bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Burner and Resonator Impedances on the Acoustic Behavior of Annular Combustion Chambers
Authors: Forte Annalisa , Camporeale Sergio , Fortunato Bernardo , Di Bisceglie Francesca , Mastrovito Marco
Published: September 2008

Premixed combustion is the commonly adopted technique to reduce NOx emissions from gas turbine combustion chambers, but it has been proved to be susceptible to thermo-acoustic instabilities, known as humming. These self-excited oscillations can reduce the efficiency of the turbine and generate structural damage to the combustion chamber. One of the proposed suppression methods lies in the application of Helmholtz resonators to the combustion chambers. This passive technique is advantageous in carrying out appreciable oscillation damping with modest costs and long life, but it is effective only in a restricted range of frequency, close to resonator eigenfrequency. Therefore, in order to design effective resonators, it is necessary to know the eigenfrequencies of the annular combustion chamber, because combustion instabilities arise in correspondence of these frequencies. Acoustic analysis of combustion chamber and its connected components may be carried out by means of Finite Element Method, but it requires a considerable computational effort due to the complex geometry of the complete system, which needs to be meshed by a refined grid. A combined numerical and experimental technique allows the authors to increase computational efficiency by adopting coarser and more regular meshes. First acoustic behavior of annular combustion chamber has been studied by means of numerical simulations and, therefore, the influence of the burners has been taken into account by substituting burner geometries by experimentally measured acoustic impedances. Then some Helmholtz resonators, tuned to one eigenfrequency of the combustion chamber, have been designed and manufactured. Their acoustic impedances have been experimentally measured and applied as boundary conditions into FE simulations of the annular chamber. In this way the acoustic pressure field inside the damper-equipped combustion chamber has been analyzed. Numerical simulations of the annular chamber, with burner and damper impedances applied, show that Helmholtz resonators are effective in oscillation suppression in correspondence of their resonance frequency, but may produce the splitting of the acoustic pressure peak of the chamber into two new peaks, whose frequencies lie on either side of the original common eigenfrequency. The amplitudes of these two new pressure peaks appear lower than the amplitude of the baseline one. The proposed technique can be used as an effective design tool: acoustic analysis of annular combustion chamber, with burner impedance applied, produces accurate indications about its acoustic behavior and allows the design of new passive suppression systems and the evaluation of their performances.
Blade Tip Heat Transfer and Aerodynamics in a Large Scale Turbine Cascade With Moving Endwall
Authors: Palafox P. , Oldfield M. L. G. , Ireland P. T. , Jones T. V. , LaGraff J. E.
Published: September 2008

High resolution Nusselt number (Nu) distributions were measured on the blade tip surface of a large, 1.0 meter-chord, low-speed cascade representative of a high-pressure turbine. Data was obtained at a Reynolds number of 4.0 × 105 based on exit velocity and blade axial chord. Tip clearance levels ranged from 0.56% to 1.68% design span or equally from 1% to 3% of blade chord. An infrared camera, looking through the hollow blade, made detailed temperature measurements on a constant heat flux tip surface. The relative motion between the endwall and the blade tip was simulated by a moving belt. The moving belt endwall significantly to shifts the region of high Nusselt number distribution and reduces the overall averaged Nusselt number on the tip surface by up to 13.3%. The addition of a suction side squealer tip significantly reduced local tip heat transfer and resulted in a 32% reduction in averaged Nusselt number. Analysis of pressure measurements on the blade airfoil surface and tip surface along with PIV velocity flow fields in the gap give an understanding of the heat transfer mechanism.
Management Strategies for a Compressed Air Energy Storage Plant
Authors: Arnulfi Gianmario L. , Marini Martino
Published: September 2008

Energy storage can balance supply and demand over different time scales, with technical and economical benefits. In the present paper, commercial gas turbines, just modified for storage purposes, are considered. The possibility to improve their profitability in an utility perspective is investigated. The adopted strategy is based on a fair mix of different working states (charging, discharging, stand by or mere Brayton cycle operation), according to the instant energy market price, the previous history (storage level) and the plant features (reservoir and GT size). A simple mathematical model of the plant was conceived and a dynamic self-adjusting abacus was developed in order to select a suitable sequence of working ways. The expected results consist in the improvement of the daily cash flow and in the peak power augmentation. Both of them are due to the chance of exploiting a turbo expander not loaded with the compressor driving during the hours when energy price is the highest.
Application of Hot-Wire Anemometry in a Blow-Down Turbine Facility
Authors: Yasa T. , Paniagua G. , De´nos R.
Published: September 2008

