Accepted Manuscripts

Xiaofeng Yang, Tang-wei Kuo, Kulwinder Singh, Rafat Hattar and Yangbing Zeng
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039729
Reliably starting the engine during extremely cold ambient temperatures is one of the largest calibration and emissions challenges in engine development. Although cold-start conditions comprise only a small portion of an engine's typical drive cycle, large amounts of hydrocarbon and particulate emissions are generated during this time, and the calibration of cold-start operation takes several months to complete. During the cold start period, results of previous cycle combustion event strongly influences the subsequent cycle due to variations in engine speed, residual fraction, residual wall film mass, in-cylinder charge and wall temperatures, and air flow distribution between cylinders. Include all these parameters in CFD simulation is critical in understanding the cold start process in transient and cumulative manner. Measured cold start data of a production four cylinder spark-ignition direct-injection engine was collected for this study with an ambient temperature of -30 ?C. Three-dimensional transient engine flow, spray and combustion simulation over first 3 consecutive engine cycles is carried out to provide a better understandings of the cold-start process. Measured engine speed and 1D conjugate heat transfer model are used to capture realistic in-cylinder flow dynamics and transient wall temperatures for more accurate fuel-air mixing predictions. The CFD predicted cumulative heat release trend for the first 3 cycles matches the data from measured pressure analysis. The same observation can be made for the vaporized fuel mass as well. These observations are explained in the report.
TOPICS: Engines, Simulation, Computational fluid dynamics, Ignition, Cycles, Cylinders, Transients (Dynamics), Fuels, Calibration, Combustion, Temperature, Wall temperature, Emissions, Heat transfer, Pressure, Flow (Dynamics), Heat, Particulate matter, Air flow, Engine flow, Sprays
Seyfettin Can Gulen and Chris Hall
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039733
This paper describes a gas turbine combined cycle (GTCC) power plant system, which addresses the three key design challenges of post-combustion CO2 capture from the stack gas of a GTCC power plant using aqueous amine-based scrubbing method by offering the following: (i) low heat recovery steam generator (HRSG) stack gas temperature, (ii) increased HRSG stack gas CO2 content and (iii) decreased HRSG stack gas O2 content. This is achieved by combining two bottoming cycle modifications in an inventive manner, i.e., (i) high supplementary (duct) firing in the HRSG and (ii) recirculation of the HRSG stack gas. It is shown that, compared to an existing natural gas-fired GTCC power plant with post-combustion capture, it is possible to reduce the CO2 capture penalty-power diverted away from generation-by almost 65 percent and the overall capital cost ($/kW) by about 35 percent.
TOPICS: Gas turbines, Combustion, Carbon capture and storage, Combined cycles, Heat recovery steam generators, Power stations, Carbon dioxide, Cycles, Ducts, Firing, Design, Temperature
Yu Li, Hailin Li, Hongsheng Guo, Yongzhi Li and Mingfa Yao
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039734
This research numerically simulates the formation and destruction of NO2 in a natural gas-diesel dual fuel engine using commercial CFD software CONVERGE coupled with a reduced primary reference fuel (PRF) mechanism consisting of 45 species and 142 reactions. The model was validated by comparing the simulated cylinder pressure, heat release rate, and nitrogen oxides (NOx) emissions with experimental data. The validated model was used to simulate the formation and destruction of NO2 in a NG-diesel dual fuel engine. The formation of NO2 and its correlation with the local concentration of nitric oxide (NO), methane, and temperature were examined and discussed. It was revealed that NO2 was mainly formed in the interface region between the hot NO-containing combustion products and the relatively cool unburnt methane-air mixture. NO2 formed at the early combustion stage is usually destructed to NO after the complete oxidation of methane and n-heptane, while NO2 formed during the post-combustion process survives through the expansion process and exits the engine. A detailed analysis of the chemical reactions occurring in the NO2 containing zone identified HO2 as the primary species dominating the formation of NO2. The simulation revealed the key reaction path for the formation of HO2 noted as CH4->CH3->CH2O->HCO->HO2, with conversion ratios of 98%, 74%, 90%, 98%, accordingly. The backward reaction of OH+NO2=NO+HO2 consumed 34% of HO2 for the production of NO2.
