Turbocharging an Automotive Hydrogen PEM Fuel Cell Air Processing System

Abstract

Hydrogen Polymer Electrolyte Membrane (PEM) fuel cell technology is becoming increasingly popular in the transportation sector, especially the automotive industry. It can power electric drives by converting hydrogen into electricity in a chemical reaction with oxygen, whose products consist only of water. Therefore, hydrogen PEM fuel cell-based powertrains are free of any harmful emissions, enabling clean propulsion technology. An important part of an automotive fuel cell system is the air processing subsystem, which usually features an electrical air compressor (E-compressor) to supply the necessary oxygen for the chemical reaction. This E-compressor can absorb between 10-30% of the fuel cell gross power. One way to decrease this share is to expand the fuel cell air exhaust flow in a turbine that contributes to power the E-compressor, essentially realizing an electric turbocharger (E-turbocharger). E-turbochargers for fuel cells are still in the development phase, therefore there is a lack of experience and knowledge on their benefit. In this thesis, a model of an existing automotive PEM fuel cell air processing system has been developed using the AVL Cruise M software. In addition, two prototype PEM fuel cell E-turbochargers (ETC1 and ETC2, respectively) have been modeled and integrated into the main air processing system model. Steady-state simulations have been performed for three different power levels. Moreover, the turbine inlet temperature of the ETC1-based model was varied in the range of 60°C to 150°C to quantify what benefits exhaust heating with waste heat brings in addition to the inherent turbocharging performance gains. The results show that compared to the baseline system, the model featuring ETC1 achieved an increase in net power between 3.04-6.78% or a decrease in fuel consumption between 3.19- 7.67%, depending on the power level. For the ETC2-based model, from low to high load, the net power increased between 1.88-2.04%, or fuel consumption decreased between 2.07-3.17% compared to the baseline system. When increasing the turbine inlet temperature to 150°C, the model showed an additional decrease in fuel consumption of 2.1 percentage points at full power. The models could be improved by implementing a first-principle-based model of the E-compressor and E-turbocharger, which could have been developed in this project if more detailed information on the heat flows within these components was available.