Model-Based Membrane Hydration Studies for Automotive Fuel Cell Systems

Abstract

Controlling the hydration of the polymer electrolyte membrane (PEM) is critical for reliable and durable operation of automotive fuel cell stacks. Membrane drying can lead to performance losses due to increased ohmic resistance. More importantly, sustained operation under dry conditions threatens the mechanical and chemical integrity of the membrane. Unfortunately, there is no direct control lever in an automotive fuel cell system (FCS) for membrane humidification, which is often achieved by product water resulting from the electrochemical reactions. Passive gas-to-gas humidifiers may be used in either the hydrogen (anode) or air (cathode) subsystems to circulate some of the product water back into the stack [1]. However, even with passive humidifiers, regions near the stream inlets are generally susceptible to dehydration [2], considering the wide range of operating conditions in automotive settings.Given that the membrane hydration in an automotive FCS can only be controlled indirectly via thermal management and flow and pressure regulation of the incoming gas streams [3], an understanding of the intricate coupling between various subsystems is essential. Modeling the entire FCS with all the balance-of-plant components is a vital tool in understanding these system-level interactions and devising an effective water management strategy. Therefore, a complete system model of an automotive FCS was developed to enable detailed membrane hydration studies. Specifically, the model consists of sub-models for the fuel cell stack [4], gas-to-gas humidifier [1], air compressor [5], hydrogen injector and ejector [6], and all system manifolds and valves [6]. This model is then used to analyze the membrane hydration variations in response to the changes in various practical control actions. The spatially distributed stack model allows hydration trade-offs at different locations of the stack to be analyzed. The results confirm that locations near the stream inlets are often drier than the middle of the stack and that coolant and air path control offer opportunities for effective water management. References Ahluwalia, R. K., Wang, X., Johnson, W. B., Berg, F., & Kadylak, D. (2015). Performance of a cross-flow humidifier with a high flux water vapor transport membrane. Journal of Power Sources, 291, 225-238.Tanaka, S., Nagumo, K., Yamamoto, M., Chiba, H., Yoshida, K., & Okano, R. (2020). Fuel cell system for Honda CLARITY fuel cell. eTransportation, 3, 100046.Kitamura, N., Manabe, K., Nonobe, Y., & Kizaki, M. (2010). Development of water content control system for fuel cell hybrid vehicles based on AC impedance (No. 2010-01-1088). SAE Technical Paper.Goshtasbi, A., Pence, B. L., Chen, J., DeBolt, M. A., Wang, C., Waldecker, J. R., ... & Ersal, T. (2020). A mathematical model toward real-time monitoring of automotive PEM fuel cells. Journal of The Electrochemical Society, 167(2), 024518.Moraal, P., & Kolmanovsky, I. (1999). Turbocharger modeling for automotive control applications (No. 1999-01-0908). SAE Technical Paper.He, J., Ahn, J., & Choe, S. Y. (2011). Analysis and control of a fuel delivery system considering a two-phase anode model of the polymer electrolyte membrane fuel cell stack. Journal of Power Sources, 196(10), 4655-4670.