bluuebunny/crossref_metadata_2025 huggingface dataset:
Cost Reduction Through Digital Mock-Up
Authors: Demouzon F. , Chevrin P. A.
Published: December 2014

Digital mockups have become an integral part of the design of aircraft engines and their environment (nacelle, pylon). In this paper, we show that the conventional physical mockup is not a necessity any more. In fact, the experience of the CFM56-7 design shows that the adjustments required to compensate for the absence of a physical mockup have brought with them a considerable amount of flexibility and reactivity. Thus the deletion of tile physical mockup means a lot more than the corresponding direct savings it generates. Relying solely on the digital mockup is a major change in the design process, and greatly contributes to the global quality of the product.
Rotating Stall Control in a High-Speed Stage With Inlet Distortion: Part II — Circumferential Distortion
Authors: Spakovszky Z. S. , van Schalkwyk C. M. , Weigl H. J. , Paduano J. D. , Suder K. L. , Bright M. M.
Published: December 2014

This paper presents the first attempt to stabilize rotating stall in a single-stage transonic axial flow compressor with inlet distortion using active feedback control. The experiments were conducted at the NASA Lewis Research Center on a single-stage transonic core compressor inlet stage. An array of 12 jet injectors located upstream of the compressor was used for forced response testing and feedback stabilization. Results for a circumferential total pressure distortion of about one dynamic head and a 120° extent (DC(60) = 0.61) are reported in this paper. Part I (Spakovszky et al. (1998)) reports results for radial distortion.

Control laws were designed using empirical transfer function estimates determined from forced response results. Distortion introduces coupling between the harmonics of circumferential pressure perturbations, requiring multi-variable identification and control design techniques. The compressor response displayed a strong first spatial harmonic, dominated by the well known incompressible Moore-Greitzer mode.

Steady axisymmetric injection of 4% of the compressor mass flow resulted in a 6.2% reduction of stalling mass flow. Constant gain feedback, using unsteady asymmetric injection, yielded a further range extension of 9%. A more sophisticated robust controller allowed a reduction in stalling mass flow of 10.2% relative to steady injection, yielding a total reduction in stalling mass flow of 16.4%.
Characteristics of Discharge Coefficient in a Rotating Disk System
Authors: Maeng D. J. , Lee J. S. , Jakoby R. , Kim S. , Wittig S.
Published: December 2014

The discharge coefficient of a long orifice in a rotating system is measured to examine the rotational effect on discharge behavior. The rotating system is comprised of a rotating disk and two stators on both sides of the rotating disk. Test rig is constructed to simulate the real turbine operating conditions. Pressure ratios between upstream and downstream cavities of the orifice range from 1.05 to 1.8, and rotational speed of the rotor disk is varied up to 10,000 rpm. The orifice hole bored through the rotor disk has length-to-diameter ratio of 10. For a better interpretation of discharge behavior, three-dimensional velocity field in the downstream and upstream cavities of the rotor is measured using a Laser Doppler Velocimetry. A new definition of the rotational discharge coefficient is introduced to consider the momentum transfer from the rotor to the orifice flow. Additional loss in the discharge coefficient due to pressure loss in the orifice hole at the inlet and exit regions is quantitatively presented in terms of the Rotation number and the compressibility factor. The effect of comer radiusing at the orifice inlet is also investigated at various rotational conditions.
Integrated Testing of the Full Authority Digital Control and Redundant Independent Mechanical Start System for the U.S. Navy’s DDG-51 Ship Service Gas Turbine Generator Sets
Authors: Kozuhowski Helen J. , Hoffman Matthew G. , Mako C. David , Overton Leonard L. , Masincup William E.
Published: December 2014

The U.S. Navy and Allison Engine Company successfully completed a second round of testing which integrated a new Woodward Governor Full Authority Digital Control (FADC) system for gas turbine control and a Redundant Independent Mechanical Start System (RIMSS). This integrated system will be installed on Allison Model AG9140 Ship Service Gas Turbine Generators (SSGTGs) on hull numbers DDG-86 and follow of the U.S. Navy’s Arleigh Burke (DDG-51) class destroyers.

The Full Authority Digital Control (FADC) Local Operating Panel (LOCOP) will be a direct replacement of the original AG9140 LOCOP and will control both the Allison 501-K34 gas turbine and the RIMSS unit. RIMSS is a gas turbine powered, mechanically coupled start system for the SSGTGs and is designed to replace the high pressure start air system on DDG-51 class ships.

