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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
research-article  
Pascal Jolly, Mihai Arghir, Olivier Bonneau and Mohamed-Amine Hassini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040177
The present work presents the comparison between experimental and theoretical results obtained for three straight annular seals. One of the annular seals has smooth rotor and stator while the others have a textured stator. The textures are equally spaced shallow round holes, with two different depths. The experimental results were obtained on a test rig dedicated to the identification of the dynamic coefficients of high Reynolds bearings and annular seals. The test rig uses hot water (<50°C) as a working fluid. Dynamic excitations imposed by piezoelectric shakers to the rotor enable the identification of dynamic coefficients via complex impedances. Theoretical results compared with experimental findings were obtained by numerically solving the "Bulk Flow" equations (film thickness averaged equations dominated by inertia effects). The numerical model was extensively validated for smooth annular seals but is less confident for textured surfaces. The present comparisons between experimental and numerical results enable to estimate the accuracy of the numerical model employed for the textured seals.
TOPICS: Inertia (Mechanics), Flow (Dynamics), Fluids, Seals, Computer simulation, Hot water, Texture (Materials), Bearings, Rotors, Film thickness, Stators, Water, Excitation
research-article  
Jonathan Aguilar, Leslie Bromberg, Alexander Sappok, Paul Ragaller, Jean Atehortua and Xiaojin Liu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040198
Motivated by increasingly strict NOx limits, engine manufacturers have adopted selective catalytic reduction (SCR) technology to reduce engine-out NOx. In the SCR process, nitrogen oxides (NOx) react with ammonia (NH3) to form nitrogen and water vapor. The reaction is influenced by several variables, including stored ammonia on the catalyst, exhaust gas composition, and catalyst temperature. Currently, measurements from NOx and/or NH3 sensors upstream and downstream of the SCR are used with predictive models to estimate ammonia storage levels on the catalyst and control urea dosing. This study investigated a radio frequency (RF) -based method to directly monitor the ammonia storage state of the SCR. This approach utilizes the catalyst as a cavity resonator, in which an RF antenna excites electromagnetic waves within the cavity to monitor changes in the catalyst state. Ammonia storage causes changes in the dielectric properties of the catalyst, which directly impacts the RF signal. Changes in the RF signal relative to stored ammonia (NH3) were evaluated over a wide range of frequencies, temperatures and exhaust conditions. The RF response to NH3 storage, desorption, and oxidation on the SCR was well-correlated with changes in the catalyst state. Calibrated RF measurements demonstrate the ability to monitor the adsorption state of the SCR to within 10% of the sensor full scale. The results indicate direct measurement of SCR ammonia storage levels, and resulting catalyst feedback control, via RF sensing to have significant potential for optimizing the SCR system to improve NOx conversion and decrease urea consumption.
TOPICS: Catalysts, Storage, Nitrogen oxides, Signals, Cavities, Exhaust systems, Temperature, Sensors, Engines, Desorption, Water vapor, Electromagnetic radiation, Feedback, Nitrogen, oxidation, Selective catalytic reduction
research-article  
Chunyan Li, Suhui Li, Xu Cheng and Min Zhu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040175
Pilot flames have been widely used for flame stabilization in low-emission gas turbine combustors. Effects of pilot flame on dynamic instabilities, however, are not well understood. In this work, the dynamic interactions between main and pilot flames are studied by perturbing both flames simultaneously, i.e., with a dual-input forcing. A burner is used to generate a premixed axi-symmetric V-shaped methane flame stabilized by a central pilot flame. Servo valve and sirens are used to produce forcing in the pilot and main flames, respectively. A diagnostic system is applied to measure the flame structure and heat release rate. The effects of forcing frequency, forcing amplitude, phase difference between the two forcing signals as well as the Reynolds number are studied. Both the flame transfer function (FTF) and the flame dynamic position are measured and analyzed. It is found that the total flame response can be modified by the perturbation in the pilot flame. The mechanism can be attributed to the effect of pilot flame on the velocity field of the burnt side. Vortex is found to be able to amplify the pilot-main dynamic interactions under certain conditions. An analytical model is developed based on the linearized G-equation, to further understand the flame interactions through the velocity perturbations in the burnt side. Good agreements were found between the prediction and the experiment results.
