Accepted Manuscripts

Mina Shahi, J.B.W. Kok, Juan Carlos Roman Casado and Artur K. Pozarlik
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038234
Due to the high temperature of the flue gas flowing at high velocity and pressure, the wall cooling is extremely important for the liner of a gas turbine engine combustor. The liner material is heat resistant steel with relatively low heat conductivity. To accommodate outside wall forced air cooling, the liner is designed to be thin, which unfortunately facilitates the possibility of high amplitude wall vibrations (and failure due to fatigue) in case of pressure fluctuations in the combustor. The latter may occur due to a possible occurrence of a feedback loop between the aerodynamics, the combustion, the acoustics and the structural vibrations. The structural vibrations act as a source of acoustic emitting the acoustic waves to the confined fluid. This leads to amplification in the acoustic filed and hence the magnitude of instability in the system. The aim of this paper is to explore the mechanism of fluid-structure interaction on the LIMOUSINE setup which leads to limit cycle of pressure oscillations (LCO). Computational fluid dynamics (CFD) analysis using a RANS approach is performed to obtain the thermal and mechanical loading of the combustor liner and finite element model (FEM) renders the temperature, stress distribution, and deformation in the liner. Results are compared to other numerical approaches like zero-way interaction and conjugated heat transfer model (CHT). To recognize the advantage/disadvantage of each method validation is made with the available measured data for the pressure and vibration signals.
TOPICS: Oscillations, Combustion chambers, Fluid structure interaction, Three-dimensional models, Limit cycles, Vibration, Pressure, Acoustics, Computational fluid dynamics, Cooling, Finite element model, Flue gases, Reynolds-averaged Navier–Stokes equations, Signals, High temperature, Combustion, Fluids, Stress concentration, Thermal conductivity, Gas turbines, Failure, Feedback, Specialty steels, Exterior walls, Waves, Fluctuations (Physics), Aerodynamics, Deformation, Fatigue, Temperature, Heat transfer
Teresa Siebel, Jan Zanger, Andreas Huber, Manfred Aigner, Karsten Knobloch and Friedrich Bake
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038159
Auxiliary power unit (APU) operators face increasingly stricter airport requirements concerning exhaust gas and noise emission levels. To simultaneously reduce exhaust gas and noise emissions and to satisfy the increasing demand of electric power on board, optimization of the current technology is necessary. Prior to any possible demonstration of optimization potential, detailed data of thermodynamic properties and emissions have to be determined. Therefore, the investigations presented in this paper were conducted at a full-scale APU of an operational aircraft. A Pratt & Whitney APS3200, commonly installed in the Airbus A320 aircraft family, was used for measurements of the reference data. In order to describe the APS3200, the full spectrum of feasible power load and bleed air mass flow combinations were adjusted during the study. Their effect on different thermodynamic and performance properties, such as exhaust gas temperature, pressure as well as electric and overall efficiency is described. Furthermore, the mass flows of the inlet air, exhaust gas and fuel input were determined. Additionally, the work reports the exhaust gas emissions regarding the species CO2, CO and NOx as a function of load point. Moreover the acoustic noise emissions are presented and discussed. With the provided data the paper serves as a database for validating numerical simulations and provides a baseline for current APU technology.
TOPICS: Noise (Sound), Air pollution, Cycles, Emissions, Exhaust systems, Aircraft, Optimization, Stress, Flow (Dynamics), Temperature, Electricity (Physics), Fuels, Acoustics, Computer simulation, Pressure, Carbon dioxide, Databases, Nitrogen oxides
Alok Sinha
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038183
This paper deals with the estimation of forcing functions on a mistuned bladed rotor from measurements of harmonic response via Kalman Filter in time domain. An unique feature of this approach is that the number of estimated variables can be far greater than the number of measurements. The robustness of this method to measurement errors is shown. It is also shown that direct prediction of amplitude and phase of sinusoidal force vector from input/output frequency response function has a large amount of errors in the presence of unavoidable measurement noise. Numerical examples contain both frequency mistuning and geometric mistuning.
