Feasibility studies on regional aircraft retrofitted with hybrid-electric powertrains

Abstract

Hybrid-electric powertrains are considered a promising technology for mitigating noxious emissions and promoting aviation decarbonization, particularly in regional segments with limited flight energy requirements. However, assessing their potential quantitatively proves challenging owing to system complexity and enlarged dimensions of the design space. Traditional aircraft design methods may not guarantee optimal integration of electrical systems, in particular considering batteries current low technology readiness. Therefore, a multidisciplinary optimization framework has been developed and employed to quantitatively assess the potentials of an ATR42-600 regional aircraft retrofitted with hybrid-electric powertrains. The new framework has been conceived to extend the open-source program OpenConcept available design capability to regional turboprop aircraft retrofitted with different hybrid-electric powertrain and thermal management system architectures. Different discipline modules were improved and adapted to commercial aviation by integrating CS/FAR 25 requirements and airworthiness constraints. Optimization campaigns assessed the performance of both serial-hybrid and parallel-hybrid configurations on reference and short-range missions, considering different future battery technology energy densities. Retrofitted solutions were assessed in terms of fossil fuel consumption and CO2 emissions per kg of payload and km of range. Significant emission reductions can only be obtained for future battery technologies providing a specific energy of 1500 Wh/kg for a reduced payload of 3 t. Parallel-hybrid powertrains offer a more integrated solution for regional retrofitted aircraft. However, when CO2 emissions are normalized by a variable payload, the advantages of the retrofit are only observed for ranges smaller than 600 NM. Analysis of the optimization results has yielded valuable insights on the optimal battery use, which must be allowed along all the mission including diversion to minimize CO2 emissions. Hybridization strategies, using battery as booster during the most energetically-demeaning flight phases, such as take-off and climb, are not efficient for retrofitted aircraft, as optimal performance requires a combustion engine redesign.