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RESEARCH PAPERS

J. Eng. Gas Turbines Power. 1984;106(4):716-724. doi:10.1115/1.3239629.

The paper describes a throughflow computational method that combines wet steam theory with an axisymmetric streamline curvature technique in order to predict nonequilibrium effects in low-pressure steam turbines. The computer program developed is able to deal with both subsonic and fully choked supersonic flows, and steam properties are represented by a truncated virial equation of state. A number of theoretical test cases have been investigated, including the nonequilibrium flow in the primary nucleating stage of a low-pressure turbine and the complete analysis of a six-stage, 320-MW operational turbine. The calculations are the first of their kind in being able to provide information on the spanwise variation of the Wilson point, the average droplet size nucleated, the degree of supercooling throughout the flowfield, the thermodynamic wetness loss, and the nonequilibrium choking mass flow rate in addition to the aerodynamic parameters which are of interest to the designer.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):725-730. doi:10.1115/1.3239630.

During the decade of the 1960s, industrial users recognized the gas turbine as a reliable prime mover for base load process applications. Gas turbine cogeneration systems were installed in various industries, including chemical, petroleum refining, pulp and paper, and metals. Typically, the size of the cogeneration system considered, and thus the gas turbine size, was governed by the internal heat and power demands of the specific plant. More recently, worldwide concern with regard to the cost and efficient use of energy is providing continuing opportunities for gas turbine cogeneration systems. In some locations, legislation is being enacted to encourage the development of cogeneration to the benefit of the public. This legislation can increase the number of alternative methods in which a cogeneration system can be developed. This paper will briefly review cogeneration principles applicable to the development of gas turbine energy supply systems. The wide range of conditions that can be satisfied using gas turbine cogeneration systems will be introduced. Brief discussions of recent installations are presented, illustrating the actual applications of some of these concepts.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):731-736. doi:10.1115/1.3239631.

Under Gas Research Institute (GRI) sponsorship, a new gas turbine cogeneration system was developed by Mechanical Technology, Inc., (MTI) for installation at a General Motors plant in early 1985. Specific emphasis was placed on system integration. A single, prime-reliable drive train and a single control center replace a wide assortment of nonintegrated, free-standing power drives and control centers. On-line availability, installation costs, and overall user acceptance are improved. The cogeneration set produces 3 MWe and 8,860 kg/hr (19,500 lb/hr) of 1825 kPa (250 psig) saturated steam using an Allison 501-KH gas turbine and a natural circulation waste heat boiler. The system is designed for multifuel operation using either natural gas or distillate oil. A steam injection feature is employed to increase output to 4 MWe when process steam demand diminishes. The system is prepackaged, skid mounted, and delivered in four modules: one each for the machinery, duct burner, waste heat boiler, and controls.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):737-742. doi:10.1115/1.3239632.

A new thermodynamic energy cycle has been developed using a multicomponent working agent. This cycle is designed to replace the currently used Rankine Cycle as a bottoming cycle for a combined-cycle energy system as well as for generating electricity using low-temperature heat sources. Several combined power systems based on this cycle have been designed and cost-estimated. The efficiency of this cycle is from 1.6 to 1.9 times higher than that of the Rankine Cycle system, at the same border conditions. The investment cost per unit of power output for this cycle is lower than that for the Rankine Cycle system in approximately direct proportion to the energy advantage. The application of this cycle as a bottoming cycle in combined-cycle systems involves the use of an energy system which utilizes heat from the exhaust of a gas turbine, resulting in an increase in overall efficiency of up to 20 percent above the efficiency of the combined systems using the Rankine bottoming cycle. As a result, a thermal efficiency in the range of 50–52 percent can be achieved using a conventional gas turbine. The project to build the first experimental installation is now in progress. This installation is to become operational at the end of 1984.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):743-749. doi:10.1115/1.3239633.

