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Accepted Manuscripts

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research-article  
Aron P. Dobos and Allan T. Kirkpatrick
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038521
This paper studies the differences in spray structure and emissions trends between diesel and biodiesel fuels in a compression ignition engine. A computationally efficient and predictive quasidimensional simulation model is combined with fuel-specific physical properties and chemical kinetic mechanisms to predict spray mixing, combustion, and emissions behavior. Results underscore the complex relationships between NOx emissions, operational parameters, and fuel chemistry, and provide further evidence of a link between stoichiometry near the flame lift-off length and formation of NOx.
TOPICS: Chemical kinetics, Combustion, Emissions, Biodiesel, Fuels, Sprays, Nitrogen oxides, Chemistry, Diesel, Diesel engines, Flames, Simulation models, Stoichiometry
research-article  
Leiyong Jiang, Yinghua Han and Prakash Patnaik
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038523
To understand the physics of volcanic ash impact on gas turbine hot-components and develop much-needed tools for engine design and fleet management, the behaviours of volcanic ash in a gas turbine combustor and nozzle guide vanes (NGV) have been numerically investigated. High-fidelity numerical models are generated, and volcanic ash sample, physical and thermal properties are identified. A simple critical particle viscosity - critical wall temperature model is proposed and implemented in all simulations to account for ash particles bouncing off or sticking on metal walls. The results indicate that due to the particle inertia and combustor geometry, the volcanic ash concentration in the NGV cooling passage increases with ash size, density and inlet velocity in general, and can reach three and half times as high as that at the air inlet for the conditions investigated. More importantly, the majority of the ash particles entering the NGV cooling chamber are trapped in the cooling flow passage for all four turbine inlet temperature conditions. This may reveal another volcanic ash damage mechanism originated from engine cooling flow passage. Finally, some suggestions are recommended for further research and development in this challenging field. To the authors' knowledge, it is the first study on detailed ash behaviours inside practical gas turbine hot-components in open literature.
TOPICS: Combustion chambers, Gas turbines, Nozzle guide vanes, Cooling, Particulate matter, Flow (Dynamics), Temperature, Physics, Density, Inertia (Mechanics), Viscosity, Computer simulation, Engines, Industrial research, Simulation, Metals, Thermal properties, Engineering simulation, Turbines, Engine design, Geometry, Wall temperature, Damage
research-article  
Kai Kadau, Phillip Gravett and Christian Amann
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038524
We developed and successfully applied a direct simulation Monte-Carlo scheme to quantify the risk of fracture for heavy duty rotors commonly used in the energy sector. The developed Probabilistic Fracture Mechanics high-performance computing methodology and code ProbFM routinely assesses relevant modes of operation for a component by performing billions of individual fracture mechanics simulations. The methodology can be used for new design and life-optimization of components, as well as for the risk of failure quantification of in service rotors and their re-qualifications in conjunction with non-destructive examination techniques, such as ultrasonic testing. The developed probabilistic scheme integrates material data, ultra-sonic testing information, duty-cycle data, and finite element analysis in order to determine the risk of failure. The methodology provides an integrative and robust measure of the fitness for service and allows for a save and reliable operation management of heavy duty rotating equipment.
TOPICS: Fracture mechanics, Gas turbines, Risk, Failure, Rotors, Simulation, Nondestructive evaluation, Ultrasonic testing, Fracture (Materials), Design, Finite element analysis, Fracture (Process), Testing, Cycles, Optimization, Fitness-for-service
research-article  
Jin Young Heo, Jinsu Kwon and Jeong Ik Lee
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038476
For the concentrating solar power (CSP) applications, the supercritical carbon dioxide (s-CO2) power cycle is beneficial in many aspects, including high cycle efficiencies, reduced component sizing, and potential for the dry cooling option. More research is involved in improving this technology to realize the s-CO2 cycle as a candidate to replace the conventional power conversion systems for CSP applications. In this study, an isothermal compressor, a turbomachine which undergoes the compression process at constant temperature to minimize compression work, is applied to the s-CO2 power cycle layout. To investigate the cycle performance changes of adopting the novel technology, a framework for defining the efficiency of the isothermal compressor is revised and suggested. This study demonstrates how the compression work for the isothermal compressor is reduced, up to 50%, compared to that of the conventional compressor under varying compressor inlet conditions. Furthermore, the simple recuperated and recompression Brayton cycle layouts using s-CO2 as a working fluid are evaluated for the CSP applications. Results show that for compressor inlet temperatures (CIT) near the critical point, the recompression Brayton cycle using an isothermal compressor has 0.2-1.0% point higher cycle thermal efficiency compared to its reference cycle. For higher CIT values, the recompression cycle using an isothermal compressor can perform above 50% in thermal efficiency for a wider range of CIT than the reference cycle. Adopting an isothermal compressor in the s-CO2 layout can imply larger heat exchange area for the compressor which requires further development.
