Mike Kuznetsov, PhD | Karlsruhe Institute of Technology (KIT) (original) (raw)

Papers by Mike Kuznetsov, PhD

Combustion and Flame, 2023

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recent... more 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, radius, heat losses and Lewis numbers at which the self-drifting flamelet exists. Novelty and significance statement: The existence and limits of self-propagating 2D flame-balls have been substantiated theoretically for the first time. They have been investigated analytically, displaying the crucial role of heat losses. The regime arises in praxis in thin enclosures such as Hele-Shaw cells. The design of flame arresters may well be influenced by these findings.

International Journal of Hydrogen Energy, 2023

Deterministic risk assessment for hydrogen installations offers an integrated solution for H2 ris... more 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.

Combustion and Flame, 2023

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recent... more 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.

Journal of Loss Prevention in the Process Industries, 2022

This study developed a model of methane one-step combustion mechanism based on the CFD code GASFL... more 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.

Fuel, 2023

The addition of hydrogen to methane changes its deflagration characteristics and increases the co... more 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 deflagration 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 addition, 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.

International Journal of Hydrogen Energy

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening con... more Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening 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.

Physics of Fluids, 2022

Dendritic combustion in Hele-Shaw cells is investigated qualitatively using a simplified one-dime... more 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.

International Journal of Hydrogen Energy, 2022

A series of combustion experiments was made at cryogenic temperatures from 90 to 130 K. Critical ... more A series of combustion experiments was made at cryogenic temperatures from 90 to 130 K. Critical conditions for flame acceleration to the speed of sound and then to detonation have been found. Detonation cell sizes at cryogenic temperature T ¼ 100 K are evaluated in a wide range of concentrations. Maximum combustion pressure is 2e3 times higher due to the density factor.

Optics and Lasers in Engineering, 2022

Structures formed as a result of mixing of hydrogen with air are analyzed by optical methods usin... more 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.

International Journal of Hydrogen Energy, 2017

Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks... more Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks for materials handling in a warehouse facility, fuel cells located in a room, or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons, to isolate them from the end-user and the public, or from weather conditions.

Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks, including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture, or can result in jet-fires. Within Hyindoor European Project, carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation, vented deflagrations, jet fires and including under-ventilated flame regimes (e.g., extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.

International Journal of Hydrogen Energy, 2021

This paper presents results of experimental investigations on spherical and cylindrical flame pro... more This paper presents results of experimental investigations on spherical and cylindrical flame propagation in pre-mixed H2/air-mixtures in unconfined and semi-confined geometries. The experiments were performed in a facility consisting of two transparent solid walls with 1 m2 area and four weak side walls made from thin plastic film. The gap size between the solid walls was varied stepwise from thin layer geometry (6 mm) to cube geometry (1 m). A wide range of H2/air-mixtures with volumetric hydrogen concentrations from 10% to 45% H2 was ignited between the transparent solid walls. The propagating flame front and its structure was observed with a large scale high speed shadow system. Results of spherical and cylindrical flame propagation up to a radius of 0.5 m were analyzed. The presented spherical burning velocity model is used to discuss the self-acceleration phenomena in unconfined and unobstructed pre-mixed H2/air flames.

International Journal of Hydrogen Energy, 2021

In the present work, a newly developed CFD deflagration model incorporated into the ADREA-HF code... more In the present work, a newly developed CFD deflagration model incorporated into the ADREA-HF code is evaluated against hydrogen vented deflagrations experiments carried out by KIT and FM-Global in a medium (1 m3) and a real (63.7 m3) scale enclosure respectively. A square vent of 0.5 m2 and 5.4 m2 respectively is located in the center of one of side walls. In the case of the medium scale enclosure the 18% v/v homogeneous hydrogen-air mixture and back-wall ignition case is examined. In the case of the real scale enclosure the examined cases cover different homogeneous mixture concentrations (15% and 18% v/v), different ignition locations (back-wall and center) and different levels of initial turbulence. The CFD model accounts for flame instabilities that develop as the flame propagates inside the chamber and turbulence that mainly develops outside the vent. Pressure predictions are compared against experimental measurements revealing a very good performance of the CFD model for the back-wall ignition cases. For the center ignition cases, the model overestimates the maximum overpressure. The opening of the vent cover is identified as a possible reason for the overprediction. The analysis indicates that turbulence is the main factor which enhances external explosion strength causing the sudden pressure increase, confirming previous findings.

