bluuebunny/crossref_metadata_2025 huggingface dataset:
High Pressure Test Results of a Catalytic Combustor for Gas Turbine
Authors: Fujii T. , Ozawa Y. , Kikumoto S. , Sato M. , Yuasa Y. , Inoue H.
Published: February 2008

Recently, the use of gas turbine systems, such as combined cycle and cogeneration systems, has gradually increased in the world. But even when a clean fuel such as LNG (liquefied natural gas) is used, thermal NOx is generated in the high temperature gas turbine combustion process. The NOx emission from gas turbines is controlled through selective catalytic reduction processes (SCR) in the Japanese electric industry. If catalytic combustion could be applied to the combustor of the gas turbine, it is expected to lower NOx emission more economically. Under such high temperature and high pressure conditions, as in the gas turbine, however, the durability of the catalyst is still insufficient. So it prevents the realization of a high temperature catalytic combustor. To overcome this difficulty, a catalytic combustor combined with premixed combustion for a 1300°C class gas turbine was developed. In this method, catalyst temperature is kept below 1000°C, and a lean premixed gas is injected into the catalytic combustion gas. As a result, the load on the catalyst is reduced and it is possible to prevent the catalyst deactivation. After a preliminary atmospheric test, the design of the combustort was modified and a high pressure combustion test was conducted. As a result, it was confirmed that NOx emission was below 10 ppm (at 16 percent O2) at a combustor outlet gas temperature of 1300°C and that the combustion efficiency was almost 100 percent. This paper presents the design features and test results of the combustor.
Model Based Fuzzy Logic Sensor Fault Accommodation
Authors: Healy T. A. , Kerr L. J. , Larkin L. J.
Published: February 2008

Sensor in-range fault accommodation is a fundamental challenge of dual channel control systems in modern aircraft gas turbine engines. An on-board, real-time engine model can be used to provide an analytical third sensor channel that may be used to detect and isolate sensor faults. A fuzzy-logic-based accommodation approach is proposed that enhances the effectiveness of the analytical third channel in the control system’s fault isolation and accommodation scheme. Simulation studies show the fuzzy accommodation scheme to be superior to current accommodation techniques.
Heavy-Duty Gas Turbine Plant Aerothermodynamic Simulation Using Simulink
Authors: Crosa G. , Pittaluga F. , Trucco A. , Beltrami F. , Torelli A. , Traverso F.
Published: February 2008

This paper presents a physical simulator for predicting the off-design and dynamic behavior of a single shaft heavy-duty gas turbine plant, suitable for gas-steam combined cycles. The mathematical model, which is nonlinear and based on the lumped parameter approach, is described by a set of first-order differential and algebraic equations. The plant components are described adding to their steady-state characteristics the dynamic equations of mass, momentum, and energy balances. The state variables are mass flow rates, static pressures, static temperatures of the fluid, wall temperatures, and shaft rotational speed. The analysis has been applied to a 65 MW heavy-duty gas turbine plant with two off-board, silo-type combustion chambers. To model the compressor, equipped with variable inlet guide vanes, a subdivision into five partial compressors is adopted, in serial arrangement, separated by dynamic blocks. The turbine is described using a one-dimensional, row-by-row mathematical model, that takes into account both the air bleed cooling effect and the mass storage among the stages. The simulation model considers also the air bleed transformations from the compressor down to the turbine. Both combustion chambers have been modeled utilizing a sequence of several sub-volumes, to simulate primary and secondary zones in presence of three hybrid burners. A code has been created in Simulink environment. Some dynamic responses of the simulated plant, equipped with a proportional-integral speed regulator, are presented.
Environmental Influence on the Thermoeconomic Optimization of a Combined Plant With NOx Abatement
Authors: Agazzani A. , Massardo A. F. , Frangopoulos C. A.
Published: February 2008

Methods to analyze, improve, and optimize thermal energy systems have to take into account not only energy (exergy) consumption and economic resources, but also pollution and degradation of the environment. The term “environomics” implies a method that takes thermodynamic, economic, and environmental aspects systematically into consideration for the analysis and optimization of energy systems. For optimization of energy systems, the environmental aspects are quantified and introduced into the objective function. In this particular work, the environomic approach is followed for the analysis and optimal design of a combined-cycle plant. In addition to the basic configuration, two alternatives for NOx abatement are studied: Selective Catalytic Reduction (SCR) and steam injection. The optimization problem is solved for each configuration, and the results are compared with each other. The effect of the unit pollution penalties and of the limits imposed by regulations is studied. Some general conclusions are drawn.
Experimental Investigation and Mathematical Modeling of Clearance Brush Seals
Authors: Turner M. T. , Chew J. W. , Long C. A.
Published: February 2008