TOPICS: Rotors, Errors, Frequency response, Kalman filters, Robustness, Noise (Sound)
Tao Ren, Michael F. Modest and Somesh Roy
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038153
Radiative heat transfer is studied numerically for reacting swirling flow in an industrial gas turbine burner operating at a pressure of 15 bar. The reacting field characteristics are computed by Reynolds-averaged Navier-Stokes (RANS) equations using the k-epsilon model with the partially stirred reactor (PaSR) combustion model. The GRI-Mech 2.11 mechanism, which includes nitrogen chemistry, is used to demonstrate the the ability of reducing NOx emissions of the combustion system. A Photon Monte Carlo (PMC) method coupled with a line-by-line spectral model is employed to accurately account for the radiation effects. Optically thin and PMC-gray models are also employed to show the differences between the simplest radiative calculation models and the most accurate radiative calculation model, i.e., PMC-LBL, for the gas turbine burner. It was found that radiation does not significantly alter the temperature level as well as CO2 and H2O concentrations. However, it has significant impacts on the NOx levels at downstream locations.
TOPICS: Radiative heat transfer, Simulation, Industrial gases, High pressure (Physics), Combustion chambers, Turbines, Nitrogen oxides, Emissions, Carbon dioxide, Chemistry, Nitrogen, Reynolds-averaged Navier–Stokes equations, Swirling flow, Water, Combustion systems, Gas turbines, Radiation effects, Pressure, Temperature, Photons, Combustion, Radiation (Physics)
Craig R. Nolen and Melissa Poerner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038151
The distribution of water in the diffuser of a wet gas compressor is not well understood. Measurements of water film thickness across the diffuser surface would improve the understanding of two-phase flow phenomena in wet gas compressors. Electromagnetic probes were designed in order to measure water film thickness in the diffuser of a SwRI-designed wet gas compressor. The probes consisted of two electrode foils plated on a thin insulating substrate, allowing them to be bonded in place without drilling through the diffuser. An AC signal was passed between the electrodes, and the voltage across a resistor in series with the electrodes was recorded. As the water level covering the electrodes increased, the recorded voltage increased. A method of calibrating the probes was developed and used prior to installation in the diffuser. Testing showed the probes to be effective at detecting the presence of water in the diffuser and indicating the general water level. Improvements in probe design, calibration, and installation are needed to provide more precise water film thickness data.
TOPICS: Gas compressors, Diffusers, Design, Testing, Calibration, Film thickness, Probes, Water, Electrodes, Two-phase flow, Drilling, Water distribution, Resistors, Signals
Iacopo Rossi, Alberto Traverso, Martina Hohloch, Andreas Huber and David Tucker
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038152
This paper presents the development, implementation and validation of a simplified dynamic modeling approach to describe SOFC/GT hybrid systems in three real emulator test-rigs installed at University of Genoa (UNIGE, Italy), German Aerospace Center (DLR, Germany) and National Energy Technology Laboratory (NETL, USA), respectively. The proposed modeling approach is based on an experience-based simplification of the physical problem to reduce model computational efforts with minimal expense of accuracy. Traditional high fidelity dynamic modelling requires specialized skills and significant computational resources. This innovative approach, on the other hand, can be easily adapted to different plant configurations, predicting the most relevant dynamic phenomena with a reduced number of states: such a feature will allow, in the near future, the model deployment for monitoring purposes or advanced control scheme applications (e.g. model predictive control). The three target systems are briefly introduced and dynamic situations analyzed for model tuning, first, and validation, then. Relevance is given to peculiar transients where the model shows its reliability and its weakness. Assumptions introduced during model definition for the three different test-rigs are discussed and compared. The model captured significant dynamic behavior in all analyzed systems (in particular those regarding the GT) and showed influence of signal noise on some of the SOFC computed outputs.
