bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Investigation of the Startup Transient in a Wave Rotor
Authors: Paxson D. E.
Published: February 2008

The startup process is investigated for a hypothetical four-port wave rotor, envisioned as a topping cycle for a small gas turbine engine. The investigation is conducted numerically using a multi-passage, one-dimensional CFD based wave rotor simulation in combination with lumped volume models for the combustor, exhaust valve plenum, and rotor center cavity components. The simulation is described and several startup transients are presented which illustrate potential difficulties for the specific cycle design investigated. In particular it is observed that, prior to combustor light-off, or just after, the flow through the combustor loop is reversed from the design direction. The phenomenon is demonstrated and several possible modification techniques are discussed that avoid or overcome the problem.
Erosion-Oxidation of Carbon Steel in the Convection Section of an Industrial Boiler Cofiring Coal–Water Fuel and Natural Gas
Authors: Xie J. J. , Walsh P. M.
Published: February 2008

Walsh et al. (1994) reported measurements of erosion of carbon steel by fly ash and unburned char particles in the convective heat transfer section of an industrial boiler cofiring coal–water fuel and natural gas. Erosion was enhanced by directing a small jet of nitrogen, air, or oxygen toward the surface of a test coupon mounted on an air-cooled tube. Ash and char particles that entered the jet from the surrounding flue gas were accelerated toward the surface of the specimen. Samples were exposed for 2 hours with metal temperature at 450, 550, and 650 K (350, 530, and 710°F). Changes in shape of the surface were measured using a surface profiler. Time-averaged maximum erosion rates were obtained from the differences between the original surface height and the lowest points in the profiles. Erosion was slowest at the lowest metal temperature, regardless of the jet gas composition. When the oxygen partial pressure at the sample surface was very small, under the nitrogen jet, erosion increased with increasing temperature over the range of temperatures investigated. At the intermediate oxygen level, in the air jet, erosion was most rapid at the intermediate temperature. In the presence of the pure oxygen jet erosion was slow at all three temperatures. A model was developed by Xie (1995) to describe wastage of tube material in the presence of the erosion by particle impacts and oxidation of the metal. The observed changes in erosion rate with temperature and oxygen concentration were consistent with a mechanism based upon the following assumptions: (1) Metal was eroded as a ductile material, at a rate that increased with increasing temperature. (2) Oxide was eroded as a brittle material, at a rate independent of temperature. (3) The oxide scale was strongly attached to the metal. (4) The erosion resistance of metal and scale was a linear combination of the resistances of the individual components. (5) Oxide formed according to the parabolic rate law, with a rate coefficient proportional to the square root of the oxygen partial pressure. (6) Erosion resistance from particles sticking to, or embedded in, the surface was negligible. Using the model and rate coefficients for metal and oxide erosion derived from the measurements, estimates were made of the erosion rate of a boiler tube as functions of impaction angle and gas velocity. Under the conditions of metal temperature, gas composition, particle size, particle concentration, and particle composition investigated, erosion of carbon steel is expected to be slower than 0.05 μm/h when the gas velocity in the convection section is less than approximately 8 m/s.
REVAP® Cycle: A New Evaporative Cycle Without Saturation Tower
Authors: De Ruyck J. , Bram S. , Allard G.
Published: February 2008

A new evaporative cycle layout is disclosed that is shown to have a performance similar to the HAT cycle, but where the saturation tower has been eliminated. This new cycle is a result of a combined exergetic and composite curve analysis discussed in a previous paper, assuming one intercooler and no reheat (De Ruyck et al., 1995). The new cycle uses two-phase flow heat exchange in the misty regime, which is a well-known process. Existing aeroderivative gas turbine equipment can be adapted for application of this cycle, which therefore needs a minimum of development.
Sensitivity Analysis on Brayton Cycle Gas Turbine Performance
Authors: Negri di Montenegro G. , Peretto A.
Published: February 2008

This paper evaluates the performance of a Brayton cycle gas turbine, in terms of power output and conversion efficiency. Sensitivity of this performance to the realistic value of each input variable considered is analyzed. Sensitivity is evaluated by introducing a parameter, defined as the ratio between the logarithmic differential of the power output or efficiency functions and the logarithmic differential of each variable considered. These analytical functions and their derivatives correspond to a gas turbine model developed by the authors. The above-mentioned sensitivity parameter can be also evaluated by means of a numerical procedure utilizing a common gas turbine power plant computational model. The values calculated with the two procedures turn out to be substantially the same. Finally, the present analysis permits the determination of the weight of the input variable and of its value on the obtainable numerical performance. Such weights are found to be less important for some variables, while they are of marked significance for others, thus indicating those input parameters requiring a very precise verification of their numerical values.
Improved Turbine Cylinder Bolting System
Authors: Gosling M. C.
Published: February 2008

