bluuebunny/crossref_metadata_2025 huggingface dataset:
Global Daily Reference Evapotranspiration Modeling and Evaluation1
Authors: Senay G.B. , Verdin J.P. , Lietzow R. , Melesse A.M.
Published: April 2008

Abstract:  Accurate and reliable evapotranspiration (ET) datasets are crucial in regional water and energy balance studies. Due to the complex instrumentation requirements, actual ET values are generally estimated from reference ET values by adjustment factors using coefficients for water stress and vegetation conditions, commonly referred to as crop coefficients. Until recently, the modeling of reference ET has been solely based on important weather variables collected from weather stations that are generally located in selected agro‐climatic locations. Since 2001, the National Oceanic and Atmospheric Administration’s Global Data Assimilation System (GDAS) has been producing six‐hourly climate parameter datasets that are used to calculate daily reference ET for the whole globe at 1‐degree spatial resolution. The U.S. Geological Survey Center for Earth Resources Observation and Science has been producing daily reference ET (ETo) since 2001, and it has been used on a variety of operational hydrological models for drought and streamflow monitoring all over the world. With the increasing availability of local station‐based reference ET estimates, we evaluated the GDAS‐based reference ET estimates using data from the California Irrigation Management Information System (CIMIS). Daily CIMIS reference ET estimates from 85 stations were compared with GDAS‐based reference ET at different spatial and temporal scales using five‐year daily data from 2002 through 2006. Despite the large difference in spatial scale (point vs. ∼100 km grid cell) between the two datasets, the correlations between station‐based ET and GDAS‐ET were very high, exceeding 0.97 on a daily basis to more than 0.99 on time scales of more than 10 days. Both the temporal and spatial correspondences in trend/pattern and magnitudes between the two datasets were satisfactory, suggesting the reliability of using GDAS parameter‐based reference ET for regional water and energy balance studies in many parts of the world. While the study revealed the potential of GDAS ETo for large‐scale hydrological applications, site‐specific use of GDAS ETo in complex hydro‐climatic regions such as coastal areas and rugged terrain may require the application of bias correction and/or disaggregation of the GDAS ETo using downscaling techniques.
Oncogenic activities of metabotropic glutamate receptor 1 (Grm1) in melanocyte transformation
Authors: Shin Seung‐Shick , Namkoong Jin , Wall Brian A. , Gleason Ryan , Lee Hwa Jin , Chen Suzie
Published: April 2008

Previously, we reported a transgenic mouse line, TG‐3, that develops spontaneous melanoma with 100% penetrance. We demonstrated that ectopic expression of Grm1 in melanocytes was sufficient to induce melanoma in vivo. In this present study, the transforming properties of Grm1 in two cultured immortalized melanocytes were investigated. We showed that, in contrast to parental melanocytes, these Grm1‐clones have lost their requirement of TPA supplement for proliferation and have acquired the ability to form colonies in semi‐solid medium. Xenografts of these cells formed robust tumors in both immunodeficient nude and syngeneic mice with a short latency (3–5 days). The malignancy of these cells was demonstrated by angiogenesis and invasion to the muscle and the intestine. The requirement of Grm1 expression for the maintenance of transformation was demonstrated by an inducible siRNA system. Induction of expression of siRNA for Grm1 reduced the number of proliferating/viable cells in vitro and suppressed in vivo xenografted tumor growth in comparison with control. Taken together, these results showed that expression of exogeneously introduced Grm1 is sufficient to induce full transformation of immortalized melanocytes.
Trabeculectomy surgery augmented with intra‐Tenon injection of mitomycin C
Authors: Lee Edward , Doyle Eddie , Jenkins Christopher
Published: April 2008

Purpose:  To describe a novel approach to mitomycin C (MC) application during trabeculectomy surgery and to report the 1‐year results of surgery using this technique.

Methods:  One hundred and eight consecutive trabeculectomies and phaco‐trabeculectomies using MC were performed by a single consultant surgeon, using a standardized technique. This technique involved injecting MC into the Tenon’s layer during the procedure, rather than applying it directly to the under‐surface of the conjunctiva.

Results:  Preoperative mean intraocular pressure (IOP) was 23.6 ± 5.8mmHg. Mean IOP 12 months following surgery was 12.2 ± 3.9 mmHg. Seventy‐six eyes (70.3%) had an IOP less than 2/3 listing IOP at 12 months without the need for anti‐glaucoma medication. Ninety‐three eyes (86%) had an IOP <21 mmHg, 79 (73%) had an IOP <16 mmHg and 62 (57%) had an IOP <14 mmHg without anti‐glaucoma medication at 12 months. Transient complications included hyphaema, bleb leak and choroidal detachment in 14.8%, 5.6% and 15.7% of cases, respectively. Hypotony (defined as IOP <7 mmHg, excluding the first day postoperatively) was seen in 21.3% of cases. At 12 months, 21 eyes (19.4%) had cystic blebs and five (4.6%) had Tenon’s cysts with an IOP greater than 20 mmHg.

