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Ammonia/hydrogen fuel mixture is considered to be a new type of sustainable and environmentally friendly energy. However, their explosive properties are not well understood. This study investigated the explosion of NH 3 /H 2 /air fuel mixture in a 1.67-litre constant-volume combustion chamber using hydrogen ratios (H 2 = 15, 20, 25, and 30%), equivalence ratios (ϕ = 0.8–1.4), starting temperatures (T i = 298, 363, and 428 K), and pressures (P i = 1, 2, and 3 bar). The explosivity of NH 3 /H 2 /air was characterized using the maximum explosion pressure (P max), maximum pressure rise rate (dP/dt max), and deflagration index (K G). Also, the maximum heat release rate (HRR max) and heat loss were used to account for variations in heat generated by the explosion. The findings indicate that P max decreases with increasing temperature but P max , dP/dt max , and K G increase with an increase in pressure. Overall, an increase in pressures, hydrogen ratios, and equivalence ratio enhances the explosion severity, but the pressure has a significant effect on the explosion severity. Furthermore, a cubic polynomial provides a superior match to the correlations between the P max , dP/dt max , K G , and HRR max and equivalence ratio. This study deeply explores the safe use mechanism of NH 3 /H 2 mixed fuel and provides an essential reference for the safe application of NH 3 /H 2 mixed fuel. • Studied confined explosion of NH 3 /H 2 mixed fuel under different initial conditions. • K p shows max explosion pressure sensitivity decreases then slightly increases with higher equivalence ratio. • Hydrogen content's impact on explosion parameters is more significant in lean fuel than rich fuel. • Deflagration index shows H 2 makes NH 3 more flammable with little increase in hazard. [ABSTRACT FROM AUTHOR]

In this work, the explosion of hydrogen/nitrous oxide/carbon dioxide mixtures with various equivalence ratios (0.6–1.0), initial pressures (40–100 kPa), and carbon dioxide fractions (20%–40 %) at ambient temperature (298 K) was conducted inside a normative 15.625-L cubic container. The maximum explosion pressure and pressure rise speed were obtained and analyzed. The results show that carbon dioxide plays a crucial role in weakening H 2 /N 2 O explosion intensity, flame instabilities, as well as the tendency of deflagration to detonation. In addition, the addition of carbon dioxide has affected the two competitive effects between adiabatic temperature and molecular number. The variations of maximum explosion pressure and pressure rise speed with equivalence ratios depend on the carbon dioxide fraction. Only a linear dependence was found between maximum pressure rise speed and original pressure. These results would be useful in developing explosion-proof devices in the event of potential fire and explosion hazards. • Highlights (for review). • Carbon dioxide plays a significant role in weakening H 2 /N 2 O explosion intensity. • The variations of (d p /d t) max - φ depend on the carbon dioxide fraction. • The competitive effects between adiabatic temperature and molecular number are affected by CO 2. • The addition of CO2 effectively suppresses the tendency of deflagration to detonation. [ABSTRACT FROM AUTHOR]

• Effects of hydrogen content on pressure development in H2/ethanol are studied. • Explosion parameters are obtained from the experiment and analyzed. • The deflagration index of mixture has been experimentally measured. With the anticipated widespread integration of biofuels and hydrogen fuels within the future energy landscape, the potential explosion hazards after their release within confined spaces under the atmospheric are deserving of heightened attention. The present work takes the mixtures of ethanol and hydrogen as the objects and experimentally studies the impacts of hydrogen fraction and equivalence ratio on the explosion characteristics in a constant-volume explosion vessel at 0.10 MPa and 400 K. The data reveals that an increase in the hydrogen fraction leads to a rise in the maximum explosion pressure during lean explosions but causes a decrease during rich explosions. Nonetheless, the duration of the explosion decreases with the increase of hydrogen fraction in all the explosions. In consideration of explosion pressure, the maximum pressure rise is found to be exponential in relation to the maximum explosion pressure. However, the confidence level diminishes significantly with an increase in the hydrogen fraction. Conversely, the maximum rate of pressure rise during an explosion appears to be a function of the duration of the explosion, suggesting that the reaction rate plays a more pivotal role in determining the hazardous level. Meanwhile, the duration of fast combustion steadily occupies approximately 83 % of the explosion duration. Furthermore, the deflagration index is no more than 30 MPa*m/s, namely, ethanol/hydrogen mixture is a promising fuel with mild hazardous potential. [ABSTRACT FROM AUTHOR]

In order to evaluate the effect of mixing hydrogen on the explosive characteristics of ammonia, this work explored the evolution of explosion overpressure and flame propagation characteristics of ammonia/hydrogen/air mixture under different hydrogen blending ratios in closed pipelines through experimental research. Experimental results show that as the hydrogen blending ratio increase, the instability of flame increases, and flame surface changes from smooth to wrinkled. Flame propagation undergoes the evolution of jellyfish-shaped/near-spherical, finger-shaped, plane-shaped, irregularly protruding flame and tulip flame. Flame surface area is constantly changing, accompanied by violent flame tip velocity pulsations. The maximum explosion pressure and the maximum explosion pressure rise rate are consistent with the evolution law of adiabatic flame temperature. They first increase and then decrease with increase of the equivalence ratio, and their peak value appears near the equivalence ratio of 1.1. On the contrary, the explosion duration and rapid combustion period first decrease and then increase with increase of equivalence ratio, and decrease monotonically with increase of hydrogen blending ratio. The conclusions obtained in this work will contribute to the structural design of flame arresters and the formulation of explosion venting strategies during the preparation, transportation and utilization of ammonia/hydrogen mixtures. • The effects of equivalence ratio and hydrogen blending ratio on the explosion characteristics of ammonia/air mixtures were investigated. • Hydrogen blending significantly increased the explosion intensity and flame instability. • The formation of concave flames has a significant dependence on equivalence ratio and the composition of the mixture. • The flame tip speed evolution can be divided into acceleration stage, deceleration stage and velocity pulsation stage. [ABSTRACT FROM AUTHOR]