In this paper, an experimental program and a CFD based mathematical model using a brush seal at two bristle to rotor clearances (0.27 mm and 0.75 mm) are presented. The experimental program examined the radial pressure distributions along the backing ring, the axial pressure distribution along the rotor, and the mass flow through the seal through a range of pressure ratios while exhausting to atmosphere. The results from this experimental program have been used to further calibrate a CFD-based model. This model treats the bristle pack as an axisymmetric, anisotropic porous region, and is calibrated by the definition of nonlinear resistance coefficients in three orthogonal directions. The CFD analysis calculates the aerodynamic forces on the bristles, which are subsequently used in a separate program to estimate the bristle movements, stresses, and bristle and rotor loads. The analysis shows that a brush seal with a build clearance produces a very different flow field within the bristle pack to one with an interference, and the need to understand the bulk movements of the bristles. These are shown to be affected by the level of friction between the bristles and the backing ring, which has an important effect on the bristles wear and seal leakage characteristics.
Rotodynamic Modeling of an Actively Controlled Magnetic Bearing Gas Turbine Engine
Authors: Antkowiak B. M. , Nelson F. C.
Published: February 2008

This paper summarizes the development of a finite element rotordynamic solution used in a closed loop simulation for a magnetic bearing rotor system in a gas, turbine engine. A magnetic bearing controlled rotor is analyzed, and the state dynamics matrix [A], the shaft control influence matrix [B], and the sensor matrix [C] are constructed. Bode plots of the state-space transfer function are also constructed and compared to the results of the rotor dynamic model.
The Effect of Misalignment on Rotor Vibrations
Authors: Nikolajsen J. L.
Published: February 2008

Rotors with three or more fluid-film bearings (or fluid seals) have “redundant” supports, and, therefore, interdependent bearing loads that are generally unknown both in magnitude and direction. The steady-state bearing eccentricities and the dynamic stiffness and damping coefficients of the bearings are, therefore, also unknown since both are functions of the bearing loads. Thus, the dynamic behavior of multibearing rotors generally cannot be predicted with good accuracy without access to a procedure for calculating the steady-state bearing loads and eccentricities. This paper outlines such a procedure in terms of both the influence coefficient method, the transfer matrix method, and the finite element method. Radial bearing misalignment and flexibility of the bearing back-up structures are accounted for. Once the eccentricities are available, the bearing stiffness and damping coefficients can be calculated in the usual way and used to predict critical speeds, instability threshold speed, and rotor response to imbalance. A numerical example is presented that illustrates some of the nonlinear effects of bearing support redundancy, notably the large variations in instability threshold speed with radial bearing misalignment. The example shows how the method can be used to determine the level of bearing misalignment that leads to optimum rotor stability. It is concluded that no simple guide lines exist by which optimum stability can be achieved. Neither perfect bearing alignment nor equal load sharing between bearings necessarily lead to optimum stability.
The Diesel Engine for Cars—Is There a Future?
Authors: Pischinger F. F.
Published: February 2008

The diesel engine is known as the most fuel efficient combustion engine. Its acceptance for use in passengers cars, however, varies geographically. Today, the diesel car plays an important role in Europe; in France, for instance, it is achieving a remarkable market share of about 42 percent, while in the US its market penetration can be neglected. Many questions are expressed concerning the future of diesel powered cars. The question affecting market acceptance is as follows: can the significantly better fuel efficiency of a diesel car outweigh perceived detrimental characteristics? Such unfavorable properties are thought to be low specific power, objectionable noise, higher exhaust emissions (including smoke), and higher vehicle price. These features are closely influenced by the state of passenger car diesel engine technology. This technology state and its potential must be evaluated with respect to current and future demands, for instance, tighter exhaust emission regulations. In addition, the commercial value and consumer acceptance of high fuel economy must be evaluated. It is clear that the ultimate result of weighing the pros and cons will depend not only on technological factors, but also on political factors such as fuel taxation. Regarding the state of technology, the diesel car is very promising. First, by employing a direct injection combustion system, the fuel efficiency can be improved by about 15 percent over current swirl chamber engines. Furthermore, the specific power (hp/ltr) can be increased by efficient supercharging to achieve values of today’s gasoline engines. By tuning the combustion system, low noise engine design features and incorporation of careful noise reduction measures on the vehicle, the noise behavior of a spark ignited vehicle can be reached. Exhaust emissions can currently be reduced to a level to satisfy today’s European and US Tier 1 emission limits. However, significant development effort remains. More stringent emission levels (California US, Tier 2 ULEV, and Stage 3 in Europe) require further advancements in diesel combustion. The strong development potential of 4-value engines and new unique injection systems is evident. In addition, there are promising developments with lean NOx catalysts and regenerative particulate filters. These technologies offer the potential to meet the very stringent future emission standards. It is anticipated that the sophisticated technology needed to meet these standards will make the future diesel car more expensive compared to a gasoline fueled vehicle. This raises the issue of what price will the consumer pay for the higher fuel economy of a diesel car. In light of the worldwide rapid increase in passenger car population and of the dwindling oil reserves and their global distribution, the fuel efficient diesel engine will play an important role in the future of passenger cars.
Optimum Cylinder Cooling for Advanced Diesel Engines
Authors: Trenc F. , Rodman S. , Skerget L. , Delic M.
Published: February 2008

