Fuel cell air compressor concepts to enhance the efficiency of FCEV

Abstract

The thermal management system and the balance-of-plant (BoP) in fuel cell electric vehicles (FCEV) are characterized by a particularly high level of complexity and a number of interfaces. Optimizing the efficiency of the overall vehicle is of special importance to maximize the range and increase the attractiveness of this technology to customers. This paper focuses on the optimization potential of the air supply system in the BoP, whereby the charging concepts of the electric supercharger (ESC) and the electrically assisted turbocharger (EAT) as well as the integration of water spray injection (WSI) at the compressor inlet are investigated in the framework of an FCEV complete vehicle co-simulation. As a benchmark for the integration of these optimization measures, the complete vehicle co-simulation is designed for a fuel cell electric passenger car of the current generation. Here, thermo-hydraulic fluid circuits in the thermal management software KULI are coupled with mathematical-physical models in MATLAB/Simulink. Applying advanced simulation methodologies for the components of fuel cell, powertrain and vehicle cabin enables the mapping of the effects of realistic operating conditions on the FCEV characteristics. The EAT offers the advantage over the ESC that, due to the arrangement of an exhaust gas turbine, a part of the exhaust gas enthalpy flow downstream of the fuel cell stack can be recovered, which reduces the electrical compressor drive power. Moreover, an additional reduction of this power consumption can be achieved by WSI, as the effect of evaporative cooling lowers the initial compression temperature. For analysis and comparison, these concepts are again modeled with high degree of detail and integrated into the benchmark overall vehicle simulation. The results indicate considerable reductions in the electric compressor drive power of the EAT compared to the ESC, with noteworthy potential for reducing the vehicle’s hydrogen consumption. At an operating point in Worldwide harmonized Light Duty Test Cycle (WLTC) under 35 \(^{\circ }\)C ambient temperature and 25 % relative humidity, the electrical compressor drive power shows a reduction potential of −40 %, which corresponds to a vehicle-level hydrogen consumption reduction of up to −3 %. In addition, the results also highlight the effect of the WSI in both charging concepts, whereby its potential to reduce the hydrogen consumption on the overall vehicle level is relatively small. In WLTC, at 35 \(^{\circ }\)C ambient temperature and 25 % relative humidity, the compressor drive power reduction potential for ESC and EAT averages −5 %, while the effect on hydrogen consumption is only around −0.25 %.