bluuebunny/crossref_metadata_2025 huggingface dataset:
Ash Deposition at Coal-Fired Gas Turbine Conditions: Surface and Combustion Temperature Effects
Authors: Richards G. A. , Logan R. G. , Meyer C. T. , Anderson R. J.
Published: April 2008

A study of ash deposition from a cleaned bituminous and conventional bituminous coal is presented. An electrically heated drop tube furnace is used to burn the coal and provide deposition conditions representative of proposed coal-fired gas turbines. Variations in the combustion temperature and deposit surface temperature demonstrate that surface cooling may significantly reduce ash deposition, or may provide little benefit, depending on the combustion conditions. Lower temperature combustion produced larger ash particles, with a greater fraction of ash adhering to the deposition test surface. Although the sticking coefficient was higher at the lower combustion temperature, the deposits were readily removed. A modest numerical simulation suggests that the smallest ash particles can experience significant boundary layer cooling and may account for the reduction in sticking observed at some conditions.
Self-Tuning Control of a Coal-Fired Fluidized Bed Combustor
Authors: Junk K. W. , Fullmer R. R. , Brown R. C.
Published: April 2008

This paper investigates the temperature control of a two-bed fluidized combustor using a self-tuning control algorithm to vary secondary air flow rate. The controller consists of a recursive least-squares parameter estimator, an observer, and a linear optimal control design procedure. This combination enables the controller to estimate the system parameters and update the feedback gains when necessary. Further, this study addresses the tracking form of optimal control, accomplished by augmenting the state vector with an integrator. The self-tuning control algorithm was compared with a simple PI controller, which was tuned using the Ziegler-Nichols method. In this study, self-tuning control provided improved performance over classical control. Compared with conventional, constant-gain control, self-tuning control reduced steady-state variance by a factor of 6.67 while maintaining good tracking characteristics.
Relationship Between Feedstock Characteristics and Erosivity of FBC Bed Materials
Authors: Levy A. V. , Wang B. Q. , Geng G. Q.
Published: April 2008

The erosion-corrosion (E-C) metal wastage mechanisms and rates that occur in 1018 plain carbon steel used in tubular heat exchangers of fluid bed combustors (FBC) are discussed. The characteristics of FBC bed material erodent particles such as composition, shape, size, and strength were found to have a major effect on the surface degradation mechanisms and rates that occurred. A total of 16 different bed material particles from ten different FBCs were tested. It was determined that when the particles were strong enough not to shatter when they impacted the steel’s surface, their shape and composition were the most important factors in determining their erosivity. The relative amounts of SiO2, CaO, CaCO3, CaSO4, and alkali compounds in the bed materials were related to the metal wastage by using laboratory mixtures of the compounds as erodents. The ratio of SiO2 to CaO and CaCO3 was especially important in determining the erosivity of the bed materials. It was found that increasing this ratio increased the metal wastage. A sharp transition ratio occurred on either side of which the metal wastages were linear. The slope of the linear curve was low for the lower sand content mixtures and higher for higher sand content mixtures. The transition ratio required a higher CaO content for higher velocity particles.
The Role of Primary Jets in the Dome Region Aerodynamics of a Model Can Combustor
Authors: Richards C. D. , Samuelsen G. S.
Published: April 2008

The role of the primary jets in the aerothermal behavior and overall performance of a gas turbine combustor is explored through an experimental study. The study is performed in a model laboratory combustor that possesses the essential features of practical combustors. The test bed is designed to accommodate optical access for laser diagnostics and overall flow visualization, and is capable of incorporating variable inlet geometries. In the present case, the combustor is operated on JP-4 at atmospheric pressure. A parametric variation in the number of jets per row and axial location of the jet row is performed. The aerodynamic and thermal fields are characterized using laser anemometry and a thermocouple probe, respectively. Species concentrations are acquired via extractive probe sampling. The results demonstrate the importance of primary jet location with respect to the dome swirler. The percent mass recirculated into the dome region, as well as the overall uniformity of mixing and combustion efficiency, are substantially influenced by jet row location. The momentum ratio of the incoming primary jet stream to that of the approaching crossflow of reacting dome gases has a direct impact on the mixing patterns as well. An increase in the number of primary jets leads, in the present case, to more uniform mixing.
Full Annular Rig Development of the FT8 Gas Turbine Combustor
Authors: Fox T. G. , Schlein B. C.
Published: April 2008

The results of developmental testing in a high-pressure, full annular combustion section of the FT8 industrial gas turbine are presented. Base power conditions were simulated at approximately 60 percent of burner pressure. All aspects of combustion performance with liquid fuel were investigated, including starting, blowout, exit temperature signature, emissions, smoke, and liner wall temperature. Configurational change were made to improve liner cooling, reduce emissions, adjust pressure loss, and modify exit temperature profile. The effects of water injection on emissions and performance were evaluated in the final test run. Satisfactory performance in all areas was demonstrated with further refinements to be carried out during developmental engine testing.
An Experimental Study of the Effects of Liquid Properties on the Breakup of a Two-Dimensional Liquid Sheet
Authors: Stapper B. E. , Sowa W. A. , Samuelsen G. S.
Published: April 2008

