bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation of the Effects of Flue Gas Injection on Natural Draft Cooling Tower Performance
Authors: Eldredge T. V. , Benton D. J. , Hodgson J. W.
Published: February 2008

This paper addresses an investigation of flue gas injection on natural draft cooling tower performance through numerical simulation. The control volume finite difference method was used for discretizing the governing equations in axisymmetric form on a boundary-fitted grid. The five independent variables addressed in this study are flue gas flow rate, flue gas temperature, radial injection location, injection orientation, and liquid entrainment in the flue gas. The flue gas temperature was found to have the most significant effect on tower performance (cold water temperature), because it strongly affects the buoyancy within the tower. The total air flow through a tower is driven by buoyancy forces, and the cooling performance is a strong function of the airflow rate.
Development of a Combustor Liner Composed of Ceramic Matrix Composite (CMC)
Authors: Nishio K. , Igashira K.-I. , Take K. , Suemitsu T.
Published: February 2008

The Research Institute of Advanced Materials Gas-Generator (AMG), which is a joint effort by the Japan Key Technology Center and 14 firms in Japan, has, since fiscal year 1992, been conducting technological studies on an innovative gas generator that will use 20 percent less fuel, weigh 50 percent less, and emit 70 percent less NOx than the conventional gas generator through the use of advanced materials. Within this project, there is an R&D program for applying ceramic matrix composite (CMC) liners to the combustor, which is a major component of the gas generator. In the course of R&D, continuous SiC fiber-reinforced SiC composite (SiCF/SiC) was selected as the most suitable CMC for the combustor liner because of its thermal stability and formability. An evaluation of the applicability of the SiCF/SiC composite to the combustor liner on the basis of an evaluation of its mechanical properties and stress analysis of a SiCF/SiC combustor liner was carried out, and trial SiCF/SiC combustor liners, the largest of which was 500-mm in diameter, were fabricated by the filament winding and PIP (polymer impregnation and pyrolysis) method. Using a SiCF/SiC liner built to the actual dimensions, a noncooling combustion test was carried out and even when the gas temperature was raised to 1873K at outlet of the liner, no damage was observed after the test. Through our studies we have confirmed the applicability of the selected SiCF/SiC composite as a combustor liner. In this paper, we describe the present state of the R&D of a CMC combustor liner.
A Quasi-Two-Dimensional Method for the Rotordynamic Analysis of Centered Labyrinth Liquid Seals
Authors: Arghir M. , Freˆne J.
Published: February 2008

The work presents a method for analyzing the dynamic regime of labyrinth liquid seals. By using the traditional simplifying assumptions for the centered seal (sinusoidal, harmonically varying, first order dynamic perturbation), the approach can be addressed as “quasi” two-dimensional. A numerical coordinate transformation capable to treat displacement perturbations is introduced. The first order mathematical model is then deduced following the same steps as in a previously published work (Arghir and Freˆne, 1997b). From this standpoint, the present method can be regarded as an extension of the above mentioned approach which was able to deal only with stator-grooved seals. The method is validated by comparisons with Nordmann and Dietzen’s (1988) theoretical results for a seal with grooves on both stator and rotor and with the experimental results of Staubli’s (1993) test case concerning a general seal.
Experimental Rotordynamic Coefficient Results for (a) a Labyrinth Seal With and Without Shunt Injection and (b) a Honeycomb Seal
Authors: Soto E. A. , Childs D. W.
Published: February 2008

Centrifugal compressors are increasingly required to operate at higher pressures, speeds, and fluid density. In these conditions, compressors are susceptible to rotordynamic instabilities. To remedy this situation, labyrinth seals have sometimes been modified by using shunt injection. In shunt injection, the gas is taken from the diffuser or discharge volute and injected into an upstream chamber of the balance-piston labyrinth seal. The injection direction can be radial or against rotation. This study contains the first measured rotordynamic data for labyrinth seals with shunt injection. A comparison has been made between conventional labyrinth seals, labyrinth seals with shunt injection (radial and against rotation), and a honeycomb seal. Labyrinth seals with injection against rotation are better able to control rotordynamic instabilities than labyrinth seals with radial injection; however, the leakage is slightly higher. The leakage comparison for all seals demonstrates that the honeycomb seal has the best flow control. Test data are presented for a top rotor surface velocity of 110 m/sec, a supply pressure of 13.7 bars, and IPr = 0.95 (injection pressure is 1.05 = 1/0.95 times the seal inlet pressure). For these conditions, and considering effective damping, the labyrinth seal with injection against rotation is better than the honeycomb seal when the pressure ratio across the seal PR < 0.45. On the other hand, the honeycomb seal is better when PR > 0.45. The effectiveness of the shunt-injection against rotation in developing effective damping is reduced with increasing rotor surface velocity.
High Temperature Proximity Measurement in Aero and Industrial Turbomachinery
Authors: Sheard A. G. , O’Donnell S. G. , Stringfellow J. F.
Published: February 2008

