Full Heusler alloys of the series Fe2-xNixVAl, 0 <= x <= 0.2, were prepared and characterized, and their physical properties, relevant to the thermoelectric performance of such materials, were studied in a wide temperature range. The starting material Fe2VAl is characterized by a pseudogap of the electronic density of states near the Fermi energy, with a gap width of the order of 1 eV. Density functional theory calculations were performed by application of two approaches. In the framework of the local-spin-density approximation and coherent potential approximation, the electronic densities of states of substitutional alloys were calculated, revealing that with increasing Ni content the Fermi energy moves toward the conduction band, and consequently, the nature of electronic transport changes from p type to n type. It appears that Ni, due to its extra electrons, provides a narrow impurity band near the Fermi level. These states can be made responsible for the experimentally observed evolution of transport properties. Furthermore, the Vienna ab initio Simulation package (VASP) was utilized for deriving electronic, structural, and vibrational properties of ordered Fe2VAl and Fe1.75Ni0.25VAl. In particular, it is found that due to Ni substitution there is a general shift to lower phonon frequencies by about 2 THz as compared to the undoped case. Associated to these modifications, the electrical resistivity, rho(T), changes from a semiconducting-like behavior to a nonsimple metallic behavior, while the Seebeck coefficient reaches values of the order of -80 mu V/K around room temperature for the sample x = 0.2. The increase of the Ni content, in addition, goes along with a substantial reduction of the lattice part of the thermal conductivity. This change is analyzed in detail in terms of a disorder parameter Gamma, characterizing the derangement of the crystalline lattice due to the substitution of Fe by Ni. Ab initio calculations of the phonon dynamics carried out for Fe2VAl and for Fe1.75Ni0.25VAl support these analyses.

This work presents the development of a 1D model describing water and charge transport through the polymer electrolyte membrane (PEM) in the fuel cell. The considered driving forces are electrical potential, concentration and pressure gradients. The membrane properties such as water diffusion and electro-osmotic coefficients, water sorption and ionic conductivity are treated as temperature dependent functions. The dependencies of diffusion and electro-osmotic coefficients on the membrane water concentration are described by linear functions. The membrane conductivity is computed in the framework of the percolation theory under consideration that the conducting phase in the PEM is formed by a hydrated functional groups and absorbed water. This developed membrane model was implemented in the CFD code AVL FIRE using 1D/3D coupling. The simulated polarization curves at various humidification of the cathode are found in good agreement with the experiments thus confirming the validity of the model.

The EU-sponsored project METSOFC, completed at the end of 2011, resulted in a number of advancements toward implementing a mechanically robust metal support as the structural element in SOFC. Technical University of Denmark (DTU) Energy Conversion's research into planar metal supported cells (MSCs) has produced an advanced cell design with high performance and mechanical robustness. At low operation temperatures (650 degrees C), these cells have shown low Area-specific resistances (ASRs): 0.35cm(2) in cell tests (16cm(2) active area) and under 0.3cm(2) in button cells (0.5cm(2) active area). Further success was attained with even larger cell areas of 12x12cm(2) squares, which facilitated integration into small stacks at Topsoe Fuel Cell having powers approaching 1/2kW. Development of MSC stacks showed that the MSCs could achieve similar or better performance, compared to most standard industrial anode supported ceramic cells. The best stacked MSCs had power densities approaching 275mWcm(-2) (at 680 degrees C and 0.8V). Furthermore, extended testing at AVL determined extra stack performance and reliability characteristics, including behavior toward sulfur and simulated diesel reformate, and tolerance to thermal cycles and load cycles. These and other key outcomes of the METSOFC consortium are covered, along with associated work supported by the Danish National Advanced Technology Foundation.

Damage modeling can be used as a highly useful and cost effective tool to support the product development process. Models, referring to physics and chemistry of damage, generate a robust basis for reliability and lifetime assessment. They deliver reliable relationships between load and damage kinetics, which is used to evaluate damage kinetics under various operation conditions and boundaries. Simplified damage models, based on the relationship between operation conditions and damage kinetics can be used already during early phases of product development, when component load data measurements are not yet available. Thus, relevant input for decision making can be generated already within the concept phase. Throughout the development process accuracy rises step-by-step with the quality of available probes and data. This analysis method is in particular useful for decision making in situations with a limited amount of information. This paper describes the physics of failure approach to support SOFC development ranging from concept to validation. It describes the approach and lines out some typical failure modes. Further it describes typical applications to support component layout, test design, validation planning and failure assessment.