This paper describes the design and development of a new cylinder bolting system to replace the main joint hardware for both combustion (and steam) turbine applications. The new bolts are designed to be hydraulically tensioned to the specified preload and utilize ultrasonic verification of elongation. The new bolting system uses a reduced number of components in each assembly and the individual components themselves are of a simplified design. The new hardware can be applied to new equipment without modification and retrofitted to customer-owned equipment as a direct replacement for existing joint hardware. The prototype, production, and field testing of this hardware, the installation tooling; and ultrasonic elongation measuring equipment are described. This testing has shown significant savings in assembly and disassembly cycle times even after prolonged exposure to turbine operating temperatures in a corrosive environment. The new design of bolting is now standard equipment for the CW251B11/B12 combustion turbine manufactured by Westinghouse P.G.B.U.
On the Concept of Separate Aftercooling for Locomotive Diesel Engines
Authors: Uzkan T. , Lenz M. A.
Published: February 2008

This paper describes a patented cooling system concept for a turbocharged diesel engine. In particular, it defines a cooling system having the capability of transferring some of the cooling capacity of engine jacket and engine oil cooling to cool the cylinder inlet air when more than the cooling capacity built into the system through the size of the radiators and fans is needed. This increased aftercooling will improve the engine performance and reduce emission levels. The cooling capacity of a locomotive is essentially determined by the radiator and fan size, among other factors, and is designed to cool the engine within acceptable metal temperatures at a specified maximum ambient temperature and at the maximum engine power. On the other hand, at lower ambient temperatures or engine power levels, the cooling needs of the engine will be less than this maximum cooling capacity of the cooling system. There remains some excess capacity. This paper describes the concept called the “Separate Aftercooling System” that uses some of this excess cooling capacity to cool the engine inlet air at the aftercoolers. It shows the feasibility of such a system, describes the order of magnitude of benefits that can be expected from such a system, and outlines the implementation of this concept to EMD built Locomotives.
A Computational Model for the Study of Gas Turbine Combustor Dynamics
Authors: Costura D. M. , Lawless P. B. , Fankel S. H.
Published: February 2008

A dynamic combustor model is developed for inclusion into a one-dimensional full gas turbine engine simulation code. A flux-difference splitting algorithm is used to numerically integrate the quasi-one-dimensional Euler equations, supplemented with species mass conservation equations. The combustion model involves a single-step, global finite-rate chemistry scheme with a temperature-dependent activation energy. Source terms are used to account for mass bleed and mass injection, with additional capabilities to handle momentum and energy sources and sinks. Numerical results for cold and reacting flow for a can-type gas turbine combustor are presented. Comparisons with experimental data from this combustor are also made.
Testing of a Low Cooled Ceramic Nozzle Vane Under Transient Conditions
Authors: Dilzer M. , Gutmann C. , Schulz A. , Wittig S.
Published: February 2008

At the Institut fu¨r Thermische Stro¨mungsmaschinen, University of Karlsruhe (ITS), a design technology has been introduced to reduce the mechanically and especially the thermally induced stresses in ceramic components. The concept is based on a three-layered construction (outer ceramic shell, heat insulating layer, and metallic core) and an optimization of the thicknesses of the single layers, in order to obtain a homogenous temperature distribution in the ceramic structure. The optimization is performed by finite element analyses in combination with failure probability calculations. This methodology has been applied to increase the reliability of a first stage Sintered Silicon Carbide (SSiC) ceramic nozzle vane of a stationary gas turbine (70 MW/1400°C). As a result it was found that the mechanically and thermally induced loads have been reduced considerably and do not exceed 100 MPa, thus achieving adequate life based upon failure probability calculations. Even in a trip situation (fuel cutoff), when the highest loads do occur, the calculations demonstrate a significantly reduced failure probability. The results of the finite element analyses were verified by simulating the typical operating conditions after fuel cutoff in a test rig.
Vibration of a Rotor System With a Switching Crack and Detection of the Crack
Authors: Zheng G. T.
Published: February 2008

The existence of a “breathing” crack can not only cause variations in harmonic components but also produce extra transient components into vibration signals of a rotor system. In the present paper, the composition of cracked rotor vibration signals is studied first by some analytical methods. Based on this study, an approach of signal processing is suggested to detect transient components of the vibration signals and thereby the crack.
A Viscoplastic Constitutive Theory for Monolithic Ceramics—I
Authors: Janosik L. A. , Duffy S. F.
Published: February 2008

This paper, which is the first of two in a series, provides an overview of a viscoplastic constitutive model that accounts for time-dependent material deformation (e.g., creep, stress relaxation, etc.) in monolithic ceramics. Using continuum principles of engineering mechanics, the complete theory is derived from a scalar dissipative potential function first proposed by Robinson (1978), and later utilized by Duffy (1988). Derivations based on a flow potential function provide an assurance that the inelastic boundary value problem is well posed, and solutions obtained are unique. The specific formulation used here for the threshold function (a component of the flow potential function) was originally proposed by Willam and Warnke (1975) in order to formulate constitutive equations for time-independent classical plasticity behavior observed in cement and unreinforced concrete. Here constitutive equations formulated for the flow law (strain rate) and evolutionary law employ stress invariants to define the functional dependence on the Cauchy stress and a tensorial state variable. This particular formulation of the viscoplastic model exhibits a sensitivity to hydrostatic stress, and allows different behavior in tension and compression.
Progress on the European Gas Turbine Program “AGATA”
Authors: Gabrielsson R. , Holmqvist G.
Published: February 2008