Continuous demand for higher specific engine output simultaneously introduces problems of higher mechanical and thermal stresses of the engine components. Uneven temperature distribution in the cylinder wall of a diesel engine, especially when air-cooled, is well known. Peak local temperatures, large circumferential and longitudinal temperature gradients provoke deformations that, in turn, affect the reliability of the engine. As the result of intensive numerical and experimental investigations, a horizontal, curved channel fed with engine lubrication oil was introduced in the upper part of the air-cooled cylinder. Optimization of the channel design, its position, and determination of suitable asymmetrical split oil flow have led to more favorable cylinder temperature distribution, similar to that obtained by advanced water-cooled engines. Analyses of the local laminar oil-flow phenomena and local heat transfer distribution in curved channels are discussed in the paper and can be successfully applied to advanced liquid-cooled engines.
A New Criterion for Judging SI Engine In-Cylinder Pressure Development for Its Effect on Combustion Noise
Authors: Yang J. , Anderson R. W.
Published: February 2008

The effect of engine in-cylinder pressure development on combustion noise is studied based on measured pressure traces and the attenuation-curve theory by Austen and Priede (1958). A new criterion is proposed that correlates better to the noise levels predicted by the attenuation theory than the commonly used maximum pressure rise rate. The effect of engine bore size on combustion noise is studied next with the same engine speed, the same piston mean speed, or the same power output, respectively. For the first two cases, a smaller bore size results in a lower noise level.
Oil Layer as Source of Hydrocarbon Emissions in SI Engines
Authors: Min K. , Cheng W. K.
Published: February 2008

The role of lubrication oil film on the cylinder liner as a source of hydrocarbon emissions in spark-ignition engines is assessed. First, the “source strength” is examined via an analytical model of the gasoline vapor absorption/desorption process. The solution shows that depending on engine operating conditions, there are three regimes. The process could be (1) limited by the gas side diffusion process, (2) limited by the liquid phase diffusion process, with the absorbed fuel fully penetrating the oil layer thickness (thin oil film regime), and (3) again limited by the liquid phase diffusion process, but with the absorbed fuel penetration depth small compared to the oil layer thickness (thick oil film regime). In regime (1), the source strength (the integrated absorption or desorption flux over one cycle) is proportional to the inverse of the square root of the rpm, but independent of oil layer parameters. In regimes (2), the strength is proportional to the oil film thickness divided by the Henry’s constant. In regime (3), the strength is independent of the oil film thickness, but is proportional to the fuel penetration depth divided by the Henry’s constant. Then, the oxidation of the desorbed fuel (using iso-octane as fuel) is examined with a one-dimensional reaction/diffusion model. The novel feature of the model is that the desorbed fuel is being exposed to the piston crevice hydrocarbon, which is laid along the liner as the piston descends. At stoichiometric conditions, the oxidation of the crevice HC is reduced by the presence of the desorbed HC from the oil layer.
Development of a Dynamic Model for Predicting the Rigid and Flexible Motions of the Crank Slider Mechanism
Authors: Nehme H. , Chalhoub N. G. , Henein N.
Published: February 2008

A continuous model is developed to predict the rigid and flexible motions of the piston assembly/connecting rod/crankshaft mechanism for a single cylinder engine. The model accounts for the torsional vibration and the out-of-plane transverse deformation of the crankshaft along with the out-of-plane transverse deformation of the connecting rod. The eigenvalue problem of the crankshaft, including the counterweights, the flywheel, and the crank gear, is solved to obtain the analytical expressions for the elastic modes of the crankshaft. The resulting mode shapes are then used in the assumed modes method to approximate the structural flexibility terms. The differential-algebraic equations of motion are obtained by implementing the Lagrange principle. The digital simulation results illustrate the role played by the topological nonlinearities inherent in the system and reveal the relationships with which the rigid and flexible motions of the crank-slider mechanism would interact.
A Fast-Response Total temperature Probe For Unsteady compressible Flows
Authors: Buttsworth D. R. , Jones T. V.
Published: February 2008

A fast-response probe for the measurement of total temperature in unsteady or fluctuating compressible flows is discussed. The operation of the device is based on the measurement of transient heat flux at different probe operating temperatures. The heat flux gauges used in the present investigation were thin film platinum resistance thermometers painted onto the stagnation region of hemispherical fused quartz probes. The quartz probes had a diameter of approximately 3 mm. Uncertainty estimates indicate that temperature measurements with an accuracy of better than ±3 K are possible. As a demonstration of the accuracy and utility of the device, total temperature and convective heat transfer coefficient measurements were obtained in a number of supersonic nozzle tests and in a compressible turbulent jet experiment.
Evaluation of CH4/NOx Reduced Mechanisms Used for Modeling Lean Premixed Turbulent Combustion of Natural Gas
Authors: Mallampalli H. P. , Fletcher T. H. , Chen J. Y.
Published: February 2008

