Search

Nitrous oxide has a wide range of applications, and the explosion in presence of nitrous oxide can cause serious disaster. In this study, we reported the explosion characteristics of hydrogen-methane-nitrous oxide mixtures with different equivalence ratios (ϕ) in a closed cylindrical explosion vessel at sub-atmosphere pressure (40 kPa). The equivalence ratio (ϕ) is defined as the ratio of the actual N2O–blended fuel ratio to the stoichiometric N2O–blended fuel ratio in this study. The key parameters were obtained experimentally which reflected the explosion characteristics such as the maximum explosion pressure, maximum pressure rise rate, and deflagration index. The results demonstrated that the experimental explosion pressure was greater than the adiabatic explosion pressure and N2O made explosion have potential of deflagration to detonation transition (DDT). The addition of methane increased the peak of both the maximum explosion pressure and the maximum pressure rise rate when the value of ϕ is constant. The effect of methane fraction on the maximum pressure rise rate was negligible when the equivalence ratio was higher than 0.6. In addition, with the increase of methane content, the equivalence ratio of the maximum explosion pressure peak would increase, but the peak of the pressure rise rate was stable at where the equivalence ratio is about 0.7. [ABSTRACT FROM AUTHOR]

An experimental investigation on the explosion characteristics of hydrogen-air mixtures diluted with inert gases (Ar, N 2 , CO 2) was carried out in a cylinder chamber at room temperature (298 K) sub-atmospheric pressures (40 kPa, 60 kPa, 80 kPa, 100 kPa). Based on the pressure history recording, some explosion parameters, e.g., maximum explosion pressure ( P m a x ), maximum rate of pressure rise ( (d p / d t) m a x ), deflagration index ( K G ) and combustion duration (θ) were derived. Effects of initial pressure ( P 0 ), equivalence ratio (φ) and dilution fraction (Z %) on these explosion indices were discussed. The results show that with the increase of initial pressure, the maximum explosion pressure, maximum rate of pressure increase and deflagration index increase monotonously while the combustion duration decrease. The diluent effect on these parameters is increased in the order of Ar, N 2 and CO 2. Linear correlations P m a x / P 0 = f (Z) , P m a x = f (P 0) and (d p / d t) m a x = f (P 0) were found. In addition, the heat loss to the walls during the explosion propagation was estimated on the basis of the difference between the adiabatic and experimental measured pressure. The energy loss increases with the increase of initial pressure and specific heat of the dilutions. • Effects of dilutions on explosion behaviors of hydrogen-air are studied at reduced pressure. • Explosion indices are derived from the experiment and analyzed. • Heat loss to walls during the explosion propagation is estimated. [ABSTRACT FROM AUTHOR]

Abstract In this study, we performed experiments in a cylinder vessel with a single orifice plate to study the explosion characteristics of hydrogen-air mixtures at room temperature (298K) and ambient pressure (1atm). The blockage ratio (B R) and position of the orifice plate were various. Explosion characteristics, i.e., maximum explosion pressure ( P m a x ), combustion duration (θ) and maximum pressure rise rate ( (d p / d t) m a x ) were derived based on the pressure evolution. The results show that both the maximum explosion pressure and combustion duration are independent of the orifice plate. However, the effects of the orifice plate on the maximum rate of pressure rate are significant. Depending on the position and blockage ratio, the effects are different. The orifice plate acts as a heat sink when the distance between the orifice plate (S) is very close, making (d p / d t) m a x decrease (compared with that obtained without the orifice plate). The orifice plate acts as "turbulence-generator" as S increases; thus, (d p / d t) m a x increases. Further, the influences of the blockage ratio as well as laminar burning velocity on the maximum pressure rise rate are also analyzed. Highlights • Effect of an orifice plate on hydrogen-air explosions was studied. • Maximum explosion pressure is independent of a baffle in this study. • The orifice plate plays a dual role on the maximum pressure rise rate. [ABSTRACT FROM AUTHOR]

