Experimental and numerical investigation of hydrogen-air and hydrogen-oxygen detonation parameters was performed. A new detonation model was introduced and validated against the experimental data. Experimental set-up consisted of 9 m long tube with 0.17 m in diameter, where pressure was measured with piezoelectric transducers located along the channel. Numerical simulations were performed within OpenFoam code based on progress variable equation where the detonative source term accounts for autoignition effects. Autoignition delay times were computed at a simulation run-time with the use of a multivariate regression model, where independent variables were: pressure, temperature and fuel concentration. The dependent variable was the autoignition delay time. Range of the analyzed gaseous mixturecomposition varied between 20% and 50% of hydrogen-air and 50%–66% of hydrogen in oxygen. Simulations were performed using LES one-equation eddy viscosity turbulencemodel in 2D and 3D. Calculations were validated against experimental data

A study with PIV-measurements for gas explosion in hydrogen-air mixtures is presented in this paper. The present work is part of an ongoing research project. The experiments are performed with hydrogen-air mixture at atmospheric pressure and room temperature. The experimental rig is a square channel with 4.5 X 2.0 cm2 cross section, 30 cm long with a single cylindrical obstacle of blockage ratio 1/3. The equipment used for the PIV-measurements was a Firefly diode laser from Oxford lasers, Photron SA-Z high speed camera and a particle seeder producing 1 µm droplets of water. The gas concentrations used in the experiments was between 14 and 17% hydrogen in air. The resulting explosion can be characterized as slow. Explosions in the gas mixtures at the highest hydrogen concentration produced measured flow velocities of up to 17 m/s as the flame passed the obstacle. Similar velocities was also measured one channel height behind the obstacle. The flow vortices produced behind the obstacle seemed to give separation between the liquid droplets and gas flow. The experimental results can be used for reference in validation of CFD-codes.

Hydrogen gas explosions in homogeneous reactive mixtures have been widely studied both experimentally and numerically. However, in practice, combustible mixtures are usually inhomogeneous and subject to both vertical and horizontal concentration gradients. There is still very limited understanding of the hydrogen explosion characteristics in such situations. The present numerical investigation aims to study the effect of mixture concentration gradient on the process of Deflagration to Detonation Transition, and the effect of different hydrogen concentration gradient in the obstructed channel of hydrogen/air mixtures. An obstructed channel with 30% blockage ratio (BR=30), and three different average hydrogen concentrations of 20 %, 30% and 35% have been considered using a specially developed density-based solver within the OpenFOAM toolbox. A highresolution grid was built with the using adaptive mesh refinement technique providing 10 grid points in half reaction length. The numerical results are in reasonably good agreement with the experimental observations [1]. These studies show that the concentration gradient has a considerable effect on the accelerated flame tip speed and the location of transition to detonation in the obstructed channel. In all the three cases the first localised explosion occurred near the bottom wall where the shock and flame interacted, and the mixture was most lean; and the second localised explosion occurred at the top wall due to the reflection of shock and flame front and later develops to form the leading detonation wave. The increase in the fuel concentration was found to increase the flame acceleration (FA) and having a faster transition to detonation.

Experiments in an obstructed semi-confined vertical combustion channel with a height of 6 m (cross-section 0.4 × 0.4 m) inside a safety vessel of the hydrogen test center HYKA at the Karlsruhe Institute of Technology (KIT) are reported. In the work, homogeneous hydrogen-air-mixtures as well as mixtures with different well-defined H2-concentration gradients were ignited either at the top or at the bottom end of the channel. The combustion characteristics were recorded using pressure sensors and sensors for the detection of the flame front that were distributed along the complete channel length. In the tests slow subsonic and fast sonic deflagrations as well as detonations were observed and the conditions for the flame acceleration (FA) to speed of sound and deflagration-to-detonation transition (DDT) are compared with the results of similar experiments performed earlier in a larger semi-confined horizontal channel.

Delayed explosions of accidental high pressure hydrogen releases are an important risk scenario for safety studies of production plants, transportation pipelines and fuel cell vehicles charging stations. As a consequence, the assessment of the associated consequences requires accurate and validated prediction based on modeling and experimental approaches. In the frame of the French working group dedicated to the evaluation of computational fluid dynamics (CFD) codes for the modeling of explosion phenomena, this study is dedicated to delayed explosions of high pressure releases. Two participants using two different codes have evaluated the capacity of CFD codes to reproduce explosions of high pressure hydrogen releases. In the first step the jet dispersion is modeled and simulation results are compared with experimental data in terms of axial and radial concentration dilution, velocity decay, and turbulent characteristics of jets. In the second step a delayed explosion is modeled and compared to experimental data in terms of overpressure at different monitor points. Based on this investigation several recommendations for CFD modeling of high pressure jets explosions are suggested.