In order to test HP turbine stages under engine representative conditions on a heat transfer point of view, blow-down test rigs are often used. In these rigs the evolution of gas temperature, pressure and density is similar to a step function. Hence, the use of hot-wires, which are sensitive to flow velocity, density and temperature is more difficult than in an incompressible flow at constant temperature. This investigation describes how the data reduction can be performed in such environment in order to extract the velocity. The gas temperature is measured with a thermocouple and the gas density is derived from the measurement of the total pressure thanks to an iterative procedure. Once the velocity is derived, the turbulence can be computed. The effectiveness of the method is first demonstrated in a heated jet where both pressure and temperature are varied. Tests in the turbine facility are performed at turbine inlet temperatures of 480 K. Thus, overheat ratios up to 1.9 had to be used leading to a very high temperature of the tungsten platinum coated wire. The aging of the probe was very fast causing a drift in the voltage output between the successive tests. A technique is proposed to minimize the aging effect. It consists in adapting the calibration based on the resistance of the wire measured before each test. Measurements were carried out at the turbine inlet and rotor outlet. At the turbine inlet, velocity radial profiles are obtained together with measurements of the turbulence intensity. The time-averaged data is compared with pneumatic probe measurements. At the rotor exit, the time-resolved periodic velocity fluctuations are analyzed using a phase-locked average technique.
Syngas Mixture Composition Effects Upon Flashback and Blowout
Authors: Noble David R. , Zhang Qingguo , Shareef Akbar , Tootle Jeremiah , Meyers Andrew , Lieuwen Tim
Published: September 2008

This paper reports experimental data on flashback and lean blowout characteristics of H2/CO/CH4 mixtures. Data were obtained over a range of fuel compositions at fixed approach or burned flow velocity, reactant temperature, and combustor pressure at several conditions up to 4.4 atm and 470 K inlet reactants temperature. Consistent with prior studies, these results indicate that the percentage of H2 in the fuel dominates the mixture blowout characteristics. These blowout characteristics can be captured with classical Damko¨hler number scalings to predict blowoff equivalence ratios to within 10%. Counter-intuitively, the percentage of hydrogen had far less effect on flashback characteristics, at least for fuels with hydrogen mole fractions less than 60%. This is due to the fact that two mechanisms of “flashback” were noted: rapid flashback into the premixer, presumably through the boundary layer, and movement of the static flame position upstream along the centerbody. The former and latter mechanisms were observed at high and low hydrogen concentrations. In the latter mechanism, flame temperature, not flame speed, appears to be the key parameter describing flashback tendencies. We suggest that this is due to an alteration of the vortex breakdown location by the adverse pressure gradient upstream of the flame, similar to the mechanism proposed by Sattelmayer and co-workers [1]. As such, a key conclusion here is that classical flashback scalings derived from, e.g., Bunsen flames, may not be relevant for many parameter regimes found in swirling flames.
A Contextual Framework for Enhancing an Undergraduate Thermo-Propulsion Sequence
Authors: Rouser Kurt P. , Boyer Keith M. , Byerley Aaron R.
Published: September 2008

This paper describes various techniques employed in a novel approach to instruction and assessment of an undergraduate sequence in thermo-propulsion at the United States Air Force (USAF) Academy. Integrated motivational contexts aid development of foundations in thermodynamics, compressible gas dynamics, and propulsion while reinforcing engineering problem solving skills. Students are first oriented to the context of new material. Subsequent lessons fortify the context, giving students the opportunity to collaborate on team design projects and interact with industry and government guest speakers. Real-world, practical examples and homework further motivate and help students grasp key concepts. Tests are administered in both oral and written formats with open-ended, scenario-based questions to assess student understanding of fundamentals. Grading procedures focus on analytical methods as opposed to numerical results. Specific performance criteria validate the achievement of course educational outcomes. Student course critique scores and written comments further support the assertion that a contextual framework is highly effective in teaching fundamental thermo-propulsion concepts.
Development of a Detailed JP-8/Jet-A Chemical Kinetic Mechanism for High Pressure Conditions in Gas Turbine Combustors
Authors: Mawid M. A. , Sekar B.
Published: September 2008

Pressure conditions under which chemical reactions proceed in gas turbine combustors impact the behavior of the combustion process by either increasing or decreasing the reaction rates depending on whether these reactions are unimolecular/recombination or chemically activated bimolecular reactions. Some reactions are pressure independent such as H-abstraction reactions, while others are conditionally pressure independent if they are not at their either low or high limits. The recombination and decomposition of kinetic reactions rate constants change relative to their limiting values as the pressure and/or temperature conditions vary and as a result the reactants concentrations and reactions pathways are also influenced. In this study, pressure-dependent kinetic rate parameters for 39 elementary reactions have been added to our detailed JP-8/Jet-A kinetic reaction mechanism, we have developed [1–3, 23, 58], to model ignition of JP-8 and Jet-A fuels behind a reflected shock wave. The main objective is to develop a detailed chemical kinetic reaction mechanism for low and high pressure combustion conditions, using a 6-component surrogate fuel blend considered to represent the actual (petroleum-derived) JP-8 and Jet-A fuels. The pressure-dependent kinetic rate parameters for 39 reactions have been incorporated into our low pressure detailed JP-8 chemical kinetic reaction mechanism to generate the fall-off curves for the Arrehnius rate parameters required for low and high pressure ignition analysis. The new JP-8 detailed mechanism has been evaluated, using a stoichiometric JP-8/02/N2 and Jet-A/air mixtures, over a temperature range of 968–1639 K and a pressure range of 10 to 34 atmosphere by predicting auto-ignition delay times and comparing them to the shock tube ignition data of Minsk, Sarikovskii, and Hanson [56]. The results indicated that the developed JP-8/Jet-A reaction mechanism is capable of reproducing the qualitative ignition trends of the measured ignition data behind a reflected shock wave. However, the detailed kinetic reaction mechanism overestimated the measured ignition delay times. The results also suggested that additional more reactions are high pressure-dependent under the conditions considered in this study and as such a need still exists for experimentally measured kinetic rate coefficients for high pressure ignition and combustion conditions. This study, therefore, warrants further experiments and detailed kinetic analysis.
An Assessment of High-Fogging Potential for Enhanced Compressor Performance
Authors: Kim Kyoung Hoon , Perez-Blanco Horacio
Published: September 2008