TOPICS: Dynamic response, Flames, Modeling, Valves, Vortices, Methane, Signals, Emissions, Heat, Servomechanisms, Reynolds number, Transfer functions, Combustion chambers, Gas turbines
research-article  
Luke Hagen, Baine Breaux, Michael Flory, Joel Hiltner and Scott Fiveland
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040179
The North American oil and gas industry has experienced a market pull for dual fuel (DF) engines that can run on any ratio of fuels ranging from 100% diesel to a high proportion of field gas relative to diesel, while also meeting the US Tier 4 Nonroad emissions standards. A DF engine must meet complex and at times competing requirements in terms of performance, fuel tolerance, and emissions. The challenges faced in designing a DF engine to meet all of the performance and emissions requirements require a detailed understanding of the trade-offs for each pollutant. This paper will focus on the details of NOx formation for high substitution DF engines. Experimental results have demonstrated that NOx emission trends (as a function of lambda) for DF engines differ from both traditional diesel engines and lean burn natural gas engines. For high energy substitution (>70%) conditions, NOx emissions are a function of the premixed gas lambda and contain a local minimum, with NOx increasing as lambda is either leaned or richened beyond the local minimum which occurs from approximately 1.7 - 1.85. It is hypothesized that at richer conditions (premixed lamda < 1.7), NOx formed in the burning of gaseous fuel results in increased total NOx emissions. At leaner conditions (lng> 1.85) the NOx formed in the diesel post flame regions, as a result of increased oxygen availability, results in increased total NOx emissions. Between these two regions there are competing effects which result in relatively constant NOx.
TOPICS: Fuels, Engines, Nitrogen oxides, Emissions, Diesel, Diesel engines, Flames, Oxygen, Pollution, Design, Petroleum industry, Tradeoffs, Gas engines, Combustion
research-article  
Ebigenibo Genuine Saturday and Thank-God Isaiah
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040106
The effect of engine degradation in the form compressor fouling and compressor turbine degradation on the creep life consumption of the first stage blades of the high pressure (HP) turbine of a LM2500+ industrial gas turbine engine is investigated in this work. An engine model was created in Cranfield gas turbine performance and diagnostics software, PYTHIA and adapted to the real engine operation conditions. Using the Larson-Miller Parameter method for creep life analysis, a thermal model and a stress model were developed to provide temperatures and stresses at various locations along the span of the blades. The sensitivity of engine life consumption to each effect is examined by evaluating the percentage decrease in creep life due to the given effect. The degradation of each engine component is provided in the form of engine health parameter indices define by the flow capacity and the isentropic efficiency of the component. For the engine considered, it is found that compressor flow capacity degradation has more impact on creep life than compressor isentropic efficiency degradation. Compressor degradation has more impact on creep life than compressor turbine degradation. In terms of percentage decrease in engine creep life, compressor degradation has more impact on engine creep life towards peak power operation while HP turbine degradation has more impact on creep life at lower power of engine operation. The results of this work will give engine operators an idea of how engine components creep life is consumed and make reasonable decisions concerning operating at part loads.