TOPICS: Physics, Solid oxide fuel cells, Dynamic models, Dynamic modeling, Predictive control, Signals, Reliability, Transients (Dynamics), Noise (Sound), Aerospace industry, Modeling
Luigi Carassale and Mirko Maurici
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038154
The component mode synthesis based on the Craig-Bampton method has two strong limitations that appear when the number of the interface degrees of freedom is large. First, the reduced-order model obtained is overweighed by many unnecessary degrees of freedom. Second, the reduction step may become extremely time consuming. Several interface reduction techniques addressed successfully the former problem, while the latter remains open. In this paper we address this latter problem through a simple interface-reduction technique based on an a-priory choice of the interface modes. An efficient representation of the interface displacement field is achieved adopting a set of orthogonal basis functions determined by the interface geometry. The proposed method is compared with other existing interface reduction methods on a case study regarding a rotor blade of an axial compressor.
TOPICS: Compressors, Degrees of freedom, Rotors, Disks, Blades, Displacement, Geometry, Polynomials
Giuseppe Fabio Ceschini, Nicolò Gatta, Mauro Venturini, Thomas Hubauer and Alin Murarasu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038155
The reliability of gas turbine health state monitoring and forecasting depends on the quality of sensor measurements directly taken from the unit. Outlier detection techniques have acquired a major importance, as they are capable of removing anomalous measurements and improve data quality. This paper aims at evaluating the benefits of implementing robust statistical estimators for the BFMW framework. Three different approaches are considered in this paper. The first methodology, k-MAD, replaces mean and standard deviation of the k-s methodology with median and mean absolute deviation (MAD), respectively. The second methodology, s-MAD, is a novel hybrid scheme combining the k-s and the k-MAD methodologies for the backward and the forward windows, respectively. Finally, the bi-weight methodology implements bi-weight mean and bi-weight standard deviation as location and dispersion estimators. First, the parameters of these methodologies are tuned and the respective performance is compared by means of simulated data. Different scenarios are considered to evaluate statistical efficiency, robustness and resistance. Subsequently, the performance of these methodologies is further investigated by injecting outliers in field data sets taken on selected Siemens gas turbines. Results prove that all the investigated methodologies are suitable for outlier identification. Advantages and drawbacks of each methodology allow the identification of different scenarios in which their application can be most effective.
TOPICS: Gas turbines, Time series, Weight (Mass), Sensors, Reliability, Robustness
Georg A. Mensah, Luca Magri and Jonas P. Moeck
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038156
Thermoacoustic instabilities are a major threat for modern gas turbines. Frequency-domain based stability methods, such as network models and Helmholtz solvers, are common design tools because they are fast compared to compressible CFD computations. Frequency-domain approaches result in an eigenvalue problem, which is nonlinear with respect to the eigenvalue. . Thus, the influence of the relevant parameters on mode stability is only given implicitly. Small changes in some model parameters, which are obtained by experiments with some uncertainty, may have a great impact on stability. The assessment of how parameter uncertainties propagate to system stability is therefore crucial. This question is addressed by uncertainty quantification. A common strategy for uncertainty quantification in thermoacoustics is risk factor analysis. It quantifies the uncertainty of a set of parameters in terms of the probability of a mode to become unstable. A new and fast way to obtain algebraic parameter models in order to tackle the implicit nature of the eigenfrequency problem is using adjoint perturbation theory. This paper aims to further utilize adjoint methods for the quantification of uncertainties. This analytical method avoids the usual random Monte Carlo simulations, making it particularly attractive for industrial purposes. Using network models and the open-source Helmholtz solver PyHoltz it is also discussed how to apply the method with standard modeling techniques. The theory is exemplified based on a simple ducted flame and a combustor of EM2C laboratory for which experimental validation is available.
