Markus Richter

Decarbonizing aviation requires innovative propulsion technologies and thermodynamic systems that enable efficient, sustainable energy conversion. The Institute of Thermodynamics at Leibniz University Hannover is engaged in several interdisciplinary research projects focusing on advanced, low-emission aircraft propulsion solutions. Two major areas of research are presented: high-temperature solid oxide fuel cells (SOFCs) for hybrid aircraft propulsion and thermal management systems for proton exchange membrane (PEM) fuel cell propulsion, including additively manufactured heat exchangers for aviation applications. These research activities contribute to the technological foundation of more climate-friendly aviation. Concepts are investigated through numerical simulations, experiments, and system-level analyses to develop future propulsion solutions. This paper provides a comprehensive overview of the Institute of Thermodynamics’ ongoing research and the synergies between its various fields. It offers insights into the challenges and opportunities of more sustainable aviation technologies.

Carnot batteries are a scalable option for medium-duration energy storage, yet their thermodynamic optimization remains challenging. Systems based on two-phase Ruths-type steam accumulators have received little attention. We introduce a simple reference Carnot battery using two steam accumulators at different pressure levels, a compressor, an expander, and a pump. By minimizing the number of components and avoiding external heat exchangers, the concept can achieve high round-trip efficiency. Reusing existing pressure tanks could further avoid costs for newly built tanks. However, its transient behavior complicates analysis, especially when embedded in energy systems. To address this, we develop a dynamic model, optimize key design parameters, and couple it to an inverse energy system optimization. This co-optimization links design choices with break-even cost, operating strategy, and efficiency. For the explored parameter space, the system reaches an energy density of 10.5 kWhel/m3 with a round-trip efficiency above 70% using liquid injection into the compressor. Coupling to the system optimization affects the achievable efficiency and thus dimensioning and dispatch. A case study integrates the Carnot battery, based on an existing 9000 m3 pipe storage tank, into an industrial behind-the-meter energy system. At a converging efficiency, the results indicate an allowable tank retrofitting budget of 2.33 M€, an energy-to-power ratio of about 100 MWh/MW, and 11 full equivalent load cycles per year. The reference model provides a transparent baseline for assessing Ruths-based Carnot battery architectures, while the methodology is transferable to other emerging energy technologies with operation-dependent efficiencies.

A triple-port automatic high-pressure volumetric sorption analyzer was set up for sorption measurements over the temperature range of (273.15–368.15) K and pressures up to 10 MPa. The main function of this apparatus is to rapidly screen porous materials for the separation of a specific gas mixture by measuring adsorption isotherms. Measurements with empty sample containers were carried out to evaluate potential systematic errors. Validation measurements on commonly studied cases (CO₂ adsorption on Zeolite 4A, ZIF-8, and Zeolite 13X) were performed, and the excellent agreement with results of literature indicates the high reliability of the measurement system. A comprehensive uncertainty analysis was carried out to determine the uncertainty of measurement results and to propose future improvements of the system. Later, the measurement system was applied to screen suitable materials for the separation of refrigerant blends, which are composed of six pure refrigerants (R-32, R-125, R-1234yf, R-134a, R-1234ze(E), and R-290). The studied porous materials include six metal–organic framework samples, five zeolite samples, and one activated carbon sample. The results show that all zeolite samples investigated (Köstrolith 3AK, 3ABFK, 3ABFK(HSD), 4AK, and 4ABFK) exhibit a higher adsorption capacity for R-32 than for the other five refrigerants, with Köstrolith 4ABFK showing the highest selectivity. This makes it possible to use any of these zeolite samples to separate R-32 from the R-410A blend (a mixture of R-32 + R-125, to be phased down in the European Union) or even separate R-32 from the mixtures composed of any of these six refrigerants. The other studied porous samples do not yield any promising results for the refrigerant blend separation.