The breakup of a liquid sheet is of fundamental interest in the atomization of liquid fuels. The present study explores the breakup of a two-dimensional liquid sheet in the presence of co-flow air with emphasis on the extent to which liquid properties affect breakup. Three liquids, selected with varying values of viscosity and surface tension, are introduced through a twin-fluid, two-dimensional nozzle. A pulsed laser imaging system is used to determine the sheet structure at breakup, the distance and time to breakup, and the character of the ligaments and droplets formed. Experiments are conducted at two liquid flow rates with five flow rates of co-flowing air. Liquid properties affect the residence time required to initiate sheet breakup, and alter the time and length scales in the breakup mechanism.
Mixing of an Acoustically Excited Air Jet With a Confined Hot Crossflow
Authors: Vermeulen P. J. , Grabinski P. , Ramesh V.
Published: April 2008

The mixing of an acoustically pulsed air jet with a confined hot crossflow has been assessed by temperature profile measurements. These novel experiments were designed to examine the effects of acoustic driver power and Strouhal number on jet structure, penetration, and mixing. The results showed that excitation produced strong changes in the measured temperature profiles. This resulted in significant increases in mixing zone size, penetration (at least 100 percent increase), and mixing, and the length to achieve a given mixed state was shortened by at least 70 percent. There was strong modification to the jet-wake region. The increase in jet penetration and mixing was saturating near 90 W, the largest driving power tested. The jet response as determined by penetration and mixing was optimum at a Strouhal number of 0.27. Overall, pulsating the jet flow significantly improved the jet mixing processes in a controllable manner.
Jet Shear Layer Turbulent Diffusion Flames for Ultralow NOx Emissions
Authors: Al-Shaikhly A. F. Ali , Andrews G. E. , Aniagolu C. O.
Published: April 2008

Direct fueling of each shear layer generated by an array of holes in a grid plate was shown to have ultralow NOx emissions combined with a good flame stability, compared with a premixed system. Two methods of fuel injection were investigated that had opposite NOx/stability characteristics. Four shear layers in a 76-mm combustor were used at gas turbine primary zone operating conditions with 60 percent simulated primary zone air at one bar pressure. The fuels used were propane and natural gas and a minimum NOx emission of 2.5 ppm at 15 percent oxygen, compatible with a 0.1 percent inefficiency, was demonstrated for natural gas with a reasonable stability margin. These designs have the potential for a dry NOx solution to any current or proposed gas turbine NOx regulation for natural gas.
Experimental Measurement of the Vortex Development Downstream of a Lobed Forced Mixer
Authors: Eckerle W. A. , Sheibani H. , Awad J.
Published: April 2008

An experimental study was conducted to investigate the mixing processes downstream of a forced mixer. A forced mixer generates large-scale, axial (stirring) vorticity, which causes the primary and secondary flow to mix rapidly with low loss. These devices have been successfully used in the past where enhanced mixing of two streams was a requirement. Unfortunately, details of the mixing process associated with these lobed forced mixers are not well understood. Performance sensitivity to design variables has not been documented. An experiment was set up to investigate the mixing processes downstream of a mixer. Air flow was independently supplied to each side of the forced mixer by separate centrifugal blowers. Pressures were measured at the entrance to the lobes with a pitot-static probe to document the characteristics of the approaching boundary layer. Interior mean and fluctuating velocities were nonintrusively measured using a two-component laser-Doppler velocimetry (LDV) system for velocity ratios of 1:1 and 2:1. The wake structure is shown to display a three-step process where initially secondary flow was generated by the mixer lobes, the secondary flow created counterrotating vortices with a diameter on the order of the convolute width, and then the vortices broke down resulting in a significant increase in turbulent mixing. The results show that the mean secondary motion induced by the lobes effectively circulated the flow passing through the lobes. This motion, however, did not homogeneously mix the two streams. Turbulent mixing in the third step of the mixing process appears to be an important element in the enhanced mixing that has been observed with forced mixers. The length required for the flow to reach this third step is a function of the velocity ratio across the mixer. The results of this investigation indicate that both the mean secondary motion and the turbulent mixing occurring after vortex breakdown need to be considered for prediction of forced mixer performance.
Experimental Study of the Effect of Dense Spray on Drop Size Measurement by Light Scattering Technology
Authors: Chin Ju Shan , Li Wei Ming , Zhang Yan
Published: April 2008

The effect of dense spray on drop size measurement by light scattering technology was studied using a Malvern instrument with five duplicated internal mixing airblast atomizers aligned with a laser beam. The correction factor data for multiple scattering were obtained. By regression analysis, an empirical equation was obtained that correlated the correction factor as a function of obscuration (OBS), Sauter mean diameter under dilute spray condition (SMD0), and drop size distribution parameter for Rosin-Rammler distribution under dilute spray conditions (N0). The experimental data showed definitely that the correction factor is not only a function of OBS and SMD0, as proposed by Dodge, but also is a function of N0. The correlation fits the experimental data very well, and can be used for practical purposes to correct the data from the Malvern drop sizer at high obscuration conditions.
Energy Considerations in Twin-Fluid Atomization
Authors: Lefebvre A. H.
Published: April 2008

