bluuebunny/crossref_metadata_2025 huggingface dataset:
The Institute of Power Engineering Activity in the Solid Oxide Fuel Cell Technology
Authors: Golec Tomasz , Antunes Rui , Jewulski Janusz , Miller Mirosław , Kluczowski Ryszard , Krauz Mariusz , Krząstek Kazimierz , Błesznowski Marcin
Published: November 2009

Electrolyte supported cells (ESC) were manufactured using tape casting and screen printing technology and the corresponding anode supported cells (ASC) manufacturing is currently under development. In the present study, “symmetrical” cathode-electrolyte-cathode solid oxide fuel cell (SOFC) single cells were also fabricated and tested using electrochemical impedance spectroscopy and scanning electron microscopy. The functional and contact layer properties were characterized by means of microscopic and electrochemical methods. Influence of thickness and grain size of layers on the cell performance was systematically investigated. the design of cell, stack and system was helped by computational fluid dynamics and system modeling. The gas flow distribution in the SOFC stack was systematically investigated. The ESC-SOFC cells developed at the Institute of Power Engineering achieved good performance as a result of improvements in ceramic processing. The present activities concentrate on ASC-SOFC cell development, cell testing and cell/stack/system design.
Lattice Boltzmann Modeling of Three-Dimensional, Multicomponent Mass Diffusion in a Solid Oxide Fuel Cell Anode
Authors: Joshi Abhijit S. , Grew Kyle N. , Izzo John R. , Peracchio Aldo A. , Chiu Wilson K. S.
Published: November 2009

The lattice Boltzmann method (LBM) was used to study the three-dimensional (3D) mass diffusion of three species (H2, H2O, and N2) in the pore phase of a porous solid oxide fuel cell (SOFC) anode. The method used is an extension of a two-dimensional (2D) LBM model (2007, “Lattice Boltzmann Method for Continuum, Multi-Component Mass Diffusion in Complex 2D Geometries,” J. Phys. D, 40, pp. 2961–2971) to study mass transport in SOFC anodes (2007, “Lattice Boltzmann Modeling of 2D Gas Transport in a Solid Oxide Fuel Cell Anode,” J. Power Sources, 164, pp. 631–638). The 3D porous anode geometry is initially modeled using a set of randomly packed and overlapping solid spheres. Results using this simple geometry model are then compared with results for an actual SOFC anode geometry obtained using X-ray computed tomography (XCT) at sub-50 nm resolution. The effective diffusivity Deff of the porous anode is a parameter, which is widely used in system-level models. However, empirical relationships often used to calculate this value may not be accurate for the porous geometry that is actually used. Solution of the 3D Laplace equation provides a more reliable and accurate means to estimate the effective diffusivity for a given anode geometry. The effective diffusivity is calculated for different geometries and for a range of porosity values, both for the 3D sphere packing model and for the real geometry obtained by XCT. The LBM model is then used to predict species mole fractions within the spherical packing model geometry and the XCT geometry. The mole fraction variation is subsequently used to calculate the concentration polarization. These predictions compare well with previously obtained 2D results and with results reported in the literature. The 3D mass transport model developed in this work can be eventually coupled with other transport models and be used to optimize the anode microstructure geometry.
Design of Anode Materials for IT SOFC: Effect of Complex Oxide Promoters and Pt Group Metals on Activity and Stability in Methane Steam Reforming of Ni/YSZ (ScSZ) Cermets
Authors: Sadykov Vladislav A. , Mezentseva Natalia V. , Bunina Rimma V. , Alikina Galina M. , Lukashevich Anton I. , Zaikovskii Vladimir I. , Bobrenok Oleg F. , Irvine John , Vasylyev Oleksandr D. , Smirnova Alevtina L.
Published: November 2009

Ni/YSZ or Ni/ScCeSZ cermets were promoted by up to 10 wt % of fluoritelike (Pr–Ce–Zr–О, La–Ce–Zr–О, and Ce–Zr–О) or perovskitelike (La–Pr–Mn–Cr–O) oxides and small (up to 1.4 wt %) amounts of Pt group metals (Pd, Pt, or Ru). Reactivity of samples, their lattice oxygen mobility, and their ability to activate methane were characterized by temperature-programed reduction by CH4. The catalytic properties of these samples in methane steam reforming were studied at 500–850°C and short contact times (10 ms) in feeds with 8 mol % of CH4 and steam/methane ratio of 1:3. Oxide promoters ensure stable performance of cermets in stoichiometric feeds at T>650°C by suppressing carbon deposition. Copromotion with precious metals enhances performance in the intermediate temperature (450–600°C) range due to more efficient activation of methane. Factors determining specificity of these cermet materials’ performance (chemical composition, microstructure, oxygen mobility in oxides, interaction between components, and reaction media effect) are considered. The most promising systems for practical application are Pt/Pr–Ce–Zr–O/Ni/YSZ and Ru/La–Pr–Mn–Cr–O/Ni/YSZ cermets demonstrating a high performance in the intermediate temperature range under broad variation in steam/CH4 ratio.
Geometrical Optimization of Double Layer LSM/LSM-YSZ Cathodes by Electrochemical Impedance Spectroscopy
Authors: Antunes Rui , Golec Tomasz , Miller Mirosław , Kluczowski Ryszard , Krauz Mariusz , Krząstek Kazimierz
Published: November 2009

