Laminar flame velocity determination for H2_2-air-steam mixtures using the spherical bomb method

The present work reports experimental results on the determination of laminar flame velocities of hydrogen– air - diluent mixtures initially at 100 kPa and for 2 different initial temperatures 298 and 353 K. The diluent was water vapor or a mixture containing helium and carbon dioxide. The data obtained in this study are compared with the literature ones. The experimental setup consists of a spherical bomb coupled to a schlieren system and a high speed camera. The effect of the stretch on the flame velocity is characterized for all the investigated mixtures. Computed laminar flame velocities are obtained using PREMIX and CHEMKIN codes. Two different kinetic mechanisms are used, and the computed values are compared to the experimental ones

Expanding the boundaries of the explosion risk assessment for H2_2/O2_2/N2_2 mixtures in conditions relevant to radioactive materials transportation

International audienceThe aim of the paper is to present the major results of a three years study which goal was to assess therisk of explosion due to hydrogen accumulation in closed containments used for the transportation ofradioactive materials. To do so, an experimental work on the flammability domain of multiple ternaryH$_2$/O$_2$/N$_2$ mixtures has been conducted at the CNRS-ICARE laboratory in collaboration with the CEA.The flammability limits of H$_2$/O$_2$/N$_2$ mixtures were assessed using two spherical bombs equipped with acentral ignition system consisting of two tungsten electrodes linked to a controlled high voltage dischargedevice. The combustion is monitored using two different diagnostics: pressure measurements during thecombustion test and the recording of the flame with a high-speed camera. A mixture is considered asflammable when both the imaging and the pressure indicate a successful ignition followed by a flamepropagation.The first part of the study has been focused on the precise determination of lower flammability limits ofH$_2$/O$_2$/N$_2$ mixtures at a wide range of pressure (from 0.3 bar up to 4 bar) and for different initialtemperatures ranging between 25°C and 100°C. The limit of the total inerting of a H$_2$/O$_2$ mixture by N$_2$has also been determined. In addition, the lower flammability limits of H$_2$/Air/H$_2$O$_{vapor}$ mixtures has alsobeen studied from 0.3 bar to 2 bar and from 25°C up to 200°C.The study has then been extended to the flammable domain close to the lower flammability limit and upto hydrogen concentration of 13%. The visualization of the flame coupled with the pressure monitoringhas allowed the observation and characterization of three sub-domains, each one with very specificbehaviour in terms of combustion parameters (maximum overpressure, explosion index).The first sub-domain close to the lower flammability limit allows the introduction of a new limit for thestudy of hydrogen risk in nuclear transport safety studies: the explosion severity low limit. Indeed, in thisdomain beginning after the low flammability limit, the overpressure stays very limited and opens a newway of considering safety studies related to hydrogen risk of explosion

Experimental study of laminar and turbulent flame speed of a spherical flame in a fan-stirred closed vessel for hydrogen safety application

International audienceThe aim of this paper is to report new experimental results on the effect of turbulence on the propagation speed of hydrogen/air flames. To do so, a new experimental setup, called the spherical bomb, has been designed and built at CNRS-ICARE laboratory. With this new setup, the effect of a given and well-characterized turbulence intensity on the increase of hydrogen/air flame speed can be investigated. This new facility consists of a spherical vessel equipped (563 mm internal diameter) equipped with 8 motors which are linked to fans inside the bomb. Fan actuation induces the generation of a turbulent flow inside the vessel prior to any ignition. The spherical bomb is equipped with 4 quartz windows (200 mm optical diameter) that allow the use of a Particle Image Velocimetry diagnostic in order to characterize the turbulence level inside the bomb. The flame propagation was recorded using a high speed camera at 19,002 frames per second. These experiments were performed for lean to stoichiometric hydrogen/air mixtures (16–20% of H2 in air), initially at ambient temperature and pressure, and for a rotation speed from 1000 to 5000 rpm. The PIV measurements showed that a homogeneous and isotropic turbulence is created with a fluctuation speed that can reach 4 m/s at 5000 rpm. © 2016 Elsevier B.V

Fundamental combustion properties of oxygen enriched hydrogen/air mixtures relevant to safety analysis: Experimental and simulation study

In order to face the coming shortage of fossil energies, a number of alternative methods of energy production are being considered. One promising approach consists in using hydrogen in replacement of the conventional fossil fuels or as an additive to these fuels. In addition to conventional hydro-electric and fission-based nuclear plants, electric energy could be obtained in the future using nuclear fusion as investigated within the framework of the ITER project, International Thermonuclear Experimental Reactor. However, the operation of ITER may rise safety problems including the formation of a flammable dust/hydrogen/air atmosphere. A first step towards the accurate assessment of accidental explosion in ITER consists in better characterizing the risk of explosion in gaseous hydrogen-containing mixtures. In the present study, laminar burning speeds, ignition delay-times behind reflected shock wave, and detonation cell sizes were measured over wide ranges of composition and equivalence ratios. The performances of five detailed reaction models were evaluated with respect to the present data