Direct alcohol vs. alcohol-to-jet SPK utilisation in commercial aviation-an energetic-operational analysis

To support renewable energy utilisation in aviation apart from kerosene-based sustainable aviation fuel (SAF), a direct use of renewable alcohols (methanol, ethanol, propanol, butanol, pentanol) is analysed and compared to their use as alcohol-to-jet (ATJ) conversion intermediates. The energy demands in the form of alcohol and operational payload-range implications are analysed for two aircraft types, using a Breguet range equation and a mass/energy balance approach. From an energetic perspective a direct alcohol usage is significantly more efficient compared to the ATJ pathway requiring 40% to 60% more alcoholic energy. Even considering low process losses and high kerosene fractions (95%), the ATJ conversion still requires about 16% (26% for methanol) more alcoholic energy. Especially for methanol and ethanol that lead to significant payload-range losses compared to kerosene of approx. 70% and 50%. These effects are less significant for propanol, butanol, and pentanol with range reductions of 40%, 30%, and 25%.