The present-day high-temperature solid oxide fuel cells (SOFCs), based on yttria-stabilized zirconia (YSZ) electrolyte, a lanthanum-strontium manganite (LSM) cathode and a nickel-YSZ cermet anode, operate at 800–1000°C. Cathode materials are restricted to doped lanthanum manganites due to their stability in oxidizing atmosphere, sufficient electrical conductivity, and thermal expansion match to the YSZ electrolyte. Reduction in the operating temperature of SOFCs is desirable to lower the costs and to overcome the technological disadvantages associated with elevated temperatures. However, as the operating temperature is reduced, the decrease in the LSM conductivity and increase in interfacial polarization resistances between the LSM cathode and YSZ electrolyte become critical. Therefore, different approaches have been proposed to improve interfacial quality and electrochemical performance of the LSM/YSZ cathode. The length of the triple-phase boundary (TPB) correlates well with the interfacial resistances to electrochemical oxidation of hydrogen at the anode and reduction in oxygen at the cathode. The extension of the TPB or the number of active reaction sites becomes, therefore, a determining factor in improving electrode performance. This can be achieved by developing electrode materials of higher ambipolar conductivity and by optimizing the microstructure of the electrodes. In order to improve SOFC performance, both composition and structure of the LSM/YSZ interface and of the cathode should be optimized. Recently, functional grade materials (FGMs) were introduced for SOFC technology. However, all studies reported in the literature so far, were focused on cathodes with only compositional gradient. On the other hand, intuitionally the best structure for a functional SOFC should be characterized by both compositional and porosity gradients. Fine grains (and high surface area) close to the electrode/electrolyte surface and large grains (and thus large pore size) at the air/oxygen side are expected to be of advantage. In the present study, “symmetrical” cathode-electrolyte-cathode SOFC single cells were fabricated. The cells consisted of the functional grade LSM cathode with YSZ/LSM cathode functional layer and LSM contact layer. The effects of various geometrical and microstructural parameters of cathode/functional layers on the overall cell performance were systematically investigated. The parameters investigated were the (1) cathode functional layer thickness and grain size and (2) the LSM contact layer thickness. Cathode performances were tested by means of electrochemical impedance spectroscopy (EIS) over a temperature range of 650–950°C, using air as oxidant. The dependence of cell performance on various parameters was rationalized by a comprehensive microscale model. A cathode polarization corresponding to 0.14–0.4 Ω cm2 at 750°C was achieved in this manner.
Investigation of Chromium Vaporization From Interconnector Steels With Spinel Coatings
Authors: Trebbels R. , Markus T. , Singheiser L.
Published: November 2009

The vaporization of Cr-rich volatile species from interconnector materials for high temperature solid oxide fuel cells (SOFCs) is considered to be a major source of degradation that limits the lifetime of planar SOFC systems (Fujita et al., 2004, “Prevention of SOFC Cathode Degradation in Contact With Cr-Containing Alloy,” J. Power Sources, 131(1–2), pp. 261–269; Hilpert, 1996, “Chromium Vapor Species Over Solid Oxide Fuel Cell Interconnect Materials and Their Potential for Degradation Processes,” J. Electrochem. Soc., 143(11), pp. 3642–3647; Kurukowa et al., 2007, “Chromium Vaporization of Bare and of Coated Iron-Chromium Coatings,” Solid State Ionics, 178, pp. 287–296; Quadakkers, Greiner, and Köck, 1994, “Metals and Alloys for High Temperature SOFC Application,” SOFC Forum, Lucern, Switzerland; Quadakkers et al., 1996, “The Chromium Base Metallic Bipolar Plate-Fabrication, Corrosion and Cr Evaporation,” European Oxide Fuel Cell Forum, Oslo, Norway; Yang, 2006, “Evaluation of Ni-Cr-Base Alloys for SOFC Interconnect Applications,” J. Power Sources, 160(2), pp. 1104–1110). For a longer lifetime of these systems, the Cr vaporization of the interconnector material shall be reduced (Collins, Lucas, and Buchanan, 2006, “Chromium Volatility of Coated and Uncoated Steel Interconnects for SOFCs,” Surf. Coat. Technol., 201(7), pp. 4467). The potential of reduction in the Cr vaporization using coatings with spinel layers is the subject of the present work. In this study the influence of processing parameters for Crofer22APU coated with a spinel based on (Mn,Co,Fe)3O4 on the Cr vaporization rates was studied at 800°C in air using the transpiration method. The measured Cr release of the coated samples was compared with an uncoated Crofer22APU. The aim of this work was to find the optimum conditions to prepare the spinel coating regarding to Cr vaporization. By using such a coating, the Cr vaporization rate was found to be two orders of magnitude lower than uncoated steel. The sintering temperature and pretreatment of the sample showed a high influence on the Cr release.
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Gel Based Polymer Electrolyte Membrane Fuel Cells Under the Influence of Reformates
Authors: Bandlamudi George C. , Saborni M. , Beckhaus P. , Mahlendorf F. , Heinzel A.
Published: November 2009