TOPICS: Fuels, Engines, Diesel, Methane, Combustion, Nitrogen oxides, Heptane, Emissions, Chemical reactions, oxidation, Pressure, Heat, Temperature, Simulation, Computational fluid dynamics, Computer software, Cylinders
Torsten Methling, Sandra Richter, Trupti Kathrotia, Marina Braun-Unkhoff, Clemens Naumann and Uwe Riedel
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039731
Over the last years, global concerns about energy security and climate change have resulted in many efforts focusing on the potential utilization of non-petroleum-based, i.e. bio-derived, fuels. In this context, n-butanol has recently received high attention because it can be produced sustainably. A comprehensive knowledge about its combustion properties is inevitable to ensure an efficient and smart use of n-butanol if selected as a future energy carrier. In the present work, two major combustion characteristics, here laminar flame speeds applying the cone-angle method and ignition delay times applying the shock tube technique, have been studied, experimentally and by modeling exploiting detailed chemical kinetic reaction models, at ambient and elevated pressures. The in-house reaction model was constructed applying the RMG-method. A linear transformation method recently developed, linTM, was exploited to generate a reduced reaction model needed for an efficient, comprehensive parametric study of the combustion behavior of n butanol/hydrocarbon mixtures. All experimental data were found to agree with the model predictions of the in-house reaction model, for all temperatures, pressures, and fuel-air ratios. On the other hand, calculations using reaction models from the open literature mostly overpredict the measured ignition delay times by about a factor of two. The results are compared to those of ethanol, with ignition delay times very similar and laminar flame speeds of n butanol slightly lower, at atmospheric pressure.
TOPICS: Combustion, Energy generation, Ignition delay, Fuels, Flames, Petroleum, Shock tubes, Climate change, Security, Temperature, Atmospheric pressure, Modeling, Ethanol
Feijia Yin, Floris S. Tiemstra and Arvind Gangoli Rao
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039732
As the Overall Pressure Ratio (OPR) and Turbine Inlet Temperature (TIT) of modern gas turbines are constantly being increased in the pursuit of increasing efficiency and specific power, the effect of bleed cooling air on the engine performance is increasingly becoming important. During the thermodynamic cycle analysis and optimization phase, the cooling bleed air requirement is either neglected or is modelled by simplified correlations, which can lead to erroneous results. In the current research, a physics-based turbine cooling prediction model, based on semi-empirical correlations for heat transfer and pressure drop is developed and verified with turbine cooling data available in the open literature. Based on the validated model, a parametric analysis is performed to understand the variation of turbine cooling requirement with variation in TIT and OPR of future advanced engine cycles. It is found that the existing method of calculating turbine cooling with simplified correlation underpredicts the amount of turbine cooling air for higher OPR and TIT, thus overpredicts the efficiency of the engine.
TOPICS: Cooling, Design, Gas turbines, Turbines, Engines, Thermodynamic cycles, Optimization, Physics, Pressure, Temperature, Heat transfer, Cycles, Pressure drop
Jian Gao, Ronald O. Grover, Venkatesh Gopalakrishnan, Ramachandra Diwakar, Wael Elwasif, K. Dean Edwards, Charles E.A. Finney and Russell A. Whitesides
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039735
The prospect of analysis-driven pre-calibration of a modern diesel engine is extremely valuable in order to significantly reduce hardware investments and accelerate engine designs compliant with stricter fuel economy regulations. Advanced modeling tools, such as CFD, are often used with the goal of streamlining significant portions of the calibration process. The success of the methodology largely relies on the accuracy of analytical predictions, especially engine-out emissions. The standard approach has been to use skeletal kinetic mechanisms (~50 species) which consume acceptable computational time but with degraded accuracy. In this work, a comprehensive demonstration and validation of the analytical pre-calibration process is presented for a passenger car diesel engine using CFD simulations and a GPU-based chemical kinetics solver (Zero-RK, developed at Lawrence Livermore National Laboratory) on high performance computing resources to enable the use of detailed kinetic mechanisms. Diesel engine combustion computations have been conducted over 600 operating points spanning in-vehicle speed-load map, using massively parallel ensemble simulation sets on the Titan supercomputer located at the Oak Ridge Leadership Computing Facility. The results with different mesh resolutions have been analyzed to compare differences in combustion and emissions (NOx, Carbon Monoxide CO, Unburned Hydrocarbons UHC, and Smoke) with actual engine measurements. The results show improved agreement in combustion and NOx predictions with a large n-heptane mechanism consisting of 144 species and 900 reactions with refined mesh resolution; however; agreement in CO, UHC and Smoke remain a challenge.