TOPICS: Engines, Compressors, Creep, Turbines, Stress, Flow (Dynamics), Gas turbines, Blades, Computer software, Temperature, Industrial gases, High pressure (Physics)
Technical Brief  
Yifei Guan and Igor Novosselov
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040091
Lean blowout (LBO) prediction based on the local parameters in the laboratory Toroidal Jet-Stirred Reactor (TJSR) is investigated. The reactor operated on methane is studied using 3D computational fluid dynamics (CFD); the results are compared with the experimental data. Skeletal chemical kinetic mechanism with the eddy dissipation concept (EDC) model is used. Flow bifurcation in the radial (poloidal) plane due to the interaction between counter-rotating vortices creates one dominating poloidal recirculation zone (PRZ) and one weaker toroidal recirculation zone (TRZ). The Da number in the reactor is the highest in the stabilization vortex; it varies from about Da~2 at ?=0.55 to Da~0.2-0.3 at LBO conditions. Due to the reduced turbulent dissipation rate in PRZ, the Da number is an order of magnitude higher than in TRZ. The global blowout event is predicted at the local Da=0.2 in PRZ. Local blowout events in the regions of low Da can lead to flame instability and to a global flame blowout at a higher fuel-air ratio than predicted by the CFD. Local Da non-uniformity can be used for optimization and analysis of combustion system stability, further research in the process parameterization and application to the practical combustion system is needed.
TOPICS: Stability, Flow (Dynamics), Fuels, Turbulence, Eddies (Fluid dynamics), Energy dissipation, Combustion systems, Computational fluid dynamics, Optimization, Vortices, Bifurcation, Flames, Methane
research-article  
Jue Li, Timothy J. Jacobs, Tushar Bera and Michael Parkes
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040092
This study investigates the effects of engine bore size on performance characteristics including: in-cylinder pressure, ignition delay, burn duration, and fuel conversion efficiency, using experiments between two engines of different bore sizes. The two engines are nearly identical, except bore size, stroke length, and consequently displacement. Although most of this diagnosis is done with experimental results, a 1-D model is also used to calculate turbulence intensities with respect to geometric factors; these results help to explain observed differences in heat transfer characteristics. The results are compared at the same brake mean effective pressure, and show that engine bore size has a significant impact on the indicated efficiency. The larger bore engine has a higher indicated efficiency. Although the larger engine has higher turbulence intensities and longer burn duration, the lower surface area to volume ratio and lower reaction temperature leads to lower heat losses to the cylinder walls. The difference in the heat loss to the cylinder walls between the two engines is found to increase with increasing load. In addition, due to the smaller volume-normalized friction loss, the larger sized engine also has higher mechanical efficiency. In the net, since the brake efficiency is a function of indicated efficiency and mechanical efficiency, the larger sized engine has higher brake efficiency with the difference in brake efficiency between the two engines increasing with increasing engine load. In the interest of efficiency, larger bore designs for a given displacement could be a means for future efficiency gains
TOPICS: Combustion, Engines, Diesel engines, Brakes, Cylinders, Turbulence, Displacement, Heat losses, Stress, Pressure, Mechanical efficiency, Friction, Temperature, Heat transfer, Fuels, Performance characterization, Ignition delay
research-article  
James Sevik, Michael Pamminger, Thomas Wallner, Riccardo Scarcelli, Steven Wooldridge, Brad Boyer, Scott Miers and Carrie Hall
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040090
The present paper represents a small piece of an extensive experimental effort investigating the dual-fuel blending operation of a light-duty spark ignited engine. Natural gas (NG) was directly injected into the cylinder and gasoline was injected into the intake-port. Direct injection of NG was used in order to overcome the power density loss usually experienced with NG port-fuel injection as it allows an injection after intake valve closing. EGR was used to increase efficiency at low and part-load operation and reduce the propensity of knock at higher compression ratios (CR) thereby enabling blend levels with greater amount of gasoline across a wider operating range. CR and in-cylinder turbulence levels were varied in order to study their influence on efficiency, emissions and performance over a specific speed and load range. Increasing the CR from 10.5 to 14.5 allowed an absolute increase in indicated thermal efficiency of more than 3% for 75% NG (25% gasoline) operation at 8 bar IMEP and 2500 RPM. However, the achievable peak load at CR 14.5 with 100% gasoline was reduced due to its lower knock resistance. The in-cylinder turbulence level was varied by means of tumble plates as well as an insert for the NG injector that guides the injection "spray" to augment the tumble motion. The usage of tumble plates showed a significant increase in EGR dilution tolerance for pure gasoline operation, however, no such impact was found for blended operation of gasoline and NG.