The measurement of disc and shaft displacement has been performed for many years as part of the development, commissioning and monitoring of all classes of turbomachinery. This measurement has traditionally been performed using sensors that cannot operate above the curie point of rare earth magnets. In this paper a programme of work is described that was undertaken to develop a measurement system that could make a measurement of target proximity in a high temperature environment. The specific objectives were to make possible the measurement of turbine disc axial movement and shaft motion in the engine core, close to the combustion chamber or turbine; and secondly to make possible the measurement of tip clearance over shrouded turbine rotors.
Elevated-Temperature “Ultra” Fast Fracture Strength of Advanced Ceramics: An Approach to Elevated-Temperature “Inert” Strength
Authors: Choi S. R. , Gyekenyesi J. P.
Published: February 2008

The determination of “ultra” fast fracture strengths of five silicon nitride ceramics at elevated temperatures has been made by using constant stress-rate (“dynamic fatigue”) testing with a series of “ultra” fast test rates. The test materials included four monolithic and one SiC whisker-reinforced composite silicon nitrides. Of the five test materials, four silicon nitrides exhibited the elevated-temperature strengths that approached their respective room-temperature strengths at an “ultra” fast test rate of 3.3 × 104 MPa/s. This implies that slow crack growth responsible for elevated-temperature failure can be eliminated or minimized by using the “ultra” fast test rate. These ongoing experimental results have shed light on laying a theoretical and practical foundation on the concept and definition of elevated-temperature “inert” strength behavior of advanced ceramics.
A Numerical Analysis of the Emissions Characteristics of Biodiesel Blended Fuels
Authors: Choi C. Y. , Reitz R. D.
Published: February 2008

Computer simulations were conducted to study the combined effects of methyl soyate (biodiesel) blends with no. 2 diesel fuel on diesel engine (D.I.) performance. Diesel engine emissions and heat release rates were some of the parameters studied. The results from the computer simulations were compared against previously published results (Choi et al., 1997) from engine tests conducted on a single cylinder version of the Caterpillar 3400 series heavy duty diesel engine. The experiments and simulations were performed over a range of injection timings allowing particulate versus NOx trade-off curves to be a generated. Phillips 66 certified no. 2 diesel fuel was used as the baseline; mixtures of 20 percent and 40 percent by volume of methyl soyate with the baseline no. 2 diesel fuel were used as the biodiesel blends. The multidimensional KIVA-II code (ERC version 2.4) was used to better understand the factors controlling the formation of NOx and soot. KIVA-II modeled the high load, single injection combustion of the baseline #2 diesel fuel and the biodiesel blends. The code was changed to account for different fuel effects and the computational results were then compared against the experimental data. It is concluded that the increased NOx observed with the use of biodiesel fuels (in spite of their lower heats of combustion) is due to increased local temperatures as a result of enhanced fuel/air mixing and increased spray penetration. The increased spray penetration results from the higher fuel viscosity of the biodiesel blended fuels which leads to reduced injection durations.
Final Report on the Development of a Hydrogen-Fueled Combustion Turbine Cycle for Power Generation
Authors: Bannister R. L. , Newby R. A. , Yang W. C.
Published: February 2008

Through its New Energy and Industrial Technology Development Organization (NEDO) the Japanese government is sponsoring the World Energy Network (WE-NET) Program. WE-NET is a 28-year global effort to define and implement technologies needed for hydrogen-based energy systems. A critical part of this effort is the development of a hydrogen-fueled combustion turbine system to efficiently convert the chemical energy stored in hydrogen to electricity when hydrogen is combusted with pure oxygen. A Rankine cycle, with reheat and recuperation, was selected by Westinghouse as the general reference system. Variations of this cycle have been examined to identify a reference system having maximum development feasibility, while meeting the requirement of a minimum of 70.9 percent low heating value (LHV) efficiency. The strategy applied by Westinghouse was to assess both a near-term and long-term Reference Plant. The near-term plant requires moderate development based on extrapolation of current steam and combustion turbine technology. In contrast, the long-term plant requires more extensive development for an additional high pressure reheat turbine, and is more complex than the near-term plant with closed-loop steam cooling and extractive feedwater heating. Trade-offs between efficiency benefits and development challenges of the near-term and long-term reference plant are identified. Results of this study can be applied to guide the future development activities of hydrogen-fueled combustion turbine systems.
Co-Pyrolysis of Coal/Biomass and Coal/Sewage Sludge Mixtures
Authors: Storm C. , Ru¨diger H. , Spliethoff H. , Hein K. R. G.
Published: February 2008

Biomass and sewage sludge are attracting increasing interest in power plant technology as a source of carbon-dioxide-neutral fuels. A new way to reduce the consumption of fossil fuels could be the co-combustion or co-gasification of coal and biomass or coal and sewage sludge. In both cases, pyrolysis is the first step in the technical process. In order to obtain detailed information about the pyrolysis of coal/biomass and coal/sewage sludge mixtures as well as unblended fuels, the “Institute fu¨r Verfahrenstechnik und Dampfkesselwesen (IVD)” at the University of Stuttgart has carried out investigations using an electrically heated entrained flow reactor. The test runs provided information about fuel conversion efficiency, pyrolysis gas and tar yield, and composition of pyrolysis gas and tar. Besides gas and tar analysis investigations regarding the path of trace elements, like heavy metals, alkali, chlorine and nitrogen components, during the pyrolysis process varying different parameters have been carried out. The fuel nitrogen distribution between pyrolysis gas, tar, and char has been analyzed, as well as the ash composition, and, thus, the release of mineral components during pyrolysis.
An Investigation of the Formation and Venting of Flammable Mixtures Formed Within Liquid Fuel Vessels
Authors: Bunama R. , Karim G. A. , Zhang C. Y.
Published: February 2008

