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October 15, 2024 at 11 am CST (Click to Join)
Tennessee Tech
University’s Pressurized SOFC Test Stand Updates and Progress Through 2024
David Schafer
Tennessee Tech University currently has a solid oxide fuel cell (SOFC) test stand capable of testing SOFCs using multiple fuels and at various temperatures and pressures. This test stand allows for the characterization of tubular SOFCs through a DC programmable load cell which allows the building of polarization curves (also known as i-v or v-i curves). The test stand is also built to the conditions an SOFC would experience within an SOFC gas turbine hybrid. The PPATS group here at TnTech continues to make upgrades to this test stand, especially within the last year. In that timeframe, graduate students have improved the test stand to allow for better temperature gradients along the length of the SOFC tube, updated the test stand to allow for a maximum of 2kW SOFC bundle capabilities, and worked towards implementing a mass spectrometer allowing for gas flow composition characterization. The test stand is also being upgraded for more fuels with both ammonia (NH3) and jet fuel capabilities set to be implemented within the next few months. These improvements and upgrades will allow the PPATS team at TnTech to understand the performance and operation of SOFCs and SOFC technologies within larger integrated power generation and propulsion systems for various fuels.
Archived
September 17, 2024 at 11 am CST (Click to watch)
Investigation of Ammonia Fed SOFCC-GT Hybrid System for Commercial Aviation
Griffin Layhew
Carbon emissions can be reduced in the aviation industry with the introduction of electric aircraft and hybridization of existing architecture. A hybrid electric mixed turbofan using ammonia fueled SOFCC-GT could eliminate all carbon emissions while still being able to meet the thrust and power demanded by commercial aircraft for domestic applications. Ammonia was chosen as a carbonless fuel due to its higher volumetric energy density than hydrogen (~1.5x higher), though it lacks in specific energy density compared to hydrogen (~6x less). This higher volumetric energy density, as well as its less restrictive storage solutions, makes ammonia a reasonable candidate for carbonless electric aviation. Though ammonia is considered a candidate fuel, it also has its own operational and safety risks. Ammonia decomposition, called cracking, is an endothermic process requiring external heat to break down into nitrogen and hydrogen that the fuel cells use to generate electrical power. Though the fuel cell’s environment is hospitable for ammonia to crack due to the high operational temperature (750 ºC), as well as catalysts in the ceramic structure, this endothermic reaction could cause a sizable temperature gradient to form along the ceramic tubes, which in turn could result in structural damage to the cell. To mitigate this issue, the ammonia in this system is cracked using the turbine’s exhaust. This recuperation also has the added benefit of increasing system efficiency. Size, weight, and power (SWaP) analysis was integrated with aerodynamics and electrical disciplines to aid in choosing the ideal design from a design space that meets the criteria and requirements for a commercial aircraft. Dynamic models have shown that this hybrid system is able to dynamically react to a given thrust profile, while being able to reduce emissions with increased system efficiencies.
February 13, 2024
Design and Manufacture of an Anode Ejector to Boost System Efficiency of a 1kW SOFC
Fuel cell technologies have existed for several decades and are reaching a more mature stage in development. However, many advances can still be made to boost the overall efficiency of these systems. One such advancement is in the effective control of anode gas throughout the system to increase the overall fuel utilization. This has potential to boost the system’s overall efficiency by ~10% when applied to a Solid Oxide Fuel Cell (SOFC) system. The ejector has seen much success in other applications with much success and use for circulating the anode off-gas within a fuel cell system will be discussed. Specific application within a 1 kW SOFC system is also discussed. A setup for safely testing ejectors separate from the use environment is shown. Several of the tested styles of ejectors and some of these results are given to showcase a few key design points for ejectors. An analytical method for designing an ejector for fuel cell system is presented along with specific design data for a 1kW SOFC system. A novel 3D CFD model using ANSYS Fluent for validation and future testing is also presented.
November 14, 2023 11 am CST (Click to Watch)
This study is part of the on-going research focusing on hybrid power system utilizing solid oxide fuel cell and gas turbine (SOFC-GT) for low emission, highly efficient power generation towards stationary and mobile applications. Pressurization of SOFC is known to provide cell-to-system level benefits in terms of improved power density and integration with bottom cycling device. At this point literature data studying the electrochemical behavior of the SOFC as a function of operating pressure is relatively scarce[[1]], especially for tubular configuration which is considered advantageous toward mobile application. In this study, electrochemical performances of anode supported SOFC tubes (courtesy Special Power Sources LLC, OH) in H2 and CH4 fuels are evaluated at 750oC under different pressures (up to 58 psi) to identify corresponding impact on the electrode reaction kinetics. Electrochemical impedance spectroscopy (EIS) is collected with Solartron 1260/PAR 263 or Gamry 3000 electrochemical testing system in 4-point connection measurement to obtain SOFC impedance spectra as Nyquist and Bode plots. EIS together with scanning electron microscopy (SEM) results indicate correlation between cell performance improvement and anode microstructure as impedance associated with gas mass transport/conversion processes are reduced by pressurization. From non-linear, least-square (NLS) cell impedance fitting, equivalent-circuit model (ECM) is used to characterize impedance responses of different electrode processes at various resonance frequency, such as gas-conversion impedance (GCI) at <1Hz due to concentration gradient along flow channel. Particular pressurization impacts on anode and cathode kinetics are differentiated by adjusting respective reactants partial pressures through independent variation of gas component concentration and operation pressure. The analysis suggest anode response is more dynamically driven by pressure change, while for cathode chemical potential of reactant dominates. Overall, the study demonstrates pressurization can effectively boost cell performance by overcoming both fuel-side and air-sides mass-transport limited processes and certain cell configuration and operation parameters can be more favorable for pressurized SOFC operation.
