Xin Gao

Reactant maldistribution at high current density limits PEM fuel cell power density. Acoustic airflow excitation (AAE) emerges as a promising technique to improve reactant distribution and facilitate effective expulsion of liquid water by applying acoustic pressure pulses to the cathode airstream. AAE is still in its early stages of research, leaving open questions regarding its feasibility under operational conditions. This work experimentally assesses the feasibility and operation limits of AAE in an operando fuel cell. A test setup is devised, incorporating a PEM fuel cell, a speaker for AAE, a microphone arrangement for AAE validation, and a differential pressure sensor for flooding quantification. A strong dependence of the sound attenuation via the cathode flow field on the flooding state of the cell was measured. A frequency sweep during dry operation at rated power point did not significantly impact water balance and voltage through application of AAE. Under gradually-flooding operation at 80 Hz, a paired t-test across eight alternations established a small but statistically significant cell-voltage shift under AAE ( +1.79 %, 95 % CI, p = 0.034) without a reduction in cathode pressure drop ( +1.4 %, 95 % CI, p = 0.45). Therefore, the voltage enhancement cannot be directly attributed to AAE-induced liquid-water displacement.

Proton exchange membrane fuel cells (PEMFCs) are seen as one possible future means of driving the change towards a zero-emission society. In a civil aircraft, fuel cell systems can have multiple potential benefits, such as reduced noise, lowered emissions and higher fuel economy compared to jet aircraft. For controlling the fuel cell temperature, thermal management systems are required which can be optimized for aircraft applications regarding their weight and reliability. In this work, a simplified and light-weight thermal management system relying on hydrogen cooling is presented and analysed. To investigate the feasibility, a test rig and a three-dimensional, singular channel model in ANSYS Fluent were designed. Fuel cell temperature could be maintained within the set threshold in the model and the test rig, thus showing that controlling the fuel cell temperature via the hydrogen reactant flow is a viable alternative thermal management system. Results from the model indicate that both the hydrogen mass flow and hydrogen inlet temperature should be used to control the fuel cell temperature. Furthermore, operating the fuel cell at medium to low current densities is favourable for hydrogen cooling. Future studies will explore alternate flow field designs to facilitate thermal management system relying on hydrogen.

Proton exchange membrane fuel cells (PEMFCs) are seen as of one of many possible future means of driving the change towards a zero-emission society. In a civil aircraft, fuel cell systems can have multiple potential benefits, such as reduced noise, lowered emissions and higher fuel economy. For controlling the fuel cell temperature, thermal management systems are required which can be optimized for aircraft applications regarding their weight and reliability. In this work, a novel, simplified and light-weight thermal management system relying on hydrogen cooling is presented and analysed. To investigate the feasibility, a test rig and a three-dimensional, singular channel model in ANSYS Fluent® were designed. Fuel cell temperature could be maintained within the set threshold in the model and the test rig, thus showing that controlling the fuel cell temperature via hydrogen is a viable alternative thermal management system. Results from the model indicate that both the hydrogen mass flow and hydrogen inlet temperature should be used to control the fuel cell temperature. Furthermore, operating the fuel cell at medium to low current densities is favourable for hydrogen cooling. Future studies will explore the advantages of alternate flow field designs to facilitate thermal management system relying on hydrogen.

For future hypersonic and supersonic flight, clean, sustainable and energy-efficient propulsion should be addressed in the general background of the sensational clean electric transition of aircraft. This chapter is to draw the attention of the research communities on the possible feasibilities and challenges of hydrogen-electric propulsion in hypersonic and supersonic flight. This chapter is structured with the following aspects, (1) general design and hybridisation concepts of hydrogen-electric propulsion for general aircraft and their hypersonic and supersonic considerations; (2) merits of hydrogen-electric propulsion on thermofluids process integrations; (3) potential merits of hydrogen-electric propulsion projected through thermofluids structural engineering and re-engineering; (4) storage options and their challenges in design and operation; and (5) reliability considerations.