With certain types of prefilming airblast atomizers, the manner in which the atomizing air impinges on the liquid sheet prohibits the wave formation that normally precedes the breakup of a liquid sheet into drops. Instead, the liquid is shattered almost instantaneously into drops of various sizes. This prompt atomization process is characterized by a broad range of drop sizes in the spray and by a lack of sensitivity of mean drop size to variations in liquid viscosity, atomizing air pressure, and initial liquid sheet thickness. Evidence is presented to show that which of these two different modes of atomization will occur in any given flow situation is largely dependent on the angle at which the atomizing air impinges on the liquid sheet. An equation for mean drop size, derived from the assumption that the main factor controlling prompt atomization is the ratio of the energy required for atomization to the kinetic energy of the atomizing air, is shown to provide a good fit to experimental data acquired from atomization studies on water and heating oil, carried out over wide ranges of air velocity, air/liquid ratio, and ambient air pressure.
A Method for the Design of Optimum Annular Diffusers of Canted Configuration
Authors: Adkins R. C. , Wardle M. H.
Published: April 2008

A simple method is presented for the design of annular diffusers that can take into account the effects of compressibility and of canted configurations by use of the area bisector line. No complex boundary layer calculations are required.
Parametric Analysis of the Kalina Cycle
Authors: Marston C. H.
Published: April 2008

The Kalina Cycle utilizes a mixture of ammonia and water as the working fluid in a vapor power cycle. When the liquid mixture is heated the more volatile ammonia tends to vaporize first and at a lower temperature than does pure water. This property of ammonia-water mixtures makes possible a better match to the enthalpy-temperature curve of a hot gas heat source such as a gas turbine exhaust and also permits circulation of fluids of different composition in different parts of the cycle. Taking advantage of the latter feature, condensation (absorption) can be done at slightly above atmospheric pressure with a low concentration of ammonia, while heat input is at a higher concentration for optimum cycle performance. Computer models have been used to optimize a simplified form of the cycle and to compare results for a more complex version proposed by El-Sayed and Tribus. A method of balancing the cycle was developed and key parameters for optimizing the cycle identified.
Performance Evaluation of Selected Combustion Gas Turbine Cogeneration Systems Based on First and Second-Law Analysis
Authors: Huang F. F.
Published: April 2008

The thermodynamic performance of selected combustion gas turbine cogeneration systems has been studied based on first-law as well as second-law analysis. The effects of the pinch point used in the design of the heat recovery steam generator, and pressure of process steam on fuel-utilization efficiency (first-law efficiency), power-to-heat ratio, and second-law efficiency, are examined. Results for three systems using state-of-the-art industrial gas turbines show clearly that performance evaluation based on first-law efficiency alone is inadequate. Decision makers should find the methodology contained in this paper useful in the comparison and selection of cogeneration systems.
Second-Law Analysis of Diesel Engine Combustion
Authors: Van Gerpen J. H. , Shapiro H. N.
Published: April 2008

A second-law analysis of the combustion process in a diesel engine is presented for a single-zone model. Expressions for availability and the availability balance are developed in detail from the energy and entropy balances and applied in a manner that allows the irreversibility due to combustion to be separated from that associated with heat transfer to the walls. Availability is divided into two components: thermomechanical and chemical availability. For the first time, chemical availability of the cylinder contents is dealt with rigorously, which allows for a correct determination of combustion irreversibilities. The analysis is applied in a parametric study of the effects of combustion timing, mass burning rate, and heat transfer rate on the irreversibility and system availability.
Thermodynamic Analysis of Indirect Injection Diesel Engines by Two-Zone Modeling of Combustion
Authors: Kouremenos D. A. , Rakopoulos C. D. , Hountalas D.
Published: April 2008

This work presents a thermodynamic analysis of a naturally aspirated, four-stroke, diesel engine with a swirl prechamber, under firing conditions during the open and closed part of the cycle. For calculating the heat exchange between gas and walls in both the main chamber and (swirl) prechamber, the relevant characteristic velocities and lengths are calculated by setting up a zero-dimensional energy cascade turbulence model. One-dimensional, quasi-steady, compressible flow with heat transfer inside the throat passageway connecting the two chambers is used. Combustion in both the main chamber and the swirl prechamber is attacked by proposing a two-zone combustion model, and following the movement of the spray plume inside an air solid body rotation environment in the prechamber and its later progression into the main chamber through the connecting throat. To validate the analysis, an extensive experimental investigation is undertaken at the laboratory of the authors on a flexible Ricardo, single-cylinder, swirl chamber diesel engine, and evaluating its performance in a wide range of operating conditions. The experimental results are found to be in good agreement with the theoretical results obtained from the computer program implementing the analysis.
The Influence of Fluid Physical Properties on Coal-Water Slurry Atomization
Authors: Smith C. F. , Sojka P. E. , Thames J. M.
Published: April 2008

