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Accepted Manuscripts

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research-article  
Kenneth Clark, Michael Barringer, Dave Johnson, Karen A. Thole, Eric Grover and Christopher Robak
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040308
Secondary air is bled from the compressor in a gas turbine engine to cool turbine components and seal the cavities between stages. Unsealed cavities can lead to hot gas ingestion, which can degrade critical components or, in extreme cases, can be catastrophic to engines. For this study, a 1.5 stage turbine with an engine-realistic rim seal was operated at an engine-relevant axial Reynolds number, rotational Reynolds number, and Mach number. Purge flow was introduced into the inter-stage cavity through distinct purge holes for two different configurations. This paper compares the two configurations over a range of purge flow rates. Sealing effectiveness measurements, deduced from the use of CO2 as a flow tracer, indicated that the sealing characteristics were improved by increasing the number of uniformly distributed purge holes and improved by increasing levels of purge flow. For the larger number of purge holes, a fully sealed cavity was possible while for the smaller number of purge holes, a fully sealed cavity was not possible. For this representative cavity model, sealing effectiveness measurements were compared with a well-accepted orifice model derived from simplified cavity models. Sealing effectiveness levels at some locations within the cavity were well-predicted by the orifice model, but due to the complexity of the realistic rim seal and the purge flow delivery, the effectiveness levels at other locations were not well-predicted.
TOPICS: Flow (Dynamics), Rotors, Sealing (Process), Cavities, Stators, Engines, Reynolds number, Gas turbines, Compressors, Mach number, Turbine components, Turbines, Carbon dioxide
research-article  
Mozhgan Rahimi Boldaji, Aimilios Sofianopoulos, Sotirios Mamalis and Benjamin Lawler
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040309
Homogeneous Charge Compression Ignition combustion has the potential for high efficiency with very low levels of NOx and soot emissions. However, HCCI has thus far only been achievable in a laboratory setting due the lack of control over the start and rate of combustion and its narrow operating range. In the present work, direct water injection was investigated to solve the aforementioned limitations of HCCI. This new advanced combustion mode is called Thermally Stratified Compression Ignition (TSCI). A 3-D CFD model was developed using CONVERGE CFD coupled with detailed chemical kinetics to gain a better understanding of the underlying phenomena of the water injection event in a homogeneous, low temperature combustion strategy. The CFD model was first validated against previously collected experimental data. The model was then used to simulate TSCI combustion and the results indicate that injecting water into the combustion chamber decreases the overall unburned gas temperature and increases the level of thermal stratification prior to ignition. The increased thermal stratification results in a decreased rate of combustion, thereby providing control over its rate. The results show that the peak pressure and gross heat release rate decrease by 37.8% and 83.2%, respectively, when 6.7 mg of water were injected per cycle at a pressure of 160 bar. Finally, different spray patterns were simulated to observe their effect on the level of thermal stratification prior to ignition. The results show that symmetric patterns with more nozzle holes were generally more effective at increasing thermal stratification.
TOPICS: Combustion, Simulation, Stress, Computational fluid dynamics, Engineering simulation, Underground injection, Thermal stratification, Homogeneous charge compression ignition engines, Ignition, Pressure, Water, Nitrogen oxides, Emissions, Heat, Temperature, Chemical kinetics, Combustion chambers, Soot, Compression, Cycles, Low temperature, Nozzles, Sprays
research-article  
William Northrop, Darrick Zarling and Xuesong Li
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040306
In this work, engine-out particulate matter (PM) mass emissions from an off-highway diesel engine measured using a low-cost photometer, scanning mobility particle sizer, elemental versus organic carbon analysis, and a photo-acoustic analyzer are compared. Tested engine operating modes spanned the range of those known to result in high semi-volatile particle concentration and those that emit primarily solid particles. Photometer measurements were taken following a primary dilution stage and a sample conditioner to control relative humidity prior to the instrument. Results of the study show that the photometer could qualitatively track total particle mass trends over the tested engine conditions though it was not accurate in measuring total carbon mass concentration. Further, the required photometric calibration factor (PCF) required to accurately measure total PM mass changed with the organic carbon (OC) fraction of the particles. Variables that influence PCF include particle effective density, which changes both as a function of particle diameter and OC fraction. Differences in refractive index between semi-volatile and solid particles are also significant and contribute to high error associated with measurement of total PM using the photometer. This work illustrates that it may be too difficult to accurately measure total engine PM mass with a photometer without knowing additional information about the sampled particles. However, removing semi-volatile organic materials prior to the instrument may allow the accurate estimation of elemental carbon mass concentration alone.
