In a Hele-Shaw cell, unconventional fragmented flame propagation occurs for Peclet numbers less than 15. Until now, the regimes arising were organized in a simple taxonomy. Here, we endeavor to classify our experiments in view of the Theory of Solitons, a part of Synergetics discipline. This approach allows us to recognize new general patterns previously unidentified. Furthermore, this permits us to identify a much richer variety of topologies and typologies of regimes than initially thought.

Ultra-lean near-limit hydrogen flames evolving in narrow gaps of Hele-Shaw cells may undergo a possibly unexpected propagation mode by breaking the reaction front into isolated flamelets forming fractal-like structures. The combined effect of diffusive-thermal instability and intense heat losses act as two main mechanisms that explain experimental observations. The current study offers an extension of the earlier buoyancy-free reaction–diffusion model over the Boussinesq formulation, accounting for the buoyancy effect present in recent experimental studies of vertical Hele-Shaw burners. It is found that for upward-propagating flames, the bouyancy markedly expands the limits of propagation ability and reduces the limits for downward-propagation.

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recently become a subject of active research. In this paper, the flamelets resulting from the disintegration of the continuous front are interpreted in terms of the Zeldovich flame-balls stabilized by volumetric heat losses. A complicated free-boundary problem for 2D self-drifting near circular flamelets is reduced to a 1D model. The 1D formulation is then utilized to obtain the locus of the flamelet velocity, size, heat losses and Lewis numbers at which the self-drifting flamelets may exist.

In this study, the influence of vent burst pressure and ignition location on vented hydrogen explosions was investigated numerically using the Computational Fluid Dynamics (CFD) code GASFLOW-MPI. The numerical model accounts for two fundamental flame instabilities-thermal-diffusive instability and hydrodynamic instability-along with heat transfer mechanisms. To validate the accuracy of GASFLOW-MPI in simulating vented hydrogen explosions, the computed internal and external overpressure-time histories were compared with experimental data, demonstrating good agreement, particularly for external overpressure profiles. A detailed numerical analysis of the flow field was conducted to elucidate the mechanisms governing internal and external overpressure peaks under central and back ignition scenarios. Quantitative evaluations were performed on the expelled and consumed moles of hydrogen and oxygen, expelled nitrogen, and generated steam. Furthermore, the energy released by hydrogen combustion, as well as heat transfer via convection and radiation, was systematically quantified. Finally, the correlation between maximum internal and external overpressures and vent burst pressure was analyzed to provide deeper insights into explosion dynamics.

This study investigated the impact of obstacle volume blockage ratio (VBR) on vented hydrogen explosions using both experimental and numerical approaches. Experiments were conducted with hydrogen concentrations ranging from 34 vol% to 42 vol% and VBRs between 0% and 24%. The Computational Fluid Dynamics (CFD) software GASFLOW-MPI was validated by comparing simulated pressure-time curves with experimental results across various hydrogen concentrations and VBRs. Numerical simulations provided insights into the mechanisms driving the observed overpressure peaks. For hydrogen-air mixtures with concentrations of 34 vol% and 38 vol%, the maximum overpressure increased with the VBR, from 88 kPa to 179 kPa and from 70 kPa to 151 kPa, respectively. However, for the 42 vol% hydrogen-air mixture, the maximum overpressure stabilized at approximately 80 kPa when VBR exceeded 12%. The analysis revealed that the initial hydrogen mass, expelled hydrogen mass, and residual hydrogen mass within the vessel at the point of maximum overpressure decreased as VBR increased. In contrast, the energy released inside the vessel increased with VBR. Additionally, heat transfer via convection and radiation, as well as the steam mass at the maximum overpressure, were quantified. The relationship between maximum overpressure and VBR for different hydrogen concentrations was quantitatively analyzed, considering the released energy and the volume of combustion products.

The objective of vented hydrogen explosion studies is to elucidate the relationship between maximum overpressure, flame dynamics, and vent area. The effect of vent area on vented hydrogen explosions was numerically investigated in this paper. Initially, the performance of the computational fluid dynamics (CFD) software GASFLOW-MPI was evaluated by comparing overpressure histories and flame behavior from experimental data with simulation results. The findings indicate that the predicted overpressure-time curves and flame behavior align closely with experimental observations for different ignition locations and vent areas. Furthermore, the mechanisms underlying maximum internal overpressure for different vent areas were elucidated. By analyzing the total energy, heat transfer between combustion products and vessel walls, and the moles of hydrogen, nitrogen, steam, and oxygen, the relationship between maximum overpressure and vent areas for different ignition locations was quantitatively analyzed.