This study reports the atomization behavior of coal-water slurries (CWS) at conditions typical of a gas turbine combustor. Slurry atomization characteristics were determined for a plain-jet airblast research nozzle and six slurries. Atomization quality is reported in terms of the spray’s Sauter mean diameter (SMD) and the radial distribution of fuel mass flux (patternization). The drop size data demonstrate that SMD can be predicted from a knowledge of slurry velocity, the relative velocity between the airblast air and the slurry, the air-to-fuel mass flow ratio (AFR), and the slurry rheology. Slurry rheology is represented here by a power law expression.
Chemical Aspects of Deposition/Corrosion From Coal-Water Fuels Under Gas Turbine Conditions
Authors: Wenglarz R. A. , Fox R. G.
Published: April 2008

A staged, subscale turbine combustor based on a promising rich-quench-lean combustion approach to reduce NOx emissions was used to evaluate deposition, erosion, and corrosion (DEC) from coal-water fuels (CWF). This combustor was operated with three CWF at conditions of a recuperated turbine. Specimens were exposed in two test sections at temperature conditions of the first stator vanes and first rotor blades of the recuperated turbine. The resulting deposits were chemically analyzed. Deposit-covered segments of specimens were placed in a furnace to extend their exposure to the potentially corrosive deposits. The deposits produced at higher temperature first stator conditions differed significantly from those produced at lower temperature first rotor conditions. The rates of formation of the higher temperature deposits were high and the deposit chemistries were similar to the coal ash chemistry. The rates of formation of the lower temperature deposits were one to two orders of magnitude less and deposit chemistries were not the same as the coal ash chemistry. Some corrosion of a CoCrAlY coating was detected after a few hours of exposure in the DEC tests. Corrosion penetration up to one-half of the coating thickness was observed after an additional 460 h furnace exposure. Much more testing is needed to explore whether the deposition and corrosion produced by the fuels evaluated are typical of this fuel form and to assess benefits of alternate turbine protection measures.
The Performance of a Compact Oil-Designed Utility Boiler When Firing Coal-Water Fuel
Authors: Rankin D. M. , Whaley H. , Read P. J. , Burnett D. J.
Published: April 2008

The Canadian coal-water fuel technology development program has been in progress since 1980. This phase of the work is the final stage in the demonstration of practicability of burning coal-water fuel in a boiler designed to burn oil. Early tests in small coal-capable front-wall and tangentially fired utility boilers have shown that two of the major problems to be addressed are both burner related: atomizer durability and poor carbon conversion performance. The present paper describes tests that were conducted in a 20 MWe compact, oil-designed boiler. Five burners were modified to burn coal-water fuel and oil with minimum changeover time. No changes were made to the boiler heat transfer tubes or to the flat furnace bottom to facilitate ash removal. The addition of a fabric filter bag house to contain fly ash emissions is the subject of another paper at this conference. The performance of the unit on coal-water fuel and oil is compared and evidence given that the derating was not as severe as had been predicted. The commercial burner supplied did show some atomizer wear, part of which could be attributed to manufacturing deficiences. It is suggested that the performance of this small unit should be applicable to larger units in the 100 MWe range.
Solution of Combustor Noise in a Coal Gasification Cogeneration Application of 100-MW-Class Combustion Turbines
Authors: Scalzo A. J. , Sharkey W. T. , Emmerling W. C.
Published: April 2008

The field conversion of two W501D5 combustion turbines to burn medium Btu fuel gas supplied by a Dow Chemical coal gasification process at Plaquemine, LA resulted in excessive 105-Hz airborne sound and a corresponding unacceptable nonsynchronous engine vibration when burning natural gas. A joint Westinghouse and Dow Chemical corrective action program is described including field tests. Test results indicated that the combustion noise phenomenon was related to the strength of the primary air scoop recirculation pattern and its compatibility with the fuel and steam momentum vectors. A design was selected that eliminated the nonsynchronous combustion noise generated vibration and reduced the 100-Hz third-octave noise from 115 db to 97 db, an intensity reduction of 64 to 1.
Influence of the Continuous and Dispersed Phases on the Symmetry of a Gas Turbine Air-Blast Atomizer
Authors: McDonell V. G. , Samuelsen G. S.
Published: April 2008

Current trends in liquid-fueled practical combustion systems are leaving less tolerance for fuel injection deficiencies such as poor spray field symmetry. The present paper evaluates the symmetry of the flowfield produced by a practical airblast atomizer. Specifically, the influence of both the continuous phase and dispersed phase on the spray field symmetry is assessed. In the present case, asymmetry in volume flux is associated principally with disparities in the injection of the dispersed phase, which is manifested by a maldistribution of larger drops. Asymmetries observed in the continuous phase without the dispersed phase are reduced in magnitude by the presence of the dispersed phase, but still contribute to asymmetry in radial spread of the dispersed phase.
Spray Characterization and Turbulence Properties in an Isothermal Spray With Swirl
Authors: Bren˜a de la Rosa A. , Bachalo W. D. , Rudoff R. C.
Published: April 2008