Humidified gas turbines have the potential of enhanced cycle efficiencies with moderate initial cost. Evaporatively-cooled air compression is of importance to the power generation industry. The present work is aimed at contributing to a number of unanswered questions concerning the wet-compression process. Current operational margins limit the vapor mass fraction to 1∼2% by mass of the inlet flow. Yet, machines specifically designed to accommodate higher mass fractions are conceivable. Our aim is to explain the theoretical limits of those machines via a heat and mass transfer model. Continuous compression cooling via evaporation is modeled numerically based on droplet evaporation analysis. Parametric studies show the effect of variables such as droplet size, water injection ratio or compression ratio on transient behavior. Wet compression parameters such as evaporation time, compressor outlet temperature and compression work are estimated.
A Study of the Diffusion Brazing Process Applied to the Single Crystal Superalloy CMSX-4
Authors: Schnell A. , Stankowski A. , de Marcos E.
Published: September 2008

The requirement for economic reconditioning of the latest ALSTOM gas turbine generation with Single Crystal (SX) superalloys has lead to the development of advanced repair processes such as Diffusion Brazing or Transient Liquid Phase bonding. Diffusion Brazing (DB) of conventionally cast polycrystalline turbine components has been carried out for many years but the requirement for this joining and repair technique to be applied to DS and SX superalloys has emerged only more recently. The main concern for the use of a braze-repair process for the more highly loaded SX components is the ability to guarantee sufficient thermal and mechanical integrity throughout the component lifetime. Such high strength braze joints in SX superalloys can be achieved by combining a brittle phase-free and high γ′ content microstructure, while maintaining the crystallographical orientation of the SX parent material within the repair zone. Prior to the brazing process, a suitable crack surface preparation is essential, and this is achieved by the employment of specifically optimized Fluoride Ion Cleaning (FIC) process. This guarantees the complete removal of oxide from the crack surfaces and promotes the flow of the braze alloy for complete filling down to the crack tip. This paper presents the development of the DB process which has been specifically tailored for the repair of SX superalloys. The principles of the diffusion brazing process as applied to the CMSX-4 superalloy are discussed and the parameters which control the brazing kinetics are outlined. The optimization of the brazing heat treatment cycle will be presented. This paper also demonstrates the retention of the single crystal micro-structure in the repair zone, and demonstrates the test procedures developed to achieve the required thermal and mechanical integrity of braze repairs for application in SX gas turbine components.
Designing a Radial Swirler Vortex Breakdown Burner
Authors: Burmberger Stephan , Hirsch Christoph , Sattelmayer Thomas
Published: September 2008

Most gas turbine premix burners without centrebody employ the breakdown of a swirling flow at the transition between the mixing section and the combustor for aerodynamic flame stabilization [1]. As the formation of the desired vortex breakdown pattern depends very sensibly on the distribution of axial and azimuthal velocity in the mixing section, the design of suitable swirlers is usually a cumbersome iterative process. The presented burner design was found through the implementation of design guidelines derived from CFD-calculations and on the basis of analytical considerations [5]. The swirling flow is generated by a radial swirler with tangential inlets. In order to stabilize the flow pattern, the swirling flow confines a slow non-swirling flow on the centreline. The centre flow being set into azimuthal motion creates increasing azimuthal velocity in streamwise direction in the vortex core. This process is reinforced by a conical nozzle and leads to the production of positive azimuthal vorticity inside the nozzle which stabilizes the flow field. First atmospheric test runs and Large Eddy Simulations of the isothermal as well as reactive flow field prove that the design goals have been reached: The burner creates stable vortex breakdown in the primary zone of the combustion chamber without flame flashback or backflow on the centreline over the entire operating range and even for difficult fuels like hydrogen containing gases. This finding indicates that reliable vortex breakdown burners with remarkable fuel flexibility can be designed using the guidelines presented in [5].
Investigation of Velocity Profiles for Effusion Cooling of a Combustor Liner
Authors: Scrittore J. J. , Thole K. A. , Burd S. W.
Published: September 2008