The paper describes results of a parametric study obtained while using an analytical model described earlier (Bunama and Karim, 1997b) investigating the combined effects of mass, energy, and momentum transfer with variable transport and thermodynamic properties on the formation of fuel vapor-air mixtures above a stagnant liquid fuel surface within the confines, of a vertical cylindrical vessel. This was done mainly to examine the establishment of the formation of flammable mixtures and their changes in size and location with time within liquid fuel tanks that are partially empty. The effects of changes in the ambient and wall temperatures, presence of liquid on the walls and vessel geometry were considered. Moreover, the results of a corresponding experimental investigation are presented. Much of the data relates to the high volatility fuel n-pentane that represents the lighter fuel fractions in commercial fuels which through their early evaporation contribute much to the fire hazards in fuel tanks.
The Development of a Computer Code for the Estimation of Combustor Exhaust Temperature Using Simple Gas Analysis Measurements
Authors: Bideau R. J.
Published: February 2008

Advances in gas turbine technology have led to levels of turbine inlet temperature that preclude the use of thermocouple and simple gas analysis techniques for gas temperature determination. Simple gas analysis schemes rely on the measurement of a very limited range of species in the gas sample: typically, CO2, CO, and hydrocarbons (UHC). A method of estimating the other important species is required. Simple gas analysis schemes that rely only on elemental mass balance equations to determine the concentration of species are inadequate where high temperature results in significant dissociation. A method has been developed to enable temperature determination at levels that render simple schemes inaccurate. The procedure is based on the measurement of CO2, CO, UHC, and oxides of nitrogen in the exhaust gas. Other species concentrations are calculated using an assumption of partial thermodynamic equilibrium. This allows the calculation of many important combustion parameters. The method has been implemented as a computer code, with an object orientated design approach using the C++ language. The paper details the theory behind the approach and its implementation. The expected errors for practical applications are discussed and quantified. The method is illustrated by an exhaust temperature pattern factor investigation of an annular combustor. Temperatures determined by thermocouples are compared with those calculated from gas samples.
CFD Modeling of a Gas Turbine Combustor From Compressor Exit to Turbine Inlet
Authors: Crocker D. S. , Nickolaus D. , Smith C. E.
Published: February 2008

Gas turbine combustor CFD modeling has become an important combustor design tool in the past few years, but CFD models are generally limited to the flow field inside the combustor liner or the diffuser/combustor annulus region. Although strongly coupled in reality, the two regions have rarely been coupled in CFD modeling. A CFD calculation for a full model combustor from compressor diffuser exit to turbine inlet is described. The coupled model accomplishes the following two main objectives: (1) implicit description of flow splits and flow conditions for openings into the combustor liner, and (2) prediction of liner wall temperatures. Conjugate heat transfer with nonluminous gas radiation (appropriate for lean, low emission combustors) is utilized to predict wall temperatures compared to the conventional approach of predicting only near wall gas temperatures. Remaining difficult issues such as generating the grid, modeling Swirled vane passages, and modeling effusion cooling are also discussed.
Coupled Shaft-Torsion and Blade-Bending Vibrations of a Rotating Shaft–Disk–Blade Unit
Authors: Huang S. C. , Ho K. B.
Published: February 2008

A new approach to analyzing the dynamic coupling between shaft torsion and blade bending of a rotating shaft–disk–blade unit is introduced. The approach allows the shaft to vibrate freely around its rotation axis instead of assuming a periodic perturbation of the shaft speed that may accommodate the shaft flexibility only to a limited extent. A weighted residual method is applied, and the receptances at the connections of blades and shaft–disk are formulated. Numerical examples are given for cases with between two and six symmetrically arranged blades. The results show not only coupling between the shaft, disk, and blades, but also coupling between individual blades where the shaft acts as a rigid support and experiences no torsional vibration. The blade-coupling modes occurred only in repeated frequencies. Finally, the effect of shaft speed on the modal frequencies was investigated. Plots illustrating the occurrence of critical speeds and flutter instabilities are presented.
Development of a Low-Emission Combustor for a 100-kW Automotive Ceramic Gas Turbine (II)
Authors: Kumakura H. , Sasaki M. , Suzuki D. , Ichikawa H.
Published: February 2008

Performance tests were conducted on a low-emission combustor, which has a pre-vaporization–premixing lean combustion system and is designed for a 100 kW automotive ceramic gas turbine. The results of steady-state combustion tests performed at an inlet temperature of 1000–1200 K and pressure of 0.1–0.34 MPa indicate that the combustor would meet Japan’s emission standards for gasoline engine passenger cars without using an aftertreatment system. Flashback was suppressed by controlling the mixture velocity and air ratios. Strength tests conducted on rings and bars cut from the actual ceramic parts indicate that the combustor has nearly the same level of strength as standard test specimens.
SPSLIFE: A User-Friendly Approach to the Structural Design and Life Assessment of Ceramic Components
Authors: Bornemisza T. , Saith A.
Published: February 2008

