Potential of Reducing the Environmental Impact of Civil Subsonic Aviation by Using Liquid Hydrogen

FOI-R--1636--SE
April 2005
ISSN 1650-1942
Scientific report

Fredrik Svensson

Abstract
Mainly owing to the dwindling fossil oil resources and the environmental concerns of discharging greenhouse gases into the atmosphere, it is essential to find an alternative to kerosene for civil aviation.

The overall objective of this thesis is to evaluate the potential of reducing the environmental impact of civil subsonic aviation by using hydrogen fuel. Mainly due to the complex interactions among a number of different fields affected by the introduction of hydrogen in aviation and due to the nature of the research question, the chosen scientific approach for this thesis is to carry out a broad study covering a number of selected fields. Engine and combustion chamber design are studied in detail, along with the cruise altitude for minimum environmental impact. Airport implications, and available and envisioned methods for hydrogen production are discussed. From a technical point of view, it seems to be feasible to use hydrogen for aero gas turbines. In terms of pollutant emissions, hydrogen use offers the possibility of a significantly reduced number of emission species, resulting in only H2O and small quantities of NOx emissions.

For minimum environmental impact, the results suggest that cryoplanes should cruise at an altitude of about 2-3 km below where conventional aircraft cruise today. If the priority is to lower the mission fuel consumption, the results indicate that an engine employing increased combustor outlet temperature, overall pressure ratio and by-pass ratio, seems to be the most attractive choice. The mission NOx emissions, on the other hand, seem to be reduced by using engines with a weak core and lowered by-pass ratio. Ignoring the cost implications, from an airport infrastructure point of view, it seems feasible to change to hydrogen use. With respect to the availability of energy, it would be reasonable to change from kerosene to liquid hydrogen as fuel for all civil aviation refuelling in Sweden.

The report as a pdf-file (2,8 Mb)

Acknowledgements
The work accomplished in the thesis was financially sponsored by the Swedish Energy Agency, the Swedish Defence Research Agency and the European Commission. I would like to thank Professor Riti Singh, my supervisor, for giving me the valuable support and advice which have enabled me to carry out this project. His technical knowledge and kindness for support in both technical and practical matters are gratefully acknowledged.

The work has greatly benefited from contacts and discussions with Anders Hasselrot and Anette Näs at FOI, Matthew Whellens at Rolls-Royce plc, Anthony Jackson consultant at Cranfield University, Professor Friedemann Suttrop at Fachhochschule Aachen, Germany, and Stefano Boggia at MTU Aero Engines. I thank you all. Special thanks go to Anders Hasselrot for providing advice on aircraft aerodynamics, and to Anette Näs, Sven-Erik Thor (FOI) and Susan Raia Canali for help in the proof reading of the thesis.

Rachel Smith and Sue Gow are greatly acknowledged for solving all the administrative issues. I would also like to thank Jan Westerberg formerly at FOI who contributed to the initiation of this Ph.D. project.

Last, but not least, I would like to thank my fiancée Jenny for always supporting me.