The four-year European Gas Turbine Program “AGATA” was started in January 1993 with the objective of developing three critical components aimed at a 60 kW turbogenerator in an hybrid electric vehicle: a catalytic combustor, a radial turbine wheel and a static heat exchanger. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst, and ceramic material fields in both France and Sweden. This paper outlines the main results of the AGATA project for the first three-year period. Experimental verification of the components started during the third year of the program. A high-pressure/temperature test rig for the combustor and the heat exchanger tests has been built and is now being commissioned. A high-temperature turbine spin rig will be ready late 1995. The turbine wheel design is completed and ceramic Si3N4 spin disks have been manufactured by injection molding and Hot Isostatic Pressing (HIP). A straight blade design has been selected and FEM calculations have indicated that stress levels that occur during a cold start are below 300 MPa. The catalytic combustor final design for full-scale testing has been defined. Due to the high operating temperature, 1350°C, catalyst pilot tests have included aging, activity, and strength tests. Based on these tests, substrate and active materials have been selected. Initial full-scale tests including LDV measurements in the premix duct will start late 1995. The heat exchanger design has also been defined. This is based on a high-efficiency plate recuperator design. One critical item is the ceramic thermoplastic extrusion manufacturing method for the extremely thin exchanger plates another is the bonding technique: ceramic to ceramic and ceramic to metal. Significant progress on these two items has been achieved. The manufacturing of quarter scale prototypes is now in process.
The Applicability of Jet-Shear-Layer Mixing and Effervescent Atomization for Low-NOx Combustors
Authors: Colantonio R. O.
Published: February 2008

An investigation has been conducted to develop appropriate technologies for a low-NOx, liquid-fueled combustor. The combustor incorporates an effervescent atomizer used to inject fuel into a premixing duct. Only a fraction of the combustion air is used in the premixing process. This fuel-rich mixture is introduced into the remaining combustion air by a rapid jet-shear-layer mixing process involving radial fuel–air jets impinging on axial air jets in the primary combustion zone. Computational modeling was used as a tool to facilitate a parametric analysis appropriate to the design of an optimum low-NOx combustor. A number of combustor configurations were studied to assess the key combustor technologies and to validate the three-dimensional modeling code. The results from the experimental testing and computational analysis indicate a low-NOx potential for the jet-shear-layer combustor. Key features found to affect NOx emissions are the primary combustion zone fuel–air ratio, the number of axial and radial jets, the aspect ratio and radial location of the axial air jets, and the radial jet inlet hole diameter. Each of these key parameters exhibits a low-NOx point from which an optimized combustor was developed. Also demonstrated was the feasibility of utilizing an effervescent atomizer for combustor application. Further developments in the jet-shear-layer mixing scheme and effervescent atomizer design promise even lower NOx with high combustion efficiency.
The Spray Structure of Air-Shrouded Dual-Stream Port Fuel Injectors With Different Air-Mixing Mechanisms
Authors: Zhao F.-Q. , Yoo J.-H. , Lai M.-C.
Published: February 2008

An experimental study of the spray structure from air-shrouded dual-stream injectors with different air mixing mechanisms was carried out extensively to understand the spray characteristics of dual-stream port injectors for applications to four-valve gasoline engines. The injectors were tested under both steady and transient conditions at different injection pressures and air shrouding pressure differentials. The global spray structure was visualized using the planar laser Mie scattering technique and spray atomization processes were characterized by the phase-Doppler anemometry method. The experimental results showed that spray atomization characteristics are improved markedly by the air-shrouding technique and also strongly dominated by the air-mixing mechanisms. When the air flows into the injector tip mainly from the radial direction, two streams of the spray are forced to merge together and as a result a single-stream spray is formed. When the radial velocity component of the air is reduced and the air is made to mix well with the fuel inside the injector tip, however, the two streams of the spray are well separated over different injection conditions. Moreover, other spray parameters are also modified by the air shrouded into the injector, which must be optimized in order to achieve the best performance of the air-shrouded injector.
Fast-Burn Combustion Chamber Design for Natural Gas Engines
Authors: Evans R. L. , Blaszczyk J.
Published: February 2008