This study has identified useful reduced kinetic schemes that can be used in comprehensive multidimensional gas-turbine combustor models. Reduced mechanisms lessen computational cost and possess the capability to accurately predict the overall flame structure, including gas temperatures and key intermediate species such as CH4, CO, and NOx. In this study, four new global mechanisms with five, six, seven, and nine steps based on the full GRI 2.11 mechanism, were developed and evaluated for their potential to model natural gas chemistry (including NOx chemistry) in gas turbine combustors. These new reduced mechanisms were optimized to model the high pressure and fuel-lean conditions found in gas turbines operating in the lean premixed mode. Based on perfectly stirred reactor (PSR) and premixed code calculations, the five-step reduced mechanism was identified as a promising model that can be used in a multidimensional gas-turbine code for modeling lean-premixed, high-pressure turbulent combustion of natural gas. Predictions of temperature, CO, CH4, and NO from the five-to nine-step reduced mechanisms agree within 5 percent of the predictions from the full kinetic model for 1 < pressure (atm) < 30, and 0.6 < φ < 1.0. If computational costs due to additional global steps are not severe, the newly developed nine step global mechanism, which is a little more accurate and provided the least convergence problems, can be used. Future experimental research in gas turbine combustion will provide more accurate data, which will allow the formulation of better full and reduced mechanisms. Also, improvement in computational approaches and capabilities will allow the use of reduced mechanisms with larger global steps, perhaps full mechanisms.
Numerical Predication of the Dynamic Behavior of Turbulent Diffusion Flames
Authors: Bohn D. , Deutsch G. , Kru¨ger U.
Published: February 2008

Environmental compatibility requires low-emission burners for gas turbine power plants as well as for jet engines. In the Past, significant progress has been made developing low NOx and CO burners. Unfortunately, these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations. The oscillations may be excited to such an extent that pronounced pulsation may possibly occur; this is associated with a risk of engine failure. The stability of a burner system can be investigated by means of a stability analysis under the assumption of acoustical behavior. The problem with all these algorithms is the transfer function of the flame. A new method is presented here to predict the dynamic flame behavior by means of a full Navier-Stokes simulation of the complex combustion process. The first step is to get a steady-state solution of a flame configuration. After that a transient simulation follows with a sudden change in the mass flow rate at the flame inlet. The time-dependent answer of the flame to this disturbance is then transformed into the frequency space by a Laplace Transformation. This leads, in turn, to the frequency response representing the dynamic behavior of the flame. In principle, this method can be adapted for both diffusion as well as premixed flame systems. However, due to the fact that diffusion flames are more controlled by the mixing process than by the chemical kinetic, the method has first been used for the prediction of the dynamic behavior of turbulent diffusion flames. The combustion has been modelled by a mixed-is-burnt model. The influence of the turbulence has been taken into account by a modified k-ε model and the turbulence influences the combustion rate by presumed probability density functions (pdf). The steady state as well as the transient results have been compared with experimental data for two different diffusion flame configurations. Although the burner configuration is relatively complex, the steady-state results collaborate very well with the experiments for velocity, temperature, and species distribution. The most important result is that the heat release that drives the oscillations can be modeled sufficiently accurately. The effect of using different pdf models has been discussed and the best model has been used for the transient calculations of the dynamic flame behavior. The results for the frequency response of the flame are very encouraging. The principal behavior of the flame—higher order time element with a delay time—can be predicted with sufficient precision. In addition, the qualitative results collaborate fairly well with the experiments.
Development of a Corrosion Resistant Directionally Solidified Material for Land Based Turbine Blades
Authors: Cheruvu N. S.
Published: February 2008

Advanced turbines with improved efficiency require materials that can operate at higher temperatures. Availability of these materials would minimize cooling flow requirements, and, thus, improve the efficiency of a turbine. Advanced processing. such as directional solidification (DS), can improve temperature capability of the majority of Ni based superalloys. However, results of earlier work on IN-738 reveal that the DS process does not significantly improve temperature capability of this alloy. A research program was initiated to develop a corrosion resistant Ni-based DS blade material for land based turbines. In this program, eight heats with varied Cr, Al, Ti, Ta, and W contents were selected for evaluation. Screening tests performed on these heats in the DS condition include tensile, creep, and corrosion. The Results of experimental heats were compared with those of IN-738 in the equiaxed condition. From these results, two chemistries offering approximately 100°F temperature advantage at typical row I turbine blade operating stress were selected for castability and further mechanical property evaluation. Several row 1 solid and cored turbine blades were successfully cast. The blades were evaluated for grain structure and mechanical properties. Tests were also conducted to evaluate the effects of withdrawal rates on properties. These results are summarized in this paper.
Characterization of Laws of Friction in the Context of Engine Blade Dynamics
Authors: Srinivasan A. V. , McFarland D. M.
Published: February 2008

