Employing Liquid Hydrogen for Fuel Cell Heat Recovery in Aircraft

Employing Liquid Hydrogen for Fuel Cell Heat Recovery in Aircraft

de Boer, Pim (TU Delft Aerospace Engineering)

Gangoli Rao, A. (mentor)
Kiselev, Sergey (graduation committee)

Delft University of Technology

Aerospace Engineering

2022-10-31

This work describes the benefits of exploiting cold hydrogen in a 2 MW liquid hydrogen-electric powertrain. Hydrogen is stored in a liquid state in the aircraft at its boiling point of 20 K (at 1 bar). Fuel cells require an input temperature of at least zero degrees Celsius to operate. The heating process can either be done by drawing current from the fuel cell to power an electric heater that heats the hydrogen, or it can be done by using fuel cell waste heat in a heat exchanger. These two powertrain configurations
are referred to as ’baseline’ and ’proposed’, respectively. It is hypothesized that 2.5% of the hydrogen’s energy content can be saved by opting for the latter. This corresponds to an estimated 6.3% shaft efficiency gain. The case study uses a flight mission that is typical for the ATR 72. A power balance is constructed that contains all power consuming or producing components in the liquid hydrogen-electric powertrain. This set of components consists of the fuel cell, compressor, pumps, motor, inverter, and
heat exchangers. A model structure is conceived showing all interdependencies between the various components. The research methodology describes the theoretical basis for analysis of all the individual components. The scope of the analysis is thermal and thermodynamical behavior. A systematic trade-off is made to select a concept solution for the hydrogen heat exchanger with the help of a morphological overview and a multi-criteria analysis. This resulted in the selection of a heat exchanger located outside of the LH2 storage reservoir that uses FC waste heat which is transported by a liquid One chapter has been dedicated to the exploration of power regeneration possibilities. It is shown that the hydrogen flow has a high exergetic potential but that it is hard in practice to exploit this effectively. Hence, no power generation cycle is implemented in the proposed configuration. Model validation has been conducted for all components of the power balance except for the humidifier. Normalized root mean square errors ranging between 0.01 and 0.23 have been identified. The effect of the stack pressure on the fuel cell performance is also evaluated. It is explained why a constant compressor pressure ratio of 3 is targeted. The sizing process for the components that are used in the model is explained as well as the flow control strategy. The powertrain uses two separate cooling loops, a high temperature and a low temperature cooling loop (referring to the average coolant temperatures within the loops). The model results show that the shaft efficiency of the powertrain on average increases from 0.367 in the baseline configuration to 0.409 in the experimental configuration. The model uncertainty is less
than 1%. This is because the component models with a high normalized root mean square error have a small effect on the overall power balance while the most dominant components have been calibrated to a high level of accuracy. This leads to the conclusion that using fuel cell waste heat for hydrogen heating substantially increases the shaft efficiency in the ZA2000 powertrain and in liquid hydrogen-electric powertrains in general. Other observations include a strong increase in FC performance and a decrease in the parasitic load. The flight mission requires an average of 2.1 MW of shaft power during which the cold hydrogen flow provides 204 kW of cooling. Finally, recommendations are made for further research in the fields of enhanced heat dissipation methods, weight optimization of hydrogen-electric powertrains, and aerodyanmic analysis of the effect of hydrogen-electric powertrains on aircraft.

hydrogen
Turboprop
efficiency
Liquid hydrogen
Fuel cell
PEMFC

http://resolver.tudelft.nl/uuid:61c71c50-f77e-42d0-b37b-e00c7747e414

2024-10-31

Student theses

master thesis

© 2022 Pim de Boer