Near-zero environmental impact aircraft

Abstract

The fundamental challenge facing today's aviation industry is to achieve net zero climate impacts while simultaneously sustaining growth and global connectivity. Aviation's impact on surface air quality, which is comparable to aviation's climate impact when monetized, further heightens this challenge. Prior studies have proposed solutions that aim to mitigate either aviation's climate or air quality impacts. No previous work has proposed an aircraft-energy system that simultaneously addresses both aviation's climate and air quality impacts. In this paper we (1) use a multi-disciplinary design approach to optimize aircraft and propulsion systems, (2) estimate lifecycle costs and emissions of producing sustainable fuels including the embodied emissions associated with electricity generation and fuel production, (3) use trajectory optimization to quantify the fuel penalty to avoid persistent contrail formation based on a full year of global flight operations (including, for the first time, contrail avoidance for a hydrogen burning aircraft), and (4) quantify climate and air quality benefits of the proposed solutions using a simplified climate model and sensitivities derived from a global chemistry transport model. We propagate uncertainties in environmental impacts using a Monte-Carlo approach. We use these models to propose and analyze near-zero environmental impact aircraft, which we define as having net zero climate warming and a greater than 95% reduction in air quality impacts relative to present day. We contrast the environmental impacts of today's aircraft-energy system against one built around either “drop-in” fuels or hydrogen. We find that a “zero-impact” aircraft is possible using either hydrogen or power-to-liquid “drop-in” fuels. The proposed aircraft-energy systems reduce combined climate and air quality impacts by 99%, with fuel costs increasing by 40% for hydrogen and 70% for power-to-liquid fueled aircraft relative to today's fleet (i.e., within the range of historical jet fuel price variation). Beyond the specific case presented here, this work presents a framework for holistic analysis of future aviation systems that considers both climate and air quality impacts.