High temperature polymer electrolyte membrane fuel cells (HT PEMFCs) offer tremendous flexibility when used as energy converters in stationary as well as mobile power devices. Coupling HT PEMFC stacks with fuel processors that use liquid as well as gaseous fuels to generate hydrogen rich gas is a promising prospect, which paves the way for a possible hydrogen economy. The current paper deals with the performance aspects of a 150 Wel HT PEMFC stack, which potentially could be coupled to (i) a natural gas reformer, (ii) a propane reformer, or (iii) a methanol reformer. A 12 cell HT PEMFC stack with a total active area of about 600 cm2 was operated in a test rack, and the results show that HT PEMFCs are principally suited for operation with reformates.
Manufacturing of High-Temperature Polymer Electrolyte Membranes—Part I: System Design and Modeling
Authors: Harris Tequila A. L. , Walczyk Daniel F. , Weber Mathias M.
Published: November 2009

The most important component of the fuel cell is the membrane electrolyte, having the fundamental responsibility of separating protons and electrons. Minor defects (e.g., pin holes) in the film will cause premature and/or catastrophic failure. As such, special attention should be given to the manufacturing of this fuel cell component. Increased interest in identifying and overcoming the technical and manufacturing challenges associated with fuel cells has surfaced over the past few years. To this end, a design methodology, the science, and the technology to manufacture unique high-temperature polymer electrolyte membranes in a uniform and continuous manner are presented, specifically focusing on system conceptualization, design, and modeling. It has been shown that an overall manufacturing system can be designed for a power-law fluid with time-temperature varying properties.
Manufacturing of High-Temperature Polymer Electrolyte Membranes—Part II: Implementation and System Model Validation
Authors: Harris Tequila A. L. , Walczyk Daniel F. , Weber Mathias M.
Published: November 2009

In this paper, a complex system of theoretical models, which predicts flow rate as a function of pressure drop, formulated previously by Harris et al. (2007, “Manufacturing of High-Temperature Polymer Electrolyte Membranes—Part I: System Design and Modeling,” ASME J. Fuel Cell Sci. Technol., 7, p. 011007), are validated through a case study. Specifically, the flow behavior of a power law polymer electrolyte membrane solution, as it flows through a novel manufacturing system, is investigated. It is found that a strategic design methodology can be used to develop a complete manufacturing system to fabricate a defect free film. Moreover, the casting method offers significant improvements for the thickness uniformity of the membrane film, compared with film that is fabricated using scaled laboratory processes. The pressure losses predicted throughout the system are validated accordingly, not only from experimental results but also from computational fluid dynamics modeling.
Fabrication of Anode-Supported Tubular Solid Oxide Fuel Cells by Slip Casting in Combination With Dip Coating Technique
Authors: Zhang Yaohui , Liu Jiang , Yin Juan
Published: November 2009

Dense and microcrack free yttria-stabilized zirconia (YSZ) was deposited onto porous NiO-YSZ anode tubes by dip coating without any vacuum assistance. The anode tubes were prepared by slip casting. Open circuit voltage of 1.05 V was obtained at 800°C, implying that the gas tightness of dip coating YSZ membranes is eligible for solid oxide fuel cell application. A fuel cell of Ni-YSZ/YSZ(20 μm)/La0.7Sr0.3MnO3-YSZ provides maximum power densities of 0.24 W/cm2, 0.46 W/cm2, 0.81 W/cm2, and 1.1 W/cm2 at 650°C, 700°C, 750°C, and 800°C, respectively. The impedance data indicate that the resistivity of the YSZ electrolyte membrane is about 40.5 Ω cm at 800°C. At the same temperature, the electrode polarization resistance accounts for 74.8% of the cell’s total resistance under maximum power density condition.
Efficient and Robust Power Management of Reduced Cost Distributed Power Electronics for Fuel-Cell Power System
Authors: Mazumder Sudip K. , Pradhan Sanjaya
Published: November 2009

Batteries in a fuel-cell power system are essential to providing the additional power during the sharp load-transients. This necessitates a power-electronics subsystem (PES), which controls the energy flow between the fuel-cell stack, the battery, and the application load during the transient and in the steady states. In this paper, a distributed PES (comprising a multimodule dc-dc boost converter) is proposed for a fuel-cell and battery based hybrid power system, which provides higher cost effectiveness, efficiency, and footprint savings. This is realized by interfacing both the fuel-cell stack and the battery to the distributed PES using transfer switches, which are so controlled such that during a load transient, power from both the battery power and the fuel-cell stack is fed to the load via the PES while the stack energy input is adjusted for the new load demand. During the steady-state, the control implements a dynamic-power-management strategy such that only an optimal number of power converter modules of the distributed PES are activated yielding improved optimal energy-conversion efficiency and performance. Furthermore, using a composite Lyapunov-method-based methodology, the effect of dynamic change in the number of active power converter modules with varying load conditions on the stability of the PES is also outlined. Finally, the PES concept is experimentally validated by interfacing a multimodule bidirectional dc-dc boost converter with Nexa® proton exchange membrane (PEM) fuel-cell stacks from Ballard Power Systems.
Temperature and Current Distribution Along the Air Channel in Planar SOFC Stack: Model and Asymptotic Solution
Authors: Kulikovsky A. A.
Published: November 2009