International Journal of Hydrogen Energy, 2022

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening con... more Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening 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.

International Journal of Hydrogen Energy, 2022

The anticipated upscaling of hydrogen energy applications will involve the storage and transport ... more The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen at cryogenic conditions. Understanding the potential hazard arising from leaks in high-pressure cryogenic storage is needed to improve hydrogen safety. The manuscript reports a series of numerical simulations with detailed chemistry for the transient evolution of ignited high-pressure cryogenic hydrogen jets. The study aims to gain insight of the ignition processes, flame structures and dynamics associated with the transient flame evolution. Numerical simulations were firstly conducted for an unignited jet released under the same cryogenic temperature of 80 K and pressure of 200 bar as the considered ignited jets. The predicted hydrogen concentrations were found to be in good agreement with the experimental measurements. The results informed the subsequent simulations of the ignited jets involving four different ignition locations. The predicted time series snapshots of temperature, hydrogen mass fraction and the flame index are analyzed to study the transient evolution and structure of the flame. The results show that a diffusion combustion layer is developed along the outer boundary of the jet and a side diffusion flame is formed for the near-field ignition. For the far-field ignition, an envelope flame is observed. The flame structure contains a diffusion flame on the outer edge and a premixed flame inside the jet. Due to the complex interactions between turbulence, fuel-air mixing at cryogenic temperature and chemical reactions, localized spontaneous ignition and transient flame extinguishment are observed. The predictions also captured the experimentally observed deflagration waves in the far-field ignited jets.

International Journal of Hydrogen Energy, 2022

A series of more than 100 experiments with hydrogen-air mixtures have been performed at cryogenic... more A series of more than 100 experiments with hydrogen-air mixtures have been performed at cryogenic temperatures from 90 to 130 K and ambient pressure. A wide range of hydrogen concentrations from 8 to 60%H2 in a shock tube of 5-m long and 54 mm id was tested. Flame propagation regimes were investigated for all hydrogen compositions at three different blockage ratios 0, 30% and 60% as a function of initial temperature. Piezoelectric pressure sensors and InGaAs photo-diodes have been applied to monitor the flame and shock propagation velocity of the combustion process. More than 150 experiments at ambient pressure and temperature were conducted as the reference data for cryogenic experiments. The critical expansion ratio σ∗ for an effective flame acceleration to the speed of sound was experimentally found at cryogenic temperatures. The detonability criteria for smooth and obstructed channels were used to evaluate the detonation cell sizes at cryogenic temperatures as well. The main peculiarities of cryogenic combustion with respect to the safety assessment were that the maximum combustion pressure was several times higher and the run-up-distance to detonation was two times shorter compared to ambient temperature independent of lower chemical reactivity at cryogenic conditions.