TOPICS: Particulate matter, Photometers, Instrumentation, Exhaust systems, Diesel engines, Carbon, Engines, Density, Acoustics, Calibration, Refractive index, Errors, Highways, Emissions, Mechanical admittance
research-article  
Kevin Jupe, Roger Gorges, Anil Rathod, John Carey and John Stearns
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040292
The move to lead-free bearing materials is well known and upcoming legislation, such as the Restriction of Hazardous Substances (RoHS), is increasing the drive to extend this trend towards heavy duty diesel truck and off-highway applications. During the development of lead-free systems, new electroplated overlays and bronze-based substrates have been developed by various suppliers, but little attention has been given to the interlayer or diffusion barrier between the overlay and substrate materials. This interlayer is particularly necessary for tin-based solutions as it prevents the rapid diffusion of overlay species into the bronze substrate. The present development focuses on improving this often overlooked element in the system and provides a further robustness that could even be adapted to lead-based systems where increased performance is required. The incorporation of hexagonal boron nitride as a solid lubricant in the nickel interlayer changes dramatically the interlayer properties and provides more typical bearing-like behavior for seizure resistance scuff performance compared to nickel alone. The paper details findings of respective rig tests as well as an actual engine test supporting the change in material characteristics and the associated improvement in seizure resistance.
TOPICS: Overlays (Materials engineering), Bearings, Highways, Trucks, Diffusion (Physics), Nickel, Bronze, Engines, Hazardous substances, Lubricants, Robustness, Diesel, Boron
research-article  
Alberto Broatch, J. Javier Lopez, Jorge García-Tíscar and Josep Gomez-Soriano
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040287
As noise pollution remains one of the biggest hurdles posed by thermal engines, increasing efforts are made to alleviate the generation of combustion noise from the early design stage of the chamber. Since the complexity of both modern chamber geometries and the combustion process itself precludes robust analytic solutions, and since the resonant, highly 3D pressure field is difficult to be measured experimentally, focus is put on the numerical modelling of the process. However, in order to optimize the resources devoted to this simulation, an informed decision must be made on which formulations are followed. In this work, the experimental cyclic dispersion of the in-cylinder pressure is analyzed in two typical compression-ignited (CI) and spark-ignited (SI) engines. Acoustic signatures and pressure rise rates are derived from this data, showing how while the preponderance of flame front propagation and dependency of previous cycle in SI engine noise usually calls for multi-cycle, more complex turbulence modelling such as Large Eddy Simulation (LES), simpler Unsteady Reynolds-Averaged Navier-Stokes (URANS) formulations can accurately characterize the more consistent pressure spectra of CI thermal engines, which feature sudden autoignition as the main noise source.
TOPICS: Combustion, Noise (Sound), Modeling, Experimental analysis, Spark-ignition engine, Pressure, Engines, Cycles, Cylinders, Compression, Pollution, Large eddy simulation, Flames, Simulation, Design, Spectra (Spectroscopy), Turbulence, Acoustics, Resonance
research-article  
Zhe Kang, Zhijun Wu, Lezhong Fu, Jun Deng, Zongjie Hu and Liguang Li
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040288
The internal combustion Rankine cycle (ICRC) engine utilizes pure oxygen as the oxidant instead of air during combustion to prevent the generation of nitrogen oxide emissions and lower the cost of CO2 recovery. To control combustion intensity and increase efficiency, water injection technology is implemented as it can increase the in-cylinder working fluid during combustion process. To further enhance the system thermal efficiency, the injected water is heated using coolant and waste heat before being directly injected into combustion chamber. The main challenge of controlling the ICRC engine is the interaction between water injection process and combustion stability. Ion current detection provides a potential solution of real-time detection of in-cylinder combustion status and water injection process simultaneously. In this paper, the characteristics of ion current signal in an ICRC engine were studied. The results indicate the ion current signal is primarily affected by the combination of trapped water vapor injected in the last cycle and in-cylinder combustion intensity. The water vapor contributes to the ionization reactions which lead to enhanced ion current signals under water cycle. The ion current signal is capable of reflecting the operating conditions of the in-cylinder water injector. The phase of the ion current peak value has a linear relation as the water injection timing is delayed, and ion current detection technology has the potential to detect the combustion phase under different engine loads in an internal combustion Rankine cycle engine.