TOPICS: Stability, Uncertainty quantification, Uncertainty, Eigenvalues, Network models, Perturbation theory, Probability, Thermoacoustics, Flames, Algebra, Simulation, Combustion chambers, Computational fluid dynamics, Design, Engineering simulation, Gas turbines, Modeling, Computation, Information technology risk
Stacie Tibos, Christos Georgakis, Joao A. Teixeira and Simon Hogg
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038136
Varying clearance, rotor-following seals are a key technology for meeting the demands of increased machine flexibility for conventional power units. These seals follow the rotor through hydrodynamic or hydrostatic mechanisms. Forward facing step (FFS) and Rayleigh step designs are known to produce positive fluid stiffness. However, there is very limited modelling or experimental data available on the hydrostatic fluid forces generated from either design. A quasi-1D method has been developed to describe both designs and validated using test data. Tests have shown that the FFS and the Rayleigh step design are both capable of producing positive film stiffness and there is little difference in hydrostatic force generation between the two designs. This means any additional hydrodynamic features in the Rayleigh step design should have a limited effect on hydrostatic fluid stiffness. The analytical model is capable of modelling both the inertial fluid forces as well as the viscous fluid losses and the predictions are in good agreement with the test data.
TOPICS: Clearances (Engineering), Hydrostatics, Fluids, Turbomachinery, Design, Stiffness, Modeling, Rotors, Fitness-for-service, Machinery
Yonatan Cadavid, Andres Amell, Juan Alzate, Gerjan Bermejo and Gustavo Alfonso Ebratt Herazo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038137
The wet compressor (WC) has become a reliable way to reduce gas emissions and increase gas turbine efficiency. However, fuel source diversification in the short and medium terms presents a challenge for gas turbine operators to know how the wet compressor will respond to changes in fuel composition. For this study, we assessed the operational data of two thermal power generators, with outputs of 610 MW and 300 MW, in Colombia. The purpose was to determine the maximum amount of water that can be added into a gas turbine with a WC system, as well as how the NOx/CO emissions vary due to changes in fuel composition. The combustion properties of different gaseous hydrocarbon mixtures at wet conditions did not vary significantly from each other - except for the laminar burning velocity. It was found that the fuel/air equivalence ratio in the turbine reduced with lower CH4 content in the fuel. Less water can be added to the turbine with leaner combustion; the water/fuel ratio was decreased over the range of 1.4 to 0.4 for the studied case. The limit is mainly due to a reduction in flame temperature and major risk of lean blowout (LBO) or dynamic instabilities. A hybrid reaction mechanism was created from GRI MECH 3.0 and NGIII to model hydrocarbons up to C5 with NOx formation. The model was validated with experimental results published previously in literature. Finally, the effect of atmospheric water in the premixed combustion was analyzed and explained.
TOPICS: Fuels, Compressors, Gas turbines, Water, Combustion, Turbines, Nitrogen oxides, Emissions, Risk, Flames, Generators, Methane, Temperature, Thermal energy
Bugra Ertas, Adolfo Delgado and J. Jeffrey Moore
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038121
The present work advances experimental results and analytical predictions on the dynamic performance of an integral squeeze film damper (ISFD) for application in a high-speed super-critical CO2 (sCO2) expander. The test campaign focused on conducting controlled orbital motion mechanical impedance testing aimed at extracting stiffness and damping coefficients for varying end seal clearances, excitation frequencies, and vibration amplitudes. In addition to the measurement of stiffness and damping; the testing revealed the onset of cavitation for the ISFD. Results show damping behavior that is constant with vibratory velocity for each end seal clearance case until the onset of cavitation/air ingestion, while the direct stiffness measurement was shown to be linear. Measurable added inertia coefficients were also identified. The predictive model uses an isothermal finite element method to solve for dynamic pressures for an incompressible fluid using a modified Reynolds equation accounting for fluid inertia effects. The predictions revealed good correlation for experimentally measured direct damping, but resulted in grossly overpredicted inertia coefficients when compared to experiments.