International Journal of Hydrogen Energy, 2021

Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have draw... more Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open-air environment will disperse quickly, hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place, i.e. parking garages and tunnels. Prediction the main accident process, including the hydrogen release, dispersion, and combustion, is important for hydrogen safety assessment, and ensuring the safety installations during accidents. Hence, a postulated accident scenario induced by the operation of Thermal Pressure Relief Device in a tunnel is analysed for hydrogen fuel cell vehicles with GASFLOW-MPI in this study. GASFLOW-MPI is a well validated parallel CFD code focusing on the transport, combustion, and detonation of hydrogen. It solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method; hence can cover both the non-compressible flow during the hydrogen release and dispersion phases, and the compressible flow during deflagration and detonation. In this study, a 3D model of real-scaled tunnel is modelled, firstly. Then the hydrogen dispersion in the tunnel is calculated to evaluate the risk of Flame acceleration and the Deflagration-Detonation Transient (DDT). The case with jet fire is analysed with assuming that the hydrogen is ignited right after being injected forming a jet fire in the tunnel, the consequence of this case is limited considering the small hydrogen inventory. The detonation in the tunnel is calculated by assuming a strong ignition at the top of the tunnel at an unfavourable time and location. The pressure loads are calculated to evaluate the consequence of the hazard. The analysis shows that the GASFLOW-MPI is applicable at a widely range for tunnel accidents, meanwhile, the safety issues related to tunnel accidents is worthy further study considering the complexity of tunnels.

Combustion and Flame, 2022

The problem of sudden flame acceleration in narrow channels and subsequent Deflagration to Detona... more The problem of sudden flame acceleration in narrow channels and subsequent Deflagration to Detonation Transition (DDT) is revisited. The hydrogen-oxygen combustion system is considered both experimentally and numerically. The flame is initiated at one open end of a square narrow channel of different widths (4, 8, 10 and 20 mm) and propagates to another open end. Experimental results show a high sensitivity to the mixture composition: for higher mixture reactivity, an abrupt flame acceleration is reported. In 4 × 4 mm 2 channel, when the mixture composition is close to stoichiometry (2:1), the DDT is observed without any evidence of shock waves prior to the detonation transition. Two complementary sub-models are combined to account for the effect of walls on flow and on flame front geometry. A pseudo-spectral numerical scheme is used to integrate the system of equations both in time and in space. The simulation results show how the suggested model reproduces main features of the phenomenon. A simple criterion is suggested for the onset of the flame self-acceleration. There exists a critical flame folding factor for the DDT, which is an invariant of the system. The reported critical folding factor is compared to the theoretical estimation introduced by Gordon et al (2020).

International Journal of Hydrogen Energy

In the present paper the results of experiments on study of high-speed deflagrations in flat laye... more In the present paper the results of experiments on study of high-speed deflagrations in flat layer of hydrogen-air mixtures unconfined from below are presented. The experiments were performed in two different rectangular channels: small-scale with mixture volume up to 0.4 m 3 and large-scale with volume up to 5.5 m 3 . The main goal of the experiments was to examine the possibility of the layer geometries to maintain high-speed deflagration and detonation. With the aim to study a range of combustion regimes the experiments were performed varying degree of channel obstruction, hydrogen concentration and thickness of the layer. Depending on the experimental conditions all major combustion regimes were observed: slow flame, fast – 'choked' flame and steady-state detonation. It was found that minimum layer thickness in the range of 8 to 15 detonation cell widths is required for sustainable detonations.

Journal of Loss Prevention in the Process Industries, 2013

ABSTRACT This paper presents results of an experimental investigation on fast flame propagation a... more ABSTRACT This paper presents results of an experimental investigation on fast flame propagation and the deflagration-to-detonation transition (DDT) and following detonation propagation in a semi-confined flat layer filled with stratified hydrogeneair mixtures. The experiments were performed in a trans-parent, rectangular channel open from below. The combustion channel has a width of 0.3 m and a length of 2.5 m. The effective layer thickness in the channel was varied by using different linear hydrogen concentration gradients. The method to create quasi-linear hydrogen concentration gradients that differ in the range and slope is also presented. The ignited mixtures were accelerated quickly to sonic flame speed in the first obstructed part of the channel. The interaction of the fast flame propagation with different obstacle set-ups was studied in the second part of the channel. The experimental results show an initiation of DDT by one additional metal grid in the obstructed semi-confined flat layer. Detonation propagation and failed detonation propagation were observed in obstructed and unobstructed parts of the channel.

