Y. Bultel

Grenoble Institute of Technology, Grenoble, Rhône-Alpes, France

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Publications (50)45.47 Total impact

  • D. Riu, M. Montaru, Y. Bultel
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    ABSTRACT: For electric vehicle (EV) or hybrid EV (HEV) development and integration of renewables in electrical networks, battery monitoring systems have to be more and more precise to take into account the state-of-charge and the dynamic behavior of the battery. Some non-integer order models of electrochemical batteries have been proposed in literacy with a good accuracy and a low number of parameters in the frequential domain. Nevertheless, time simulation of such models required to approximate this non-integer order system by an equivalent high integer order model. An adapted algorithm is then proposed in this article to simulate the non-integer order model without any approximation, thanks to the construction of a 3-order generalized state-space system. This algorithm is applied and validated on a 2.3 A.h Li-ion battery.
    Communications in Nonlinear Science and Numerical Simulation 06/2013; 18(6):1454–1462. · 2.77 Impact Factor
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    ABSTRACT: This paper evaluates electrochemical noise (EN) technique as a possible tool for the diagnosis of Proton Exchange Membrane Fuel Cells (PEMFC) during operation. EN was employed to survey PEM single cell under various operating conditions at different humidification levels so as to focus on flooding or drying tendencies. Data was investigated in the frequency domain by means of power spectrum densities that showed to be sensitive to changes in the PEMFC operating conditions. EN seems an interesting way for an innovative and non-invasive on-line diagnosis tool.
    Electrochemistry Communications - ELECTROCHEM COMMUN. 12/2011;
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    ABSTRACT: This article presents experiments conducted with two single rectangular mini-channels of same hydraulic diameter (1.4 mm) and different aspect ratios for conditions of horizontal boiling flow. The Forane® 365 HX used was subcooled (ΔTsub = 15 °C) for all the boiling curves presented in the paper. Local heat transfer coefficients were measured for heat flux ranging from 25 to 62 kW m−2 and mass flux from 200 kg m−2 s−1 to 400 kg m−2 s−1. The boiling flows were observed with two different cameras (depending on the flow velocity) through a visualization window. The flow patterns in the two channels were compared for similar conditions. The results show that the boiling heat transfer coefficient and the pressure drop values are different for the two single mini-channels. For low heat flux condition, the channel with lowest aspect ratio (H/W = 0.143) has a higher heat transfer coefficient. On the other hand, for high heat flux condition, the opposite situation occurs, namely the heat transfer coefficient becomes higher for the channel with highest aspect ratio (H/W = 0.43). This is probably due to the earlier onset of dryout in the channel with lowest aspect ratio. For the two cases of heating, the pressure drop for the two-phase flow remains lower for the channel with lowest aspect ratio. These results show that the aspect ratio plays a substantial role for boiling flows in rectangular channels. As for single-phase flows, the heat transfer characteristics are significantly influenced (even though the hydraulic diameter remains the same) by this parameter.
    Experimental Thermal and Fluid Science 01/2011; 35(5):797-809. · 1.60 Impact Factor
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    ABSTRACT: This paper deals with one of the needs for PEMFC to be economically reliable: diagnosis tool for water management. This issue is actually a key parameter for both performance and durability improvement. Acoustic emission (AE) technique was employed to survey PEM single cell under various operating conditions. AE events coming from different sources have thus been identified, classified and finally ascribed to different phenomena induced by MEA water uptake and/or biphasic flow in the gas channel thanks to a statistical post-treatment of the acoustic data. Results, although qualitative, seems trusty enough to unravel hidden correlations between AE hits and physicochemical phenomena taking place during the cell operation and open up the way for an innovative and non-invasive online diagnosis tool.
    Journal of Power Sources 01/2010; 195(24):8124-8133. · 4.68 Impact Factor
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    ABSTRACT: The diagnosis of flooding or drying is an important factor in improving the reliability and durability of PEMFCs. Indeed, flooding and drying lead to a reduction in the output voltage delivered by the fuel cell. Among the various diagnostic techniques, electrochemical impedance spectroscopy (EIS) is a powerful tool. In this study, EIS measurements were carried out on a 500W stack comprised of 16 elementary cells. Electrochemical impedance spectra were recorded either on each cell or on the stack. Use of an electrical equivalent circuit model revealed that flooding mainly affects the transfer resistance and the cathodic Warburg impedance. A diagnostic tool based on these two components is proposed. KeywordsPEMFC-EIS-Water management-Diagnosis
    Journal of Applied Electrochemistry 01/2010; 40(5):911-920. · 1.84 Impact Factor
  • J. M. Klein, S. Georges, Y. Bultel