TOPICS: Computational fluid dynamics, Calibration, Chemistry, Diesel engines, Steady state, Graphics processing units, Combustion, Engines, Smoke, Simulation, Emissions, Nitrogen oxides, Heptane, Fuel efficiency, Leadership, Hardware, Stress, Resolution (Optics), Carbon, Modeling, Vehicles, Automobiles, Chemical kinetics, Engine design, Regulations, Corporate average fuel economy, Computation
Dimitrios Chatzianagnostou and Stephan Staudacher
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039704
Composite cycle engines comprising piston engines as well as piston compressors to achieve hecto pressure ratios represent a target area of current research surpassing gas turbine efficiency. An unclear broad range of design parameters is existing to describe the design space of piston machines for this type of engine architecture. Previously published work focuses on thermodynamic studies only partially considering limitations of the design space. To untie the problem of piston engine design, a dimensional analysis is carried out reducing the number of parameters and deriving two basic similarity relations. The first one is a function of the mean effective pressure as well as the operating mode and is a direct result from the thermodynamic cycle. The second one is constituted of the stroke-to-bore ratio and the ratio of effective power to piston surface. Similarity relations regarding the piston compressor design are based on Grabow [1]. A further correlation for piston compressors is based on the specific compression work and the piston speed. In Part I data of existing piston engines have been subjected to the above similarity parameters unveilling the state of the art design space. This allows a first discussion of current technological constraints. Applying this result to the composite cycle engine gives the design space and a first classification as a low-speed engine. Investigating various design points in terms of number and discplacement volume of cylinders confirms the engine speed classification. Part II will expand this investigation using preliminary design studies.
TOPICS: Composite materials, Engines, Design, Cycles, Pistons, Piston engines, Compressors, Pressure, Machinery, Dimensional analysis, Thermodynamic cycles, Gas turbines, Compression, Cylinders
Bryan P. Maldonado and Anna G. Stefanopoulou
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039728
At a given speed and load, the spark advance (SA) is tuned to reach the maximum break torque (MBT) timing to maximize efficiency. The use of exhaust gas recirculation (EGR) can further improve fuel economy at the same speed and load. As EGR increases, MBT moves towards a more advanced timing that can be limited by the high variability in the combustion process, reflected in unacceptable torque fluctuations. This variability is rapidly increased by the random occurrence of partial burns and/or misfires. In order to operate close to the misfire limit, a stochastic misfire controller has been designed to momentarily move from an undesired to an allowable misfire rate, without significantly increasing variability in the combustion process. Control-oriented models for the combustion process and misfire events are discussed. Simulation of the closed-loop system shows that the feedback misfire controller, on average, stays closer to the misfire limit than a more conventional controller designed to react when a misfire is detected.
TOPICS: Combustion, Cycles, Feedback, Exhaust gas recirculation, Control equipment, Stress, Torque, Fluctuations (Physics), Closed loop systems, Corporate average fuel economy, Simulation, Fuel efficiency
Cosmin E. Dumitrescu, Vishnu Padmanaban and Jinlong Liu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039616
Improved internal combustion (IC) engine simulations of natural gas (NG) combustion under conventional and advanced combustion strategies have the potential to increase the use of NG in the transportation sector in the United States. This study focused on the physics of turbulent flame propagation. The experiments were performed in a single-cylinder heavy-duty compression-ignition (CI) optical engine with a bowl-in piston that was converted to spark ignition (SI) NG operation. The size and growth rate of the early flame from the start of combustion until the flame filled the camera field-of-view were correlated to combustion parameters determined from in-cylinder pressure data, under low-speed, lean-mixture, and medium-load conditions. Individual cycles showed evidence of turbulent flame wrinkling, but the cycle-averaged flame edge propagated almost circular in the 2D images recorded from below. More, the flame-speed data suggested a different flame propagation inside a bowl-in piston geometry compared to a typical SI engine chamber. For example, while the flame front propagated very fast inside the piston bowl, the corresponding mass fraction burn was small, which suggested a thick flame region. In addition, combustion images showed flame activity after the end of combustion inferred from the pressure trace. All these findings support the need for further investigations of flame propagation under conditions representative of CI engine geometries, such as those in this study.