We report a model for coupled temperature and current distributions along the single channel in planar solid-oxide fuel cell stack. Approximate analytical solution to model equations is derived; the solution predicts that air and stack temperatures are close to each other and linearly increase with the distance along the channel. Maximal temperature at the channel outlet is proportional to the average stack current and inversely proportional to the air flow velocity. This means that temperature oscillations due to variable load can be compensated for by the respective variation in air flow velocity.
Numerical Simulation of Two-Phase Water Behavior in the Cathode of an Interdigitated Proton Exchange Membrane Fuel Cell
Authors: Quan Peng , Lai Ming-Chia
Published: November 2009

As an alternative to traditional reactant flow field design, interdigitated flow field configuration is also of interest to fuel cell design engineers and academic researchers. In this work, the two-phase flow behavior inside the cathode of an interdigitated proton exchange membrane fuel cell, including both gas flow channel and porous gas diffusion layer, is numerically studied. The effects of variable design and operational parameters, including channel surface wettability and operating pressure, on water behavior are investigated. A Darcy’s law based porous media model is used for the simulation of the two-phase transport inside the cathode gas diffusion layer, and some interesting two-phase behaviors, such as liquid water distribution under different operating condition, are observed. Compared with the water transport characteristics of a serpentine flow field, the current study shows significant difference for an interdigitated configuration, in terms of two-phase water transport. Although the interdigitated design is generally not considered viable for practical applications in fuel cell, it does provide a convenient platform for fundamental studies of multiphase transport and valuable insights in fuel cell design and optimization.
Steady-State and Transient Analysis of a Steam-Reformer Based Solid Oxide Fuel Cell System
Authors: Das Tuhin , Narayanan Sridharan , Mukherjee Ranjan
Published: November 2009

In this paper we perform a model-based analysis of a solid oxide fuel cell (SOFC) system with an integrated steam reformer and with methane as a fuel. The objective of this study is to analyze the steady-state and transient characteristics of this system. For the analysis, we develop a detailed control-oriented model of the system that captures the heat and mass transfer, chemical kinetics, and electrochemical phenomena. We express the dynamics of the reformer and the fuel cell in state-space form. By applying coordinate transformations to the state-space model, we derive analytical expressions of steady-state conditions and transient behaviors of two critical performance variables, namely, fuel utilization and steam-to-carbon balance. Using these results, we solve a constrained steady-state fuel optimization problem using linear programming. Our analysis is supported by simulations. The results presented in this paper can be applied in predicting steady-state conditions and certain transient behaviors and will be useful in control development for SOFC systems.
Cogeneration of Heat and Electricity: A Comparison of Gas Turbine, Internal Combustion Engine, and MCFC/GT Hybrid System Alternatives
Authors: Bargigli S. , Cigolotti V. , Pierini D. , Moreno A. , Iacobone F. , Ulgiati S.
Published: November 2009

The purpose of this paper is to present the results of a feasibility study of the supply of electricity and heat to a large user (i.e., a public hospital in Northern Italy) by means of a molten carbonate fuel cell (MCFC) hybrid system in comparison with other technologies. The study investigated three alternative options in order to meet the user’s demand: internal combustion engine, gas turbine, and a hybrid system (molten carbonate fuel cells and gas turbine, MCFC-HS), which is currently under development by Ansaldo Fuel Cell Ltd. and ENEA. The user requirement was the yearly supplies of 6.65 GWhe/year and 21.64 GWhth/year. Due to demand fluctuations over the year, integration by electric grid and/or additional thermal boilers was also required and investigated. The approach integrates the usual mass balance with large scale material flow accounting, embodied energy analysis, exergy efficiency, and emergy synthesis, within a LCA perspective. Results show that the best performance from the point of view of energy and exergy efficiency is shown by the MCFC-hybrid system. The latter is also characterized by the lowest embodied energy demand and cumulative material demand as well as by the lowest requirement for direct and indirect environmental support (emergy method). However, the small thermal energy supply of the MCFC-HS compared with the large thermal needs of the hospital calls for a larger use of the additional boiler. The latter device worsens the local-scale emissions of the system, compared with the other alternatives investigated. Results point out that a proper choice cannot only be based on the individual performance of an even well performing technological device, but also needs to be tailored on the system’s characteristics and dynamics, in order to adequately match supply and demand.
A New Approach for Modeling the Thermal Behavior of Methane Catalytic Partial Oxidation Monolith Reactors
Authors: Cordiner S. , de Simone G.
Published: November 2009

A comprehensive computational model for the design of methane catalytic partial oxidation monolith reactors for hydrogen production has been developed and tested with respect to available experimental data. Allowing a simplified description of the heat release mechanism associated with the reforming process, the model represents a useful tool to address performances and durability issues in the design process of full scale catalytic reformers. The characteristic temperature peak along the catalyst channels, which is experimentally observed as a result of the competitive action of fuel complete oxidation and steam reforming is, in fact, a fundamental parameter to be controlled during the design process and is a complex function of catalyst formulation, mixture composition, and actual operating conditions. To address this issue in the present paper the heat release law mechanism has been studied with a new approach named heat release curves model (HRCM), which decouples the thermofluid dynamic analysis of real geometries from the modeling of heterogeneous chemistry. The model uses heat release curves extrapolated from detailed heterogeneous chemistry calculation or experimental measurements as the basis of a simplified, although still predictive, evaluation of the heat released, which allows a substantial reduction in computational costs. Validation of HRCM model (including heat release profiles approximation) with respect to more detailed simulations and available experimental data shows very good predictive capabilities with a maximum error lower than the 4% over a wide number of analyzed cases (accounting for several O/C ratios, inlet velocities, channel dimensions, and mean temperatures). Although presented for natural gas reforming the present model may be easily extended to different fuels.
Enhancing Polymeric Electrolyte Membrane Fuel Cell Control by Means of the Perturb and Observe Technique
Authors: Giustiniani A. , Petrone G. , Spagnuolo G. , Arsie I. , Di Domenico A. , Pianese C. , Sorrentino M. , Vitelli M.
Published: November 2009

