Semi-Empirical Models for Stack and Balance of Plant in Closed-Cathode Fuel Cell Systems for Aviation

Abstract

In recent years, there has been a growing interest in utilizing hydrogen as an energy carrier across various transportation sectors, including aerospace applications. This interest stems from its unique capability to yield energy without generating direct carbon dioxide emissions. The conversion process is particularly efficient when performed in a fuel cell system. In aerospace applications, two crucial factors come into play: power-to-weight ratio and the simplicity of the powerplant. In fact, the transient behavior and control of the fuel cell are complicated by the continuously changing values of load and altitude during the flight. To meet these criteria, air-cooled open-cathode Proton Exchange Membrane (PEM) fuel cells should be the preferred choice. However, they have limitations regarding the amount of thermal power they can dissipate. Moreover, the performances of fuel cell systems are significantly worsened at high altitude operating conditions because of the lower air density. Consequently, they find suitability primarily in applications such as Unmanned Aerial Vehicles (UAVs) and Urban Air Mobility (UAM). In the case of ultralight and light aviation, liquid-cooled solutions with a separate circuit for compressed air supply are adopted. The goal of this investigation is to identify the correct simulation approach to predict the behavior of such systems under dynamic conditions, typical of their application in aerial vehicles. To this aim, a detailed review of the scientific literature has been performed, with specific reference to semi-empirical and control-oriented models of the whole fuel cell systems including not only the stack but also the complete balance of plant.

Simulation Approaches and Validation Issues for Open-Cathode Fuel Cell Systems in Manned and Unmanned Aerial Vehicles

“…The semi-empiric models adopted to analyze the behavior of the stack in OCPEMFCs and CCPEMFCs are the same because the two systems differ only for the BOP. A detailed analysis of static and dynamic models for the stack of CCPEMFCs can be found in [24]. Here, a summary is reported.…”

“…The values of the parameters in this equation are assumed equal to α = 0.2571, I n /S act = 0.00037707 A/cm 2 and I 0 = 0.0047758 A/cm 2 in [8] for a OCPEMFC with a nominal power of 500 W. However, the transfer coefficient α is affected by temperature [96] and oxygen partial pressure [30]. For more details, please refer to [24].…”

“…where B is assumed equal to RT st 2F in [42,80,92] but can be expressed as function of current, temperature, and/or other parameters [24].…”

“…A review of semi-empirical models for CCPEMFCs has already been proposed by the author in a previous review paper [24]. The present investigation focuses on open-cathode fuel cell systems with forced air-cooling that will be simply referred to as OCPEMFCs.…”

“…The investigation also addresses the effect of flight altitude to identify a correct simulation practice for OCPEMFCs used in drones and manned aerial vehicles. A previous review by the author [24] dealt with closed-cathode configurations adopted in light aviation The two configurations are characterized using quite different BOPs. These systems are subject to different transient effects and introduce the necessity for different control actions.…”