TOPICS: Combustion, Natural gas, Compression, Cylinders, Gasoline, Stress, Exhaust gas recirculation, Plates (structures), Fuels, Turbulence, Engines, Sprays, Valves, Emissions, Peak load, Ejectors, Power density, Thermal efficiency
research-article  
Marcus Grochowina, Michael Schiffner, Simon Tartsch and Thomas Sattelmayer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040089
Dual-Fuel (DF) engines offer great fuel flexibility since they can either run on gaseous or liquid fuels. In the case of Diesel pilot ignited DF-engines the main source of energy is provided by gaseous fuel, whereas the Diesel fuel acts only as an ignition source. Therefore, a proper autoignition of the pilot fuel is of utmost importance for combustion in DF-engines. However, autoignition of the pilot fuel suffers from lower compression temperatures of Miller valve timings. These valve timings are applied to increase efficiency and lower nitrogen oxide engine emissions. In order to improve the ignition, it is necessary to understand which parameters influence the ignition in DF-engines. For this purpose, experiments were conducted and the influence of parameters such as injection pressure, pilot fuel quantity, compression temperature and air-fuel equivalence ratio of the homogenous natural gas-air mixture were investigated. The experiments were performed on a periodically chargeable combustion cell using optical high-speed recordings and thermodynamic measurement techniques for pressure and temperature. The study reveals that the quality of the Diesel pilot ignition significantly depends on the injection parameters and operating conditions. In most cases, the pilot fuel suffers from too high dilution due to its small quantity and long ignition delays. This results in a small number of ignited sprays and consequently leads to longer combustion durations. Furthermore, the experiments confirm that the natural gas of the background mixture influences the autoignition of the Diesel pilot oil.
TOPICS: Combustion, Fuels, Engines, Ignition, Diesel, Temperature, Pressure, Valves, Compression, Natural gas, Sprays, Nitrogen oxides, Emissions, Ignition delay
research-article  
Moritz Lipperheide, Frank Weidner, Manfred Wirsum, Martin Gassner and Stefano Bernero
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040009
Accurate monitoring of gas turbine performance is a means to an early detection of performance deviation from the design point and thus to an optimized operational control. In this process, the diagnosis of the combustion process is of high importance due to strict legal pollution limits as aging of the combustor during operation may lead to an observed progression of NOx emissions. The method presented here features a semi-empirical NOx formulation incorporating aging for the GT24/GT26 heavy duty gas turbines: Input parameters to the NOx-correlation are processed from actual measurement data in a simplified gas turbine model. Component deterioration is accounted for by linking changes in air flow distribution and control parameters to specific operational measurements of the gas turbine. The method was validated on three different gas turbines of the GE GT24/GT26 fleet for part- and baseload operation with a total of 374,058 long-term data points (5 min average), corresponding to a total of 8.5 years of observation, while only commissioning data was used for the formulation of the NOx correlation. When input parameters to the correlation are adapted for aging, the NOx prediction outperforms the benchmark prediction method without aging by 35.9, 53.7 and 26.2 % in terms of RMSE yielding a root-mean-squared error of 1.27, 1.84 and 3.01 ppm for the investigated gas turbines over a three year monitoring period.