In this paper, the use of an adaptive technique aimed at controlling a polymeric electrolyte membrane fuel cell is introduced. It is demonstrated that a hill climbing-based method, acting on the compressor speed and/or the cathode back-pressure valve, allows to better take into account the effect of exogenous variables on stack performance. Particularly, the proposed technique has proven to perform better than classical feedforward/feedback approaches when well known aging mechanisms deteriorate cell efficiency. Numerical results based on experimentally derived models confirm the potential of the proposed control method and its intrinsic reliability.
Effect of Flame Structure on the Flame Transfer Function in a Premixed Gas Turbine Combustor
Authors: Kim Daesik , Lee Jong Guen , Quay Bryan D. , Santavicca Domenic A. , Kim Kwanwoo , Srinivasan Shiva
Published: November 2009

The flame transfer function in a premixed gas turbine combustor is experimentally determined. The fuel (natural gas) is premixed with air upstream of a choked inlet to the combustor. Therefore, the input to the flame transfer function is the imposed velocity fluctuations of the fuel/air mixture without equivalence ratio fluctuations. The inlet-velocity fluctuations are achieved by a variable-speed siren over the forcing frequency of 75–280 Hz and measured using a hot-wire anemometer at the inlet to the combustor. The output function (heat release) is determined using chemiluminescence measurement from the whole flame. Flame images are recorded to understand how the flame structure plays a role in the global heat release response of flame to the inlet-velocity perturbation. The results show that the gain and phase of the flame transfer function depend on flame structure as well as the frequency and magnitude of inlet-velocity modulation and can be generalized in terms of the relative length scale of flame to convection length scale of inlet-velocity perturbation, which is represented by a Strouhal number. Nonlinear flame response is characterized by a periodic vortex shedding from shear layer, and the nonlinearity occurs at lower magnitude of inlet-velocity fluctuation as the modulation frequency increases. However, for a given modulation frequency, the flame structure does not affect the magnitude of inlet-velocity fluctuation at which the nonlinear flame response starts to appear.
Ignition and Flame Speed Kinetics of Two Natural Gas Blends With High Levels of Heavier Hydrocarbons
Authors: Bourque Gilles , Healy Darren , Curran Henry , Zinner Christopher , Kalitan Danielle , de Vries Jaap , Aul Christopher , Petersen Eric
Published: November 2009

High-pressure experiments and chemical kinetics modeling were performed to generate a database and a chemical kinetic model that can characterize the combustion chemistry of methane-based fuel blends containing significant levels of heavy hydrocarbons (up to 37.5% by volume). Ignition delay times were measured in two different shock tubes and in a rapid compression machine at pressures up to 34 atm and temperatures from 740 K to 1660 K. Laminar flame speeds were also measured at pressures up to 4 atm using a high-pressure vessel with optical access. Two different fuel blends containing ethane, propane, n-butane, and n-pentane added to methane were studied at equivalence ratios varying from lean (0.3) to rich (2.0). This paper represents the most comprehensive set of experimental ignition and laminar flame speed data available in the open literature for CH4/C2H6/C3H8/C4H10/C5H12 fuel blends with significant levels of C2+ hydrocarbons. Using these data, a detailed chemical kinetics model based on current and recent work by the authors was compiled and refined. The predictions of the model are very good over the entire range of ignition delay times, considering the fact that the data set is so thorough. Nonetheless, some improvements to the model can still be made with respect to ignition times at the lowest temperatures and for the laminar flame speeds at pressures above 1 atm and at rich conditions.
Emission Characteristics of a Premixed Cyclic-Periodical-Mixing Combustor Operated With Hydrogen-Natural Gas Fuel Mixtures
Authors: Brückner-Kalb Jochen R. , Krösser Michael , Hirsch Christoph , Sattelmayer Thomas
Published: November 2009

