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Chemistry of a Jet Engine

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Chemistry of a Jet Engine

Old 20th Sep 2000, 03:04
  #1 (permalink)  
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Question Chemistry of a Jet Engine

Greetings all,

I have a chemistry project coming, and I was thinking of Jet Engines.
Can you give me some pointers where to start? I was thinking of combustion (typical subject) but are there other interesting things (chemistry related) that happen in there?

Old 20th Sep 2000, 03:49
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I'd have thought that the chemistry aspect was about covered when Otto invented his Cycle, as that is little different, Chemistry-wise in a jet. The things that do count are physics, fluid & thermo dynamics and mechanical engineering. Even single crystal metallurgy if you want to get esoteric.

Chemistry between the flight deck and the trolley dollies is a far more interesting study. (Note the applicability of Bolzmanns constant to this situation...)

Have fun!
Old 20th Sep 2000, 06:34
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C'mon, there shiould be something in there!
I'd hate to work on coffe extraction from seeds (though that can keep you awake on the long flights )

[This message has been edited by Smurfjet (edited 20 September 2000).]
Old 20th Sep 2000, 06:49
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You could look at how they prevent oxidation etc of the turbine blades, and what sort of oils need to be used in these extreme temps and pressures.

But, as someone else said, most of the wear & tear aspect is related to the physics of crystals and alloys.

Old 20th Sep 2000, 15:20
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Good suggestion, I will look into it. I am not majoring in chemsistry so its ok to have some physics in there. Its not pure chemistry, thank god

Keep them coming
Old 20th Sep 2000, 16:19
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I guess that most of it is related to the various branches physical sciences (mechanical & materials engineering / fluid dynamics)

The areas that perhaps relate more to conventional chemistry are probably more limited - corrosion; fluid chemistry (fuel / fuel combustion / contaminants / trace substances etc.)

If you can include closely related subjects such as metallurgy, polymer science or tribology as 'chemistry' then you open up a whole raft of options.

Not a lot of helo I know, but might propmt some ideas ! Good luck !
Old 20th Sep 2000, 16:35
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Jet engines use synthetic oils - why? Also you never need to do an oil change on a jet engine because it works via a replace via replenishment.

Another topic for study could be CRP (Carbon Reiforced Plastics) although not strictly chemical you could look at the types of CRP use in aerospace applications as opposed to other industries. Look at what polymers are used to bond the material. Look at Pre impregnated materials and study why these are so succcessful.

Another area is hydraulics. You could do an assignment bassed on pneumatic vrs a sealed synthetic system. What are benefits and disadvantages of both and relate each of these back to a chemical stand point.

Combustion seems like an easy concept, you put fuelin and you burn it - ta da. I think though if you went to some detail it might be a bit heavy and messy.

However saying that, if you can get your hands on some applicable data, you could do a comparison of NOx omissions from the early 70's to current data. ICAO might be a good place to start with that also EPA organisations that monitor levels could be interesting.

Hey another topic could be crazing of aircraft windows, thats where due to sunlight the plastic window starts to delaminate internally and its transparency is reduced.

Also do some basic analysis on the hygroscopic paste that is used for detection of water in JETA1 or the addetive that is used to prevent fungus growing in fuel tanks of a large transport aircraft.

You could also do a project on paints used by the industry and the removal and disposal of such, which as mentioned on this site is a bit of a problem. Getting back to basics you could do something on plating. Most metallic a/c components are cad plated to provide a protective corrosion layer, you could extend this out to include anodizing, and chrome plating of oleo struts.

I could probably go on but I wont. Feel free to drop me aline WRT to any of these ideas. My only advice is go with the option that has the most data that you can get your hands on, it make less work for you in the long run.

Its life Jim, but not as we know it!!
Old 20th Sep 2000, 16:45
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Thanks for the suggestions.

Great suggestions! Thanks a lot! I have 6 weeks to do the work, so it is not a big project. The main goal is to explain chemistry principles behind the concept. I choose jet engines simply because in 7 years I plan to have my ATPL
I'll drop you a line when things start rolling Thanks for the help...

If you guys have interesting links/suggestions feel free to post. Hopefully it will be an A+

Old 21st Sep 2000, 13:03
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Smurfjet - why not phone up one or more of the big three gas turbine manufacturers and explain what you are doing? Rolls-Royce sent me some fairly technical info on the Trent 700 just for the asking....
Old 21st Sep 2000, 22:57
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Yep, good idea mik! Thanks.

Old 22nd Sep 2000, 09:10
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Join Date: Aug 1998
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Smurfjet, You might want to have a look at my post halfway down the page on:
Why are jet engines more fuel efficient at high altitude?

from the Tech Log archive.
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Old 23rd Sep 2000, 13:04
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There's always the mystery of the Blue Water (why is it blue?), and why you're not allowed to carry mercury on a flight (though that's metallurgy, and I've never been sure whether metallurgy is physics or chemistry).