Highlights • The effects of different hollow plates on 2H 2 + O 2 detonation behaviors were studied. • The effective diameter is an appropriate indicator for the characterization of the limits. • Long soot foils were adopted to study the cellular pattern evolution. • The re-initiation processes of 2H 2 + O 2 detonation were analyzed. Abstract In this study, experiments were carried out in a circular tube (5300 mm long, 48 mm inner-diameter) filled with orifice plates to investigate the detonation behaviors of stoichiometric hydrogen-oxygen mixture. Two kinds of orifice plates, i.e., round orifice plates and square orifice plates were used to generate obstacle configurations with various spacings. The blockage ratios of these orifice plates are 0.56. Evenly spaced photodiodes were mounted on the tube wall to record the detonation velocity. Long soot foils were adopted to study the evolution of the cellular structure. The detonation propagation limits (also the quasi-detonation limits) were found to be in agreement with d eff /λ > 1, where d eff and λ are the effective diameter of the orifice and the detonation cell size. The measured velocity as well as the propagation limits are independent of the opening geometry as long as the effective diameters are identical. Soot foils obtained with various sensitivity (or initial pressure) exhibit that the re-initiation of detonation occurs via a variety of modes. Well within the limits, the detonation could recover via the generation of hot spots. In some cases, a detonation can propagate without the formation of hot spots. Near the limits, only a few transverse wave traces or streaks can be observed, indicating that the propagation mechanisms are changed. [ABSTRACT FROM AUTHOR]

In order to improve the detonation performance of emulsion explosives, a new type of emulsion explosives with TiH2 powders is developed. The influences of the amount of sensitizers GMs and energetic additives TiH2 on explosion characteristics of emulsion explosives are studied to determine the optimum compositions. Underwater explosion and brisance testing experiments show that, compared to traditional GMs sensitized emulsion explosives, the shock wave specific impulse I and total energy E of GMs-TiH2 sensitized emulsion explosives are improved significantly, and the effect of TiH2 powders on improving the explosion power of emulsion explosives is better than that of Ti powders. The brisance of GMs-TiH2 emulsion explosives is 23.80 mm compression of lead block, 7.7 mm more than that of the emulsion explosives sensitized by GMs alone. Therefore, the hydrogen containing material TiH2 could be a promising energetic additive for developing high-power emulsion explosives. [ABSTRACT FROM AUTHOR]

The laminar burning velocity and cellular instabilities of premixed flame in H 2 -N 2 O mixtures were studied experimentally at various equivalence ratios (φ) and initial pressures (p 0). High-speed schlieren was used to record the morphology of the spherical flame. Based on the spherical flame method, the laminar burning velocity and Markstein length were derived. In addition, the Lewis number, flame thickness, thermal expansion and Zel'dovich number were evaluated numerically. The results show that both the laminar burning velocity and Markstein length increase with the equivalence ratio. The Lewis number (less than unity) increases with the equivalence ratio while the flame thickness exhibits an inverse evolution. Hence, the most unstable flames were found to be at φ = 0.4–0.6 due to the combined effects of the thermal-diffusion and hydrodynamic instabilities. At lower initial pressure, the flame front is smooth in spite of the diffusion-thermal instability. With the increase of initial pressure, both the diffusion-thermal instability and hydrodynamic instability dominate the cellular structure of the flame front. The flames undergo self-acceleration at φ = 0.4–0.6 and p 0 = 40 kPa, with the acceleration exponents close to 1.5 (the value of self-turbulization). Due to the local oscillation of velocity, the flame propagation speed decreases after the self-similar regime. [ABSTRACT FROM AUTHOR]