The isothermal (or multiple-reheat) gas turbine performs the combustion/work extraction process at a sustained, elevated temperature. This has distinct thermodynamic advantages in combined cycles for given peak temperature constraints. A thermodynamic model for this cycle is developed. Although based on a simple CO/CO2 /O2 chemcial system the results are applicable to other reactants and dilutants. Combined cycle efficiency is reported for different gas turbine pressure ratios, peak temperatures, reactant dilution and steam cycle conditions. The range of parameters investigated starts from present-day advanced technologies and examines the potential of higher pressures and temperatures. Balances of thermodynamic availability are used to interpret the results. They show that for a given steam cycle and gas turbine pressure ratio, increasing peak temperature beyond a certain value provides sharply diminishing return. This is because the reduction in combustion irreversibility is offset by increased heat transfer irreversibility. Higher pressure ratios or steam cycle temperatures can raise this optimum peak temperature. In view of the various technological constraints, the authors’ conclusion is that an isothermal gas turbine with a peak temperature and pressure-ratio of about 1600K and 100:1, respectively, represents the most promising next step in technology. Coupled with existing advanced steam cycles this should provide efficiencies in the 60 percent range.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):750-755. doi:10.1115/1.3239634.

A comparative study of the influence of different means of cooling on the thermodynamic efficiency and specific power of combined (gas and steam turbines) cycle is presented. The study extends the previously developed methodology evaluating the influence of cooling and coolant requirements on gas turbine performance. In this study, the exhaust gases of the gas turbine are used as the heat source to a steam cycle using single reheat with a specified temperature difference at the pinch point. The sensitivity of the overall cycle efficiency to each key input parameter is reported.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):756-764. doi:10.1115/1.3239635.

Recent developments in high-performance and high-reliability gas turbine engines necessitate enforced cooling to maintain the blade temperature at reasonably low levels associated with increased turbine inlet temperature and compressor pressure ratio. However, the gas turbine performance is strongly penalized by the consumption of cooling flow, resulting in temperature dilution of hot mainstream, aerodynamic mixing loss, and pumping power loss. In this paper, a new practical blade cooling system using state-of-the-art engineering, which aims at minimizing the dilution effect, is presented. Trade-off studies between performance and reliability in terms of blade metal temperature are performed to evaluate cooling systems. Analytical comparison of different cooling systems demonstrates that the proposed cooling system provides significant improvements in performance gain and growth potential over conventional air cooling systems.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):765-770. doi:10.1115/1.3239636.

Evaporative cooling towers and cooling ponds are in ever-increasing use for the dissipation of waste heat. The modeling of moist plumes from these facilities has received considerable attention in recent years. The simulation of plume thermodynamics is a necessary part of the modeling of a moist plume. This paper describes an algorithm which, when supplied with the ambient atmospheric distribution of various thermodynamic properties, performs the necessary psychrometric calculations to simulate the thermodynamics within the moist plume. A unique feature of this algorithm is the modeling of the condensation of “excess” water vapor, which simulates the formation and deposition of water droplets from the moist plume.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):771-776. doi:10.1115/1.3239637.

Previous measurements of the spectral emissivity of coal ashes are converted to total absorptivities and emissivities. Below the temperature at which ash sinters, the total absorptivity of an ash layer—which is necessary for the estimation of radiative transfer in furnaces—is shown to depend on both the source (flame) temperature and the ash temperature. Synthetic mixtures of the oxides Al2 O3 , SiO2 , and Fe2 O3 are shown to give the same trends as those for ashes of the same Fe2 O3 content.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):777-781. doi:10.1115/1.3239638.

The performance of high-temperature slagging coal-utilization systems depend on the collection of coal ash on the reactor surfaces and the flow of the slag out of the reactor through a slag-tap hole. In order to develop an analytical model for flow of the slag on a reactor wall, existing data for slag viscosity were reviewed in light of new emerging-process conditions. A Bingham model was selected for viscosity and the flow characteristics along a reactor wall are developed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):782-788. doi:10.1115/1.3239639.

Municipal refuse-derived fuel and coal were cofired in a retrofitted 125,000 lb steam/hr (55,000 kg/hr) spreader-stoker boiler. Results from 19 tests, which include fuel characteristics, boiler performance, particulate and gaseous emissions, and trace element emissions, are reported. System design and economic considerations are also discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):789-794. doi:10.1115/1.3239640.