The concept of the cyclic periodical mixing combustion process (Kalb, and Sattelmayer, 2004, “Lean Blowout Limit and NOx-Production of a Premixed Sub-ppm-NOx Burner With Periodic Flue Gas Recirculation,” Proceedings of the ASME Turbo Expo 2004, Paper No. GT2004-53410; Kalb, and Sattelmayer, 2006, “Lean Blowout Limit and NOx-Production of a Premixed Sub-ppm-NOx Burner With Periodic Recirculation of Combustion Products,” ASME J. Eng. Gas Turbines Power, 128(2), pp. 247–254) for the extension of the lean blowout limit had been implemented in an atmospheric experimental combustor for testing with both external perfect (Brückner-Kalb, Hirsch, and Sattelmayer, 2006, “Operation Characteristics of a Premixed Sub-ppm NOx Burner With Periodical Recirculation of Combustion Products,” Proceedings of the ASME Turbo Expo 2006, Paper No. GT2006-90072) and technical (Brückner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, “Development of a Fuel-Air Premixer for a Sub-ppm NOx Burner,” Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779) premixing of reactants. It had been tested with natural gas and has now been tested with a mixture of 70%vol of hydrogen and 30%vol of natural gas (98% CH4) as fuel. With natural gas the NOx emissions are unaffected by the limited technical premixing quality, as long as the air preheat is in the design range of the premixers (Brückner-Kalb, Napravnik, Hirsch, and Sattelmayer, 2007, “Development of a Fuel-Air Premixer for a Sub-ppm NOx Burner,” Proceedings of the ASME Turbo Expo 2007, Paper No. GT2007-27779). Then, for adiabatic flame temperatures of up to 1630 K NOx emissions are below 1 ppm(v) with CO emissions below 8 ppm(v) in the whole operation range of the test combustor (15% O2, dry). With the “70%volH2−30%volCH4” mixture the NOx emissions increase by nearly one order of magnitude. Then, NOx emissions below 7 ppm(v) (15% O2, dry) are achieved for adiabatic flame temperatures of up to 1600 K. They approach the 1 ppm(v) level only for flame temperatures below 1450 K. CO emissions are below 4 ppm(v). The reason for the increase in the NOx emissions is the higher reactivity of the mixture, which leads to earlier ignition in zones of still elevated unmixedness of reactants near the premixer-injector exits. This effect was investigated by chemical reactor network simulations analyzing a pressure effect and an additional chemical effect of hydrogen combustion on NOx formation.
Experimental Study on Effects of Nozzle Hole Geometry on Achieving Low Diesel Engine Emissions
Authors: Karra Prashanth K. , Kong Song-Charng
Published: November 2009

Three injectors with different nozzle geometries were tested in a multicylinder diesel engine with a high-pressure common-rail injection system. Various injection pressures were tested along with exhaust gas recirculation to achieve low NOx and soot emissions. The injectors used in the study included a six-hole nozzle, a ten-hole nozzle, and a six-hole convergent nozzle with a K-factor of 3. All three injectors had the same flow numbers. All three injectors tested were effective in reducing NOx and soot emissions at appropriate conditions. It was found that low temperature combustion can be achieved by using high levels of exhaust gas recirculation with late injection timings. High injection pressures significantly reduced soot emissions at conventional injection timings. The effect of injection pressure was not significant at retarded injection timings, i.e., 5 ATDC. The convergent nozzle was found to produce higher soot emissions compared with the straight-hole nozzle under the same injection conditions. Effects of the convergent nozzle on NOx emissions and fuel consumption were not significant. The small nozzle size in the ten-hole injector can generate smaller fuel drops and lead to better atomization. The ten-hole injector appeared to have better air utilization and resulted in significant reductions in NOx and soot emissions over a wide range of operating conditions.
Computationally Efficient Whole-Engine Model of a Cummins 2007 Turbocharged Diesel Engine
Authors: Kulkarni Anup M. , Shaver Gregory M. , Popuri Sriram S. , Frazier Tim R. , Stanton Donald W.
Published: November 2009

This paper describes an accurate, flexible, and computationally efficient whole engine model incorporating a multizone, quasidimension combustion submodel for a 6.7-l six-cylinder turbocharged diesel engine with cooled exhaust gas recirculation (EGR), cooled air, and multiple fuel injections. The engine performance and NOx emissions predicative capability of the model is demonstrated at 22 engine operating conditions. The only model inputs are physical engine control module “control actions,” including injection rates, injection timings, EGR valve position, and variable geometry turbocharger rack position. The model is run using both “open” and “closed” loop control strategies for air/EGR path control, in both cases achieving very good correlation with experimental data. Model outputs include in-cylinder pressure and heat release, torque, combustion timing, brake specific fuel consumption, EGR flow rate, air flow rate, exhaust and intake pressure, and NOx emissions. The model predicts engine performance and emissions with average absolute errors within 5% and 18%, respectively, of true values with “open-loop” air/EGR control, and within 5% and 11% with “closed-loop” air/EGR control. In addition, accurate prediction of the coupling of the in-cylinder combustion and emission-production processes with the boosted, cooled air/EGR gas dynamics is a key characteristic of the model.
A Convective Mass Transfer Model for Predicting Vapor Formation Within the Cooling System of an Internal Combustion Engine After Shutdown
Authors: Piccione Rocco , Vulcano Antonio , Bova Sergio
Published: November 2009

In the usual liquid cooling system of an internal combustion engine a centrifugal pump is driven by the crankshaft and imposes a coolant flow, which transfers heat from the engine walls to the radiator. Therefore, as the engine is switched-off, the coolant flow also stops, while metal temperature may be particularly high after a period of high load operation; coolant vaporization in the cylinder head passages may occur in these conditions, with a pressure increase inside the cooling circuit. A numerical dynamic model was developed to predict this phenomenon, often called after-boiling among engine manufacturers. The model structure includes thermodynamic equations to compute heat transfer as well as mass transfer equations to determine the vaporized mass of the coolant, which occurs in cylinder head passages and the vapor condensation within the radiator. The developed mathematical model was validated against test data carried out on a production four-stroke spark-ignition engine, and simulation results show good agreement with experimental data.
Extrapolation and Curve-Fitting of Calibration Data for Differential Pressure Flow Meters
Authors: Keyser David R. , Friedman Jeffrey R.
Published: November 2009