TOPICS: Bearings, Dampers, Carbon dioxide, Damping, Inertia (Mechanics), Stiffness, Testing, Cavitation, Finite element methods, Clearances (Engineering), Mechanical impedance, Vibration, Excitation, Accounting, Fluids, Incompressible fluids
Patrick Buchwald, Damian M. Vogt, Julien Grilliat, Wolfgang Laufer, Michael B. Schmitz, Andreas Lucius and Marc Schneider
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038122
One of the main design decisions in the development of low-speed axial fans is the right choice of the blade loading versus rotational speed, since a target pressure rise could either be achieved with a slow spinning fan and high blade loading or a fast spinning fan with less flow turning in the blade passages. Both the blade loading and the fan speed have an influence on the fan performance and the fan acoustics and there is a need to find the optimum choice in order to maximize efficiency while minimizing noise emissions. The present paper addresses this problem by investigating five different fans with the same pressure rise but different rotational speeds in the design point. In the first part of the numerical study, the fan design is described and steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are conducted in order to identify the performance of the fans in the design point and in off-design conditions. The investigations show the existence of an optimum in rotational speed regarding fan efficiency and identify a flow separation on the hub causing a deflection of the outflow in radial direction as the main loss source for slow spinning fans with high blade loadings. Subsequently, Large Eddy Simulations (LES) along with the acoustic analogy of Ffowcs Williams and Hawkings (FW-H) are performed in the design point to identify the main noise sources and to determine the far-field acoustics.
TOPICS: Fans, Design, Blades, Acoustics, Spinning (Textile), Spin (Aerodynamics), Noise (Sound), Pressure, Engineering simulation, Simulation, Deflection, Flow separation, Reynolds-averaged Navier–Stokes equations, Steady state, Large eddy simulation, Emissions, Flow turning, Outflow
Felix Klein and Stephan Staudacher
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038124
Enabling high overall pressure ratios, wave rotors and piston concepts seem to be solutions surpassing gas turbine efficiency. Therefore, a comparison of a wave rotor and three piston concepts relative to a reference gas turbine is offered. The piston concepts include a Wankel, a 2-stroke reciprocating engine and a free-piston. All concepts are investigated with and without intercooling. An additional combustion chamber downstream the piston engine is investigated, too. The shaft power chosen corresponds to large civil turbofans. Relative to the reference gas turbine a maximum efficiency increase of 11.2 percent for the piston concepts and 9.8 percent for the intercooled wave rotor is demonstrated. These improvements are contrasted by a 5.8 percent increase in the intercooled reference gas turbine and a 4.2 percent increase due to improved gas turbine component efficiencies. Intercooling the higher component efficiency gas turbine leads to a 9.8 percent efficiency increase. Furthermore, the study demonstrates the high difference between intercooler and piston engine weight and a conflict between piston concept efficiency and chamber volume, highlighting the need for extreme lightweight design in any piston engine solution. Improving piston engine technology parameters is demonstrated to lead to higher efficiency, but not to a chamber volume reduction. Heat loss in the piston engines is identified as the major efficiency limiter.
TOPICS: Pressure, Aircraft engines, Piston engines, Gas turbines, Pistons, Rotors, Waves, Combustion chambers, Design, Heat losses, Turbofans, Weight (Mass)
Francesco Crespi, Giacomo Gavagnin, David Sánchez and Gonzalo S. Martínez
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038125
Since the renewed interest in supercritical carbon dioxide cycles, a large number of cycle layouts have been proposed in literature. These analyses, which are essentially theoretical, consider different operating conditions and modelling assumptions and thus the results are not comparable. There are also works that aim to provide a fair comparison between different cycles in order to assess which one is most efficient. These analyses are very interesting but, usually, combine thermodynamic and technical restrictions thus making it difficult to draw solid and general conclusions with regards to which the cycle of choice in the future should be. With this background, the present work provides a systematic thermodynamic analysis of twelve supercritical carbon dioxide cycles under similar working conditions, with and without technical restriction in terms of pressure and/or temperature. This yields very interesting conclusions regarding which the most interesting cycles are amongst those proposed in literature. Also, useful recommendations are extracted from the parametric analysis with respect to the directions that must be followed when searching for more efficient cycles. The analysis is based on efficiency and specific work diagrams with respect to pressure ratio and turbine inlet temperature in order to enhance their applicability to plant designs driven by fuel economy and/or footprint.