This paper describes the FADC and RIMSS systems and details Phase II testing that was conducted on the AG9140 SSGTG located at the Naval Surface Warfare Center, Carderock Division - Ship Systems Engineering Station (NSWCCD-SSES) DDG-51 Land Based Engineering Site (LBES), Figure 1. The test program embodied the second portion of RIMSS testing which included the addition of the final prototype FADC control system. The test agenda included electric plant operations with the FADC and a second 500 start endurance test of RIMSS. The primary objective of Phase II testing was to evaluate the FADC control system and to further validate engine life predictions for the RIMSS engine.
The Ultimate NOx Solution for Gas Turbines
Authors: Solt J. Charles
Published: December 2014

Since the introduction of emission standards for gas turbines in the late ‘70s and early ‘80s, the gas turbine industry has responded with a variety of combustion and cleanup alternatives that have improved emissions. While the emissions were being reduced, the cost of control, and the negative environmental impacts were often significant.

Thanks to a technological breakthrough, catalytic combustion has now been achieved, and can fulfill the promise of low cost NOx elimination without the high cost of SCR or the operational problems associated with Lean Pre-Mix.
Acoustically Controlled Combustor NOx
Authors: Vermeulen Peter J. , Ramesh Venkataramanayya
Published: December 2014

Successful NOx measurements in the end plane of the primary zone of a small tubular gaseous fuelled combustor of conventional gas turbine design, employing acoustic driving of the combustor via the air inlet pipe, have been made at scaled 1/8 load operating conditions. The acoustic drive caused partial blockage of the combustor primary zone air flow which increased the equivalence ratio in the plane of the NOx measurements. The mixing was acoustically augmented which together with the blockage richening significantly changed the combustor mean NOx–mean equivalence ratio characteristic in the end plane of the combustor primary zone. Under lean-conditions at 1/8 load and “with-drive” at 246 Hz mean NOx was reduced indicating that a value of 10ppm (50% reduction) is possible, confirming previous results. Under rich-conditions NOx “with-drive” at 246 Hz might be reduced by 23%, relative to previous results, and even might reach the “no-drive” value of about 25ppm, which was possibly due to acoustic augmentation of the primary zone aerodynamics. The NOx at the combustor exhaust “with-drive” should be even lower than that measured “with-drive” because of normal dilution. Therefore, the technique has the potential to create a low NOx conventional combustor without requiring the complicated design-changes of current industry efforts.
Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations
Authors: Mongia Rajiv , Dibble Robert , Lovett Jeff
Published: December 2014

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer.

The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.
Construction, Startup, Commissioning and Testing of a 240 MW Gas Turbine Spinning Reserve Power Plant, Cambalache, Puerto Rico
Authors: Parece Neil M. , van der Linden Septimus , Diaz Ismael Brito
Published: December 2014

The Cambalache Power Station, engineered from 1993 to 1995, and constructed from 1996 to 1997, provides the island grid of Puerto Rico with 240 MW of flexible gas turbine power. The plant, now in commercial operation, has demonstrated the capability of a steam enhanced gas turbine to provide highly efficient simple cycle base load power and spinning reserve power to an island network which cannot rely on outside power generators to supplement demand in the event of forced outages and emergencies in other power stations. The plant also demonstrates the first application of a high temperature selective catalytic reactor for NOx reduction to less than 10 ppm (No. 2 fuel oil) on a volume basis corrected to 15% O2.

Finally, the installation demonstrated the benefits to the owner, the Puerto Rico Electric Power Authority (PREPA), of a turnkey contract with the entire plant, including offsite oil barge delivery facilities, water wells, and 230 kV substation, designed, supplied and installed by one contractor. The power station was engineered, constructed and started by a limited partnership led by ABB Power Generation Inc. with Metric Constructors. Civil, structural and balance of plant engineering was performed by Lockwood Greene Scott and Associates., Cambalache Limited Partnership (CLP).
Effect of Upstream Rotor Vortical Disturbances on the Time-Average Performance of Axial Compressor Stators: Part 2 — Rotor Tip Vortex/Streamwise Vortex-Stator Blade Interactions
Authors: Valkov T. V. , Tan C. S.
Published: December 2014

In a two-part paper, key computed results from a set of first-of-a-kind numerical simulations on the unsteady interaction of axial compressor stator with upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-average performance of stator. Detailed interrogation of the computed flowfield showed that for both wakes and tip leakage vortices, the impact of these mechanisms can be described on the same physical basis. Specifically there are two generic mechanisms with significant influence on performance: reversible recovery of the energy in the wakes/tip vortices (beneficial) and the associated non-transitional boundary layer response (detrimental). In the presence of flow unsteadiness associated with rotor wakes and tip vortices, the efficiency of the stator under consideration is higher than that obtained using a mixed-out steady flow approximation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends on the following parameters: axial spacing, loading, and the frequency of wake fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative velocity defect and the associated relative total pressure defect, which is perceived by the stator in the same manner as a wake. In Part 2, the focus will be on the interaction of stator with the moving upstream rotor tip and streamwise vortices, the controlling parametric trends, and implications on design.
Rotor Power Losses in Planar Radial Magnetic Bearings — Effects of Number of Stator Poles, Air Gap Thickness, and Magnetic Flux Density
Authors: Allaire P. E. , Kasarda M. E. F. , Fujita L. K.
Published: December 2014