In order to expedite the structural analysis of ceramic components, Sundstrand Power Systems has developed a proprietary computer code called “SPSLIFE,” which can substantially reduce the time spent on the design assessment of ceramic components. The life assessment computations for the various failure modes are performed using the structural analysis and materials files as input data. A number of “menus” are incorporated to request user input data and to guide the user through the problem definition process. The user has the capability to select existing material data files or create new ones. The computational modules are based on the analytical approaches currently used in the industry. The modular construction of the code facilitates making revisions or adding new modules. Graphic display is used to provide a visual summary of the life assessment calculations for the various failure modes. The output files generated provide a detailed review of the results, which is helpful for design optimization. Independently derived component fast fracture and static fatigue survival probabilities using the NASA CARES and CARES/LIFE codes are displayed for reference. The paper provides an application example using a patented design of a ceramic monorotor for the Sundstrand Power Systems TJ-50 small gas turbine engine.
Early Detection of Feedwater-Heater Leaks
Authors: Hansen E. , Godwin R. , Wood D. , Turner L.
Published: February 2008

This work describes a method of early detection of feedwater heater leaks. The method uses existing pressure, temperature, and flow measurements. The four leak indicators found were feedwater flow rate, drain temperature, drain cooler approach, and extraction line pressure drop. Deviations from normal operation were plotted for each of these indicators. Statistical process control was applied to these deviations. The progressive enlargement of leaks could be seen over a 10 hour period. The four indicators were shown to be good evidence of a tube leak. This method is an alternative to existing acoustic leak detection methods.
Magnetism and Stray Currents in Rotating Machinery
Authors: Nippes P. I.
Published: February 2008

The case for elimination of stray currents and magnetism in turbomachinery is being recognized as an issue to be dealt with in industries that design and operate rotating machinery. Of main concern are bearings, seals, gears, couplings, etc. Resulting problems extend from surface damage to unit crashes. It is important to recognize the symptoms, to heed the warnings, and to enact preventive and corrective measures. Recommendations are to eliminate or minimize the source, and to bond the machinery to ground, especially the shaft, with a reliable shaft brush and a qualified current monitor. Information and guidance are provided from MPS job files covering some of the 200 installations visited in the past 15 years.
A Coal-Fired Heat Exchanger for an Externally Fired Gas Turbine
Authors: Solomon P. R. , Serio M. A. , Cosgrove J. E. , Pines D. S. , Zhao Y. , Buggeln R. C. , Shamroth S. J.
Published: February 2008

Significant improvements in efficiency for electricity generation from coal can be achieved by cycles that employ a high-temperature, highly recuperative gas turbine topping cycle. The principal difficulty of employing a gas turbine in a coal-fired power generation system is the possible erosion and corrosion of the high-temperature rotating gas turbine components caused by the coal’s inorganic and organically bound constituents (ash, sulfur, and alkali metals). One route to overcome this problem is the development of an externally fired gas turbine system employing a coal fired heat exchanger. The solution discussed in this paper is the design of a Radiatively Enhanced, Aerodynamically Cleaned Heat-Exchanger (REACH-Exchanger). The REACH-Exchanger is fired by radiative and convective heat transfer from a moderately clean fuel stream and radiative heat transfer from the flame of a much larger uncleaned fuel stream, which supplies most of the heat. The approach is to utilize the best ceramic technology available for high-temperature parts of the REACH-Exchanger and to shield the high-temperature surfaces from interaction with coal minerals by employing clean combustion gases that sweep the tube surface exposed to the coal flame. This paper presents a combined experimental/computational study to assess the viability of the REACH-Exchanger concept. Experimental results indicated that the REACH-Exchanger can be effectively fired using radiation from the coal flame. Both computation and experiments indicate that the ceramic heat exchanger can be aerodynamically protected by a tertiary stream with an acceptably low flow rate.
Low-Nox Premixed Combustion of MBtu Fuels Using the ABB Double Cone Burner (EV Burner)
Authors: Do¨bbeling K. , Kno¨pfel H. P. , Polifke W. , Winkler D. , Steinbach C. , Sattelmayer T.
Published: February 2008

