ABSTRACT
Decarbonisation of heavy-duty vehicles has an important impact on reducing emissions. More specifically, in the United States, medium and heavy-duty trucks are responsible for 23% of total CO2 emissions at present. Furthermore, the annual road freight traffic is expected to grow by 54% by 2050. The recent growth in lithium-ion battery use in Light Duty Vehicles (LDV) has resulted in reductions in battery costs. However, for Medium and Heavy Duty (MDV and HDV) applications, fuel cells offer important advantages in terms of energy density and refuelling time, which makes this technology more attractive for these classes of vehicles. Recent US DOE targets for Class 8 long haul trucks highlight the importance of even longer driving ranges and increased efficiency demands for fuel cell systems. To this end, it important to design and optimize the components of a fuel cell system, such as the compressor, not in isolation, but as part of the integrated system under real-driving conditions, thus capturing the strong co-dependencies among subsystems and the intricacies of real-life operation.
This paper presents a novel methodology, that uses a system-level simulation platform to create a complete vehicle model and simulate the performance of a fuel cell powered truck in order to obtain the key fuel cell compressor operating points together with the resulting residence time spent on each point based on real driving condition. The key compressor operating points are then fed into a meanline compressor design optimization code which uses a map prediction model for a range of compressor speeds, impeller diameters, hub diameters and axial length ratios to find the optimum settings that meet the same weighting factor obtained from real driving conditions. This initial flow path and design conditions obtained from the meanline design optimization are then used by a 3D Inverse design method to generate an initial 3D impeller geometry. Automatic optimization is then used to optimize the impeller geometry. The casing is also designed by using a unique inverse design method and the performance of the resulting stage is computed by using a 3D CFD simulation package. Furthermore, the structural integrity of the compressor is analysed with a 3D structural analysis software package. The resulting full stage compressor map is then fed into the system-level model and the impact of the new design on the energy consumption over the actual real-life driving scenario is assessed and analysed. The methodology highlights the importance of rigorous simulation as a means for improving component performance and system efficiency, while reducing time-to-market and thus development costs.161
