Hybrid systems (HS) are highly attractive in power generation due to their potential for higher power outputs and efficiencies by integrating different technologies. Among solid oxide fuel cell (SOFC) plants, the SOFC-Micro-Gas Turbine (mGT) system is particularly innovative. In this setup, the SOFC replaces the mGT combustion chamber, with an afterburner completing fuel combustion before the expander. Various configurations and control systems have been explored over the years, and prototypes have demonstrated satisfactory efficiency. However, these systems have predominantly used NG and Biogas, which do not achieve zero carbon emissions. The growing global demand for carbon-free energy production is increasing, highlighting the importance of alternative fuels in the power generation sector: among them, thanks to its chemical and physical properties, ammonia is gaining more and more interest. This work investigates an innovative ammonia-to-power system based on an SOFC-mGT HS, focusing on thermodynamic parameters, system features, and technical and environmental challenges. A MATLAB/Simulink model, built on a validated HS model fueled by NG, was developed to analyze the new system configuration. This configuration replaces the SOFC prereformer with an ammonia cracker, allowing for the exploration of anode gas recirculation effects and optimal system design. Key operating parameters such as anodic recirculation factor, fuel utilization, performance, and gas turbine characteristics are discussed. Finally, a comparison is made between hybrid systems and mGTs powered by methane, biogas, and ammonia.

Proton-exchange membrane fuel cell (PEMFC) systems are one of the most promising technologies for the decarbonization of the transportation and power sectors. This article investigates the dynamics of an innovative turbocharged PEMFC system. A detailed dynamic model of the turbocharger-proton-exchange membrane fuel cell (TC-PEMFC) is developed in Matlab-Simulink. 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 turbocharger (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, proper operation of the system is always guaranteed, whereas load reductions are limited by the possibility of compressor surge (35 A/s of maximum ramp rate). To overcome this limit, a possible modification to the control logics is tested in the final part of the study.

A validation study has been done to provide evidence on the reliability of Reynolds-averaged simulations for supersonic ejectors operating in the single-choked condition. The existing works show that the simulation accuracy for a given turbulence model strongly depends on ejector geometry and the working conditions. In addition, the performance of different turbulence models is usually presented by comparing the results without discussing the origins of their failures. Part 1 of the present work highlights the importance of properly modeling the turbulence response to the varying shear intensity that characterizes the ejector flow-field. The key elements related to this point have been analyzed for commonly used eddy viscosity models and for a new $K-\epsilon$ model. The models described in Part 1 are tested here on two complementary test cases. A free jet with detailed turbulence measurements in the initial region is used to provide information on the models’ behavior, data which could hardly be obtained directly for ejectors. The simulation of a supersonic ejector is then presented, comparing the results with the measured velocity and pressure distributions. The assessed validity of the new eddy viscosity model is exploited to give insightful considerations on ejector flow-field development.