The present work reports an experimental study of the effect of swirl on the dynamic behavior of drops and on the velocity and turbulence fields of an isothermal spray using a two-component Phase Doppler Particle Analyzer (PDPA). It represents the first phase of an effort to investigate the effect of swirl on the structure of liquid spray flames, the stability of the flame, and its effect on the emission of pollutants. A vane-type swirler was placed on the liquid supply tube of a pressure atomizer and tested in the wind tunnel under specified conditions. Mean velocity and turbulence properties were obtained for the gas phase. In addition, drop velocity and drop size distributions, particle number densities, and volume flux were measured at different locations within the swirling flow. Large differences in the spatial distribution of the drops over its size, velocity, and number density are observed when the spray in coflowing air with the same axial velocity is compared with the atomizer spraying into the swirling flow field. Large drops seem to be recirculated into the core of the swirling flow, while rather small drops surround this central region. The radial distribution of particle number density and the liquid volume flux are also different when the atomizer spraying into the coflowing air and into the swirling field are compared. Particle number densities for the latter exhibit higher peak values close to the nozzle; but show almost the same peak values as in the coflowing case but at a different radial location further downstream. The velocity of specific drop sizes was also obtained. Drops as large as 5μm are seen to follow closely the mean velocity of the gas. The turbulence properties of the swirling flow show significant influence on the dynamic behavior of the drops. Radial distributions of turbulence kinetic energy, normal Reynolds stresses, and Reynolds shear stresses exhibit double peak values, which delineate the boundaries of the central recirculation region and the external free stream. Within these boundaries the radial distribution of both particle number density and volume flux are seen to attain their maximum values.
Improvements to the Performance of a Prototype Pulse, Pressure-Gain, Gas Turbine Combustor
Authors: Kentfield J. A. C. , Fernandes L. C. V.
Published: April 2008

A description is given of a simple, prototype, pulse, pressure-gain combustor for a gas turbine. The work reported was targeted at alleviating problems previously observed with the prototype combustor. These were related to irreversibilities, causing a performance deficiency, in the secondary flow passage. The work consisted of investigating experimentally the effect of tuning the secondary-flow path length, adding a flow restrictor at the combining-cone entry station, and redesigning the combining cone itself. The overall result was to eradicate the previously noted performance deficiency, thereby increasing the maximum pressure gain obtained in the gas turbine from 1.6 to 4.0 percent of the compressor absolute delivery pressure.
The Influence of Dilution Hole Geometry on Jet Mixing
Authors: Carrotte J. F. , Stevens S. J.
Published: April 2008

Measurements have been made on a fully annular test facility, downstream of a row of heated dilution jets injected normally into a confined crossflow at a momentum flux ratio of 4. The investigation concentrated on the consistency of mixing between the jets, as indicated by the regularity of the temperature pattern around the crossflow annulus. When the heated air was supplied from a representative feed annulus, the exit velocity profile across each plunged hole was significantly altered and caused a distortion of the temperature distribution in the ensuing jet. The degree of distortion varies in a random manner, so that each jet has its own mixing characteristics, thereby producing irregularity of the temperature pattern around the annulus. With the same approach and operating conditions some of the plunged dilution holes were modified, and tests on this modified sector indicated a significant improvement in the circumferential regularity of the temperature pattern. Further tests showed that these modifications to the dilution holes had a negligible effect on the values of the discharge coefficients.
Flow Guiding and Distributing Devices on the Exhaust Side of Stationary Gas Turbines
Authors: Fleischer F. , Koerner C. , Mann J.
Published: April 2008

Following repeated cases of damage caused to exhaust silencers located directly beyond gas turbine diffusers, this paper reports on investigations carried out to determine possible remedies. In all instances, an uneven exhaust gas flow distribution was found. The company’s innovative approach to the problem involved constructing a scale model of a complete gas turbine exhaust system and using it for flow simulation purposes. It was established for the first time that, subject to certain conditions, the results of tests conducted on a model can be applied to the actual turbine exhaust system. It is shown that when an unfavorable duct arrangement might produce an uneven exhaust flow, scale models are useful in the development of suitable flow-distributing devices.
The Design and Performance Optimization of Thermal Systems
Authors: von Spakovsky M. R. , Evans R. B.
Published: April 2008

