bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Performance Analysis of a Turbocharged PEMFC System
Authors: Mantelli Luca , Iester Federico , Crosa Silvia , Bozzolo Michele , Magistri Loredana , Massardo Aristide 
Published: August 2024

Abstract
Proton-exchange membrane fuel cell (PEMFC) systems are one of the most promising technologies for the decarbonization of the transportation and power sectors, thanks to their high efficiency, fast dynamics, and use of hydrogen as fuel.
This article investigates the dynamics of an innovative layout based on the integration of two PEMFC stacks with an electrically assisted turbocharger (TC), which is characterized by high power density and efficiencies up to almost 60%, making it very interesting for transportation applications.
A detailed dynamic model of the TC-PEMFC is developed in Matlab-Simulink including all the main devices of the cathode, anode and cooling circuits. This model is used to study the dynamic performance of the system, considering the fluid-dynamic and thermal transients of its components.
At first, the model is used to simulate the response of the TC-PEMFC to step changes of multiple input variables: openings of fuel valve and humidifier bypass valve, rotational speeds of TC, blower and cooling pump. These simulations highlight the strong sensitivity of the system to the fuel valve opening, making the need for a feedback controller clear. Many control logics are then implemented on the model to keep the operative parameters of the TC-PEMFC within an acceptable range.
The dynamic model is used to simulate the performance of the TC-PEMFC system during different power load ramps. From the results of these simulations, it is possible to assess the effectiveness of each controller and to verify the compliance of all the system constraints. During load increases, no issues are detected. Even for the fastest considered ramp rate, equal to 100 A/s, proper operation of the system is always guaranteed, and the final power setpoint is reached in less than 5 s. On the other hand, load reductions are limited by the possibility of compressor surge. A maximum ramp rate of 35 A/s is identified in this case. To overcome this limit, a possible modification to the control logics is tested in the final part of the study.
Numerical and Experimental Comparison of a Single Stage Axial sCO2 Compressor
Authors: Ghimire Saugat , Holder Justin , Ha Matthew , Turner Mark , Kang Jeongseek , Morris Scott C. , Sedlacko Kyle , Held Timothy J. 
Published: August 2024

Abstract
The growing shift towards renewable energy sources has underscored the need for large-scale, environmentally sustainable energy storage solutions. Among these solutions, the Supercritical Carbon Dioxide (sCO2) power cycle has emerged as a promising avenue for advanced energy conversion. In such systems, the performance of the compressor is critical to the overall system’s performance and efficiency. A multistage axial compressor has been designed using an optimization-based methodology and the first stage of this design has been built and tested experimentally. This paper compares rigorous computational simulations with detailed experimental data including the readings from total pressure rakes, total temperature rakes, mass flow measurements and casing static pressure measurements. In addition, average measured tip clearance values are used in the simulations along with the detailed prescription of the experimental boundary conditions. The Computational Fluid Dynamics (CFD) simulations do show very good comparison with the data. Additionally, the study serves as a robust validation of the design and optimization process, as the experimental results closely mirror the CFD predictions. Furthermore, computational simulations offer a deeper understanding of the associated flow physics within the compressor. The real gas effects of (sCO2) are also studied and described in how they affected the design and testing, especially considering running to the right corrected flow and corrected speed. Reynolds number effects are also studied and described.
Validation of a Methodology to Assess the Flutter Limit Cycle Oscillation Amplitude of Low-Pressure Turbine Bladed-Disks - Part II: Shaft Speed Effects
Authors: Escudero Alvaro , Rodríguez-Blanco Salvador , Corral Roque 
Published: August 2024

Abstract
The effect of the operating conditions on the vibration amplitude trends of an isolated low-pressure turbine rotor is described. The study utilizes an analytical model correlating the aerodynamic and dry-friction work introduced in Part I of the paper. In this Part II, the analysis has been extended to incorporate the influence of shaft speed. The force distribution and the penetration length of the fir-tree contact surfaces are key parameters within the heuristic micro-slip model used to characterize the friction forces. These parameters change with shaft speed, consequently influencing the dry-friction work involved in the process. The model is closed with numerical simulations to compute the aerodynamic damping, and it is compared against experimental data gathered from the experimental campaign detailed in Part I. The results demonstrate a significant impact of the shaft speed on flutter vibration amplitude. It has been observed that the vibration amplitude reaches a maximum near the on-design conditions. The analytical model can correctly capture this trend indicating that the essential physics is retained in it. Nonlinear friction, mistuning and 3D unsteady aerodynamics have shown to play a predominant role to explain the change of vibration amplitude with the shaft speed.
Performance Assessment of Smart District Heating Networks: The Influence of Distributed (Co)Generation on the Network Primary Energy Consumption
Authors: Alleori Riccardo , Ancona Maria Alessandra , Branchini Lisa , Melino Francesco , Ottaviano Saverio 
Published: August 2024

