OK, let's take this hydrogen fuel thing one step further.
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Join Date: Dec 2005
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OK, let's take this hydrogen fuel thing one step further.
Suppose you fill up a main fuel tank with distilled water (obtained through solar-powered or nuclear-powered desalination plants) and a smaller tank with jet fuel, or a mix of ethanol and hydrocarbon fuel; or even bio-diesel.
Then you wrap around these fuel tanks a tri-jet design, with one conventional engine in the tail, plus an APU, and two hydrogen-burning engines, either underwing, or under a T-tail.
OK, here's the deal: The APU and conventional engine run generators that convert the water to hydrogen and oxygen by electrolysis...plus the conventional engine provide thrust. The hydrogen and oxygen get piped to the hydrogen-burning engines and produce thrust and water vapor. You wouldn't need an inlet on these engines, because no additional oxygen would be required for the combustion equation (2H + O = H2O); thus parasite drag would be greatly reduced (the H.B. engines could even be completly conformal with the fuselage, except for the nozzle(s), of course).
When you get to cruise, with reduced power required, the APU is shut off and the conventional engine's generator should be able to provide sufficient electric power to produce enough hydrogen and oxygen to keep things going.
Perhaps one of the H.B. engines could even be shut down as well, reducing oxygen and hydrogen demand. Of course this would only be practical if the H.B. engine installation were such that this resulted in no asymmetric thrust, which would add drag and spoil, or partly spoil, any efficiency gained.
The engine(s) (conventional or H.B.) could also run an air cycle machine to cool some of the gaseous hydrogen, and compress it to some extent (through an engine accessory drive), so that you'd have an small supply of hydrogen fuel in the (extremely unlikely) case of total electric generating failure compounded with failure of the conventional engine; in this case, the drill would be to glide engine out as much as possible, then open up emergency intakes for ambient air on the H.B. engines, then feed the emergency store of hydrogen in for a restart to powered flight and landing.
This power-failure scenario would probably only be feasible for overland routes, or for routes with very short over-water segments, where suitable emergency landing fields would be within glide + emergency-fuel-powered-segment distance.
OK. So let's here it from you guys who can run the numbers: Can a rig like I've described generate enough electrical power so that the electrolysis process could keep up with the fuel demand? Obviously the size of the aircraft is open...100 seats...200...whatever...the largest that would be economically feasible, given the basic premise that only 1/3 of thrust would be driven by hydrocarbons, thus resulting in a net savings of 2/3 of the hydrocarbon fuel burn.
So, whaddaya think?
P.S. In case of the 1 in a billion chance that this thing would work, I hereby claim the idea as intellectual property. I'm registered with pprune, so they know who I am and where to find me....
Then you wrap around these fuel tanks a tri-jet design, with one conventional engine in the tail, plus an APU, and two hydrogen-burning engines, either underwing, or under a T-tail.
OK, here's the deal: The APU and conventional engine run generators that convert the water to hydrogen and oxygen by electrolysis...plus the conventional engine provide thrust. The hydrogen and oxygen get piped to the hydrogen-burning engines and produce thrust and water vapor. You wouldn't need an inlet on these engines, because no additional oxygen would be required for the combustion equation (2H + O = H2O); thus parasite drag would be greatly reduced (the H.B. engines could even be completly conformal with the fuselage, except for the nozzle(s), of course).
When you get to cruise, with reduced power required, the APU is shut off and the conventional engine's generator should be able to provide sufficient electric power to produce enough hydrogen and oxygen to keep things going.
Perhaps one of the H.B. engines could even be shut down as well, reducing oxygen and hydrogen demand. Of course this would only be practical if the H.B. engine installation were such that this resulted in no asymmetric thrust, which would add drag and spoil, or partly spoil, any efficiency gained.
The engine(s) (conventional or H.B.) could also run an air cycle machine to cool some of the gaseous hydrogen, and compress it to some extent (through an engine accessory drive), so that you'd have an small supply of hydrogen fuel in the (extremely unlikely) case of total electric generating failure compounded with failure of the conventional engine; in this case, the drill would be to glide engine out as much as possible, then open up emergency intakes for ambient air on the H.B. engines, then feed the emergency store of hydrogen in for a restart to powered flight and landing.
This power-failure scenario would probably only be feasible for overland routes, or for routes with very short over-water segments, where suitable emergency landing fields would be within glide + emergency-fuel-powered-segment distance.
OK. So let's here it from you guys who can run the numbers: Can a rig like I've described generate enough electrical power so that the electrolysis process could keep up with the fuel demand? Obviously the size of the aircraft is open...100 seats...200...whatever...the largest that would be economically feasible, given the basic premise that only 1/3 of thrust would be driven by hydrocarbons, thus resulting in a net savings of 2/3 of the hydrocarbon fuel burn.
So, whaddaya think?
P.S. In case of the 1 in a billion chance that this thing would work, I hereby claim the idea as intellectual property. I'm registered with pprune, so they know who I am and where to find me....
Join Date: Jun 2001
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Nice try...
Converting H20 to H and O, then converting it back again, would involve a net loss of energy. If it takes x joules to split the water molecules, you'll only get x minus e joules back again by burning the hydrogen, where 'e' represents the energy lost due to ineffiency in the process.
(Side rant - Advertising that describes hydrogen fuel cells as "non-polluting" is dishonest. Fuel cells do pollute - how can you run a giant electrolysis factory to split water into H2 and O2 without polluting? Even solar cells cause environmental pollution to some extent. Rant over.)
Hydrogen as a fuel works well either where there is no atmospheric oxygen - rockets - or where it is easier and cheaper to do the electrolytic splitting of water molecules in a big industrial plant and harvesting the hydrogen energy in your aeroplane, where you don't have a nuclear reactor or 4.2 gazillion solar cells. But in your aeroplane you certainly wouldn't carry, or generate, your own O2.
Nice try!
O8
(Side rant - Advertising that describes hydrogen fuel cells as "non-polluting" is dishonest. Fuel cells do pollute - how can you run a giant electrolysis factory to split water into H2 and O2 without polluting? Even solar cells cause environmental pollution to some extent. Rant over.)
Hydrogen as a fuel works well either where there is no atmospheric oxygen - rockets - or where it is easier and cheaper to do the electrolytic splitting of water molecules in a big industrial plant and harvesting the hydrogen energy in your aeroplane, where you don't have a nuclear reactor or 4.2 gazillion solar cells. But in your aeroplane you certainly wouldn't carry, or generate, your own O2.
Nice try!
O8
