Development Study of an Air Independent Fuel Cell System for an Autonomous Underwater Vehicle (AUV)
Authors: Hitscherich Manuel , Cremers Carsten , Stolten Detlef , Pinkwart Karsten , Tübke Jens 
Published: February 2020

In this work a design process for the development of an air independent fuel cell system operating a commercial fuel cell stack as a range extender in an AUV is presented. The development follows an optimization strategy which has been derived from the universal fuel cell development plan proposed by Ang et al.[1] The first step is defining the constraints and the objectives in the design process. While constraints set the boundary conditions of the system the identified objectives are used as optimization parameters. The design plan follows the schematic in figure1:

Figure 1: design concept for an optimized system used in an AUV

The development of fuel cell systems used in a submarine environment will need to consider different boundary conditions than the development of a fuel cell system for automobiles. These constraints result from the sea water environment which can’t be used as an oxygen source and additionally hinders mass exchange with the fuel cell system because of pressure differences. As a result a closed fuel cell system relying on a pure oxygen supply has to be developed. The fuel cell is powering the AUV with a stationary output while a battery is buffering the power differential between the output und the consumption of the AUV. The AUV is used as a testing platform by the German navy and thereby sets very unique constraints on the system development. Additionally the commercial fuel cell stack is setting boundary conditions for the system development, which has to meet the stacks individual operating conditions. After identifying the boundary conditions the system size was identified as the optimization parameter.
To optimize the system size different setups for the cooling system as well as the gas supply system found in the literature are evaluated. Setups meeting the boundary conditions are validated in a test bench with hardware-in-the-loop tests. Based on these measurements a volume-optimized system can be found. Challenges which deviate from this setup are identified and can be tackled in the subsequent design step.
The next step is a discussion of the different concepts and an evaluation of their impact on the system operation. While the discussed solutions are still meeting the maximum system size, an evaluation of their influence on other design parameters can be made. From this different system designs are derived and the resulting operation strategies are compared to further improve the volume-optimized system. Also solutions targeting specific challenges like standby mode and system shutdown are evaluated and presented.
In a last step the qualitative connections between the found system designs and the boundary conditions in this system are discussed leading to a more general approach for the development of air independent fuel cell systems for AUVs.
[1] S. M. C. Ang, E. S. Fraga, N. P. Brandon, N. J. Samsatli, and D. J. L. Brett, “Fuel cell systems optimisation – Methods and strategies,” Int. J. Hydrogen Energy, vol. 36, no. 22, pp. 14678–14703, Nov. 2011.

Figure 1