Challenges in emissions assessment for hybrid-electric regional aircraft

Abstract This paper investigates a method for estimating emissions from hybrid-electric aircraft, providing a qualitative assessment of their potential environmental benefits. Limited data availability poses challenges, discussed in this study, for its rigorous evaluation. Proper characterisation of both ${{C}}{{{O}}_{{2}}}$ and non- ${{C}}{{{O}}_{{2}}}$ emissions across the operating envelope is crucial. Existing databases and predictive models for turboshaft engines for full-thermal regional aircraft may not be reliable for hybrid-electric configurations, which could operate under uncommon conditions, as low thermal power supply during specific flight phases. This uncertainty highlights the limitations of current emission prediction models. The first of the present study examines non- ${{C}}{{{O}}_{{2}}}$ emissions ( ${{N}}{{{O}}_{{x}}}$ , HC, ${{S}}{{{O}}_{{2}}}$ , CO) from hybrid-electric aircraft optimised for minimum block fuel, comparing them with those from thermal competitors. The second part evaluates ${{C}}{{{O}}_{{2}}}$ emissions, considering both in-flight and electricity generation contributions. Results indicate that hybrid-electric configurations could reduce non- ${{C}}{{{O}}_{{2}}}$ emissions for both the entire mission and the landing-take-off cycle. However, ${{C}}{{{O}}_{{2}}}$ reductions are only significant for short design ranges and could be marginal if electricity generation does not shift to fully renewable sources.