Experience has shown that energy dissipation due to rubbing at interfaces of engine blade shrouds provides damping of bladed disk assemblies. An accurate estimate of such damping has been a subject of study for more that a decade. The most difficult parameter that influences its accurate calculation pertains to an appropriate definition of the laws of friction that relate the rubbing motion with the forces induced. This paper develops an analysis that leads to a mathematical relationship between the forces of friction damping at a vibrating interface and the corresponding relative motion. The analysis permits calculation of forces at the interface if the displacements are known or vice. The equations are cast in terms of relative motion between mating shrouds so that degenerate cases of fully locked and freely slipping can be calculated. Examples are given showing simulation results obtained using discrete structural models. Extension of the analysis to the case of a full assembly is discussed.
Experimental Investigation and Theoretical Predication of Flutter Behavior of a Plane Cascade in Low Speed Flow
Authors: Hennings H. , Send W.
Published: February 2008

The Institute of Aeroelasticity operates a test facility which enables aeroelastic investigations of plane cascades in low-speed flow. The test stand serves as a pilot facility to develop tools for analogous investigations in transonic flow. Eleven blades are elastically suspended in a windtunnel with a 1 × 0.2 m2 cross section. This paper describes the experimental method of determining the flutter boundary by extrapolation of the results measured in subcritical flow. A two-dimensional theoretical model of the 11 blades, including the windtunnel walls, permits the computation of unsteady pressures, forces, and moments in close relation to the experiment. The prediction of flutter is compared with experimental results. In the present investigation, the motion of the blades is constrained to pitch around mid-chord. The vibrating blades are mechanically uncoupled. Any interaction between the blades is effected by the air stream, leading to a sensitive dependence on the aerodynamic forces.
Crack Identification in a Cantilever Beam Using Coupled Response Measurements
Authors: Sekhar A. S. , Prasad P. Balaji
Published: February 2008

Identification of crack location and magnitude through measurement in changes in system characteristics, such as modal measurements, has been studied by various researchers. In the present work based on the new method proposed by Gounaris et al. (1996) for crack detection through coupled response measurements, experiments were carried out on a cracked cantilever beam for eigenfrequencies, bending, and axial response measurements. It has been observed that the rate of change of direct response (bending) is much less at small cracks, while that of the coupled response (axial) changes substantially, which allows for diagnoses of smaller cracks.
A Comparison of Experimental Rotordynamic Coefficients and Leakage Characteristics Between Hole-Pattern Gas Damper Seals and a Honeycomb Seal
Authors: Yu Z. , Childs D. W.
Published: February 2008

Honeycomb annular seals are an attractive design alternative due to their superior static and dynamic performance. However, their implementation in industrial practice has been delayed by the following characteristics: a) manufacturing time can be appreciable, and b) they can seriously damage the shaft if rubbing occurs. To minimize these problems, “hole-pattern” gas damper seals, which are formed by simply drilling holes into an annular smooth seal, were manufactured and tested. The hole-pattern damper seal stator can be made of high-strength plastic materials which are less likely to damage a shaft during rubbing. The experimental results presented demonstrate that, compared to a honeycomb seal, a hole-pattern damper seal with 3.18 mm hole diameters and a high percentage of hole surface has achieved: (a) an average of 12 percent reduction in leakage rate, and(b) considerably higher effective damping, especially under high speeds and low inlet pressure ratio conditions.
A Survey of Blade Tip-Timing Measurement Techniques for Turbomachinery Vibration
Authors: Heath S. , Imregun M.
Published: February 2008

This paper aims at providing a comparative survey of current analysis methods for the interpretation of vibration data measured at turbomachinery rotor blade tips using optical laser probes. The methods are classified by the form of the vibration that they attempt to identify, namely, asynchronous and synchronous with respect to rotor speed. The performance of the various techniques is investigated by using both actual assembly measurements and simulated response data. In the latter case, synchronous vibration data are obtained via a multidegree-of-freedom numerical simulator that includes the structural and geometric properties of the bladed-disk assembly, the external forcing terms, and the characteristics of the optical probe. When using experimental data, the results of the tip timing analysis are compared to those obtained from standard strain-gauge tests and the relative merits of the two approaches are discussed with emphasis on the effects of blade mistuning. Existing industry standard, tip-timing analysis techniques are found to exhibit a number of inherent limitations and suggestions were made to address these deficiencies. A detailed tip-timing case study for a steam turbine rotor is presented in some detail, and other potential application areas are explored. Of particular note is the introduction of a new indirect analysis method for identifying the characteristics of synchronous vibration modes using measurements from two probes. Finally, new avenues for future analysis methods and further developments in tip-timing systems are also discussed.
Crack Initiation in a Coated and an Uncoated Nickel-Base Superalloy Under TMF Conditions
Authors: Johnson P. K. , Arana M. , Ostolaza K. M. , Bressers J.
Published: February 2008

