planelover
Posts: 313
Joined: Sat Dec 22, 2001 1:22 pm

Question About Hydrogen Sub-sonic Engines

Fri Jan 11, 2002 12:32 pm

Hey all,
I'm sure some of you have heard all the stuff about the new hydrogen cars that different car manufacturers are comming out with. GM says that they could probably have a hydrogen car selling in 8-10 years.
Anyways, are there any aircraft engine manufacturers that are looking into hyrogen as a possible fuel source for sub-sonic aircraft? Is this feasable? I'm not sure about all the mechanics, but from what I understand, on the GM cars, the hydrogen mixes with some other chemicals that ends up producing electricity that then turns electric motors that then turn the wheels. Is this right?
Let me know what you all think. Thanks.  Smile/happy/getting dizzy
 
IndianGuy
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RE: Question About Hydrogen Sub-sonic Engines

Fri Jan 11, 2002 3:11 pm

Can such engines fly subsonic. From what i hard, these engines only *start up* at speeds above 800kph and above or so and are most effective at speeds above 1.2M.
 
T prop
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RE: Question About Hydrogen Sub-sonic Engines

Fri Jan 11, 2002 7:29 pm

It is possible to run gas turbine engines on hydrogen, however for aircraft one of the problems is the fuel storage. Supposedly Daimler-Benz Aerospace and Tupolev are working on a DO 328 that will be powered by liquid hydrogen.

Find out more about this here.

http://www.alexstoll.com/AircraftOfTheMonth/3-01.html

T prop.


 
paulc
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RE: Question About Hydrogen Sub-sonic Engines

Fri Jan 11, 2002 9:05 pm

I think there was a TU154 with its No2 engine converted to hydrogen fuel. No sure how successful it was or if it still exists
English First, British Second, european Never!
 
LZ-TLT
Posts: 427
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RE: Question About Hydrogen Sub-sonic Engines

Sat Jan 12, 2002 10:11 am

indeed, there was an experimental Tu-154 around 1988 which got re-engineered with a hydrogen engine
 
prebennorholm
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RE: Question About Hydrogen Sub-sonic Engines

Tue Jan 15, 2002 7:37 am

Talking about hydrogen powered airliners and hydrogen powered cars are two very different things.

Airliners:
It is a minor job to convert a turbofan engine to hydrogen fuel. The problem is the on board fuel tanks.
Hydrogen boils at very close to the absolute zero temperature - roughly 30 deg Kelvin (minus 240 deg C) at sea level pressure. There is no way a pressurized tank can keep liquid hydrogen at ordinary ambient temperatures.

When using hydrogen as rocket fuel, then the temperature is kept at that low boiling point by constantly boiling off (and topping up) hydrogen on the launch pad. For obvious safety reasons that would be unacceptable at an airport. Besides that the extreme cold would create a tremendous heat isolation problem in order not to build up huge amounts of ice on the plane even on a hot summer day.

In gaseous state the hydrogen has to be compressed to extreme pressure if any considerable quantity has to be carried. Tanks will then be extremely heavy - and dangerous. Imagine that such a plane crashes near populated areas (e.g and airport) - it would be like a minor nuclear bomb.

Another huge and very expensive problem would be safe storage of large quantities of hydrogen at the airports.

I don't believe in hydrogen powered airliners. But the engines would be no problem.

Now about cars:
The future of hydrogen powered cars would require a completely different power system. First you will have a so called "fuel cell" - some device which converts hydrogen/oxygen combination directly into electric energy. Fuel cells are used today on the Space Shuttle for electric power generation.

The fuel cell then constantly charges a quite small battery in the car. The rest is an ordinary electric car. When accellerating, then you use power from the battery. When you stop for red light the battery is slowly recharged again.

The fuel cell is a much more efficient power conversion than any combustion engine, and electric motors nowadays can get close to 90% efficiency. Therefore overall fuel economy will be very favourable.

That way a small car can in fact do a lot of town traffic on what hydrogen corresponds to half a gallon of ordinary petrol or diesel fuel, and polution will be very small - exhaust would be almost clean water wapor.

Even this "half gallon fuel" converted into compressed hydrogen will require a huge and heavy tank and some very special filling facilities.

But if you forget about fast highway driving and several hundred miles range, and think about a small town car only, then it may be feasible once the fuel cell gets further developed and production costs come down to a tiny fraction of today.

Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
funny
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RE: Question About Hydrogen Sub-sonic Engines

Sun Jan 20, 2002 4:12 am

There are no unsurmountable barriers to Hydrogen fuel. There are only one or two things which need to be changed. One, is the ground facilities need to be a lot more technologically advanced for the new kind of refuelling. Hydrogen is likely to be used in aircraft as Slush or Ice-watery. Two, the wing needs to be bigger inside as you need a bigger volume of hydrogen for fuel. Three, the fuselage itself needs to be bigger to accomodate hydrogen proccessing devices.
There are, however, alot more advantages. 1 i does not pollute. Three, it makes angines much quieter, making flight much smoother. Four, it decreases the reliance on oil. Five, its A LOT cheaper. Six, I CANT THINK OF ANY MORE.