TOPICS: Compressors, Supercritical carbon dioxide, Thermodynamic power cycles, Cycles, Compression, Brayton cycle, Temperature, Thermal efficiency, Turbomachinery, Cooling, Fluids, Power conversion systems, Heat, Concentrating solar power
research-article  
Clay/S Norrbin and Dara Childs
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038482
The long length of sub-sea Electric Submersible Pumps (ESPs) requires a large amount of annular seals. Loading caused by gravity and housing curvature changes the Static Equilibrium Position (SEP) of the rotor in these seals. This analysis predicts the SEP due to gravity and/or well curvature loading. The analysis also interfaces displays the rotordynamics around the SEP. A static and rotordynamic analysis is presented for a previously studied ESP model. This study differs by first finding the SEP and then performing a rotordynamic analysis about the SEP. Predictions are shown in a horizontal and a vertical orientation. In these two configurations, viscosity and clearance are varied through 4 cases: 1X1cP, 3X1cP, 1X30cP, and 3X30cP. In a horizontal position, at 1X1cP and 3X1cP, the horizontal statics show a moderate eccentricity ratio for the shaft with respect to the housing. With 1X30cP, the predicted static eccentricity ratio is low at 0.08. With 3X30cP, the predicted eccentricity ratio increases to 0.33. Predictions for a vertical case of the same model are also presented. The curvature of the housing is varied in the $Y$-$Z$ plane until rub or close-to-wall rub is expected. The curvature needed for a rub with a 1X1cP fluid is 7.5 degrees of curvature. Curvature has little impact on stability. With both 1X30cP and 3X30cP, the maximum curvature for a static rub are over 25 degrees of curvature. Both 1X30cP and 3X30cP remain unstable with increasing curvature.
TOPICS: Equilibrium (Physics), Pumps, Submersibles, Gravity (Force), Fluids, Viscosity, Clearances (Engineering), Rotordynamics, Rotors, Statics, Seas, Stability
research-article  
Alborz Zehni, Rahim Khoshbakhti Saray and Elaheh Neshat
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038456
In this study, a numerical study is performed by KIVA-CHEMKIN code to investigate the effects of biodiesel addition and exhaust gas recirculation (EGR) on diesel engine PCCI combustion, performance and emission characteristics. The studies are performed for neat diesel fuel and mixture of 10 to 40% biodiesel addition at 67%, 50% and 40% EGR. For this purpose, a multi-chemistry surrogate mechanism using methyl decanoate (MD) and methyl-9-decenoate (MD9D) is used. The main innovation of the present work is analyzing the chemical, thermodynamic and dilution effects of biodiesel addition as well as different EGR ratios on PCCI combustion behavior. The results show that the main effect of EGR on PCCI combustion of biodiesel blend is related to the HTHR and its effect on LTHR is low. With increasing biodiesel addition, the role of the chemical effect is increased compared to the thermodynamic and dilution effects. Rate of production analysis indicate that for the different biodiesel ratios, the effect of reaction nC7H16+HO2=C7H15-2+H2O2 is more effective on the start of combustion compared to the other reactions. For a defined biodiesel addition, with decreasing EGR, THC and CO are decreased, whilst NOx and ISFC are increased.