Rotor power losses in magnetic bearings cannot be accurately calculated at this time because of the complexity of the magnetic field distribution and several other effects. The losses are due to eddy currents, hysteresis, and windage. This paper presents measured results in radial magnetic bearing configurations with 8 pole and 16 pole stators and two laminated rotors. Two different air gaps were tested. The rotor power losses were determined by measuring the rundown speed of the rotor after the rotor was spun up to speeds of approximately 30,000 rpm, DN = 2,670,000 mm-rpm, in atmospheric air. The kinetic energy of the rotor is converted to heat by magnetic and air drag power loss mechanisms during the run down. Given past publications and the opinions of researchers in the field, the results were quite unexpected. The measured power losses were found to be nearly independent of the number of poles in the bearing. Also, the overall measured rotor power loss increased significantly as the magnetic flux density increased and also increased significantly as the air gap thickness decreased.

A method of separating the hysteresis, eddy current and windage losses is presented. Eddy current effects were found to be the most important loss mechanism in the data analysis, for large clearance bearings. Hysteresis and windage effects did not change much from one configuration to the other.
Refined k-ϵ Turbulence Model Q3D-Predictions in Compressor Cascades at Design and Off-Design
Authors: Biesinger Thomas E. , Savill A. Mark , Coupland John
Published: December 2014

The performance of two refinements (non-equilibrium and non-linear) to the Low-Reynolds-Number Launder and Sharma (1974) k-ε–turbulence model in the framework of a turbomachinery Navier-Stokes code is evaluated for subsonic and transonic compressor cascades at design and off-design conditions. The non-equilibrium treatment originally developed by Rodi (1972) for extending the standard high Re-number k-ε–model to account for the imbalance of production and dissipation in far-field wakes has been applied, in combination with the well-established Kato and Launder (1993) modification, to the entire flow field by extending the scaling of the eddy viscosity to the production term of turbulent kinetic energy in its transport equation. Accounting for non-equilibrium (spectral) effects such as non-local strain history in adverse pressure gradients has been found to be essential a) in predicting early separation on the DCA blade of the subsonic compressor cascade at design conditions and b) in obtaining a more accurate position of a swallowed shock in the transonic compressor cascade at off-design. The former improvement has resulted in a better prediction of the flow exit angle and the latter is essential in capturing the physics of the shock/boundary-layer interaction but further refinements are required to improve the overall flow field and hence loss predictions. The potential of the cubic two-equation non-linear stress-strain model extension developed by Suga (1995) has been investigated. This is shown to provide a better baseline for non-equilibrium modeling than the Kato and Launder modified k-ε–model, since it accounts additionally for the misalignment of turbulence and strain tensor principal axes, streamline curvature and partially for non-equilibrium effects at very little additional computational cost. The non-linear model is found to demonstrate the correct trends, though it requires recalibration over a wider range of turbomachinery flows.
A Study of Low NOx Combustion in Medium-Btu Fueled 1300 °C-Class Gas Turbine Combustor in IGCC
Authors: Hasegawa Takeharu , Hisamatsu Tohru , Katsuki Yasunari , Sato Mikio , Yamada Masahiko , Onoda Akihiro , Utsunomiya Masaharu
Published: December 2014

The development of integrated coal gasification combined cycle (IGCC) systems ensures cost-effective and environmentally sound options for supplying future coal utilizing power generation needs. The Japanese government and the electric power industries in Japan promoted research and development of an IGCC system using an air-blown entrained-flow coal gasifier. We worked on developing a low-Btu fueled gas turbine combustor to improve the thermal efficiency of the IGCC by raising the inlet-gas temperature of gas turbine.

On the other hand, Europe and the United States are now developing the oxygen-blown IGCC demonstration plants. Coal gasified fuel produced in an oxygen-blown entrained-flow coal gasifier, has a calorific value of 8.6MJ/m 3 which is one fifth that of natural gas. However, the adiabatic flame temperature of oxygen-blown medium-Btu coal gaseous fuel is higher than that of natural gas and so NOx production from nitrogen fixation is expected to increase significantly. In the oxygen-blown IGCC system, a surplus nitrogen in quantity is produced in the oxygen-production unit. When nitrogen premixed with coal gasified fuel is injected into the combustor, the power to compress nitrogen increases. A low NOx combustion technology which is capable of decreasing the power to compress nitrogen is a significant advance in gas turbine development with an oxygen-blown IGCC system. We have started to develop a low NOx combustion technology using medium-Btu coal gasified fuel produced in the oxygen-blown IGCC process.

