Search Results (5)

Hydrogen is regarded as a promising energy source for the future due to its clean combustion products, remarkable efficiency and renewability. However, its characteristics of low-ignition energy, a wide flammable range from 4% to 75%, and a rapid flame speed may bring significant explosion risks. Typically, accidental release of hydrogen into confined enclosures can result in a flammable hydrogen–air mixture with concentration gradients, possibly leading to flame acceleration (FA) and deflagration-to-detonation transition (DDT). The current study focused on the evolutions of the FA and DDT of homogenous/inhomogeneous hydrogen–air mixtures, based on the open-source computational fluid dynamics (CFD) platform OpenFOAM and the modified Weller et al.’s combustion model, taking into account the Darrieus–Landau (DL) and Rayleigh–Taylor (RT) instabilities, the turbulence and the non-unity Lewis number. Numerical simulations were carried out for both homogeneous and inhomogeneous mixtures in an enclosed channel 5.4 m in length and 0.06 m in height. The predictions demonstrate good quantitative agreement with the experimental measurements in flame-tip position, speed and pressure profiles by Boeck et al. The characteristics of flame structure, wave evolution and vortex were also discussed. Full article

Aspects of mathematical and physical modeling of deflagration explosions emerging during atmospheric (outdoor) accidental explosions are addressed. It has been demonstrated that when physically modeling accidental deflagration explosions, a stoichiometric mixture in the shape of a sphere or hemisphere supported by the ground should be used. This allows us to research the parameters of blast loads for the worst-case accidental scenarios or address the accident using the most conservative approach. A technique has been provided allowing one to create a mixture of a given blend composition in the shape of a sphere or hemisphere supported by the ground in outdoor conditions. It has been demonstrated that there is an ability to conduct modeling studies of accidental atmospheric explosions. We have provided examples of modeling studies of accidental atmospheric explosions; a methodology for analyzing experimental results has also been reviewed. The article discusses the mathematical modeling of outdoor (unobstructed) accidental deflagration explosions. It has been demonstrated that it is most reasonable to base computational experiments on linearized (acoustic) equations of continuum motion, as the visible flame propagation rate emerging during explosive combustion is small (compared to the speed of sound). There has been a satisfactory agreement between the numerical analysis and the experimental data. Full article

Accidental flame initiation to propagation in pipes carrying flammable gases is a significant safety concern that can potentially result in loss of life and substantial damage to property. The understanding of flame propagation characteristics caused by methane–air mixtures within various extractive and associated process industries such as coal mining is critical in developing effective and safe fire prevention and mitigation countermeasures. The aim of this study is to investigate and visualise the fire and explosion properties of a methane–air mixture in a straight pipe with and without obstacles. The experimental setup included modular starting pipes, an array of sensors (flame, temperature, and pressure), a gas injection system, a gas analyser, data acquisition and a control system. The resulting observations indicated that the presence of obstacles within a straight pipe eventuated an increase in flame propagation speed and deflagration overpressure as well as a reduction in the elapsed time of flame propagation. The maximum flame propagation speed in the presence of an orifice with a 70% blockage ratio at multiple spots was increased around 1.7 times when compared to the pipe without obstacles for 10% methane concentration. The findings of this study will augment the body of scientific knowledge and assist extractive and associated process industries, including stakeholders in coal mining to develop better strategies for preventing or reducing the incidence of methane–air flame propagation caused by accidental fires. Full article

Hydrocarbon–hydrogen blends are often considered as perspective environmentally friendly fuels for power plants, piston engines, heating appliances, home stoves, etc. However, the addition of hydrogen to a hydrocarbon fuel poses a potential risk of accidental explosion due to the high reactivity of hydrogen. In this manuscript, the detonability of stoichiometric C₃H₈–H₂–air mixtures is studied experimentally in terms of the run-up time and distance of deflagration to detonation transition (DDT). The hydrogen volume fraction in the mixtures varied from 0 to 1. Three different configurations of detonation tubes were used to ensure the DDT in the mixtures of the various compositions. The measured dependences of the DDT run-up time and distance on the hydrogen volume fraction were found to be nonlinear and, in some cases, nonmonotonic with local maxima. Blended fuel detonability is shown to increase sharply only at a relatively large hydrogen volume fraction (above 70%), i.e., the addition of hydrogen to propane in amounts less than 70% vol. does not affect the detonability of the blended fuel significantly. The observed nonlinear/nonmonotonic dependences are shown to be the manifestation of the physicochemical properties of hydrogen-containing mixtures. An increase in the hydrogen volume fraction is accompanied by effects leading to both an increase and a decrease in mixture sensitivity to the DDT. Thus, on the one hand, the increase in the hydrogen volume fraction increases the mixture sensitivity to DDT due to an increase in the laminar flame velocity and a decrease in the self-ignition delay at isotherms above 1000 K and pressures relevant to DDT. On the other hand, the mixture sensitivity to DDT decreases due to the increase in the speed of sound in the hydrogen-containing mixture, thus leading to a decrease in the Mach number of the lead shock wave propagating ahead of the flame, and to a corresponding increase in the self-ignition delay. Moreover, for C₃H₈–H₂–air mixtures at isotherms below 1000 K and pressures relevant to DDT, the self-ignition delay increases with hydrogen volume fraction. Full article

The study here presents data from the literature regarding the characteristic parameters of explosion propagation in gaseous ethane–air mixtures. The maximum explosion pressures, maximum explosion times, maximum rates of pressure increase, and deflagration indices from experimental measurements are discussed and analyzed against the initial pressure, initial temperature, and equivalence ratio, as well as the explosion vessel characteristics. Ethane is used for ethylene production, as a refrigerant in cryogenic systems, as an alternative clean fuel in the power generation industry and automotive propulsion, and for many other applications. Therefore, the explosion characteristics of its mixtures with air are of great interest for explosions occurring after accidentally forming flammable mixtures, as well as for the prediction of combustors’ performances and/or engines that work in different conditions. Full article