Effusion cooling of combustor liners for gas turbine engines is quite challenging and necessary to prevent thermal distress of the combustor liner walls. The flow and thermal patterns in the cooling layer are affected by the closely spaced film-cooling holes. It is important to fully document how the film layer behaves with a full-coverage cooling scheme to gain an understanding into surface cooling phenomena. This paper discusses experimental results from a combustor simulator tested in a low-speed wind tunnel. Engine representative, non-dimensional coolant flows were tested for a full-coverage effusion plate. Laser Doppler velocimetry was used to measure the flow characteristics of the cooling layer. These experiments indicate that the full-coverage film cooling flow has unique and scaleable velocity profiles that result from the closely spaced effusion holes. A parametric study of the cooling flow behavior illustrates the complex nature of the film flow and how it affects cooling performance.
Aerodynamic Blockage Effect on the Spray Characteristics of a Liquid Jet Atomized by Crossflowing Air
Authors: Arienti M. , Madabhushi R. K. , Van Slooten P. R. , Soteriou M. C.
Published: September 2008

We study the role of jet-induced wake and vortical structures on the transport of drops formed by mass stripping and jet breakup due to crossflowing gas. Gas and liquid phases are computed as a single-fluid Eulerian continuum by tracking the gas-liquid interface with a Volume of Fluid (VOF) methodology. Droplets (numerically treated as parcels) are injected at fixed locations near the jet, based on near-field experimental observations. Their trajectories are evolved in time so that patterns of volumetric flux, axial velocity and Sauter Mean Diameter (SMD) can be compared with experimental measurements in the far field. We find that vortical structures due to aerodynamic blockage are maintained up to several orifice diameters downstream of the jet, affecting the droplet trajectories and ultimately the spray distribution. We also demonstrate that an interface-tracking algorithm for capturing the jet bulk features allows the prediction of far field spray characteristics when coupled to a simple set of rules for spray distribution after primary breakup.
New Running Strategies of a STIG Power Plant for District Heating
Authors: Caresana F. , Comodi G. , Pelagalli L. , Salvi D.
Published: September 2008

We describe the running plan of a 5.5-MWe-STIG-plant. Located in a medium-sized town in the centre of Italy, the plant both produces electric power and partially satisfies the thermal load of a nearby city district. An account of the Italian energy market is provided and the impact of recent legislation on plant operation is analysed. The liberalization of the Italian energy market in 1999 has significantly affected the technical and economic scenario for both existing and future power plants. As an example, we analyse the effects of liberalization on the overall performances of the plant described herein as well as the main changes in its running-strategies. A better economic result is shown to be possible in the new scenario mainly thanks to plant flexibility when operating as CHP (Combined Heat and Power) unit. The pursuit of optimum economic performance however prevents the plant from working at its best energetic efficiency.
Pressure Influence on the Flame Transfer Function of a Premixed Swirling Flame
Authors: Freitag E. , Konle H. , Lauer M. , Hirsch C. , Sattelmayer T.
Published: September 2008

In order to assess the stability of gas turbine combustors measured flame transfer functions are frequently used in thermoacoustic network models. Although many combustion systems operate at high pressure, the measurement of flame transfer functions was essentially limited to atmospheric conditions in the past. With the test rig employed in the study presented in the paper transfer function measurements were made for a wide range of combustor pressures. The results show similarities of the amplitude response in the entire pressure range investigated. However, the increase of the pressure leads to a considerable amplitude gain at higher frequencies. In the low frequency regime the phase is also independent of pressure, whereas above this region the pressure increase results in a considerably smaller phase lag. These observations are particularly important when evaluating Rayleigh’s criterion: Interestingly, the choice of the operating pressure can render a system stable or unstable, so that the common procedure of applying flame transfer functions measured at ambient pressure for the high pressure engine case may not always be appropriate. The detailed analysis of high speed camera images, which were recorded to get locally resolved information on the flame response reveal different regions of activity within the flame that change in strength, size and location with changing operating conditions. The observed transfer function phase behavior is explained by the interaction of those regions and it is shown that the region of highest dynamic activity dominates the phase.
Thermoeconomic Analysis of Hybrid SOFC Fuel Cell Systems With Decarbonization of Natural Gas
Authors: Franzoni A. , Magistri L. , Traverso A. , Massardo A. F.
Published: September 2008

In this paper the results of the thermodynamic and economic analyses of large size power plants (450 MWe) and distributed power plants (1.5 MWe) are compared and described. The work is focused on the decarbonization of natural gas through a CO2 separation unit, which employs a technology (amine chemical absorption) viable for short-term implementation in real installations. Plant layouts, analyzed in previous open literature works, were taken as references. The plants proposed in this paper are seven: three belong to large-scale centralized electricity production while the remaining four belong to distributed power generation. The first three consist of: 1- a Combined Cycle fed by natural gas; 2- a Combined Cycle fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes; 3- a Combined Cycle fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes including a more detailed mathematical model of the CO2 separation unit that properly considers the amount of steam needed by the stripping towers. Four different power plants solutions are proposed for the Distributed Generation: 1- a simple cycle gas turbine fed by natural gas; 2- a Hybrid System with tubular SOFC fed by natural gas with internal reforming; 3- a 1.5 MWe gas turbine fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes; 4- Hybrid System fed by syngas obtained through Auto Thermal Reforming, Shift, CO2 Separation processes. The results were obtained with WTEMP software, developed by the TPG of the University of Genoa, and showed that the thermodynamic and economic impact of the adoption of zero-emission cycle layouts is relevant: advanced alternative technologies, such membrane-based separation units, are highly desirable to improve plant performance.
Advanced Materials for Mercury™ 50 Gas Turbine Combustion System
Authors: Price Jeffrey , Kimmel Josh , Chen Xiaoqun , Bhattacharya Arun , Fahme Anthony , Otsuka Joel
Published: September 2008

