Experiments and modeling of fuel cell humidity control through water injection and its effect on root compressor performance

Abstract

Hydrogen fuel cells offer a promising and environmentally friendly solution for future ground transportation systems, especially for heavy-duty truck applications. The fuel cell system generates electricity to power the vehicle through the chemical reaction between hydrogen and oxygen in the fuel cell stack. Oxygen is supplied by pumping compressed air into the fuel cell stack. To achieve optimal performance with minimal electrochemical losses, precise control of air and hydrogen flow within the fuel cell stack is crucial. One key factor affecting fuel cell performance is the air relative humidity (RH). In this study, we focus on developing an efficient air humidity management system through the direct injection of water into a twin vortices series compressor (TVS R1320). The goal is to experimentally measure the effect of water injection on compressor efficiency and the attainable RH without water droplet formation at the inlet of the fuel cell stack. The experimental results show that for high air mass flow rates, specific work and mechanical power can be reduced by up to 7.83% and 2.3%, respectively, while the system isothermal efficiency improved by 2.95%. However, the RH required by fuel cells cannot be achieved solely by direct water injection without the risk of water droplet formation that can lead to fuel cell flooding. Other operating points will be discussed in detail. Furthermore, modeling activities were conducted to identify trends and better explain the effects of injected water. Limitations were also found in 1D simulation codes when modeling evaporation. A simplex nozzle was positioned at the compressor inlet to continuously inject water, and optically accessible sections located upstream and downstream of the compressor allowed for recording the air-water flow status.