Combustion and Flame, 2023

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recent... more 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, radius, heat losses and Lewis numbers at which the self-drifting flamelet exists. Novelty and significance statement: The existence and limits of self-propagating 2D flame-balls have been substantiated theoretically for the first time. They have been investigated analytically, displaying the crucial role of heat losses. The regime arises in praxis in thin enclosures such as Hele-Shaw cells. The design of flame arresters may well be influenced by these findings.

International Journal of Hydrogen Energy, 2023

Deterministic risk assessment for hydrogen installations offers an integrated solution for H2 ris... more 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.

Combustion and Flame, 2023

The disintegration of near limit flames propagating through the gap of Hele-Shaw cells has recent... more 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.

Journal of Loss Prevention in the Process Industries, 2022

This study developed a model of methane one-step combustion mechanism based on the CFD code GASFL... more 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.

Fuel, 2023

The addition of hydrogen to methane changes its deflagration characteristics and increases the co... more 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 deflagration 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 addition, 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.

International Journal of Hydrogen Energy

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening con... more Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening 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.

Physics of Fluids, 2022

Dendritic combustion in Hele-Shaw cells is investigated qualitatively using a simplified one-dime... more 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.

International Journal of Hydrogen Energy, 2022

A series of combustion experiments was made at cryogenic temperatures from 90 to 130 K. Critical ... more A series of combustion experiments was made at cryogenic temperatures from 90 to 130 K. Critical conditions for flame acceleration to the speed of sound and then to detonation have been found. Detonation cell sizes at cryogenic temperature T ¼ 100 K are evaluated in a wide range of concentrations. Maximum combustion pressure is 2e3 times higher due to the density factor.

Optics and Lasers in Engineering, 2022

Structures formed as a result of mixing of hydrogen with air are analyzed by optical methods usin... more 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.

International Journal of Hydrogen Energy, 2017

Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks... more Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks for materials handling in a warehouse facility, fuel cells located in a room, or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons, to isolate them from the end-user and the public, or from weather conditions.

Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks, including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture, or can result in jet-fires. Within Hyindoor European Project, carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation, vented deflagrations, jet fires and including under-ventilated flame regimes (e.g., extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.

International Journal of Hydrogen Energy, 2021

This paper presents results of experimental investigations on spherical and cylindrical flame pro... more This paper presents results of experimental investigations on spherical and cylindrical flame propagation in pre-mixed H2/air-mixtures in unconfined and semi-confined geometries. The experiments were performed in a facility consisting of two transparent solid walls with 1 m2 area and four weak side walls made from thin plastic film. The gap size between the solid walls was varied stepwise from thin layer geometry (6 mm) to cube geometry (1 m). A wide range of H2/air-mixtures with volumetric hydrogen concentrations from 10% to 45% H2 was ignited between the transparent solid walls. The propagating flame front and its structure was observed with a large scale high speed shadow system. Results of spherical and cylindrical flame propagation up to a radius of 0.5 m were analyzed. The presented spherical burning velocity model is used to discuss the self-acceleration phenomena in unconfined and unobstructed pre-mixed H2/air flames.

International Journal of Hydrogen Energy, 2021

In the present work, a newly developed CFD deflagration model incorporated into the ADREA-HF code... more In the present work, a newly developed CFD deflagration model incorporated into the ADREA-HF code is evaluated against hydrogen vented deflagrations experiments carried out by KIT and FM-Global in a medium (1 m3) and a real (63.7 m3) scale enclosure respectively. A square vent of 0.5 m2 and 5.4 m2 respectively is located in the center of one of side walls. In the case of the medium scale enclosure the 18% v/v homogeneous hydrogen-air mixture and back-wall ignition case is examined. In the case of the real scale enclosure the examined cases cover different homogeneous mixture concentrations (15% and 18% v/v), different ignition locations (back-wall and center) and different levels of initial turbulence. The CFD model accounts for flame instabilities that develop as the flame propagates inside the chamber and turbulence that mainly develops outside the vent. Pressure predictions are compared against experimental measurements revealing a very good performance of the CFD model for the back-wall ignition cases. For the center ignition cases, the model overestimates the maximum overpressure. The opening of the vent cover is identified as a possible reason for the overprediction. The analysis indicates that turbulence is the main factor which enhances external explosion strength causing the sudden pressure increase, confirming previous findings.

