HYDROGEN AVIATION

At the present time, ecological and energy problems of fuel use around the world became more and more visible, factual, and global. The best results from present progress and world development we can get from fuel exchange for our transportation system. The escalating of organic fuel use will be impossible soon. It is caused by limitation of oil resources, increasing of oil requirement of other industries, pollution of an environment.

Hydrogen (liquid and gaseous) is the most perspective power supply now.

Today, quantity of airplanes, engines, and airports are so huge, that the exchange of fuel seems very expensive and long time process.

Basic ideas of fuel exchange are briefly described in this article. For more information, please, contact me (Filas@mail.ru). This work doesn’t contain any secret information. 

Hydrogen satisfies many requirements for aviation fuel. Hydrogen gives a minimum pollution of the environment. The high heat of hydrogen combustion exceeds heat of kerosene one in 2,8 times; high completeness of hydrogen combustion allows to increase engine efficiency, to reduce specific fuel consumption, to reduce weight and overall engine dimensions.

There are many advantages of hydrogen as an aviation fuel. LH₂ (liquid hydrogen) easily exhales and fast diffuses on all volume of the combustion chamber, promoting a quick engine start. Minor energy and wide diapason of hydrogen-air mix ignition also promotes a quick engine start at different temperatures and altitudes. Hydrogen combustion gives a flame with low radiation and burns down without fouling, increasing safe life and reliability of engines. Hydrogen has a small corrosion activity. Engines on LH₂ don’t pollute environment. Hydrogen heat-absorption capacity is higher, than kerosene one in 30 (!) times. So, hydrogen can be used in engine cooling systems and A\C (aircraft) one. Increasing of turbines cooling efficiency allows increasing the temperature in front of a turbine, and a compressor pressure ratio. Other results are decreasing specific fuel consumption (15-20 %) and increasing a specific thrust of the engine. Smaller weight of A\C reduces a wing load and a wing size. So noise in an airport will be decreased. LH₂ allows creating compact combustion chambers with more constant temperature field. Because of high hydrogen thermal capacity, temperature in a turbine entrance will be lower, etc.

Flight performances of LH2 A\C tend to optimization at M ~ 6. So, the more airplane weight and speed, the more expediently hydrogen using. The majority disadvantages of LH₂ as an aviation fuel are its very low density (63-70 kg / ì³) and low boiling temperature (20Ê). So, aircraft tanks should be large and have the configuration with minimized relation of a surface to a volume to minimize evaporation losses and isolation weight. Also, some materials become friable in LH₂. 

There are three steps of fuel exchange to cryogenic fuel.

1. Only a few airports have cryogenic systems. At this step, custom (kerosene) A\C and bifuel (kerosene + LH₂) A\C will be used. Bifuel A\C is existing airplane with an established cryogenic tank. Required weight of hydrogen is less than kerosene one in 2,8 times, but because of low density of hydrogen, the required volume of tanks is higher in 4,3 times. Such fuel volume can be placed above a fuselage. It is possible to place tank inside, but a passenger seat capacity will be decreased. Bifuel A\C can use both kerosene, and hydrogen. Their application is justified about two causes: à) they don’t demand availability of a cryogenic system in each airport, b) they boost development of a cryogenic infrastructure.

2. Largest airports have cryogenic systems. About 50 % of passengers are transported by hydrogen. At this step, the most widespread type of A\C are bifuel. Kerosene A\C disappears by appearance of cryogenic one, including hypersonic. Such A\C are initially designed for hydrogen using. A flat fuselage makes majority lift. Small wings extend along A\C and have elevators. A cryogenic tank is arranged in center of a fuselage. There are passenger cabins on both sides of it. There are two turbine engines where the fuselage passes to wings. There are hypersonic engines of external combustion in tailpiece or under wings. Turbine engine will be used during takeoff, landing, and on speeds up to 1,5-2Ì. The main flight will be on speed 6-12Ì at the altitude above 18 km, using an engine of external combustion. Aerodynamic parts will close input and the outlet openings of turbine engines at this time. After little change of a design and installation of a RE (rocket engine, such A\C can reach to the orbit. This A\C have no turbine engine. Liquid oxygen tanks are installed instead them. Installation of extra tanks is also possible. A\C will start from any airport, using RE. Using lift of a fuselage and wing, it will accelerate up to 2Ì. Then RE will be switch off, and engines of external combustion will be switcheded on (they will use oxygen from atmosphere). A\C will reach the greatest possible altitude and speed, and rocket engine will be turned on again.