TOPICS: Gas turbines, Nitrogen oxides, Emissions, Errors, Pollution, Combustion, Air flow, Combustion chambers, Design
research-article  
Daniel Probst, Peter K. Senecal, Peter Z. Chien, Max Xu and Brian Leyde
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040006
This study describes the use of an analytical model, constructed using sequential design of experiments (DOEs), to optimize and quantify the uncertainty of a Diesel engine operating point. A genetic algorithm (GA) was also used to optimize the design. The engine simulation was completed with a sector mesh in the commercial computational fluid dynamics (CFD) software CONVERGE, which predicted the combustion and emissions using a detailed chemistry solver with a reduced mechanism for n-heptane. The analytical model was constructed using the SmartUQ software using DOE responses to construct kernel emulators of the system. The sequential DOE optimization was compared to an optimization performed using a GA. This study highlighted the strengths of both methods for optimization. The GA (known to be an efficient and effective method) found a better optimum, while the DOE method found a good optimum with fewer total simulations. The DOE method also ran more simulations concurrently, which is an advantage when sufficient computing resources are available. In the second part of the study, the analytical model developed in the first part was used to assess the sensitivity and robustness of the design. The uncertainty propagation was studied over the reduced design region found with the sequential DoE in the first part. Finally, the predictions from the analytical model were validated against CFD results for sweeps of the input parameters. The predictions of the analytical model were found to agree well with the results from the CFD simulation.
TOPICS: Computational fluid dynamics, Optimization, Diesel engines, Uncertainty analysis, Simulation, Design, Computer software, Uncertainty, Experimental design, Genetic algorithms, Robustness, Heptane, Emissions, Chemistry, Combustion, Engines
research-article  
Sandeep Jella, Pierre Gauthier, Gilles Bourque, Jeffrey M. Bergthorson, Ghenadie Bulat, Jim Rogerson and Suresh K. Sadasivuni
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040007
Finite-rate chemical effects at gas turbine conditions lead to incomplete combustion and well-known emissions issues. Although a thin flame front is preserved on an average, the instantaneous flame location can vary in thickness and location due to heat losses or imperfect mixing. Post-flame phenomena (slow CO oxidation or thermal NO production) can be expected to be significantly influenced by turbulent eddy structures. Since typical gas turbine combustor calculations require insight into flame stabilization as well as pollutant formation, combustion models are required to be sensitive to the instantaneous and local flow conditions. Unfortunately, few models that adequately describe turbulence-chemistry interactions are tractable in the industrial context. A widely used model capable of employing finite-rate chemistry, is the Eddy Dissipation Concept (EDC) model of Magnussen. Its application in large eddy simulations (LES) is problematic mainly due to a strong sensitivity to the model constants which were based on an isotropic cascade analysis in the RANS context. The objectives of this paper are: (i) To formulate the EDC cascade idea in the context of LES; and (ii) To validate the model using experimental data consisting of velocity (PIV measurements) and major species (1-D Raman measurements), at four axial locations in the near-burner region of a Siemens SGT-100 industrial gas turbine combustor.
TOPICS: Chemistry, Flames, Swirling flow, Large eddy simulation, Combustion, Turbulence, Eddies (Fluid dynamics), Cascades (Fluid dynamics), Combustion chambers, Gas turbines, Turbines, Energy dissipation, Industrial gases, Emissions, Pollution, Heat losses, oxidation, Reynolds-averaged Navier–Stokes equations, Flow (Dynamics)
research-article  
Andrew L. Carpenter, Troy L. Beechneer, Brian E. Tews and Paul E. Yelvington
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040012
Electrically-assisted engine boosting systems lend themselves to better throttle response, wider effective operating ranges, and can provide the ability to extract excess energy during deceleration and high-load events (and store it in a vehicle’s onboard batteries). This can lead to better overall vehicle performance, emissions, and efficiency while allowing for further engine downsizing and increased power density. A hybrid-electric turbocharger, variable-frequency drive (VFD), and novel sensorless control algorithm has been developed. An 11kW permanent-magnet machine was coupled to a commercial turbocharger via an in-line, bolt-on housing attached to the compressor inlet. A high-efficiency, high-temperature variable-frequency drive, consisting of custom control and power electronics, was also developed. The variable-frequency drive uses SiC MOSFETS to achieve high-switching frequency and can be cooled using an existing engine coolant loop operating at up to 105 °C at an efficiency greater than 98%. A digital sliding mode-observer (DSMO) sensorless speed control algorithm was created to command and regulate speed and achieved ramp rates of over 68,000 rpm/sec. This paper intends to present a design overview of the in-line, hybrid-electric device, VFD, and performance characterization of the electronics and sensorless control algorithm.