A thermomechanical fatigue (TMF) cycle, intended to represent aeroengine blade working conditions, was selected for carrying out tests on uncoated and aluminide coated SRR99 samples until test piece failure. Optical images of the surface of test pieces were collected during testing to monitor surface crack initiation and accompanying transformations. Using these images, surface changes were quantified as a function of time. Post test each sample was taken through an incremental polishing procedure to allow damage in the tested material to be studied as a function of depth, using optical microscope-based quantitative metallography and scanning electron microscopy (SEM). The relationship between the observed surface changes and the damage built-up subsurface was examined. Differences in damage density on the surface and subsurface planes between coated and uncoated samples could accommodate the observed life reductions.
Theory and Methodology of Optimally Measuring Vibratory Strains in Closely Spaced Modes
Authors: Yang M.-T. , Griffin J. H.
Published: February 2008

Stress ratios are traditionally used to infer maximum stresses in blades from strain measurements. This method may not be applicable to all the modes of modern low aspect ratio (LAR) blades since LAR blades often have high frequency “tip” modes that are so closely spaced that slight changes in structural properties can cause significant mode shape changes. In this paper, it is first shown that the actual tip modes of a LAR blade can be well approximated as linear combinations of the “nominal” modes. The stress field of the blade can then be estimated by calculating the modal content from multiple strain measurements. However, since placement and gage inaccuracies can introduce significant errors in the calculation, it is necessary to find the optimal gage placement that minimizes the error in estimated stresses. An error estimate using “norms” and an efficient optimization method are developed for this purpose.
An Experimental Determination of Losses in a Three-Port Wave Rotor
Authors: Wilson J.
Published: February 2008

Wave rotors, used in a gas turbine topping cycle, offer a potential route to higher specific power and lower specific fuel consumption. In order to calculate this potential realistically, a knowledge of the loss mechanisms is required. The experiment reported here was designed as a statistical experiment to identify the losses due to finite passage opening time, friction, and leakage, using a three-port, flow divider, wave rotor cycle. Incidence loss was also found to be important. Rotors of 12 in. diameter were used, with two different lengths, 9 in. and 18 in., and two different passage widths, 0.25 in. and 0.54 in., in order to vary friction and opening time. To vary leakage, moveable end walls were provided so that the rotor to end wall gap could be adjusted. The experiment is described, and the results are presented, together with a parametric fit to the data.
The Development of a Combustion System for a 110 MW CAES Plant
Authors: Hounslow D. R. , Grindley W. , Loughlin R. M. , Daly J.
Published: February 2008

The use of stored energy systems is receiving increased attention for power generation. Alabama Electric Co-operative (AEC) have installed a 110 MW Compressed Air Energy Storage (CAES) plant at McIntosh, Alabama. The plant employs tandem high and low-pressure fired expanders with the high-pressure combustors operating at 44 atm and the low-pressure units at 15 atm. Both are designed to operate with natural gas, or on No. 2 fuel oil, as a standby fuel. This paper describes the development of both the high and low-pressure combustors for this unique application, the testing of prototypes at simulated conditions at up to 8 atm using customized test rigs, and the definition of a design for application to the plant. Problems encountered during the first three years of operation are described and the solutions to overcome these are also presented.
Rapid Characterization of Fuel Atomizers Using an Optical Patternator
Authors: Sankar S. V. , Maher K. E. , Robart D. M. , Bachalo W. D.
Published: February 2008

Planar laser scattering (PLS) and planar laser-induced fluorescence (PLIF) techniques are currently being used for rapid characterization of fuel sprays associated with gas turbine atomizers, diesel injectors, and automotive fuel injectors. These techniques can be used for qualitative, quantitative, and rapid measurement of fuel mass, spray geometry, and Sauter mean diameters in various sprays. The spatial distribution of the fuel mass can be inferred directly from the PLIF image, and the Sauter mean diameter can be measured by simultaneously recording the PLIF and PLS images and then ratioing the two. A spray characterization system incorporating the PLS and/or PLIF techniques has been loosely termed an optical patternator, and in this study, it has been used to characterize both steady and pulsed sprays. The results obtained with the optical patternator have been directly validated using a phase Doppler particle analyzer (PDPA).
Nonlinear Heat-Release/Acoustic Model for Thermoacoustic Instability in Lean Premixed Combustors
Authors: Peracchio A. A. , Proscia W. M.
Published: February 2008