Performance test codes require primary mass-flow accuracies that in many applications require laboratory quality calibration of differential pressure meters. It is also true that many performance tests are conducted at Reynolds numbers and flows well above the laboratories' capacities, and sound extrapolation methods had to be developed. Statistical curve fits and regression analyses by themselves, absent fluid-dynamic foundations, are not valid procedures for extrapolation. The ASME PTC 19.5-2004 discharge coefficient equations reproduced in this paper for nozzles, orifices, and venturis are suitable for use whenever calibration data are to be applied in a flow measurement and/or extrapolated to higher Reynolds numbers as necessary. The equations may also be used for uncalibrated differential pressure meters by using nominal values. It is necessary to note that the metering runs must be manufactured with dimensions, tolerances, smoothness, etc., and installed in strict accordance with ASME PTC 19.5 for these equations to be valid. Note that for compressible flow, the value of the expansion factor term in the PTC 19.5 equation must be the one corresponding to the published PTC 19.5 equation.
Manufacturing Optimization for Bondcoat/Thermal Barrier Coating Systems
Authors: Bossmann Hans-Peter , Bachegowda Sharath , Schnell Alexander
Published: November 2009

A reliable lifetime prediction rule for bondcoat/thermal barrier coating (BC/TBC) coated parts in gas turbine operation is necessary to determine remnant service life. The specimens investigated were coated with MCrAlY plus yttria partially stabilized zirconia applied by vacuum plasma spraying and atmospheric plasma spraying processes, respectively. The performances of these laboratory specimens were statistically assessed, combining long term oxidation testing with thermal cycling, thus superimposing thermomechanical loading on the laboratory specimens to more accurately represent engine conditions. A design of experiment (DOE) approach was used for manufacturing optimization of the BC/TBC system. The life of the coating system is influenced by several manufacturing parameters such as BC thickness, BC roughness, TBC thickness, TBC porosity, and TBC stiffness. Specimens with a suitable variation in these parameters were produced to ensure a balanced test matrix of fractional factorial DOE. Based on results derived from laboratory testing the specifically tailored parts, first and second order effects of manufacturing parameters on lifetime were quantified. The findings revealed that the second order effects (the interaction of manufacturing parameters) were more important on the lifetime of the BC/TBC system than the corresponding first order effect (single parameter). For instance, the variation in BC thickness or BC roughness led to a scatter of lifetimes of 10% and 60%, respectively, whereas their interaction resulted in a scatter of lifetime of 150% for the same range of coating parameters. Further examples of such pairings are also demonstrated. Finally, a lifetime prediction for three quality classes (high, medium, and low qualities) has been demonstrated. The difference in achievable lifetime highlights the importance of manufacturing parameters in determining the life of the BC/TBC system.
Determination of the Instantaneous Fuel Flow Rate Out of a Fuel Nozzle
Authors: Yi Tongxun , Santavicca Domenic A.
Published: November 2009

Reported is a practical method for accurate and fast determination of the instantaneous fuel flow rate out of a fuel injector. Both gaseous and liquid fuels are considered. Unsteady fuel flow rates introduced into a combustor can be caused by both self-excited pressure pulsations and fuel modulations. During combustion instability, the air flow rate into a combustor also varies in response to pressure pulsations. Accurate determination of the instantaneous fuel and air flow rates is important for both modeling and control of combustion instability. The developed method is based on the acoustic wave theory and pressure measurements at two locations upstream of a fuel injector. This method bypasses the complexities and nonlinearities of fuel actuators and fuel nozzles, and works for systems with slow-time-varying characteristics. Acoustic impedance of a gaseous fuel nozzle is found to be a function of multivariables, including the forcing frequency, the acoustic oscillation intensity, and the mean fuel flow rate. Thus, it is not an intrinsic property of the fuel injector alone. In the present study, sharp tubing bending with almost zero radii is found to have minimal effects on the distribution of 1D acoustic wave. This is probably because vortex shedding and recirculation at tubing corners do not alter the globally 1D characteristics of acoustic wave distribution. Different from the traditional two-microphone method, which determines the acoustic velocity at the middle locations of the two microphones, the present method allows the acoustic velocity, the acoustic mass flux, and the specific acoustic impedance to be determined along the fuel tubing or an air pipe.
Onset of 12X Vibration and Its Prevention
Authors: Yu John J.
Published: November 2009

This paper discusses real cases on three different machines where subsynchronous vibration occurred suddenly at a frequency exactly equal to one-half (12X) of the operational speed of 3600 rpm. In two cases, vibration amplitude increased from around 2 mils (51 μm) pp to over 12 mils (305 μm) pp, causing the machine to trip unexpectedly. The 12X vibration was even sustained during shutdown at speed below 3600 rpm after trip. Unlike other reported experimental results, shaft orbit measured by proximity probes was fairly circular and dominantly composed of the 12X component without significant components at multiple orders of the 12X. The onset of the subsynchronous 12X vibration was sometimes triggered by changes in bearing lube oil temperature and supply pressure, which would typically be believed to be caused by oil whirl that could occur at close to the 12X frequency. An upward shift in shaft centerline plot was observed to occur prior to the onset of the subsynchronous vibration. The 12X vibration was successfully prevented by changing bearing clearance or adjustment of bearing oil temperature and supply pressure. Parametric excitation analysis on 12X vibration is also given in this paper. The main purpose of this paper, unlike previously published papers on analytical or experimental results, is to show shaft orbital and centerline plots as well as spectrum data due to the 12X vibration, including effects of operating conditions in real rotating machines.
Effects of Coating Thickness, Test Temperature, and Coating Hardness on the Erosion Resistance of Steam Turbine Blades
Authors: Wang Shun-sen , Liu Guan-wei , Mao Jing-ru , He Qun-gong , Feng Zhen-ping
Published: November 2009

