Turbocharged Polymeric Electrolyte Membrane Fuel Cell for land, maritime, and aerospace applications

Polymeric Electrolyte Membrane Fuel Cell (PEMFC) systems are among the most promising technologies for decarbonizing the transportation and power sectors, thanks to their high efficiency, rapid dynamics, and high power density. Additionally, the use of pure hydrogen as fuel, combined with low-temperature operation (60-80°C), ensures net-zero local emissions. PEMFC performance can be further enhanced by increasing the cell's operating pressure, typically achieved in the air circuit using either a blower or a compressor. A compressor allows for higher pressures, which improves stack performances but at the cost of increased power consumption by the Balance of Plant (BoP). In contrast, a blower has lower power consumption but is limited to achieving lower pressures. Within this context, this thesis explores an innovative turbocharged PEMFC (TC-PEMFC) system designed for maritime, land-based, and aerospace applications. The use of a turbocharger enables high pressures at high currents and low pressures at low currents, and, at the same time, the BoP's power consumption is reduced by partially recovering exhaust gas energy through the expander. The TC-PEMFC system is analysed using a Matlab/Simulink model, with its component models based on a library of 0D, 1D, and 2D models previously developed and validated at the Thermochemical Power Group (TPG) of the University of Genoa. Some models were specifically developed for this study, and all components are sized to achieve the desired performance. When possible, the components are calibrated based on specifications and experimental data from real devices. This thesis firstly investigates the TC-PEMFC system designed for maritime and land-based applications. In this case, a twin stack configuration is considered, with an installed power up to 300 kW. The system power output and net efficiency are studied through an off-design analysis between the 30% till the 156% of the nominal current, showing an efficiency of the system which ranges between 51.6% and 59.8%, confirming that the use of the turbocharger can significantly enhance the system performances. A dynamic characterization of the system is then performed, characterizing the system's response to variations in input variables and evaluating its responsiveness under different current ramps and a real naval load profile. 2 Besides, the model is applied to investigate common faults in PEMFC operation, including low reactant humidity leading to membrane drying, deviations in stack operating temperature, either lower or higher than standard conditions, which can result in flooding or membrane drying respectively, and oxygen deficiency during operation. All these conditions are simulated by acting on the system manipulated variable by the controllers in the model, and the effects on the cell and system components are analysed. While the simulations show no significant impact on system efficiency or power output, these operating conditions pose a serious risk to the cell, potentially accelerating its degradation. In this context, this analysis is valuable for studying how the fault can be quickly detected according to the actual layout of the system, thereby preventing the cell from remaining in these critical conditions. Then, the impact of cell degradation, simulated as a reduction in cell active area compared to new conditions, is analysed to evaluate whether using a turbocharger instead of a standard compressor in the air circuit can extend the lifetime of the PEMFC system. The analysis is conducted for 35% and 15% reductions in cell active area. Two recovery strategies aimed at restoring system performance to pre-degradation levels are then explored. The first strategy involves increasing the turbocharger's rotational speed to restore cell voltage, while the second strategy involves increasing the degraded cell's operating current to meet power requirements. Finally, the TC-PEMFC system is analysed for aerospace applications, focusing on a single- stack configuration capable of delivering a net power output of up to 300 kW. Various system layouts are proposed and evaluated, considering the impact of changing ambient conditions (pressure and temperature) at different altitudes. The study examines different plant configurations based on various turbochargers: a single-shaft turbocharger designed for sea level (SS-S), a single-shaft turbocharger designed for cruise at 15,000 ft (SS-C), and a double-shaft turbocharger designed for cruise at 15,000 ft, either with (DSIC-C) or without (DS-C) intercooling between compression stages. The on-design and off-design performance of each TC-PEMFC configuration is simulated using a detailed MATLAB-Simulink model, covering both take-off and cruise conditions, with altitudes ranging from sea level to 15,000 ft. 3 The results of this analysis identify the SS-C as the optimal system configuration. Subsequently, an off-design analysis is conducted to examine how variations in ambient conditions impact the performance of the TC-PEMFC system. The model simulates the TC-PEMFC under different ambient conditions encountered during various flight phases, defining its operational range. These conditions are established by combining four pressure values (1, 0.75, 0.50, and 0.25 bar) with six temperature values (- 50, -25, 0, 15, 30, and 40 °C). For each condition, the system is tested across a broad range of PEMFC currents, from 30% to 100% of its nominal value. All operational constraints are monitored to ensure that both the PEMFC and the turbocharger function correctly.