Conclusion:  A novel means of applying intraoperative MC is described. The 12‐month outcome data show it to be an effective technique that compares favourably with others in the literature.
Dynamic Modeling of a Combined-Cycle Plant
Authors: Ahluwalia K. S. , Domenichini R.
Published: April 2008

Greater use is being made of dynamic simulation of energy systems as a design tool for selecting control strategies and establishing operating procedures. This paper discusses the dynamic modeling of a gas-fired combined-cycle power plant with a gas turbine, a steam turbine, and an alternator—all rotating on a common shaft. A waste-heat boiler produces steam at two pressures using heat from the gas turbine flue gas. The transient behavior of the system predicted by the model for various upset situations appears physically reasonable and satisfactory for the operating constraints.
Comparative Controller Design for a Marine Gas Turbine Propulsion System
Authors: Smith D. L. , Stammetti V. A.
Published: April 2008

Controller design for marine gas turbine systems should consider three measures of performance: transient control, steady-state accuracy, and disturbance rejection. This paper presents and compares two common types of controller design in terms of these measures. The goal of the controllers was shaft speed control. To meet this goal, a classical Proportional-plus-Integral controller was designed and compared to a modern Linear Quadratic Regulator design. The controllers’ performances were evaluated with respect to the three measures mentioned above, with disturbances being input as oscillations in shaft torque due to seaway cycling.
Configuration E-7 Supersonic Fighter/Attack Technology Program
Authors: Jenista J. E. , Bodden D. S.
Published: April 2008

The program covering the design and early technology development of Configuration E-7, a supersonic STOVL Fighter/Attack aircraft, is described. This aircraft uses the ejector principle to augment engine fan air for vertical lift. The initial design objectives selected in 1980 are listed and discussed. Some design considerations applicable to the propulsion concept and the chosen configuration are mentioned. The test program accomplished thus far, including wind tunnel models plus other test articles and activities, is outlined. The program has proceeded without major technological obstacles and a full-scale engine-powered model will soon be ready for testing.
A Method of Sizing Multi-Cycle Engines for Hypersonic Aircraft
Authors: Kolden J. J.
Published: April 2008

A method of sizing multi-cycle engines for integration with hypersonic vehicles has been developed. The new procedure independently sizes the inlet, each engine cycle, and the nozzle during the vehicle sizing loop to optimize propulsion/aircraft integration. Using uninstalled engine performance for each cycle of a multi-cycle engine along with inlet and nozzle performance and an estimate of aircraft drag, an iterative procedure is utilized to size each component simultaneously. A propulsion system is defined that meets the aircraft thrust requirements at all mission points. The inlet is sized to provide airflow such that the maximum Mach cruise and/or combat thrust conditions are met. Each cycle is sized independently to meet all thrust requirements while minimizing either inlet drag or engine size. Nozzle sizing must trade off thrust, drag and nozzle weight. This methodology has been incorporated into a computer code entitled “Multi-Cycle Engine Sizing Program,” MCESP.
Evaluation of Control Techniques for Aircraft Propulsion Systems
Authors: Rosenblad L. E.
Published: April 2008

This paper discusses the evaluation of modern controls for aircraft propulsion systems. Modern control techniques offer potential advantages over classical approaches. The benefits of multivariable optimization and guaranteed robustness are becoming increasingly attractive as aircraft become more highly integrated and complex. However, validation of modern control techniques has remained theoretical and applications have been restricted to the laboratory. To apply these techniques, the airframer must establish means to understand, evaluate, and verify them. Douglas has established an approach based on digital computer simulation facility to meet these ends. The major elements of this facility are: real-time dynamic system simulation; multivariable compensator generation; and hardware-in-the-loop closure. The facility is intended to serve as a stepping stone to flight test capability while retaining design and test flexibility. Features such as sensor synthesis and noise injection will ensure applicability to real-world implementation. This facility is being used in the evaluation of an integrated secondary system.
Life Assessment of an HP-IP Rotor Under Creep Service Conditions
Authors: Swaminathan V. P. , Cheruvu N. S. , Saxena A.
Published: April 2008

A CrMoV high and intermediate-pressure (HP-IP) rotor exhibited in-service cracking in the blade groove walls. Cracks initiated from a notch and propagated under creep conditions to a depth of 0.255 in. (6.5 mm). Since the unit was base loaded, the contribution of cyclic loading (startups and shutdowns) was not significant. The total life of the groove walls is predicted by applying a life prediction approach that accounts for both crack initiation and propagation. Crack initiation life is based on short-term creep tests extrapolated to long times using a time-temperature parameter. Crack propagation time is estimated using a newly developed time-dependent fracture mechanics concept. A parameter Ct is used to express the crack growth rate under creep loading conditions. Pertinent material properties such as creep deformation and creep crack growth rate were obtained by testing the material from the subject rotor. The results obtained by this analysis show that about 50 percent of the estimated life was spent in crack propagation. Predicted service life time compares very favorably with the actual operating life of the rotor.
Laser Anemometry Measurements of Natural Circulation Flow in a Scale Model PWR System
Authors: Kadambi J. R. , Schneider S. J. , Stewart W. A.
Published: April 2008