This paper experimentally examines the influence of coating thickness, test temperature, coating hardness, and defects on the erosion resistance of boride coatings, ion plating CrN coatings, and thermal spraying coatings. The results demonstrate that the erosion rate of coating can be reduced effectively by improving coating hardness and thickness with the absence of the cracks of coating during the coating process. In comparison with thermal spraying coatings, boride coatings and ion plating CrN coatings are more suitable for protecting steam turbine blades from solid particle erosion due to higher erosion resistance. However, blades cannot be protected effectively when coating is thinner than a critical value θcrit. Based on our results, it is recommended that the protective coating for the steam turbine blade should be thicker than 0.02 mm. In addition, the effect of temperature on erosion resistance of the coating is strongly dependent on the properties of transition layer between coating and substrate material. For the coating without pinholes or pores in the transition layer, the variation in erosion rate with temperature is consistent with that of uncoated substrate material. However, the erosion rate of coating descends with the elevation of test temperature when a lot of pinholes or pores are produced in the transition layer.
Role of Platinum in Thermal Barrier Coatings Used in Gas Turbine Blade Applications
Authors: Tawancy H. M. , Al-Hadhrami Luai M.
Published: November 2009

Current technology of thermal barrier coating systems used in gas turbine blade applications relies on the use of a metallic bond coat, which has a twofold function: (i) it develops a thin layer of aluminum oxide enhancing the adhesion of the ceramic top coat and (ii) it provides an additional resistance to oxidation. It was the objective of this study to develop an understanding of the role of platinum in bond coats of the diffusion-type deposited on a nickel-based superalloy. Two Pt-containing bond coats were included in the study: (i) a platinum-aluminide and (ii) a bond coat formed by interdiffusion between an electroplated layer of platinum and the superalloy substrate. In both cases, the top ceramic coat was yttria-stabilized zirconia. For reference purposes, a simple aluminide bond coat free of Pt was also included in the study. Thermal exposure tests at 1150°C with a 24 h cycling period at room temperature were used to compare the coating performance. Microstructural features were characterized by various electron-optical techniques. Experimental results indicated that Pt acts as a “cleanser” of the oxide-bond coat interface by decelerating the kinetics of interdiffusion between the bond coat and superalloy substrate. This was found to promote selective oxidation of Al resulting in a purer Al2O3 scale of a slower growth rate increasing its effectiveness as “glue” holding the ceramic top coat to the underlying metallic substrate. However, the exact effect of Pt was found to be a function of the state of its presence within the outermost coating layer. Of the two bond coats studied, a surface layer of Pt-rich gamma prime phase (L12 superlattice) was found to provide longer coating life in comparison with a mixture of PtAl2 and beta phase. This could be related to the effectiveness of gamma prime phase as a sink for titanium minimizing its detrimental effect on the adherence of aluminum oxide.
A Sparse Estimation Approach to Fault Isolation
Authors: Borguet S. , Léonard O.
Published: November 2009

Least-squares-based methods are very popular in the jet engine community for health monitoring purposes. In most practical situations, the number of health parameters exceeds the number of measurements, making the estimation problem underdetermined. To address this issue, regularization adds a penalty term on the deviations of the health parameters. Generally, this term imposes a quadratic penalization on these deviations. A side effect of this technique is a relatively poor isolation capability. The latter feature can be improved by recognizing that abrupt faults impact at most one or two component(s) simultaneously. This translates mathematically into the search for a sparse solution. The present contribution reports the development of a fault isolation tool favoring sparse solutions. It is very efficiently implemented in the form of a quadratic program. As a validation procedure, the resulting algorithm is applied to a variety of fault conditions simulated with a generic commercial turbofan model.
Micro Gas Turbine Recuperator: Steady-State and Transient Experimental Investigation
Authors: Ferrari Mario L. , Pascenti Matteo , Magistri Loredana , Massardo Aristide F.
Published: November 2009

The aim of this work is the experimental analysis of a primary-surface recuperator, operating in a 100 kW micro gas turbine, as in a standard recuperated cycle. These tests, performed in both steady-state and transient conditions, have been carried out using the micro gas turbine test rig, developed by the Thermochemical Power Group at the University of Genova, Italy. Even if this facility has mainly been designed for hybrid system emulations, it is possible to exploit the plant for component tests, such as experimental studies on recuperators. The valves installed in the rig make it possible to operate the plant in the standard recuperated configuration, and the facility has been equipped with new probes essential for this kind of tests. A wide-ranging analysis of the recuperator performance has been carried out with the machine, operating in stand-alone configuration, or connected to the electrical grid, to test different control strategy influences. Particular attention has been given to tests performed at different electrical load values and with different mass flow rates through the recuperator ducts. The final section of this paper reports the transient analysis carried out on this recuperator. The attention is mainly focused on thermal transient performance of the component, showing the effects of both temperature and flow steps.