TOPICS: Thermodynamic potentials, Cycles, Supercritical carbon dioxide, Pressure, Temperature, Corporate average fuel economy, Modeling, Turbines, Fuel efficiency, Plant design
Michael Severin, Oliver Lammel, Holger Ax, Rainer Lückerath, Wolfgang Meier, Manfred Aigner and Johannes Heinze
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038126
A model FLOX® combustor, featuring a single high momentum premixed jet flame, has been investigated using laser diagnostics in an optically accessible combustion chamber at a pressure of 8bar. The model combustor was designed as a large single eccentric nozzle main burner (Ø 40mm) together with an adjoining pilot burner and was operated with natural gas. To gain insight into the flame stabilization mechanisms with and without piloting, simultaneous Particle Image Velocimetry (PIV) and OH Laser Induced Fluorescence (LIF) measurements have been performed at numerous two-dimensional sections of the flame. Additional OH-LIF measurements without PIV-particles were analyzed quantitatively resulting in absolute OH concentrations and temperature fields. The flow field looks rather similar for both the unpiloted and the piloted case, featuring a large recirculation zone next to the high momentum jet. However, flame shape and position change drastically. For the unpiloted case, the flame is lifted, widely distributed and isolated flame kernels are found at the flame root in the vicinity of small scale vortices. For the piloted flame, on the other hand, both pilot and main flame are attached to the burner base plate, and flame stabilization seems to take place on much smaller spatial scales with a connected flame front and no isolated flame kernels. The single shot analysis gives rise to the assumption that for the unpiloted case small scale vortices act like the pilot burner flow in the opposed case and constantly impinge and ignite the high momentum jet at its root.
TOPICS: Pressure, Momentum, Flames, Combustion chambers, Lasers, Particulate matter, Flow (Dynamics), Vortices, Shapes, Temperature, Fluorescence, Natural gas, Nozzles
Stefano Puggelli, Davide Bertini, Lorenzo Mazzei and Antonio Andreini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038127
During the last years aero-engines are progressively evolving toward design concepts that permit improvements in terms of engine safety, fuel economy and pollutant emissions. With the aim of satisfying the strict NOx reduction targets imposed by ICAO-CAEP, lean burn technology is one of the most promising solutions even if it must face safety concerns and technical issues. Hence a depth insight on lean burn combustion is required and Computational Fluid Dynamics (CFD) can be a useful tool for this purpose. In this work a comparison in Large-Eddy Simulation (LES) framework of two widely employed combustion approaches like the Artificially Thickened Flame (ATF) and the Flamelet Generated Manifold (FGM) is performed using ANSYS Fluent v16.2. Two literature test cases with increasing complexity in terms of geometry, flow field and operating conditions are considered. Firstly, capabilities of FGM are evaluated on a single swirler burner operating at ambient pressure with a standard pressure atomizer for spray injection. Then a second test case, operated at 4 bar, is simulated. Here kerosene fuel is burned after an injection through a pre-filming airblast atomizer within a co-rotating double swirler. Obtained comparisons with experimental results show the different capabilities of ATF and FGM in modelling the partially-premixed behaviour of the flame and provides an overview of the main strengths and limitations of the modelling strategies under investigation.
TOPICS: Modeling, Sprays, Flames, Large eddy simulation, Flamelet generated manifold, Pressure, Combustion, Safety, Computational fluid dynamics, Design, Engines, Corporate average fuel economy, Fuels, Flow (Dynamics), Geometry, Pollution, Nitrogen oxides, Fuel efficiency, Aircraft engines, Emissions
Vera Hoferichter and Thomas Sattelmayer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038128
Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame flashback. This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100-350 Hz). The excitation amplitude is varied from 0 to 36 % of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the flashback limit of confined flames. Consequently, flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.