Experimental studies were conducted to investigate the natural circulation of a singlephase fluid in a scale model pressurized water reactor system during a postulated degraded core accident. A half-section of a 1/7 scale model with a plexiglass adiabatic window was used. Water and sulfurhexafluoride (SF6) were used as the fluid. Laser-Doppler anemometry (LDA) was used in making the velocity measurements along the center plane of the model at five elevations.
A Magnetic Damper for First-Mode Vibration Reduction in Multimass Flexible Rotors
Authors: Kasarda M. E. F. , Allaire P. E. , Humphris R. R. , Barrett L. E.
Published: April 2008

Many rotating machines such as compressors, turbines, and pumps have long thin shafts with resulting vibration problems. They would benefit from additional damping near the center of the shaft. Magnetic dampers have the potential to be employed in these machines because they can operate in the working fluid environment, unlike conventional bearings. This paper describes an experimental test rig that was set up with a long thin shaft and several masses to represent a flexible shaft machine. An active magnetic damper was placed in three locations: near the midspan, near one end disk, and close to the bearing. With typical control parameter settings, the midspan location reduced the first mode vibration 82 percent, the disk location reduced it 75 percent, and the bearing location attained a 74 percent reduction. Magnetic damper stiffness and damping values used to obtain these reductions were only a few percent of the bearing stiffness and damping values. A theoretical model of both the rotor and the damper was developed and compared to the measured results. The agreement was good.
Some Composite Bearing and Seal Materials for Gas Turbine Applications—A Review
Authors: Sliney H. E.
Published: April 2008

A review is given of the selection and tribological testing of materials for high-temperature bearings and seals. The goal is to achieve good tribological properties over a wide range of temperatures, because bearings and seals must be functional from low-temperature start-up conditions on up to the maximum temperatures encountered during engine operation. Plasma-sprayed composite coatings with favorable tribological properties from 25 to 900°C are discussed. The performance of these coatings in simple tribological bench tests is described. Examples are also given of their performance in high-speed sliding contact seals, as Stirling cylinder liner materials, and as backup lubricants for compliant foil gas bearings.
A Review of Failure Models for Ceramic Matrix Composite Laminates Under Monotonic Loads
Authors: Tripp D. E. , Hemann J. H. , Gyekenyesi J. P.
Published: April 2008

Ceramic matrix composites offer significant potential for improving the performance of turbine engines. In order to achieve their potential, however, improvements in design methodology are needed. In the past most components using structural ceramic matrix composites were designed by “trial and error” since the emphasis on feasibility demonstration minimized the development of mathematical models. To understand the key parameters controlling response and the mechanics of failure, the development of structural failure models is required. A review of short-term failure models with potential for ceramic matrix composite laminates under monotonic loads is presented. Phenomenological, semi-empirical, shear-lag, fracture mechanics, damage mechanics, and statistical models for the fast fracture analysis of continuous fiber unidirectional ceramic matrix composites under monotonic loads are surveyed.
Fracture Energy for Short Brittle Fiber/Brittle Matrix Composites With Three-Dimensional Fiber Orientation
Authors: Wetherhold R. C.
Published: April 2008

Adding brittle fibers to a brittle matrix can create a composite that is substantially tougher than the monolithic matrix by providing mechanisms for energy dissipation during crack propagation. A model based on probabilistic principles has been developed to calculate the increased energy absorption during fracture for a brittle matrix reinforced with very short, poorly bonded fibers. This model, previously developed for planar fiber orientations, is extended to consider the three-dimensional fiber orientations that may occur during composite fabrication. The fiber pull-out energy is assumed to dominate other fracture energy terms, and simple parametric studies are performed to demonstrate the effect of fiber orientation, fiber length, fiber diameter, and fiber-matrix interfacial shear stress. In particular, the fiber orientation effects may be grouped into an effective “orientation parameter.” The model predictions compare satisfactorily with the limited data available, and offer a conceptual framework for considering the effect of changing the physical variables on the fracture energy of the composite.
Automated Welding of Turbine Blades
Authors: Liburdi J. , Lowden P. , Pilcher C.
Published: April 2008

The welding of superalloys has been regarded, generally, as an art requiring the highest degree of welder skill and discipline. These highly alloyed materials are prone to micro-cracking and, in some cases, even the best welders cannot achieve satisfactory results. Now, however, advances in automation technology have made it possible to program precisely the complex airfoil shapes and the welding parameters. Consequently, turbine blades can be welded in a repeatable manner, with a minimum of heat input, resulting in better metallurgical quality both in the base metal and the weld deposit. The application of this technology to the automated welding of high-pressure compressor turbine blade tips and the refurbishment of low-pressure turbine blade shrouds are presented in this paper.
Development of the HIDEC Inlet Integration Mode
Authors: Chisholm J. D. , Nobbs S. G. , Stewart J. F.
Published: April 2008