Seriously, I think the emissions side of things would be most interesting. All that stuff being injected directly into the stratosphere -- how willing are we to examine the problem soberly?

About the crazing on the windows: someone told me that this was also related to high-altitude pollutants. Anyone know about that, or was it green propaganda?

Old 28th Sep 2000, 03:58
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As a metalurgist (a long time ago in a distant galaxy called working for a living) you may be interested to know that all turbine blades are single crystals, from the root to the tip. This is because at high temperatures the grain boundary, the interface between the crystals, is an area of high energy suseptable to chemical attack and is the first part of a metal to melt allowing creep at high temp.

Also the nimonic alloys used for turbine blades are prone to corrosion in salty atmospheres, which is why turbine blanks are always fitted to carrier aircraft, and turbine washing routinely carried out.


All leave is cancelled until morale improves.

Never confuse experience with competence
Old 28th Sep 2000, 07:31
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Checkers erudite exposition of "Why are..." is as clear and simple as any I have seen.

The controversy continues between the chemists and physicists as to which comes first and where do they start and end.
The fact that more than a few significant chemical reactions were predicted from physics ilustrates the fuzziness of this argument. Is single crystal turbine blade technology physics or chemistry. I personally tend towards the physicists because they tend to work from first principle with chemists being more empirical in their methods, but I'm sure I'll get an argument on that.


One of the most fascinating thingys to me in this "engine" stuff is the combustion process or oxidising/converting hydrocarbons with O2 to produce another product with the energy produced/released providing a really useful byproduct that we use to indulge our mechanical fantasies

"Flamefront" relative to its speed and propagation and what's happening behind and in front of it in the combustion process is the operative principle.

You need to keep a few balls up in the air at the same time on this one and forgive me if I am teaching you to suck eggs mix a few metaphors here.

For example;

Light a biggish candle and carefully study the flame and the different colours emanating from the wick to the outside of the flame. They indicate different temperatures and therefore levels of combustion or chemical efficiency.

The ONLY difference between a burning candle and a substantial explosion is the SPEED or RATE at which the wax is converted to vapour and "combusted" or "burnt". This is a function of the interface or surface area available for the hydrocarbon and oxidant to interact. That defines the 'speed' of the "flamefront".

The total energy available in the candle is released over a long period of time, as the 'flamefront' or surface area of the 'flame' over which the combustion process of mixing the fuel with the O2 is occuring, is quite small and as such is quite benign and usefully beautiful.

If however you were able to vapourise the wax (hydrocarbon) from the same candle in a relatively confined space and were able to devise a method of delivering the exact amount of oxidant to each individual molecule, then you would have a infinitely large surface area/flamefront, the energy is delivered instantaneously and results in a very large explosion. Enough to flatten your and your neighbours houses yet.

Whilst we are on the subject of candles, a question for you.
In medieval times, before the invention of electricity, the local flour miller would not operate outside daylight hours.?

So taking for example Checkers "Why are.." post as a start point it is easy to see why the efforts of so many very bright engineers (F1 and aviation) and chemists have spent so much time and effort working on controlling the SPEED/RATE and efficiency of this flamefront in internal combustion and turbine engines. Both just ways of controlling the same process and converting it to mechanical energy without blowing or burning itself to bits.
The higher the temps the greater the thermal efficiency, but are harder to control. How do they control temps at the flamefront in turbines that are way above the melting point of the surrounding materials?

Another question,
Why does richening the mixture (adding fuel) have the opposite effect in a turbine engine to that of a piston?

I wont spoil the research fun by giving you all the answers but I believe that understanding the chemistry/physics of "flamefronts" is fundamental to understanding what's really happening at the end of those levers.

Some fascinating but entirely useless info, various grades of primer cord, used for example in mining applications, have a flame front capable of covering several hundreds of metres to all intents and purposes instantaneously.
Old 28th Sep 2000, 20:07
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gaunty -

Nothing is useless around here (maybe jet blast?)!!

I'll try to answer your questions, since I was reading at the speed of light due to lack of time, tonight (if I have time) I will go through the posts thouroughly!!

Thank you all of you, I meeting the professor today to kick start the project.



In this life, you have to think ahead to survive, not only on the flightdeck.
Old 28th Sep 2000, 23:17
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Red face


Not all turbine blades are single crystal. Depending on engine type and generation, and where the blades sit in the engine (high, intermediate, or low pressure), they may be single crystal, directionally solidified (polycrystalline with logitudinally aligned boundaries and no transverse boundaries), or equiaxial, with differing amounts of grain boundary strengtheners and different alloying elements.

The chemistry/physics/metallurgy of turbine blades is actually quite interesting, including oxidation, corrosion, creep and fatigue, and processing considerations.

Oh, and like you, before I went to college, I couldn't even spell metaLLurgist, and now I are one
Old 28th Sep 2000, 23:27
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And I still can't spell longitudinally.

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