HYDEA Project Work Package 6: Contrail formation pathways for hydrogen combustion

Aviation’s contribution to climate change stems from both CO2 and non-CO2 emissions. Among the latter, the warming effect generated by contrail-cirrus is recognised as a major contributor, albeit large uncertainties remain (Lee et al. 2021). 

A condensation trail - or contrail - is composed of ice crystals which form behind an aircraft at high altitudes in sufficiently cold air. The formation is also influenced by engine technology, operating conditions and the fuel type. On the other hand, contrails are persistent in Ice Super-Saturated Regions (ISSRs) and their transition into contrail-cirrus depends on many atmospheric parameters and also on early contrail properties. ISSRs are local atmospheric air masses characterised by low temperatures and a high humidity level that is saturated versus ice. 

In order to reduce aviation’s climate impact, hydrogen propulsion has been considered as one promising alternative, in line with the European Green Deal and Clean Aviation Strategic Research and Innovation Agenda (SRIA). In this context, the EU-funded HYDEA project was launched in 2023. 

The advantage of a hydrogen-powered aircraft compared to kerosene is that the former combustion is free of carbon-dioxide emissions as well as soot particles and sulphur oxides, classical pathways to ice formation. However, H2 combustion also produces NOx and approximately 2.6 times more water-vapour than kerosene combustion. In this case, a need for modelling new ice crystal formation pathways is required to understand how ice crystals are formed and what properties they would have in order to ultimately understand their climate impacts. 

Consequently in HYDEA WP6, we investigate several aspects of ice crystal formation modelling for a hydrogen-powered engine. Three distinct ice crystal (IC) formation pathways were considered and  investigated. On one hand ONERA uses their 3D CFD model, CEDRE, to perform high-fidelity simulations and their box model MOMIE to investigate the potential role of NOx to act as condensation nuclei. On the other hand, DLR uses their Lagrangian Cloud Module (LCM) box model approach to investigate the role of background aerosols and that of lubrication oil on IC formation. However, they need dilution information from an engine exhaust in order to perform such a study. 

Several simulations were performed using ANSYS CFX solver by GEAP and FLUSEPA solver by AIRBUS to “feed” DLR’s box model. The use of two distinct solvers allows for an inter-model comparison and their potential impact on the IC formation. The use of the Common Research Model (engine and aircraft) allows comparison of isolated versus installed configurations. Three configurations were considered: an isolated engine, an engine-pylon and a full aircraft configuration. While we limit our simulations to the “jet regime” (approx. 300 m downstream of the exhaust), these configurations should provide insights on their influence on the mixing process in the plume.

References:

Lee, David S., et al. "The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018." Atmospheric environment 244 (2021): 117834.