Lean premixed combustors, such as those used in industrial gas turbines to achieve low emissions, are often susceptible to the thermoacoustic combustion instabilities, which manifest themselves as pressure and heat release oscillations in the combustor. These oscillations can result in increased noise and decreased durability due to vibration and flame motion. A physically based nonlinear parametric model has been developed that captures this instability. It describes the coupling of combustor acoustics with the rate of heat release. The model represents this coupling by accounting for the effect of acoustic pressure fluctuations on the varying fuel/air ratio being delivered to the flame, causing a fluctuating heat release due to both fuel air ratio variations and flame front oscillations. If the phasing of the fluctuating heat release and pressure are proper, an instability results that grows into a limit cycle. The nonlinear nature of the model predicts the onset of the instability and additionally captures the resulting limit cycle. Tests of a lean premixed nozzle run at engine scale and engine operating conditions in the UTRC single nozzle rig, conducted under DARPA contract, exhibited instabilities. Parameters from the model were adjusted so that analytical results were consistent with relevant experimental data from this test. The parametric model captures the limit cycle behavior over a range of mean fuel air ratios, showing the instability amplitude (pressure and heat release) to increase and limit cycle frequency to decrease as mean fuel air ratio is reduced.
High Pressure Test Results of a Catalytically Assisted Ceramic Combustor for a Gas Turbine
Authors: Ozawa Y. , Tochihara Y. , Mori N. , Yuri I. , Kanazawa T. , Sagimori K.
Published: February 2008

A catalytically assisted ceramic combustor for a gas turbine was designed to achieve low NOx emission under 5 ppm at a combustor outlet temperature over 1300°C. This combustor is composed of a burner system and a ceramic liner behind the burner system. The burner system consists of 6 catalytic combustor segments and 6 premixing nozzles, which are arranged in parallel and alternately. The ceramic liner is made up of the layer of outer metal wall, ceramic fiber, and inner ceramic tiles. Fuel flow rates for the catalysts and the premixing nozzles are controlled independently. Catalytic combustion temperature is controlled under 1000°C, premixed gas is injected from the premixing nozzles to the catalytic combustion gas and lean premixed combustion over 1300°C is carried out in the ceramic liner. This system was designed to avoid catalytic deactivation at high temperature and thermal and mechanical shock fracture of the honeycomb monolith of the catalyst. A combustor for a 10 MW class, multican type gas turbine was tested under high pressure conditions using LNG fuel. Measurements of emission, temperature, etc. were made to evaluate combustor performance under various combustion temperatures and pressures. This paper presents the design features and the test results of this combustor.
Active Control of Combustion for Optimal Performance
Authors: Jackson M. D. , Agrawal A. K.
Published: February 2008

Combustion-zone stoichiometry and fuel-air premixing were actively controlled to optimize the combustor performance over a range of operating conditions. The objective was to maximize the combustion temperature, while maintaining NOx within a specified limit. The combustion system consisted of a premixer located coaxially near the inlet of a water-cooled shroud. The equivalence ratio was controlled by a variable-speed suction fan located downstream. The split between the premixing air and diffusion air was governed by the distance between the premixer and shroud. The combustor performance was characterized by a cost function evaluated from time-averaged measurements of NOx and oxygen concentrations in products. The cost function was minimized by the downhill simplex algorithm employing closed-loop feedback. Experiments were conducted at different fuel flow rates to demonstrate that the controller optimized the performance without prior knowledge of the combustor behavior.
Flow Measurements in a Curved-Wall Annular Contraction
Authors: Agrawal A. K. , Tinneti A. , Gollahalli S. R.
Published: February 2008

Flow development in an annular contraction is of fundamental and practical importance in various applications including the gas turbine systems. This paper describes an experimental study of flow characteristics in a curved wall annular contraction. The results are presented in terms of the velocity vectors, surface pressure coefficients, static and stagnation pressure distributions, and profiles of mean velocities, turbulence intensity, and Reynolds shear stress. The flow conditions at the entrance were varied to evaluate how they affected the flow development in the passage. Results show that the contraction produced uniform static pressure and axial velocity profiles at the exit plane. Higher inlet turbulence affected the Reynolds shear stress in the contraction although the change in the static and total pressure fields was insignificant. The overall stagnation pressure loss was only 2 to 3 percent of the dynamic head at the contraction exit plane. Results showing only typical data are included in this paper. More extensive data sets to validate computer codes are available from the authors.
Minimization of the Local Rates of Entropy Production in the Design of Air-Cooled Gas Turbine Blades
Authors: Natalini G. , Sciubba E.
Published: February 2008

The paper presents the results of a numerical configuration study made on a two dimensional model of an internally cooled gas turbine vane. The analysis applies to a two-dimensional cascade at medium Reynolds number, subsonic Mach number, and steady state. The full Navier-Stokes equations of motion for turbulent viscous flow, together with the appropriate energy equation, are solved via a standard finite-element code with a k-ε closure, to obtain complete velocity and temperature fields. These fields are then used to compute the entropy generation rates corresponding to the viscous (sv) and thermal (st) dissipation. The thermo-fluid dynamic efficiency of difference versions of the same base configuration is assessed comparing the global (or integral) entropy generation rate in the passage. The procedure is general, can be extended to different configurations and different operational conditions, and provides the designer with a rational and effective tool to assess the actual losses in the fixed and rotating turbomachinery cascades.
Stability Analysis and Testing of a Train of Centrifugal Compressors for High Pressure Gas Injection
Authors: Memmott E. A.
Published: February 2008