TOPICS: Natural gas, Flames, Spark-ignition engine, Combustion, Pistons, Ignition, Cycles, Cylinders, Turbulence, Engines, Pressure, Physics, Transportation systems, Compression, Simulation, Stress, Engineering simulation, Diesel engines, Geometry
Suhyeon Park, David Gomez Ramirez, Siddhartha Gadiraju, Sandeep Kedukodi, Srinath V. Ekkad, Hee Koo Moon, Yong Kim and Ram Srinivasan
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039462
In this study, we provide detailed wall heat flux measurements and flow details for reacting flow conditions in a model combustor. Heat transfer measurements inside a gas turbine combustor provides one of the most serious challenges for gas turbine researchers. Gas turbine combustor improvements require accurate measurement and prediction of reacting flows. Flow and heat transfer measurements inside combustors under reacting flow conditions remains a challenge. The mechanisms of thermal energy transfer must be investigated by studying the flow characteristics and associated heat load. This paper experimentally investigates the effects of combustor operating conditions on the reacting flow in an optical single can combustor. The swirling flow was generated by an industrial lean pre-mixed, axial swirl fuel nozzle. Planar particle image velocimetry (PIV) data were analyzed to understand the characteristics of the flow field. Liner surface temperatures were measured in reacting condition with an infrared camera for a single case. Experiments were conducted at Reynolds numbers ranging between 50000 and 110000 (with respect to the nozzle diameter, D_N); equivalence ratios between 0.55 and 0.78; and pilot fuel split ratios of 0 to 6%. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a fundamental part of the investigation. Self-similar characteristics were observed at different reacting conditions. Swirling exit flow from the nozzle was found to be unaffected by the operating conditions with little effect on the liner. Comparison between reacting and non-reacting flows yielded very interesting and striking differences.
TOPICS: Flow (Dynamics), Combustion chambers, Wall temperature, Gas turbines, Nozzles, Heat transfer, Fuels, Swirling flow, Heat flux, Turbulence, Kinetic energy, Reynolds number, Stress, Particulate matter, Heat, Temperature
Zhang Zilai, Shusheng Zang, Ge Bing and Sun Peifeng
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039463
The paper presents an experimental investigation of the thermoacoustic oscillations detection in a lean premixed pre-evaporation (LPP) combustor using acoustic signals. The LPP model combustion chamber oscillation combustion test platform was designed and built, the thermal parameters signal, the acoustic signal and the dynamic pressure signal were collected under the steady condition and the transition condition, and been analyzed comparatively. The experimental result shows that, at the same inlet air speed, the dominant frequency of the combustion chamber is proportional to the thermal load, while at the same fuel flow, the main frequency of the combustion chamber does not change with the changing of air speed. In addition, the doubling frequency of the acoustic signal is more obvious than the pressure signal’s, which show that the interference of the acoustic signal is less. In the transition condition, the pulse energy of the acoustic signal is obviously increased after ignition. The dominant frequency energy increases when the working condition begins to change in the stable to oscillation combustion condition. The dominant frequency energy decreases when the working condition begins to change in the oscillation to stable combustion condition. During the flameout condition, the oscillating energy begins to decay from the high frequency region. For the acoustic signal is less disturbed than the pressure signal and it can obtained the same result with the pressure signal in the oscillation condition and the transition condition, acoustic diagnostic is an auxiliary method for combustion oscillation in LPP combustor
TOPICS: Oscillations, Combustion, Acoustics, Combustion chambers, Evaporation, Signals, Pressure, Flow (Dynamics), Fuels, Ignition, Stress
Joseph K. Ausserer, Marc D. Polanka, Paul J. Litke and Jacob A. Baranski
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039466
The rapid expansion of the market for remotely-piloted aircraft (RPA) includes a particular interest in 10-25 kg vehicles for monitoring, surveillance, and reconnaissance. Power-plant options for these aircraft are often 10-100 cm3 internal combustion engines (ICEs). The present study builds on a previous study of loss pathways for small, two-stroke engines by quantifying the trade space among energy pathways, combustion stability, and engine controls. The engine controls considered in the present study are speed, equivalence ratio, combustion phasing (ignition timing), cooling-air flow rate, and throttle. Several options are identified for improving COTS-engine efficiency and performance for small, remotely-piloted aircraft. Shifting from rich equivalence ratios to lean operation results in a 4% (absolute) increase in fuel-conversion efficiency at the expense of a 10% decrease in power. The stock, linear timing maps are excessively retarded below 3000 rpm, and replacing them with custom spark timing improves ease of engine start. Finally, in comparison with conventional-size engines, the fuel-conversion efficiency of the small, two-stroke ICEs improves at throttled conditions by as much as 4-6% (absolute) due primarily to decreased short-circuiting. A case study shows that at 6000 rpm, the 3W 55i engine at partial throttle will yield an overall weight saving compared to the 3W 28i engine at wide-open throttle for missions exceeding 2.5 hr (at a savings of ~5 g/min).