International Journal of Hydrogen Energy, 2022

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening con... more Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening 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.

International Journal of Hydrogen Energy, 2022

The anticipated upscaling of hydrogen energy applications will involve the storage and transport ... more The anticipated upscaling of hydrogen energy applications will involve the storage and transport of hydrogen at cryogenic conditions. Understanding the potential hazard arising from leaks in high-pressure cryogenic storage is needed to improve hydrogen safety. The manuscript reports a series of numerical simulations with detailed chemistry for the transient evolution of ignited high-pressure cryogenic hydrogen jets. The study aims to gain insight of the ignition processes, flame structures and dynamics associated with the transient flame evolution. Numerical simulations were firstly conducted for an unignited jet released under the same cryogenic temperature of 80 K and pressure of 200 bar as the considered ignited jets. The predicted hydrogen concentrations were found to be in good agreement with the experimental measurements. The results informed the subsequent simulations of the ignited jets involving four different ignition locations. The predicted time series snapshots of temperature, hydrogen mass fraction and the flame index are analyzed to study the transient evolution and structure of the flame. The results show that a diffusion combustion layer is developed along the outer boundary of the jet and a side diffusion flame is formed for the near-field ignition. For the far-field ignition, an envelope flame is observed. The flame structure contains a diffusion flame on the outer edge and a premixed flame inside the jet. Due to the complex interactions between turbulence, fuel-air mixing at cryogenic temperature and chemical reactions, localized spontaneous ignition and transient flame extinguishment are observed. The predictions also captured the experimentally observed deflagration waves in the far-field ignited jets.

International Journal of Hydrogen Energy, 2022

A series of more than 100 experiments with hydrogen-air mixtures have been performed at cryogenic... more A series of more than 100 experiments with hydrogen-air mixtures have been performed at cryogenic temperatures from 90 to 130 K and ambient pressure. A wide range of hydrogen concentrations from 8 to 60%H2 in a shock tube of 5-m long and 54 mm id was tested. Flame propagation regimes were investigated for all hydrogen compositions at three different blockage ratios 0, 30% and 60% as a function of initial temperature. Piezoelectric pressure sensors and InGaAs photo-diodes have been applied to monitor the flame and shock propagation velocity of the combustion process. More than 150 experiments at ambient pressure and temperature were conducted as the reference data for cryogenic experiments. The critical expansion ratio σ∗ for an effective flame acceleration to the speed of sound was experimentally found at cryogenic temperatures. The detonability criteria for smooth and obstructed channels were used to evaluate the detonation cell sizes at cryogenic temperatures as well. The main peculiarities of cryogenic combustion with respect to the safety assessment were that the maximum combustion pressure was several times higher and the run-up-distance to detonation was two times shorter compared to ambient temperature independent of lower chemical reactivity at cryogenic conditions.

