The group of researchers from the engineering college of the joint Florida Agriculture and Mechanics University and from the Florida State University developed an innovative system for storing and supplying liquid hydrogen, which may become the basis for the future aviation. According to the scientists this development allows for using hydrogen not only as an environmentally clean fuel, but also as a cooling medium for the key energy components of e-planes.
The results of the research were published in Applied Energy. They describe the project for 100-seater local hybrid-electrical airplane. The proposed system solves three tasks simultaneously: reliable hydrogen storage at super-low temperature, hydrogen supply to power plants and cooling of aircraft hardware.
It is known that using hydrogen requires a lot of space and super-low temperature (circa -253 °C). To solve this problem, the group of scientists comprising specialists in cryogenics, superconductivity and energy systems developed advanced cryogenic tanks and performed all-round optimization of the system. One of the important outcomes of this effort was development of a new effectiveness criterion – the so-called gravimetric index. It shows, what part of the total fueling system mass is fuel, and what part is auxiliary elements: cryogenic tank, thermal insulation, piping, heat exchangers and other components. In the configuration proposed by the researchers this index reached 0.62, i.e., the liquid hydrogen made 62% of the total mass, which significantly exceeds the traditional technologies’ metrics.
Instead of installing a separate cooling system, they proposed to use liquid hydrogen per se: passing through the cascade of heat exchangers, it first cools the components operating under super-low temperatures (such as superconducting generators and cables), and then absorbs heat from warmer elements including electric motors and power electronics.
Supplying hydrogen inside the aircraft was one of the key technical tasks. Taking into account high level of risks associated with using pumps in cryogenic conditions, the researchers decided not to use pumps and to provide for hydrogen movement driven by controlled pressure in the tank. This pressure is adjusted automatically: it may be increased when needed to let in gaseous hydrogen, or decreased to bleed the steam. Such approach allows for accurate control of fuel consumption depending on the stage of the flight. According to the estimates, the system is capable of supplying up to 0.25 kg of hydrogen per second — this is enough to feed on-board power plants up to 16.2 MW, which is especially important during take-off or in case of urgent ascend.
Until recently it remained unclear if the functions of cooling and fuel supply could be effectively combined in one single system. The research performed by specialists from Florida not only confirmed it is technically possible, but showed that in case of adequate optimization such system may be even more efficient than separate solutions. During the next stage, the researchers plan to create a pilot system and test it in the Advanced Energy Systems Center of the Florida State University. The project is supported by NASA and is part of the Federal Program for developing aviation technologies with zero emissions.