TOPICS: Combustion, Diesel engines, Exhaust gas recirculation, Emissions, Biodiesel, Innovation, Nitrogen oxides, Chemistry, Diesel
research-article  
Lidui Wei, Haijun Wei, Haiping Du and Shulin Duan
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038457
To predict the vibration characteristics of the crankshaft of the larger marine diesel engine accurately and comprehensively, based on the finite element models of the crankshaft and the engine block reduced by a component mode synthesis method as well as extended Reynolds equation and Greenwood-Tripp theory, a mixed thermo-elasto-hydro-dynamic lubrication coupling model between a whole flexible engine block and a rotating flexible crankshaft is set up. According to this strongly coupled nonlinear model, the torsional-axial-lateral three-dimensional vibration of the crankshaft can be calculated simultaneously. The method is verified through comparison with other computational methods. Also, the vibrations are compared under different support models and whether to consider the effect of temperature. Specific three-dimensional vibrations are displayed, and some stage nonlinear characteristics are showed in three-dimensional direction. The modeling method will contribute to reveal the vibration mechanism and optimize the design of the shafting system.
TOPICS: Lubrication, Engines, Vibration, Diesel engines, Finite element model, Computational methods, Design, Modeling, Temperature
research-article  
Lilas Deville and Mihai Arghir
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038469
Brush seals are a mature technology that has generated extensive experimental and theoretical work. Theoretical models range from simple correlations with experimental results to advanced numerical approaches coupling the bristles deformation with the flow in the brush. The present work follows this latter path. The bristles of the brush are deformed by the pressure applied by the flow, by the interference with the rotor and with the back plate. The bristles are modeled as linear beams but a non-linear numerical algorithm deals with the interferences. The brush with its deformed bristles is then considered as an anisotropic porous medium for the leakage flow. Taking into account the variation of the permeability with the local geometric and flow conditions represents the originality of the present work. The permeability following the principal directions of the bristles are estimated from CFD calculations. A representative number of bristles is selected for each principal direction and the CFD analysis domain is delimited by periodicity and symmetry boundary conditions. The parameters of the CFD analysis are the local Reynolds number and the local porosity estimated from the distance between the bristles. The variations of the permeability are thus deduced for each principal direction and for Reynolds numbers and porosities characteristic for brush seal. The leakage flow rates predicted by the present approach are compared with experimental results from the literature. The results depict the variations of the pressures, of the local Reynolds number, of the permeability and of the porosity through the entire brush seal.
TOPICS: Permeability, Seals, Computational fluid dynamics, Theoretical analysis, Leakage, Reynolds number, Flow (Dynamics), Leakage flows, Porosity, Pressure, Deformation, Porous materials, Anisotropy, Algorithms, Rotors, Boundary-value problems
research-article  
James Scobie, Fabian Hualca, Carl Sangan and Gary Lock
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038458
Engine designers require accurate predictions of ingestion (or ingress) principally caused by circumferential pressure asymmetry in the mainstream annulus. Cooling air systems provide purge flow designed to limit metal temperatures and protect vulnerable components from the hot gases which would otherwise be entrained into disc cavities through clearances between rotating and static discs. Rim seals are fitted at the periphery of these discs to minimise purge. The mixing between the efflux of purge (or egress) and the mainstream gases near the hub end-wall results in a deterioration of aerodynamic performance. This paper presents experimental results using a turbine test rig with wheel-spaces upstream and downstream of a rotor disc. Ingress and egress was quantified using a CO2 concentration probe, with seeding injected into the upstream and downstream sealing flows. The probe measurements have identified an outer region in the wheel-space and confirmed the expected flow structure. For the first time, asymmetric variations of concentration have been shown to penetrate through the seal clearance and the outer portion of the wheel-space between the discs. For a given flow coefficient in the annulus, the concentration profiles were invariant with rotational Reynolds number. The measurements also reveal that the egress provides a film-cooling benefit on the vane and rotor platforms. Further, these measurements provide unprecedented insight into the flow interaction, and provide quantitative data for CFD validation, which should help reduce the use of purge and improve engine efficiency.