3. All airports have cryogenic systems. Cryogen hypersonic planes are ordinary aircraft. Bifuel planes gradually disappear. 

Development hydrogen infrastructure is divided into three steps too.

1. Liquid hydrogen storehouses will be built in airports (such facilities are already exist). Liquid hydrogen delivery will carry out by railway from nearest LH₂ plants. They will receive gaseous hydrogen from pipelines, or produce it. The refueling of A\C will be made by cryogenic pipelines, or from cryogen tank lorries. All described objects already exist and successfully use.

2. The nuclear plants for producing gaseous hydrogen will arise on ocean coasts. The hydrogen pipelines will be under construction or upgraded from existing ones. Unified hydrogen industry will arise. Let's notice, that power transmission by hydrogen pipeline is cheaper, than by electric lines. So, hydrogen can be used on electric power stations. It will refine ecology of large cities. Transportation of gaseous hydrogen is more safety, than natural gas one. At outflow, hydrogen rises up fast, and solves in atmosphere, but natural gas accumulates, forming explosion-dangerous mixes (two passenger trains burnt down in Russia in 80-s). Hydrogen industry will make power engineering and national economy independent of oil crisis and prices. Any country can produce hydrogen, especially if it uses oceanic water (this water contains fuel for the reactor). Large airports will have LH2 plants. They will receive gaseous hydrogen by pipeline. A part of LH₂ will be sent to the nearest airports, which have no plant, yet. A part of gaseous hydrogen can be used for providing an airport and city with electric power.

3. All airports will have own LH₂ plant. The large airports will launch and receive freights from orbit.

There are four types of cryogenic engines.

1. Bifuel engines are created on the basis of existing engines. Only a hydrogen system is added. It consists of a hydrogen tank, a buster pump, hydrogen highways and valves, a universal turbine pump, evaporator, fuel injectors. The cryogen system is universal and can be used in cryogenic engines of next generation, including hypersonic. A basic unit of the system is a universal turbine pump, which can run with any type of engines (the author proved in his degree work a basic opportunity of such unit creation). Unfortunately, its description is too large and will be given in next article. The turbine pump gives liquid hydrogen into an evaporator. Hydrogen evaporates, heats up and actuates a turbine of the turbine pump. Then hydrogen moves into fuel injectors of engine combustion chamber. The evaporator can be located behind the turbine of the engine or on a fuselage surface of a hypersonic liner. Let me notice, that an upgrade of an engine consists only of installation of the hydrogen fuel injectors and the evaporator. Such engine has two fuel systems and can run, using any available fuel (but not both fuel at the same time!).

2. Cryogenic GTE (Gas Turbine Engine). Such engines are created for hydrogen use only, but kerosene GTE is their prototype. The hydrogen system is similar to bifuel engines. Cryogenic GTE will be used with subsonic planes, and also hypersonic ones as a low-speed engine (take off – landing).

3. Hypersonic engines of external burning. Their fuel system is like cryogen GTE one, but all the rest devices are completely different. The hypersonic engine has no rotating parts (compressor, turbine). Fuel goes directly on an A\C surface, and burns down without initial, because of high air temperature.

4. Rocket engines. Uses hydrogen and oxygen from cryogenic tanks.

As you see, fuel exchange to liquid hydrogen affects energy industries of countries. Fuel exchange will improve an ecological situation; create new workplaces, reduce time and cost of flights. Launching of the spaceships will be easier, and cheaper. Fuel exchange requires decades, but can be start today, because EVERYTHING necessary for the first step already exists. A hydrogen system and a turbine pump were already tested with an engine NK–88 on an airplane Tu–155.

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