Abstract
The European and US strategies — providing for energy efficiency increase, pollutant emissions reduction and fossil fuel consumption reduction — leads to an increasing attention on the concept of complex energy networks and/or smart cities. In this scenario, an innovative approach in the heat sector is the integration between District Heating Networks and distributed generation systems, such as solar thermal panels or micro-combined heat and power generators. This approach allows to realize a bidirectional thermal energy exchange at the final users and, consequently, the development of the so-called Smart District Heating in which one or more of the thermal users are converted into prosumers.
The aim of this paper is — starting from the thermo-hydraulic analysis of an existing network located in the North of Italy which is set as case study — the evaluation of the influence on the network energy performance of the thermal prosumers location and distributed generation system typology, in order to optimize the network smart transformation and operation. Based on the optimization analysis, two smart configurations are proposed (respectively considering the transformation of one and two traditional users into smart ones) and analyzed for a whole year of operation. The analysis allowed to appropriately design the distributed cogeneration systems and to quantify the annual obtainable reduction in the electrical consumption for the pumping station, network thermal losses and primary energy consumption.
The results show that the conversion of a traditional District Heating Network into a smart one with Combined Heat and Power generators allows an increase in efficiency and goes towards the rational use of fossil fuels, increasing the fuel utilization factor of the whole system. This study also shows how the choice of the optimal smart users should be developed with reference to the introduction of two bidirectional substations in the same network.
Experimental Characterization and Emission Analysis of Hydrogen-Enriched Fuel Blends in Gas Turbine Applications
Authors: Bonuso Sara , Marseglia Guido , Di Gloria Pasquale , Otón-Martínez Ramón Antonio , Ficarella Antonio , De Giorgi Maria Grazia 
Published: August 2024

Abstract
The gas turbine industry is actively exploring lean premixed combustion with hydrogen (H2)-enriched fuel blends to decrease greenhouse gas and Nitrogen Oxides (NOx) emissions. Hydrogen enrichment is a crucial area for investigation, aiming to enhance combustion processes and reduce emissions. This study explores the potential of hydrogen-enriched blends to improve energy efficiency and mitigate greenhouse gas emissions.
Two flame configurations — lean and rich — are investigated at constant thermal power outputs. In rich condition and pure CH4 a lifted flame is established. Scenarios with incremental H2 additions to air/methane mixtures are examined using chemiluminescence techniques and spectral filtering for OH species. Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD) methods identify coherent structures and frequency ranges of flame fluctuations. Acoustic microphone analysis provides insights into flame fluctuations, and Power Spectral Density (PSD) evaluation is performed. Measurements of exhaust temperature and emissions (NOx, CO2) further contribute to understanding hydrogen’s role in cleaner and more efficient combustion.
Techno-Economic Analysis of Green Hydrogen Energy Storage in a Cryogenic Flux Capacitor
Authors: Schmitt Joshua , Roychowdhury Bikram , Swanger Adam , Otto Marcel , Kapat Jayanta 
Published: August 2024

Abstract
The Cryogenic Flux Capacitor (CFC) is a cold, dense energy storage core that is being studied in the cryo-compressed, about 300 bar and 80K, region of gaseous hydrogen (GH2) storage and liquid hydrogen (LH2) region near the normal boiling point. Hydrogen storage is improved by physically bonding the molecules within the nanoscale pores of the aerogel composite blanket material. The process of bonding or debonding is governed by principles of physical adsorption (physisorption) and thermodynamics. The large surface area afforded by the nanoporous aerogel (∼1,000 m2/g) allows its storage performance to easily exceed capacities of high-pressure GH2 storage for an equivalent volume. With the integrated aerogel, subscale tests have shown that storage is increased by about 36% over a simple tank filled with GH2 at the same operating temperature and pressure. For LH2 conditions, the CFC is shown to operate at improved densities, but testing is ongoing.
For the techno-economic analysis (TEA), the source of hydrogen is compared between onsite steam methane reforming (SMR) and onsite solar photovoltaic (PV) panels providing power to electrolyzers to produce green GH2. The TEA compares pure hydrogen produced at a small scale for a 25 MW power system and at a large scale in a 500 MW power system. The system allowed for hydrogen imports and exports at a set price with a tank sized for 10 hours of power production. The two power producing technologies are a combined cycle gas turbine (CCGT) and hydrogen fuel cells. The SMR system uses natural gas as an input and includes a carbon capture and storage (CCS) system. The levelized cost of electricity (LCOE), levelized cost of hydrogen (LCOH), and levelized cost of storage (LCOS) are developed based on the capital cost and operating cost of the systems.
The results are shown for current costs using a 2021 benchmark and DOE projections for cost improvements by 2030. The TEA showed that onsite hydrogen generation from SMR has an LCOH of about 1.4 to 2 USD per kg over the life of the plant and the PV hydrogen production LCOH is about 5.2 to 5.5 USD per kg. The LCOS of conventional GH2 systems is estimated to be $210/MWh and cost of storage for LH2 systems is $205/MWh for fuel cell systems and $249/MWh for CCGT systems. CFC improved the LCOS of all these systems to $198/MWh, $191/MWh and $233/MWh respectively. The LCOE also improved with conventional systems between $171/MWh and $228/MWh improved by CFC to between $167/MWh and $212/MWh. Using projections for improvement in costs following DOE’s goals by 2030, green hydrogen improved to as low as $78/MWh LCOS and LCOE for conventional cases. CFC improved over conventional storage with the lowest LCOS being $62/MWh and the lowest LCOE being $73/MWh. These results correspond to an LCOH of $2/kg. Finally, the TEA shows how LCOE is improved for hydrogen conditioning and storage over conventional systems and caverns in the 10 to 50 hour range.
Pilot-Scale Testing of a Transcritical CO2-Based Pumped Thermal Energy Storage (PTES) System
Authors: Held Timothy J. , Miller Jason , Mallinak Jason , Avadhanula Vamshi , Magyar Luke 
Published: August 2024