The work presented in this paper compares the performance and emissions of the UBC “Squish-Jet” fast-burn combustion chamber with a baseline bowl-in-piston (BIP) chamber. It was found that the increased turbulence generated in the fastburn combustion chambers resulted in 5 to 10 percent faster burning of the air–fuel mixture compared to a conventional BIP chamber. The faster burning was particularly noticeable when operating with lean air–fuel mixtures. The study was conducted at a 1.7 mm clearance height and 10.2:1 compression ratio. Measurements were made over a range of air–fuel ratios from stoichiometric to the lean limit. At each operating point all engine performance parameters, and emissions of nitrogen oxides, unburned hydrocarbons, and carbon monoxide were recorded. At selected operating points a record of cylinder pressure was obtained and analyzed off-line to determine mass-burn rate in the combustion chamber. Two piston designs were tested at wide-open throttle conditions and 2000 rpm to determine the influence of piston geometry on the performance and emissions parameters. The UBC squish-jet combustion chamber design demonstrates significantly better performance parameters and lower emission levels than the conventional BIP design. Mass-burn fraction calculations showed a significant reduction in the time to burn the first 10 percent of the charge, which takes approximately half of the time to burn from 10 to 90 percent of the charge.
Development of a Dry Ultra-Low NOx Double Swirler Staged Gas Turbine Combustor
Authors: Sato H. , Mori M. , Nakamura T.
Published: February 2008

This paper describes the development of an ultra-low NOx gas turbine combustor for cogeneration systems. The combustor, called a double swirler staged combustor, utilizes three-staged premixed combustion for low NOx emission. The unique feature of the combustor is its tertiary premix nozzles located downstream of the double swirler premixing nozzles around the combustor liner. Engine output is controlled by simply varying the fuel gas flow, and therefore employs no complex variable geometries for airflow control. Atmospheric combustion tests have demonstrated the superior performance of the combustor. NOx level is maintained at less than 3 ppm (O2 = 15 percent) over the range of engine output between 50 and 100 percent. Assuming the general relationship that NOx emission is proportional to the square root of operating pressure, the NOx level is estimated at less than 9 ppm (O2 = 15 percent) at the actual pressure of 0.91 MPa (abs.). Atmospheric tests have also shown high combustion efficiency; more than 99.9 percent over the range of engine output between 60 and 100 percent. Emissions of CO and UHC are maintained at 0 and 1 ppm (O2 = 15 percent), respectively, at the full engine load.
Reliability of a Conceptual Ceramic Gas Turbine Component Subjected to Static and Transient Thermomechanical Loading
Authors: DiMascio P. S. , Orenstein R. M. , Rajiyah H.
Published: February 2008

A three year program to evaluate the feasibility of using monolithic silicon nitride ceramic components in gas turbines was conducted. The use of ceramic materials may enable design of turbine components which operate at higher gas temperatures and/or require less cooling air than their metal counterparts. The feasibility evaluation consisted of the following three tasks: (1) expand the materials properties database for candidate silicon nitride materials; (2) demonstrate the ability to predict ceramic reliability and life using a conceptual component model; and (3) evaluate the effect of proof testing on conceptual component reliability. The overall feasibility goal was to determine whether established life and reliability targets could be satisfied for the conceptual ceramic component having properties of an available material. Fast and delayed fracture reliability models were developed and validated via thermal shock and tensile experiments. A creep model was developed using tensile creep data. The effect of oxidation was empirically evaluated using four-point flexure samples exposed to flowing natural gas combustion products. The reliability and life-limiting failure mechanisms were characterized in terms of temperatures, stress, and probability of component failure. Conservative limits for design of silicon nitride gas turbine components were established.
Biomass Gasification for Gas Turbine-Based Power Generation
Authors: Paisley M. A. , Anson D.
Published: February 2008

The Biomass Power Program of the US Department of Energy (DOE) has as a major goal the development of cost-competitive technologies for the production of power from renewable biomass crops. The gasification of biomass provides the potential to meet this goal by efficiently and economically producing a renewable source of a clean gaseous fuel suitable for use in high-efficiency gas turbines. This paper discusses the development and first commercial demonstration of the Battelle high-throughput gasification process for power generation systems. Projected process economics are presented along with a description of current experimental operations coupling a gas turbine power generation system to the research scale gasifier and the process scaleup activities in Burlington, Vermont.
Aerodynamically Induced Radial Forces in a Centrifugal Gas Compressor: Part 1—Experimental Measurement
Authors: Moore J. J. , Flathers M. B.
Published: February 2008

Net radial loading arising from asymmetric pressure fields in the volutes of centrifugal pumps during off-design operation is well known and has been studied extensively. In order to achieve a marked improvement in overall efficiency in centrifugal gas compressors, vaneless volute diffusers are matched to specific impellers to yield improved performance over a wide application envelope. As observed in centrifugal pumps, nonuniform pressure distributions that develop during operation above and below the design flow create static radial loads on the rotor. In order to characterize these radial forces, a novel experimental measurement and post-processing techniquesis employed that yields both the magnitude and direction of the load by measuring the shaft centerline locus in the tilt-pad bearings. The method is applicable to any turbomachinery operating on fluid film radial bearings equipped with proximity probes. The forces are found to be a maximum near surge and increase with higher pressures and speeds. The results are nondimensionalized, allowing the radial loading for different operating conditions to be predicted.
Effect of Fuel Moisture Content on Biomass-IGCC Performance
Authors: Hughes W. E. M. , Larson E. D.
Published: February 2008