TOPICS: Engines, Two-stroke engines, Aircraft, Internal combustion engines, Combustion, Fuels, Ignition, Surveillance, Power stations, Vehicles, Weight (Mass), Stability, Flow (Dynamics), Cooling
Technical Brief  
Binyang Wu, Zhiqiang Han, Xiaoyang Yu, Shuikai Zhang and Xiaokun Nie
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039461
Matching of a two-stage turbocharging system is important for high efficiency engines because the turbocharger is the most effective method of exhaust heat recovery. In this study, we propose a method to match a two-stage turbocharging system for high efficiency over the entire range of operational conditions. Air flow is an important parameter because it influences combustion efficiency and heat load performance. First, the thermodynamic parameters of the engine and the turbocharging system are calculated in eight steps for selecting and matching the turbochargers. Then, by designing the intercooler intensity, distribution of pressure ratio, and compressor operational efficiency, it is ensured that the turbochargers not only meet the air flow requirements but also operate with high efficiency. The concept of minimum total drive power of the compressors is introduced at a certain boost pressure. It is found that the distribution of pressure ratio of the high- and low-pressure turbocharger should be regulated according to the engine speed by varying the rack position of the variable geometry turbocharger (VGT) to obtain the minimum total drive work. It is verified that two-stage turbochargers have high efficiency over the entire range of operational conditions by experimental research. Compared with the original engine torque, low-speed torque is improved by more than 10%, and the engine low fuel consumption area is broadened.
TOPICS: Engines, Turbochargers, Pressure, Torque, Compressors, Air flow, Heat recovery, Stress, Design, Exhaust systems, Geometry, Fuel consumption, Heat, Combustion
Chirag Trivedi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039423
This work investigates the unsteady pressure fluctuations and inception of vortical flow in a hydraulic turbine during no-load-speed conditions. The focus of the present study is to experimentally measure and numerically characterize time-dependent pressure amplitudes in the vaneless space, runner and draft tube of a model Francis turbine. The numerical model consists of the entire turbine including Labyrinth seals. Compressible flow was considered for the numerical study to account for the effect of flow compressibility and the reflection of pressure waves. The results clearly showed that the vortical flow in the blade passages induces high-amplitude stochastic fluctuations. A distinct flow pattern in the turbine runner was found. The flow near the blade suction side close to the crown was more chaotic and reversible (pumping), whereas the flow on the blade pressure side close to the band was accelerating (turbine) and directed toward the outlet. Flow separation from the blade leading edge created a vortical flow, which broke up into four parts as it traveled further downstream and created high-energy turbulent eddies. The source of reversible flow was found at the draft tube elbow, where the flow in the center core region moves toward the runner cone. The vortical region located at the inner radius of the elbow gives momentum to the wall-attached flow and is pushed toward the outlet, whereas the flow at the outer radius is pushed toward the runner.
