Preliminary Safety Assessment of PEM Fuel Cell Systems for Electrified Propulsion Systems in Commercial Aviation

Kurzfassung

This paper analyses polymer electrolyte membrane fuel cell systems (PEMFCSs) as main energy provider for electrified aircraft propulsion, identifies potential weaknesses as well as safety challenges and presents potential solutions. The general design, operating principles and main characteristics of hydrogen-fuelled low temperature PEMFCSs are described. The safety assessment process in aviation according to Aerospace Recommended Practices ARP4754A and selected methods according to ARP4761 are introduced. The functions of fuel cell systems in electrified aircraft powertrains are analysed and visualised in functional structure trees on aircraft, powertrain and fuel cell system level. By means of a Functional Hazard Analysis (FHA), potential malfunctions and their effects are investigated and their severity is evaluated. Critical failure modes are identified and requirements for acceptable failure probabilities are stipulated. Within the scope of a Fault Tree Analysis (FTA), the components of a fuel cell system are assigned to the identified functional structure trees and potential causes of critical failure modes are examined. The results of the mentioned analyses reveal design challenges associated with the application of fuel cell systems in electrified aircraft propulsion, for instance concerning functional independence as well as solutions for cold start conditions, heat transfer and lightweight design.