Potential of reducing the environmental impact of civil subsonic aviation by using liquid hydrogen
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 H₂0 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.