Solar Turbines Incorporated (Solar), under cooperative agreement number DE-FC26-00CH 11049, is improving the durability of gas turbine combustion systems while reducing life cycle costs. This project is part of the Advanced Materials in Advanced Industrial Gas Turbines program in DOE’s Office of Distributed Energy. The targeted engine is the Mercury™ 50 gas turbine, which was developed by Solar under the DOE Advanced Turbine Systems (ATS) program (DOE contract number DE-FC21-95MC31173). The ultimate goal of the program is to demonstrate a fully integrated Mercury 50 combustion system, modified with advanced materials technologies, at a host site for 4,000 hours. The program has focused on a dual path development route to define an optimum mix of technologies for the Mercury 50 turbine and future Solar products. For liner and injector development, multiple concepts including high thermal resistance thermal barrier coatings (TBC), oxide dispersion strengthened (ODS) alloys, continuous fiber ceramic composites (CFCC), and monolithic ceramics were evaluated. An advanced TBC system for the combustor was down-selected for field evaluation. ODS alloys were down-selected for the fuel injector tip application. Preliminary component and sub-scale testing was conducted to determine material properties and demonstrate proof-of-concept. Full-scale rig and engine testing were used to validate engine performance prior to field evaluation. Field evaluation of ceramic matrix composite liners in the Centaur® 50 gas turbine engine [1–3] which was previously conducted under the DOE sponsored Ceramic Stationary Gas Turbine program (DE-AC02-92CE40960), is continuing under this program. This paper is a status review of the program, detailing the current progress of the development and field evaluations.
Adiabatic Effectiveness Measurements in a First Stage Nozzle Cascade Having Endwall Contouring, Leakage and Assembly Features
Authors: Piggush J. S. , Simon T. W.
Published: September 2008

The first stage vane section of a modern gas turbine engine is assembled with a gap between the combustor and the vane platform and a second gap on the platform. To prevent ingression, leakage flow is provided through each gap. In this paper, the effectiveness of the leakage flow as an endwall film coolant is measured. The cascade geometry includes axial contouring of the cooled endwall and several step configurations for each gap. The steps reflect assembly or differential thermal growth misalignment. Various blowing rates are applied through each gap to allow assessment of the changes in effectiveness with changes in leakage rate. Thus, the results presented herein show how the gaps, steps, and leakage rates alter the cooling effectiveness of the leakage flow. Shown are some cases where steps improve the film cooling effectiveness. In other cases, enhanced mixing due to gaps, steps, or increased leakage reduces effectiveness.
Chemical Analysis of Combustion Products From a High-Pressure Gas Turbine Combustor Rig Fueled by Jet A1 Fuel and a Fischer-Tropsch-Based Fuel
Authors: Hermann Fredrik , Klingmann Jens , Gabrielsson Rolf , Pedersen Jo¨rgen R. , Olsson Jim O. , Owrang Farshid
Published: September 2008

A comparative experimental investigation has been performed, comparing the emissions from a synthetic jet fuel and from Jet A1. In the investigation, the unburned hydrocarbons were analyzed chemically and the regulated emissions of NOx, CO and HC were measured. All combustion tests were performed under elevated pressures in a gas turbine combustor rig. A Swedish company, Oroboros AB, has developed a novel clean synthetic jet fuel, LeanJet®. The fuel is produced synthetically from synthesis gas by a Fischer-Tropsch process. Except for the density, the fuel conforms to the Standard Specification for Aviation Turbine Fuels. The low density is due to the lack of aromatics and polyaromatics. Organic emissions from the gas turbine combustor rig were collected by adsorption sampling and analyzed chemically. Both the fuels and the organic emissions were analyzed by gas chromatography/flame ionization (GC/FID) complemented with gas chromatography/mass spectrometry (GC/MS). Under the operating conditions investigated, no significant differences were found for the regulated emissions, except for emission of CO from the synthetic fuel, which, at leaner conditions, was one-quarter of that measured for Jet A1. Detailed analysis of the organic compounds showed that the emissions from both fuels were dominated by fuel alkanes and a significant amount of naphthalene. It was also found that Jet A1 produced a much higher amount of benzene than the synthetic fuel.
The Effects of Pressure on Gas Turbine Combustor Performance: An Investigation via Numerical Simulation
Authors: Cui Yufeng , Xu Gang , Yu Bin , Nie Chaoqun , Huang Weiguang
Published: September 2008