Abstract
As the world moves toward an electrical generation system that relies heavily upon non-dispatchable resources such as solar photovoltaic and wind power, reliable, low-cost means to store electrical energy and dispatch it as supply and demand fluctuate are vital. Pumped thermal energy storage (PTES) consists of a reversible heat pump / heat engine cycle, where thermal energy is transferred between two reservoirs, one at high temperature and the other at low temperature. During the charging phase of operation, thermal energy is extracted from a low temperature reservoir (LTR), increased in temperature, and then stored in a high temperature reservoir (HTR) using an electrically driven heat pump cycle. During the generating process, the stored heat in the HTR is converted back into electricity using a heat engine cycle — essentially the heat pump operating in reverse — and the residual low-temperature thermal energy is stored in the LTR.
A simplified thermodynamic analysis of a general PTES system provided insights into the governing physics of the system, which were used to select the cycle architecture, working fluid and thermal reservoirs. A pilot-scale (c.a. 100 kW) PTES system using CO2 as the working fluid was then designed, built and tested, including two HTR concepts and an ice/water slurry LTR. Data from this test sequence was used to validate component and system steady-state performance and transient system models. Further, this experience has informed the conceptual design of a 100 MW, 12 hour PTES system that is planned for deployment in 2028.
Nonpremixed Approaches for Fuel Flexible, Low NOx Combustors in High-Efficiency Gas Turbines
Authors: Emerson Benjamin , Patel Shivam J. , Gubbi Srujan , McKinney Randal G. , Wu David , Noble David R. , Lieuwen Timothy C. 
Published: August 2024

Abstract
Lean, premixed combustor designs have almost completely replaced non-premixed combustors for industrial gas turbine applications where NOx emissions are regulated. Nonetheless, these designs have also introduced turndown and fuel flexibility constraints and made combustion instabilities and flashback more problematic. Moreover, modern high-efficiency machines have high enough turbine inlet temperatures that additional fuel staging is needed to manage NOx. These issues are becoming increasingly problematic in a decarbonizing energy sector. First, combustors must also be able to accommodate a range of fuels, including hydrogen or ammonia, whose levels can vary from 0–100%, blended with natural gas. Second, operational flexibility for gas turbines will become increasingly important, as their role evolves from a primary provider of energy to one of providing capacity and resilience. Moreover, they must compete for these services with a host of new technologies, including energy storage and fuel cells, and these cost-pressures require higher-efficiency machines. This pushes pressures and flame temperatures higher, both of which accelerate NOx formation rates. In this environment, having systems with broad operational boundaries, ultra-low emissions, and extreme fuel flexibility will become increasingly important.
The purpose of this paper is to propose nonpremixed, multistage designs for the next generation of high turndown, high fuel flexibility, low NOx combustion designs — referred to here as a Nonpremixed, Rich, Relaxation, Lean (NRRL) combustor. The key concept we explore is non-premixed combustion, followed by additional fuel mixing to locally fuel-rich conditions, a relaxation stage, and then a lean stage. This non-premixed approach can handle essentially any fuel composition, including pure hydrogen, liquid fuels, pure methane, pure ammonia, and any combination in between while breaking the NOx-CO tradeoff and reducing combustion instability risk. This paper provides chemical reactor network modeling calculations to identify key kinetic processes and time scales required for such a concept.
This concept has completely inverted sensitivities from lean, premixed systems which prefer short residence times, low pressures, and low temperatures to minimize NO formation. This concept prefers long residence times, high pressures, and high temperatures, indicating a very different set of design trades for part load and off-design performance.
Wall-Modeled Large Eddy Simulation and Conjugate Heat Transfer for Combustor Aerothermal Applications
Authors: Ansari Naseem , Arguinzoni Carlo , Orsino Stefano , Farokhi Reza , Verma Ishan 
Published: August 2024