TOPICS: Stress, Stators, Vortex flow, Large eddy simulation, Francis turbines, Rotors, Flow (Dynamics), Pressure, Blades, Turbines, Fluctuations (Physics), Compressible flow, Flow separation, Hydraulic turbines, Momentum, Compressibility, Waves, Turbulence, Eddies (Fluid dynamics), Suction, Computer simulation, Reflection
Jordan Easter and Stanislav V. Bohac
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039424
Low temperature and dilute Homogenous Charge Compression Ignition (HCCI) and Spark Assisted Compression Ignition (SACI) can improve fuel efficiency and reduce engine-out NOx emissions, especially during lean operation. However, under lean operation these combustion modes are unable to achieve EPA Tier 3 emissions standards without the use of lean aftertreatment. The TWC-SCR lean aftertreatment concept investigated in this work uses periodic rich operation to produce NH3 over a TWC to be stored on an SCR catalyst for NOx conversion during subsequent lean operation. Experiments were performed with a modified 2.0 L gasoline engine that was cycled between lean HCCI and rich SACI operation and between lean and rich SI (spark ignited) combustion to evaluate NOx conversion and fuel efficiency benefits. Results are compared to a baseline case in which the engine is always operated at stoichiometric conditions. With the configuration used in this study, lean/rich HCCI/SACI operation resulted in a maximum NOx conversion efficiency of only 10%, while lean/rich SI operation resulted in a maximum NOx conversion efficiency of 60%. If the low conversion efficiency of HCCI/SACI operation could be improved through higher brick temperatures or additional SCR bricks, calculations indicate TWC-SCR aftertreatment has the potential to provide attractive fuel efficiency benefits and near-zero tailpipe NOx. Calculated potential fuel efficiency improvement relative to stoichiometric SI is 7 to 17% for lean/rich HCCI/SACI with zero tailpipe NOx and -1 to 5% for lean/rich SI with zero tailpipe NOx emissions.
TOPICS: Combustion, Gasoline engines, Homogeneous charge compression ignition engines, Nitrogen oxides, Fuel efficiency, Emissions, Compression, Ignition, Engines, Bricks, Low temperature, Catalysts, Temperature
Alessandro Ferrari and Federica Paolicelli
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039348
An analysis of a Common Rail fuel injection system has been performed in the frequency domain. A lumped parameter model of the high-pressure hydraulic circuit, from the pump delivery to the injector nozzle, has been realized. The model outcomes have been validated through a comparison with frequency values that were obtained by applying the peak-picking technique to the experimental pressure traces acquired from the pipe that connects the injector to the rail. The eigenvectors associated with the eigenfrequencies have been physically interpreted, thus providing a methodology for the modal analysis of hydraulic systems. Three main modes have been identified and the possible resonances with the external forcing terms have been discussed. The rail is involved in the first two vibration modes. In the first mode, the rail performs a decoupling action between the high-pressure pump and the downstream hydraulic circuit. Consequently, the oscillations generated by the pump flow rates mainly remain confined to the pipe between the pump and the rail. The second mode is centered on the rail and involves a large part of the hydraulic circuit, both upstream and downstream of the rail. Finally, the third mode principally affects the injector internal hydraulic circuit. It has been found that some geometric features of the injection apparatus have a significant effect on the system dynamics and can induce hydraulic resonance phenomena. Furthermore, the lumped parameter model has been used to determine a simplified transfer function between the rail pressure and injected flow-rate.
TOPICS: Pressure, Fuels, Transfer functions, Rails, Modal analysis, Hydraulic circuits, Pumps, Ejectors, Lumped parameter models, High pressure (Physics), Flow (Dynamics), Resonance, Pipes, Common rail fuel injectors, Oscillations, System dynamics, Nozzles, Performance, Vibration, Eigenvalues, Hydraulic drive systems
Fengnian Zhao, Penghui Ge, Hanyang Zhuang and David L.S. Hung
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039082
In-cylinder air flow structure makes significant impacts on fuel spray dispersion, fuel mixture formation, and flame propagation in spark ignition direct injection (SIDI) engines. While flow vortices can be observed during the early stage of intake stroke, it is very difficult to clearly identify their transient characteristics because these vortices are of multiple length scales with very different swirl motion strength. In this study, a high-speed time-resolved 2D particle image velocimetry (PIV) is applied to record the flow structure of in-cylinder flow field along a swirl plane at 30 mm below the injector tip. First, a discretized method using flow field velocity vectors is presented to identify the location, strength, and rotating direction of vortices at different crank angles. The transients of vortex formation and dissipation processes are revealed by tracing the location and motion of the vortex center during the intake and compression strokes. In addition, an analysis method known as the wind-rose diagram, which is implemented for meteorological application, has been adopted to show the velocity direction distributions of 100 consecutive cycles. Results show that there exists more than one vortex center during early intake stroke and their fluctuations between each cycle can be clearly visualized. In summary, this approach provides an effective way to identify the vortex structure and to track the motion of vortex center for both large-scale and small-scale vortices.