In this paper, the effect of nitrogen injected directly into the combustor on the thermal efficiency of the plant is discussed. A 1300 °C-class gas turbine combustor with a swirling nitrogen injection function designed with a stable and low NOx combustion technology was constructed and the performance of this combustor was evaluated under atmospheric pressure conditions. Analyses confirmed that the thermal efficiency of the plant improved by 0.2 percent (absolute), compared with a case where nitrogen is premixed with coal gasified fuel before injection into the combustor. Moreover, this new technique which injects nitrogen directly into the high temperature region in the combustor results in a significant reduction in NOx production from nitrogen fixation. We estimate that CO emission concentration decreases to a significant level under high pressure conditions, while CO emission concentration in contrast to NOx emission rises sharply with increases in quantity of nitrogen injected into the combustor.
Evaporative Compressor Cooling for NOx Suppression and Enhanced Engine Performance for Naval Gas Turbine Propulsion Plants
Authors: Sexton Michael R. , Urbach Herman B. , Knauss Donald T.
Published: December 2014

Water, in the liquid or vapor phase, injected at various locations into the gas turbine cycle has frequently been employed to improve engine performance while simultaneously reducing NOx emissions. Commercial steam injected gas turbines have been designed to inject small amounts of steam (less than 15% of air flow), generated in a heat recovery boiler, into or downstream of the combustor. Recently, it has been proposed to inject larger amounts of water (as high as 50% of air flow) and operate combustors near stoichiometric conditions. All these methods increase turbine mass flow rate without increasing air flow rate and consequently increase specific power. The increase in specific power for naval applications means smaller intake and exhaust stacks and therefore less impact on topside space.

The present paper presents a new concept, in naval propulsion plants, to decrease NOx production and increase specific power with a water fog (droplet spray) injected (WFI) directly into the inlet of the engine compressor. The simulated performance of a simple-cycle gas turbine engine using WFI is reported. The paper describes the computer model developed to predict compressor performance resulting from the evaporation of water passing through the stages of an axial flow compressor. The resulting effects are similar to those of an intercooled compressor, without the complications due to the addition of piping, heat exchangers, and the requirement for a dual spool compressor. The effects of evaporative cooling on compressor characteristics are presented. These results include compressor maps modified for various water flow rates as well as estimates of the reductions in compression work and compressor discharge temperature.

These modified compressor performance characteristics are used in the engine simulation to predict how a WFI engine would perform under various water injection flow rates. Estimates of increased output power and decreased air flow rates are presented.
Characterization of Fatigue Mechanisms of Thermal Barrier Coatings by a Novel Laser-Based Test
Authors: Rettig Uwe , Bast Ulrich , Steiner Dinorah , Oechsner Matthias
Published: December 2014

The use of high performance ceramic thermal barrier coatings in stationary gas turbines requires fundamental knowledge of their fatigue behavior under high temperature gradients and thermal cycling. An experimental method based on rapid laser heating complemented with finite-element calculations was developed in order to identify the major damage mechanisms and to obtain a data set for reliability assessment of thermal barrier coatings for temperature and stress fields similar to gas turbine conditions.

The observed failures are strongly related to the pretreatment procedures such as annealing under high temperature gradients and isothermal long-term oxidation. The vertical crack patterns observed close to the top surface of the Zirconia coating are generated at the moment of rapid cooling. These cracks are induced by high biaxial tensile stresses caused by the temperature gradient and the stress reversion after relaxation of compressive stresses at high temperatures. The long-term fatigue behavior is decisively determined by two processes:

(i) The porous Zirconia loses its damage tolerant properties by densification.

(ii) The growth of an oxide layer at the bond coat degrades adhesion and produces localized stress fields at the interface.

Cyclic loads increase the length of existing in-plane cracks and delaminations rather than enlarging their number. Misfit of the crack flanks and wedge effects are the driving forces for continued crack propagation.

These experimental results are discussed in terms of fracture mechanics.
Combined Biomass and Black Liquor Gasifier/Gas Turbine Cogeneration at Pulp and Paper Mills
Authors: Larson Eric D. , Kreutz Thomas G. , Consonni Stefano
Published: December 2014