The moisture level in biomass fuels potentially impacts efficiency in conversion to power. This paper examines the efficiency and net power output of a fluidized bed gasifier-combined cycle with flue gas drying for a range of as-received raw biomass moisture contents and levels of pregusification drying. Due to the lack of empirical data available, a modeling approach is used to simulate the effect of varying moisture content in the gasifier feed biomass. For a specified as-received biomass moisture content, drying prior to gasification increases overall efficiency, but the gains in efficiency decrease with increasing levels of drying. For a specified post-dryer gasifier feed moisture content, cycle efficiency and power output increase with decreasing as-received biomass moisture down to 30 percent, below which the change in cycle performance is negligible.
Effect of Pressure on Emission Characteristics in LBG-Fueled 1500°C-Class Gas Turbine
Authors: Hasegawa T. , Sato M. , Ninomiya T.
Published: February 2008

Developing integrated coal gasification combined cycle (IGCC) systems ensures cost-effective and environmentally sound options for supplying future power generation needs. In order to enhance thermal efficiency of IGCC and to reduce NOx emission, a 1500°C-class gas turbine combustor for IGCC was designed, tested, and the performance of the combustor was evaluated under pressurized conditions. The designed combustor had the following three characteristics: (1) in order to assure the stable combustion burning low-Btu gas (LBG), an auxiliary combustion chamber was installed at the entrance of the combustor; (2) to reduce fuel NOx emission that was produced from the ammonia (NH3) in the fuel, the rich-lean combustion method was introduced; and (3) to compensate for the declined cooling-air associated with the higher temperature of the gas turbine, the tested combustor was equipped with a dual-structure transition piece so that the cooling air in the transition piece can be recycled to cool down the combustor liner wall. As a result of combustor tests, it is confirmed that CO emission is less than 20 ppm, the conversion rate of NH3 which contains about 1000 ppm in the coal gasified fuel to NOx shows 40 percent or below, and the liner wall temperature remained below almost 850°C under high pressure (1.4 MPa), rated load condition.
Aspects of Jet Fuel Oxidation
Authors: Zabarnick S. , Whitacre S. D.
Published: February 2008

A quartz crystal microbalance (QCM)/Parr bomb system with a headspace oxygen sensor is used to measure oxidation and deposition during thermal oxidative stressing of jet fuel. The advantages of the oxygen sensor technique in monitoring fuel oxidation is demonstrated. Simultaneous measurement of deposition using the QCM shows a strong correlation between oxidation and deposition in jet fuels. Studies performed over the temperature range 140 to 180°C show that surface deposition peaks at an intermediate temperature, while bulk deposition increases with temperature. In studies of jet fuel antioxidants, we find that rapid increases in oxidation rate occur upon consumption of the antioxidant. The antioxidant appears to be consumed by reaction with alkylperoxy radicals. In studies of metal deactivator (MDA) additives, we find that MDA is consumed during thermal stressing, and this consumption results in large increases in the oxidation rate of metal containing fuels. Mechanisms of MDA consumption are hypothesized.
Dual Brayton Cycle Gas Turbine Pressurized Fluidized Bed Combustion Power Plant Concept
Authors: Yan X. L. , Lidsky L. M.
Published: February 2008

High generating efficiency has compelling economic and environmental benefits for electric power plants. There are particular incentives to develop more efficient and cleaner coal-fired power plants in order to permit use of the world’s most abundant and secure energy source. This paper presents a newly conceived power plant design, the Dual Brayton Cycle Gas Turbine PFBC, that yields 45 percent net generating efficiency and fires on a wide range of fuels with minimum pollution, of which coal is a particularly intriguing target for its first application. The DBC-GT design allows power plants based on the state-of-the-art PFBC technology to achieve substantially higher generating efficiencies, while simultaneously providing modern gas turbine and related heat exchanger technologies access to the large coal power generation market.
Coating Life Prediction Under Cyclic Oxidation Conditions
Authors: Chan K. S. , Cheruvu N. S. , Leverant G. R.
Published: February 2008

The hot gas path section components of land based turbines require materials with superior mechanical properties and good hot corrosion and oxidation resistance. These components are generally coated with either a diffusion coating (aluminide or platinum aluminide) or with an overlay coating (MCrAlY) to provide additional hot corrosion and/or oxidation protection. These coatings degrade due to inward and outward diffusion of elements during service. Outward diffusion of aluminum results in formation of a protective oxide layer on the surface. When the protective oxide spalls, Aluminum in the coating diffuses out to reform the oxide layer. Accelerated oxidation and failure of coating occur when the Al content in the coating is insufficient to reform a continuous alumina film. This paper describes development of a coating life predictions model that accounts for both oxidation and oxide spallation under thermal mechanical loading as well as diffusion of elements that dictate the end of useful life. Cyclic oxidation data for aluminide and platinum aluminide coatings were generated to determine model constants. Applications of this model for predicting cyclic oxidation life of coated materials are demonstrated. Work is underway to develop additional material data and to qualify the model for determining actual blade and vane coating refurbishment intervals.
Industrial Gas Turbine Performance Uprates: Tips, Tricks, and Traps
Authors: Ragland T. L.
Published: February 2008