Optimization techniques are, in general, still not used today in the design and performance analysis of thermal systems and their components. The engineer’s search for the best system configuration is based solely on rules-of-thumb and not on a systematic, analytical determination of what the optimal design or performance should be. In addition, economic factors are not directly tied to thermodynamic ones; therefore, the economic ramifications of thermodynamic changes to the system are not usually, if ever, immediately apparent. A general analytical approach that directly determines the optimum thermodynamic and econmic behavior of thermal systems is discussed and illustrated using Rankine cycles. Utilizing the Second Law and typical Second Law costing techniques, this method provides for the creation of mathematical models that balance a cycle’s operating costs and capital expenditures. Such models can be solved numerically, subject to various constraints, for the optimum design and performance of thermal systems.
The Role of Piston Distortion on Lubrication in a Reciprocating Engine
Authors: Blair W. L. , Hoult D. P. , Wong V. W.
Published: April 2008

The microgeometry of the piston, rings, and skirt relative to the liner strongly influences lubrication in a reciprocating engine. This study develops an approximation technique that decouples the thermomechanical piston-skirt distortions from the complex lubricant support in a large diesel engine. The model considers the limiting case of starved skirt lubrication with large clearance. It permits efficient design of machined three-dimensional piston-skirt contours for piston support. In the calculations, a three-dimensional finite-element model is coupled with a postprocessing algorithm to predict skirt distortions, piston tilt, operating clearance, and oil-film contact area as a function of machined profile, thermal expansion, cylinder pressure, piston inertia, and transient side loads. A piston dynamics model is developed that defines the transient piston side force based on engine geometry, cylinder pressure, inertial loads, and wrist-pin offset. The results of this study indicate that (1) the transient skirt distortions due to cylinder pressure on the compression and power strokes result in a significant increase in oil-film contact area; (2) the piston skirt operating shape depends on the location and area of oil-film contact; (3) the contact area and location during intake and exhaust strokes vary substantially from that during the compression and power strokes; (4) the wrist-pin offset reduces the maximum side load and piston slap intensity occurring in the region of maximum cylinder pressure; (5) effective three-dimensional skirt profile design may result in significant changes in oil-film contact area and location on the skirt throughout the cycle.
Combustion Engine Performance Diagnostics by Kinetic Energy Measurement
Authors: Mauer G. F. , Watts R. J.
Published: April 2008

The diagnostic technique described in this paper is based on measuring the instantaneous angular speed of both the front end and the flywheel on internal-combustion engines, recording more than 400 speed measurements per engine cycle. Two noncontacting transducers are added to an existing drive train without requiring drive train modifications. A digital circuit, which includes a microprocessor, samples and processes the raw speed data. The numerical analysis includes data noise filtering, and the numerical determination of front end and flywheel speed waveforms. When operating without external load, the engine accelerates only the inertial load. When neglecting friction and the small amount of torsional energy in the crankshaft, it is shown that the engine energy can be modeled as a lumped parameter system consisting of inertia on both engine front and flywheel ends, coupled by a torsional spring. The results from measurements on an eight-cylinder diesel engine with various cylinder faults show that reduced cylinder performance produces a drop of kinetic energy for the faulty cylinder. An engine performance criterion evaluates the performance of each cylinder, based on its contribution to total engine kinetic energy. The results demonstrate that fault conditions are detected with high reliability.
Autoignition of Heavy Fuel Oil Sprays at High Pressures and Temperatures
Authors: Baert R. S. G.
Published: April 2008

This paper reports on an experimental study of the autoignition behavior of several heavy fuel oils in a large constant-volume combustion chamber with single-shot injection. In the experiments the pressure and the temperature of the air in the combustion chamber before fuel injection varied between 30 and 70 bar and between 730 and 920 K. Illumination delay and pressure delay values have been correlated with these pressures and temperatures. It is shown that for all but one of the fuels examined, ignition delay ranking changes little with the choice of ignition delay definition, but more with the pressure and temperature conditions in the combustion chamber. The usefulness of the Calculated Carbon Aromaticity Index is discussed.
Comparison Between Measured Radiance and a Radiation Model in a Spark-Ignition Engine
Authors: Yang J. , Plee S. L. , Remboski D. J. , Martin J. K.
Published: April 2008

Measurements of the radiant emission in the near infrared have been obtained in a spark-ignition engine over a wide range of operating conditions. The system includes an in-cylinder optical sensor and associated detector. Prior work has shown correlations between the measured radiance and pressure quantities such as maximum cylinder pressure, crank angle of maximum pressure, and Indicated Mean Effective Pressure. Here are presented comparisons between the radiant intensity and a simplified model of the radiation emission, which demonstrate that the measured intensity is a function of the mass-burn fraction, mean burned-gas temperature, and the exposed combustion-chamber surface area. Further simplification leads to the conclusion that the time of the maximum rate of change of radiant intensity is the same as for the maximum heat-release rate, leading to the possibility of feedback control of spark timing. In addition, the magnitudes of the maximum rate of change of radiant emission and maximum heat-release rate have a linear relationship over a range of different operating conditions.
Autocorrelation and Autospectra Estimation of Reciprocating Engine Turbulence
Authors: Catania A. E. , Mittica A.
Published: April 2008