Kraft pulp and paper mills generate large quantities of black liquor and byproduct biomass suitable for gasification. These fuels are used today for onsite cogeneration of heat and power in boiler/steam turbine systems. Gasification technologies under development would enable these fuels to be used in gas turbines. This paper reports results of detailed full-load performance modeling of pulp-mill cogeneration systems based on gasifier/gas turbine technologies and, for comparison, on conventional steam-turbine cogeneration technologies. Pressurized, oxygen-blown black liquor gasification, the most advanced of proposed commercial black liquor gasifier designs, is considered, together with three alternative biomass gasifier designs under commercial development (high-pressure air-blown, low-pressure air-blown, and low-pressure indirectly-heated). Heavy-duty industrial gas turbines of the 70-MWe and 25-MWe class are included in the analysis. Results indicate that gasification-based cogeneration with biomass-derived fuels would transform a typical pulp mill into a significant power exporter and would also offer possibilities for net reductions in emissions of carbon dioxide relative to present practice.
A Computational Model for the Study of Gas Turbine Combustor Dynamics
Authors: Costura David M. , Lawless Patrick B. , Frankel Steven H.
Published: December 2014

A dynamic combustor model is developed for inclusion into a one-dimensional full gas turbine engine simulation code. A flux-difference splitting algorithm is used to numerically integrate the quasi-one-dimensional Euler equations, supplemented with species mass conservation equations. The combustion model involves a single-step, global finite-rate chemistry scheme with a temperature-dependent activation energy. Source terms are used to account for mass bleed and mass injection, with additional capabilities to handle momentum and energy sources and sinks. Numerical results for cold and reacting flow for a can-type gas turbine combustor are presented. Comparisons with experimental data from this combustor are also made.
Gas Turbine Cycle Design Methodology: A Comparison of Parameter Variation With Numerical Optimization
Authors: Kurzke Joachim
Published: December 2014

In gas turbine performance simulations often the question arises: What is the best thermodynamic cycle design point? This is an optimization task which can be attacked in two ways: One can do a series of parameter variations and pick from the resulting graphs the best solution or one can employ numerical optimization algorithms that produce a single cycle which fulfills all constraints.

The conventional parameter study builds strongly on the engineering judgement and gives useful information over a range of parameter selections. However, when values for more than a few variables have to be determined while several constraints are existing, then numerical optimization routines can help to find the mathematical optimum faster and more accurately. Sometimes even an outstanding solution is found which was overlooked while doing a preliminary parameter study.

For any simulation task a sophisticated graphical user interface is of great benefit. This is especially true for automated numerical optimizations. It is quite helpful to see on the screen of a PC how the variables are changing and which constraints are limiting the design. A quick and clear graphical representation of trade studies is also of great advantage. The paper describes how numerical optimization and parameter studies are implemented in a Windows-based PC program.

As an example, the cycle selection of a derivative turbofan engine with a given core shows the merits of numerical optimization. The parameter variation is best suited for presenting the sensitivity of the result in the neighborhood of the optimum cycle design point.
Pressurized Gasification of Biomass
Authors: Salo K. , Horvath A. , Patel J.
Published: December 2014

Biomass is a fuel of increasing interest in power generation since it is clean and renewable. Besides conventional power generating systems biomass fuel will be utilized in Integrated Gasification Combined Cycle (IGCC) power plants in the near future.

Carbona Inc. (the successor to Enviropower Inc.) is commercializing a biomass fueled IGCC system. This system is based on a simplified IGCC process which applies the gasification technology originally developed by the Institute of Gas Technology (IGT) and further developed by Enviropower before licensing the technology to Carbona and an advanced hot gas clean-up system.

An extensive pilot test program has been carried out by Enviropower/Carbona covering all aspects of a biomass based gasification process. More than 5000 tons of different biomass feedstocks have been gasified at the pilot plant in Tampere, Finland. The pilot plant converts 15 MW (51 MMBtu/h) thermal input of fuel to product gas. Several biomass qualities/mixtures have been used during the test runs including hard wood, soft wood with and without branches, needles and bark. Short rotation biomass like willow and alfalfa have also been tested.

This paper concentrates on the results and differences in gasification of different biomass materials with special emphasis on the suitability of product gas for gas turbines, the fate of ammonia, vapor phase alkali metals and air toxics. The development of demonstration projects is also discussed in this paper.
Case Study on Simultaneous Gasification of Black Liquor and Biomass in a Pulp Mill
Authors: Ahlroth Mikael , Svedberg Gunnar
Published: December 2014

One of the main limiting factors when a green field pulp mill intends to increase its production is the capacity of the Tomlinson boiler by which the cooking chemicals are recovered. Since a boiler of this kind has a service life of some thirty years and represents a substantial investment, it is not an easy decision to replace it for a minor production increase. This study takes a novel approach to the problem. The excess black liquor is assumed to be recovered in a black liquor gasifier, an emerging technology for alternative black liquor recovery. Black liquor gasification in itself has been studied considerably during the last decade. In this study it is combined with the gasification of biomass, i.e. bark and wood, which is already available at a pulp mill. The resulting hybrid energy system, with a gas turbine and a gas expander, offers interesting possibilities: good off-design performance and high efficiency with respect to the fuel quality.
Determination of the Realistic Turbocharger Efficiency With Pulsating Gas-Flow Compared on a 4-Cylinder Engine
Authors: Trenc Ferdinand , Čer Matej , Bizjan Frančišek , Hribernik Aleš
Published: December 2014