Performance tests of a gas turbine combustor are usually conducted at atmospheric or medium pressure which is quite different from its real operating condition. The effects of pressure on the performance of a gas turbine combustor for burning medium-heating-value syngas are researched by numerical simulation in this paper. The geometry of the combustor is modeled by coupling all its components including nozzle, combustor liner and sealant tube. In the simulation a laminar flamelet model and P-1 radiation model are adopted. The numerical results show that at the same fuel and air inlet temperature and the same equivalence ratio, the operation pressure has less effect on the flow fields, but its effect on the temperature distribution is obvious. Both the highest temperature in the combustor and the outlet temperature increase with increasing operating pressure because of the weakening of the dissociation of the H2O, CO2 and so on. Moreover, as pressure increases, the concentration of H2O and CO2 in the combustor increase, and so to does the absorption coefficient and the emissivity of gas inside the liner. As a result, the radiation heat transfer between the gas and the combustion liner wall is enhanced, and the wall temperature of the liner increases. The NOx emissions of the combustor are also distinctly higher at high pressure than at low pressure.
MCFC-GT Hybrid System Aiming at 70% Thermal Efficiency
Authors: Koda Eiichi , Takahashi Toru
Published: September 2008

The thermal efficiency improvement of fossil power generation is important to reduce both CO2 emission and power generating cost. To date, 60% (LHV) has been achieved with ACC (Advanced Combined Cycle) and a calculation result of 70% (LHV) or more has been reported for SOFC-GT hybrid. Then, we examined the thermal efficiency improvement considering the features of the gas turbine and the fuel cell, and designed the epoch-making cycle. By markedly improving the single-cell voltage of MCFC using oxygen as an oxidant, and having adopted a semiclosed cycle configuration in which gas turbine exhaust heat is effectively used almost completely, this cycle not only enables us to obtain an ultrahigh efficiency, but also can facilitate CO2 recovery. First, the thermal efficiency of a 300MW-class power plant using this cycle was examined, and it was confirmed that a net efficiency of 70% (HHV) or more was possible. Then, a 1MW-class system that can be realized in the near future is examined. As a result, it has been understood that it is promising as a small power supply, too. In this paper, the concept and basic configuration of this cycle were explained, and the detailed configuration and the thermal efficiency calculation results for both the 300MW-class system and the 1MW-class system are described.
How to Change Over Heat Recovery Steam Generators After Gas Turbine Trip
Authors: Brandstetter Gottfried , Oberleitner Wolfgang , Pichler Michael
Published: September 2008

Heat recovery steam generators downstream of gas turbines are often used in combination with process steam applications. Because of the high importance of the required process steam, a boiler trip is more severe than in usual applications, where only electricity is produced. In most cases these boilers are equipped with a supplementary and fresh air firing system having the capacity of replacing the whole waste heat coming from the gas turbine or even more. A fresh air firing system offers the possibility to keep the boiler in operation without the gas turbine running. If the boiler has to stay in operation even after a gas turbine trip a change over from waste heat firing to fresh air firing has to follow immediately. Due to the very sharp breakdown of the gas turbine speed after trip, the change over procedure has to be carried out within a few seconds to avoid a boiler shut down. The problems are — on the one hand — not to have to switch off the supplementary firing, on the other hand not to exceed the backpressure of the gas turbine because of too fast closing of dampers necessary for fresh air firing. The first would cause a necessary purging with a certain time period without firing, the second would lead to damages of the gas turbine exhaust system. Backpressure and oxygen supply have to be managed carefully to provide a smooth and save change over. In addition it has to be considered, that the first time period after gas turbine trip, the oxygen supply of the boiler’s firing has to be ensured by the running out gas turbine. Special investigations allow to predict the amount of exhaust gas mass flow after gas turbine trip by using the speed behavior of a reference gas turbine trip. At an Austrian steel mill (VOESTALPINE) these procedures were investigated in detail, and a lot of measurements were done. Based on this the existing change over procedure was optimized and the possibility of a quick change over procedure was realized.
Advanced Hydraulic Seal Design for High Temperature Environments
Authors: Denecke J. , Schramm V. , Dullenkopf K. , Bauer H.-J. , Klingsporn M. , Hein S. , Peitsch D.
Published: September 2008