[1] S. Lee, T. Ohrn, Z. Liu, Z. Xing, R. Goettler. ECS Transactions, 45 (1) 441-452 (2012)
September 26, 2023 11 am CST (Click to Watch )
Zero/Low Emission Commercial Aircraft Powered by Solid Oxide Fuel Cell Turbogenerator Hybrid
Introduction of high efficiency power generation methods to the commercial aviation industry can lead to the reduction of carbon emissions and other environmental impacts. Aircraft are estimated to consume 9% of the transportation energy in the US and 12% of the carbon emissions. The US Energy Information Administration (EIA) projects commercial air travel in terms of seat miles to increase > 60% by 2050. Therefore, there is a strong drive for zero-emissions aircraft or low emission aircraft to off-set the potential increase in emissions. Hybrid electric aircraft provide a path for achieving zero/low-emissions, and the choice of fuel and system architecture is very important. An SOFC combustor hybrid turbogenerator power generation cycle can provide a method for high efficiency power generation that can significantly lower fuel burn and carbon emissions. This paper describes the simulated steady state modeling of the SOFC-C-TG SWaP (size, weight, and power) utilizing the flight conditions and the power requirements of a Boeing 737 class narrow body aircraft which needs a peak power of approximately 30MW. It was found that the SOFC-C-TG is a promising solution for the power generation needs of a fully electric zero/low emission commercial passenger aircraft. The modeling of the dynamics in the thermal fluid interactions used to capture the integrated system behavior is discussed in detail. The system performance of the SOFC-C-TG is also discussed when applied to the flight conditions of a 737-class commercial fully electric aircraft. It was found that the proposed power generation method could be applicable to the power requirements of said fully electric aircraft as well as having comparable range and passenger payload as the typical flight of the 737-class aircraft. The SOFC Combustor (SOFC-C) concept allows for precise thermal management of the SOFC stack which is a critical requirement of an SOFC hybrid system. The SOFC-C allows for the removal of cathode heat exchangers, high temperature valves, and other high thermal mass and slow thermal actuators that have been present in traditional SOFC hybrids. The SOFC-C can do this by utilizing the unspent fuel in the anode-off gas in a combustion process that is then used to maintain the SOFC stack in the desired temperature range. Dynamic simulations of the SOFC-C-TG display the ability to successfully thermally manage the SOFC stack in conjunction with the turbogenerator load to control airflow. The SOFC combustor is designed for increased power density but also allows for a decrease in system complexity.
March 30, 2023 3 pm CST (Click to Watch)
Design and Operation of Solid Oxide Electrochemical Cell Systems for Space Applications
Constraints on modern spacecraft electrical power delivery are created by the overall lack of gravimetric energy density in modern batteries and in particular the inability for solar panels to deliver high power output for a prolonged period of time. To reduce these constraints, we seek to design a solid oxide fuel cell (SOFC) system which will consume onboard bipropellants usually reserved for on-orbit maneuvering thrusters and enhance current fuel cell materials technology to enhance performance and ensure against degradation. Atmosphere independent fuel cells have higher theoretical specific energy than batteries. Solid oxide fuel cells are widely considered to be an ideal power source across a range of industries in the near future due to their high efficiency, high power output potential, and quiet operation. Vehicle implementation, especially in the aerospace field, can benefit from fuel cell operation where the high volumetric energy density of liquid fuels allows for much longer duration operation than electric batteries would allow. In aerospace, mission length, low weight, and high-power output are necessary criterion for any mobile power generation solution. This research aids the progress of solid oxide fuel cell systems for space applications through a multi-scale approach. Microstructural and electrochemical theory is applied to design SOFC electrodes with higher performance while also reducing risk of damage during launch and thermal cycling. Three plant designs, and their respective dynamic models for analysis, are put forward as candidates for power systems utilizing solid oxide electrochemical cells; a hypergolic bipropellant-enabled variant, a regenerative variant, and an electrochemical heat engine.