Small single or twin entry radial turbines are mostly used to drive compressors of the turbocharged internal combustion engines. There are two general possibilities to feed the turbine of a four-stroke, 4-cylinder turbocharged Diesel engine: 1) by preserving most of the available exhaust kinetic energy, or 2) by mixing exhaust pulses from all cylinders in one common manifold. In the first case, better utilization of the dynamic pulse energy increases efficiency of the turbine; highly unsteady mass flow of the exhaust gasses, on the other hand, and thus periods of partial exhaust flow admission at the turbine inlet simultaneously reduces this gain in the turbine efficiency. More steady mass-flow of the exhaust gasses is created in the case of the exhaust system 2), however some kinetic energy is lost during the mixing phase in the common exhaust manifold. Calculation of the overall turbocharger and turbine efficiency is normally based on average values of the measured pressures and temperatures. As the result apparent efficiencies are obtained; the more the flow is pulsating, the bigger is the difference between the real and the apparent efficiency. The ratio between these two efficiencies is known as the energy pulsation factor β. It depends generally on the “pulse intensity”-pressure deviation from its mean value, shape of the pressure pulse, number of the individual pulses feeding separate gas turbine inlets, turbocharger, and can be successfully used to determine real efficiency of a turbocharger and to define some working parameters of the engine.

A field of β factors for different engine running conditions and for the 4-cylinder engine with 2-cylinder group pulse system (rarely applied), and the commonly applied exhaust system with 4-cylinder group and moderate pressure fluctuation is presented in the paper. Influence of the dynamic exhaust temperatures on the β value is discussed as well.
High Temperature Silicon Integrated Circuits and Passive Components for Commercial and Military Applications
Authors: Grzybowski Richard R. , Gingrich Ben
Published: December 2014

Advances in silicon-on-insulator (SOI) integrated circuit technology and the steady development of wider band gap semiconductors like silicon carbide are enabling the practical deployment of high temperature electronics. High temperature civilian and military electronics applications include distributed controls for aircraft, automotive electronics, electric vehicles and instrumentation for geothermal wells, oil well logging and nuclear reactors. While integrated circuits are key to the realization of complete high temperature electronic systems, passive components including resistors, capacitors, magnetics and crystals are also required. This paper will present characterization data obtained from a number of silicon high temperature integrated evaluated over a range of elevated temperatures and aged at a selected high temperature. This paper will also present a representative cross section of high temperature passive component characterization data for device types needed by many applications. Device types represented will include both small signal and power resistors and capacitors. Specific problems encountered with the employment of these devices in harsh environments will be discussed for each family of components. The goal in presenting this information is to demonstrate the viability of a significant number of commercially available silicon integrated circuits and passive components that operate at elevated temperatures as well as to encourage component suppliers to continue to optimize a selection of their product offerings for operation at higher temperatures. In addition, systems designers will be encouraged to view this information with an eye toward the conception and implementation of reliable and affordable high temperature systems.
Investigation of Pre-Stall Mode and Pip Inception in High Speed Compressors Through the Use of Correlation Integral
Authors: Bright Michelle M. , Qammar Helen K. , Wang Leizhen
Published: December 2014

Five high speed compressor configurations are used to identify pre-stall pressure signal activity under clean and distorted inlet conditions, and under steady injection and controlled injection conditions. Through the use of a nonlinear statistic called correlation integral, variations in the compressor dynamics are identified from the pre-stall pressure activity far before variations (modal or pip) are observed visually in the wall static pressure measurements. The correlation integral not only discerns changing dynamics of these compressors prior to stall, but is now used to measure the strength of the tip flow field for these five high speed compressors. Results show that correlation integral value changes dramatically when the stall inception is modal; and it changes less severely when the stall inception is through pip disturbances. This algorithm can therefore distinguish from the pre-stall pressure traces when a machine is more likely to stall due to pips versus modes. When used in this manner, the correlation integral thus provides a measure of tip flow strength. The algorithm requires no predisposition about the expected behavior of the data in order to detect changing dynamics in the compressor, thus no pre-filtering is necessary. However, by band-pass filtering the data, one can monitor changing dynamics in the tip flow field for various frequency regimes. An outcome of this is to associate changes in correlation integral value directly to frequency specific events occurring in the compressor, i.e. blade length scale events versus long length scale acoustic events. The correlation integral provides a potential advantage over linear spectral techniques because a single sensor is used for detection and analysis of the instabilities.
Experimental Investigation of Unsteady Flow Phenomena in a Centrifugal Compressor Vaned Diffuser of Variable Geometry
Authors: Justen Friedrich , Ziegler Kai U. , Gallus Heinz E.
Published: December 2014

The behaviour of vaned radial diffusers is generally considered to be due to the flow phenomena in the vaneless and the semi-vaned space in the diffuser inlet region. Even considering unsteady aspects, the adjacent diffuser channel is regarded as less important. The flat wedge vaned diffuser of the investigated centrifugal compressor stage allows an independent continuous adjustment of the diffuser vane angle and the radial gap between impeller outlet and diffuser vane inlet, so that information about the importance of these geometric parameters can be obtained.