Regards

Jase
 
Alessandro
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RE: Question About Hydrogen Sub-sonic Engines

Sun Jan 20, 2002 4:21 am

The Tu-155 used LNG (liqiud natural gas) and was a version of the Tu-154. Problem is that LNG takes a lot
of space, so why did the Russians want one? Well, they
have to fly in fuel to remote areas with loads of LNG,
so using LNG would cut the amount of cargo. Pure economics....
From New Yorqatar to Califarbia...
 
Klaus
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RE: Question About Hydrogen Sub-sonic Engines

Sun Jan 20, 2002 11:53 am

Another thing to think of is that there is no natural supply of elemental hydrogen. Hydrogen is more or less just used as a form of "battery":

You need huge amounts of (usually electrical) energy for generating it (by separating it from oxygen in water) and it is basically just that energy (or rather just a part of it) that you can recover in combustion or in a fuel cell.

So in order to use hydrogen for cars or planes, you need to find economical and ecologically sound ways to generate hydrogen in the first place! And that would probably mean using nuclear energy.

Not a really pleasant thought for most people.

All the other problems mentioned are just the icing on the cake...
 
planelover
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RE: Question About Hydrogen Sub-sonic Engines

Thu Jan 31, 2002 8:03 am

Ok. I'm back you all! When I was writing this post, I was thinking more along the lines of not using converted plane engines. Here's what I was thinking: If a plane had a fuel cell on it and uses electric motors to turn a large blade or prop, would this work? The hydrogen in the hydrogen cars reacts some how with the metal in the fuel cell and makes electricity. Then, instead of having engines, you would simply have electric motors, like I said above. Maybe this would be too slow and not provide enough thrust for larger commercial jets, but do you think it would work for smaller piston engine planes and turboprops? This is sorta like back a long time ago when cars and planes both had piston engines. I know for some of you this is probably a really crazy question, but I was just wondering about it.  Smile/happy/getting dizzy Thanks you all.
 
prebennorholm
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RE: Question About Hydrogen Sub-sonic Engines

Thu Jan 31, 2002 8:46 am

Dear Planelover, sorry, that system won't work on planes. The system would be way too heavy.

What they think of in cars is also quite heavy stuff, which will generate only some 5 or 10 horsepower continuously.

That would be OK in a small town car. The fuel cell would constantly feed electric power corresponding to 5-10 HP into a battery, very likely an ordinary, but large lead-acid battery. You would pull maybe up to 50 HP from that battery when starting at green light or climbing a steep hill, but the fuel cell would deliver its 5-10 HP to the battery also at "idle" at red light and when driving downhill. You might even use the electric motor as a brake delivering energy back to the battery.

Flying, however, requires constant high energy. A large and heavy wide body plane requires something comparable to 100,000 to 200,000 HP to get in the air and for initial climb. And much less for level cruise of course - 25,000 to 50,000 HP. Fuel cells with that sort of capacity would be way too heavy if we don't dream up a technology break-through which nobody can imagine today. It is not a question about making it 50 or 75% lighter. We are talking about an entirely different scale.

Also imagining four electric motors driving the fans on a B747 at 200,000 HP, they would be prohibitively heavy. Have a look at a 2,000 HP electric motor in a train locomotive. And multiply by 100.

But hydrogen is a perfect turbine fuel. Only the storage is a huge problem. And of course producing it.

Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
jwenting
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RE: Question About Hydrogen Sub-sonic Engines

Thu Jan 31, 2002 9:01 am

Another major problem with hydrogen is that it is extremely explosive.
With normal fuels used today will burn rather than explode when in liquid form.
Hydrogen will explode as soon as oxygen is added, the slightest leak anywhere in the system will create an explosion that can wipe away an airport terminal.
Not a happy thought if you have 2 dozen bombs like that sitting on the ground around a building containing thousands of passengers and staff and any employee not connecting a nozzle correctly can cause the whole thing to go up like in a nuclear blast.
I wish I were flying
 
prebennorholm
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RE: Question About Hydrogen Sub-sonic Engines

Thu Jan 31, 2002 9:14 am

You are right, Jwenting. A hundred percent right. Well, at least 99.9% right.

You make it look like just blending hydrogen and oxygen (atmospheric air) creates an instant blast. It does need to be ignited. But the tiniest spark from switch-on or switch-off of a kid's diskman will do the job. So it doesn't change anything.

