Alternative Fuels in Aero Engine Performance Calculations

This paper presents a method for gas turbine performance calculations with alternative fuels with a particular focus on their use in aircraft engines. The effects of various alternative aviation fuels on fuel consumption, CO2 emissions, and contrail formation are examined in a comparative study. We use the GasTurb performance software and calculate heat release and hot section gas properties using a chemical equilibrium solver. Fuels with complex compositions are included in the calculation via surrogates of a limited number of known species that mimic the relevant properties of the real fuel. An automated method is used for the fuel surrogate formulation. We compare the results of this rigorous approach with the simplified approach of calculating the heat release using an alternative fuel’s heating value while still using the gas properties of conventional Jet A-1. The results show that the latter approach systematically overpredicts fuel consumption by up to 0.2% for aromaticsfree synthetic kerosene (e.g., “biofuels”). Overall, aircraft engines running on alternative fuels tend to be more fuel efficient due to their often higher hydrogen contents and thus fuel heating values. We find reductions in fuel consumption of up to 2.8% during cruise when using aromatics-free synthetic kerosene. We further assess how alternative fuels affect contrail formation based on the Schmidt-Appleman criterion. Contrails can form 200 m lower under cruise conditions when burning aromatics-free synthetic kerosene instead of Jet A-1 with identical thrust requirements and under the same atmospheric conditions, mainly due to their higher hydrogen content. In summary, we present a flexible yet easy-to-use method for studying fuel effects in performance calculations that avoids small but systematic errors by rigorously calculating the heat release and hot section gas properties for each fuel.