Explosions can occur in different oxidizer atmospheres in confined spaces, which should be given attention in regard to the fire safety in process industries. In this study, experiments were carried out in a closed cylindrical vessel (7.3 L) to compare the explosion behaviors of hydrogen (H 2) and ethylene (C 2 H 4) with air, nitrous oxide (N 2 O), and oxygen (O 2) at various equivalence ratios. The initial pressures of the hydrogen and ethylene mixtures were 50 kPa and 30 kPa, respectively. Explosion indices such as the maximum explosion pressure (P m a x ), maximum rate of pressure rise ( (d p / d t) m a x ) and deflagration index (K G) were determined experimentally. The results showed that the pressure evolutions obtained with N 2 O and O 2 exhibited strong oscillations due to flame instabilities and cellular structures. The maximum explosion pressure increased in the order of air, O 2 and N 2 O while the maximum rate of pressure rise increased in the order of air, N 2 O and O 2. Unlike those of air and O 2 , the maximum values of (d p / d t) m a x obtained with N 2 O were found to be at the fuel-lean side. This indicated that the instability feature of N 2 O supported combustions at the fuel-lean side. Compared with air, the maximum explosion pressure obtained in N 2 O and O 2 atmospheres could be very close to the adiabatic pressure when considering no heat loss during an explosion. Therefore, there was a flame acceleration and deflagration to detonation transition (DDT) mechanism in the explosions with N 2 O and O 2. Additionally, two dimensionless pressure rise coefficients were derived and discussed. The flames in very lean H 2 -N 2 O were very unstable, resulting in scattered coefficients as a function of equivalence ratio. At the fuel-rich side, the dimensionless coefficients were very close. In practice, the potential DDT mechanism in the explosions, especially in N 2 O and O 2 atmospheres, needed to be considered. [ABSTRACT FROM AUTHOR]

• A comparative study of H 2 /N 2 O/N 2 and CH 4 /N 2 O/N 2 explosions was conducted. • The extrema of explosion parameters are reached at the fuel-lean side or stoichiometric condition. • Flame instability has more dominant effect on the explosion behavior. In this study, we performed experiments in a closed cylinder vessel to investigate the explosion behaviors of H 2 /N 2 O and CH 4 /N 2 O mixtures with various equivalence ratios (φ) diluted with 40%, 50% and 60% N 2. Explosion parameters, including the maximum explosion pressure, the explosion time, the maximum pressure rise rate, the deflagration index as well as the dimensionless pressure rise coefficients were derived and evaluated. Meanwhile, the adiabatic flame temperature and the laminar burning velocity were calculated. Lastly, the heat loss to the wall during the combustion process was computed. The results show that the explosion characteristics are influenced by the flame instability more significantly than the laminar burning velocity and the adiabatic flame temperature. The maximum explosion pressures of hydrogen- and methane- mixtures are found to be at φ = 0.8 and φ = 1.0, respectively. The minimum explosion time was attained at φ = 0.6–0.8 and φ = 1.0, and the inflection of the maximum pressure rise rate and the deflagration index occur at φ = 0.6–0.8 and φ = 0.8–1.0. The normalized pressure rise coefficients are relatively scattered at the fuel-lean side due to the highly unstable feature of N 2 O supporting explosions while at the fuel-rich side, the variations of the dimensionless coefficients are very small. Furthermore, the heat loss during the explosion also reaches its minimum value at the fuel-lean side. [ABSTRACT FROM AUTHOR]

The explosibility of hybrid H 2 /Ti dust in the production of metal hydride TiH 2 was simulated and studied using a 20-L spherical vessel. The influential factors for the explosion performance of hybrid H 2 /Ti dust, including particle size distribution and polydispersity, humidity, temperature, hydrogen content, inert gas and degree of reaction, on hybrid explosion were investigated. Results showed that both the mean particle sizes and particle size polydispersity had significant effects on the dust severity of hybrid H 2 /Ti dust. The explosion severity of hybrid H 2 /Ti dust was enhanced at a higher temperature in a certain range, and it presented a trend of increasing at the early stage and then decreased both for the increasing humidity and hydrogen pressure. Explosion inhibition effects of typical inert gases for hybrid H 2 /Ti dust increased in the following order: argon < helium < nitrogen. The values of (d P /d t) ex and V f decreased along with the reaction process, while the value of P ex kept stable, which showed that the hydrogen state had no obvious impact on P ex but significantly affected the explosion risk of hybrid H 2 /Ti dust, and special attention should be paid to the initial stages of the production process of TiH 2. • Simulated production conditions of TiH 2 using a 20-L spherical vessel. • Investigated typical influential factors on the explosibility of hybrid H 2 /Ti dust. • Studied the explosion hazards in different production stages of metal hydride TiH 2. • Improved understanding of hazards associated with hybrid H 2 /Ti dust explosion. [ABSTRACT FROM AUTHOR]