TOPICS: Combustion, Engines, Rankine cycle, Signals, Cylinders, Underground injection, Water, Cycles, Water vapor, Ionization, Fluids, Stress, Coolants, Combustion chambers, Ejectors, Stability, Carbon dioxide, Oxygen, Waste heat, Nitrogen oxides, Emissions, Thermal efficiency
research-article  
Clare Bonham, Mark Brend, Adrian Spencer, Katsuyoshi Tanimizu and Dylan Wise
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040285
Steady-state stagnation temperature probes are used during gas turbine engine testing as a means of characterising turbomachinery component performance. The probes are located in the high-velocity gas-path, where temperature recovery and heat transfer effects cause a shortfall between the measured temperature and the flow stagnation temperature. To improve accuracy, the measurement shortfall is corrected post-test using data acquired at representative Mach numbers in a steady aerodynamic calibration facility. However, probes installed in engines are typically subject to unsteady flows, which are characterised by periodic variations in Mach number and temperature caused by the wakes shed from upstream blades. The present work examines the impact of this periodic unsteadiness on stagnation temperature measurements by translating probes between jets with dissimilar Mach numbers. For conventional Kiel probes in unsteady flows, a greater temperature measurement shortfall is recorded compared to equivalent steady flows, which is related to greater conductive heat loss from the temperature sensor. This result is important for the application of post-test corrections, since an incorrect value will be applied using steady calibration data. A new probe design with low susceptibility to conductive heat losses is therefore developed, which is shown to deliver the same performance in both steady and unsteady flows. Measurements from this device can successfully be corrected using steady aerodynamic calibration data, resulting in improved stagnation temperature accuracy compared to conventional probe designs. This is essential for resolving in-engine component performance to better than +/-0.5% across all component pressure ratios.
TOPICS: Temperature measurement, Flow (Dynamics), Steady state, Probes, Temperature, Mach number, Calibration, Unsteady flow, Heat losses, Engines, Wakes, Jets, Design, Gas turbines, Testing, Blades, Pressure, Heat transfer, Temperature sensors, Turbomachinery
research-article  
Yonas Niguse and Dr. Ajay Agrawal
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040286
The effect of chamber pressure on combustion of a twin-fluid-atomized spray of straight vegetable oil (VO) in a swirl stabilized combustion system is experimentally studied. A system with high pressure capabilities was developed, and flame and emissions characteristics of VO are investigated at elevated pressures, up to about 5 bars, different heat release rates and atomizing air to liquid ratio (ALR) by mass. An image analysis technique was developed to infer flame and soot characteristics from visual images acquired by a digital camera. Increase in ALR resulted in improved combustion characterized by blue flames, lower CO and NOx emissions, and minimal soot formation. For a given fuel flow rate, an increase in pressure resulted in smaller volume flames with lower CO levels but higher NOx emissions. Diesel flame and emission characteristic are also compared with straight VO results at select operating conditions. Compared to diesel, as pressure increased, straight VO flames produced lower NOx and more voluminous flames characterized by more distributed combustion with less soot formation. Overall, straight VO could be atomized and combusted at elevated pressures using the twin-fluid atomizer of the present study, and resulting VO flames exhibited less sensitivity to chamber pressure variations.
TOPICS: Combustion, Fluids, Sprays, Vegetable oils, Flames, Emissions, Pressure, Soot, Nitrogen oxides, Diesel, Flow (Dynamics), Heat, Fuels, High pressure (Physics), Combustion systems
research-article  
Tomas Radnic, Jindrich Hala, Martin Luxa, David Simurda, Jiri Furst, Dan Hasnedl and Josef Kellner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040093
Focus of this paper is aerodynamic investigation of tie-boss stabilization devices for extremely long rotor blades. This investigation covered measurements on multiple blade cascades and CFD simulation of the flow past these cascades. Conclusions were drawn from results of the measurements and CFD and from the knowledge of prior investigation of the used blade cascade. Main focus of this paper is to describe influence of a tie-boss stabilization device on flow field in interblade channel. Tie-boss with more massive shape proved to cause lesser losses, while tie-boss with a tailored trailing edge showed lesser influence on flow turning.