After industrial gas turbines have been in production for some amount of time, there is often an opportunity to improve or uprate the engine’s output power, cycle efficiency, or both. Typically, the manufacturer would like to provide these uprates without compromising the proven reliability and durability of the product. Further, the manufacturer would like the development of this uprate to be low cost, low risk, and result in an improvement in customer value over that of the original design. This Paper describes several options available for enhancing the performance of an existing industrial gas turbine engine, and discusses the implications for each option. Advantages and disadvantages of each option are given along with considerations that should be taken into account in selecting one option over another. Specific options discussed include dimensional scaling, improving component efficiencies, increasing massflow compressor zero staging, increasing firing temperature (thermal uprate), adding a recuperator, increasing cycle pressure ratio, and converting to a single shaft design. The implications on output power, cycle efficiency, off-design performance engine life or time between overhaul (TBO), engine cost, development time and cost, auxiliary requirements, and product support issues are discussed. Several examples are provided where these options have been successfully implemented in industrial gas turbine engines.
Time-Dependent Crack Initiation and Growth in Ceramic Matrix Composites
Authors: Begley M. R. , Cox B. N. , McMeeking R. M.
Published: February 2008

Matrix cracking in ceramic matrix composites with fine grained fibers at high temperatures will be governed by fiber creep, as relaxation of the fibers eliminates crack tip shielding. Using a time dependent bridging law that describes the effect of creeping fibers bridging a crack in an elastic matrix, crack growth initiation and history have been modeled. For a stationary crack, crack tip stress intensity factors as a function of time are presented to predict incubation times before subcritical crack growth. Two crack growth studies are reviewed: a constant velocity approximation for small-scale bridging, and a complete velocity history analysis which can be used to predict crack length as a function of time. The predictions are summarized and discussed in terms of identifying various regimes of crack growth initiation, subcritical growth, and catastrophic matrix cracking.
Ceramic Coating Edge Failure Due to Thermal Expansion Interference
Authors: Nied H. A.
Published: February 2008

An investigation of thermal barrier coatings on a metal substrate was conducted when the assembly was subjected to both thermal heating and mechanical edge loads generated by interference in adjoining expansion gaps. Both finite element and closed form solution models were developed and compared. The results of the analyses predict that the application of both thermal and mechanical edge loads on the edge of ceramic/metal composites can produce severe local edge spallation in the ceramic coating when an inadequate expansion gap is provided.
Use of an Expert System to Study the Effect of Steam Parameters on the Size and Configuration of Circulating Fluidized Bed Boilers
Authors: LaFanechere L. , Basu P. , Jestin L.
Published: February 2008

CFBCAD©, an Expert system developed jointly by the authors, is used to investigate into the effect of steam parameters on the size and configuration of circulating fluidized bed (CFB) boilers. Resulting data would assist designers and users to appreciate the influence of steam cycle parameters on the overall design of CFB boilers. The paper studies the effect of different steam cycles ranging from small capacity, low pressure boilers without reheat, to large capacity, high pressure reheat boilers. The drum pressure exerts an important influence on the area as well as the configuration of heating surfaces. The temperature difference between the flue gas and the feed water inlet temperature has an optimum value for minimum heat transfer surface requirement.
A Parametric Starting Study of an Axial-Centrifugal Gas Turbine Engine Using a One-Dimensional Dynamic Engine Model and Comparisons to Experimental Results: Part I—Model Development and Facility Description
Authors: Owen A. K. , Daugherty A. , Garrard D. , Reynolds H. C. , Wright R. D.
Published: February 2008

A generic one-dimensional gas turbine engine model, development at the Arnold Engineering Development Center, has been configured to represent the gas generator of a General Electric axial-centrifugal gas turbine engine in the six kg/sec airflow class. The model was calibrated against experimental test results for a variety of initial conditions to insure that the model accurately represented the engine over the range of test conditions of interest. These conditions included both assisted (with a starter motor) and unassisted (altitude windmill) starts. The model was then exercised to study a variety of engine configuration modifications designed to improve its starting characteristics, and, thus, quantify potential starting improvements for the next generation of gas turbine engines. This paper discusses the model development and describes the test facilities used to obtain the calibration data. The test matrix for the ground level testing is also presented. A companion paper presents the model calibration results and the results of the trade-off study.
Acoustic Sensitivities of Lean-Premixed Fuel Injectors in a Single Nozzle Rig
Authors: Kendrick D. W. , Anderson T. J. , Sowa W. A. , Snyder T. S.
Published: February 2008