A novel combustion technique, based on the Double Cone Burner, has been developed and tested. NOx emissions down to very low levels are reached without the usual strong dilution of the fuel for MBtu syngases from oxygen-blown gasification of coal or residual oil. A limited amount of dilution is necessary in order to prevent ignition during the mixing of fuel and combustion air. The relevant properties of the fuel are reviewed in relation to the goal of achieving premixed combustion. The basic considerations lead to a fuel injection strategy completely different from that for natural gas. A high-speed premixing system is necessary due to the very short chemical reaction times of MBtu fuel. Fuel must be prevented from forming ignitable mixtures inside the burner for reliability reasons. A suitable fuel injection method, which can be easily added to the ABB double cone burner, is described. In common with the design of the standard EV burner, the MBtu EV burner with this fuel injection method is inherently safe against flashback. Three-dimensional flow field and combustion modeling is used to investigate the mixing patterns and the location of the reaction front. Two burner test facilities, one operating at ambient and the other at full gas turbine pressure, have been used for the evaluation of different burner designs. The full-pressure tests were carried out with the original gas turbine burner size and geometry. Combining the presented numerical predictive capabilities and the experimental test facilities, burner performance can be reliably assessed for a wide range of MBtu and LBtu fuels (residue oil gasification, waste gasification, coal gasification, etc.). The atmospheric tests of the burner show NOx values below 2 ppm at an equivalence ratio equal to full-load gas turbine operation. The NOx increase with pressure was found to be very high. Nevertheless, NOx levels of 25 vppmd (@ 15 percent O2) have been measured at full gas turbine pressure. Implemented into ABB’s recently introduced gas turbine GT13E2, the new combustion technique will allow a more straightforward IGCC plant configuration without air extraction from the gas turbine to be used.
Residual Reactivity of Burned Gases in the Early Expansion Process of Future Gas Turbines
Authors: Leide B. , Stouffs P.
Published: February 2008

The present study investigates the chemical evolution of the burned gases in a first-stage nozzle operated under high inlet temperature and pressure conditions as they are foreseen for next-generation high-efficiency gas turbine machinery. Coupled aerothermochemical simulations are performed up to the extreme case of stoichiometric combustion without ulterior dilution. The intent is to provide an estimation of possible consequences arising from the residual reactivity of gases downstream from the combustor. These consequences might affect the future design of the expansion path in order to render nonstationary chemistry compatible with aerodynamics, energetics, and environmental aspects.
Flow Behavior With an Oscillating Motion of the Impinging Jet in a Dump Diffuser Combustor
Authors: Honami S. , Shizawa T. , Sato A. , Ogata H.
Published: February 2008

This paper presents flow behavior with an oscillating motion of an impinging jet upon a flame dome head and its reattachment to the casing wall, when a distorted flow is provided at the inlet of the dump diffuser combustor. A Laser-Doppler Velocimeter was used for the measurements of the time-averaged flow within a sudden expansion region. A surface pressure fluctuation survey on the flame dome head and flow visualization by a smoke wire technique with a high-speed video camera were conducted from the viewpoint of the unsteady flow features of the impinging jet. There exists a high-vorticity region at the jet boundary, resulting in the production of turbulence kinetic energy. In particular, higher vorticity is observed in the higher velocity side of the jet. The jet near the dome head has favorable characteristics about the flow rate distribution into the branched channel. Reynolds shear stress and turbulence energy are produced near the reattachment region. The jet has an oscillating motion near the dome head with asymmetric vortex formation at the jet boundary.
Studies of Lean Blowout in a Step Swirl Combustor
Authors: Durbin M. D. , Ballal D. R.
Published: February 2008

The design requirements of a modern gas turbine combustor are increasingly dictated by wide stability limits, short flame length, and uniform mixing. To achieve the best trade-off between these three factors, flame characteristics (length, shape, mixedness), lean blowout (LBO), and optimum combustor configuration should be investigated over a wide range of inner and outer air velocities, inner and outer vane angles, and co- versus counterswirl arrangements. Such an investigation was performed in a step swirl combustor (SSC) designed to simulate the fuel–air mixing pattern in a gas turbine combustor dome fitted with an airblast atomizer. It was found that an increase in the outer vane angle and a decrease in inner air velocity decreased the flame length. LBO was improved when outer flow swirl intensity was increased. An optimum hardware and velocity configuration for the SSC was found for inner swirl = 45 deg, outer swirl = 60 deg, coswirl direction, and inner air velocity = outer air velocity = 16 m/s. This optimum SSC configuration yielded: (i) low values of LBO, (ii) short flame length, (iii) uniformly mixed stable flame, and (iv) little or no variation in these characteristics over the range of operation of SSC. Finally, the co- versus counterswirl arrangements and the operation of the optimized combustor configuration are discussed.
Reducing Gas Turbine Emissions Through Hydrogen-Enhanced, Steam-Injected Combustion
Authors: Maughan J. R. , Bowen J. H. , Cooke D. H. , Tuzson J. J.
Published: February 2008

The Potential for reducing emissions from gas turbines by injecting steam for Nox control and hydrogen for Co control is evaluated through laboratory-scale combustion experiments. Results showed that hydrogen addition into a steam-injected diffusion combustor at hydrogen/fuel molar ratios of approximately 20 percent was associated with somewhat increased NOx production and reduced CO emissions. Both effects are attributed to an increase in the local stoichiometric flame temperature. However, the decrease in CO was greater than the increase in NOx, resulting in a net emissions benefit, or a shifting of the NOx–CO curve toward the origin. Consequently, a greater range of NOx/CO emissions targets could be achieved when hydrogen was available. Additional experiments on premixed systems with hydrogen injection showed a significant increase in operability. Cost estimates for producing hydrogen with a conventional fired steam reformer suggested high capital costs unless ample steam, is already available. Hence, the technology is particularly well suited for turbines that use steam for power augmentation. Alternate reforming technology, such as catalytic partial oxidation, offers the potential for reduced capital costs.
Effect of Cyclic Loading on the Creep Performance of Silicon Nitride
Authors: Wereszczak A. A. , Ferber M. K. , Kirkland T. P. , Lin C.-K. J.
Published: February 2008