Delayed explosions of accidental high pressure hydrogen releases are an important risk scenario in safety studies of production plants, transportation pipelines and fuel cell vehicles charging stations. Such explosions were widely explored in multiple experimental and numerical investigations. Explosion of high pressure releases in highly obstructed geometries with high blockage ratio is a much more complicated phenomenon. This paper is dedicated to the experimental investigation of the influence of obstacles on a delayed deflagration of hydrogen jets. The computational fluid dynamics (CFD) code FLACS is used to reproduce experimental data. In the current study the computed overpressure signals are compared to the experimentally measured ones at different monitoring points. Simulations are in close agreement with experimental results and can be used to predict overpressure where experimental pressure detectors were saturated. For homogenous stationary clouds a new approach of equivalent mixture of H2/air (~16.5%) to stoichiometric mixture of CH4/air is suggested. This approach is validated versus experimental data from the literature in terms of overpressure maxima. A parametric study is performed using FLACS for various concentrations in the same geometry in order to identify a possible transition from deflagration to detonation.

The numerical simulations on the high-pressure hydrogen jet are performed by using the unsteady threedimensional compressible Navier-Stokes equations with multi-species conservation equations. The present numerical results show that the highly expanded hydrogen free jet observes and the distance between the Mach disc and the nozzle exit agrees well with the empirical equation. The time-averaged H2 concentration of the numerical simulations agrees well with the experimental data and the empirical equation. The numerical simulation of ignition in a hydrogen jet is performed to show the flame behaviour from the calculated OH isosurface. We predicted the ignition and no-ignition region from the present numerical results about the forced ignition in the high-pressurized hydrogen jet.

The formation of hydrogen jets from pressurized sources and its ignition when hitting hot devices has been studied by many projects. The transient jets evolve with high turbulence depending on the configuration of the nozzle and especially the pressure in the hydrogen reservoir. In addition the length of the jets and the flames generated by ignition at a hot surface varies. Parameters to be varied were initial pressure of the source (2.5, 10, 20 and 40 MPa), distance between the nozzle and the hot surface (3, 5 and 7 m) and temperature of the hot surface (between 400 and 1000 K). The interaction of the hydrogen jets is visualized by high-speed cinematography techniques which allow analysing the jet characteristics. By combination of various methods of image processing, the visibility of the phenomena on the videos taken at 15 000 fps was improved. In addition, high-speed NIR spectroscopy was used to obtain temperature profiles of the expanding deflagrations. The jets ignite already above 450 K for conditions mainly from the tubular source at 40 MPa. In addition, the propagation of the flame front depends on all three varied parameters: temperature of the hot surface, pressure in the reservoir and distance between nozzle and hot surface. In most cases also upstream propagation occurs. A high turbulence seems to lead to the strong deflagrations. At high temperatures of the ignition sources, the interaction leads to fast deflagration and speeds up- and downstream of the jet. The deflagration velocity is close to velocity of sound and emission of pressure waves occurs.

Integral type models to describe stationary plumes and jets in cross-flows (wind) have been developed since about 1970. These models are widely used for risk analysis, to describe the consequences of many different scenarios. Alternatively, CFD codes are being applied, but computational requirements still limit the number of scenarios that can be dealt with using CFD only. The integral models, however, are not suited to handle transient releases, such as releases from pressurized equipment, where the initially high release rate decreases rapidly with time. Further, on gas ignition, a second model is needed to describe the rapid combustion of the flammable part of the plume (flash fire) and a third model has to be applied for the remaining jet fire. The objective of this paper is to describe the first steps of the development of an integral-type model describing the transient development and decay of a jet of flammable gas after a release from a pressure container. The intention is to transfer the stationary models to a fully transient model, capable to predict the maximum extension of short-duration, high pressure jets. The model development is supported by conducting a set of transient ignited and unignited spontaneous releases at initial pressures between 25bar and 400bar. These data forms the basis for the presented model development approach.

Development of modern safety standards for hydrogen infrastructure requires fundamental insight into the physics of buoyant gas dispersion into ambient air, from realistic flow geometries. In the present study, inert compressible air and helium releases from a round opening in a curved pipe were considered, experimentally. Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) techniques were employed simultaneously to provide instantaneous and timeaveraged patterns of flow velocity and gas concentrations. A range of gas densities and Reynolds numbers were considered in order to quantify their effects on the resulting flow structure. Significant differences were found between the spreading rate of round jets and those considered here. The findings indicate that use of conventional round jet assumptions are inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of the gas leak.