Naked Science Forum
Non Life Sciences => Technology => Topic started by: katieHaylor on 19/06/2017 10:19:07
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David says:
In jet engine technology, could you combine and ignite hydrogen and oxygen as a fuel, instead of using oil?
What do you think?
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Yes, you most certainly can. Concepts for jet aircraft powered by liquid hydrogen have been done before (one example being the Lockheed CL-400 Suntan, although it was never built). Hydrogen has the benefit of burning cleanly, but it has the disadvantage of needing to be refrigerated to keep it liquid. It also has a lower energy density per unit volume than traditional hydrocarbon-based jet fuels. An aircraft that carries 1,000 gallons of liquid hydrogen will have a shorter range than that same aircraft if it carried 1,000 gallons of hydrocarbon fuel instead.
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Many rocket engines are powered by liquid Hydrogen and liquid Oxygen.
It does require cryogenic tanks to store Hydrogen with reasonable density.
If you want to burn it efficiently, you set the mixture to burn at a high temperature; unfortunately, most solid materials will melt and boil at these temperatures.
One solution used in the Apollo upper stage was to make the fuel ports out of sintered (porous) metal, so that the cryogenic hydrogen percolated through the metal, keeping it cool despite the incredibly hot flame that was projected from the port.
Of course, the combustion chamber had to be surrounded by cryogenic cooling, and gas flow organized so that a surface film of cooler gas insulated the walls from the hot gas in the center of the combustion chamber.
To feed the hydrogen into the combustion chamber under pressure, you need a cryogenic turbopump, which is like a little rocket engine.
So hydrogen has been used as a fuel, but it is a high-cost engineering challenge, used when you have multiple high-cost engineering challenges (like escaping Earth's gravity well).
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The answer to your question is a BIG YES, but why do you want to carry a large Oxidizer tank with you, when you can have an air breather engine like HOTOL ? https://en.wikipedia.org/wiki/HOTOL
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I agree with you, Kryptid.
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If you mean can you carry oxygen with you, yes, but it tends to burn too hot for gas turbine rotor blades and they tend to burn out. Normal jet engines use air because the nitrogen dilutes the combustion reaction and keeps it cooler. It also avoids having to carry (liquid) oxygen because it's expensive, weighs down the plane and reduces range.
So if you restrict yourself to the oxygen in the air, the answer is a resounding yes, you can use hydrogen for powering jet engines, and it burns and works extremely well and doesn't get too hot or anything. Indeed, Hans von Ohain built the very first working jet engine and that used hydrogen for fuel!
Hydrogen fueled airliners are on the drawing board, and actually work better than normal aircraft, they could fly much further on a single load of fuel, non stop half way around the world even supersonically, but the liquid hydrogen they would need to burn is relatively expensive, and basically because the hydrogen has very low density, the aircraft would be very big and few existing airports would be able to handle them.
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I see the future of "Aviation" using Hydrogen and as the primary fuel.
Here we will find that the Hotol Oxygen capturing technology, will enable E-Planes to tank cryogenic Hydrogen and to capture Oxygen from the atmosphere during the flight, to power the on board fuel cells.
For super sonic flights, we will probably see a new new type of Concord, able to travel to continents and fly into the earth orbit and beyond, using Hotol technology, again with Hydrogen as the primary fuel and captured Oxygen.
The future of Aviation, in my humble opinion is with Hydrogen.
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Little point in carrying fuel cells if you have atmospheric oxygen available: you can run a conventional alternator from the jet rotor or a bleed duct, or even have an entire turbine as an APU, just as on any other aircraft.
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Your are correct in every which way, but I wanted to bring our fine UK HOTOL inventor back into the equations. As innovation can be a soul destroying for a small inventor, as I know from personal experience. Have your tried to persuade a multi national company to even look at something, outside their range of experience and current product mix. I have ... and it is a roller-coaster, personally and financial.
But please do not consider my comment as a cheap ploy to bring HOTOL back into focus, because their oxygen capturing system would enable future jet-planes to fly higher, considerable faster and cheaper.
It has never crossed my mind, that a powerful APU unit (as a bolt on system) could be used power an E-propulsion plane, what a brilliant idea you have had here.
Thank You.
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On a quick reading of the runes, HOTOL good, LACE bad. The idea of using liquid hydrogen to concentrate atmospheric oxygen is amusing, but only if you have plenty of spare LH. This is OK for research and military vehicles, but commercial transport has to run at a profit, with short turnround times, high payload ratios, and very low values for acceleration and deceleration - not the characteristics we associate with orbital rockets.
Call me oldfashioned, but a hot dinner and a movie in a 747 is a pleasant start to a holiday or a perk of business. 4g acceleration and no windows is not. If I want to talk urgently to colleagues in Australia, I pick up the phone.
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The Reaction Engines A2 is the aircraft version, and doesn't pull 4g, it's relatively normal takeoff and acceleration, it's just that it keeps accelerating to Mach 5, and it should have tremendous range because liquid hydrogen is so very light.
https://en.wikipedia.org/wiki/Reaction_Engines_A2
Skylon is the orbital version, that's much more sporty, it pulls 3g on the way up:
https://en.wikipedia.org/wiki/Skylon_(spacecraft)
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Please count me in for the maiden flight, 3 G will do nicely for me. LOL
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Of course there was a real-world jet propelled aircraft that was propelled by liquid hydrogen fuel. Can anyone name it? (n.b. Slight trick question).