International Journal of Hydrogen Energy, 2021

Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have draw... more Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open-air environment will disperse quickly, hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place, i.e. parking garages and tunnels. Prediction the main accident process, including the hydrogen release, dispersion, and combustion, is important for hydrogen safety assessment, and ensuring the safety installations during accidents. Hence, a postulated accident scenario induced by the operation of Thermal Pressure Relief Device in a tunnel is analysed for hydrogen fuel cell vehicles with GASFLOW-MPI in this study. GASFLOW-MPI is a well validated parallel CFD code focusing on the transport, combustion, and detonation of hydrogen. It solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method; hence can cover both the non-compressible flow during the hydrogen release and dispersion phases, and the compressible flow during deflagration and detonation. In this study, a 3D model of real-scaled tunnel is modelled, firstly. Then the hydrogen dispersion in the tunnel is calculated to evaluate the risk of Flame acceleration and the Deflagration-Detonation Transient (DDT). The case with jet fire is analysed with assuming that the hydrogen is ignited right after being injected forming a jet fire in the tunnel, the consequence of this case is limited considering the small hydrogen inventory. The detonation in the tunnel is calculated by assuming a strong ignition at the top of the tunnel at an unfavourable time and location. The pressure loads are calculated to evaluate the consequence of the hazard. The analysis shows that the GASFLOW-MPI is applicable at a widely range for tunnel accidents, meanwhile, the safety issues related to tunnel accidents is worthy further study considering the complexity of tunnels.

Combustion and Flame, 2022

The problem of sudden flame acceleration in narrow channels and subsequent Deflagration to Detona... more The problem of sudden flame acceleration in narrow channels and subsequent Deflagration to Detonation Transition (DDT) is revisited. The hydrogen-oxygen combustion system is considered both experimentally and numerically. The flame is initiated at one open end of a square narrow channel of different widths (4, 8, 10 and 20 mm) and propagates to another open end. Experimental results show a high sensitivity to the mixture composition: for higher mixture reactivity, an abrupt flame acceleration is reported. In 4 × 4 mm 2 channel, when the mixture composition is close to stoichiometry (2:1), the DDT is observed without any evidence of shock waves prior to the detonation transition. Two complementary sub-models are combined to account for the effect of walls on flow and on flame front geometry. A pseudo-spectral numerical scheme is used to integrate the system of equations both in time and in space. The simulation results show how the suggested model reproduces main features of the phenomenon. A simple criterion is suggested for the onset of the flame self-acceleration. There exists a critical flame folding factor for the DDT, which is an invariant of the system. The reported critical folding factor is compared to the theoretical estimation introduced by Gordon et al (2020).

International Journal of Hydrogen Energy

In the present paper the results of experiments on study of high-speed deflagrations in flat laye... more In the present paper the results of experiments on study of high-speed deflagrations in flat layer of hydrogen-air mixtures unconfined from below are presented. The experiments were performed in two different rectangular channels: small-scale with mixture volume up to 0.4 m 3 and large-scale with volume up to 5.5 m 3 . The main goal of the experiments was to examine the possibility of the layer geometries to maintain high-speed deflagration and detonation. With the aim to study a range of combustion regimes the experiments were performed varying degree of channel obstruction, hydrogen concentration and thickness of the layer. Depending on the experimental conditions all major combustion regimes were observed: slow flame, fast – 'choked' flame and steady-state detonation. It was found that minimum layer thickness in the range of 8 to 15 detonation cell widths is required for sustainable detonations.

Journal of Loss Prevention in the Process Industries, 2013

ABSTRACT This paper presents results of an experimental investigation on fast flame propagation a... more ABSTRACT This paper presents results of an experimental investigation on fast flame propagation and the deflagration-to-detonation transition (DDT) and following detonation propagation in a semi-confined flat layer filled with stratified hydrogeneair mixtures. The experiments were performed in a trans-parent, rectangular channel open from below. The combustion channel has a width of 0.3 m and a length of 2.5 m. The effective layer thickness in the channel was varied by using different linear hydrogen concentration gradients. The method to create quasi-linear hydrogen concentration gradients that differ in the range and slope is also presented. The ignited mixtures were accelerated quickly to sonic flame speed in the first obstructed part of the channel. The interaction of the fast flame propagation with different obstacle set-ups was studied in the second part of the channel. The experimental results show an initiation of DDT by one additional metal grid in the obstructed semi-confined flat layer. Detonation propagation and failed detonation propagation were observed in obstructed and unobstructed parts of the channel.