An experimental and numerical investigation into the attenuation of combustion induced pressure oscillations in a single nozzle rig was undertaken at the United Technologies Research Center. Results from these investigations indicated a high combustor exit Mach number, similar to that used in a gas turbine engine, was required to correctly simulate the combustor dynamics and evaluate acoustic characteristics of lean premixed fuel injectors. Comparisons made between aerodynamically stabilized and bluff-body stabilized nozzles and the use of premixed and diffusion pilots showed that small levels of diffusion piloting behind a bluff-body yielded the best acoustic/emission performance. Their success is due to increased flame stabilization (superior anchoring ability), which reduced flame motion and thermal/acoustic coupling. For cases where diffusion piloting was not present, both designs exhibited similar dynamical behavior. Increases in the combustor exit Mach number and reductions in the inlet air temperature were shown to degrade acoustic performance of both nozzle designs. The bluff-body configuration with small levels of diffusion piloting, however, was found to be less sensitive to these changes when compared to its aerodynamic counterpart.
Dynamic Behavior of Geared Rotors
Authors: Shiau T. N. , Rao J. S. , Chang J. R. , Choi S.-T.
Published: February 2008

This paper is concerned with the dynamic behavior of geared rotor systems supported by squeeze film dampers, wherein coupled bending torsion vibrations occur. Considering the imbalance forces and gravity, it is shown that geared rotors exhibit chaotic behavior due to nonlinearity of damper forces. The route to chaos in such systems is established. In geared rotor systems, it is shown that torsional excitation can induce lateral vibrations. It is shown that squeeze film dampers can suppress large amplitudes of whirl arising out of torsional excitation.
Past Experiences With Automotive External Combustion Engines
Authors: Amann C. A.
Published: February 2008

GMR (General Motors Research Laboratories, now GM R&D Center) has a history of improving the internal combustion engine, especially as it relates to automotive use. During the quarter century from 1950–75, considerable effort was devoted to evaluating alternative powerplants based on thermodynamic cycles different from those on which the established spark-ignition and diesel engines are founded. Two of these, the steam engine and the Stirling engine, incorporated external combustion. Research on those two alternatives is reviewed. Both were judged to fall short of current needs for commercial success as prime movers for conventional automotive vehicles.
Mixing of Multiple Jets With a Confined Subsonic Crossflow: Part II—Opposed Rows of Orifices in Rectangular Ducts
Authors: Holdeman J. D. , Liscinsky D. S. , Bain D. B.
Published: February 2008

This paper summarizes experimental and computational results on the mixing of opposed rows of jets with a confined subsonic crossflow in rectangular ducts. The studies from which these results were excerpted investigated flow and geometric variations typical of the complex three-dimensional flowfield in the combustion chambers in gas turbine engines. The principal observation was that the momentum-flux ratio, J, and the orifice spacing, S/H, were the most significant flow and geometric variables. Jet penetration was critical, and penetration decreased as either momentum-flux ratio or orifice spacing decreased. It also appeared that jet penetration remained similar with variations in orifice size, shape, spacing, and momentum-flux ratio when the orifice spacing was inversely proportional to the square-root of the momentum-flux ratio. It was also seen that planar averages must be considered in context with the distributions. Note also that the mass-flow ratios and the orifices investigated were often very large (jet-to-mainstream mass-flow ratio > 1 and the ratio of orifices-area-to-mainstream-cross-sectional-area up to 0.5, respectively), and the axial planes of interest were often just downstream of the orifice trailing edge. Three-dimensional flow was a key part of efficient mixing and was observed for all configurations.
Ceramic Stationary Gas Turbine Development Program—Fifth Annual Summary
Authors: Price J. R. , Jimenez O. , Faulder L. , Edwards B. , Parthasarathy V.
Published: February 2008

A program is being performed under the sponsorship of the United States Department of Energy, Office of Industrial Technologies, to improve the performance of stationary gas turbines in cogeneration through the selective replacement of metallic hot section components with ceramic parts. The program focuses on design, fabrication, and testing of ceramic components, generating a materials properties data base, and applying life prediction and nondestructive evaluation (NDE). The development program is being performed by a team led by Solar Turbines Incorporated, and which includes suppliers of ceramic components, U.S. research laboratories, and an industrial cogeneration end user. The Solar Centaur 50S engine was selected for the development program. The program goals included an increase in the turbine rotor inlet temperature (TRIT) from 1010°C (1850°F) to 1121°C (2050°F), accompanied by increases in thermal efficiency and output power. The performance improvements are attributable to the increase in TRIT and the reduction in cooling air requirements for the ceramic parts. The ceramic liners are also expected to lower the emissions of NOx and CO. Under the program uncooled ceramic blades and nozzles have been inserted for currently cooled metal components in the first stage of the gas producer turbine. The louvre-cooled metal combustor liners have been replaced with uncooled continuous-fiber reinforced ceramic composite (CFCC) liners. Modifications have been made to the engine hot section to accommodate the ceramic parts. To date, all first generation designs have been completed. Ceramic components have been fabricated, and are being tested in rigs and in the Centaur 50S engine. Field testing at an industrial co-generation site was started in May, 1997. This paper will provide an update of the development work and details of engine testing of ceramic components under the program.
High Temperature Silicon Integrated Circuits and Passive Components for Commercial and Military Applications
Authors: Grzybowski R. R. , Gingrich B.
Published: February 2008