TOPICS: Acoustics, Boundary layers, Flames, Hydrogen, Excitation, Flow (Dynamics), Gas turbines, Cycles, Risk, Oscillations, Dynamics (Mechanics), Combustion, Design, Combustion chambers, Ducts, Nitrogen oxides, Emissions
M. H. Padzillah, S. Rajoo and R. F. Martinez-Botas
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038076
The application of guide vanes in a turbocharger turbine has increased the complexity of flow interactions regardless of whether the vanes are fixed or variable geometry. Although it is enticing to assume that the performance of the vaned turbine is better than the one without (vaneless), there are currently no tangible evidences to support this claim, particularly during the actual pulsating flow operations. Therefore, this research looks into comparing the differences between the two turbine arrangements in terms of their performance at flow field level. For this purpose, a three-dimensional ‘full-stage’ unsteady turbine Computational Fluid Dynamics models for both volutes are constructed and validated against the experimental data. These models are subject to identical instantaneous inlet pressure profile of 60Hz which is equivalent to an actual 3-cylinder 4-stroke engine rotating at 2400rpm. A similar 95.14 mm diameter mixed-flow turbine rotor rotating at 48000rpm is used for both models to enable direct comparison. The complete validation exercises for both steady and unsteady flow conditions are also presented. Results have indicated that neither vaned nor vaneless turbine is capable of maintaining constant efficiency throughout the pulse cycle. Despite that, the vaneless turbine indicated better performance during peak power instances. This work also showed that the pulsating pressure at the turbine inlet effected the vaned and vaneless turbine differently at the flow field level. Furthermore, results also indicated that both the turbines matched its optimum incidence angle for only a fraction of pulse cycle, which is unfavourable.
TOPICS: Flow (Dynamics), Turbochargers, Turbines, Vaneless turbines, Pressure, Cycles, Cylinders, Geometry, Pulsatile flow, Unsteady flow, Computational fluid dynamics, Rotors, Four-stroke engines, Guide vanes
Junhyeong Oh, Kyunghan Min, Manbae Han and Myoungho Sunwoo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038078
Particulate matters (PM) accumulation through a low-pressure exhaust gas recirculation (LP-EGR) path may hinder to obtain the desired LP-EGR rate and thus causes an increase of nitrogen oxides (NOx). The degree of lack of the LP-EGR rate should be detected, i.e. an LP-EGR fault, and a remedy to compensate for the lack of LP-EGR rate should be a mandate to suppress NOx emission, i.e. a fault management. In order to accomplish those objectives, this paper proposes an LP-EGR fault management system which consists of a fault diagnosis algorithm, fault tolerant control algorithm, and an LP-EGR rate model. The model applies a combustion parameter derived from in-cylinder pressure information to the conventional orifice valve model. Consequently, the LP-EGR rate estimation was improved to the maximum error of 2.38 % and RMSE of 1.34 % at various operating condition even under the fault condition compared to that of the conventional model with the maximum error of 7.46 % and RMSE of 5.39 %. Using this LP-EGR rate model as a virtual sensor, the fault diagnosis algorithm determines an LP-EGR fault state, the fault tolerant control determines whether or not to generate the offset of the exhaust throttle valve position. This offset combines with the LUT based feedforward controller to control an LP-EGR rate. As a result of real-time verification of the fault management system in fault condition, the NOx emission decreased by up to about 15 %.
TOPICS: Pressure, Cylinders, Diesel engines, Exhaust gas recirculation, Nitrogen oxides, Emissions, Algorithms, Valves, Fault diagnosis, Errors, Exhaust systems, Combustion, Sensors, Control equipment, Particulate matter, Feedforward control, Control algorithms

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