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    ABSTRACT: In recent years, fuel cell technology has attracted considerable attention from several fields of scientific research as fuel cells produce electric energy with high efficiency, emit little noise, and are non-polluting. Solid oxide fuel cells (SOFCs) are particularly important for stationary applications due to their high operating temperature (1,073–1,273K). Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. Unfortunately, internal steam reforming in SOFC leads to inhomogeneous temperature distributions which can result in mechanical failure of the cermet anode. Moreover this concept requires a large amount of steam in the fed gas. To avoid these problems, gradual internal reforming (GIR) can be used. GIR is based on local coupling between steam reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained by the hydrogen oxidation. However, with GIR, Boudouard and cracking reactions can involve a risk of carbon formation. To cope with carbon formation a new cell configuration of SOFC electrolyte support was studied. This configuration combined a catalyst layer (0.1%Ir–CeO2) with a classical anode, allowing GIR without coking. In order to optimise the process a SOFC model has been developed, using the CFD-Ace+ software package, and including a thin electrolyte. The impact of a thin electrolyte on previous conclusions has been assessed. As predicted, electrochemical performances are higher and carbon formation is always avoided. However a sharp decrease in the electrochemical performances appears at high current densities due to steam clogging. KeywordsSOFC-Gradual internal reforming-Simulation-CFD-Ace+
    Journal of Applied Electrochemistry 01/2010; 40(5):943-954. · 1.84 Impact Factor
  • Conference Proceeding: Fuel cell-based hybrid systems
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    ABSTRACT: This paper presents different works which are actually developed in the field of fuel-cell hybrid systems in different public laboratories in France. These works are presented in three sections corresponding to: 1. hybrid fuel cell/battery or supercapacitor power sources; 2. fuel-cell multi-stack power sources; 3. fuel cell in hybrid power systems for distributed generation. The presented works combine simulation and experimental results.
    Advanced Electromechanical Motion Systems & Electric Drives Joint Symposium, 2009. ELECTROMOTION 2009. 8th International Symposium on; 08/2009
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    ABSTRACT: Composite electrodes for Solid Oxide Fuel Cells (SOFC) are generally obtained through partial sintering of a mixture of ionic and electronic conducting powders. Enhancing the electrochemical performances of SOFC electrodes requires the multiplication of so-called Triple Phase Boundary points (where the gas and the ionic and electronic conducting materials meet), some residual porosity, and the percolation of the two particle networks (ionic and electronic). Also, the poor intrinsic conductivity of ionic particles requires the reinforcement of the ionic network. Thus, the optimization of the electrode micro structure is a complex task and must take into account the particulate nature of the partially sintered material of the electrode. We propose to model the electrode material as a 3D packing of spheres, which sintering is simulated by the Discrete Element Method (DEM). This allows the generation of a realistic numerical microstructure for which the geometric features of each contact is known. Typically we generate electrodes with 40 000 spherical particles and residual porosity of 25%. For the determination of the electrochemical performance, the packing is sandwiched between a current collector and an electrolyte. The packing is then replaced by a network of electronic, ionic and electrochemical resistances, and the effective conductivity of the electrode is calculated. Our simulations allow the importance of percolation effects to be demonstrated. We also compute the effective conductivity of composition graded electrodes and compare them to non-graded composite electrodes. We show that only slightly graded electrodes can compete with non-graded composite electrodes. In any case, the simulations show that due to percolation problems, one should not expect large gains in terms of electrochemical performance when grading electrodes. Instead, we propose a new and more effective microstructural architecture for which the electronic network percolation is imposed.
    06/2009;
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    ABSTRACT: The diagnosis and modelling of flooding or drying is an important factor in improving the reliability and durability of PEMFCs. Indeed, flooding and drying lead to a reduction in the output voltage delivered by the fuel cell. Among the various techniques, electrochemical impedance spectroscopy (EIS) and Acoustic Emission (EA) are powerful tools. In this study, EIS and AE measurements were carried out respectively on a 500 W stack and on a 25 cm2 fuel cell. EIS measurements and its modelling by an electrical equivalent circuit model revealed that flooding mainly affects the transfer resistance and the cathodic Warburg impedance. AE measurements show that it is possible to follow the water content within the fuel cell. Coupling this two methods seem to be an interesting diagnosis tool.
    01/2009;