I am rather comfident that in our lifetime I will still be selling millions of gallons of smelly and smoking Jet A to keep the world moving.

Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
ryu2
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Methane?

Thu Jan 31, 2002 10:08 am

How about methane (CH4)? Production is not a problem, as it is more or less extracted from natural gas.

It has many of the advantages of H2 over jet fuel (greater energy density, cleaner burning)

The density and boiling point is much greater than hydrogen, so it can be stored in a lesser space and under warmer conditions.

It is only in gaseous form, and in the right percentage with air, so it is much more safer than hydrogen. It is more difficult to leak because of greater molecular size and mass, and it is heavier than air.
 
twr75
Posts: 110
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RE: Question About Hydrogen Sub-sonic Engines

Thu Jan 31, 2002 12:05 pm

Ryu2,

Burning Methane will still produce CO2.
Like a seagull on the MCG of life...
 
ryu2
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RE: Question About Hydrogen Sub-sonic Engines

Fri Feb 01, 2002 6:09 am

Yes, methane will still produce CO2, but not any of the other harmful byproducts of kerosene, like NOx, sulfur compounds, etc.
 
prebennorholm
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RE: Question About Hydrogen Sub-sonic Engines

Fri Feb 01, 2002 8:41 am

Ryu2: How about methane (CH4)? Production is not a problem, as it is more or less extracted from naturar gas.

Well, methane and natural gas is the same thing - except that natural gas most often is a mixture of methane (CH4) and ethane (C2H6).

Agree, it would be easier to use than hydrogen.

But natural gas is in heavy demand all over the world. Propane (C3H8) and butane (C4H10) on the other hand is hard to get rid of (butane hardly used for anything but spray cans and cigaret lighters) and it would be much easier to use than methane and ethane.

But all of them are ordinary CO2 producing fossile fuels. So why not just continue to use kerosene instead.

There is in each oil well a certain percentage of kerosene. If that would not be burned in airliners, what would we then use it for?

Hydrogen might be interesting since it can be extraxted from water and is CO2 neutral. Its exhaust - water vapor - would just fall back in the oceans as rain.

Methane, ethane, propane, buthane and kerosene are all expended fossile fuels which contribute to the CO2 buildup.

The carbon contents isn't equal. But when an oil well is producing oil and/or natural gas, then all components have to be burned somewhere. If we burn the natural gas in airliners and kerosene in electricity power plants, or visa versa, that's the same thing for the CO2 buildup. So why not just choose the easier to handle and safer fuel for airliners? That's how it's gonna be in our lifetime, I'm sure.

Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
prebennorholm
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RE: Question About Hydrogen Sub-sonic Engines

Fri Feb 01, 2002 9:17 am

Ryu2:

1. Sulfur compound contents in kerosene is negligible. Even in diesel oil it is now down to 0.02% (much lower in kerosene). In all developed countries it is extracted at the refineries and sold for furtilizer production.

2. About NOx (nitrogen-oxides): It would be very hard to make a methane fueled turbine engine which doesn't emit more NOx than a kerosene fueled turbine. And the worst NOx producer would be the hydrogen fueled turbine.

But NOx is not the biggest of problems. It is short lived in the atmosphere. And in a turbine it is almost only produced at high power, not at startup on the ramp or during taxiing, but at take-off, away from people.

NOx is not a product from the fuel. It is a chemical reaction between the two major components of the atmospheric air, nitrogen and oxygen. NOx is produced when air is compressed to very high pressure and exposed to extreme heat at the same time. Methane and especially hydrogen will at the same pressure burn at considerably higher temperature than kerosene.

By far the biggest concern with NOx is diesel powered cars/busses/trucks in town traffic. Not airliners. The way to reduce NOx emission from diesel engines is to make the combustion as "gradual" as possible. The fuel pump shall not just deliver the whole thing when the piston is at top, but deliver it gradually in such a way that there is is rather constant pressure in the cylinder until the exhaust valve opens.

In a turbine engine, however, only the compressor rpm dictates the crompression ratio in the combustion chambres.

Regards, Preben Norholm
Always keep your number of landings equal to your number of take-offs
 
planelover
Posts: 313
Joined: Sat Dec 22, 2001 1:22 pm

RE: Question About Hydrogen Sub-sonic Engines

Thu Feb 07, 2002 6:06 am

Hey all,
Thanks for you all's help. I just read an article in Aviation Week and it said that Boeing is working on using fuel cell technology instead of APUs. I'm assuming it uses the same principle as the car. It's suppose to do all the same things a regular APU does. I don't recal the article saying what it would use as a fuel source. Probably not hydrogen. Boeing is going to try and have the first aircraft with this technology flying by 2003. Anyways, that's the way I understood it. If anybody can elaborate more on this please do. Thanks.

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