,,,,- DLR Oberpfaffenhofen, Institute of Physics of the Atmospere, Wessling, Germany (simon.unterstrasser@dlr.de)
A climate-friendly aviation sector requires the development of new propulsion technologies to replace conventional kerosene-based propulsion. Hydrogen propulsion is regarded as a promising alternative, and we assess its implications for the contrail effect. For hydrogen propulsion, water vapor emissions are higher, and soot particles—serving as condensation nuclei for ice crystal formation—are absent.
Using high-resolution simulations, we analyze contrails from hydrogen propulsion systems (either direct combustion or fuel-cell based) throughout their entire life cycle and compare them with contrails from conventional kerosene combustion.
The formation of H₂ contrails on entrained ambient aerosols is simulated, and the potential role of oil droplets and homogeneous droplet nucleation (HDN) is discussed. Because ambient aerosols are typically less abundant than soot particles in kerosene combustion, H₂ contrails contain fewer ice crystals. However, in unfavorable scenarios, ice crystal formation on oil droplets or via HDN can become the dominant mechanism.
We further analyze the early evolution of contrails in the presence of downward-moving wake vortices (age ≲ 5 min) and their transition into contrail cirrus over several hours.
To evaluate the effect of H₂ propulsion on contrail development, we adjust two key input parameters: the water vapor emission and the initial number of ice crystals (to reflect altered formation processes). We examine how the radiative properties of contrail cirrus change in response to systematic variations in the initial ice crystal number. Our results show that factors such as the initial ice crystal number, ambient temperature, and relative humidity strongly influence the contrail life cycle, whereas the increased water-vapor emissions have only a secondary effect. Contrails with fewer ice crystals are shown to have a substantially reduced radiative impact.
This work contributes to the joint efforts of the German Aerospace Center (DLR) and Airbus to evaluate the climatic impact of H₂ contrails.
How to cite: Unterstrasser, S., Lottermoser, A., Zink, J., Hillenbrand, D., and Thi, W.-F.: High-resolution simulations of contrails from hydrogen combustion and fuel cell propulsion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19535, https://doi.org/10.5194/egusphere-egu26-19535, 2026.