An integrated flight propulsion control mode called Inlet Integration has been developed and will be flight demonstrated on an F-15 test aircraft in the Highly Integrated Digital Electronic Control (HIDEC) program. The HIDEC program is conducted by the NASA Ames/Dryden Flight Research Center. The development of the Inlet Integration mode is described in this paper, including the Inlet Integration concept, the control law, its implementation on the test bed aircraft, and the predicted performance benefits. The Inlet Integration system will increase excess thrust (thrustdrag) during supersonic operation. This improvement in aircraft performance is accomplished by utilizing a calculation of engine corrected airflow from the Digital Electronic Engine Control (DEEC) to improve the scheduling of the inlet ramp positions in real time. The improvement in scheduled ramp positions will result in increased inlet performance, hence aircraft performance, while maintaining stable inlet operation. Analyses have shown the Inlet Integration system can increase excess thrust by as much as 13 percent at Mach 2.3, 40,000 ft. This thrust increase will result in increased supersonic acceleration. Inlet integration has the additional feature of improving aircraft supportability by eliminating the need for replacing inlet controllers when higher thrust derivative engines are installed in the F-15.
Influence of Geometric Features on the Performance of Pressure-Swirl Atomizers
Authors: Chen S. K. , Lefebvre A. H. , Rollbuhler J.
Published: April 2008

The spray characteristics of several different simplex pressure-swirl nozzles are examined using water as the working fluid. Measurements of mean drop size, dropsize distribution, effective spray cone angle, and circumferential liquid distribution are carried out over wide ranges of injection pressure. Eight different nozzles are employed in order to achieve a wide variation in the length/diameter ratio of the final discharge orifice. Generally, it is found that an increase in discharge orifice length/diameter ratio (lo/do) increases the mean drop size in the spray and reduces the spray cone angle. The circumferential liquid distribution is most uniform when lo/do=2. If lo/do is raised above or lowered below this optimum value, the circumferential uniformity of the liquid distribution is impaired. The observed effects of lo/do on spray characteristics are generally the same regardless of whether the change in lo/do is accomplished by varying lo or do.
Future Engine Technology: Lessons From the 1980s for the 1990s
Authors: Heywood J. B.
Published: April 2008

The past twenty years has seen an explosion in our knowledge of engine processes, steadily improving engine power density and efficiency, major reductions in exhaust emissions, and a substantial increase in engine sophistication and complexity. This paper explains how engineering analysis has played a major enabling role in realizing these improvements in spark-ignition engine performance. Examples are given of the many different types of analysis tool in areas such as combustion, emissions, stress analysis, system dynamics, and fluid flow that have been found useful in resolving different engine development and design problems and opportunities. The significant improvements achieved in engine fuel consumption, power density, and emissions control are then reviewed. It is argued, however, that the improvements in urban air quality do not correspond to the reductions achieved in vehicle exhaust emissions. Our current understanding of the link between vehicle emissions and air quality does not explain this discrepancy. What matters is low enough in-use emission, and future regulations do not adequately focus on this essential requirement. An available energy analysis of the four-stroke spark-ignition engine operating cycle is used to identify where opportunities for further increases in efficiency and power are to be found. Approaches that would improve combustion efficiency, reduce heat losses, increase expansion stroke work, reduce pumping work, and decrease friction are discussed. It is concluded that many analysis tools are now available to identify more precisely how large these opportunities are, and how best they might be realized. The potential of various modifications to the four-stroke cycle SI engine cycle, and alternative spark-ignition and diesel cycles, are reviewed. Finally, it is argued that relative to Europe and Japan, the United States lacks a sufficiently broad and organized research effort designed to support the exploration and development of these opportunities.
Medium-Speed Engine Bearings—Development Experience
Authors: Warriner J. F. , Westerling D. L.
Published: April 2008

After a brief history of the introduction of galvanically applied overlays to the surface of thin-walled half-bearings, the paper goes on to describe experiences in service engines. This shows that from the mid-1970s, overlay life could be sharply reduced due to a variety (or combination) of factors. These are described, the possible causes explained, and various palliatives investigated. The principle factor in the mid-1970s was the rapid rise in the use of lower quality heavy fuels initiated by escalating oil costs. The consequence of using these fuels was often rapid overlay loss, which in turn resulted in further problems, particularly: large areas of exposed nickel interlay, corrosion of the overlay, and/or corrosion of the base lining material. Four palliatives, elimination of the overlay, harder overlays, elimination of the interlayer, and modified surface topography are described and results of development testing and field service experience are presented.
Heavy-Duty Spark Ignition Engines Fueled With Methane
Authors: Gambino M. , Iannaccone S. , Unich A.
Published: April 2008

Pollution reduction in urban areas is a major driving force to upgrade mass transportation systems. Options to the urban planner include electric traction and combustion engine upgrade. Electric traction centralizes the emission source, usually removed from urban areas, but requires substantial capital costs and lead time for the transportation infrastructure. Engine emission improvement is possible through both fuel changes and engine upgrade. Natural gas engines are a viable option for clean-operating urban buses. In the near term, conversion of existing diesel bus engines to spark-ignited natural gas is an attractive solution in terms of capital costs and lead time. This paper contains the analysis required to transform diesel engines into spark-ignited natural gas engines. Experimental data are shown for both a turbocharged and a naturally aspirated conversion. Emission data are presented showing the natural gas conversion to meet present EEC emission requirements.
Oxygen-Enriched Diesel Engine Performance: A Comparison of Analytical and Experimental Results
Authors: Sekar R. R. , Marr W. W. , Assanis D. N. , Cole R. L. , Marciniak T. J. , Schaus J. E.
Published: April 2008

Use of oxygen-enriched combustion air in diesel engines can lead to significant improvements in power density, as well as reductions in particulate emissions, but at the expense of higher NOx emissions. Oxygen enrichment would also lead to lower ignition delays and the opportunity to burn lower grade fuels. Analytical and experimental studies are being conducted in parallel to establish the optimal combination of oxygen level and diesel fuel properties. In this paper, cylinder pressure data acquired on a single-cylinder engine are used to generate heat release rates for operation under various oxygen contents. These derived heat release rates are in turn used to improve the combustion correlation—and thus the prediction capability—of the simulation code. It is shown that simulated and measured cylinder pressures and other performance parameters are in good agreement. The improved simulation can provide sufficiently accurate predictions of trends and magnitudes to be useful in parametric studies assessing the effects of oxygen enrichment and water injection on diesel engine performance. Measured ignition delays, NOx emissions, and particulate emissions are also compared with previously published data. The measured ignition delays are slightly lower than previously reported. Particulate emissions measured in this series of tests are significantly lower than previously reported.
Gaseous and Particulate Emissions From Diesel Locomotive Engines
Authors: Fritz S. G. , Cataldi G. R.
Published: April 2008

Steady-state gaseous and particulate emissions data are presented from two 12-cylinder diesel locomotive engines. The two laboratory engines, a EMD 645E3B and a GE 7FDL, are rated at 1860 kW (2500 hp) and are representative of the majority of the locomotive fleet in North America. Each engine was tested for total hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), and particulate. Emissions were measured at all steady-state operating conditions that make up the eight discrete locomotive throttle notch positions, plus idle, low idle, and dynamic brake. Emissions are reported for each engine with two different diesel fuels: a baseline diesel fuel with a sulfur content of 0.33 weight percent, and a commercially available low-sulfur diesel fuel with a sulfur content of 0.01 weight percent.
A Study of Indicator Passage Error Correction Schemes
Authors: Shiva Prasad B. G. , Heidrich F. L.
Published: April 2008

The passage length between the cylinder and the measuring transducer is known to cause distortion of pressure time traces due to pulsations caused by dynamic effects. This paper attempts to arrive at a simple and efficient calculation scheme for correcting those distortions. Both time domain (method of characteristics approach) and frequency domain methods are evaluated to assess the importance of considering various effects for improving the prediction accuracy. The predictions from both methods are compared with experimental data as well as the results of Heidrich [6], who used simpler versions of these methods.
Optimum Probe Design for Precise TDC Measurement Using a Microwave Technique
Authors: Yamanaka T. , Kinoshita M.
Published: April 2008

The microwave method has advantages, such as a high degree of precision and dynamic measurement capability, for measuring TDC (Top Dead Center) in an engine. However, there are marked discrepancies between the calculation from a simplified model and experiments. Especially in the indirect-injection diesel engine, the concept of this method is not generally understood and the probe design for this method has not been established. It has been experimentally clarified that these discrepancies result mainly from the structure of the main chamber in the indirect-injection diesel engine and the measuring method of the sharpness of a microwave resonance. An optimum probe design for measuring TDC is proposed. A simple laboratory engine simulator is also proposed to simplify determination of the design parameters.
A Study of Inlet Flow Distortion Effects on Automotive Catalytic Converters
Authors: Bella G. , Rocco V. , Maggiore M.
Published: April 2008

This paper will focus on the influence exerted by a nonuniform flow distribution at the inlet of oxidizers to catalytic converters on conversion efficiency evaluated channel by channel. To this aim the flow inside the whole domain, constituted by the exhaust manifold and an elliptic-cross-sectional pipe connecting it with the converter shell, is simulated by means of a three-dimensional fluid-dynamic viscous model. In this way, after assigning typical converter size and geometry (i.e., elliptic) the gas flow rate distribution can be described at its inlet surface, also varying the total mass flow rate. After calculating the flow field at converter inlet by means of a three-dimensional model, evaluation is possible of local flow distortion in comparison with the ideal conditions of constant velocity of the gas entering the honeycomb converter channels. The abovementioned distorted flow field is then assigned as a local boundary condition for another model, developed by the authors, able to describe, through a one-dimensional fluid-dynamic approach, the reacting flow into the converter channels. It was also shown that, due to this flow distortion, honeycomb converters are not uniformly exploited in terms of pollutants of different quantities to be converted in each channel (i.e., a nonuniform exploitation of all the metals coating the ceramic monolith). Finally, the positive effects determined by a diffuser upstream of the converter on flow distribution are analyzed.
Three-Dimensional Computations of Flow and Fuel Injection in an Engine Intake Port
Authors: Kuo T.-W. , Chang S.
Published: April 2008

An existing multidimensional in-cylinder flow code, KIVA, was modified to calculate gas flow and fuel injection in a simplified (no valve stem and simplified valve-head geometry) engine intake port. A single-cylinder engine simulation program was used to specify the initial and boundary conditions for flow calculations. A previously developed spray model was also used to simulate pressure-atomized spray with isooctane as the fuel. Three cases with increasing degrees of complexity were considered: (1) an impulsively started port flow with both port ends open (the inlet-boundary velocity was changed from zero to a finite value at the start of computation), (2) an impulsively started port flow with one port end partially blocked to simulate gas flow through the valve annulus, and (3) port flow driven by the time-varying gas flow rate through the valve annulus calculated using a single-cylinder engine simulation program. A spray calculation was also made for each case. The calculations indicate that the KIVA code can be modified to conduct computations with complicated port geometries and open flow boundary conditions. The results also indicate that both gas flow and fuel-injection processes and port geometry have a strong influence on the details of fuel induction into the cylinder. This confirms that consideration of both gas flow and fuel-injection processes is necessary in order to understand the mechanisms of fuel-air mixing in an engine intake port employing port fuel injection.
Intake Swirl Process Generated by an Engine Head: a Flow Visualization Study
Authors: Khalighi B.
Published: April 2008

In-cylinder charge swirl is used in many internal combustion engines to promote combustion. The purpose of this work is to investigate the in-cylinder swirl characteristics generated by an engine head during the induction process by means of flow visualization and Particle Tracking Velocimetry (PTV). The study was carried out for an engine head with a shrouded intake valve in a special single-cylinder transient water analog. The results revealed that the in-cylinder swirl generated by the shroud is characterized by a strong single vortex with its center of rotation eccentric to the cylinder axis. The location of the center rotation differs from plane to plane along the cylinder axis. Furthermore, velocity data obtained for this study suggest that the in-cylinder swirl is not solid body rotation. Finally, the velocity fields were integrated and an equivalent swirl was calculated for the engine under transient conditions.
Global What? Control Possibilities of CO2 and Other Greenhouse Gases
Authors: Springer K. J.
Published: April 2008

Global what? is a frequent response by those who first hear of the potential for global warming, global climate change, and global catastrophe, potentially brought on by excessive greenhouse gases in the upper atmosphere. The principal greenhouse gas, CO2, is joined by methane, N2O, and other trace gases in absorbing infrared radiation, which would otherwise escape into space, a process thought to be responsible for gradual increase in temperature that will melt ice caps and raise ocean levels. This paper discusses control possibilities that could be considered once there is agreement that CO2 must be controlled. Many of the responses to the energy crisis of 1974 are applicable for CO2 control. A variety of technologies, energy sources, and ideas are offered that, in combination, could be the basis for a global energy policy. Conversion and replacement of coal, oil, and eventually natural gas fired electric power plants with other energy sources such as nuclear, solar, wind, tidal, and geothermal, could significantly reduce CO2 emissions. There are, however, no good alternatives to fossil fuels used in transportation that significantly reduce CO2 emissions. Of all the fossil fuels, natural gas has the least CO2 production. Electric vehicles and hydrogen-fueled engines are future possibilities, but the electricity for the electric cars and for making hydrogen must be from nonfossil fuel driven generators. Conservation, efficiency, and tax incentives are other parts of a control strategy, once the amount of control considered necessary is established. Renewed interest in nonfossil fuel energy sources and their research and development is obviously needed.
Flame Speeds of Low-Cetane Fuels in a Diesel Engine
Authors: Stroia B. J. , Abata D. L.
Published: April 2008

A theoretical and experimental investigation of the flame speeds of low-cetane fuels during the initial stage of heat release in a Diesel engine is described. This information is important for developing a fundamental background in the understanding of fuel injection rate-controlled heat release in a Diesel engine. In this study, a theoretical model based on droplet size, turbulent intensity, and equivalence ratio was developed for the flame propagation through a fuel droplet/air matrix. The results of the theoretical model were compared to experimental high-speed photographs of flame growth in a Diesel engine. For successful injection rate controlled heat release to occur using pilot injdection, the model determined that the combustion zone due to a pilot fuel spray must flow to a distance of at least 30 orifice diameters from the nozzle tip before the main injection event can take place. Results of the model were verified by experiment for the two limiting cases of X/D less than 30 and X/D greater than 30. As expected, rate-controlled heat release was to achieved for the case of X/D less than 30. However, for the case of X/D greater than 30, the main fuel injectin ignited upon injection into the cylinder, and heat release was controlled by rate of injection.
Diesel Engine Cold Starting: P-C Based Comprehensive Heat Release Model: Part I—Single Cycle Analysis
Authors: Zahdeh A. R. , Henein N. A. , Bryzik W.
Published: April 2008

A portable PC-based heat release model for diesel engines with an emphasis on cold starting was developed to be used on an IBM PC or compatible. The model features normalized variables, the inclusion of blowby and heat transfer models, smoothing using a combination of error detection methods and low pass FFT. The derivative of the pressure data was calculated using cubical splines, from which the analytical first and second derivatives were derived. This method had the advantage of no data shifting, the ability to calculate the derivatives at any point (intermediate or original data point) and the error of both the first and second derivatives of the same order. The inclusion of the blowby model during starting was essential as losses due to blowby were found to be just as significant as other major loss factors. Smoothing angular velocity and the pressure signal using polynomial and cubical splines did not prove to be as efficient or as accurate as using the combination of error detection methods and FFT. Combustion during cold starting is mostly of the premixed type.
Combined Cycle Plants With Frame 9F Gas Turbines
Authors: Lugand P. , Parietti C.
Published: April 2008

The new 200 MW class MS 9001F gas turbines allow combined cycle plants to reach even higher output levels and greater efficiency ratings. Size factor and higher firing temperatures, with a three-pressure level steam reheat cycle, offer plant efficiencies in excess of 53 percent. Heat recovery steam generators have been designed to accommodate catalytic reduction elements limiting flue gas NOx emissions to as low as 10 ppm VD (15 percent O2). A range of steam turbine models covers the different possible configurations. Various arrangements based on the 350 or 650 MW power generation modules can be optimally configured to the requirements of each site.
MS3002 Advanced Tech Upgrade Application and Operating Experience
Authors: Grondahl C. M. , Guiler M. E.
Published: April 2008

Modernization of MS3002 gas turbines produced by GE from 1951 to 1973 has been accomplished with the application of advanced technology components in a redesigned turbine hot section. Texas Eastern installed the first modernization package in 1986 and now has 10 units in service totalling more than 135,000 operating hours. This paper presents the user’s motivation to refurbish 30-year-old gas turbines, including details of the uprate installation and subsequent operating experience. Specifics of the advanced technology components in these units are provided including their impact on unit performance and reliability.
Thermodynamic Optimization of Irreversible Power Cycles With Constant External Reservoir Temperatures
Authors: Swanson L. W.
Published: April 2008

An extended version of the Bejan model of irreversible power plants is proposed using a log-mean temperature difference (LMTD) representation for both the high and low-temperature heat exchangers. The analysis focuses on minimizing the irreversibilities associated with the hot and cold heat exchangers. The results indicate that the maximum power output, external conductance allocation ratio, and second law efficiency are functions of the number total heat exchanger transfer units (N), and are asymptotic to Bejan’s original results as N → O. This asymptote represents a global power output maximum and occurs for either extremely high cycle flow rates or cycle phase change processes in both heat exchangers. The LMTD representation also shows that under optimal conditions, more conductance should be allocated to the low-temperature heat exchanger as N increases.
Optimum Heat Power Cycles for Specified Boundary Conditions
Authors: Ibrahim O. M. , Klein S. A. , Mitchell J. W.
Published: April 2008

Optimization of the power output of Carnot and closed Brayton cycles is considered for both finite and infinite thermal capacitance rates of the external fluid streams. The method of Lagrange multipliers is used to solve for working fluid temperatures that yield maximum power. Analytical expressions for the maximum power and the cycle efficiency at maximum power are obtained. A comparison of the maximum power from the two cycles for the same boundary conditions, i.e., the same heat source/sink inlet temperatures, thermal capacitance rates, and heat exchanger conductances, shows that the Brayton cycle can produce more power than the Carnot cycle. This comparison illustrates that cycles exist that can produce more power than the Carnot cycle. The optimum heat power cycle, which will provide the upper limit of power obtained from any thermodynamic cycle for specified boundary conditions and heat exchanger conductances is considered. The optimum heat power cycle is identified by optimizing the sum of the power output from a sequence of Carnot cycles. The shape of the optimum heat power cycle, the power output, and corresponding efficiency are presented. The efficiency at maximum power of all cycles investigated in this study is found to be equal to (or well approximated by) η=1−TL,in/φTH,in where φ is a factor relating the entropy changes during heat rejection and heat addition.
Thermal-Hydraulic Analysis of the Fort St. Vrain Modular Vault Dry Store System
Authors: Cho S. M. , Seltzer A. H. , Blackbourn M.
Published: April 2008

A passive, natural thermosyphon, air-cooled modular vault dry store (MVDS) system is being constructed for the storage of nuclear spent fuel for the Fort St. Vrain (FSV) Nuclear Power Station. In support of this FSV-MVDS system, thermal-hydraulic design analyses have been performed. The objective of the analyses is to determine flow and temperature distributions within the system and thus to ensure that the maximum fuel element temperatures shall not exceed specified design limit values under various loading and unloading conditions. This paper presents the method of analysis and discusses the resulting thermal-hydraulic characteristics of the MVDS system.
Compressor Coating Effects on Gas Turbine Engine Performance
Authors: MacLeod J. D. , Laflamme J. C. G.
Published: April 2008

In an attempt to increase the time between maintenance actions and to improve performance retention of turboprop engines installed in transport and maritime patrol aircraft, the Canadian Department of National Defence is evaluating an erosion and corrosion-resistant blade coating, for use on compressors. As coatings could appreciably alter engine performance by virtue of their application thickness and surface quality, the National Research Council of Canada was asked to quantify any performance changes that could occur. A project was initiated, utilizing a new Allison T56 turboprop engine, to assess not only the performance changes resulting from the coating, but also those from dismantling and reassembling the compressor, since the compressor must be completely disassembled to apply the coating. This paper describes the project objectives, the experimental installation, and the measured effects of the coating application on compressor performance. Performance variations due to compressor rebuilds on both engine and compressor characteristics are discussed. As the performance changes were small, a rigorous measurement uncertainty analysis is included. The coating application process and the affected overhaul procedures are examined. The results of the pre- and postcoating compressor testing are presented, with a discussion of the impact on engine performance.
Development of an Efficient Oil Film Damper for Improving the Control of Rotor Vibration
Authors: Zhang Shiping , Yan Litang
Published: April 2008

An efficient oil film damper known as a porous squeeze film damper (PSFD) was developed for more effective and reliable vibration control of high-speed rotors based on the conventional squeeze film damper (SFD). The outer race of the PSFD is made of permeable sintered porous metal materials. The permeability allows some of the oil to permeate into and seep out of the porous matrix, with remarkable improvement of the squeeze film damping properties. The characteristics of PSFD oil film stiffness and damping coefficients and permeability, and also, the steady-state unbalance response of a simple rigid rotor and flexible Jeffcott’s rotor supported on PSFD and SFD are investigated. A typical experiment is presented. Investigations show that the nonlinear vibration characteristics of the unpressurized SFD system such as bistable jump phenomena and “lockup” at rotor pin-pin critical speeds could be avoided and virtually disappear under much greater unbalance levels with properly designed PSFD system. PSFD has the potential advantage of operating effectively under relatively large unbalance conditions.
An Approach to Describing the Simultaneous Erosion and High-Temperature Oxidation of Alloys
Authors: Wright I. G. , Sethi V. K. , Nagarajan V.
Published: April 2008

The rate of wastage of an alloy surface subjected to erosion under conditions where high-temperature oxidation can occur can be significantly greater than that arising from erosion alone. This is because the erosion conditions can act to accelerate the oxidation process by causing regular shedding of the otherwise protective oxide scale. It is suggested that an important parameter in determining the rate of erosion-oxidation is the erodent flux, since the time available for oxide growth (or regrowth) in a given area is determined by the interval between successive erodent impacts. Using this simple premise, an approach is suggested by which the rate of erosion-oxidation can be related to the factors that control the alloy oxidation process, and those that describe the erosive environment. The assumptions made are examined, and some of the implications of this approach are discussed.
Experimental and Computed Performance Characteristics of High-Speed Silicon Nitride Hybrid Ball Bearings
Authors: Hosang G. W.
Published: April 2008

Development testing of hybrid bearings with M.50 rings and HIPed silicon nitride balls in small high-speed turbojet engines was carried out for several minutes at speeds up to 110,000 rpm. The main rotor system comprised an overhung radial compressor and turbine monorotor assembly with a pair of preloaded 101-size bearings. Estimated aerodynamic thrust of up to 750 N (170 lb) was added to the 200 N (45 lb) preload on the bearing adjacent to the compressor. Some testing was carried out with MIL-L-7808 air/oil mist and some with JP-10 fuel supplied in a similar fashion. After each test phase the bearings were removed for examination and re-used or replaced. Four of the bearings were submitted to inspection with special equipment to measure operating contact angles, as evidenced by the visible ball tracks, and any wear present. Contact angles and other operating characteristics estimated with the Jones, “SHABERTH,” and “ADORE” computer codes were compared with the experimental data.
Second-Generation Low-Emission Combustors for ABB Gas Turbines: Burner Development and Tests at Atmospheric Pressure
Authors: Sattelmayer T. , Felchlin M. P. , Haumann J. , Hellat J. , Styner D.
Published: April 2008

Based on fundamental research concerning swirling flows, including the vortex breakdown phenomenon, as well as on stability considerations of premixed flames, a second generation of low-emission burners has been developed. The lean premixing technique provides NOx emissions below 25 ppmv for natural gas. For liquid fuels the oxides of nitrogen are limited to 42 ppmv (oil No. 2). The novel burner technology will be applied to the well-known ABB silo combustor. As a first step the Conical Premix Burner will be used to retrofit the ABB type 11N. For the ABB gas turbine type 8 the design of a novel fully annular combustor is in progress. Most of the conceptual work concerning burner aerodynamics and burner-burner interaction has been carried out on scaled-down burner and combustor models. For a second step a sector of the combustor in 1:1 scale has been tested at atmospheric pressure. Additional high-pressure tests provide information about the combustor performance at engine conditions. The present paper summarizes the results of the first two steps beginning with the early ideas in the conceptual phase up to the 1:1 tests, which prove the low-NOx capability for both gaseous and liquid fuels under atmospheric pressure conditions.