Publications

In this work we evaluate the consequences of the combustion of a stoichiometric mixture of hydrogen-air on a mechanical device which can be considered as a long tube. In order to choose the most dangerous combustion regime for the mechanical device we devote a particular attention to the investigation of the 1D deflagration-to-detonation transition. Then once established the most dangerous combustion regime we compute the reacting  flow and the stress and strain in the mechanical device. Analyses are performed using both semi-analytical solutions and Europlexus a computer program for the simulation of  fluid-structure systems under transient dynamic loading.

As a part of the experimental work of the EC-funded project HYPER Pro-Science GmbH performed experiments to evaluate the hazard potential of a severe hydrogen leakage inside a fuel cell cabinet. During this study hydrogen distribution and combustion experiments were performed using a generic enclosure model with the dimensions of the fuel cell "Penta H2" provided by ARCOTRONICS (now EXERGY Fuel Cells) to the project partner UNIPI for their experiments on small foreseeable leaks. Hydrogen amounts of 1.5 to 15 g H2 were released within one second into the enclosure through a nozzle with an internal diameter of 8 mm. In the distribution experiments the effects of different venting characteristics and different amounts of internal enclosure obstruction on the hydrogen concentrations measured at fixed positions in- and outside the model were investigated. Based on the results of these experiments combustion experiments with ignition positions in- and outside the enclosure and two different ignition times were performed. BOS (Background-Oriented-Schlieren) observation combined with pressure and light emission measurements were performed to describe the characteristics and the hazard potential of the induced hydrogen combustions. The experiments provide new experimental data on the distribution and combustion behaviour of hydrogen that is released into a partly vented and partly obstructed enclosure with different venting characteristics.

Distributed hydrogen optical fiber sensor with Brillouin scattering is an innovative solution to measure hydrogen in harsh environment as nuclear industry. Glass composition is the key point to enhance the sensing parameter of the fiber in the target application. Several optical fiber with different doping element were used for measuring hydrogen saturation. Permeability of optical plays a major role to the kinetic of hydrogen diffusion. Fluorine doped fiber increase the sorption and the desorption of hydrogen.

The use of hydrogen as an energy carrier is going to widen exponentially in the next years. In order to ensure the public acceptance of the new fuel not only the environmental impact has to be excellent but also the risk management of its handling and storage must be improved. As a part of modern risk assessment procedure CFD modeling of the accident scenario development must provide reliable data on the possible pressure loads resulted from explosion processes. The expected combustion regimes can be ranged from slow flames to deflagration-to-detonation transition and even to detonation. In the last case the importance of the reliability of simulation results is particularly high since detonation is usually considered as a worst case state of affairs. A set of large-scale detonation experiments performed in Kurchatov Institute at RUT facility was selected as benchmark. RUT has typical industry-relevant characteristic dimensions. The CFD codes possibilities to correctly describe detonation in mixtures with different initial and boundary conditions were surveyed. For the modeling two detonation tests HYD05 and HYD09 were chosen; both tests were carried out in uniform hydrogen/air mixtures; first one with concentration of 20.0% vol. and the second one with 25.5% vol. In the present exercise three CFD codes using a number of different models were used to simulate these experiments. A thorough inter-comparison between the CFD results including codes models and obtained pressure predictions was carried out and reported. The results of this inter comparison should provide a solid basis for the further code development and detonation models’ validation thus improving CFD predictive capabilities.

The production of hydrogen from renewable sources is essential to develop the future hydrogen economy. Biomass is an abundant clean and renewable energy source and it can be important in the production of hydrogen. The Valencian Community due to its great agricultural and forestry activities generates an important quantity of biomass residues that can be used for energy generation approximately 778 kt of wet biomass residues per year. This great quantity of biomass can be transformed into a hydrogen-rich gas by different thermochemical conversion processes. In this article the potential of production of hydrogen-rich gas is analyzed considering several factors affecting the conversion yield of these processes. As a result of this analysis it could be possible to produce 1271 MNm3 of H₂ per year considering the total biomass residues of the community and selecting the gasification processes.

