| Abstract | The purpose of this project was to begin with a baseline diesel-combustion military heavy logistics vehicle and evaluate the technical feasibility of changing the fuel supply to solid-state hydrogen, moving towards a hybrid electrified configuration, and additionally understand the implications to the overall powertrain mass and volume. Towards that end five vehicle concepts were proposed and analyzed. The concepts were (1) conventional H2-internal combustion engine (ICE), (2) H₂-ICE parallel-hybrid, (3) H₂-ICE series-hybrid, (4) power dense fuel cell and (5) efficiency optimized fuel cell.
Prior to analyzing the vehicle concepts, a set of high-level vehicle requirements was established as well as two drive cycles; one a simplified flat-road cycle and the other modelled on a logistics vehicle mission profile. The high-level vehicle requirements presented the concept of peak, continuous and average power demand. Combustion engines and fuel cells can sustain power output continuously, while batteries provide shorter bursts of high power; creating trade-offs in system sizing and powertrain mass.
The logistics vehicle mission drive cycle was derived from aggregate real-world vehicle performance and validated by subject matter experts. The aim in using two such disparate drive cycles was to demonstrate the impact requirements and drive cycles have on vehicle components power rating, mass and volume. The average power demand of the flat-road cycle was higher than the logistics cycle. The flat-road cycle produced vehicles with larger engines, smaller batteries, larger fuel tanks and overall larger mass powertrains while the logistics drive cycle produced powertrains with smaller engines, larger batteries, smaller fuel tanks and overall smaller mass powertrains. Using “today” technology values, and the logistics drive cycle, even in a best-case scenario, the efficiency optimized fuel cell powertrain mass was still 200 kg greater than the diesel-baseline.
Two vehicle concepts, H₂-ICE series-hybrid and efficiency optimized fuel cell, were selected to extrapolate out their designs for tomorrow (~10 years) and future (~15 to 20 years) technology values. As the technologies evolve, and system efficiencies increase, and both volumetric and gravimetric power and energy densities improve, the two concepts were comparable or better than the diesel-ICE baseline. On-board hydrogen storage energy density and energy release penalty are the parameters which need the largest improvements. Hydrogen storage dominates the mass and volume of the concept powertrains, with battery size and efficiency assumptions also contributing significantly.
This project demonstrates that, depending on requirements and drive cycle, a heavy logistics hydrogen-fueled vehicle using today’s technology assumptions, can be designed to a mass of no more than 10% of the diesel-ICE baseline. A detailed design phase is recommended to refine these concepts further. |
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