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The explosion venting experiments of 150 nm polymethyl methacrylate (PMMA) dust with different lengths (L) and diameters (D) of the vent tube are conducted. The effect of tube size on overpressure and flame propagation behavior is explored. High-frequency and low-frequency Helmholtz oscillations are observed on the overpressure curves in the chamber. The (d P /dt) max in the chamber is increased with high-frequency oscillations, while the maximum flame width is also visible with low-frequency Helmholtz oscillations. As the L increases from 0 m to 2 m, the P red,max increases by 29.2–145.1% and the (d P /dt) max increases by 38.4% − 127.7%. With the increase of the D , the P red,max in the chamber and vent tube decreases, and the flame transforms from an under-expansion jet flame to a subsonic jet flame. Due to the interaction between the external flow field and the concentration of unburned particles, the maximum external overpressure increases alongside with the incease of the tube length and diameter. In addition, the maximum calculation error of EN14491 is 1100%, while NFPA68 seriously underestimates the explosion venting pressure. A modified prediction model is established to provide a design method for a safe vent through the vent tube of the nano-dust explosion. [Display omitted] [ABSTRACT FROM AUTHOR]

The primary purpose of this paper is to reveal the mechanism of suppressing hydrogen cloud explosion by micron-size water mist. On the basis of experimentally obtaining the characteristics of flame behavior and explosion pressure by changing equivalence ratio and water mist density, the physical and chemical mechanism of suppressing hydrogen cloud explosion is analyzed. The results indicated that with the increase of micron-size water mist density, the explosion-related parameters (including mean flame front speed, peak explosion pressure, peak rate of pressure rise and positive pressure impulse) of ER = 0.8 and ER = 1.0 decrease monotonously, the explosion-related parameters of ER = 2.0 increases firstly and then decreases which peak value is appeared at 26.73 g/m3. A considerable part of micron-size water mist is difficult to be completely evaporated in the reaction region, the temperature of combustion products region will be reduced due to subsequent continuous evaporation. In addition, the gasified micron-size water mist mainly interacts with H radicals through the elementary reactions of R3, R38 and R84. Due to incompletely evaporated micron-size water mist, the mist-induced turbulence is generated, which is the reason of enhancing hydrogen cloud explosion at lower micron-size water mist density of ER = 2.0. • Fine flame structure under micron-size water mist is captured. • Explosion pressure characteristics are obtained. • Physical and chemical mechanism of micron-size water mist is revealed. [ABSTRACT FROM AUTHOR]

This work is aimed at evaluating unrestricted duct-vented explosion of hydrogen-air mixture and hydrogen-methane-air mixture. The flame behavior in the venting zone and explosion pressure inside explosion chamber are obtained in the experiments. On the assumption of only fresh mixture venting or only combustion product venting, a mathematical model of unrestricted duct-vented explosion is established by considering chocked venting. The results indicated that the chocked venting could be achieved for unrestricted hydrogen and hydrogen-methane explosion venting due to the fact that the Mach disc structure is appeared in venting zone. Maximum explosion pressure and maximum pressure rise rate could be reduced significantly by unrestricted duct-venting. For the unrestricted hydrogen explosion venting, maximum explosion pressure and maximum pressure rise rate increases until Φ = 1.5, then decreases monotonously with the increase of equivalence ratio. For the unrestricted hydrogen-methane explosion, maximum explosion pressure and maximum pressure rise rate continue to decrease with the increase of methane addition. Maximum explosion pressure in the experiment is between theoretical values of fresh mixture venting and combustion product venting. Maximum explosion pressure and pressure rise rate are increased with increasing burning velocity whether it is fresh mixture venting or combustion product venting. Maximum explosion pressure is increased linearly with increasing nondimensional vent coefficient. • Flame behavior and explosion pressure of duct-vented explosion are analyzed. • The mathematical model of duct-vented explosion is established. • Maximum explosion pressure of duct-vented explosion is evaluated. [ABSTRACT FROM AUTHOR]

• Flame suppression mechanism of nano PMMA dust explosion by KHCO 3 was investigated. • The effect of KHCO 3 particle size on the physical suppression mechanism was analyzed. • A numerical model was established to reveal chemical suppression mechanism. Flame suppression mechanism of KHCO 3 for 100 nm PMMA dust explosions was investigated experimentally and computationally. The effect of KHCO 3 particle size on the suppression efficiency was examined. The study revealed that the larger the proportion of added KHCO 3 , the more significant the suppression effect on flame, for KHCO 3 particles with a fixed particle size distribution. The suppression effects were significantly increased with the decreasing of KHCO 3 particle size distributions. For endothermic mechanism, when the KHCO 3 particles with three particle sizes were mixed with 100 nm PMMA, the heat absorption peaks exhibited at the initial stage, in which the heat absorption values were 28 J/g, 26 J/g and 21 J/g, respectively. A kinetics model was established to reveal the chemical suppression mechanism. It was presented that the mole fractions of key flame radicals (H and OH) were obviously reduced during the chain reaction processes with the addition of KHCO 3. For KHCO 3 particles, the formation of catalytic cycle K ⇔ KOH converted H and OH radicals into a stable combustion product H 2 O, resulting in a lower flame speed and flame temperature. [ABSTRACT FROM AUTHOR]

The purpose of this work is to evaluate the characteristics of hydrogen-blend methane explosion. The explosion characteristics without initial turbulence or with initial turbulence are firstly explored. Then the factors affecting laminar burning velocity and turbulent flame regime are revealed. Finally, the different prediction models are developed to evaluate peak explosion pressure of hydrogen-blended methane fuel. The results indicated that the MFFV, PEP, PRPR and laminar burning velocity of MR = 10% and MR = 30% continue to increase with the increase of ER, the peak value of MFFV, PEP, PRPR and laminar burning velocity of other MRs is arrived at ER = 1.0. The MFFV, PEP and PRPR increase gradually with increasing root-mean-square velocity. Regardless of initial turbulence, the MFFV, PEP and PRPR continue to decrease with increasing MR, the PEP and PRPR decrease obviously with increasing distance from ignition location. The turbulent flame regime is highly sensitive to MR, not root-mean-square velocity. The predicted value of laminar model, wrinkled model and turbulent model is relatively conservative, maximum wrinkling coefficient induced by flame instabilities and flame front itself needs to accurately evaluated. • Characteristics of hydrogen-blended methane explosion are explored. • Laminar burning velocity and turbulent flame regime are revealed. • Different theoretical models of predicting PEP are established. [ABSTRACT FROM AUTHOR]

The flame behavior and pressure characteristics of vented propane-air explosions at elevated static activation pressures (P stat) were investigated in a duct with a length-to-diameter (L/D) ratio of 7. The impact of the discharge traction and the coupling effect of the internal flame front and pressure waves on the flame propagation behavior were captured. The effect of increasing P stat on the vented flame length and width under a fixed vent was weak. The influences of P stat on the pressure profiles and maximum reduced pressure (P red) were investigated. The increase of P stat mitigated the blocking effect of external explosion on P red and further promoted the discharge pressure drop rate to be controlled within the limit of the discharge capacity of the vent. The formation mechanisms of the two main external pressure peaks were analyzed. For the larger D v conditions, the sensitivity of high P stat to the increase of maximum external pressure was higher than that of low P stat. A modified model of P red was developed considering the effects of elevated P stat and vent coefficient K V , which is proved to have a good performance in vented explosion ducts with a large L/D ratio. [ABSTRACT FROM AUTHOR]