Environmental implications of hybrid-electric regional aircraft: emissions and climate change

This paper presents a performance analysis of hybrid-electric aircraft focused on emissions estimation. Specifically, the aim is to provide a broad overview of emissions reduction potential and the environmental impact related to the introduction of hybrid-electric propulsion in the regional sector. The discussion, based on outcomes of conceptual studies and information available in the literature, aims to provide a qualitative picture that highlights both the potential gains and the critical issues connected with the practical technological utilization of hybrid-electric propulsion for regional aircraft, and its general implications on environmental issues. The conceptual design of the hybrid-electric aircraft was carried out using an in-house multidisciplinary optimization framework, whereas the ‘Boeing fuel flow method 2’ was used to estimate pollutant emissions. The paper is divided into two parts: the first part is aimed at comparing the non-CO2 emissions, i.e. NOx, HC, SO2, CO, of a hybrid-electric aircraft designed to minimize block fuel, with a thermal aircraft designed by the same methodology and according to same requirements; the second part presents a similar assessment but focusing on CO2 emissions. The CO2 assessment takes both flight and electricity generation emissions into account. The results of the first part show that the hybrid-electric configuration could provide room for non-CO2 emissions reduction, both during the entire mission the landing and take-off cycle. However, further refinement of predictive models for emissions computation are needed to improve these predictions. The results of the second part show that the hybrid-electric configuration could provide CO2 emissions reductions for design ranges below 600 nm; however, if the ground electric energy production does not shift towards a full renewable-based scenario, these benefits could result marginal.