Cryogenic Aircraft

In the middle of the 1970s the USSR developed an energy strategy, according to which, first of all, it was planned to use nuclear energy, and oil and gas in view of the smallness of reserves [as then it was counted] was planned to be replaced with alternatives under a second plan. The program of hydrogen power engineering began to be achieved.

Tupolev did not remain outside this program. As it was repeatedly in the history of the firm, Aleksey Andreevich Tupolev made the daring decision - to construct "hydrogen" aircraft. This aircraft was built and successfully tested without the a serious incident. This preceded the large long-standing program of bench and ground tests, directed both toward performance checkout of the new systems (but them on the aircraft it was about 30) and, in the first place, to the guarantee of safe operation.

The energy strategy proved to be not entirely precise. Nuclear energy did not obtain the prevailing development. Basic place in the development program of power engineering of the country engaged the natural gas, which exceeded in the course of time by the specific weight in energy balance 50%.

It should be noted that liquid hydrogen has a number of properties, exceptionally useful for the use as the aviation fuel. This, first of all, high heat of combustion, enormous cooling capacity and high ecological cleanliness. Liquid hydrogen makes it possible to substantially improve technical flight characteristics, to create aircraft with flight speeds of M > 6. Therefore our works on liquid hydrogen they made it possible to create the unique scientific and technical reserve, which will compulsorily find a use in not this already distant future. However, the extremely high cost of liquid hydrogen for a prolonged time excludes its commercial use.

As far as recent time is concerned, the task of tomorrow is the introduction as the aviation fuel [SPG], that also was reflected in "the development program of civil aviation equipment of Russia during the years 2002-2010 and for the period until 2015". The oil shortage is constantly aggravated. For past quarter of a century the specific weight of oil in the world energy balance were lowered by more than 10%. The cost of aviation kerosene in Russia on the average is at present 8000 rub. for the ton, the cost of ton [SPG] - 3000 rub. Gain is 5000 rub. for each ton of substituted aviation kerosene. Subsequently, in the opinion many experts, it follows to expect a gradual increase in this gain.

In recent years in the world and, in particular, in Russia occurred the unique scientific "explosion", which led to the idea, that the traditional and nontraditional resources of free natural gas can be increased more than by an order, also, as a whole exceed the resources of entire remaining traditional mineral of fuel on the planet.

Natural gas with the aid of the conduits is supplied practically to each airfield, i.e., questions of its transport in essence are already solved. Its high energy content, enormous cooling capacity make it possible to create aircraft with considerably the higher technical flight indices than aircraft on aviation kerosene. The fuel efficiency of flight on [SPG] can comprise to 10 [g]/[pass], km.

Tupelov began work in this area in 1986 and a bi-national program began in 1990. DaimlerChrysler Aerospace Airbus co-operated in a German-Russian effort started in 1990 to investigate environmentally compatible airliner using fuel other than kerosene. A two-year feasibility study by Deutsche (now DaimlerChrysler) Aerospace Airbus, completed in September 1992, concluded that liquid hydrogen is safer than natural gas, kinder to environment and more readily available over long term. Following this feasibility study, a new three-year phase was begun to develop critical technology and components such as tanks for liquid hydrogen storage at -253ºC at 1.5 bars (21.75 lb/sq in), together with pumps and seals. This was supported by German Ministry of Economics.

Participants in the Cryoplane project, under leadership of DaimlerChrysler Aerospace Airbus, include Tupolev, Samara, DaimlerChrysler Aerospace, Munich, Linde, MAN Technologie, Messer-Griesheim, UHDE, Honeywell, Bodenseewerk, Drägerwerk, Deutsche Lufthansa, Munich Airport, Berlin Airport Corporation and Hamburg's Max Planck Meteorological Institute.