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    ABSTRACT: A solid oxide fuel cell was designed to be operated with pure hydrocarbons, without additive or carrier gas, in order to bring technological simplifications, cost reductions and to extend the fuel flexibility limits. The cell was built-up from a conventional cell (LSM/YSZ/Ni-YSZ), to which was added a Ir–CeO2 catalyst layer at the anode side and an original current collecting system. The cell was first operated with steam in gradual internal reforming (GIR) conditions (R=[H2O]/[CH4]
    Journal of Power Sources 01/2009; 193(1):331-337. · 4.68 Impact Factor
  • Electrochemical and Solid State Letters - ELECTROCHEM SOLID STATE LETT. 01/2009; 12(7).
  • J.-M. Klein, Y. Bultel, M. Pons, P. Ozil
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    ABSTRACT: One of the major obstacles to improving electrochemical performance of SOFCs is the limitation with respect to current collecting. The aim of this study is to examine these limitations on the basis of a model of a single cell of tubular SOFC. The simulation results allow us to understand and analyze the effects of ionic and electronic ohmic drops on cell performance. This paper describes a model using the CFD-Ace software package to simulate the behaviour of a tubular SOFC. Modelling is based on solving conservation equations of mass, momentum, energy, species and electric current by using a finite volume approach on 3D grids of arbitrary topology. The electrochemistry in the porous gas diffusion electrode is described using Butler-Volmer equations at the triple phase boundary. The electrode overpotential is computed at each spatial location within the catalyst layer by separately solving the electronic and ionic electric potential equations. The 3D presentation of the current densities and the electronic and ionic potentials allows analysis of the respective ohmic drops. The simulation results show that the principal limitations are at the cathodic side. The limitations due to ionic ohmic drops, classically considered to be the main restrictions, are confirmed. The particular interest of our study is that it also shows that, because of the cylindrical geometry, there is a significant electronic ohmic drop.
    Journal of Applied Electrochemistry 03/2008; 38(4):497-505. · 1.84 Impact Factor
  • Source
    P-X Thivel, Y Bultel, F Delpech
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    ABSTRACT: Thermal and chemical conversion processes that convert in energy the sewage sludge, pasty waste and other pre-processed waste are increasingly common, for economic and ecological reasons. Fluidized bed combustion is currently one of the most promising methods of energy conversion, since it burns biomass very efficiently, and produces only very small quantities of sulphur and nitrogen oxides. The hazards associated with biomass combustion processes are fire, explosion and poisoning from the combustion gases (CO, etc.). The risk analysis presented in this paper uses the MADS-MOSAR methodology, applied to a semi-industrial pilot scheme comprising a fluidization column, a conventional cyclone, two natural gas burners and a continuous supply of biomass. The methodology uses a generic approach, with an initial macroscopic stage where hazard sources are identified, scenarios for undesired events are recognized and ranked using a grid of SeverityxProbability and safety barriers suggested. A microscopic stage then analyzes in detail the major risks identified during the first stage. This analysis may use various different tools, such as HAZOP, FMEA, etc.: our analysis is based on FMEA. Using MOSAR, we were able to identify five subsystems: the reactor (fluidized bed and centrifuge), the fuel and biomass supply lines, the operator and the environment. When we drew up scenarios based on these subsystems, we found that malfunction of the gas supply burners was a common trigger in many scenarios. Our subsequent microscopic analysis, therefore, focused on the burners, looking at the ways they failed, and at the effects and criticality of those failures (FMEA). We were, thus, able to identify a number of critical factors such as the incoming gas lines and the ignition electrode.
    Journal of Hazardous Materials 03/2008; 151(1):221-31. · 3.93 Impact Factor
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    ABSTRACT: The aim of this work is to optimize an interconnect design. A three-dimensional model have been developed in order to investigate the effect of interconnect design on electrical performance and degradation process. Oxygen concentration, potential, current density and temperature distribution in interconnect and SOFC cathode have been calculated. Cathode degradation has been supposed to be due to temperature gradient non-uniformity. Our studies have demonstrated the impact of cathode/interconnect contact on thermal and electrical behavior. Thus, an optimization of the cathode/interconnect contact using COMSOL Multiphysics® software has been investigated. In this investigation, the effects of the two geometrical parameters are considered. This paper presents the modification of cathode/interconnect contact area and electrical collecting pins size. Simulations show a decreasing power density and a reduction of temperature gradient for an increasing contact area. With a decreasing size of collecting pins, better temperature homogeneity and power density are recorded.
    01/2008;
  • J.-M. Klein, S. Georges, Y. Bultel
    Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2008; 155(4).
  • Electrochemical and Solid State Letters - ELECTROCHEM SOLID STATE LETT. 01/2008; 11(8).