TOPICS: Turbines, Disks, Flow (Dynamics), Wheels, Rotors, Annulus, Gases, Engines, Probes, Reynolds number, Sealing (Process), Space, Clearances (Engineering), Computational fluid dynamics, Metals, Temperature, Cooling, Carbon dioxide, Cavities, Pressure, Film cooling
research-article  
Xijia Lu, Scott Martin, Michael McGroddy, Michael Swanson, Joshua Stanislowski and Jason Laumb
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038459
The Allam Cycle is a high performance oxy-fuel, supercritical CO2 power cycle that offers significant benefits over traditional hydrocarbon fuel-based power generation systems. A major benefit arises in the elimination of costly pre-combustion acid gas removal (AGR) for sulfur- (SOX) and nitrogen-based (NOX) impurities by utilizing a novel, embedded cleanup process that utilizes combustion derived NOX as a gas phase catalyst to effect SOX oxidation, followed by NOX removal. The reactions required for this process, which have been well-demonstrated for the cleanup of exhaust gases, convert SOX and NOX species to sulfuric and nitric and nitrous acid for removal from the supercritical CO2 stream. The process results in simplified and significantly lower cost removal of these species and utilizes conditions inherent to the Allam Cycle that are ideally suited to facilitate this process. 8 Rivers Capital and the Energy & Environmental Research Center (EERC) are testing and optimizing this impurity removal process for supercritical CO2 cycles such as the Allam Cycle. Both reaction kinetic modeling and on-site testing have been completed. Initial results show that both SOX and NOX are substantially removed from CO2-rich exhaust gas containing excess oxygen operating under 20 bar utilizing a simple packed spray column. Sensitivity of the removal rate to the concentration of oxygen and NOX was investigated. Follow-on work will focus on system optimization of removal efficiency and removal control, minimization of metallurgy and corrosion risks from handling concentrated acids, and reduction of overall system CAPX/OPEX.
TOPICS: Combustion, Energy / power systems, Cycles, Testing, Nitrogen oxides, Supercritical carbon dioxide, Oxygen, Exhaust systems, Fuels, Corrosion, Gases, Metallurgy, Modeling, Optimization, Sprays, Nitrogen, oxidation, Sulfur, Rivers, Carbon dioxide, Catalysts, Thermodynamic power cycles
research-article  
Alexander Bucknell, Matthew McGilvray, David R.H. Gillespie, Geoffrey B Jones, Alasdair Reed and Dr. David R Buttsworth
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038460
It has been recognised in recent years that high altitude atmospheric ice crystals pose a threat to aircraft engines. It is believed that solid ice particles can accrete inside the core compressor, although the exact mechanism by which this occurs remains poorly understood. Development of analytical and empirical models of the ice crystal icing phenomenon is necessary for both future engine design and this-generation engine certification. A comprehensive model will require the integration of a number of aerodynamic, thermodynamic and mechanical components. This paper studies one such component, specifically the thermodynamic and mechanical processes experienced by ice particles impinging on a warm surface. Results are presented from an experimental campaign using a heated and instrumented flat plate. The plate was installed in the Altitude Icing Wind Tunnel (AIWT) at the National Research Council of Canada (NRC). The heated plate is designed to measure the heat flux from a surface at temperatures representative of the early core compressor, under varying convective and icing heat loads. Heat transfer enhancement was observed to rise approximately linearly with both total water content and particle diameter over the ranges tested. A Stokes number greater than unity proved to be a useful parameter in determining whether heat transfer enhancement would occur. A particle energy parameter was used to estimate the likelihood of fragmentation. Results showed that when particles were both ballistic and likely to fragment, heat transfer enhancement was independent of both Mach and Reynolds numbers over the ranges tested.
TOPICS: Heat transfer, Crystals, Compressors, Ice, Particulate matter, Engines, Reynolds number, Stress, Heat, Temperature, Engine design, Flat plates, Water, Wind tunnels, Aircraft engines, Heat flux
research-article  
Daniele Massini, Tommaso Fondelli, Antonio Andreini, Bruno Facchini, Lorenzo Tarchi and Federico Leonardi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038471
Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. An evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Mechanical power losses are usually distinguished in two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid-dynamics of the environment which surrounds the gears. The relative magnitude of these phenomena is dependent on the operative conditions of the transmission: load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. A new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry measurements for investigating the flow-field surrounding the rotating gear. The experiment has been computationally replicated, performing RANS simulations in the context of conventional eddy viscosity models, achieving good agreement for all of the speed of rotations.
