Fault Tree Analysis of Failure Modes related to Water Management in a PEM Fuel Cell System for Aerospace Applications

Alternative all-electric propulsion concepts, for example based on proton-exchange membrane fuel cells, must comply with the established safety and reliability requirements of the aviation industry. Hence, failure analysis have to be conducted in early system design phases. One potential method for such analysis are fault trees. The complexity of fuel cell propulsion systems make the development of fault trees an extensive task. In this work, the fault tree analysis is especially applied to failure conditions connected to the intrinsically important water management of the fuel cells. Close physical relations of multiple parameters linked to the failure conditions complicate the development of respective fault trees. Therefore, an approach with three dedicated fault tree layers is proposed in this work, including a physical-level resolving the correlations of the influencing physical parameters. This method increases the structure, the completeness and the modularity of the fault trees. Furthermore, the physical-level can be a valuable input for future developments of failure detection, and mitigation mechanisms. The developed fault trees can thus be used as an input in the design phase of a fuel cell based aircraft propulsion system as well as a basis for preparatory certification activities.