TOPICS: Turbochargers, Control algorithms, Engines, Electronics, Emissions, Machinery, High temperature, Performance characterization, Power density, Compressors, Stress, Coolants, Permanent magnets, Design, Vehicles
research-article  
Rasoul Salehi, Jason Martz, Anna G. Stefanopoulou, Bruce Vernham, Lakshmidhar Uppalapati and Bantwal Prashant Baliga
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040008
A novel decentralized control architecture is developed based on a feedback from the pressure difference across the engine which is responsible for the pumping losses and the Exhaust Gas Recirculation (EGR) flow in diesel engines. The controller is supplemented with another feedback loop based on NOx emissions measurement. Aiming for simple design and tuning, the two control loops are designed and discussed; one manipulates the Variable Geometry Turbine (VGT) actuator and the other manipulates the EGR valve. An experimentally validated mean-value diesel engine model is used to analyze the best pairing of actuators and set points. Emphasis is given to the robustness of this pairing based on gain changes across the entire operating region, since swapping the pairing needs to be avoided. The VGT loop is designed to achieve fast cylinder air charge increase in response to a rapid pedal tip-in by a feedforward term based on the real-time derivative of the desired boost pressure. The EGR loop relies on a feedback measurement from a NOx sensor and a real-time estimation of cylinder oxygen ratio, Xcyl . The engine model is used for evaluating the designed controllers over the federal test procedure (FTP) for heavy duty vehicles. Results indicate that the control system meets all targets, namely fast air charge and Xcyl control during torque transients, robust NOx control during steady state operation and controlled pumping losses in all conditions.
TOPICS: Diesel engines, Feedback, Nitrogen oxides, Emissions, Exhaust gas recirculation, Control equipment, Engines, Cylinders, Pressure, Actuators, Design, Turbines, Valves, Flow (Dynamics), Construction equipment, Sensors, Control systems, Torque, Transients (Dynamics), Feedforward control, Geometry, Oxygen, Robustness, Steady state
research-article  
Michael J. Walock, Vann Heng, Andy Nieto, Anindya Ghoshal, Muthuvel Murugan and Daniel Dreimeyer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040011
Future gas turbine engines will operate at significantly higher temperatures (~ 1800 °C) than current engines (~ 1400 °C) for improved efficiency and power density. As a result, the current set of metallic components (titanium-based and nickel-based superalloys) will be replaced with ceramics and ceramic matrix composites (CMCs). These materials can survive the higher operating temperatures of future engines at a significant weight savings over the current metallic components, i.e. advanced ceramic components will facilitate more powerful engines. While oxide-based CMCs may not be suitable candidates for hot-section components, they may be suitable for structural and/or exhaust components. However, a more thorough understanding of performance under relevant environment of these materials is needed. To this end, this work investigates the high temperature durability of a family of oxide-oxide CMCs under an engine relevant environment. Flat oxide-oxide CMC panels were cyclically exposed to temperatures up to 1150 °C, within 240 m/s (~0.3 M) gas flows and hot sand impingement. Front and backside surface temperatures were monitored by a single-wavelength pyrometer and thermocouple, respectively. In addition, an infrared camera was used to evaluate the damage evolution of the samples during testing. Flash thermography nondestructive evaluation was used to elucidate defects present before and after thermal exposure.
