - 13 PB - Elsevier Ltd. AN - OPUS4-55057 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Su, Bin A1 - Luo, Zhenmin A1 - Krietsch, Arne A1 - Wu, Dejian A1 - Wang, Tao A1 - Zhou, Shangyong A1 - Deng, Jun T1 - Quantitative investigation of explosion behavior and spectral radiant characteristics of free radicals for syngas/air mixtures N2 - The combustion characteristics and explosive hazard of syngas (H2/CO)/air mixtures are affected by its exact composition and equivalence ratios. In this paper, the explosion pressure and spectral radiant intensity of free radicals were quantitatively examined for syngas with different H2 proportions ([H2 in syngas] = 0, 30, 50, 70, 100 vol%) and equivalence ratios (φ = 0.8, 1.0, 1.2, 1.4, 1.6, 2.0, 2.5). The results show that the explosion process of syngas/air mixtures can be separated into the initial slow combustion stage, the violent deflagration stage and the deflagration ending stage. The peaks of explosion pressure, pressure rise rate, OH*spectral intensity and rise rate of spectral intensity first increase and then decrease with increasing the equivalence ratio, and they reduce gradually with the decrease of H2 proportion in syngas. The H2 content in syngas greatly affects the heat release and the concentration of excited state OH*, especially for the syngas/air mixtures with smaller proportion of H2. Additionally, the presence of H2 greatly increases the deflagration index and spectral radiant index of OH* for syngas/air mixtures. The average rise rates of explosion pressure and spectral intensity of free radicals are introduced and the coupling model between them is established based on the first law of thermodynamics and the principle of chain reaction. The established model is furthermore verified by the experimental results. It is indicated that there is a linear relationship between average rise rates of explosion pressure and spectral intensity (OH*). The results can be used to improve the combustion efficiency of syngas and to guide theoretically the prevention, mitigation and control of syngas explosions. KW - Syngas KW - Hydrogen KW - Explosion pressure KW - Free radicals KW - Spectral intensity PY - 2024 DO - https://doi.org/10.1016/j.ijhydene.2023.10.280 SN - 0360-3199 VL - 50 IS - Part A SP - 1359 EP - 1368 PB - Elsevier Ltd. AN - OPUS4-59482 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Guo, Yongzheng A1 - Ren, Kaiyue A1 - Huang, Weixing A1 - Wu, Dejian T1 - An alternative explosion criterion of combustible dusts based on combustion duration time: Applications for minimum explosion concentration and limiting oxygen concentration N2 - minimum explosion concentration (MEC) and limiting oxygen concentration (LOC) in our recent works. This work further studies the reasonability and reliability of the alternative method experimentally and theoretically. Six different dust samples were tested via a 20-L spherical explosion chamber. The experimental results showed that the data of MEC and LOC determined by using the alternative and the standardized methods are in good agreement. The minimum flame propagation velocity (Sf) and the corresponding maximum combustion duration time (tc) were found at its MEC and LOC, suggesting that the theoretical analysis can well explain all the experimental data. It is the first time to study the theoretical basis of the explosion criterion, thus helping to improve our understandings of dust explosion characteristics, and to amend the explosion criterion in future test standards. KW - General Chemical Engineering PY - 2022 DO - https://doi.org/10.1016/j.powtec.2022.117851 SN - 0032-5910 VL - 409 SP - 1 EP - 13 PB - Elsevier BV CY - Amsterdam AN - OPUS4-59323 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Dejian A1 - Schmidt, Martin A1 - Krietsch, Arne A1 - Krause, U. T1 - Effect of oxygen concentration, inert gas and CH4/H2 addition on the minimum ignition energy of coal dusts N2 - MIKE III apparatus tests were conducted to investigate the minimum ignition energy (MIE) of coal dusts in air and O2/CO2 atmospheres with and without small amount of CH4/H2. The O2 mole fraction (XO2) in the gas mixtures varied from 21% to 50% with the CH4/H2 mole fraction from 0 to 2%. Experimental result showed that MIE of coal dusts significantly decreases even by three orders of magnitude in mJ with increasing XO2 and the addition of CH4/H2. Compared with CH4, H2 had a relatively strong promotion effect on the spark ignition of coal dusts. The inhibiting effect of CO2 was found to be much stronger than N2, but this inhibiting effect of CO2 could be eliminated by 9% increment of XO2. The effect on MIE of coal dusts thus followed by the order: 9% increment of XO2 > CO2 replacing N2 > 2% CH4 or H2 addition. Moreover, two empirical models were used to estimate the MIE of hybrid dust-gas mixture (HMIE), and the results showed that calculated data can well reflect the promoting effect of elevated XO2 and flammable gas addition, and the inhibiting effect of inert gas KW - Ignition energy KW - Hybrid mixture KW - Oxygen rich KW - Inerting effect KW - Empirical model PY - 2022 DO - https://doi.org/10.1016/j.jlp.2022.104772 SN - 0950-4230 VL - 77 SP - 1 EP - 10 PB - Elsevier Ltd. AN - OPUS4-55888 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Dejian A1 - Zhu, Z. A1 - Bao, Z. T1 - Optimization of the content distribution of expanded natural graphite in a multilayer metal hydride bed for thermochemical heat storage N2 - The poor thermal conductivity of MH beds limits hydrogen absorption in metal hydride (MH) reactors for thermochemical heat storage. The compaction of MH powder with expanded natural graphite (ENG) is an efficient and cost-effective approach for the heat transfer enhancement of MH beds. However, the addition of ENG reduces the hydrogen storage density of the compacted composites. How to optimize the allocation of a limited amount of ENG in the MH bed has not been studied. In this study, a multilayer MH bed configuration with an ENG grade content was adopted to improve the heat transfer performance of an MH reactor for thermochemical heat storage. The effect of the ENG content gradient on the performance of the MH reactor was