TOPICS: Flow (Dynamics), Simulation, Turbine blades, Cascades (Fluid dynamics), Computational fluid dynamics, Rotors, Blades, Shapes, Flow turning
research-article  
Nitish Anand, Salvatore Vitale, Matteo Pini, Gustavo J. Otero-Rodríguez and Rene Pecnik
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040182
The stator vane of high-temperature Organic Rankine Cycle radial-inflow turbines operates under severe expansion ratios and the associated fluid-dynamic losses account for nearly two-third of the total losses generated inside the machine. The efficiency of the machine can strongly benefit from specialized high-fidelity design methods able to provide shapes attenuating shock wave formation. Shape optimization is certainly a viable option to deal with supersonic ORC stator design, but it is computationally expensive and often case specific. In this work, a robust method to approach the problem in a more systematic manner is documented. The methodology involves an optimization procedure encompassing the method of characteristics extended to non-ideal fluid flow for profiling the diverging part of the nozzle. The subsonic section and semi-bladed suction side are retrieved using a simple conformal geometrical transformation. The method is applied to the design a supersonic ORC stator working with Toluene vapors, for which two blade shapes were already available. The comparison of fluid-dynamic performance clearly indicates that the MoC-Based method is able to provide the best results with the lowest computational effort, and is suitable to be used to draw general design guidelines.
TOPICS: Flow (Dynamics), Design methodology, Design, Stators, Organic Rankine cycle, Shapes, Fluids, Machinery, Suction, Shock waves, Vapors, Nozzles, Optimization, Turbines, Blades, Shape optimization, High temperature, Inflow, Fluid dynamics
research-article  
Niklas Neupert, Janneck Christopher Harbeck and Franz Joos
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040180
In recent years overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Despite the positive thermodynamic effect on the cycle droplets entering the compressor increase the risk of erosion and lead to a higher fouling sensitivity. Therefore erosion resistant hydrophobic coatings are applied to the first stages of compressors. Although some patents claim the use of such coatings the aerodynamic impact of a different wettability is not regarded so far. In this study the issue of a different blade surface wettability in a linear transonic compressor cascade is addressed. Different coatings are applied resulting in contact angles of 51-95?. The inflow Mach number was fixed at design inflow Mach number and the inflow angle was varied over a broad range. The effect on the water film pattern is analyzed in terms of position of film breakup, rivulet width and totally wetted surface. The performance of the cascade under two-phase flow was analyzed using LDA/PDA measurement technique in terms of loss coefficient based on wake momentum thickness and flow turning. It is shown that the wettability of the surface has significant effects on the water structure leading to a lower fraction of wetted surface with increasing contact angle. The influence on performance is limited to effects in the proximity of the surface and is dependent on operation point. While in design conditions hydrophilic coating show lower losses the trend is vice-versa for off-design conditions.
TOPICS: Compressors, Cascades (Fluid dynamics), Two-phase flow, Coatings, Inflow, Design, Erosion, Mach number, Water, Flow turning, Risk, Blades, Cycles, Patents, Momentum, Industrial gases, Turbines, Drops, Wakes
research-article  
Tingting Wei, Dengji Zhou, Di Huang, Shixi Ma, Wang Xiao and Huisheng Zhang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040181
IGHAT cycle is an advanced power generation system, combining gasification technology and HAT cycle. It draws great attention in the energy field considering its high specific power, high efficiency and low emission. There are only a few HAT cycle plants and IGHAT cycle is still on the theory research stage. Therefore, the study on control strategies of IGHAT cycle has great significance in the future development of this system. A design method of control strategy is proposed for the unknown gas turbine systems. The control strategy design is summarized after IGHAT control strategy and logic is designed based on the dynamic simulation results and the operation experience of gas turbine power station preliminarily. Then, control logic is configured and a virtual control system of IGHAT cycle is established on the Ovation distribution control platform. The model-in-loop control platform is eventually set up based on the interaction between the simulation model and the control system. A case study is implemented on this model-in-loop control platform to demonstrate its feasibility in the practical industry control system. The power in IGHAT cycle is increased by 24.12% and 32.47% respectively, compared to the ones in the simple cycle and the regenerative cycle. And the efficiency of IGHAT cycle is 1.699% higher than that of the regenerative cycle. Low component efficiency caused by off-design performance and low humidity caused by high pressure are the main limits for system performance.
TOPICS: Turbines, Cycles, Fuel gasification, Control systems, Design, Gas turbines, Power stations, Design methodology, Energy / power systems, High pressure (Physics), Simulation models, Simulation results, Emissions
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)
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
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

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