A general method for analyzing the time-correlation and frequency-spectral structure of turbulence in IC reciprocating engines was developed and applied to the cycle-resolved turbulent velocity fluctuation and to the fluctuating motion in its more conventional sense. It is based on an alternative definition of the Eulerian temporal autocorrelation coefficient so as to reduce this to an even function solely of the separation time within specific correlation periods into which the engine cycle is divided. This procedure was shown to be a refined version of a previous approach to spectral analysis of engine turbulence used by the authors, and was compared to the one based on the rough application of two definitions of nonstationary autocorrelation coefficients in the standard approach for stationary flows. It was proved to be suitable for studying the average statistical properties of segmented nonstationary turbulence sample records, being easily extensible from temporal to spatial records. The method was applied to the analysis of the effects of different swirl flow conditions on correlation and spectral turbulence quantities in an automotive engine. The spatial distribution of the in-cylinder dissipation time scale of turbulence and, in particular, the influence of the wall on this parameter were also investigated.
A Comprehensive Model for Pilot-Ignited, Coal-Water Mixture Combustion in a Direct-Injection Diesel Engine
Authors: Wahiduzzaman S. , Blumberg P. N. , Keribar R. , Rackmil C. I.
Published: April 2008

A combustion model has been developed for a direct-injected diesel engine fueled with coal-water slurry mixture (CWM) and assisted by diesel pilot injection. The model combines the unique heat and mass transport and chemical kinetic processes of CWM combustion with the normal in-cylinder processes of a diesel engine. It includes a two-stage evaporation submodel for the drying of the CWM droplet, a global kinetic submodel for devolatilization, and a char combustion submodel describing surface gasification by oxygen, carbon dioxide, and water vapor. The combustion volume is discretized into multiple zones, each of whose individual thermochemistry is determined by in-situ equilibrium calculations. This provides an accurate determination of the boundary conditions for the CWM droplet combustion submodels and the gas phase heat release. A CWM fuel jet development, entrainment, and mixing submodel is used to calculate the mass of unburned air in each of the burned zones. A separate submodel of diesel pilot fuel combustion is incorporated into the overall model, as it has been found that pilot fuel is required to achieve satisfactory combustion under many operating conditions. The combustion model is integrated with an advanced engine design analysis code. The integrated model can be used as a tool for exploration of the effects of fuel characteristics, fuel injection parameters, and engine design variables on engine performance, and in the assessment of the effects of component design modifications on the overall efficiency of the engine and the degree of coal burnout achieved.
Single-Cylinder Testing of a High-Pressure Electronic Pilot Fuel Injector for Low NOx Emission Dual Fuel Engines: Part II—Optimization, Startability, and Inflammability Testing
Authors: Workman J. , Beshouri G. M.
Published: April 2008

Single-cylinder testing of an Electronic Pilot Fuel Injection (EPFI) system (reported in Part I) indicated that a 45 percent reduction in NOx emissions could be obtained with a 3 percent improvement in fuel consumption by replacing the mechanical system, delivering 6 percent pilot, with the EPFI at 2.9 percent delivery. Further optimization testing of this system at pilot levels down to 0.7 percent over a wide range of timings and air/fuel ratios resulted in even further reductions in NOx emissions without fuel penalty. The EPFI system can yield NOx emissions levels significantly below 2 g/BHP-h with an improvment in fuel consumption of at least 3–4 percent, and probably yield emissions level as low as 0.5 g/BHP-h without substantial penalties in efficiency or operability.
A New Method of Predicting the Performance of Gas Turbine Engines
Authors: Yonghong Wang
Published: April 2008

This paper points out that the turbine performance computation method used widely at present in solving the performance of gas turbine engines is a numerically unstable algorithm. Therefore a new method, namely an inverse algorithm, is proposed. This paper then further proposes a new mathematical model for solving the stable performance of gas turbine engines. It has the features of not only being suitable for an inverse algorithm for turbine performance, but also having fewer dimensions than existing models. It has the advantages of high accuracy, rapid convergence, good stability, fewer computations, and so forth. It has been fully proven that the accuracy of the new model is much greater than that of the common model for gas turbine engines. Additionally, the time consumed for solving the new model is approximately 1/4~1/10 of that for the common model. Therefore, it is valuable in practice.
Thermal Barrier Characteristics of Partially Stabilized Zirconia Coatings on INCOLOY Alloy 909 (A Controlled Expansion Alloy)
Authors: Smith G. D.
Published: April 2008

INCOLOY alloy 909 is a low-expansion alloy used in critical seal and shaft applications within the gas turbine engine. However, because of its poor oxidation resistance at elevated temperatures, the maximum service temperature is limited. Since its coefficient of expansion is similar to that of partially stabilized zirconia for temperatures to 1200°F (649°C), it has been proposed to use this metal-ceramic combination for dimensionally critical, air-cooled jet engine components. This coating system should extend temperature limitations by reducing metal temperatures and providing oxidation resistance. The performance advantage offered by a thermal barrier coating has been investigated at temperatures up to 2000°F (1093°C) and the results are presented in this paper. Metal temperatures and heat flow rates of coated and bare specimens are compared for two air-cooling flow rates.
Application of HOST Technology to the SSME HPFTP Blade
Authors: McKnight R. L. , Cook T. S. , Bechtel G. S. , Huang H. T.
Published: April 2008

