Highly-resolved simulations of contrail formation generatedby fuel cell-propelled aircraft

Aviation emissions are estimated to contribute approximately 3.5% of the global anthropogenic effective radiative forcing [3]. The goal to reduce this forcing can only be realized by a combination of measures including also new propulsion technologies. Aircraft powered by fuel cells operated with hydrogen are one promising future technology as they avoid both CO2 and NOx emissions. Additional to the reduction of these emissions generating strong contrail-cirrus has to be avoided to reduce the overall radiative forcing due to aviation emissions. Therefore it is important to investigate the contrail properties from fuel cell aircraft since they may significantly differ from current aircraft.
The number of ice crystals formed in the first few seconds of the exhaust is crucial for the radiative impact of the evolving contrail-cirrus. Among other effects the changed dynamics behind the propellers and the expected higher moisture-to-temperature ratio of the fuel cell exhaust will alter the number of formed ice crystals compared to classical jet combustion exhausts. Additional nucleation processes become important due to larger supersaturation values during the cooling of the plume. We will present the influence of these processes and different fuel cell setups on the number of formed ice crystals after the formation phase.
We simulate the formation of contrails by means of the Lagrangian Cloud Module (LCM) with detailed particle-based microphysics. To avoid computational overload we use a 0-D offline approach: suitably averaged data from a priori 3D CFD simulations of the exhaust dilution are used as input in the 0D LCM box model. This model has been used in recent studies for contrail formation simulations of a classical turbo-fan aircraft with kerosene or hydrogen combustion [1, 2]. During this work the LCM model has been adapted and extended to enable the simulation of contrail formation behind fuel cell powered aircraft. The model was applied and results are shown.
This work contributes to the collaborative effort of DLR and Airbus in assessing the climate impact of H2 contrails.