The power output of a thermoelectric generator (TEG) was investigated under engine partial-load operation based on measured exhaust gas temperatures and mass flow rates. Materials with properties required for highend temperature TE couples (>500°C) were evaluated. Various possible material combinations for p- and n-legs of these couples as well as the conflicting targets of high efficiency and low cost as required for automotive mass production are discussed. New skutterudite materials for both p- and n-legs as identified during a joint research project are presented, which can help to overcome this conflict. Efficiencies >10% were achieved with these new materials, which have potentially twofold lower production costs than telluride-based materials due to the price of their elements. Some potential for improvement in efficiency and costs has been identified by developing highly integrated TEG units, specifically designed for automotive applications. These initial results of the material development and the evaluation of different integration concepts will be applied in a subsequent step for the fabrication of a pilot number of TEG modules/units.

In comparison to state of the art fuel cell stack monitoring techniques, where for reliability and durability reasons either single cell or cell-block voltages are monitored separately, the new approach derives information about critical cell and stack status from the stack sum voltage only. The motivation for the development of such a technology is to establish a strongly simplified and low cost stack diagnosis unit. In comparison to the cell voltage monitoring (CVM) technology, where up to several hundreds voltage channels have to be measured separately or at least in pairs, the effort for wiring, contacting and instrumentation can be reduced dramatically.Critical cell operation occurs, if e.g. low air stoichiometry causes a sharp drop of voltage at a certain cell current. If in such case the current is superimposed by a small amplitude signal with specific frequency pattern, then the system response (i.e. stack voltage) will be distorted in the frequency domain. Particularly, this means that even if only one single cell is in a critical operation mode, it would cause distorted frequency fractions extractable from the entire stack voltage. Since this approach is related to the distortion of the frequency pattern only, noise and EMC issues are not significantly influencing the measuring quality. The instrumentation and processing effort is rather low and can be realized with a low cost DSP board.Measurement results for different critical stack operation modes, e.g. operation at low air or low hydrogen stoichiometry, with their correlation to the frequency distortion will be described and discussed. (c) 2006 Elsevier B.V. All rights reserved.

Direct methanol fuel cells (DMFCs) are capable of utilising a liquid fuel directly in the fuel cell and they are therefore an interesting option for a variety of mobile and portable applications. Still there are several barriers which have to be overcome before DMFCs are able to compete with conventional technologies. A major restriction in reaching high efficiencies with DMFCs is methanol crossover from anode to cathode. This work discusses several methods to characterise the methanol crossover and introduces a newly developed measurement method which allows an exact determination of methanol crossover in DMFCs with liquid and solid electrolytes.

The DEXA Cluster consisted of three closely interlinked projects. In 2003 the DEXA Cluster concluded by demonstrating the successful development of critical technologies for Diesel exhaust particulate after-treatment, without adverse effects on NO x emissions and maintaining the fuel economy advantages of the Diesel engine well beyond the EURO IV (2000) emission standards horizon. In the present paper the most important results of the DEXA Cluster projects in the demonstration of advanced particulate control technologies, the development of a simulation toolkit for the design of diesel exhaust after-treatment systems and the development of novel particulate characterization methodologies, are presented. The motivation for the DEXA Cluster research was to increase the market competitiveness of diesel engine powertrains for passenger cars worldwide, and to accelerate the adoption of particulate control technology.

Today, engine cycle simulation codes are widely accepted tools for turbocharger (TC) matching and steady state engine performance predictions at the design stage. However, recently the investigation of the transient engine performance especially in relation to TC response is gaining increasing importance. In addition, thermodynamic cycle simulation can give access to data which otherwise can be measured only with complicated and costly techniques. This study shows the potential in the optimisation of the turbocharger and engine control strategy by means of gas exchange simulation tools.Based on measured and simulated engine performance data of two High Speed Direct Injection (HSDI)-Diesel engines with Variable Turbine Geometry (VTG) turbochargers, the potential for optimising the transient engine load response by means of VTG control strategies and exhaust system layout are evaluated using cycle simulations to analyse the engine performances.