The adoption of liquid hydrogen (LH2) as an energy carrier presents significant opportunities for distributing large quantities of hydrogen efficiently. However, ensuring safety of LH2 transfer operations requires the evolution of suitable technologies and regulatory framework. This study offers an extensive overview of technical considerations and safety aspects pertaining to liquid hydrogen installations and mobile applications. A significant lack of regulations specifically tailored for LH2 transfer operations is highlighted. Additionally, experimental findings and outcomes of the modelling activities carried out in previous research are presented, shedding light on the combustion and ignition behaviour of liquid hydrogen during accident scenarios. The identification of research gaps and ongoing research projects underscores the importance of continued investigation and development of this critical area.

Turbulence in the hydrogen combustion field influences flame propagation and its consequences, which is of great importance for the safety of hydrogen/nuclear energy systems. The large-scale deflagration experiment of the premixed H2-air-steam cloud with initial high turbulence in the large closed two-compartment system is conducted. The Computational Fluid Dynamics (CFD) tool GASFLOW-MPI developed to assess hydrogen safety during accidents, is utilized here to simulate this experiment. The objectives encompass exploring the numerical and experimental aspects of H2 flame propagation and deflagration consequences with turbulence effect, and validating the CFD code through this experiment. The agreements between the prediction and the experimental data indicate that simulation modeling with the Large Eddy Simulation (LES) turbulence model and turbulent flame speed closure is recommended for investigating the H2 deflagration. The experimental and predicted results indicate the following highlights. 1. The hydrogen flame can propagate in the opposite direction of the gas flow when there is an intense turbulent fluctuation upstream. 2. Turbulence accelerates the combustion velocity, causing the pressure to rise to its maximum in less than 2 s 3. So, the pre-calculation of flow turbulence before ignition and during hydrogen deflagration is essential for predicting flame propagation. 4. The peak combustion pressure increases significantly with the hydrogen concentration in a premixed lean H2 cloud. 5. Convection and radiation contribute comparably to heat loss, leading to a decrease in system temperature and pressure. The longterm hydrogen combustion load is primarily governed by heat transfer and heat dissipation within the structures.

Deterministic risk assessment for hydrogen installations offers an integrated solution for H2 risk assessment, incorporating a hydrogen release model, a site-specific 3D geometry model, a Computational Fluid Dynamics (CFD) tool, and a consequence analysis methodology. Empirical engineering models expedite the preparation of source terms and harm evaluations, while CFD generates 3D contours of radiation and overpressure loads. A case study is provided by investigating a gaseous hydrogen leak of a truck in a refueling station with a large roof. The effects of leak diameters, roof configurations, and ignition locations on hydrogen dispersion, combustion, and hazard analysis are examined. Results indicate that the majority of the burnable cloud accumulates in a half-meter layer under the ceiling, diminishing within a minute. The impact of thermal radiation on individuals is insignificant, but overpressures increase the likelihood of structure failures, indirectly affecting human fatality. These findings inform the optimization of refueling station design and safety management.

In the current study, numerical study of vented hydrogen explosions was performed utilizing computational fluid dynamics (CFD) software GASFLOW-MPI. A turbulent combustion model based on Schmidt correlation was formulated. Within this model, flame instabilities resulted from two intrinsic effects, Hydrodynamic instability, and Landau-Darrieus and Thermal-Diffusive instabilities were incorporated. The numerical simulation results revealed the mechanism of overpressure evolution inside and outside the vessel. Notably, the mechanism of the overpressure peak induced by the external explosion was revealed. The effects of turbulence models on overpressure time profiles were investigated. Moreover, it was determined that heat transfer, arising from thermal radiation and convection, exerts only a negligible influence on the maximum internal overpressure. Subsequently, the performance of GASFLOW-MPI in simulating vented hydrogen explosions for different ignition locations (center and rear ignitions) and varying hydrogen concentrations (22%-38%) was assessed against experimental data. Comparative analysis revealed a close agreement between the predicted results and experimental data. Furthermore, the competency of GASFLOW in simulating medium-scale vented hydrogen explosions was validated against experimental data.

To build methane anti-explosion storage equipment, the influence of the ignition location on the CH4/air explosion in a spherical equipment was investigated. A two-step CH4/air reaction mechanism was developed and it considered the effect of heat transfer on the explosion. The effect of methane explosion pressure on heat loss was studied. The results show that the maximum explosion pressure of central ignition is 0.72 MPa under the heat loss simulation. The peak pressure of the upper and lower end-wall explosion is about 79.2 % and 83.3 % of the central ignition explosion, respectively, and the experimental results verifies the simulation results. Therefore, the reason for the highest peak pressure of central ignition methane explosion is that the reaction speed of central ignition methane explosion is the fastest, and the heat loss is the lowest. The difference in peak pressure between the upper and lower wall surfaces is due to the buoyancy effect accelerates the reaction rate of the lower end-wall ignition. In the simulation time range, the heat radiation at different ignition locations accounts for more than 70 % of the total heat loss, and radiation heat transfer plays a leading role in the total heat loss.