The sooting tendencies of various fuel blends containing either single-ring or polycyclic aromatics have been studied in a model gas turbine combustor at a pressure of 1.0 MPa and varying values of air/fuel ratio. Sooting tendencies were determined by flame radiation, exhaust soot, and infra-red absorption measurements. The results of this study have indicated that, even for fuels containing high concentrations of naphthalenes or tetralins (> 10 percent v), fuel total hydrogen content correlates well with fuel sooting tendency. The present results are explained by a hypothesis that assumes that the majority of soot is formed in regions of high temperature, low oxygen content, and low fuel concentration, e.g., the recirculation zone.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):795-800. doi:10.1115/1.3239641.

Two stage premixed combustor with variable geometry has been developed to meet stringent NOx goals in Japan without the use of water or steam injection. This combustion system is planned to be applied for 120-MW gas turbine in 1090-MW LNG combined cycle plant. The full-pressure, full-scale combustion tests were conducted over a wide range of operating conditions for this gas turbine. The combustion tests proved that NOx levels as well as mechanical characteristics were well within the goals.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):801-805. doi:10.1115/1.3239642.

A nominal 293 kw (1 MBtu/hr) atmospheric pressure, refractory-lined combustor has been used to investigate the effects of a number of combustor and fuel dependent variables on combustion efficiency and flue gas characteristics for minimally cleaned, coal-derived gas (MCG) and coal water mixtures. The variables which have been evaluted include: percent excess air, air distribution, combustion air preheat temperature, swirl number, fuel feedrate, coal particle size, coal loading in slurry, and slurry viscosity. Characterization of the flue gas included major/minor gas species, alkali levels, and particulate loading, size, and composition. These atmospheric pressure combustion studies accompanied by data from planned pressurized studies on coal-water slurries and hot, minimally cleaned, coal-derived gas will aid in the determination of the potential of these fuels for use in gas turbines.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):806-811. doi:10.1115/1.3239643.

A 14-MW, high-temperature gas turbine firing extremely low-BTU, blast-furnace gas was developed and installed in a steel works of Japan as a repowering unit. Field tests proved the stable combustion up to 590 Kcal/Nm3 calorific value and plant efficiency improvement of up to 60 percent on existing steam plant. Design features and two years operational experiences are presented.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):812-818. doi:10.1115/1.3239644.

At Qaisumah, Saudi Arabia, there are four GE MS5001P Gas Turbines operated by the Saudi Consolidated Electric Company in the Eastern Province (SCECO East). The Power Plant is not connected to the main SCECO grid and experiences near-capacity peak load demands in the summer months. Its remoteness and proximity to the Trans-Arabian Pipeline (TAPLINE) dictates the burning of Light Saudi Arabian Crude Oil which is desalted by centrifugal purification without the addition of wash water. Eliminating the need for wash water is important because of the scarcity of water at this site. Power loss is controlled and shutdowns minimized during the critical summer months by removing the ash accumulation on the turbine components by on-line nutshell cleaning. This paper describes the first application of this waterless (dry centrifuge) fuel purification system and the impact of various turbine cleaning methods (particularly on-line nutshelling) on turbine performance, availability, and maintenance.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):819-824. doi:10.1115/1.3239645.

Historically, two of the principal hindrances to the design of effective marine gas turbine inlet systems have been the inability to define the marine environment and to identify the influence of this environment on the inlet system configuration. This paper summarizes the work done by the U.S. Navy to qualitatively and quantitatively define the composition of the marine atmosphere and identify inlet system design practices that can be employed to assist in designing an effective combustion air inlet system.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):825-832. doi:10.1115/1.3239646.

The role played by oxides of nitrogen in the formation of photochemical smog has been known for many years. However, because of the relatively small fraction of power generated by gas turbines, there were no significant attempts at limiting gas turbine NOx emissions in the United States until about 15 years ago. This paper outlines General Electric’s experience with NOx abatement techniques from then until the present.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):833-840. doi:10.1115/1.3239647.

A Perfectly Stirred Reactor model, kinetic rate data, and equilibrium adiabatic flame temperatures have been incorporated into a closed form NOx prediction algorithm. The algorithm accounts for combustor inlet parameters and steam injection. Combining this model with the operating map for the gas turbine allows prediction of NOx with variation in parameters such as inlet guide vane angle, ambient temperature, and load. If the actual values of the model input variables are measured, real time prediction of NOx emissions may be generated using a microcomputer. This signal may then be used as an input to NOx abatement systems such as Selective Catalytic Reduction. The semitheoretical technique is based upon the extended Zeldovich chain reaction kinetics for the production of NOx in the post-flame zone. The temperature and concentration of major product species in the post-flame zone are taken to be those appropriate to equilibrium. Steam injection and inlet effects enter the model through their influence on the abiabatic equilibrium flame temperature. Mixing effects are accounted for empirically.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):841-848. doi:10.1115/1.3239648.