Tension–tension cyclic fatigue tests (triangular waveform, σmax = 100 MPa, R = 0.1) were conducted on hot isostatically pressed (HIPed) silicon nitride at frequencies spanning several orders of magnitude (5.6 × 10−6 to 0.1 Hz or 10−3 MPa/s to 18 MPa/s) at 1370°C in air. The amount of cyclic creep strain was found to be a function of the frequency or stressing rate, with greater strains to failure observed as the frequency or stressing rate decreased. The total strain was viewed as the sum of elastic, anelastic (or transient recoverable), and plastic (viscous or nonrecoverable) strain contributions, after the empirical Pao and Marin model. The plastic strain was found to be the dominant component of the total creep and was unsatisfactorily represented by the Pao and Marin model. To circumvent this, a time exponent was introduced in the plastic strain term in the Pao and Marin model. This modification resulted in good correlation between model and experiment at the slower frequencies examined but overpredicted the cyclic creep strain at the faster frequencies. The utility of using the modified Pao and Marin model to predict cyclic creep response from static creep and strain relaxation tests is described.
Jet Fuel Deposition and Oxidation: Dilution, Materials, Oxygen, and Temperature Effects
Authors: Zabarnick S. , Zelesnik P. , Grinstead R. R.
Published: February 2008

Quartz crystal microbalance (QCM) and pressure measurements are used for determination of jet fuel thermal stability in a batch reactor. The QCM is able to monitor extremely small amounts of deposition in situ, while the pressure measurements provide qualitative data on the oxidation process. The dependence of the deposition amount was monitored as a function of the oxygen availability for two fuels. Also, the effect of QCM electrode materials was investigated. Deposition and oxidation were compared for the following electrode materials: gold, aluminum, silver, and platinum. We also studied the effect of dilution on oxidation and deposition. Jet fuel was diluted with increasing amounts of hydrocarbon solvent. It was observed that this dilution procedure can help characterize a fuel’s effective antioxidant concentration. Fuel dilution is also shown to be a good technique for improving thermal stability characteristics of poor fuels. Additionally we have studied the temperature effect on deposition for two fuels over the range 140 to 180°C.
Modeling of Local Extinction in Turbulent Flames
Authors: Sloan D. G. , Sturgess G. J.
Published: February 2008

The Eddy Dissipation Concept (EDC), proposed by Magnussen (1985), advances the concept that the reactants are homogeneously mixed within the fine eddy structures of turbulence and that the fine structures may therefore be regarded as perfectly stirred reactors (PSRs). To understand more fully the extent to which such a subgrid scale stirred reactor concept could be applied within the context of a computational fluid dynamics (CFD) calculation to model local or global extinction phenomena: (1) Various kinetic mechanisms are investigated with respect to CPU penalty and predictive accuracy in comparisons with stirred reactor lean blowout (LBO) data and (2) a simplified time-scale comparison, extracted from the EDC model and applied locally in a fast-chemistry CFD computation, is evaluated with respect to its capabilities to predict attached and lifted flames. Comparisons of kinetic mechanisms with PSR lean blowout data indicate severe discrepancies in the predictions with the data and with each other. Possible explanations are delineated and discussed. Comparisons of the attached and lifted flame predictions with experimental data are presented for some benchscale burner cases. The model is only moderately successful in predicting lifted flames and fails completely in the attached flame case. Possible explanations and research avenues are reviewed and discussed.
Study of Flame Stability in a Step Swirl Combustor
Authors: Durbin M. D. , Vangsness M. D. , Ballal D. R. , Katta V. R.
Published: February 2008

A prime requirement in the design of a modern gas turbine combustor is good combustion stability, especially near lean blowout (LBO), to ensure an adequate stability margin. For an aeroengine, combustor blow-off limits are encountered during low engine speeds at high altitudes over a range of flight Mach numbers. For an industrial combustor, requirements of ultralow NOx emissions coupled with high combustion efficiency demand operation at or close to LBO. In this investigation, a step swirl combustor (SSC) was designed to reproduce the swirling flow pattern present in the vicinity of the fuel injector located in the primary zone of a gas turbine combustor. Different flame shapes, structure, and location were observed and detailed experimental measurements and numerical computations were performed. It was found that certain combinations of outer and inner swirling air flows produce multiple attached flames, aflame with a single attached structure just above the fuel injection tube, and finally for higher inner swirl velocity, the flame lifts from the fuel tube and is stabilized by the inner recirculation zone. The observed difference in LBO between co- and counterswirl configurations is primarily a function of how the flame stabilizes, i.e., attached versus lifted. A turbulent combustion model correctly predicts the attached flame location(s), development of inner recirculation zone, a dimple-shaped flame structure, the flame lift-off height, and radial profiles of mean temperature, axial velocity, and tangential velocity at different axial locations. Finally, the significance and applications of anchored and lifted flames to combustor stability and LBO in practical gas turbine combustors are discussed.
Advances in Steam Path Technology
Authors: Cofer J. I.
Published: February 2008