This study investigates the spontaneous ignition of high-pressure hydrogen-enriched methane in air within a rectangular tube. A computationally efficient approach has been adopted, utilizing a reduced reaction mechanism and ignition delay model within a 3D Large Eddy Simulation (LES) framework. This approach overcomes the limitations of traditional 1D and 2D simulations with detailed chemistry models, which are unable to accurately reproduce the complex 3D shock wave structures within the tube. The simulated shock wave behavior during 9 MPa hydrogen leakage (case 1) and 11 MPa 90 vol% hydrogen/10 vol% methane mixture leakage (case 2) are found to agree well with experimental observations. In case 2, the hot spots generated by reflected shock waves and Mach reflections ignite the hydrogen/methane-air mixture, resulting in three sequential spontaneous ignitions. The flame is observed to primarily propagate along the tube corners and wall centers, with the central ignition spreading across the entire cross-section. For the 25 MPa 24 vol% hydrogen/76 vol% methane mixture leakage (case 6), the shock intensity is significantly reduced due to the increased methane proportion, leading to spontaneous ignition only at the tube corners when the hemispherical shock wave reflects from the wall. The flame predominantly forms downstream along the tube corner, gradually spreading along the tube wall. It is indicated that while the probability of spontaneous ignition decreases with increasing methane content, the risk remains significant under sufficiently high pressures. To the best our knowledge, this study represents the first 3D large eddy simulation of spontaneous ignition for high-pressure hydrogen-enriched methane leakage into air, providing valuable insights into the underlying physical phenomena.

To build methane anti-explosion storage equipment, the influence of the ignition location on the CH 4 /air explosion in a spherical equipment was investigated. A two-step CH 4 /air reaction mechanism was developed and it considered the effect of heat transfer on the explosion. The effect of methane explosion pressure on heat loss was studied. The results show that the maximum explosion pressure of central ignition is 0.72 MPa under the heat loss simulation. The peak pressure of the upper and lower end-wall explosion is about 79.2 % and 83.3 % of the central ignition explosion, respectively, and the experimental results verifies the simulation results. Therefore, the reason for the highest peak pressure of central ignition methane explosion is that the reaction speed of central ignition methane explosion is the fastest, and the heat loss is the lowest. The difference in peak pressure between the upper and lower wall surfaces is due to the buoyancy effect accelerates the reaction rate of the lower end-wall ignition. In the simulation time range, the heat radiation at different ignition locations accounts for more than 70 % of the total heat loss, and radiation heat transfer plays a leading role in the total heat loss.

The addition of hydrogen to methane changes its deflagration characteristics and increases the combustion rate. However, studies on the effect of hydrogen on methane deflagration remain insufficient. Therefore, based on the CFD code GASFLOW-MPI, a four-step combustion-mechanism model was established for methane/hydrogen mixtures. The deflagration characteristics of a premixed combustible gas in a 20-L spherical device was numerically simulated using a methane/hydrogen/air equivalence ratio of 1 and hydrogen addition in the range of 0-50%; subsequently. The results were compared with experimental data. The four-step methane/hydrogen combustion-mechanism could effectively reproduce the methane/hydrogen deflagration process on considering the heat losses. With an increase in hydrogen addition, the laminar burning velocity increases, and the defla-gration duration reduces. It decreases the explosion heat loss and increased the maximum deflagration pressure. Under adiabatic simulation, the maximum deflagration pressure decreased with an increase in hydrogen addi-tion, in contrast with the experimental results. This indicates that the heat-loss effect of the methane/hydrogen/ air-mixture deflagration process should not be ignored. Moreover, the heat loss during the methane/hydrogen/ air-mixture deflagration was mainly caused by thermal radiation. Thus, the influence of the thermal-radiation and convective heat-transfer mechanisms should be considered in the numerical simulations of methane/ hydrogen/air-mixture deflagration.

Methane explosions are among the main hazards in coal mines. Shock waves from methane explosions can cause damage near the explosion site, and combustion products can spread along the tunnel to locations far from the explosion source and endanger the lives and health of personnel. Therefore, the study of the propagation patterns of methane explosion shock waves and the distribution of high-temperature combustion products in tunnels. has significance for emergency decision-making in the event of methane explosions in a mine. This study uses the 3D Computational Fluid Dynamics (CFD) program GASFLOW-MPI, which models the one-step methane combustion mechanism with the addition of a heat transfer model. The methane explosion process is simulated and reproduced at the Lake Lynn Experimental Mine (LLEM) to analyze the process of gas deflagration. The results reveal that the overpressure in the tunnel after the methane explosion oscillates and decays with time. Gaseous products of the explosion "expand and compress" and flow back and forth in accordance with the oscillation of overpressure. The maximum expansion ratio of the CO2 concentration isosurfaces of 0.5% in the heat transfer simulation is 6.21, whereas the volume expansion ratio is 3.78 once the flow field stabilizes. The distribution of combustion products along the alleyway exhibits a Gaussian decay trend. The range of gaseous product distribution and temperature fields in the adiabatic tunnel is significantly higher than that in the heat transfer simulations, thus indicating that heat loss significantly influences the temperature characteristics and distribution pattern of combustion products in the full-scale tunnel.