Several approaches have been used in the past to model the source of a high pressure under-expanded jet such as the computationally expensive resolution of the jet shock structure and the simpler pseudo-source or notional nozzle approaches. In each approach assumptions are made introducing inaccuracies in the CFD calculations. This work assesses the effect of different source modelling approaches on the accuracy of CFD calculations by comparing simulation results to experimental data of the axial distribution of the flow velocity and H2 concentration.

Experiments were conducted to assess detectability of a low-level leak of hydrogen gas and the uniformity of hydrogen concentration at selected sensor placement locations in a realistic setting. A 5%2hydrogen/95%2nitrogen gas mixture was injected at a rate of 350 L/min for about 3/4 hour into a 93m3 residential garage space through a 0.09 m2 square open-top dispersion box located on the floor. Calibrated catalytic sensors were placed on ceiling and wall locations and the sensors detected hydrogen early in the release and continued to measure concentrations to peak and diminishing levels. Experiments were conducted with and without a car parked over the dispersion box. The results show that a car positioned over the dispersion box tends to promote dilution of the hydrogen cause a longer time for locations to reach a fixed threshold and produce lower peak concentrations than with no car present.

Hydrogen impinging jets can be formed in the case of an accidental release indoors or outdoors. The CFD simulation of hydrogen impinging jets suffers from numerical errors resulting in a non-physical velocity and hydrogen concentration field with a butterfly like structure. In order to minimize the numerical errors and to avoid the butterfly effect high order schemes need to be used. The aim of this work is to give best practices guidelines for hydrogen impinging jet simulations. A number of different numerical schemes is evaluated. The number of cells which discretize the source is also examined.

A series of experiments on hydrogen flame propagation in a thin layer geometry is presented. Premixed hydrogen-air compositions in the range from 6 to 15%(vol.) H2 are tested. Semi-open vertical combustion chamber consists of two transparent Plexiglas side walls with main dimensions of 90x20 cm with a gap from 1 to 10 mm in between. Test mixtures are ignited at the open end of the chamber so that the flame propagates towards the closed end. Ignition position changes from top to bottom in order to take into account an effect of gravity on flame propagation regimes. High-speed shadow imaging is used to visualize and record the combustion process. Thermal-diffusion and Darrieus-Landau instabilities are governing the general flame behaviour. Heat losses to side walls and viscous friction in a thin layer may fully suppress the flame propagation with local or global extinction. The sensitivity to heat losses can be characterized using a Peclet number as a ratio of layer thickness to laminar flame thickness. Approaching to critical Peclet number Pec = 42 the planar or wrinkled flame surface degradants to one-or two-heads "finger" flame propagating straight (for two-heads flame) or chaotic (for one-head "finger" flame). Such a "fingering" of the flame is found for the first time for gaseous systems and very similar to that reported for smouldering or filtering combustion of solid materials and also under micro-gravity conditions. The distance between "fingers" may depend on deficit of limiting component. The processes investigated can be very important from academic and practical points of view with respect to safety of hydrogen fuel cells.

Composite cylinders with metal liner are used for the storage of compressed hydrogen in automotive application. These hybrid pressure cylinders are designed for a nominal working pressure of up to 70 MPa. They also have to withstand a temperature range between -40°C and +85°C according GRPE draft [1] and for short periods up to a maximum temperature of 140°C during filling (fast filling) [2]. In order to exploit the material properties efficiently with a high degree of lightweight optimization and a high level of safety on the same time a better understanding of the structural behavior of hybrid designs is necessary. Work on this topic has been carried out in the frame of a work package on safety aspects and regulation (Subproject SAR) of the European IP StorHy (www.storhy.net). The temperature influence on the composite layers is distinctive due to there typical polymer material behavior. The stiffness of the composite layer is a function of temperature which influences global strains and stress levels (residual stresses) in operation. In order to do an accurate fatigue assessment of composite hybrid cylinders a realistic modeling of a representative temperature load is needed. For this climate data has been evaluated which were collected in Europe over a period of 30 years [3]. Assuming that the temperature follows a Gaussian (normal) distribution within the assessed period of 30 years it is possible to generate a frequency distribution for different temperature classes for the cold extreme and the hot extreme. Combining these distributions leads to the overall temperature range distribution (frequency over temperature classes). The climatic temperature influence the filling temperature and the pressure load have to be considered in combination with the operation profile of the storage cylinder to derive a complete load vector for an accurate assessment of the lifetime and safety level.