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Name: Cheryl
Status: student
Grade: 9-12
Country: Singapore
Date: Summer 2012


Question:
Can hydrogen replace fuel in jet engines? (Mixing hydrogen with air(oxygen) instead of fuel with air) If so, how much energy will this produce, and how fast (what speed) would the jet engine propel an object? And how much energy would be needed to run the jet engine?



Replies:
Although it is possible to design a jet engine to use hydrogen as a fuel, hydrogen is completely impractical to use as a fuel for commercial jet aircraft.

Hydrogen has far less energy per liter, compared to normal jet fuel. This means that the rate of hydrogen consumption (to produce

the same thrust) would be much higher, and therefore even if liquid hydrogen were used, much larger tanks would be needed.

Then there is the problem of hydrogen storage tanks. There are only 3 ways to store hydrogen. First is storage as a highly compressed gas. This is utterly impractical for any aircraft since it would require high pressure tanks that would be so heavy, the plane would never get off the ground. The second storage method is metal hydride storage, where the hydrogen is absorbed into tanks containing a special metal powder. Once again, extreme weight makes this storage method impractical.

This leaves the final option.... storing the hydrogen as a cryogenic liquid at -253 degrees Celsius (-423 F). Hydrogen tanks would need to be insulated (further increasing their size), but even then, significant amounts of hydrogen would be lost during the flight as some of it boiled away. Clearly there is also a serious safety issue here!

The final thing worth remembering is that hydrogen is not a fuel! It is simply a means to temporarily store energy, much the same way battery does. A lot of energy is needed to make the hydrogen (usually by the inefficient method of electrolysis), and later, some of that energy is released when hydrogen is burned. If the electrical power used to make the hydrogen comes from a coal-burning power plant (as is common in the USA), then any aircraft that was using hydrogen as a "fuel", is in reality, not powered by hydrogen at all! It is, in fact, powered by coal!

Regards, Bob Wilson


While it is possible to use hydrogen as a fuel, in principle. The practical problems are daunting. Hydrogen is difficult to handle, it can cause metals to become brittle and crack, its reaction with air is difficult to control (It tends to explode rather than burn at a controlled rate.), to name just a few problems. Hydrogen has been used as a fuel in rockets, that is a special case, e.g. you do not have a hundred or so passengers!

Vince Calder





Cheryl

Anything that will burn can be used in jet (gas-turbine) engines. I do not know that anyone has tried to use hydrogen in gas-turbine engines, but Hydrogen is combined with Oxygen to loft the Space Shuttle into space.

The trick for sustained operation of the gas-turbine engine is to generate enough heat to keep the compressor blades (shown between 2 & 3 below) turning while having enough energy left over to expel high energy gases (at #8 below) out the exhaust for forward thrust.

Here is a picture that is worth a thousand words:

This picture comes from:

http://www.google.com/imgres?imgurl=http://www.grc.nasa.gov/
WWW/k-12/airplane/Images/etr.gif&
imgrefurl=http://www.grc.nasa.gov/WWW/k-12/airplane/
etr.html&h=532&w=7
10&sz=34&tbnid=DJ8NBEgVfQs1hM:&tbnh=90&tbnw
=120&prev=/search%3Fq%3Dgas%2Bturbine%2Bengines
%26tbm%3Disch%26tbo%3Du&zoom=1&q=ga
s+turbine+engines&usg=__85Ofka3Ivx6
4jRG7zYa_ctbqfiY=&docid=pE3hJx3PEf9IWM&hl=en&sa=X&ei=
CsjtT_fsBoXH6wGixJibCg&ved
=0CHAQ9QEwBQ&dur=237

and was found at http://www.google.com and searching for “gas turbine engines”.

Here is another picture from http://www.google.com/imgres?imgurl=
http://www.azom.com/work/P0449b1svbF5Tbitqclo_files/image002.gif
&imgrefurl=http://www.azom.com/article.aspx?ArticleID%3D90&h=253&w=346
&sz=23&tbnid=J987ANWuTZuF6M:&tbnh=90&tbnw=123&prev=/search%3Fq%3Dgas%2Bturbine
%2Bengines%26tbm%3Disch%26tbo%3Du&zoom=1&q=gas+turbine+engines&usg=
__DSpTwuUJ_CX8j7fTA_aWr1hgSTU=&docid=0yNFXdc-xGWEJM&hl=en&sa=X&ei=CsjtT_fsBoXH6wGixJibCg&ved=
0CGoQ9QEwAw&dur=468

How fast this engine would propel the aircraft and how much energy would be needed depends on the physical configuration of the aircraft and the engine.

Sincere regards, Mike Stewart



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