High-resolution simulations of contrails from hydrogen-powered aircraft

The transition to climate-friendly aviation necessitates the development of new propulsion technologies to replace conventional kerosene combustion engines. Hydrogen (H₂) propulsion is widely regarded as a promising and environmentally sustainable alternative. A key aspect of creating climate-friendly aviation involves evaluating the climate impact of contrails, which significantly contribute to aviation’s non-CO₂ effects. This study examines the properties of contrails produced by H₂-powered aircraft, with a particular focus on comparing them to contrails generated by conventional kerosene combustion. Using high-resolution simulations performed with the EULAG-LCM model—a large-eddy simulation (LES) model with fully coupled particle-based ice microphysics—we analyze individual contrails throughout their entire lifecycle. This includes the interaction of young contrails with the downward moving wake vortices and their evolution into contrail-cirrus over several hours.
Previous simulations of early contrail evolution during the vortex phase and the subsequent contrail-cirrus transition have extensively explored variations in meteorological and aircraft-related parameters. However, these studies have been limited to contrails from kerosene combustion.
To assess the impact of H₂ propulsion on contrail evolution, we adjust two key input parameters: increasing the water vapor emission and varying the number of initial ice crystals. Additionally, we expand the atmospheric scenarios to include higher ambient temperatures, accounting for the fact that H₂ contrails can form in warmer conditions where ice crystal formation in kerosene plumes is not possible (assuming the same droplet characteristics in both cases).
We analyze H₂ contrail evolution in various atmospheric scenarios, finding that wake vortices cause significant ice crystal loss through adiabatic heating. This loss is less pronounced with fewer initial ice crystals but increases at ambient temperatures above 225 K. In the subsequent contrail-cirrus phase, we focus on the evolution of the contrail total extinction, which serves as a proxy for relative changes in the contrail’s radiative effect. Our results demonstrate that factors such as the initial ice crystal number, ambient temperature, and relative humidity strongly influence the contrail lifecycle, while increased water vapor emissions (immanent to H2 propulsion) have a secondary effect.
This work contributes to the collaborative effort of the German Aerospace Center (DLR) and Airbus in assessing the climate impact of H2 contrails.