Comparison of Future Aviation Fuels to Minimize the Climate Impact of Commercial Aircraft

Sustainable aviation fuel (SAF) and liquid hydrogen are currently being studied to replace kerosene in commercial aviation to reduce global warming. In this study, the question is how do the airplane design variables change when minimizing the global warming impact of aircraft powered by SAF or LH2? Secondly, how do these aircraft compare in terms of climate impact and operating costs, considering regional, medium-, and long-range categories? A multidisciplinary design optimization process varies airframe, turbofan engine and mission design variables to obtain the cost- and climate-optimal design solutions. A linearized temperature response model evaluates the average temperature response over 100 years considering both CO2 and non-CO2 effects. The trade-off between climate impact reduction on the one hand and operating cost, on the other hand, is studied for each fuel type and aircraft category. We conclude that LH2 can achieve the largest reduction in temperature response in all categories. The maximum reduction of 98% compared to the cost-optimal kerosene aircraft comes at an estimated increase of 30, 42, or 69% in operating costs for regional, medium-, and long-range missions. The SAF aircraft can reduce the climate impact by 86, 82, and 72% for regional, medium-range, and long-range aircraft. These savings lead to an 8, 14, and 26% increase in operating costs. The analysis shows that the SAF-powered aircraft are preferred over the cost-optimal hydrogen aircraft for the regional and medium-range categories. Hydrogen does provide a Pareto-optimal solution for long-range aircraft, albeit at a significant in-flight energy and cost penalty.