Hydraulic seals are successfully used to seal gas turbine shaft and bearing chambers because of their main advantages: reliable operation with zero leakage. However, due to the temperature limitations of the lubrication oil their application has been limited to relatively cold areas in the engine (e.g. front bearing chamber). To employ hydraulic seals in hotter areas, particularly at the rear bearing chamber with elevated wall and air temperatures, oil degradation and coking must be taken into account. Therefore, recirculation zones which lead to hot spots must be avoided and the oil residence time must be reduced. A new seal design that enforces a defined flow pattern through the seal (Bo¨ck, U.S. Patent No. 6,568,688B1) claims to keep oil temperature below degradation limits even in hotter operational environments. However, the circumferential velocities and oil levels in the seal are altered, which must be considered in the design process. This paper compares the flow characteristics of the classic and advanced seal design. Analytical calculation approaches for both seal designs are presented. The commercial software FLUENT was used for numerical simulations, applying the ‘Volume of Fluid’ (VoF) method. To validate the numerical and analytical results, a configuration was tested experimentally in a two shaft co-rotating set-up, which was especially designed for hydraulic seals. Good agreement could be achieved in a comparison of the monitored oil levels in the seal for different engine relevant shaft speeds and pressures.
Comparative Analysis of Hydrogen Combustion Power Plants Integrated With Coal Gasification and CO2 Removal
Authors: Vascellari Michele , Cocco Daniele , Cau Giorgio
Published: September 2008

Two power generation systems with pre-combustion CO2 capture fuelled with hydrogen from coal gasification are analyzed and compared from a thermodynamic and economic standpoint. The first solution, referred as Integrated Gasification Combined Cycle with CO2 Removal (IGCC-CR), is fuelled with hydrogen produced by the integrated gasification section. The second, referred as Integrated Gasification Hydrogen Cycle (IGHC), is based on the oxycombustion of hydrogen, producing steam that expands through an advanced high temperature steam turbine. The two H2 production sections are similar for both power plants, some minor modifications having been made to achieve better integration with the corresponding power sections. System performance is investigated using coherent assumptions to enable comparative analysis on the same basis. The plants have overall efficiencies of around 39.8% for IGCC-CR and 40.6% for IGHC, slightly lower than conventional IGCCs (without CO2 capture) with a CO2 removal efficiencies of 91% and 100% respectively. Lastly a preliminary economic analysis shows an increase in the cost of electricity compared to conventional IGCCs of about 44% for IGCC-CR and 50% IGHC.
Mathematical Formulation of Model-Based Methods for Diagnostics and Prognostics
Authors: Jaw Link C. , Wang William
Published: September 2008

System health management capability strives to estimate the current and the future operating states of the system through continuous monitoring of key operating variables. Once the current and future states are estimated, this information will be used to help the dispatcher (or field commander) better respond to anticipated fault conditions, it will also help the logistician (or support crew) better prepare for maintenance actions. Estimating the current and the future operating states are commonly referred to as the diagnostic and the prognostic problems. Diagnostic and prognostic problems can be solved by two different approaches: the model-based approach and the data-based approach. The model-based approach is increasingly favored because it is able to provide more accurate estimation of these operating states, and because it is naturally extensible to the physics of failure, which has been considered a promising enhancement to the conventional prognostic technology. To apply the model-based approach more effectively to diagnostic and prognostic problems, we need to cast these problems in a unified formulation to understand the relationship between the two; furthermore, we need to integrate candidate algorithms with the problem formulation to allow sound evaluation of different solution methods. A unified formulation of the diagnostic and prognostic problems has been suggested in a paper presented at the 2005 ASME World Congress. This formulation uses a linear, time-invariant model as the foundation and expressed diagnostics and prognostics as the same threshold-checking problem. However, the formulation does not include the algorithms used in system health management. Augmenting the problem formulation with health management algorithms is the goal of this paper. This paper presents integrated mathematical formulations for several model-based methods to solve the diagnostic and prognostic problems. Each integrated formulation combines the basic problem formulation with a specific algorithm. The set of integrated formulation provides a theoretical perspective of system health management challenges.
Alternatives to Kelvin-Helmholtz Instabilities to Control Separation Bubbles
Authors: Simens Mark P. , Jime´nez Javier
Published: September 2008

We study the control of two-dimensional laminar separation bubbles on a flat plate at low Reynolds numbers, using two-dimensional DNS. A range of steady separation bubbles is obtained varying the pressure gradient. They are forced by a zero-mass flow, oscillatory wall blowing with different perturbation amplitudes and frequencies. The reduction in bubble length as a function of frequency has two minima for sufficient high amplitudes. One of them is related to the Kelvin-Helmholtz instability of the separated boundary layer, while the other, most effective one, is here denoted as the low-frequency regime. In this regime large vortices are created which are not a consequence of an instability of the original bubble. On the contrary the forcing creates an unsteady separation bubble which evolves into a large vortex. These vortices have large radii and attach to the wall due to their self-induced pressure field while convecting across the adverse pressure gradient zone. Scaling relations for the effect of the forcing are proposed and tested.
Conceptual Analysis of Air Supply Systems For In-Flight PEM-FC
Authors: Barchewitz Lukas P. , Seume Joerg R.
Published: September 2008