Factors relevant to the utilization of nonanhydrous ethanol as a blending component with gasoline for use in current on-the-road spark ignition engines are investigated. Miscibility limits are determined and key physical properties important for proper engine operation are measured. Dynamometer tests on an unmodified production engine with hydrated ethanol-gasoline blends containing varying percentages of water show potential for increased thermal efficiency and reduced oxides of nitrogen emissions.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):849-853. doi:10.1115/1.3239649.

The heating and gasification of a fuel droplet during the intake and compression strokes of an SI engine are modeled. Results show that the simultaneous increases in the gas temperature and pressure during compression tend to have compensatory effects on the droplet gasification rate such that it remains somewhat insensitive to changes in the cylinder environment. Generalized results are presented allowing for the assessment of the lower and upper bounds in the initial size of the droplet that can achieve complete gasification prior to the end of the compression stroke.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):854-859. doi:10.1115/1.3239650.
Abstract
Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):860-878. doi:10.1115/1.3239651.

Fuel costs can exceed 50 percent of the total diesel plant’s operational expenditures. To reduce fuel costs, medium-speed engines are now available with improved fuel consumption and ability to burn residual fuels. Part I of this paper reviews these engine and design changes needed for both improved fuel consumption and the ability to burn poorer quality fuels. Characteristics of these fuels and international fuel specifications are discussed. Ignition quality of residual fuels by a modified ASTM D 613 procedure are presented and correlation shown to calculated diesel index and calculated carbon aromaticity index (CCAI). Residual fuel ignition delay effects on combustion pressure rise, fuel consumption, and piston temperature in a laboratory single-cylinder diesel engine are shown.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):879-893. doi:10.1115/1.3239652.

Fuel costs can exceed 50 percent of the total diesel plant’s operational expenditures. To reduce fuel costs, medium-speed engines are now available with improved fuel consumption and ability to burn residual fuels. Part II of this paper reviews characteristics of lubricants suitable for use with distillate, residual, and blended fiels in medium-speed engines. Examples are shown of how lubricants and their additives control engine wear, deposits, and oxidation, and how fuel consumption is affected by viscosity. Control of insolubles and the purification of used lubricants are discussed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):895-900. doi:10.1115/1.3239654.

Efforts to quantify degradation of the performance of a centrifugal fan subjected to distorted inflows are presented. The study centered on examination of pressure rise, efficiency, and onset of stall for a backwardly-inclined, airfoil-bladed fan. Nonuniform flow patterns were generated in an adjustable countervane damper assembly installed upstream of the inlet box, and systematic families of performance curves were generated. Results of these tests show that significant degradation in efficiency and pressure rise—as much as 10 to 15 percent—may result from moderately to severely distorted inflow patterns. Onset of stall was significantly influenced by severely distorted inflows.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):901-905. doi:10.1115/1.3239655.

A study to evaluate the influence of increasing the clearance between blade and hub on a controllable pitch axial fan (CPAF) is presented. Fan performance was measured over a range of increasing clearance for several settings of blade pitch angles. The resulting variations of pressure rise, flow rate, and efficiency have been correlated as functions of established clearance parameters with good results. The study shows that large base clearances may result in reductions in efficiency and flow rate of 5 percent or greater in a typical CPAF configuration.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):906-912. doi:10.1115/1.3239656.

This paper describes a systematic study of the influence of the inlet clearance gap on the performance of a centrifugal fan. Overall fan performance in terms of volume flow rate, pressure rise, stall margin, and efficiency were measured over a range of values of the radial clearance between the impeller and the stationary inlet cone. These data have been correlated as functions of lumped clearance parameters. Additional data on velocity surveys in the impeller discharge are presented and discussed in relation to overall performance.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):913-919. doi:10.1115/1.3239657.