Abstract
In modern day gas turbine hot sections, active cooling of liner walls is critical due to extremely high temperatures and long continuous operation. Reduced thermal stress increases the life cycle of engines’ components while meeting the ever-greater demands for cycle efficiency and low operational costs. A secondary flow network can be introduced to shield the metal surfaces by forming a film, increasing the durability and life of the liner. The interactions of the effusion cooling with the cross flow and properly capturing wall effects are critical for accurate heat transfer predictions. High fidelity simulations are used to improve the overall performance and durability of gas turbine engines. The simulations recover the distribution of temperature in both solid and fluid zones, thereby allowing design engineers to develop designs for next generations of gas turbines, along with prognosis of existing engine designs. However, the high level of fidelity is accompanied by computational cost, along with complex numerical modeling approaches, especially for numerical models utilized for the life cycle assessment of gas turbine engines.
This paper uses a numerical study using Ansys Fluent to evaluate Wall-Modeled Large Eddy Simulation (WMLES), along with WALE as sub grid scale model, Conjugate Heat Transfer (CHT), and radiation to explore its benefits for practical use in industrial combustion applications. The predictions from various LES methods vary significantly near the wall, where the solution depends on much finer grid resolution. Various methods for modeling WMLES are compared both in the context of computational accuracy and cost. The simulations are performed using open literature experiments such as heated nozzle exhaust over an effusion cooled plate [1], and air/air effusion/slot cooling combustor liner experiment [2]. The accuracy of the simulation approach is assessed by comparing solid plate temperature data from the experiments. In this study the effects of WMLES-CHT are explored with a focus on thermal coupling, radiation, etc. The comparisons in the paper allow the selection of best practices to accurately model CHT for practical use in gas turbine applications. In general, numerical investigation matches experiments quite well, both qualitatively and quantitatively.
Characterization of Orientation Effects of Spring Energized Seals Using 2D Simulations
Authors: Roeseler Stefan , Volpe Erin , Plessinger Ryan , Noyes Tyler , Motyka Elaine , Shealy Michael , Kweder Jonathan 
Published: August 2024

Abstract
Spring energized seals, such as C-Rings, employ use of a high strength spring (Alloy-90, Alloy 718 etc.) within a soft jacket and hard liner (optional) to create high load, high performance seals. This seal design maintains its highperformance sealing capability due to the high contact pressure between the hardware and the seal jacket that is created due to the combination of the spring and optional liner. As such, spring-energized seals are widely used in critical applications such as nuclear energy and aerospace. As seal environments become more challenging, C-Rings must undergo higher temperatures, pressures, and stresses than before. This work evaluates two C-Ring orientations relative to the high pressure zone (open toward and away from the high pressure) and the effect on seal performance. For both orientations, this work examines several commonly used outer jacket sealing materials: aluminum, silver, and nickel. Spring material and liner material were kept constant for each simulation and remained within recommended design considerations for each outer jacket material. Each design was modeled using two-dimensional (2D) axis-symmetric simulations with the recommended gland/flange dimensions. 2D loading/pressurization steps were applied to each design and were as follows: loading to recommended compression displacement per seal design, then increase the inner diameter pressurization to 10,000 psi. Initial orientation of the C-Ring was away from the high pressure zone, then a similarly designed seal orientation was reversed with its opening toward the high-pressure side of the seal gland, and simulations were conducted as before to show system differences and reactionary responses of the seal. The results of this work indicate that, at high pressure, orientation is an important consideration when designing high performance metallic seals. When the internal area of the seal was subjected to high pressure with the spring oriented toward the high pressure, the liner and jacket were extruded away from the spring, resulting in a decrease in contact pressure; this increases the risk of leak path generation through the center of the seal element. Conversely, when the C-Ring is facing away from the high pressure zone and the outer area of the seal is subjected to high pressure, the spring contacts the outside of the flange and the physical constraint in the system creates additional axial force that increases contact pressure. This behavior is similar to an energizing effect. It was observed through physical trials in development that the force to compress the seal is significantly higher than any energizing effect gained due to system pressure. Secondarily, it was found that orienting the C-Ring away from the high pressure system media allows the seal design exhibit greater spring resilience while also avoiding corrosion and embrittlement effects on the spring from the system environment.