This paper describes the rotor dynamic stability analysis and the PTC-10 Class 1 test of a three body centrifugal compressor train for high pressure natural gas injection service. This train had a full load full pressure string test on hydrocarbon gasses to a final discharge pressure of 500 BAR (7250 PSIA). Each compressor is of the back to back configuration, and is equipped with tilting pad seals, damper bearings, and a honeycomb labyrinth at the division wall with shunt holes. The driver is a gas turbine.
Compression Ratio Effect on Methane HCCI Combustion
Authors: Aceves S. M. , Smith J. R. , Westbrook C. K. , Pitz W. J.
Published: February 2008

We have used the HCT (hydrodynamics, chemistry, and transport) chemical kinetics code to simulate HCCI (homogeneous charge compression ignition) combustion of methane-air mixtures. HCT is applied to explore the ignition timing, burn duration, NOx, production, gross indicated efficiency and gross IMEP of a supercharged engine (3 atm. intake pressure) with 14:1, 16:1 and 18:1 compression ratios at 1200 rpm. HCT has been modified to incorporate the effect of heat transfer and to calculate the temperature that results from mixing the recycled exhaust with the fresh mixture. This study uses a single reaction zone that varies as a function of crank angle. The ignition process is controlled by adjusting the intake equivalence ratio and the residual gas trapping (RGT). RGT is internal exhaust gas recirculation, which recycles both thermal energy and combustion product species. Adjustment of equivalence ratio and RGT is accomplished by varying the timing of the exhaust valve closure in either two-stroke or four-stroke engines. Inlet manifold temperature is held constant at 300 K. Results show that, for each compression ratio, there is a range of operational conditions that show promise of achieving the control necessary to vary power output while keeping indicated efficiency above 50 percent and NOx levels below 100 ppm. HCT results are also compared with a set of recent experimental data for natural gas.
LM2500 Gas Turbine Fuel Nozzle Design and Combustion Test Evaluation and Emission Results With Simulated Gasified Wood Product Fuels
Authors: Neilson C. E. , Shafer D. G. , Carpentieri E.
Published: February 2008

The Brazilian Wood Biomass Demonstration Project (WBP) Phase II was contracted with the United Nations Development Programme-PNUD, Setor Comerical Norte, Quadra 2-BLOCO A, EDF. Corporation-7o Andar, Brasilia-DF Brasil 70712-900 and General Electric Marine and Industrial Engines to develop the gas turbine equipment necessary to utilize fuel produced by the gasification of wood products. The program included performance studies, control specification requirements, bleed and fuel valve specifications, a modified dual gas fuel nozzle for fuel delivery to the combustor and results of two combustor component tests utilizing biomass simulated fuel. This paper will deal primarily with the fuel nozzle design elements, the setup and evaluation of the component combustor tests and resulting emissions produced by the simulated Biomass fuel. Details of the combustor test arrangement, facilities and special test equipment needed to complete the evaluation will be presented. In addition, background on the two types of combustor testing will be discussed.
CO2 Emission Abatement in IGCC Power Plants by Semiclosed Cycles: Part A—With Oxygen-Blown Combustion
Authors: Chiesa P. , Lozza G.
Published: February 2008

This paper analyzes the fundamentals of IGCC power plants where carbon dioxide produced by syngas combustion can be removed, liquefied and eventually disposed, to limit the environmental problems due to the “greenhouse effect.” To achieve this goal, a semiclosed-loop gas turbine cycle using an highly-enriched CO2 mixture as working fluid was adopted. As the oxidizer, syngas combustion utilizes oxygen produced by an air separation unit. Combustion gases mainly consists of CO2 and H2O: after expansion, heat recovery and water condensation, a part of the exhausts, highly concentrated in CO2, can be easily extracted, compressed and liquefied for storage or disposal. A detailed discussion about the configuration and the thermodynamic performance of these plants is the aim of the paper. Proper attention was paid to: (i) the modelization of the gasification section and of its integration with the power cycle, (ii) the optimization of the pressure ratio due the change of the cycle working fluid, (iii) the calculation of the power consumption of the “auxiliary” equipment, including the compression train of the separated CO2 and the air separation unit. The resulting overall efficiency is in the 38–39 percent range, with status-of-the-art gas turbine technology, but resorting to a substantially higher pressure ratio. The extent of modifications to the gas turbine engine, with respect to commercial units, was therefore discussed. Relevant modifications are needed, but not involving changes in the technology. A second plant scheme will be considered in the second part of the paper, using air for syngas combustion and a physical absorption process to separate CO2 from nitrogen-rich exhausts. A comparison between the two options will be addressed there.