The time dependent pressure distribution on the diffuser front wall and on suction and pressure surface of the diffuser vanes reveal that in the semi-vaned space mainly the region near the vane suction side is influenced by the unsteady impeller-diffuser-interaction. Downstream in the diffuser channel the unsteadiness does not decay. Here, pressure fluctuations are appearing which are distinctly higher than the pressure fluctuations in the vaneless space.

An estimation of the influence of the unsteadiness on the operating performance of the centrifugal compressor stage is made by measurements at choke and surge limit for different diffuser geometries.
On the Performance of Hybrid Foil-Magnetic Bearings
Authors: Heshmat Hooshang , Chen H. Ming , Walton James F.
Published: December 2014

Recent technological advancements make hybridization of the magnetic and foil bearings both possible and extremely attractive. Operation of the foil/magnetic bearing takes advantage of the strengths of each individual bearing while minimizing each others weaknesses. In this paper one possible hybrid foil and magnetic bearing arrangement is investigated and sample design and operating parameters are presented. One of the weaknesses of the foil bearings, like any hydrodynamic bearing, is that contact between the foil bearing and the shaft occurs at rest or at very low speeds and it has low load carrying capacity at low speeds. For high speed applications, AMBs are, however, vulnerable to rotor-bending or structural resonances that can easily saturate power amplifiers and make the control system unstable. Since the foil bearing is advantageous for high speed operation with a higher load carrying capacity, and the magnetic bearing is so in low speed range, it is a natural evolution to combine them into a hybrid bearing system thus utilizing the advantages of both.

To take full advantage of the foil and magnetic elements comprising a hybrid bearing, it is imperative that the static and dynamic characteristics of each bearing be understood. This paper describes the development of a new analysis technique that was used to evaluate the performance of a class of gas-lubricated journal bearings. Unlike conventional approaches, the solution of the governing hydrodynamic equations dealing with compressible fluid is coupled with the structural resiliency of the bearing surfaces. The distribution of the fluid film thickness and pressures, as well as the shear stresses in a finite-width journal bearing, are computed. Using the Finite Element (FE) method, the membrane effect of an elastic top foil was evaluated and included in the overall analytical procedure. Influence coefficients were generated to address the elasticity effects of combined top foil and elastic foundation on the hydrodynamics of journal bearings, and were used to expedite the numerical solution. The overall program logic proved to be an efficient technique to deal with the complex structural compliance of various foil bearings. Parametric analysis was conducted to establish tabulated data for use in a hybrid foil/magnetic bearing design analysis. A load sharing control algorithm between the foil and magnetic elements is also discussed.
Statistics of Response of a Mistuned Bladed Disk Assembly Subjected to White Noise and Narrow Band Excitation
Authors: Cha D. , Sinha A.
Published: December 2014

This paper deals with the statistics of the response of a mistuned bladed disk assembly subjected to random excitation. Analytical techniques are developed to compute this statistics for two types of random excitation: white noise and narrow band. The validity of the analytical methods has been established by comparison with the results from numerical simulations. The sensitivities of the response to mistuning have been examined as a function of the width of the frequency band of the random excitation, the dominant frequency of the random excitation and the structural coupling between adjacent blades.
CO2 Emission Abatement in IGCC Power Plants by Semiclosed Cycles: Part B — With Air-Blown Combustion and CO2 Physical Absorption
Authors: Chiesa Paolo , Lozza Giovanni
Published: December 2014

This paper analyzes the fundamentals of IGCC power plants with carbon dioxide removal systems, by a cycle configuration alternative to the one discussed in Part A (with Oxygen-Blown Combustion). The idea behind this proposal is to overcome the major drawbacks of the previous solution (large oxygen consumption and re-design of the gas turbine unit), by means of a semiclosed cycle using air as the oxidizer. Consequently, combustion gases are largely diluted by nitrogen and cannot be simply compressed to produce liquefied CO2 for storage or disposal. However, CO2 concentration remains high enough to make separation possible by a physical absorption process. It requires a re-pressurization of the flow subtracted from the cycle, with relevant consequences on the plant energy balance.