The Hot Section Technology (HOST) program has focused on providing methods to solve difficult structural analysis problems. Few structures require as much effort to analyze as the modern aircraft gas turbine engine; heat transfer, constitutive relations, linear and nonlinear analysis, and multiple advanced materials are some of the key topics requiring attention in the structural analysis of engine components. Usually based on limited information and experience, these advanced methods must evolve from expert systems to widely verified user-friendly techniques available to the design community. This paper will discuss the development of turbine blade analysis tools as they moved from research contracts under the NASA HOST program to a PC-based system for preliminary design and their use in evaluating the SSME HPFTP blade, a similar but subtly different problem. Included in the discussion will be the heat transfer and structural analysis of the blade, development of a data base for constitutive modeling of the blade materials, including coatings, and the usage of advanced nonlinear finite element methods.
A GCC Power Plant With Methanol Storage for Intermediate-Load Duty
Authors: Paffenbarger J. A.
Published: April 2008

This paper describes the design and performance of a coal gasification combined-cycle power plant with an integrated facility for producing and storing methanol (GCC/methanol power plant). The methanol is produced at a steady rate and is burned in the combined cycle to generate additional power during periods of peak electrical demand. The GCC/methanol plant provides electricity generation and energy storage in one coal-based facility. It is of potential interest to electric utilities seeking to meet intermediate-load electrical demand on their systems. The plant configuration is determined by means of an innovative economic screening methodology considering capital and fuel costs over a range of cycling duties (capacity factors). Estimated levelized electricity production costs indicate that a GCC/methanol plant could be of economic interest as premium fuel prices increase relative to coal. The plant could potentially be of interest for meeting daily peak demands for periods of eight hours or less. The conceptual plant configuration employs a Texaco gasifier and a Lurgi methanol synthesis plant. Plant performance is estimated at peak and baseload output levels. No unusual design or operational problems were identified.
Airframe/Propulsion Integration at Transonic Speeds
Authors: Henderson W. P.
Published: April 2008

A significant level of research is ongoing at NASA’s Langley Research center on integrating the propulsion system with the aircraft. This program has included nacelle/pylon/wing integration for turbofan transports, propeller/nacelle/wing integration for turboprop transports, and nozzle/afterbody/empennage integration for high-performance aircraft. The studies included in this paper focus more specifically on pylon shaping and nacelle bypass ratio studies for turbofan transports, nacelle and wing contouring, and propeller location effects for turboprop transports, empennage effects, and thrust vectoring for high-performance aircraft. The studies were primarily conducted in NASA Langley’s 16-Foot Transonic Tunnel at Mach numbers up to 1.20.
Introduction to the Basic Technology of Stealth Aircraft: Part 1—Basic Considerations and Aircraft Self-Emitted Signals (Passive Considerations)
Authors: Howe D.
Published: April 2008

This paper reviews information that may be used by a potential enemy to detect and track an aircraft. In particular it is concerned with a passive approach by the enemy, namely the interception of acoustic, infrared, visual, and miscellaneous self-emissions. The origins of these emissions are described and means of eliminating them or reducing their intensity are discussed. Emphasis is placed on the impact of these so-called stealth techniques on the design of the aircraft as a whole.
Introduction to the Basic Technology of Stealth Aircraft: Part 2—Illumination by the Enemy (Active Considerations)
Authors: Howe D.
Published: April 2008

One of the most significant considerations of stealth technology is the technique used to reduce the probability of detection of an aircraft by radar. This paper is concerned with the nature of the various contributions to the radar cross section, and the means by which their effect may be reduced. A survey of the impact of stealth technology on some specific designs is included, from which the conclusion is drawn that the achievement of good stealth characteristics demands attention to both the overall configuration and detail design.
Simulation of Aircraft Gas Turbine Engines
Authors: Ismail I. H. , Bhinder F. S.
Published: April 2008

The paper describes a computer program to simulate aircraft gas turbine engines. The program has been written for IBM-compatible microcomputers and is modular in its appraoch. Either analytical equations or detailed performance characteristics of individual components are used to model the steady-state operation of the complete engine.
Theoretical Basis for Extrapolation of Calibration Data of PTC 6 Throat Tap Nozzles
Authors: Murdock J. W. , Keyser D. R.
Published: April 2008

Equations for the extrapolation of calibration data for ASME/PTC 6 throat tap nozzles are derived from boundary layer theory. The results match published coefficients with a maximum difference of +0.03 percent. It is also shown that the effects of transition in the boundary layer extend to throat Reynolds numbers in excess of 10,000,000, far beyond the capacity of any known calibration laboratory. The present PTC 6 requirement that calibration data must be in the fully turbulent range cannot be met with current facilities.