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Accepted Manuscripts

BASIC VIEW  |  EXPANDED VIEW
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  
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  
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  
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  
Guo Bing and Tang Weixiao
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039834
Condensing flow induced vibration (CFIV) of the rotor blade is a tough problem for designers of nuclear turbines because non-equilibrium condensing flow excitation (NECFE) is hard to be directly modeled. Generally, in design, NECFE is assumed as equilibrium condensing flow excitation (ECFE), of which the pressure fluctuations caused by phase temperature difference (PTD) between gaseous and liquid are ignored. In this paper, a novel method to calculate the equivalent load of NECFE based on the principle of virtual work was proposed. This method could consider the effects of PTD-induced pressure fluctuations by simulating non-equilibrium condensation with ANSYS CFX, and improve computational efficiency. Once the equivalent NECFE load is determined, CFIV of the rotor blade, which was modeled as a pretwisted asymmetric cantilever beam, can then be predicted by the finite element method. Additionally, to estimate the effects of PTD-induced pressure fluctuations, comparisons between NECFE and ECFE as well as their induced vibrations were presented. Results show that PTD in nucleation area could change the position and type of shock waves, restructure the pressure distribution as well as enhance the pressure fluctuations. Compared with ECFE, the frequency ingredients and amplitude of the equivalent NECFE load and its induced vibrations are increased. Specifically, the amplitude of the equivalent NECFE load is increased by 9.38%, 15.34% and 7.43% in the tangential component, axial component and torsion moment. The blade vibration responses induced by NECFE are increased by 11.66% and 19.94% in tangential and axial.
TOPICS: Turbine blades, Equilibrium (Physics), Flow (Dynamics), Condensation, Vibration, Steam, Pressure, Stress, Fluctuations (Physics), Blades, Excitation, Rotors, Turbines, Cantilever beams, Shock waves, Temperature, Torsion, Nucleation (Physics), Finite element methods, Virtual work principle, Design, Flow-induced vibrations, Fracture toughness
research-article  
Elio Antonio Bufi and Paola Cinnella
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039837
A fast preliminary design methodology for supersonic ORC (Organic Rankine Cycle) stator and rotor axial turbine blades with low degree of reaction is presented. First, the stator and rotor blade mean-line profiles are designed by using the 2D method of characteristics (MOC), extended to gases governed by general equations of state. We focus more specifically on working fluids with medium to high molecular complexity, operating at thermodynamic conditions such that the fundamental derivative of gas dynamics ?? is lower than one in a significant portion of the flow field. For rotor blades, MOC is combined with a free-vortex method to achieve a smooth deflection of the supersonic incoming flow. A numerical approach is developed for solving the unique incidence problem in the case of gases governed by general equations of state. Both stator and rotor blade geometries designed according to the inviscid MOC model are subsequently corrected to account for the development of viscous boundary layers, by solving the compressible integral boundary layer equations extended to dense gases. The resulting blade designs are assessed by means of CFD simulations based on a high-order finite volume solver equipped with advanced thermodynamic and transport-property models. Properly accounting for dense gas and viscous effects at an early design stage is found to improve the expected performance of ORC turbine rows significantly and delivers valuable baseline profiles for any further optimization.
TOPICS: Design methodology, Turbines, Blades, Rotors, Gases, Stators, Organic Rankine cycle, Flow (Dynamics), Boundary layers, Equations of state, Deflection, Vortices, Engineering simulation, Optimization, Computational fluid dynamics, Design, Fluids, Simulation, Turbine blades, Gasdynamics, Accounting
Discussion  
Arvind Gangoli Rao and Piero Colonna
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039832
The acceptable complexity for any machine is mainly determined by the economic drivers and reliability constraints. In the end, the increase in efficiency achieved by the added complexity should be economically viable. With the global energy scenario changing more rapidly than ever before, due to the increase in renewable energy conversion, the future role of gas turbines (GT) in the power sector is uncertain at the moment. Such uncertainty is not conducive for introducing radical architecture changes, which is why OEMs are trying to push the performance of the current GT configuration further. Although intercooling and reheating are already applied to commercially available stationary GT and it is possible that this development will also be pursued further, the uncertainty with constant volume combustion is arguably high
TOPICS: Combustion, Machinery, Reliability, Gas turbines, Brayton cycle, Renewable energy, Uncertainty
research-article  
Ian Kennedy, Zhihang Chen, Bob Ceen, Simon Jones and Colin Copeland
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039811
Approximately 30% of the energy from an internal combustion engine is rejected as heat in the exhaust gases. An inverted Brayton cycle (IBC) is one potential means of recovering some of this energy. When a fuel is burnt, water and CO2 are produced and expelled as part of the exhaust gases. In an IBC, in order to reduce compression work, the exhaust gases are cooled before compression up to ambient pressure. If coolant with a low enough temperature is available, it is possible to condense some of the water out of the exhaust gases, further reducing compressor work. In this study the condensation of exhaust gas water is studied. The results show that the IBC installed in series on a turbocharged engine can produce an improvement of approximately 5% in BSFC at the baseline conditions chosen and for a compressor inlet temperature of 310 K. The main factors that influence the work output are heat exchanger pressure drop, turbine expansion ratio, coolant temperature and turbine inlet temperature. For conditions when condensation is possible, the water content of the exhaust gas has a significant influence on work output. The hydrogen to carbon ratio of the fuel has the most potential to vary the water content and hence the work generated by the system. Finally, a number of uses for the water generated have been presented, such as to reduce the additional heat rejection required by the cycle. It can also potentially be used for engine water injection, to reduce emissions.