• The length of duct has a great influence on the flame development of LPG/H 2 blended fuel. • There is a direct proportional relationship between the maximum explosion pressure and the length of duct. • The longer the duct, the greater the depth of the tip of the "tulip-flame" at the later stage of flame propagation. • When R H is under 40%, the duct length more significantly influences the flame propagation time than hydrogen does. The search for an efficient and clean alternative fuel is one of the research hotspots in the world's major energy countries, and the blending of different levels of hydrogen in LPG is likely to become a promising alternative energy source in the future. Therefore, this paper investigates the effects of different duct lengths and R H on the explosion characteristics of LPG/H 2 blended clean fuels under closed conditions. It reveals that the development stages of the flame and the emergence of its characteristic structures vary with duct lengths. The longer the duct, the greater the absolute position of the "plane-flame", in the late stage of flame propagation "tulip flame" tip depth, the longest tip depth of 305 mm. Hydrogenation increases the flame front speed in ducts of identical length, yet it doesn't alter the location of the characteristic "plane-flame". When R H is under 40 %, the duct length more significantly influences the flame propagation time of the LPG/H 2 blended clean fuel than hydrogen does. However, this effect reverses when R H exceeds 40 %. The P max correlates directly with duct length, the longer the length of the duct, the larger the P max. When Ф=1.0 and R H = 0.8, the P max of LPG/H 2 blended clean fuel in a 1500 mm duct is 1.51 times that of 500 mm. [ABSTRACT FROM AUTHOR]

• MPe maximum rate of pressure rise was insensitive to the initial temperature. • MPe experimental and adiabatic deflagration indices showed satisfactory agreement. • MPe explosions were hazardous at high pressures and in rich mixtures. • MPe unstable flame crack lengths and cell numbers were more sensitive to pressure. Combustible fuels like methyl pentanoate (MPe) could cause accidental explosions and fire. Therefore, MPe explosion characteristics have to be well characterized and understood for its safe and reliable use in industries and combustion devices. Considering this, MPe's explosion pressure, maximum explosion pressure, rate of pressure rise, maximum rate of pressure rise, heat release rate, etc., were investigated in this study at the initial conditions of 1, 2, and 4 bar and 423 K, 453 K, and 483 K using the equivalence ratios of 0.7–1.4. The maximum explosion pressures and maximum rate of pressure rise of MPe increased as the initial pressures increased but the maximum rate of pressure rise was insignificantly affected by the initial temperature. The explosion duration decreased with a decrease in the initial pressure. The maximum heat release rate and deflagration index increased with increasing initial pressure. The MPe maximum deflagration index was 224.8 bar•m/s, which occurred at a higher initial pressure and fuel-rich mixture. Therefore, the explosion severity of MPe was enhanced at higher initial pressures and fuel-rich mixtures. Moreover, the flame cellularity study showed that MPe unstable flame crack length and cell number were more affected by increments in the initial pressure and equivalence ratio. Therefore, flame instability and cellularity would significantly influence explosion severity at higher pressures and equivalence ratios. This study's findings provide first-hand data that could be used to further investigate and characterize MPe's explosion risk. [ABSTRACT FROM AUTHOR]

[Display omitted] • Explosion characteristic parameters of raw and oil-immersed coals were determined. • The explosive intensity of oil immersed coal dust was increased. • The MEC for finer coal dust was lower, whereas the MEC for the coarser dust was higher. • The 6 wt% oil concentration obviously increased the explosion risk of coal dust. • The pre-post explosion microstructure for the coals was analysed. To investigate the explosion hazards of oil-immersed coal dust in co-existing mine areas, the explosion characteristic parameters of coal dust under different particle dimensions, coal dust concentration, and oil-immersed concentration were studied in a 20-L explosion chamber. The maximum explosion pressure of oil-immersed coal dust first decreases and then increases as coal dust particle size increases. For oil-immersed concentration samples between 2 and10 wt.%, the K st value, and maximum explosion pressure of the oil-immersed samples were higher than those of the raw coal counterpart. The maximum explosion pressure of oil-immersed samples was 7.49%, 4.10%, 5.7%, 7.13%, and 4.10% higher than the raw samples. Moreover, when the oil-immersed concentration was 6 wt%, the minimum explosion concentration (MEC) of finer particles was the lowest, while the MEC for large particles was the highest. The impact mechanism of coal dust concentration on maximum explosion pressure is that the number of coal dust particles affects the distance between particles and heat transfer efficiency. The influence mechanism of particle size on the explosion of oil-immersed coal is that the particle size can reflect the specific surface area size, which affects the diffusion of oxygen in particles and the rate of combustible volatiles released by particles. Hydrocarbons released from the crude oil via heating and the complex organic molecules generated during high-temperature pyrolysis produced simpler hydrocarbons, generating hydrogen and higher temperatures that accelerated the onset of explosions and increased coal dust explosion intensity. These experimental results were of use to process safety working and can help prevent coal dust explosion accidents in underground coal mines. [ABSTRACT FROM AUTHOR]