Session: Student Poster Competition

Submission Number: 186897

System-Level Performance of an Integrated Ammonia-Fueled Engine 

   Due to growing concerns about CO2 emissions, industries are shifting away from fossil fuels. In response, ammonia has been proposed as a net-zero carbon fuel when used with its onboard cracking. To support this, a Brayton cycle waste heat recovery system can be integrated to preheat the ammonia using exhaust heat. Supercritical CO2 (sCO2) Brayton cycles have been recently studied and tested in terrestrial power generation, such as at the Southwest Research Institute’s Supercritical Transformational Electric Power (STEP) Pilot Plant. The STEP pilot plant is a 10MW grid-connected sCO2 power generation plant that has demonstrated higher thermal efficiencies while using smaller turbomachinery than conventional working fluids. Operating CO2 near its critical point increases the density, lowering compression work, which allows for compact compressors and turbines, and more effective printed-circuit heat exchangers. This allows the sCO2 Brayton cycle to outperform traditional cycles in terms of power and efficiency, while showing the possibility of implementation on aircraft, where volume and weight are critical. The proposed Brayton cycle is a closed-loop power cycle using supercritical CO2 as its working fluid. The feasibility of operating this sCO2 Brayton cycle on an aircraft must be determined by evaluating the performance of its turbomachinery during off-design and transient operations, as the rapid changes of the CO2 properties can affect performance. This study evaluates the performance and stability of an aviation-relevant supercritical CO2 Brayton cycle, coupled to a representative engine core thermal environment within Simcenter Amesim. This cycle is modeled using in-house compressor and turbine maps generated at their respective reference conditions: 7.58 MPa and 305.37 K for the compressor, and 19.58 MPa and 535.22 K for the turbine. Heat-exchanger interfaces are included to represent heat input from the engine exhaust and heat rejection to the ammonia fuel. A steady-state, converged baseline model of the sCO2 loop is established by varying the turbine pressure ratio, shaft speed, and heat-exchanger duty. These parameters are adjusted to achieve the target net power output of 158.22kW and cycle efficiency while maintaining sCO2 outlet thermodynamic conditions. The pressure loss on the exhaust side was limited to approximately 1.20kPa, while the low-pressure sCO2 side resulted in a pressure drop of about 0.19MPa. These limits were maintained while operating with a heat exchanger effectiveness of 0.75. In addition to cycle power production, the model tracks ammonia-side thermal demand to ensure the fuel stream can be preheated to meet cracking-temperature requirements, enabling sustained hydrogen/ammonia blend production for combustion under representative operating conditions. Coupling a sCO2 Brayton cycle to an aircraft engine introduces strong thermo-mechanical interactions that can affect component operability and overall loop stability as the operating conditions vary. This integrated core engine with the sCO2 loop with ammonia cracking provides a foundation for off-design and transient analyses, allowing assessments of system stability, engine performance, and ammonia thermal requirements under representative aircraft operating conditions.

 

Presenting Author: Kangana Patel University of Central Florida

Presenting Author Biography: I am Kangana Patel, a Ph.D. student in Mechanical Engineering at the University of Central Florida (UCF) and a research assistant at the Center for Advanced Turbomachinery and Energy Research (CATER), working under Dr. Jayanta Kapat. My research focuses on steady-state and transient simulation of turbofan engine cores and supercritical CO2 Brayton-cycle power loops, spanning component-level modeling through integrated system-level analyses. Been part of NASA’s University Leadership Initiative (ULI) project aimed at enabling zero-carbon aviation by 2050, with emphasis on waste-heat recovery, turbomachinery performance, and the integration of advanced power cycles with alternative fuels.

Authors:

Kangana Patel University of Central Florida
Nishant Brijlal University of Central Florida
Marcel Otto University of Central Florida
Jayanta Kapat University of Central Florida