To cover the increasing demand of on-board electrical power and for further reduction of emissions, the conventional auxiliary power unit (APU) shall be replaced by a fuel cell system. The main components are a compressor-turbine unit, a kerosene reformer, and the fuel cell. Polymer exchange membrane fuel cells (PEM-FC) are favoured because of their currently advanced level of development. During in-flight operation, the inlet conditions of the PEM-FC system must be kept constant in order to avoid mechanical and thermal damage of the membrane and to ensure low levels of pressure fluctuations in the reformer section. A centrifugal compressor is chosen for pressurization of the system. The advantages of turbomachinery are low specific weight, high efficiency, and good controllability by inlet guide vanes and/or adjustable diffuser vanes. To drive the compressor, a radial turbine is used so that the air supply system resembles the turbocharger for a combustion engine (Fig. 1). A steady state thermodynamic evaluation of the entire system is carried out to identify an optimal system configuration that covers the large range of pressure, temperature, and humidity of ground operation of the aircraft in various regions on the earth as well as take-off, cruise, and landing. A catalytic combustion chamber is located between the PEM-FC and the radial turbine. In this combustion chamber, the hydrogen which is not used in the fuel cell is used to raise the turbine inlet temperature (TIT) and thus the mechanical power delivered by the turbine. To overcome an additional pressure loss of the reformer section, which occurs in the anode stream, an additional low-pressure-ratio compressor is used. The result is a highly thermally integrated PEM-FC system with three centrifugal turbomachines.
Experimental Study of Air-Assist Atomizers for Fogging Systems
Authors: Levy Y. , Sherbaum V. , Ovcharenko V. , Levitsky S. P. , Levitsky M. P.
Published: September 2008

It is known that the temperature of the ambient air significantly affects the power output of gas turbines. To decrease inlet air temperature water injection at the intake of the turbine is commonly used. Existing air-assist atomizers consume significant more energy in the form of high-pressure air (about 6 bars) as compared to the jet impinging ones. Two new designs of the air-assist atomizers for fogger system are developed and studied. These atomizers differ from the existing ones by special air vortex chamber. It enables to achieve high tangential air velocities and reduce air input pressure. It is shown that at air pressure drop of 0.75–1 bar, the Sauter Mean Diameter of droplets is in the range from 20 to 25 μm when air-to-liquid flow rate ratio is equal to 4:1. Water supply pressure was in the range of 0.5–1 bar during the tests and its value did not markedly affected droplets diameter. It is expected that during optimization of the design and operating condition (air and liquid pressure), the size of the droplets would be further reduced. When air pressure was above 1 bar the droplets diameter was almost not affected by this parameter. Droplet velocity and droplet flux distribution along spray radius were also measured. It was found that the droplets distribution along radius is almost uniform. Spray cone was 30° for one device and 90° for the other.
A Feasibility Study of Life-Extending Controls for Aircraft Turbine Engines Using a Generic Air Force Model
Authors: Behbahani Al , Jordan Eric A. , Millar Richard
Published: September 2008

Turbine engine controllers are typically designed and operated to meet required or desired performance criterion within stability margins, while maximizing fuel efficiency. The U.S. Air Force turbine engine research program is seeking to incorporate sustainable cost reduction into this approach, by considering a life-cycle design objective if the life of the engine is considered as an objective during the design of the engine controller. Specifically during aircraft takeoff, the turbine engines are subject to high temperature variations that aggravate the stress of the material used in their construction and thus a negative effect in their life spans. Therefore, the control strategy needs to be re-evaluated to include operating cost, and extending the life of the engine is one way to reduce that. Life-Extending Control (LEC) is an area that deals with control action, engine component life usage, and designing an intelligent control algorithm embedded in the FADEC. This paper evaluates the LEC, based on critical components research, to demonstrate how an intelligent engine control algorithm can drastically reduce the engine life usage, with minimum sacrifice in performance. Finally, a generic turbine engine is extensively simulated using a sophisticated non-linear model of the turbine engine. The paper concludes that LEC is worth consideration and further research should include development of the damage models for turbine engines, and experimental research that could correlate the damage models to actual damage for turbine engines. This could lead to implementation of online damage models in real-time that will allow for more robust damage prevention.
Thermal and Economic Analysis of Besat Steam Power Plant Repowering
Authors: Sanaye Sepehr , Hamzeie Younes , Malekian Mohammad Reza , Sohrabi Mohammad Reza
Published: September 2008

There is a rapid growth of electricity consumption in the world. This problem needs enough resources for capital investment for construction of new power plants and/or making all efforts to increase the thermal efficiency of existing power generation cycles. Therefore this situation has lead power generation industries to repower and modify the existing steam power plants which are constructed in the recent three or four decades. In this paper an important method for repowering of old steam power plants which uses a gas turbine is analyzed. Hot Wind Box (HWB) repowering method was technically and economically evaluated to repower the Besat steam power plant. This power plant was constructed and exploited in 1967 in Tehran. The optimum design parameters such as gas turbine power output, compressor and turbine isentropic efficiency, pressure ratio, and the ratio of turbine inlet temperature to compressor inlet temperature were found by defining an objective function the total cost per unit of repowered plant power output and using numerical search optimization technique for its minimizing. The objective function, the total cost, included initial or capital investment, operation and maintenance costs during plant life cycle. The numerical values of optimum design parameters and the results of the sensitivity analysis are reported.