TOPICS: Engines, Vortices, Ignition, Flow (Dynamics), Transients (Dynamics), Fuels, Cycles, Cylinders, Flames, Compression, Wind, Meteorology, Ejectors, Sprays, Particulate matter, Air flow, Energy dissipation, Fluctuations (Physics)
Viktor Józsa and Attila Kun-Balog
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039056
The continuously stringent emission standards force the burner development to the lean combustion regime to have low CO and NOx emissions. Nevertheless, combustion stability issues emerge since the desired operating point approaches the lean blowout limit. In this paper, an atmospheric, 15 kW lean premixed prevaporizing-type swirl burner, equipped with a plain jet airblast atomizer, was investigated at various atomizing pressures and combustion air flow rates, using diffusers from 0° to 60° in 15°steps. Both the 15° and the 30° diffusers provided a 42% extended lean blowout stability compared to the original burner. However, the superior stability regime was encumbered by a rapidly increasing CO concentration while the NOx emission vanished due to the reduced mixture residence time. Interestingly, the 60° diffuser provided a moderately extended blowout stability limitation while the NOx emission slightly increased and the CO emission reduced compared to the original burner.
TOPICS: Stability, Diffusers, Pollution, Emissions, Nitrogen oxides, Combustion, Air flow
Alireza Naseri, Shervin Sammak, Masoud Boroomand, Alireza Alihosseini and Abolghasem M. Tousi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039057
An experimental study has been carried out to determine how inlet total-pressure distortion affects the performance of a micro gas turbine. An inlet simulator is designed and developed to produce and measure distortion patterns at the inlet to the gas turbine. An Air Jet Distortion Generator is used to produce non-uniform flow patterns and total pressure probes are installed to measure steady-state total-pressure distribution at the inlet. A set of wind tunnel tests have been performed to confirm the fidelity of distortion generator and measuring devices. Tests are carried out with the gas turbine exposed to inlet flow with 60-degree, 120-degree, and 180-degree circumferential distortion patterns with different distortion intensities. The Performance of the gas turbine has been measured and compared with that of clean inlet flow case. Results indicate that the gas turbine performance can be affected significantly facing with intense inlet distortions.
TOPICS: Micro gas turbines, Gas turbines, Pressure, Flow (Dynamics), Generators, Probes, Steady state, Wind tunnels, Air jets
Tao Wang, Yong-sheng Tian, Zhao Yin, Da-yue Zhang, Ming-ze Ma, Qing Gao and Chunqing Tan
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038992
This paper proposes a Hybrid Method (HMRC) comprised of a Radial Basis Function (RBF) neural net algorithm and Component-level Modeling Method (CMM) as a real-time simulation model for triaxial gas turbines with variable power turbine guide vanes in MATLAB/SIMULINK. The sample size is decreased substantially after analyzing the relationship between high and low pressure shaft rotational speeds under dynamic working conditions, which reduces the computational burden of the simulation. The effects of the power turbine rotational speed on overall performance are also properly accounted for in the model. The RBF neural net algorithm and CMM are used to simulate the gas generator and power turbine working conditions respectively, in the HMRC. The reliability and accuracy of both the traditional single CMM model (SCMM) and HMRC model are verified using gas turbine experiment data. The simulation models serve as a controlled object to replace the real gas turbine in a hardware-in-the-loop simulation experiment. The HMRC model shows better real-time performance than the traditional SCMM model, suggesting that it can be readily applied to hardware-in-the-loop simulation experiments.
TOPICS: Hardware, Gas turbines, Geometry, Simulation experiments, Turbines, Coordinate measuring machines, Algorithms, Artificial neural networks, Simulation models, Guide vanes, Matlab, Generators, Modeling, Pressure, Reliability, Simulation

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