TOPICS: Gears, Stress, Torque, Pressure, Fluid dynamics, Flow (Dynamics), Temperature, Particulate matter, Eddies (Fluid dynamics), Viscosity, Simulation, Torquemeters, Design, Engineering simulation, Reynolds-averaged Navier–Stokes equations, Spur gears, Turbomachinery, Fuel consumption, Aircraft engines
research-article  
Michael A Rohmer, Luis San Andres and Scott M Wilkinson
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038472
This paper details a water lubricated test rig for measurement of the performance of hydrostatic thrust bearings (HTBs). The rig contains two water lubricated HTBs (105 mm outer diameter), one is the test bearing and the other a slave bearing. Both bearings face the outer side of thrust collars of a rotor. The paper shows measurements of HTB axial clearance, flow rate, and recess pressure for operation with increasing static load (max. 1.4 bar) and supply pressure (max. 4.14 bar) at a rotor speed of 3 krpm (12 m/s OD speed). Severe angular misalignment, static and dynamic, of the bearing surface against its collar persisted and affected all measurements. The HTB axial clearance increases as the supply pressure increases and decreases quickly as the applied load increases. The reduction in clearance increases the flow resistance across the film lands thus reducing the through flow rate with an increase in recess pressure. In addition, an estimated bearing axial stiffness increases as the operating clearance decreases and as the supply pressure increases. Predictions from a bulk flow model qualitatively agree with the measurements. Alas they are not accurate enough. The differences likely stem from the inordinate tilts (static and dynamic) as well as the flow condition. The test HTB operates in a flow regime that spans from laminar to incipient turbulent. Quantification of misalignment at all operating conditions is presently a routine practice during operation of the test rig.
TOPICS: Hydrostatics, Stress, Thrust bearings, Water, Flow (Dynamics), Pressure, Bearings, Clearances (Engineering), Rotors, Stiffness, Turbulence, Arches, Thrust
research-article  
Maxime Huet
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038473
The noise generated by the passage of acoustic and entropy perturbations through subsonic and choked nozzle flows is investigated numerically using an energetic approach. Low-order models are used to reproduce the experimental results of the Hot Acoustic Test rig (HAT) of DLR and energy budgets are performed to characterize the reflection, transmission and dissipation of the fluctuations. Because acoustic and entropy perturbations are present in the flow in the general case, classical acoustic energy budgets cannot be used and the disturbances energy budgets proposed by Myers (J. Fluid Mech. 226 (1991) 383-400) are used instead. Numerical results are in very good agreement with the experiments in terms of acoustic transmission and reflection coefficients. The normal shock present in the diffuser for choked regimes is shown to attenuate the scattered acoustic fluctuations, either by pure dissipation effect or by converting a part of the acoustic energy into entropy fluctuations.
TOPICS: Flow (Dynamics), Nozzles, Acoustics, Fluctuations (Physics), Energy budget (Physics), Entropy, Energy dissipation, Reflectance, Diffusers, Shock (Mechanics), Noise (Sound), Reflection, Fluids
research-article  
Rachel A Berg, Choon S. Tan, Zhongman Ding, Gregory M. Laskowski, Pepe Palafox and Rinaldo Miorini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038474
Fast response pressure data acquired in a high-speed 1.5-stage turbine Hot Gas Ingestion Rig shows the existence of pressure oscillation modes in the rim-seal-wheelspace cavity of a high pressure gas turbine stage with purge flow. The experimental results and observations are complemented by computational assessments of pressure oscillation modes associated with the flow in canonical cavity configurations. The cavity modes identified include shallow cavity modes and Helmholtz resonance. The response of the cavity modes to variation in design and operating parameters are assessed. These parameters include cavity aspect ratio, purge flow ratio, and flow direction defined by the ratio of primary tangential to axial velocity. Scaling the cavity modal response based on computational results and available experimental data in terms of the appropriate reduced frequencies appears to indicate the potential presence of a deep cavity mode as well. While the role of cavity modes on hot gas ingestion cannot be clarified based on the current set of data, the unsteady pressure field associated with turbine rim cavity modal response can be expected to drive ingress/egress.