The configuration and the thermodynamic performance of this plant concept are extensively addressed in the paper. As in the first part, the influence of the pressure ratio is discussed, but values similar to the ones adopted in commercial heavy-duty machines provide here acceptable performance. Proper attention was paid to the impact of the absorption process on the energy consumption. The resulting net overall efficiency is again in the 38–39% range, with assumptions fully comparable to the ones of Part A. Finally, we demonstrated that the present scheme enables the use of unmodified machines, but large additional equipment is required for exhausts treatment and CO2 separation. A final comparison between the two semiclosed cycle concepts was therefore addressed.
Off-Design Performance of Various Gas-Turbine Cycle and Shaft Configurations
Authors: Korakianitis T. , Svensson K.
Published: December 2014

The design-point performance of various gas turbine cycles such as simple, regenerative, and intercooled-regenerative, is well understood. It is also understood that more-elaborate shaft arrangements such as one, two or three concentric or non-concentric shafts, and a separate power turbine shaft, provide better starting and operational flexibility, and wider plateaus of high off-design performance. However, the types of different off-design performance one can obtain with these different shaft arrangements has not been previously reported. In this paper we use a computer program to investigate the design-point and off-design-point performance of engines with: one single shaft joining the compressor, turbine and load; one shaft joining compressor and turbine, and one shaft for the power turbine; two shafts for compressor and turbine, and one shaft for the power turbine; and three shafts joining the compressor and turbine, and one shaft for the power turbine. This is done by specifying typical compressor and turbine maps, and computing various aspects of off-design performance. The advantages and disadvantages of the various arrangements ore investigated and discussed.
A Combustor Can With 1.8 mm Thick Plasma Sprayed Thermal Barrier Coating
Authors: Wigren Jan , Dahlin Jens , Hansson Mats-Olov
Published: December 2014

The benefits of thermal barrier coatings for protection of combustor walls are well known. However, the trend to higher combustor inlet temperatures and the reduced availability of cooling air leads to a demand for better insulation performance from the thermal barrier coating (TBC). This is of particular benefit for low emission combustors where wall quenching effects need to be minimised and often hot side cooling is not permissible.

A combustor can, for advanced stationary gas turbines, with 1.8 mm thick thermal barrier was designed and tested. The can was compared to a combustor can with a thermal barrier coating sprayed with current state-of-the-art methods, but to the same thickness.

Steps to optimise performance were taken in all development stages. The design allowed easy spray geometries, improved edges and no film cooling. Spraying was optimised in order to achieve a segmented microstructure for reduction of stresses (by decrease of the Young’s Modulus in the coating) and increase compliance of the coating. Testing in component test rigs showed excellent results. The lifetime of the optimised combustor can was beyond test capabilities, whereas the reference combustor failed immediately.

Metallographic and X-ray characterisation before and after component rig testing was performed and revealed features that explain the superiority of the segmented thermal barrier coating.

This work has been funded by the CEC under the contract BRE-CT94-0936.
A Study of Hydrogen Combustion Turbines
Authors: Aoki S. , Uematsu K. , Suenaga K. , Mori H. , Sugishita H.
Published: December 2014

A hydrogen combustion turbine system has been proposed by Mitsubishi Heavy Industries, LTD. which is the Closed Circuit Cooled Topping Recuperation Cycle (CCCTR cycle) and is part of a Japanese government sponsored program WE-NET (“World Energy Network”). This cycle is composed of closed Brayton and Rankine cycles. The efficiency of this cycle is more than 60% HHV (Higher Heat Value) with a power capacity of 500MW. This cycle was selected as the most suitable for hydrogen combustion turbine used for industrial power plant by the Japanese government.

A closed circuit steam cooling system has been proposed to cool vanes and blades of the high temperature turbine (HIT) which has inlet temperature of 1700°C and inlet pressure of 45bar.

This paper presents the comparisons of the thermal efficiency and the feasibility of components between the CCCTR cycle and other cycles.
Absorption of CO2 With Amines in a Semiclosed GT Cycle: Plant Performance and Operating Costs
Authors: Corti A. , Lombardi L. , Manfrida G.
Published: December 2014

A CO2 removal system, using aqueous solutions of amines, is applied to a Semi-Closed Gas Turbine/Combined Cycle (SCGT/CC) power plant.

The SCGT/CC is interesting because of the possibility of achieving low emissions at the stack, with a decreased overall flow rate, lower NOx concentration and an increased CO2 concentration (over 15% in volume), which facilitates the removal treatment.

Several compositions of the absorbing solution have been investigated, by means of simulations with ASPEN PLUS.

A 18% DEA + 12% MDEA composition resulted the most convenient in terms of flow rate and energy requirement for the stripping.

A cost analysis of the removal plant allows to estimate additional costs for CO2 removal with respect to conventional power plants.