TOPICS: Condensation, Brayton cycle, Exhaust systems, Water, Temperature, Gases, Fuels, Compressors, Coolants, Compression, Heat, Turbines, Underground injection, Pressure, Cycles, Carbon dioxide, Carbon, Heat exchangers, Internal combustion engines, Engines, Turbocharged engines, Emissions, Hydrogen, Pressure drop
research-article  
Martin Wissink, Scott Curran, Chaitanya Kavuri and Sage Kokjohn
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039817
Experimental work on reactivity-controlled compression ignition (RCCI) in a small-bore, multi-cylinder engine operating on premixed iso-octane and direct-injected n-heptane has shown an unexpected combustion phasing advance at early injection timings, which has not been observed in large-bore engines operating under RCCI at similar conditions. In this work, computational fluid dynamics (CFD) simulations were performed to investigate whether spray-wall interactions could be responsible for this result. Comparison of the spray penetration, fuel film mass, and in-cylinder visualization of the spray from the CFD results to the experimentally measured combustion phasing and emissions provided compelling evidence of strong fuel impingement at injection timings earlier than -90 crank angle degrees (°CA) after top dead center (aTDC), and transition from partial to full impingement between -65 and -90°CA aTDC. Based on this evidence, explanations for the combustion phasing advance at early injection timings are proposed along with potential verification experiments.
TOPICS: Engines, Sprays, Compression, Cylinders, Ignition, Computational fluid dynamics, Combustion, Fuels, Simulation, Engineering simulation, Visualization, Heptane, Large-bore engines, Emissions
Technical Brief  
Taher Halawa
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039820
This study presents additional important findings to the results of the research paper; "Optimization of the efficiency of stall control using air injection for centrifugal compressors" published in the Journal of Engineering for Gas Turbines and Power in 2015. The aim of this study is to make a fine determination of the injection angle which provides the best stable condition when the compressor operates close to stall condition. A relatively narrower range of injection angles with smaller intervals was selected comparing to the results of the referred published paper which clarified that the best injection angle is 30 deg. External air was injected close to the diffuser entrance at the shroud surface. Injection was applied with mass flow rate equals 1.5% of the design compressor inlet mass flow rate with injection angles ranged from 16 deg to 34 deg measured from the tangential direction at the vaneless region. It was found that both of injection angles of 28 deg and 30 deg achieved the best results in terms of compressor stabilization but each one of them has a specific advantage comparing to the other one. Using injection angle of 28 deg provided the lowest kinetic energy losses while the best orientation of the fluid through diffuser resulted when using an injection angle of 30 deg.
TOPICS: Compressors, Optimization, Diffusers, Flow (Dynamics), Fluids, Kinetic energy, Design, Gas turbines
research-article  
Matthew Lennie, Alireza Selahi-Moghaddam, David Holst, Georgios Pechlivanoglou, Christian Navid Nayeri and Christian Oliver Paschereit
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039818
I am appealing the no-publish recommendation made during the TE review process
TOPICS: Locks (Waterways), Wind turbines, Vortex shedding
research-article  
Seyfettin Can Gulen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039828
A detailed look at the gas turbine technology over the last three decades clearly shows that an asymptotic limit is reached in thermal efficiency in combined cycle configuration. There is little reason to expect a technology leap anytime soon to change this appreciably as long as the industry sticks to the classic Brayton cycle configuration and the brute force approach of ever higher turbine inlet temperatures. The changing landscape of electric power generation, especially integration of fossil fuel fired technologies with renewable generation and wide variation in natural gas prices, suggests that it is time to look at the direction of future development efforts differently. This paper looks at the need of a paradigm shift in gas turbine combined cycle technology using thermodynamic and economic arguments.
TOPICS: Brayton cycle, Gas turbines, Combined cycles, Thermal efficiency, Temperature, Natural gas, Turbines, Electric power generation, Fossil fuels
research-article  
Seyfettin Can Gulen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039829
Contains discussion and author closure of GTP-17-624.
research-article  
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
research-article  
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
research-article  
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
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
research-article  
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

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