Since 1988, Tupolev had tested a Tu-155 with one engine fuelled by hydrogen; it also operated on kerosene and liquid natural gas (LNG). Experience gained by Tupolev was applied to several projects, including the Tu-136, Tu-156, Tu-206, Tu-216, Tu-306, Tu-336 and Tu-338. DaimlerChrysler Aerospace Airbus planned to modify both turboprop and turbofan versions of a Fairchild Dornier 328 to operate on liquid hydrogen fuel. In parallel, Tupolev designed the Tu-130, which could use the same wings, turboprops, APU, fuel system and other components, but would operate on LNG.

The joint German-Russian team headed by Daimler-Chrysler, Airbus, and Tupolev (the former Soviet Union plane manufacturer) was developing a liquid hydrogen airplane called "Cryoplane." The project involves modifying an Airbus 310 and a Dornier 328 to use hydrogen. As of 1998 the partnership hoped to have Cryoplane serving European routes by 2010. Although the team investigated LNG, it appeared to be continuing only the hydrogen work.

The consortium believed that a combination of declining reserves of oil and concerns about greenhouse gas emissions will require an alternative fueled airliner by 2020 to 2040. In considering the various possibilities, it was decided that alcohol does not provide a viable amount of energy per mass. Natural gas and hydrogen meet requirements in that respect but gaseous storage would require unacceptably large or heavy tanks. Liquefied forms of hydrogen at very low temperature appear to be the solution.

Liquefied natural gas (LNG) is stored at -160 degrees C and provides 20% more energy per weight than jet fuel. This fuel is especially attractive to Russia, where there are ample reserves. The Russians have conducted flight trials with a testbed engine mounted on an experimental aircraft modified to run on LNG, hydrogen, or methane since 1988.

Liquid hydrogen provides 2.8 times the heat value of jet fuel per weight, but increases fuel volume by a factor of four. Designs for a modified Airbus A310 place the cryogenic fuel above the full length of the cabin in a bulbous housing. Burning hydrogen in a jet airliner will produce only water vapor and a small amount of nitrogen oxide. In part due to engine design, it appears that a hydrogen airliner would produce about 5% of the amount of N2O produced by a current turbofan jet-fueled engine.

The use of hydrogen fuel may cause concerns about safety among some, however, leaking liquefied hydrogen burns off rapidly and the flame raises quickly due to the low density of the gas. A hydrogen fire burns with little heat radiation, and it is believed that an aluminum airframe would be able to withstand a hydrogen fire and would protect the passengers.

A major challenge in using liquefied hydrogen as a jet fuel would be infrastructure. The proposal is to first convert intra-European wide-bodied airliner operations to hydrogen, ultimately involving about 500 aircraft and 70 airports. This would require an increase in hydrogen production by a factor of 200-300. The fuel would be produced by electrolysis, ideally using renewable energy sources. One proposal is to use about 100 MW of hydroelectric power produced by Hydro Quebec in Canada and to transport the fuel to Europe in container vessels similar to those used to transport liquefied natural gas.

Liquefied hydrogen currently costs several times more than jet fuel, but estimates are that there will be a crossover in costs in the 2010 to 2020 period. Jet fuel prices would rise due to reductions in production rates and possible imposition of carbon taxes.

The European Union (Airbus Deutschland GmbH 2003) funded a consortium of 35 partners from the aviation sector, led by Airbus Deutschland, to conduct a systems analysis of hydrogen-fueled aircraft-the CRYOPLANE project. This consortium examined a wide range of aircraft from business jets to large long-range aircraft such as the new jumbo Airbus A380. The key issue was to model the liquid-hydrogen fuel system. Per unit energy, liquid hydrogen has four times the volume of jet fuel; therefore, the fuel tanks must be four times larger. Analysis showed that because of the larger external surface area of the aircraft needed to accommodate the fuel tanks, the energy consumption would increase by 9 to 14%. Overall operating costs would increase by 4 to 5% based on fuel alone. It was also concluded that the engines would be equally efficient, the aircraft would have safety equivalent to that of current aircraft, and the environmental impacts would be substantially less (i.e., no carbon dioxide emissions). Further development was needed; however, such an aircraft system could be implemented within 15 to 20 years of a decision to use hydrogen as a fuel.