For many years, GE has been conducting research to understand better the loss mechanisms that degrade the aerodynamic performance of steam turbine stages, and to develop new computational fluid dynamics (CFD) computer programs to predict these losses accurately. This paper describes a number of new steam path design features that have been introduced in the GE steam turbine product line to improve turbine performance and reliability. These features include diaphragms with contoured sidewalls, advanced vortex blading with compound tangential lean, new continuously coupled last-stage buckets with improved aerodynamic efficiency and reliability, improved downward and axial flow exhaust hoods, and better steam leakage control devices. The benefits of these new features for both new units and retrofits of existing units are discussed. In addition, the paper discusses the new generation of three-dimensional viscous CFD analysis codes being used to develop new design concepts, including codes developed by GE as well as those obtained externally. Also described are the extensive laboratory test programs being conducted to validate the CFD codes and verify the predicted efficiency gains for new design features. Last, the paper describes new and unique state-of-the-art steam path design automation and optimization tools that dramatically reduce the design cycle time for new advanced aerodynamic designs.
Modeling of (Cogeneration) Power Plants on Time-Dependent Power Demands of the Consumer
Authors: Witzani M. , Pechtl P.
Published: February 2008

This paper presents a planning tool where rigorous plant performance models are used to produce accurate plant performance data reflecting real plant operation under the loads specified by load demand curves. Cumulative figures such as total fuel consumption and production efficiency serve as the basis for a subsequent detailed economic analysis. Basic inputs to the model are the energy demand curves for a specific site on a daily, hourly, or even per minute basis. The plant performance model takes into account the varying load levels, ambient conditions, fuel price, and revenues from electric power delivered off-site. The load/performance simulator calculates plant performance and basic economic parameters at each point in time of the load demand curve to exactly match the given energy demand (Fig. 1). The results are critical economic data like cumulated fuel consumption and expenses, total energy production, and overall averaged plant efficiency. The performance model delivers detailed plant performance data on an overall plant as well as component level. The results reflect real plant operation under all varying conditions, hence produce highly significant performance and economic parameters.
Air Bottoming Cycle: Use of Gas Turbine Waste Heat for Power Generation
Authors: Bolland O. , Fo̸rde M. , Ha˚nde B.
Published: February 2008

This paper presents a thermodynamic analysis of the Air Bottoming Cycle (ABC) as well as the results of a feasibility study for using the Air Bottoming Cycle for gas turbine waste heat recovery/power generation on oil/gas platforms in the North Sea. The basis for the feasibility study was to utilize the exhaust gas heat from an LM2500PE gas turbine. Installation of the ABC on both a new and an existing platform have been considered. A design reference case is presented, and the recommended ABC is a two-shaft engine with two compressor intercoolers. The compression pressure ratio was found optimal at 8:1. The combined gas turbine and ABC shaft efficiency was calculated to 46.6 percent. The LM2500PE gas turbine contributes with 36.1 percent while the ABC adds 10.5 percent points to the gas turbine efficiency. The ABC shaft power output is 6.6 MW when utilizing the waste heat of an LM2500PE gas turbine. A preliminary thermal and hydraulic design of the ABC main components (compressor, turbine, intercoolers, and recuperator) was carried out. The recuperator is the largest and heaviest component (45 tons). A weight and cost breakdown of the ABC is presented. The total weight of the ABC package was calculated to 154 metric tons, and the ABC package cost to 9.4 million US$. An economical examination for three different cases was carried out. The results show that the ABC alternative (LM2500PE + ABC) is economical, with a rather good margin, compared to the other alternatives. The conclusion is that the Air Bottoming Cycle is an economical alternative for power generation on both new platforms and on existing platforms with demand for more power.
The Installation, Testing, and Lessons Learned of the TF40B Gas Turbine Test Facility
Authors: Patterson J. S. , Harris H.
Published: February 2008

The TF40B Gas Turbine Test Facility is the only dedicated Landing Craft, Air Cushion main propulsion engine test complex available to the U.S. Navy. This facility, located at the Naval Surface Warfare Center, Carderock Division (NSWCCD) in Philadelphia, PA, began operation in August, 1992. Since then, the test engine has logged approximately 230 starts and 350 operating hours. This paper will present the installation, testing, and lessons learned of the TF40B test facility. The installation section will discuss the modifications made to the existing test facility to accept the TF40B engine. The test section will include the Foreign Object Damage (FOD) screen evaluation, both on-line and crank wash detergent fluid evaluations, cold weather fuel testing, engine vent line testing and Aerojet 5 oil evaluation. The lessons learned section will include problems related to the electric starter, waterbrake, inlet and exhaust systems, data acquisition system, instrumentation control panel, and the test cell equipment arrangement.
Experimental Leakage and Rotordynamic Results for Helically Grooved Annular Gas Seals
Authors: Childs D. W. , Gansle A. J.
Published: February 2008