TOPICS: Gas turbines, Cavities, Pressure, Flow (Dynamics), Turbines, Oscillations, Resonance, High pressure (Physics), Design
research-article  
Nicolai Stadlmair, Tobias Hummel and Thomas Sattelmayer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038475
In this paper, we present a method to determine the quantitative stability level of a lean-premixed combustor from dynamic pressure data. Specifically, we make use of the autocorrelation function of the dynamic pressure signal acquired in a combustor where a turbulent flame acts as a thermoacoustic driver. The unfiltered pressure signal including several modes is analyzed by an algorithm based on Bayesian statistics. For this purpose, a Gibbs sampler is used to calculate parameters like damping rates and eigenfrequencies by a Markov-Chain Monte-Carlo (MCMC) method. The method provides a robust solution algorithm for fitting problems without requiring initial values. First, a simulation of a stochastically forced van-der-Pol oscillator with pre-set input values is carried out to demonstrate accuracy and robustness of the method. In this context it is shown that, despite of a large amount of uncorrelated background noise, the identified damping rates are in a good agreement with the simulated parameters. Secondly, this technique is applied to measured pressure data. By doing so, the combustor is initially operated under stable conditions before the thermal power is gradually increased by adjusting the fuel mass flow rate until a limit-cycle oscillation is established. It is found that the obtained damping rates are qualitatively in line with the amplitude levels observed during operation of the combustor.
TOPICS: Combustion, Damping, Noise (Sound), Statistics as topic, Pressure, Combustion chambers, Algorithms, Signals, Limit cycles, Chain, Fittings, Flames, Robustness, Oscillations, Stability, Flow (Dynamics), Fuels, Turbulence, Thermal energy, Simulation
research-article  
Philippe Versailles, Graeme M.G. Watson, Antoine Durocher, Gilles Bourque and Jeffrey M. Bergthorson
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038416
Increasingly stringent regulations on NOx emissions are enforced by governments owing to their contribution in the formation of pollutants affecting human health and the environment. The design of low-emission combustors requires thermochemical mechanisms of sufficiently high accuracy. Recently, a comprehensive set of experimental data, collected through laser-based diagnostics in atmospheric, stagnation, premixed flames, was published for all isomers of C1-C4 alkane and alcohol fuels [1-3]. The formation of NO through the flame front via the prompt route was shown to be strongly coupled to the maximum concentration of the methylidyne radical, [CH]peak, and the flow residence time within the CH layer. A proper description of CH formation is then a prerequisite for accurate predictions of NO concentrations in hydrocarbon-air flames. However, a comparison against the experimental data of [3] revealed that modern mechanisms are unable to capture the stoichiometric dependence of [CH]peak and, for a given equivalence ratio, the predictions of different mechanisms span over more than one order of magnitude. This paper presents an optimization of the specific rate of nine elementary reactions included in the San Diego mechanism. A quasi-Newton algorithm is used to minimize an objective function defined as the sum of squares of the relative difference between the numerical and experimental data of [3]. A mechanism properly describing CH formation for lean to rich, C1-C3 alkane-air flames is obtained, which enables accurate predictions of prompt-NO formation over a wide range of equivalence ratios and fuels.
TOPICS: Fuels, Optimization, Flames, Emissions, Governments, Regulations, Pollution, Nitrogen oxides, Ethanol, Flow (Dynamics), Lasers, Combustion chambers, Algorithms, Design
research-article  
Daniel Pugh, Philip Bowen, Andrew Crayford, Richard Marsh, Jon P Runyon, Steven Morris and Anthony Giles
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038417
Recent studies have described and evidenced the enhancement of fundamental combustion parameters such as laminar flame speed due to the catalytic influence of H2O on heavily carbonaceous syngas mixtures. Direct formation of CO2 from CO is slow due to its high activation energy, and the presence of disassociated radical hydrogen facilitates chain branching species, changing the dominant path for oxidation. The observed catalytic effect is nonmonotonic, with the reduction in flame temperature eventually prevailing, and reaction rate quenched. The potential benefits of changes in water loading are explored in terms of lean blowoff, and emissions reduction in a premixed turbulent swirling flame at conditions of elevated temperature (423K) and pressure (0.1-0.3MPa). Kinetic models are used initially to characterize the influence that H2O has on the burning characteristics of the fuel blend employed, modelling flame speed and extinction strain rate. These modeled predictions are used as a foundation to investigate the experimental flame. OH* chemiluminescence and OH PLIF are employed as optical diagnostic techniques to analyze changes in heat release structure resulting from H2O addition. A comparison is made with a CH4/air flame and changes in lean blow off stability limits are quantified. The compound benefit of CO/NOx reduction are quantified also, with production first decreasing due to the thermal effect of H2O addition from a lowering of flame temperature, coupled with the potential for further reduction from the change in lean stability limit. Power law correlations have also been derived for the change in pressure.