Predicted and measured surface velocity and pressure distributions in the internal flow channels of a centrifugal fan impeller are presented for volume flow rates between 80 and 125 percent of design flow rate. Predictions are based on a fully three-dimensional, finite element analysis of the inviscid, incompressible blade channel flow. Additional predictions using a conventional quasi-three-dimensional analysis are presented for comparison. Experimental results were developed using extensive blade and sidewall surface pressure taps installed in a scale model of an airfoil-bladed centrifugal fan impeller designed for heavy industrial and power generation applications. The results illustrate the ability of both flow analyses to predict the dominant features of the impeller flow field, including peak blade surface velocities and adverse gradients at flows far from the design point. In addition, the experimental results provide valuable insight into the limiting channel diffusion values for typical centrifugal cascade performance, and the influence of viscous effects as seen in deviations from the ideal flow predictions.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):920-926. doi:10.1115/1.3239659.

A theory is presented for the calculation of stiffness and damping coefficients of the fluid-rotor interaction in centrifugal compressor labyrinth seals based on turbulent flow calculations. The theory has been confirmed by measurements on labyrinth test stands and on a centrifugal compressor impeller shroud seal at pressures up to 140 bar. Predicted rotor stability limits based on the theory are in agreement with those observed in real compressors.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):927-934. doi:10.1115/1.3239660.

In order to soften the effects of rub, the smooth stators of turbine gas seals are sometimes replaced by a honeycomb surface. This deliberately roughened stator and smooth rotor combination retards the seal leakage and may lead to enhanced rotor stability. However, many factors determine the rotordynamic coefficients and little is known as to the effectiveness of these “honeycomb seals” under various changes in the independent seal parameters. This analysis develops an analytical-computational method to solve for the rotordynamic coefficients of this type of compressible-flow seal. The governing equations for surface-roughened tapered annular gas seals are based on a modified Hirs’s turbulent bulk flow model. A perturbation analysis is employed to develop zeroth and first-order perturbation equations. These equations are numerically integrated to solve for the leakage, pressure, density, and velocity for small motion of the shaft about the centered position. The resulting pressure distribution is then integrated to find the corresponding rotor-dynamic coefficients. Finally, an example case is used to demonstrate the effect of changing from a smooth to a rough stator while varying the seal length, taper, preswirl, and clearance ratio.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):935-939. doi:10.1115/1.3239661.

The continued use of gas turbines in industrial applications and increased customer desires for trend analysis has led gas turbine suppliers to develop sophisticated, reliable, cost-effective vibration monitoring systems. This paper discusses the application of case vibration monitoring systems and the design criteria for each component. Engine installation, transducer mounting brackets, types of transducers, interconnecting cables and connectors, charge amplifiers, and signal conditioning and monitoring are considered. Examples are given of the benefits experienced with the final system in several of Dresser Clark’s engine development programs, by manufacturing and production testing, and by Dresser’s field service staff.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):940-945. doi:10.1115/1.3239662.

A computer-assisted monitoring system has been implemented on GT-61 Gas Turbines employed in offshore gas gathering. Operating load data are continuously recorded at the site and evaluated at the turbine manufacturer’s plant on a mainframe computer, where existing analysis and testing techniques are utilized to predict the service fatigue lives of the power turbine structural components. The data acquisition hardware, the data reduction software, and the life prediction techniques are each described. The data collected indicate that offshore gas gathering equipment will experience many more operating load cycles than comparable equipment in pipeline service. The fatigue life predictions reaffirm the suitability of the GT-61 for this more severe service.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):946-951. doi:10.1115/1.3239663.

An experimental evaluation of a gas turbine/compressor train yielded excellent correlation between measured and predicted torsional critical speeds. Torsional strain signals acquired at a coupling location provide basic data from which damping factors at resonance are found to vary from 1 to 6 percent, depending on mode shape. Resonant stress levels for the mode with low damping would be a factor of 2 higher than predictions based on industry accepted assumptions. Other modes are found to have considerably more damping than expected. Experimental data and a coupled torsional-lateral damped eigenvalue analysis show that this damping variation is related to pinion and gear lateral bearing motion. Conservative damping values are predicted by the coupled analysis.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):952-960. doi:10.1115/1.3239664.
Abstract
Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 1984;106(4):961. doi:10.1115/1.3239666.
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Abstract

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