Rotordynamic-coefficient and leakage test results are presented for three grooved seals with helix angles of 0, 15, and 30 deg against rotation. The seals are 50.8 mm long and 152.4 mm in diameter. Tests were done for two supply pressures (up to 17 bars), three speeds (5000, 12,000, and 16,000 rpm), four pressure ratios, and three inlet fluid prerotation conditions. The results showed that increasing the helix angle yields a progressive reduction in the cross-coupled stiffness coefficient k and a progressive increase in leakage. The helically grooved seals consistently yield negative cross-coupled stiffness coefficients for nonprerotated inlet flow; hence, k in these seals would oppose forward whirl of a rotor. Helically grooved seals become less effective at reducing k with increasing preswirl; hence, for optimum effectiveness they should be used with a swirl brake. Comparison between helically grooved and honeycomb-stator seals showed that helically grooved stators had reduced (negative) whirl-frequency ratios for nonprerotated flows but were no better than honeycomb-stator seals for elevated fluid prerotation. The 15 and 30 deg helix grooves leaked about 1.6 and 2.2 times, respectively, as much as the honeycomb-stator seals.
Application of Advanced Probabilistic Fracture Mechanics to Life Evaluation of Turbine Rotor Blade Attachments
Authors: Millwater H. R. , Wu Y.-T. , Cardinal J. W. , Chell G. G.
Published: February 2008

This paper describes the application of an advanced probabilistic fracture mechanics computational algorithm with inspection simulation to the probabilistic life assessment of a turbine blade attachment, sometimes referred to as a steeple or fir tree. The life of the steeple is limited by high cycle fatigue. The methodology utilized combines structural finite element analysis, stochastic fatigue crack growth, and crack inspection and repair. The resulting information provides the engineer with an assessment of the probability of failure of the structure as a function of operating time and the effect of the inspection procedure. This information can form the basis of inspection planning and retirement-for-cause decisions.
Fatigue Crack Growth Behavior of PWA 1484 Single Crystal Superalloy at Elevated Temperatures
Authors: Telesman J. , Ghosn L. J.
Published: February 2008

A study was done to determine the fatigue crack growth behavior of a PWA 1484 single-crystal nickel-base superalloy in a temperature range of 427°C to 871°C. Two distinctive failure modes were observed, which were a function of both temperature and frequency. At lower temperatures and higher frequencies crack growth occurred on the {111} octahedral slip planes at an oblique angle to the loading direction. Higher temperatures and decrease in frequencies favored angle to the loading direction. Higher temperatures and decrease in frequencies favored a Mode I type failure process. The failure mode transitions were explained by invoking arguments based on environmental damage mechanisms. The fatigue crack growth rate data were analyzed using three different crack driving force parameters. The parameters investigated consisted of the Mode I stress intensity parameter corrected for the inclined crack trajectory, and two different octahedral Mode II parameters, which are based on the calculation of resolved shear stresses on the {111} slip systems. The Mode I ΔK parameter did a fair job in correlating the data but did not collapse it into a single narrow band. The two octahedral crack driving force parameters, ΔKRSS and a newly proposed ΔKOCT, collapsed all the data into a single narrow band. In addition to correlating the fatigue crack growth rates, the two octahedral parameters also predicted the {111} planes on which the crack growth took place.
F117-PW-100 Hybrid Ball Bearing Ceramic Technology Insertion
Authors: Miner J. R. , Dell J. , Galbato A. T. , Ragen M. A.
Published: February 2008

Results of an Advanced Research Projects Agency (ARPA) sponsored project to demonstrate the operational benefits of incorporating advanced structural ceramic ball elements into the F117-PW-100 aircraft gas turbine engine high rotor thrust bearings is described. This program consists of design, fabrication, and experimental evaluation of candidate hybrid ball bearing designs in Pratt & Whitney and MRC Bearings test facilities. The bearing design criteria and development test conditions utilized for the project are compatible with the requirements of the F117-PW-100 engine system application. Two hybrid bearing designs were produced by analytically varying internal geometry features such as M-50 race curvatures and contact angles to optimize for the modulus of elasticity of the ceramic balls. CERBEC grade NBD 200 silicon nitride ceramic balls (1 1/8 in. size) demonstrated integrity and a quadruple rolling contact fatigue life improvement versus state-of-the-art M-50 steel balls in single ball test rigs. Thermal performance data obtained in full-scale bearing rig performance testing with 178 mm size hybrid and all-steel baseline bearings shows comparable characteristics. The hybrid bearing displayed a distinct survivability benefit in bearing liquid lubricant starvation testing. Two dozen hybrid bearings will be fabricated for full-scale bearing rig endurance tests to be conducted in 1995–1996 as a prerequisite to validation in operating F117-PW-100 engines in 1996–1997.
Predicting Steady-State Temperature, Life, Skid, and Film Thickness in a Greased Preloaded Hybrid Ball Bearing
Authors: Poplawski J. V. , Atwell D. R. , Lubas M. J. , Odessky V.
Published: February 2008

This paper describes the use of the SHABERTH computer program supplemented with experimental temperature and skid data to quantify steady-state bearing operation. Parametric studies on ball diameter and number, contact angle, curvature, grease type, and preload are presented with their influence on contact stress, fatigue life, skid load, film thickness, and inner and outer race temperatures. These results are compared for a steel versus hybrid bearing set in a DB and DFSL mounting. The method presented can be applied to the design of other steel and hybrid ball thrust bearing systems.