TOPICS: Water vapor, Syngas, Flames, Swirling flow, Nitrogen oxides, Water, Temperature, Pressure, Stability, Combustion, Fuels, Turbulence, Chemiluminescence, Temperature effects, Chain, Modeling, Heat, Carbon dioxide, Hydrogen, Methane, oxidation, Emissions
research-article  
James A. Scobie, Fabian P. Hualca, Marios Patinios, Carl M. Sangan, J Michael Owen and Gary D. Lock
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038361
In gas turbines, rim seals are fitted at the periphery of stator and rotor discs to minimise the purge flow required to seal the wheel-space between the discs. Ingestion (or ingress) of hot mainstream gases through rim seals is a threat to the operating life and integrity of highly-stressed components, particularly in the first-stage turbine. Egress of sealing flow from the first-stage can be re-ingested in downstream stages. This paper presents experimental results using a 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disc. Re-ingestion was quantified using measurements of CO2 concentration, with seeding injected into the upstream and downstream sealing flows. Here a theoretical mixing model has been developed from first principles and validated by the experimental measurements. For the first time, a method to quantify the mass fraction of the fluid carried over from upstream egress into downstream ingress has been presented and measured; it was shown that this fraction increased as the downstream sealing flow rate increased. The upstream purge was shown to not significantly disturb the fluid dynamics but only partially mixes with the annulus flow near the downstream seal, with the ingested fluid emanating from the boundary layer on the blade platform. From the analogy between heat and mass transfer, the measured mass-concentration flux is equivalent to an enthalpy flux and this re-ingestion could significantly reduce the adverse effect of ingress in the downstream wheel-space.
TOPICS: Gas turbines, Flow (Dynamics), Sealing (Process), Wheels, Disks, Rotors, Fluids, Gases, Heat, Mass transfer, Service life (Equipment), Space, Boundary layers, Turbines, Fluid dynamics, Annulus, Blades, Carbon dioxide, Enthalpy, Stators, Test facilities
research-article  
Christina Salpingidou, Dimitrios Misirlis, Zinon Vlahostergios, Stefan Donnerhack, Michael Flouros, Apostolos Goulas and Kyros Yakinthos
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038362
This work presents an exergy analysis and performance assessment of three recuperative thermodynamic cycles for gas turbine applications. The first configuration is the conventional recuperative cycle in which a heat exchanger is placed after the power turbine. In the second configuration, referred as alternative recuperative cycle, a heat exchanger is placed between the high pressure and the power turbine, while in the third configuration, referred as staged heat recovery cycle, two heat exchangers are employed, the primary one between the high and power turbines and the secondary at the exhaust, downstream the power turbine. The first part of this work is focused on a detailed exergetic analysis on conceptual gas turbine cycles for a wide range of heat exchanger performance parameters. The second part focuses on the implementation of recuperative cycles in aero engines, focused on the MTU-developed Intercooled Recuperative Aero (IRA) engine concept, which is based on a conventional recuperation approach. Exergy analysis is applied on specifically developed IRA engine derivatives using both alternative and staged heat recovery recuperation concepts to quantify energy exploitation and exergy destruction per cycle and component, showing the amount of exergy that is left unexploited, which should be targeted in future optimization actions.
TOPICS: Thermodynamic cycles, Gas turbines, Exergy analysis, Cycles, Turbines, Heat exchangers, Exergy, Engines, Heat recovery, High pressure (Physics), Optimization, Exhaust systems, Aircraft engines

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