Fig. 1.
![Relative specific fuel consumption for aircraft engines, plotted against certification year [8].](https://sciendo-parsed.s3.eu-central-1.amazonaws.com/6869a05be88a4c302353f78c/j_tar-2025-0006_fig_001.jpg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=ASIA6AP2G7AKNR5EGZMV%2F20260318%2Feu-central-1%2Fs3%2Faws4_request&X-Amz-Date=20260318T172636Z&X-Amz-Expires=3600&X-Amz-Security-Token=IQoJb3JpZ2luX2VjED8aDGV1LWNlbnRyYWwtMSJIMEYCIQDrslC1x7Qw2sY6U58lLAGUWRtMnLCN4Vg2VBK2nop1DAIhAJBW3BagEZ7u5ykwJkbPC36Smn9HUqHxiI1pMcZeVqybKrsFCAgQAhoMOTYzMTM0Mjg5OTQwIgz2f0oQIds%2FlOmhfCgqmAUyZV5sV1MV8kpPKdYZtMONzNgK4Z2MRMk8aVxMXpJXn7B%2BPlMs4HeuTVoZFPQ519vFbqfvqr0VEVcB4NkQoKP36btu02vjIK8JdwYFn2EcuPFOWhCOo5jPv0SYxLVr5ASxXmH18pbca%2FdknBbULJMEwe3kT%2Fvv2AUgHxyviUYrFwKkL5eVwT6792ZOVyIeQUkCQRmWVh%2FtgQR0VFoAvd5qRkbCKYbThRPLgzkX2vKRwHr4oQ6KT8uLOxEBGO39sPuUdkA3CsyKdW8ADIiNiAEoLHicP%2FNoo%2F3CAb50SW31ay6XF178S3nuMx222vN7E0vKqDeE0dmFEJvdeRVU31dSx08YjsB5SkgIQXUxUTdhvOlAwGOx7f%2BuhwRpFYb7xdOn39tT39tQbv4uNskNiR0FcF2lCVre9d27ZMtcvr8%2FPYVc%2Fea28LSZYUigR58%2BNi%2F2sx2LndLOsrWbEG0wkxBU273crz7LYGbLjlQ4Jj6lBLqyhKm5rtwkG7IPW1OF8EYTiwxnus%2BNnM%2FXUI3VFWphdWfP47g1ADf0RVLz7x64Fq4Qy%2BYxRQwSRucyb5V16Dc%2F3bLDaIxpdYWNrZcx4Ga3YZ%2FC3MpVRjfmA5YVktilfpQLnguZ7tnq1%2F9Q3V7l9B0zpWLBneKdqsGoYL3RLHSWsAO%2BbhAXRmmdxC5brrDtsawoUnpasu1q77j2x5jMqpcLDhfJSyP4J8VU1vdEFCJ9ArnuVjToBykLg5yXj4jeSuNxelYHjQv01mAVJz7qUtIoG6yPEc1K%2FNoPxTLIGLuJbaVhU5P%2FMCK4n1aRIhcWBYzzwtzBPWoEDDmaWMZBLpq07fMX4ipAMTuFwmuNw0S6xkhlvK0jQKFeS%2F9uE9T9IkouwNtQoKb3MOru6s0GOrAB60GJQVu22vOqGxlsVNLhLAtX33lDd0aq21WVZ4pnjqYhwFmpf1RRg6M3sbFAv6BsFmDQ37zpALX7CW5gOyXpnwU3N331KnCC3fhJe2nPW17yaDu9sIY66V2jVra8abNlY382W54YDq7TWPN8mQHlj8NjjZi479Py74DefTdZxIArreSR%2BWSJEuWmBnGC6jo5aq3wJVvJYrRa2xjf84LDB75v6QJ03HGU%2FEnSYmQWRq8%3D&X-Amz-Signature=14f76aea11e5066033266ef158920f56b69432e71892dcbdb08f08334d22791e&X-Amz-SignedHeaders=host&x-amz-checksum-mode=ENABLED&x-id=GetObject)
Fig. 2.

Energy density comparison of different fuels_
| Fuel | Energy Density [MJ/kg] | Energy Volumetric Density [MJ/liter] |
|---|---|---|
| Hydrogen (Gas at 1 bar) | 120 | 0.1 |
| Hydrogen (Gas at 300 bar) | 120 | 3.03 |
| Hydrogen (Gas at 600 bar) | 120 | 6.06 |
| Hydrogen (Liquid) | 120 | 8.49 |
| Jet-A Fuel | 45 | 34 |
| Gasoline | 44 | 31.5 |
| Diesel | 46 | 35 |
| Ethanol | 28.8 | 20 |