TOPICS: Engines, Vehicles, Exhaust systems, Ceramic matrix composites, Temperature, Wavelength, Nickel, Sands, Ceramics, Superalloys, Thermography, Nondestructive evaluation, Gas flow, Industrial ceramics, Pyrometers, Thermocouples, Titanium, High temperature, Operating temperature, Power density, Damage, Durability, Gas turbines, Testing, Weight (Mass)
research-article  
Jean Lamouroux, Stephane Richard, Quentin Malé, Gabriel Staffelbach, Antoine Dauptain and Antony Misdariis
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039940
Nowadays, models predicting soot emissions are, neither able to describe correctly fine effects of technological changes on sooting trends nor sufficiently validated at relevant operating conditions to match design office quantification needs. Yet, phenomenological descriptions of soot formation, containing key ingredients for soot modeling exist in the literature, such as the well-known Leung et al. model (Combust Flame 1991). When blindly applied to aeronautical combustors for different operating conditions, this model fails to hierarchize operating points compared to experimental measurements. The objective of this work is to propose an extension of the Leung model over a wide range of condition relevant for gas turbines operation. Today, the identification process can hardly be based on laboratory flames since few detailed experimental data are available for heavy-fuels at high pressure. Thus, it is decided to directly target smoke number values measured at the engine exhaust for a variety of combustors and operating conditions from idling to take-off. A Large Eddy Simulation approach is retained for its intrinsic ability to reproduce finely unsteady behavior, mixing and intermittency. In this framework, The Leung model for soot is coupled to the TFLES model for combustion. It is shown that pressure-sensitive laws for the modelling constant of the soot surface chemistry are sufficient to reproduce engine emissions. Grid convergence is carried out to verify the robustness of the proposed approach. Several cases are then computed to assess the prediction capabilities of the extended model.
TOPICS: Modeling, Smoke, Soot, Aircraft engines, Large eddy simulation, Emissions, Flames, Engines, Combustion chambers, Surface science, Design, Gas turbines, High pressure (Physics), Pressure, Combustion, Fuels, Robustness, Exhaust systems
research-article  
Tao Zeng, Devesh Upadhyay, Harold Sun, Eric Curtis and Guoming George Zhu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039937
Turbocharging is one technology to meet future US fuel economy mandates. Fuel economy improvements must, however, be achieved without sacrificing performance. High throughput turbochargers are especially susceptible to this dynamic and are often equipped with variable geometry turbines (VGT) to mitigate some of this effect. Assisted boosting techniques that add power directly to the TC shaft from a power source that is independent of the engine have been shown to significantly reduce turbo-lag. Single unit assisted turbochargers are either electrically assisted or hydraulically assisted. In this study a regenerative hydraulically assisted turbocharger (RHAT) system is evaluated. A custom designed RHAT system is coupled to a light duty diesel engine and is analyzed via vehicle and engine simulations for performance and energy requirements over standard test cycles. Supplier provided performance maps for the hydraulic turbine, hydraulic turbo pump were used. A production controller was coupled with the engine model and upgraded to control the engagement and disengagement of RHAT, with energy management strategies. Results show some interesting dynamics and shed light on system capabilities especially with regard to the energy balance between the assist and regenerative functions. Design considerations based on open loop simulations are used for sizing the high pressure accumulator. Simulation results show that the proposed RHAT turbocharger system can significantly improve engine transient response. Vehicle level simulations that include the driveline were also conducted and showed potential for up to 4% fuel economy improvement over the FTP 75 drive cycle.