investigated using a mathematical model of the MH reactor. Furthermore, an optimization method based on the entransy dissipation extremum principle (EDEP) was proposed to optimize the ENG distribution in magnesium hydride (MgH2)-ENG compacts. The results showed that a larger ENG content gradient resulted in faster hydrogen absorption and better heat-discharge performance. Compared with a configuration with a uniform ENG content, the optimized configuration based on the EDEP exhibited a shorter reaction time, more uniform bed temperature distribution, and 15.33% higher gravimetric exergy-output rate. In addition, the number of optimization iterations had little effect on the optimal results, which could be obtained by implementing only one optimization iteration. The optimization results showed that more ENG should be allocated to the internal layer of the MgH2-ENG compact. The compacts were divided into three layers, and the ENG content of each layer was calculated according to the optimized configuration based on the EDEP. The optimization method proposed in this study can be applied to optimize KW - Metal hydride reactor KW - Expanded natural graphite KW - Multilayer bed KW - Entransy dissipation exremum principle KW - Thermochemical heat storage PY - 2022 DO - https://doi.org/10.1016/j.applthermaleng.2022.119115 SN - 1359-4311 VL - 216 SP - 1 EP - 10 PB - Elsevier Ltd. AN - OPUS4-55890 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Xie, Yongliang A1 - Lv, Na A1 - Huang, Yan A1 - Wu, Dejian A1 - Gong, Liang A1 - Yang, Xufeng A1 - Zeng, Yikai T1 - Comparative analysis on temperature characteristics of hydrogen-powered and traditional fossil-fueled vehicle fires in the tunnel under longitudinal ventilations N2 - Vehicle fires in the tunnel are a great threat to the safe operation of the tunnel. Due to the rapid development of the hydrogen economy, the fire due to the hydrogen leakage could not be avoided and may bring great damage to the passengers and infrastructure. Due to the large difference between pool fires of traditional fossil-fueled and jet fires of hydrogen-powered vehicles, it is in doubt whether the existing longitudinal ventilation design could still be effective for the safety issue of hydrogen powered vehicles. To solve this problem, it is necessary to compare temperature characteristics of hydrogen-powered and traditional vehicle fires with and without longitudinal ventilations. In present work, we conducted a numerical investigation to discuss the different temperature distributions of traditional and hydrogen-fueled vehicle fires. Results indicate that the high temperature zone of the pool fire only exists above the ceiling of the vehicle. For hydrogen-powered vehicle fire, the high-speed hydrogen jet with the strong inertial force could push the hot smoke flows back to the ground. The ceiling temperature of hydrogen-powered vehicle fire is larger since hydrogen-powered vehicle has a larger heat release rate and the fire hazard of jet fires bring more danger compared with the pool fire. Although the temperature stratification is also obvious for the hydrogen-powered vehicle fire, the air temperature in the lower region could be heated and still high enough to bring a great damage to the passengers’ lives. This is quite different with the traditional pool fire. In addition, the critical ventilation velocity is also discussed. The theoretical equation could well predict the critical ventilation velocity of traditional vehicle fires. For hydrogen-powered vehicle fires, the critical ventilation velocity could reach up to 6 m/s. The theoretical equation could not well predict the critical ventilation velocity of hydrogen-powered vehicle fires due to exist of hydrogen jet fires. KW - Hydrogen fire KW - Tunnel KW - Longitudinal ventilation KW - Comparative study PY - 2022 DO - https://doi.org/10.1016/j.ijhydene.2022.05.203 SN - 0360-3199 VL - 47 IS - 57 SP - 24107 EP - 24118 PB - Elsevier CY - Oxford AN - OPUS4-62839 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wu, Dejian A1 - Zhao, P. A1 - Spitzer, Stefan A1 - Krietsch, Arne A1 - Amyotte, P. A1 - Krause, U. T1 - A review on hybrid mixture explosions: Safety parameters, explosion regimes and criteria, flame characteristics N2 - The hybrid mixture of combustible dusts and flammable gases/vapours widely exist in various industries, including mining, petrochemical, metallurgical, textile and pharmaceutical. It may pose a higher explosion risk than gas/vapor or dust/mist explosions since the hybrid explosions can still be initiated even though both the gas and the dust concentration are lower than their lower explosion limit (LEL) values. Understanding the explosion threat of hybrid mixtures not only contributes to the inherent safety and sustainability of industrial process design, but promotes the efficiency of loss prevention and mitigation. To date, however, there is no test standard with reliable explosion criteria available to determine the safety parameters of all types of hybrid mixture explosions, nor the flame propagation and quenching mechanism or theoretical explanation behind these parameters. This review presents a state-of-the-art overview of the comprehensive understanding of hybrid mixture explosions mainly in an experimental study level; thereby, the main limitations and challenges to be faced are explored. The discussed main contents include the experimental measurement for the safety parameters of hybrid mixtures (i.e., explosion sensitivity and severity parameters) via typical test apparatuses, explosion regime and criterion of hybrid mixtures, the detailed flame propagation/quenching characteristics behind the explosion severities/sensitivities of hybrid mixtures. This work aims to summarize the essential basics of experimental studies, and to provide the perspectives based on the current research gaps to understand the explosion hazards of hybrid mixtures in-depth. KW - Hybrid mixtures KW - Explosion protection KW - Safety characteristics PY - 2023 DO - https://doi.org/10.1016/j.jlp.2022.104969 SN - 0950-4230 VL - 82 SP - 1 EP - 54 PB - Elsevier CY - Amsterdam AN - OPUS4-56856 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -