bluuebunny/crossref_metadata_2025 huggingface dataset:
Ceramic Component Processing Development for Advanced Gas Turbine Engines
Authors: McEntire B. J. , Hengst R. R. , Collins W. T. , Taglialavore A. P. , Yeckley R. L.
Published: April 2008

Norton/TRW Ceramics (NTC) is developing ceramic components as part of the DOE-sponsored Advanced Turbine Technology Applications Project (ATTAP). NTC’s work is directed at developing manufacturing technologies for rotors, stators, vane-seat platforms, and scrolls. The first three components are being produced from a HIPed Si3N4, designated NT154. Scrolls were prepared from a series of siliconized silicon-carbide (Si-SiC) materials designated NT235 and NT230. Efforts during the first three years of this five-year program are reported. Developmental work has been conducted on all aspects of the fabrication process using Taguchi experimental design techniques. Appropriate materials and processing conditions were selected for power beneficiation, densification, and heat-treatment operations. Component forming has been conducted using thermal-plastic-based injection molding (IM), pressure slip-casting (PSC), and Quick-Set™ injection molding.1 An assessment of material properties for various components from each material and process were made. For NT154, characteristic room-temperature strengths and Weibull Moduli were found to range between ≈920 MPa to ≈1 GPa and ≈10 to ≈19, respectively. Process-induced inclusions proved to be the dominant strength-limiting defect regardless of the chosen forming method. Correction of the lower observed values is being addressed through equipment changes and upgrades. For the NT230 and NT235 Si-SiC, characteristic room-temperature strengths and Weibull Moduli ranged from ≈240 to ≈420 MPa, and 8 to 10, respectively. At 1370°C, strength values for both the HIPed Si3N4 and the Si-SiC materials ranged from ≈480 MPa to ≈690 MPa. The durability of these materials as engine components is currently being evaluated.
Fabrication and Testing of Ceramic Turbine Wheels
Authors: Takatori K. , Honma T. , Kamiya N. , Masaki H. , Sasaki S. , Wada S.
Published: April 2008

A silicon nitride (Si3N4) radial inflow turbine wheel was fabricated by injection molding at Toyota Central R&D Labs. The wheel was 142 mm in outer diameter and had 14 blades. The radial wheel was too bulky to manufacture as a homogeneous and defect-free body in one piece. It was divided into two pieces for injection molding and put together into one body by a cold isostatic pressing step after binder removal. Spin testing was executed at room temperature and the resulting photographs, taken from three directions, provided useful information about the fraction mode of the wheels. The maximum burst speed of the wheels at room temperature was 98,900 rpm, which corresponded to 145 percent of the design speed. In a hot rig test, one of the wheels survived 75,000 rpm for ten minutes at a turbine inlet temperature of 1050°C.
Research and Development of Ceramic Turbine Wheels
Authors: Watanabe K. , Masuda M. , Ozawa T. , Matsui M. , Matsuhiro K.
Published: April 2008

The bending strength of specimens of various sizes, some of which were cut from a turbine wheel, was compared with predictions using Weibull statistical theory. The stress distribution of a ceramic turbine wheel in spin testing was determined with finite elements and the results were used to analyze a wheel that was spun until it burst. The cause of the burst of the ceramic radial turbine wheel at elevated temperature is discussed and based on the tensile rupture data. A design methodology using the Larson-Miller parameter was found to be applicable to the ceramic components at elevated temperatures.
Current Status of 300 kW Industrial Ceramic Gas Turbine R&D in Japan
Authors: Honjo K. , Hashimoto R. , Ogiyama H.
Published: April 2008

This paper gives an overview of the current status of Japan’s national industrial ceramic gas turbine (CGT) project. The goals are 42 percent and higher thermal efficiency at the turbine inlet temperature (TIT) of 1350°C, and the emission from the exhaust gas should meet the regulatory values (for example, 70 ppm for NOx). Also, ceramic material properties have the goals of 400 MPa for the minimum guaranteed strength at 1500°C, and 15 MPam for the fracture toughness. Currently, the basic metal gas turbine of TIT 900°C with all metallic components has already been fabricated and is running under some test conditions. The design of the basic ceramic gas turbine of TIT 1200°C has been completed and its manufacture is in progress. Research is addressing the production of large, complicated ceramic parts, and parts with less deformation and fewer defects can now be produced.
Ceramic Matrix Composite Applications in Advanced Liquid Fuel Rocket Engine Turbomachinery
Authors: Brockmeyer J. W.
Published: April 2008

Hot gas path components of current generation, liquid fuel rocket engine turbopumps (T/P) are exposed to severe thermal shock, extremely high heat fluxes, corrosive atmospheres, and erosive flows. These conditions, combined with high operating stresses, are severely degrading to conventional materials. Advanced turbomachinery (T/M) applications will impose harsher demands on the turbine materials. These demands include higher turbine inlet temperature for improved performance and efficiency, lower density for improved thrust-to-weight ratio, and longer life for reduced maintenance of re-usable engines. Conventional materials are not expected to meet these demands, and fiber-reinforced ceramic matrix composites (FRCMC) have been identified as candidate materials for these applications. This paper summarizes rocket engine T/M needs, reviews the properties and capabilities of FRCMC, identifies candidate FRCMC materials and assesses their potential benefits, and summarizes the status of FRCMC component development with respect to advanced liquid fuel rocket engine T/M applications.
Ceramic Matrix Composites for Rocket Engine Turbine Applications
Authors: Herbell T. P. , Eckel A. J.
Published: April 2008

A program to establish the potential for introducing fiber-reinforced ceramic matrix composites (FRCMC) in future rocket engine turbopumps was instituted in 1988. A brief summary of the overall program (both contract and in-house research) is presented. Tests at NASA Lewis include thermal upshocks in a hydrogen/oxygen test rig capable of generating heating rates up to 2500°C/s. Post-thermal upshock exposure evaluation includes the measurement of residual strength and failure analysis. Test results for monolithic ceramics and several FRCMCs are presented. Hydrogen compatibility was assessed by isothermal exposure of monolithic ceramics in high-temperature gaseous hydrogen plus water vapor.
Lifetime Prediction for Ceramic Gas Turbine Components
Authors: Stu¨rmer G. , Schulz A. , Wittig S.
Published: April 2008

At the Institute for Thermal Turbomachinery, University of Karlsruhe (ITS), theoretical and experimental investigations of ceramic gas turbine components are performed. For the reliability analysis by finite element calculations the computer code CERITS has been developed. This code is used to determine the fast fracture reliability of ceramic components subjected to polyaxial stress states with reference to volumetric flaws and was presented at the 1990 IGTI Gas Turbine Conference. CERITS-L now includes subcritical crack growth. With the new code CERITS-L, failure probabilities of ceramic components can be calculated under given load situations versus time. In comparing these time-dependent failure probabilities with a given permissible failure probability, the maximum operation time of a component can be determined. The considerable influence of the subcritical crack growth upon the lifetime of ceramic components is demonstrated at the flame tube segments of the ITS ceramic combustor.
A Study on Stability and Response Analysis of a Nonlinear Rotor System With Mass Unbalance and Side Load
Authors: Shiau T. N. , Hwang J. L. , Chang Y. B.
Published: April 2008

The stability of steady-state synchronous and nonsynchronous response of a nonlinear rotor system supported by squeeze-film dampers is investigated. The nonlinear differential equations that govern the motion of rotor bearing systems are obtained by using the Generalized Polynomial Expansion Method. The steady-state response of the system is obtained by using the hybrid numerical method, which combines the merits of the harmonic balance and collocation methods. The stability of system response is examined using the Floquet-Liapunov theory. Using the theory, the performance may be evaluated with the calculation of derivatives of nonlinear hydrodynamic forces of the squeeze-film damper with respect to displacement and velocity of the journal center. In some cases, these derivatives can be expressed in closed form and the prediction of the dynamic characteristic of the nonlinear rotor system will be more effective. The stability results are compared to those using a direct numerical integration method and both are in good agreement.
Dynamic Response of Rotor-Bearing Systems With Time-Dependent Spin Rates
Authors: Young T. H. , Liou G. T.
Published: April 2008

This paper presents an investigation into the vibration of rotor-bearing systems with time-dependent spin rates. Due to this spin rate, parametric instability may take place in certain situations. In this work, the Galerkin method is used to eliminate the dependence on the spatial coordinates, and then the method of multiple scales is applied to derive periodic solutions and expressions for the boundaries of unstable regions analytically. Numerical results are given for the case where the spin rate is characterized as a small, harmonic perturbation superimposed on a constant rate. The effects of system parameters on the changes of the boundaries of unstable regions are shown.
The Effects of Friction in Axial Splines on Rotor System Stability
Authors: Artiles A. F.
Published: April 2008

An in-depth parametric evaluation of the effects of Coulomb friction in an axial spline joint on the stability of the rotor-bearing system was conducted through time transient integration of the equations of motion. The effects of spin speed, friction coefficient, spline torque, external damping, imbalance, and side load as well as asymmetric bearing stiffnesses were investigated. A subsynchronous instability is present at the bending critical speed when the spin speed is above this critical. The limit cycle orbit is circular, proportional to the product of the friction coefficient and spline torque (μT), inversely proportional to the external damping, and independent of spin speed. When imbalance is applied to the rotor, beating between the subsynchronous natural frequency and the synchronous (spin speed) frequency occurs. The subsynchronous component of the orbit is proportional to μT, while the synchronous component is proportional to the imbalance. When a static side load is applied, the unstable node at the center of the orbitally stable limit cycle grows into an ellitpical orbitally unstable limit cycle, separating stable from unstable regions of the phase plane. Below a threshold value of side load, the transient motion approaches one of two asymptotic solutions depending on the initial conditions: the larger stable limit cycle or a point at the center of the smaller unstable limit cycle. Beyond the threshold value of side load, the rotor-bearing is stable and all motions decay to a point. Asymmetry in the bearing stiffnesses reduces the size of the subsynchronous whirl orbit.
Rotordynamic Evaluation of an Advanced Multisqueeze Film Damper—Imbalance Response and Blade-Loss Simulation
Authors: Walton J. F. , Heshmat H.
Published: April 2008

In this paper results of rotordynamic response and transient tests of a novel, high load squeeze film damper design are presented. The spiral foil multisqueeze film damper has been previously shown to provide two to fourfold or larger increases in damping levels without resorting to significantly decreased damper clearances or increased lengths. By operating with a total clearance of approximately twice conventional designs, the nonlinearities associated with high-eccentricity operation are avoided. Rotordynamic tests with a dual squeeze film configuration were completed. As a part of the overall testing program, a flexible rotor system was subjected to high steady-state imbalance levels and transient simulated blade-loss events for up to 0.254 mm (0.01 in.) mass c. g. offset or 180 g-cm (2.5 oz-in.) imbalance. The spiral foil multisqueeze film damper demonstrated that the steady-state imbalance and simulated blade-loss transient response of a flexible rotor operating above its first bending critical speed could be readily controlled. Rotor system imbalance sensitivity and logarithmic decrement are presented showing the characteristics of the system with the damper installed. The ability to accommodate high steady-state and transient imbalance conditions make this damper well suited to a wide range of rotating machinery, including aircraft gas turbine engines.
The Basics of Powder Lubrication in High-Temperature Powder-Lubricated Dampers
Authors: Heshmat H. , Walton J. F.
Published: April 2008

The objective of this investigation is to develop a novel powder-lubricated rotor bearing system damper concept for use in high-temperature, high-speed rotating machinery such as advanced aircraft gas turbine engines. The approach discussed herein consists of replacing a conventional oil lubrication or frictional damper system with a powder lubrication system that uses the process particulates or externally fed powder lubricant. Unlike previous work in this field, this approach is based on the postulate of the quasi-hydrodynamic nature of powder lubrication. This postulate is deduced from past observation and present verification that there are a number of basic features of powder flow in narrow interfaces that have the characteristic behavior of fluid film lubrication. In addition to corroborating the basic mechanism of powder lubrication, the conceptual and experimental work performed in this program provides guidelines for selection of the proper geometries, materials, and powders suitable for this tribological process. The present investigation describes the fundamentals of quasi-hydrodynamic powder lubrication and defines the rationale underlying the design of the test facility. The performance and the results of the experimental program present conclusions reached regarding design requirements as well as the formulation of a proper model of quasi-hydrodynamic powder lubrication.
A Gas-Operated Bearing Damper for Turbomachinery
Authors: Vance J. M. , Cardon B. P. , San Andres L. A. , Storace A. F.
Published: April 2008

A gas-operated bearing damper for turbomachinery has been designed, analyzed, and experimentally investigated in the laboratory. The damper utilizes air bled off from the compressor to power an actuator through orifices with area modulated by the vibratory displacement at the bearing support. The design objective for this passive device is to make the actuating dynamic gas pressure phase lead the vibratory displacement by 90 deg. Several variations of the basic concept have been tested. An analysis was performed to guide the experiments. All of the designs tested to date can produce positive damping, and one particular design has produced a damping coefficient of 8756 N-s/m (50 lb-sec/in.) with a power penalty of 5.2 kW (7 hp) at 310 KPa (45 psi). This design was installed on a laboratory rotor with flexibly supported ball bearings, and significant damping of the critical speed response was demonstrated. The experimental results to date suggest that further research can produce significant improvements in performance, and the device appears to be especially adaptable to high-temperature applications for aircraft engines.
Optimal Circumferential Placement of Cylindrical Thermocouple Probes for Reduction of Excitation Forces
Authors: Cobb E. C. , Cheu T.-C. , Hoffman J.
Published: April 2008

This paper presents a design methodology to determine the optimal circumferential placement of cylindrical probes upstream of a turbine stage for reduced excitation forces. The potential flow forcing function generated by the probes is characterized by means of a Fourier analysis. A finite difference formulation is used to evaluate the sensitivity of the forcing function to the probe positions. An optimization scheme, based on the linear programming method, uses the sensitivity analysis results to reposition the probes such that the Fourier amplitudes of critical excitation orders are reduced. The results for a sample design situation are presented.
Influence of Flow Conditions on Deposits From Heated Hydrocarbon Fuels
Authors: Chin J. S. , Lefebvre A. H.
Published: April 2008

The thermal stability characteristics of two liquid hydrocarbon fuels are examined using a single-pass system whereby the fuel under test flows only once through a heated tube which is maintained at constant temperature throughout a test duration of six hours. Deposition rates on the tube walls are measured by weighing the tube before and after each test. The experimental data are used to derive empirical equations for predicting the effects on deposition rates of variation in fuel temperature, wall temperature, and Reynolds number. It is found that deposition rates are enhanced by increases in fuel temperature, wall temperature and flow velocity, and by reductions in tube diameter. Pressure has no effect on deposition rates provided it is high enough to prevent fuel boiling.
Innovative High-Temperature Aircraft Engine Fuel Nozzle Design
Authors: Stickles R. W. , Dodds W. J. , Koblish T. R. , Sager J. , Clouser S.
Published: April 2008

The objective of the Innovative High-Temperature Aircraft Engine Fuel Nozzle Program was to design and evaluate a nozzle capable of operating at a combustor inlet air temperature of 1600°F (1144 K) and a fuel temperature of 350°F (450 K). The nozzle was designed to meet the same performance requirements and fit within the size envelope of a current production F404 dual orifice fuel nozzle. The design approach was to use improved thermal protection and fuel passage geometry in combination with fuel passage surface treatment to minimize coking at these extreme fuel and air temperatures. Heat transfer models of several fuel injector concepts were used to optimize the thermal protection, while a series of sample tube coking tests were run to evaluate the effect of surface finish, coatings, and tube material on the coking rate. Based on heat transfer analysis, additional air gaps, reduced fuel passage flow area, and ceramic tip components reduced local fuel wetted wall temperatures by more than 200°F (110 K) when compared to a current production F404 fuel nozzle. Sample tube coking test results showed the importance of surface finish on the fuel coking rate. Therefore, a 1 μin. (0.025 μm) roughness was specified for all fuel passage surfaces. A novel flow divider valve in the tip was also employed to reduce weight, allow room for additional thermal protection, and provide back pressure to reduce the risk of fuel vaporization. Phase II of this program will evaluate the fuel nozzle with a series of contaminated fuel and coking tests.
Scaling of the Two-Phase Flow Downstream of a Gas Turbine Combustor Swirl Cup: Part I—Mean Quantities
Authors: Wang H. Y. , McDonell V. G. , Sowa W. A. , Samuelsen G. S.
Published: April 2008

A production gas turbine combustor swirl cup and a 3×-scale model (both featuring co-axial, counterswirling air streams) are characterized at atmospheric pressure. Such a study provides an opportunity to assess the effect of scale on the behavior of the continuous phase (gas in the presence of spray) and droplets by comparing the continuous phase velocity, droplet size, and droplet velocity at geometrically analogous positions. Spatially resolved velocity measurements of the continuous phase, droplet size, and droplet velocity were acquired downstream of the production and 3×-scale swirl cups by using two-component phase-Doppler interferometry in the absence of reaction. While the continuous phase flow fields scale well at the exit of the swirl cup, the similarity deviates at downstream locations due to (1) differences in entrainment, and (2) a flow asymmetry in the case of the production hardware. The droplet velocities scale reasonably well with notable exceptions. More significant differences are noted in droplet size, although the presence of the swirl cup assemblies substantially reduces the differences in size that are otherwise produced by the two atomizers when operated independent of the swirl cup.
Effects of Variable Liquid Properties on Multicomponent Droplet Vaporization
Authors: Kneer R. , Schneider M. , Noll B. , Wittig S.
Published: April 2008

A multicomponent droplet vaporization model, the Diffusion-Limit Model, is modified to account for the variation of liquid properties due to large temperature gradients as well as considerable concentration gradients within the droplet. The effects on the vaporization behavior are analyzed for an isolated biocomponent droplet consisting of heptane and dodecane. The results are presented for both moderate and high gas temperatures excluding combustion. During the vaporization process the liquid phase properties vary considerably. For example, the Lewis number changes by approximately one order of magnitude. The mass ratio of the liquid components seems to be rather sensitive to the variation of thermophysical property values, especially during the second half of the droplet lifetime, where about 50 percent of the droplet mass will still evaporate. The gas phase behavior is less affected by the use of constant liquid properties. For both gas temperature levels tested it was found that single component models cannot describe satisfactorily the whole vaporization process of multicomponent droplets. With regard to ignition the sharp rise of the vapor concentration in the beginning of the droplet vaporization is important. This behavior is caused by the more volatile component and cannot be achieved by the single component substitute.
Multijet Annulus/Core-Flow Mixing—Experiments and Calculations
Authors: Baker S. J. , McGuirk J. J.
Published: April 2008

LDV measurements are reported of the flow field associated with a single row of radially injected jets penetrating a core-tube flow. Emphasis is placed on the influence of small feed-annulus height on jet entry conditions and resulting trajectories and mixing patterns. Conditions of unstable jet behavior, with strong vortex patterns in the jet holes, were observed for small annulus heights and high annulus velocities. Most measurements were, however, taken under stable conditions to allow the data to be used in a CFD validation exercise. Significant differences in the strength of backflow generated at jet impingement and in the turbulence field in the immediate hole vicinity were observed for different annulus height/core diameter ratios. These were accompanied by jet trajectory and annulus flow structure changes. Measurements of all three mean velocity components and associated normal stresses enabled the data to be utilized to assess a three-dimensional CFD calculation incorporating a k-ε turbulence closure. The strength of forward and back flow generated at impingement was accurately predicted when the QUICK discretization scheme was used. However, the size of upstream vortex was overpredicted. As expected using an eddy viscosity model, the turbulence field at jet impingement and in the hole vicinity was not correctly reproduced. The turbulence generation in the flow approaching the hole was greatly overestimated by the turbulence model used.
Effects of Back-Pressure in a Lean Blowout Research Combustor
Authors: Sturgess G. J. , Heneghan S. P. , Vangsness M. D. , Ballal D. R. , Lesmerises A. L. , Shouse D.
Published: April 2008

Experimental information is presented on the effects of back-pressure on flame-holding in a gaseous fuel research combustor. Data for wall temperatures and static pressures are used to infer behavior of the major recirculation zones, as a supplement to some velocity and temperature profile measurements using LDV and CARS systems. Observations of flame behavior are also included. Lean blowout is improved by exit blockage, with strongest sensitivity at high combustor loadings. It is concluded that exit blockage exerts its influence through effects on the jet and recirculation zone shear layers.
Direct Measurements of Skin Friction in Supersonic Combustion Flow Fields
Authors: Chadwick K. M. , DeTurris D. J. , Schetz J. A.
Published: April 2008

An experimental investigation was conducted to measure skin friction along the chamber walls of supersonic combustors. A direct force measurement device was used to measure simultaneously an axial and a transverse component of the small tangential shear force passing over a nonintrusive floating element. This measurement was made possible with a sensitive piezoresistive deflection sensing unit. The floating head is mounted to a stiff cantilever beam arrangement with deflection due to the flow on the order of 0.00254 mm (0.0001 in). This allowed the instrument to be a nonnulling type. A second gage was designed with active cooling of the floating sensor head to eliminate nonuniform temperature effects between the sensor head and the surrounding wall. The key to this device is the use of a quartz tube cantilever with piezoresistive strain gages bonded directly to its surface. A symmetric fluid flow was developed inside the quartz tube to provide cooling to the backside of the floating head. Tests showed that this flow did not influence the tangential force measurement. Measurements were made in three separate combustor test facilities. Tests at NASA Langley Research center consisted of a Mach 3.0 vitiated air flow with hydrogen fuel injection at Pt = 500 psia (3466 kPa) and Tt = 3000 R (1667 K). Two separate sets of tests were conducted at the General Applied Science Laboratory (GASL) in a scramjet combustor model with hydrogen fuel injection in vitiated air at Mach = 3.3, Pt = 800 psia (5510 kPa), and Tt = 4000 R (2222 K). Skin friction coefficients between 0.001–0.005 were measured dependent on the facility and measurement location. Analysis of the measurement uncertainties indicate an accuracy to within ± 10–15 percent of the streamwise component.
Coherent Anti-Stokes Raman Scattering (CARS) Thermometry in a Model Gas Turbine Can Combustor
Authors: Zhu J. Y. , Tsuruda T. , Sowa W. A. , Samuelsen G. S.
Published: April 2008

Nonintrusive, spatially resolved instantaneous temperature measurements are presented that were obtained from a reacting spray flame in a model gas turbine can combustor using coherent anti-Stokes Raman scattering (CARS) thermometry. The results show that CARS measurements agree with thermocouple measurements at the exit of the combustor. The liquid droplet induced dielectric breakdown is not an obstacle in applying CARS to reacting sprays. The CARS measured temperature field also indicates that there is a relatively cool region (T < 1000 K) near the nozzle tip. Reaction occurs in the region where large numbers of droplets are present and in the interface of the swirl-induced recirculation zone. This study demonstrates that CARS is a viable diagnostic tool for nonintrusive, instantaneous temperature measurements in practical spray flames.
The Combustion of Droplets Within Gas Turbine Combustors: Some Recent Observations on Combustion Efficiency
Authors: Odgers J. , Kretschmer D. , Pearce G. F.
Published: April 2008

For many years investigators studying the combustion behavior within gas turbines have presumed droplet size to play a very important role in defining combustion efficiency. Recently a very large number of experiments have been conducted jointly by Laval University and the Aeronautical Research Laboratory in Melbourne. In the course of these investigations, over a wide range of operating conditions, a single combustor has been investigated using three different Simplex atomizers at each of the conditions for three fuels. In addition, the same combustor has been used to investigate a very wide range of fuels (87) at ambient inlet conditions. The measured combustion efficiencies show no measurable effects due to droplet size, although volatility effects have been noted (measured as TAV). It is thought that these effects are reflected in terms of a transfer number and related to diffusional phenomena, rather than evaporative phenomena. A great number of experimental data are reviewed, and in addition to showing the absence of effects of droplets, a small section deals with the precision of experimental values of combustion efficiency and how it might influence models predicting combustion efficiency, especially with respect to possible future pollution requirements.
Second-Generation Low-Emission Combustors for ABB Gas Turbines: Field Measurements With GT11N-EV
Authors: Aigner M. , Mu¨ller G.
Published: April 2008

In February 1991, a type GT11N gas turbine (Midland, USA) was retrofitted with ABB’s new EV-Silo-Combustor. Tests were then carried out to examine the operation concept, to demonstrate the technical reliability, and to confirm the low emission performance of this new technology. This paper will describe: the combustor design—one single silo combustor mounted on the turbine and equipped with 37 Ev burners; and the results of the extensive field measurements—the operation concept (lean premix combustion without any pilot diffusion flames, 7 burner groups) is simple and reliable. The emission targets—NOx<25 ppmv (15 percent O2, natural gas), CO<8 ppmv, UHC<5 ppmv—were reached. NOx values are even lower than 15 ppmv at base load. The NOx predictions for the GT11N-EV, based on the results of high-pressure tests in Cologne (ASME Paper No. 90-GT-308), compared very well with the results of field measurements.
Low NOx Combustor for Automotive Ceramic Gas Turbine—Reliability Assurance
Authors: Kumakura H. , Sasaki M. , Suzuki D.
Published: April 2008

Two aspects of reliability assurance are discussed. First, this paper deals with the reliability design of emissions under transient conditions. The optimization was made from the simulation results of the relationship between the response of the variable combustor geometry to follow load changes and the resulting exhaust emission levels. The load variation pattern used in this investigation was that of the Japanese ten-mode regulation. Second, this paper describes the validity of the reliability design prepared for the ceramic liner of the combustor. A service life prediction was made for the liner on the basis of stress analysis results and fatigue parameters.
Emissions Reduction by Varying the Swirler Airflow Split in Advanced Gas Turbine Combustors
Authors: Micklow G. J. , Roychoudhury S. , Nguyen H. L. , Cline M. C.
Published: April 2008

A staged combustor concept for reducing pollutant emissions is currently under investigation. A numerical study was performed to investigate the chemically reactive flow with liquid spray injection for staged combustion. The staged combustor consists of an airblast atomizer fuel injector, a rich burn section, a converging connecting pipe, a quick mix zone, a diverging connecting pipe and a lean combustion zone. For computational efficiency, the combustor was split into two subsystems, i.e., the fuel nozzle/rich burn section and the quick mix/lean burn section. The current study investigates the effect of varying the mass flow rate split between the swirler passages for an equivalence ratio of 2.0 on fuel distribution, temperature distribution, and emissions for the fuel nozzle/rich burn section of a staged combustor. It is seen that optimizing these parameters can substantially improve combustor performance and reduce combustor emissions. The optimal mass flow rate split for reducing NOx emissions based on the numerical study was the same as found by experiment.
Three-Dimensional Gas Turbine Combustor Emissions Modeling
Authors: Rizk N. K. , Mongia H. C.
Published: April 2008

An emission model that combines the analytical capabilities of three-dimensional combustor performance codes with mathematical expressions based on detailed chemical kinetic scheme is formulated. The expressions provide the trends of formation and/or the consumption of Nox, CO, and UHC in various regions of the combustor utilizing the details of the flow and combustion characteristics given by the three-dimensional analysis. By this means, the optimization of the combustor design to minimize pollutant formation and maintain satisfactory stability and performance could be achieved. The developed model was used to calculate the emissions produced by several engine combustors that varied significantly in design and concept, and operated on both conventional and high-density fuels. The calculated emissions agreed well with the measurements. The model also provided insight into the regions in the combustor where excessive emissions were formed, and helped to understand the influence of the combustor details and air admissions arrangement on reaction rates and pollutant concentrations.
Coal Gas Cleaning and Purification With Inorganic Membranes
Authors: Fain D. E. , Roettger G. E.
Published: April 2008

The economic viability of coal gasification could depend on the ability to clean and purify the coal gases at elevated temperatures. Inorganic membranes have the potential for being used for that purpose. Efforts have been undertaken at the Oak Ridge K-25 Site to develop membranes that would be useful for separating hydrogen from the coal gas at the high operating temperatures. This paper will give a brief review of some fundamentals of gas separation with membranes. Also, a brief discussion of the theory derived to guide the development process will be given. The theory can be used to indicate the pore size needed to achieve good separation. In addition, some experimental results that have been obtained with some of the membranes that have been fabricated will be discussed.
Coal Mineral Matter Transformation During Combustion and Its Effects on Gas Turbine Blade Deposition and Erosion
Authors: Rajan S. , Raghavan J. K.
Published: April 2008

The reaction pathways along which mineral matter is transformed during pulverized coal combustion and the corresponding characteristics of the ash formed are especially important from the standpoint of coal-fired gas turbine operation. Using a novel FT-IR technique and EDX analysis, these mineral matter transformations are investigated when coal is burned in a pulverized coal-dust burner. The mineral transformations of quartz, gypsum, calcite, dolomite, pyrite, and those of the aluminosilicate minerals, kaolinite and montmorillonite, have been evaluated. Discussion of the results focuses on the effect of these mineral transformations on the deposition and erosive characteristics of the resulting combustion-generated ash.
Electroplated Overlays for Crankshaft Bearings
Authors: Eastham D. R.
Published: April 2008

Overlays of either lead-indium or lead-tin-copper are electroplated onto both lead-bronze and aluminum alloy crankshaft bearings to improve seizure resistance and conformability during the initial running-in period. In addition, both the corrosion resistance, particularly of lead-bronze, and the effective fatigue strength of the composite bearing are improved by this layer. The life of the overlay is largely dependent upon the diffusion rate of the low melting point species to the substrate. Thus, migration of either the indium or the tin will determine both the corrosion and wear rates of the overlay. Owing to the processing requirements, aluminum bearings require a nickel or copper interlayer prior to final overlaying with either of the lead alloys. For diffusion control reasons, when depositing lead-tin-copper onto lead-bronze it is usual to have a thin nickel dam to retard the formation of copper-tin intermetallics, which under given conditions may reduce the overall strength and adhesion; lead-indium does not require such a dam on lead-bronze. The principal differences between the two overlays lie in their respective fatigue and wear properties. Thus, lead-indium has a higher fatigue strength but lower wear resistance than lead-tin-copper. This paper compares these two major overlays and considers the selection criteria for the overlay employed.
Field Testing to Validate Models Used in Explaining a Piston Problem in a Large Diesel Engine
Authors: Graddage M. J. , Czysz F. J. , Killinger A.
Published: April 2008

Two crankcase explosions occurred within one month in diesel engines that drive large emergency generator sets at a nuclear power plant in Eastern Pennsylvania. As a result, the electric utility conducted an extensive investigation to determine the root cause(s) of the problem. Initial inspections confirmed that the crankcase explosions were the result of pistons and liners becoming overheated. The technical challenge was to establish why the pistons and liners were overheating when other engines of the same type did not appear to have the problem in the same duty. Analytical models of piston motion, engine start, and run thermodynamics, and a finite element analysis of piston distortion during engine start and load transients were developed. Preliminary work with these models predicted a feature of the piston design that could adversely affect lubrication conditions during a rapid start and load transient. Final input data to refine the models were needed and these were obtained from tests carried out on a similar diesel generator operated by a municipality in Iowa. This paper describes the successful accomplishment of the field tests using state-of-the-art instrumentation and recording equipment. It also shows how the modeling and test work identified wear at certain locations on the piston skirt as the origin of distress leading to the crankcase explosions. Unfavorable engine starting and loading conditions as well as less than desirable piston skirt-to-liner lubrication conditions in the engines at the nuclear power plant have been identified as the root causes and corrective action has been initiated.
An Opposed-Piston Diesel Engine
Authors: Parker J. K. , Bell S. R. , Davis D. M.
Published: April 2008

Typical conventional diesel engine designs are based on arrangements of single piston and cylinder sets placed sequentially either in-line or offset (“V”) along the crankshaft. The development of other engines, such as the opposed piston type, has been motivated by potential advantages seen in such designs, which may not be viable in conventional in-line or V engine arrangements. Several alternatives to conventional engine design have been investigated in the past and some aspects of these designs have been utilized by engine manufacturers. The design and development of a proof-of-concept opposed piston diesel engine is summarized in this paper. An overview of opposed-piston engines is presented from early developments to current designs. The engine developed in this work is a two stroke and uses four pistons, which move in two parallel cylinders that straddle a single crankshaft. A prechamber equipped with a single fuel injector connects the two cylinders, forming a single combustion chamber. The methodology of the engine development process is discussed along with details of component design. Experimental evaluations of the assembled proof-of-concept engine were used for determining feasibility of the design concept. An electric dynamometer was used to motor the engine and for loading purposes. The dynamometer is instrumented for monitoring both speed and torque. Engine parameters measured include air flow rate, fuel consumption rate, inlet air and exhaust temperatures, and instantaneous cylinder gas pressure as a function of crank position. The results of several testing runs are presented and discussed.
Unsteady Flow Calculation of Sophisticated Exhaust Systems Using a Multibranch Junction Model
Authors: Bulaty T. , Widenhorn M.
Published: April 2008

The flow in a complex engine manifold is computed by generalizing the three-branch to the n-branch junction model. Energy-related pressure losses are implemented in the one-dimensional continuity equation and the effects of choked flow and changing flow patterns are considered. The computational results are compared with measurements on an engine with multi-entry pulse converter and compact single pipe exhaust systems. The influence of several parameters on the fuel consumption is determined.
The Effect of Ambient Gas Temperature and Density on the Development and Wall Impingement of High-Injection-Pressure Diesel Fuel Sprays
Authors: Yunyi Gong , Xuanming Liang
Published: April 2008

An investigation of the effect of ambient gas temperature and density on diesel fuel spray penetration, spray angle, and wall impingement at an injection pressure of 75–134 MPa was conducted in a constant-volume bomb with a reconstructed Cummins PT fuel system by using a high-speed photographic technique. The results show that penetration does not increase monotonically with injection pressure, and ambient temperature has more effect on a high-pressure spray than on those with conventional pressures. With the high temperature, the penetration of a high injection pressure spray is reduced a bit, while the spray angle increases obviously. When the high-pressure spray impinges on a wall at ordinary temperature, the rebounding droplets can hardly be seen, but at higher wall temperature, a cloud of dense spray will be observed near the wall, and sometimes a vapor layer will be formed between the spray and the wall. Based on experimental results, an empirical formula considering the effects of both the ambient temperature and injection pressure is presented.
Managing ISO 9000 Implementation
Authors: Lupear W. J.
Published: April 2008

Many companies worldwide are implementing and applying for registration for the ISO 9000 series of quality standards. This implementation has the same effect on an organization as any other process that is changing the methods, procedures, or the basic culture of the company. The management style necessary to make these changes successful is the same as that which is necessary for any other transformational process. If the correct management style is present, ISO 9000 implementation, and any other change being attempted, will be successful. Change can be accomplished without transformational management but the overall effect and the cost benefit will not be maximized. This transformational management is the most important element. The technical aspects (the ISO 9000 hows and whys) are just a matter of someone within the organization learning them and developing a plan and system for management. The correct management style to achieve change is the most difficult. Strategies need to be clearly defined and methods developed in order to control the projects. Roadblocks need to be clearly identified and action planned to compensate for any shortcomings.
From Genotype to Phenotype: Systems Biology Meets Natural Variation
Authors: Benfey Philip N. , Mitchell-Olds Thomas
Published: April 2008

The promise that came with genome sequencing was that we would soon know what genes do, particularly genes involved in human diseases and those of importance to agriculture. We now have the full genomic sequence of human, chimpanzee, mouse, chicken, dog, worm, fly, rice, and cress, as well as those for a wide variety of other species, and yet we still have a lot of trouble figuring out what genes do. Mapping genes to their function is called the “genotype-to-phenotype problem,” where phenotype is whatever is changed in the organism when a gene's function is altered.
Extending Genomics to Natural Communities and Ecosystems
Authors: Whitham Thomas G. , DiFazio Stephen P. , Schweitzer Jennifer A. , Shuster Stephen M. , Allan Gery J. , Bailey Joseph K. , Woolbright Scott A.
Published: April 2008

An important step in the integration of ecology and genomics is the progression from molecular studies of relatively simple model systems to complex field systems. The recent availability of sequenced genomes from key plants is leading to a new understanding of the molecular drivers of community composition and ecosystem processes. As genome sequences accumulate for species that form intimate associations in nature, a detailed view may emerge as to how these associations cause changes among species at the nucleotide level. This advance could dramatically alter views about the structure and evolution of communities and ecosystems.
The Epigenetic Landscape of Plants
Authors: Zhang Xiaoyu
Published: April 2008

In plants, DNA methylation, histone modifications, and RNA interference play critically important roles in regulating chromatin structure, thereby profoundly affecting transcription and other molecular events. Recent advances in microarray and high-throughput sequencing technologies have enabled genome-wide studies of these pathways in great detail. The vast amounts of “epigenomic” data generated so far have provided new insights into the mechanisms and functions of these pathways and have broadened our understanding of the structure and organization of plant chromatin as a whole.
Molecular Phylogenetics of Mastodon and
Tyrannosaurus rex
Authors: Organ Chris L. , Schweitzer Mary H. , Zheng Wenxia , Freimark Lisa M. , Cantley Lewis C. , Asara John M.
Published: April 2008

We report a molecular phylogeny for a nonavian dinosaur, extending our knowledge of trait evolution within nonavian dinosaurs into the macromolecular level of biological organization. Fragments of collagen α1(I) and α2(I) proteins extracted from fossil bones of
Tyrannosaurus rex
and
Mammut americanum
(mastodon) were analyzed with a variety of phylogenetic methods. Despite missing sequence data, the mastodon groups with elephant and the
T. rex
groups with birds, consistent with predictions based on genetic and morphological data for mastodon and on morphological data for
T. rex
. Our findings suggest that molecular data from long-extinct organisms may have the potential for resolving relationships at critical areas in the vertebrate evolutionary tree that have, so far, been phylogenetically intractable.
Efficient Inhibition of the Alzheimer's Disease β-Secretase by Membrane Targeting
Authors: Rajendran Lawrence , Schneider Anja , Schlechtingen Georg , Weidlich Sebastian , Ries Jonas , Braxmeier Tobias , Schwille Petra , Schulz Jörg B. , Schroeder Cornelia , Simons Mikael , Jennings Gary , Knölker Hans-Joachim , Simons Kai
Published: April 2008

β-Secretase plays a critical role in β-amyloid formation and thus provides a therapeutic target for Alzheimer's disease. Inhibitor design has usually focused on active-site binding, neglecting the subcellular localization of active enzyme. We have addressed this issue by synthesizing a membrane-anchored version of a β-secretase transition-state inhibitor by linking it to a sterol moiety. Thus, we targeted the inhibitor to active β-secretase found in endosomes and also reduced the dimensionality of the inhibitor, increasing its local membrane concentration. This inhibitor reduced enzyme activity much more efficiently than did the free inhibitor in cultured cells and in vivo. In addition to effectively targeting β-secretase, this strategy could also be used in designing potent drugs against other membrane protein targets.