Advances in silicon-on-insulator (SOI) integrated circuit technology and the steady development of wider band gap semiconductors like silicon carbide are enabling the practical deployment of high temperature electronics. High temperature civilian and military electronics applications include distributed controls for aircraft, automotive electronics, electric vehicles and instrumentation for geothermal wells, oil well logging, and nuclear reactors. While integrated circuits are key to the realization of complete high temperature electronic systems, passive components including resistors, capacitors, magnetics, and crystals are also required. This paper will present characterization data obtained from a number of silicon high temperature integrated evaluated over a range of elevated temperatures and aged at a selected high temperature. This paper will also present a representative cross section of high temperature passive component characterization data for device types needed by many applications. Device types represented will include both small signal and power resistors and capacitors. Specific problems encountered with the employment of these devices in harsh environments will be discussed for each family of components. The goal in presenting this information is to demonstrate the viability of a significant number of commercially available silicon integrated circuits and passive components that operate at elevated temperatures as well as to encourage component suppliers to continue to optimize a selection of their product offerings for operation at higher temperatures. In addition, systems designers will be encouraged to view this information with an eye towards the conception and implementation of reliable and affordable high temperature systems.
Nonlinear Model Predictive Control of a Laboratory Gas Turbine Installation
Authors: Vroemen B. G. , van Essen H. A. , van Steenhoven A. A. , Kok J. J.
Published: February 2008

The feasibility of model predictive control (MPC) applied to a laboratory gas turbine installation is investigated. MPC explicitly incorporates (input and output) constraints in its optimizations, which explains the choice for this computationally demanding control strategy. Strong nonlinearities, displayed by the gas turbine installation, cannot always be handled adequately by standard linear MPC. Therefore, we resort to nonlinear methods, based on successive linearization and nonlinear prediction as well as the combination of these. We implement these methods, using a nonlinear model of the installation, and compare them to linear MPC. It is shown that controller performance can be improved, without increasing controller execution-time excessively.
Off-Design Performance of Various Gas-Turbine Cycle and Shaft Configurations
Authors: Korakianitis T. , Svensson K.
Published: February 2008

The design-point performance of various gas turbine cycles such as simple, regenerative, and intercooled-regenerative, is well understood. It is also understood that more elaborate shaft arrangements such as one, two, or three concentric or nonconcentric shafts, and a separate power turbine shaft, provide better starting and operational flexibility, and wider plateaus of high off-design performance. However, the types of different off-design performance one can obtain with these different shaft arrangements has not been previously reported. In this paper we use a computer program to investigate the design-point and off-design-point performance of engines with the following: one single shaft joining the compressor, turbine and load; one shaft joining compressor and turbine, and one shaft for the power turbine; two shafts for compressor and turbine, and one shaft for the power turbine; and three shafts joining the compressor and turbine, and one shaft for the power turbine. This is done by specifying typical compressor and turbine maps, and computing various aspects of off-design performance. The advantages and disadvantages of the various arrangements are investigated and discussed.
Aerodynamically Induced Radial Forces in a Centrifugal Gas Compressor: Part 2—Computational Investigation
Authors: Flathers M. B. , Bache´ G. E.
Published: February 2008

Radial loads and direction of a centrifugal gas compressor containing a high specific speed mixed flow impeller and a single tongue volute were determined both experimentally and computationally at both design and off-design conditions. The experimental methodology was developed in conjunction with a traditional ASME PTC-10 closed-loop test to determine radial load and direction. The experimental study is detailed in Part 1 of this paper (Moore and Flathers, 1998). The computational method employs a commercially available, fully three-dimensional viscous code to analyze the impeller and the volute interaction. An uncoupled scheme was initially used where the impeller and volute were analyzed as separate models using a common vaneless diffuser geometry. The two calculations were then repeated until the boundary conditions at a chosen location in the common vaneless diffuser were nearly the same. Subsequently, a coupled scheme was used where the entire stage geometry was analyzed in one calculation, thus eliminating the need for manual iteration of the two independent calculations. In addition to radial load and direction information, this computational procedure also provided aerodynamic stage performance. The effect of impeller front face and rear face cavities was also quantified. The paper will discuss computational procedures, including grid generation and boundary conditions, as well as comparisons of the various computational schemes to experiment. The results of this study will show the limitations and benefits of Computational Fluid Dynamics (CFD) for determination of radial load, direction, and aerodynamic stage performance.