TOPICS: Turbochargers, Engines, Corporate average fuel economy, Engineering simulation, Fuel efficiency, Simulation, Vehicles, Cycles, Diesel engines, Geometry, Hydraulic turbines, Secondary cells, Simulation results, Energy management, Pumps, Turbines, Energy budget (Physics), Dynamics (Mechanics), Control equipment, High pressure (Physics), Transients (Dynamics), Design
research-article  
Joseph Saverin, Giacomo Persico, David Marten, David Holst, Vincenzo Dossena, Georgios Pechlivanoglou and Christian Oliver Paschereit
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039935
The evolution of the wake of a wind turbine contributes significantly to its operation and performance, as well as to those of machines installed in the vicinity. The inherent unsteady and three-dimensional aerodynamics of Vertical Axis Wind Turbines (VAWT) have hitherto limited the research on wake evolution. In this paper the wakes of both a troposkien and a H-type VAWT rotor are investigated by comparing experiments and calculations. Experiments were carried out in the large-scale wind tunnel of the Politecnico di Milano, where unsteady velocity measurements in the wake were performed by means of hot wire anemometry. The geometry of the rotors was reconstructed in the open-source wind-turbine software QBlade, developed at the TU Berlin. The aerodynamic model makes use of a lifting line free-vortex wake (LLFVW) formulation, including an adapted Beddoes-Leishman unsteady aerodynamic model; airfoil polars are introduced to assign sectional lift and drag coefficients. A wake sensitivity analysis was carried out to maximize the reliability of wake predictions. The calculations are shown to reproduce several wake features observed in the experiments, including blade-tip vortex, dominant and submissive vortical structures, and periodic unsteadiness caused by sectional dynamic stall. The experimental assessment of the simulations illustrates that the LLFVW model is capable of predicting the unsteady wake development with very limited computational cost, thus making the model ideal for the design and optimization of VAWTs.
TOPICS: Wakes, Vertical axis wind turbines, Wind turbines, Rotors, Vortices, Blades, Computer software, Geometry, Sensitivity analysis, Velocity measurement, Wind tunnels, Design, Engineering simulation, Optimization, Aerodynamics, Machinery, Drag (Fluid dynamics), Reliability, Wire, Simulation, Airfoils
research-article  
Georg Fink, Michael Jud and Thomas Sattelmayer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039934
In this paper, pilot-ignited high pressure dual-fuel (HPDF) combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates. The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the Shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and heat release rates. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the heat release rate is governed by the time of ignition with respect to the start of natural gas injection -- as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the heat release rate through injection timing variation is limited for a certain angle between the two jets.
TOPICS: Combustion, Natural gas, Diesel, Ignition, Heat, Ignition delay, Compression, Delays, Machinery, Fuels, High pressure (Physics), Jets, Ejectors
research-article  
Siddhartha Banerjee, Clayton Naber, Michael Willcox, Charles E.A. Finney and K. Dean Edwards
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039845
Pinnacle is developing multi-cylinder 1.2 L gasoline engine for automotive applications using high performance computing (HPC) and analysis methods. Pinnacle and Oak Ridge National Laboratory executed large-scale multi-dimensional combustion analyses at the Oak Ridge Leadership Computing Facility to thoroughly explore the design space. These HPC-led investigations show high fuel efficiency (~46% gross indicated efficiency) may be achieved by operating with extremely high charge dilution levels of exhaust gas recirculation (EGR) at a light load key drive cycle condition (2000 RPM, 3 bar BMEP), while simultaneously attaining high levels of fuel conversion efficiency and low NOx emissions. In this extremely dilute environment, the flame propagation event is supported by turbulence and bulk in-cylinder charge motion brought about by modulation of inlet port flow. This arrangement produces a load and speed adjustable amalgamation of swirl and counter-rotating tumble which provides the turbulence required to support stable low-temperature combustion (LTC). At higher load conditions, the engine may operate at more traditional combustion modes to generate competitive power. In this paper, the numerical results from these HPC simulations are presented. Further HPC simulations and test validations are underway and will be reported in future publications.
TOPICS: Pistons, Gasoline engines, Combustion, Stress, Simulation, Turbulence, Engineering simulation, Cylinders, Exhaust gas recirculation, Fuel efficiency, Emissions, Flames, Low temperature, Cycles, Leadership, Nitrogen oxides, Engines, Fuels, Flow (Dynamics), Automotive industry, Design

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