Structures formed as a result of mixing of hydrogen with air are analyzed by optical methods using detection of density non-uniformities. Methods for determination of fractal parameters for a random distribution of these non-uniformities are described, and information about the structure of gas mixing revealed is analyzed. The BOS (Background Oriented Schlieren) method is used to obtain the optical image of the formed structures and then treat by the correlation method that allows to obtain the quantitative information on the mixing. As a result, the possibility to link the characteristics of the injected gas source and the fractal parameters were demonstrated. The method can be used in the development of the non-intrusive technique for the evaluation of the gaseous system parameters based on the optical diagnostics and, potentially, for the obtaining more detailed information of the turbulence in gases.

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recently become a subject of active research. In this paper, the flamelets resulting from the disintegration of the continuous front a reinterpreted in terms of the Zeldovich flame-balls stabilized by volumetric heat losses. A complicated free-boundary problem for 2D self-drifting near circular flamelets is reduced to a 1D model. The 1D formulation is then utilized to obtain the locus of the flamelet velocity, radius, heat losses and Lewis numbers at which the self-drifting flamelet exists.

Dendritic combustion in Hele–Shaw cells is investigated qualitatively using a simplified one-dimensional thermo-diffusive model. Formulas for the velocity, size, and temperature of the flamelets are derived. The temperature and velocity of the flames increase for small radii to allow for their survival regardless of the activation energy. In addition, the results obtained with very large activation energy were compared with experimental results, finding that additional tests are required due to the strong influence of gravity on the velocity and size estimations. Conditions for the existence of this anomalous propagation are investigated, confirming analytically that it can only happen for low Lewis numbers.

Jet flames originated by cryo-compressed ignited hydrogen releases can cause lifethreatening conditions in their surroundings. Validated models are needed to accurately predict thermal hazards from a jet fire. Numerical simulations of cryogenic hydrogen flow in the release pipe are performed to assess the effect of heat transfer through the pipe walls on jet parameters. Notional nozzle exit diameter is calculated based on the simulated real nozzle parameters and used in CFD simulations as a boundary condition to model jet fires. The CFD model was previously validated against experiments with vertical cryogenic hydrogen jet fires with release pressures up to 0.5 MPa (abs), release diameter 1.25 mm and temperatures as low as 50 K. This study validates the CFD model in a wider domain of experimental release conditions - horizontal cryogenic jets at exhaust pipe temperature 80 K, pressure up to 2 MPa ab and release diameters up to 4 mm. Simulation results are compared against such experimentally measured parameters as hydrogen mass flow rate, flame length and radiative heat flux at different locations from the jet fire. The CFD model reproduces experiments with reasonable for engineering applications accuracy. Jet fire hazard distances established using three different criteria - temperature, thermal radiation and thermal dose - are compared and discussed based on CFD simulation results. (c) 2022 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

This study developed a model of methane one-step combustion mechanism based on the CFD code GASFLOW-MPI to understand the influence mechanism and degree of influence of heat transfer mechanism on methane explosion. Moreover, this study proposed the addition of heat transfer mathematical models using GASFLOW-MPI, including thermal radiation and convection heat transfer. Further, the effects of thermal radiation and convective heat transfer on the shock wave during a methane explosion in a 20 L spherical explosion tank were studied through numerical simulation and the results were compared with the experimental data. The numerical simulation results were found to reasonably predict the peak pressure value and pressure decay process of a methane explosion. In addition, through comparisons of the effects of adiabatic and numerical simulations considering heat loss, the peak pressure of gas explosion calculated via adiabatic simulation were found to be overestimated. Moreover, during the methane-air mixed explosion experiment in the 20 L spherical device, the heat loss was observed to be primarily caused by heat radiation, accounting for more than 76.01% of the total heat loss, followed by convection heat transfer, accounting for 23.99% of the total heat loss. The research results showed that heat loss significantly influenced the methane explosion process. Additionally, for the methane-air mixture explosion experiment in a 20 L spherical device, thermal radiation was the most critical factor that resulted in heat loss in the methane explosion process. Therefore, the influence of thermal radiation and convective heat transfer mechanism on methane explosion must be considered in the numerical simulation of a methane explosion.