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A hydrogen-powered aircraft is an airplane that uses hydrogen fuel as a power source. Hydrogen can either be burned in some kind of jet engine, or other kind of internal combustion engine, or can be used to power a fuel cell to generate electricity to power a propeller. Unlike normal aircraft, which use wings for storing fuel, hydrogen aircraft are usually designed with the liquid hydrogen fuel carried inside the fuselage, in order to minimize surface-area and reduce boil-off. According to research at the Pennsylvania State University in 2006, large commercial hydrogen aircraft could be built by 2020 but "will probably not enter service until closer to 2040."〔(Maniaci, David C. "Operational Performance Prediction of a Hydrogen-Fueled Commercial Transport" 2006 symposium paper )〕 The European Union's research project in cooperation with Airbus and 34 other partner companies dubbed ''CRYOPLANE'' assessed the technical feasibility, safety, environmental compatibility and economic viability of using liquid hydrogen as an aviation fuel. This was concluded in 2002 (with the final report published in 2003).〔(Airbus Deutschland "Liquid Hydrogen Fuelled Aircraft - CRYOPLANE Final Technical Report" 2003 )〕 ==Properties of hydrogen== Being an alternative to traditional jet fuel, hydrogen has a higher energy density per unit ''mass'' but a lower energy density per unit ''volume'', and containing the hydrogen at high pressure would require a heavy container. In aircraft heavy containers are not an option, and therefore regular carbon fibre tanks are often used, which can only sustain a pressure of about 350 bar. This is significantly lower compared to steel hydrogen containers (used in cars and ships) which can sustain 500 to 700 bar. This limitation decreases the amount of energy that can be spent on the propulsion by about half.〔Eos magazine, vliegen op waterstof, july&august 2008〕 Alternatively, as with some rockets, cryogenic liquid hydrogen could be employed. If hydrogen were available in quantity from renewable energy sources, its use in aircraft would produce fewer greenhouse gases (water vapor and a small amount of nitrogen) than current aircraft. Currently, however, very little hydrogen is produced using renewable energy sources, and there are several serious obstacles to the use of hydrogen in aircraft and other vehicles.〔("Hydrogen aircraft" at H2-Vehicles.com )〕 Due to the way it is produced, and the relative inefficiencies of its production given current technology, hydrogen is a much more expensive fuel than fossil fuels. Liquid hydrogen is one of the best coolants used in engineering, and it has been proposed to use this property for cooling intake air for very high speed aircraft, or even for cooling the vehicle's skin itself particularly for scramjet-powered aircraft. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hydrogen-powered aircraft」の詳細全文を読む スポンサード リンク
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