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    ABSTRACT: One approach to improve the performances of a solid oxide fuel cell (SOFC) cathodes is to use a composite electrode that typically consists of a two-phase porous mixture of a solid electrolyte (yttria-stabilized zirconia) and an electrocatalytic material. The best electrochemical performances with such a type of cathode are obtained when the composition varies within the composite cathode called graded electrode. The present modeling has been performed in order to give a complete description of the electrode microstructure, as well as the process occurring therein. A one-dimensional, homogeneous model and a discrete element method was used. The present study proposes a one-dimensional dc and ac model that takes into account mass and charge conservation, transport of species, and reaction kinetics. The influence of transport parameters and microstructure on the shape of both polarization curves and impedance diagrams is discussed.
    Journal of The Electrochemical Society. 09/2007; 154(10):B1012-B1016.
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    ABSTRACT: A solid oxide fuel cell (SOFC) composite electrode exhibits a superior performance compared to a single phase electrode since the electrochemically active zone is spread into its volume. A functionally graded composite electrode consisting of monosized spherical electrocatalyst and electrolyte particles is sintered numerically by the discrete element method (DEM). The electrochemical performance is evaluated by a resistance network approach using Kirchhoff's current law. In the network discretization each contact between two particles is substituted by a bond resistance defined by contact size and the type of materials in contact.The graded electrode is optimized by varying its composition at the electrolyte/electrode interface and the degree to which the composition decreases linearly towards the current collector/electrode interface. Regarding its electrochemical activity, the graded electrode does not perform significantly better than an optimized uniformly randomly mixed composite electrode but percolation of the graded electrode is improved. In order to demonstrate the importance of percolation effects, a novel better performing electrode is developed which contains electronically conducting particle chains arranged within a random packing of ionically conducting particles.
    Electrochimica Acta - ELECTROCHIM ACTA. 01/2007; 52(9):3190-3198.
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    ABSTRACT: A solid oxide fuel cell ($backslash$textscSOFC) composite electrode exhibits a superiorperformance compared to a single phase electrode since the electrochemicallyactive zone is spread into its volume. A functionally graded compositeelectrode consisting of monosized spherical electrocatalyst and electrolyteparticles is sintered numerically by the discrete element method (DEM).The electrochemical performance is evaluated by a resistance network approachusing Kirchhoff's current law. In the network discretization each contactbetween two particles is substituted by a bond resistance defined by contactsize and the type of materials in contact. The graded electrode is optimizedby varying its composition at the electrolyte/electrode interface and thedegree to which the composition decreases linearly towards the currentcollector/electrode interface. Regarding its electrochemical activity,the graded electrode does not perform significantly better than an optimizeduniformly randomly mixed composite electrode but percolation of the gradedelectrode is improved. In order to demonstrate the importance of percolationeffects, a novel better performing electrode is developed which containselectronically conducting particle chains arranged within a random packingof ionically conducting particles.
    Electrochim. Acta. 01/2007; 52:3190-3198.
  • Source
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    ABSTRACT: The dynamic behavior of a five cells proton exchange membrane fuel cell (PEMFC) stack operating in dead-end mode has been studied at room temperature, both experimentally and by simulation. Its performances in “fresh” and “aged” state have been compared. The cells exhibited two different response times: the first one at about 40 ms, corresponding to the time needed to charge the double-layer capacitance, and the second one at about 15–20 s. The first time response was not affected by the ageing process, despite the decrease of the performances, while the second one was. Our simulations indicated that a high amount of liquid water was present in the stack, even in “fresh” state. This liquid water is at the origin of the performances decrease with ageing, due to its effect on decreasing the actual GDL porosity that in turn cause the starving of the active layer with oxygen. As a consequence, it appears that water management issue in a fuel cell operating in dead-end mode at room temperature mainly consists in avoiding pore flooding instead of providing enough water to maintain membrane conductivity.
    Journal of Power Sources. 01/2007;

Publication Stats

303 Citations
45.47 Total Impact Points

Institutions

  • 2006–2007
    • Grenoble Institute of Technology
      Grenoble, Rhône-Alpes, France
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France
  • 2005
    • KTH Royal Institute of Technology
      • Division of Applied Electrochemistry
      Stockholm, Stockholm, Sweden