February 14, 2023 11:00 am CST ( Video not updated)
SWaP Analysis and Optimization for SOFC-C Hybrid System for Commercial Aviation
A solid oxide fuel cell combustor gas turbine hybrid system (SOFC-C-TG) is being considered to generate power for an electrified aircraft. It has been found using steady state and transient modeling that this system can generate enough power for takeoff of a Boeing 737-class aircraft which requires approximately 29MW of power while being more efficient than current state-of-the-art single aisle aircraft. The SOFC-C-TG will have independent modules so that redundancy is built into the system just as a traditional aircraft of this class. The proposed system will use bio-liquified natural gas (Bio-LNG), so it will be a carbon neutral solution while also providing cooling to the aircraft. In this study it will be shown that such a system can be packaged efficiently and be light enough to carry fuel for a flight ranging over six hours. The breakdown of mass will also be examined, and engineering equation solver (EES) will be utilized to optimize the packaging to have minimal mass. The system has also been optimized by varying system parameters such as the turbine inlet temperature and pressure ratio of the compressor to maximize flight time.
January 17, 2023 11:00 am CST (Click to Watch)
Modeling of a SOFC Combustor Hybrid Cycle for Commercial Electric Aviation
Introduction of high efficiency power generation methods to the commercial aviation industry can lead to the reduction of carbon emissions and other environmental impacts. A SOFC combustor hybrid turbogenerator power generation cycle can provide a method for high efficiency power generation. This paper describes the simulated modeling and control of the SOFC-C-TG under a transient flight analysis utilizing the flight conditions and the power requirements of a Boeing 737 class narrow body aircraft which needs a peak power of approximately 29MW. It was found that the SOFC-C-TG is a promising solution for the power generation needs of a fully electric commercial passenger aircraft. The simplified modeling of the dynamics in the thermal fluid interactions are discussed in detail to capture the integrated system behavior. The system performance of the SOFC-C-TG is also discussed when applied to the flight conditions of a 737-class commercial fully electric aircraft and it was found that the proposed power generation method could be applicable to the power requirements of a similar sized fully electric aircraft. A SOFC-C-TG warm up is also discussed as well as preliminary system mass estimates.
December 13, 2022 (Click to Watch)
Constraints on modern spacecraft electrical power delivery are created by the overall lack of gravimetric energy density in modern batteries and in particular the inability for solar panels to deliver high power output for a prolonged period of time. To reduce these constraints, this research study seeks to design a solid oxide fuel cell (SOFC) system which will consume onboard bipropellants usually reserved for on-orbit maneuvering thrusters and enhance current fuel cell materials technology to enhance performance and ensure against degradation. Atmosphere independent fuel cells have higher theoretical specific energy than batteries, even considering developments in the next decade (eg. hydrazine/NTO pairing has nominally over 11 times the specific energy of primary lithium sulfate batteries, 1.65 kWh/kg vs 0.148 kWh/kg respectively). Dynamic modeling will elucidate system components and operation critical to safe, efficient power delivery of such a high temperature fuel cell. However, for usage of SOFCs to be feasible, certain disadvantages, such as their high operating temperature, electrochemical losses, and high cost of manufacturing, must be solved. In particular, the field of materials research has a unique position of being able to quickly and simultaneously solve many of these issues through the development of material structures that do not currently exist commercially. The microstructures present in SOFC electrodes play a vital role in improving overall cell performance. To that end, a theoretical effective-medium model has been created to facilitate the design of 3D printed electrodes. This model factors in microstructure parameters, mass transfer, ionic and electrical transport, and gas-surface electrochemical reactions inside the electrodes. The technique of functional material grading, which has begun to see wide research and commercial usage for such problems as acoustic impedance matching, thermal control, and mechanical design has been leveraged for the enhancement of fuel cell electrodes. Multiobjective optimization of the effective-medium model reveals functional grading profiles which would be useful for enhanced performance and stability for long-term fuel cell usage. The interplay of system design and material component design serves as a template for future aerospace design studies.
November 15, 2022 (Click to Watch)
An electrified aircraft with bio-liquified natural gas (Bio-LNG) as its primary cooling and energy source is being suggested as a carbon neutral alternative to current aircraft propulsion systems. The aircraft will use 2 MW or greater cryogenic electric motors to produce the thrust necessary for sustained flight. The heat generated by the electric motors limits the current density thus requiring advanced cooling systems to reach the desired power density. Bio-LNG has at least ten times more thermal heat sink potential when compared to jet fuels and the proposed system takes advantage of the phase change to accomplish this. The use of the Carbon Neutral Liquid Fuel (CNFL) Bio-LNG as both the thermal heat sink and energy source provides a highly compact, light, and environmentally friendly solution to aircraft propulsion. In this study, a Matlab/Simulink transient model is developed to analyze the thermal management system of an aircraft to determine the feasibility of the proposed system. The system uses an estimated flight profile of a Boeing 737 class airplane for the vehicle thermals and fuel demand.