Aviation Fuel

[Shnoz]

Hello everyone

I've been researching the refining process to get avaition fuel from petroleum, but I can't seem to find the actual chemical equation or what is done to the petroleum.

Can anyone tell me what they do, or point out a good source to learn from?

[rat156]

Hi Sophie,

Firstly there's basically two types of aviation fuel.

1. Jet fuel. This is designed for jet applications only. It is essentially kerosene. Mostly it is lighter than petrol and it pretty much a waste product from petrol manufacture.

2. Aviation gasoline or Avgas. This is high octane petrol designed for propeller driven planes. It is essentially the old leaded (yes it still has tetraethyl lead in it) fuel, though a higher octane version of it.

Both of these are produced by the same process. Firstly crude oil is "cracked" (wikipedia will have an excellen description of this process), then distilled. After fractionation the various bit are reblended to make the raw fuel, then various additives are added to make the commercial product.

Cheers
Stuart

[peter_4059]

Stuart - not quite correct....

Jet is essentially the same as kerosine however kero is heavier than gasoline (and lighter than diesel). Jet is often the most valuable product produced in a refinery so I wouldn't call it a waste product from pertrol manufacture. You are correct that jet is used in jet (turbine) engines and is often labled avtur at the airport. Jet is distilled from raw crude and does not contain any cracked product (unless it has come from a hydrocracker in which case the percentage cracked product in the finished jet is limited.

Avgas is a leaded high octane petrol type fuel and typically blended mainly from alkylate and reformate. Both of these components are formed through reaction of other molecules (some of which are distilled from crude). Alkylate is essentially a C8 compound that is produced by combining butane with butylene in the Alkylation process. Reformate is produced by reforming heavy virgin naphtha (HVN which is distilled from crude) HVN is a whole mix of molecules that boil in the range 70-140 degC (so C6 to C10 type molecules). HVN is typically about 70 octane so it is reformed - this changes the shape of the molecule to increase the octane number - typically to 98.

Lead is added to raise the octane number to over 100.

[Shnoz]

Thanks for answering.

I've found some pretty good websites. Wikipedia and references where would we be without them!:lol:
I'm very sure I understand the refining process now. Chemically it's very complex!
Basically oil goes in chamber. Chamber boils different hydrocarbons off. Jet fuel is collected. Jet fuel is put through merox treatment. Merox catalyst removes mercaptan sulfur. Refined jet fuel is collected.
VERY basically put, but I hope that's right.

[peter_4059]

Sophie - Merox is short for MERcaptan OXidisation. This process converts smelly mercaptan sulphur into disulphide oil so strictly speaking the sulphur molecule is converted to another form rather than being removed in this process. (Ethyl Mercaptan is the rotten egg smell that is added to LPG so you can detect a leak from your gas bottle).

Refining is very complex because of the huge number and variety of long chain molecules involved. There are only a handful of processes where stoichiometry is used to describe what's going on.

Peter.

[GeoffW1]

And what about vodka ? :P

[Shnoz]

Ah, so mercaptan sulphur is just turned into another, less unpleasent form. That makes sense when you think about conservation of mass and energy laws.
So does mercaptan sulphur have any technical problems, or do they just get rid of it because it smells bad?

[peter_4059]

Sophie,

Mainly to get rid of the smell. It is possible that the jet would fail other quality control tests (Doctor test, Copper Strip, JFTOT) if the mercaptan sulphur was not treated but I'm not sure as it is usually only fully tested post mercaptan treatment.

Here is a copy of the specification:
http://www.dstan.mod.uk/data/91/091/00000600.pdf


Peter

[Shnoz]

Cool, thanks for your help!:thumbsup:

[caleb]

I thought I could give some input to educate myself some more as I'm a student pilot:)

The AVGAS used in a Cessna 150 at my flying school is 110LL and is colour coded blue. The grade of fuel is its octane rating although it is impossible to have an octane rating highter than 100 so this is a performance number. MOGAS for you car is 80-90 im prety sure.

And the LL stand for low-lead, I gather you know what lead helps with...

I didn't realy anwser your question...

[Shnoz]

Thanks for your input!:)

I've learnt loads about the initial refinery process to get fuel from crude oil. It was just for a chemistry assignment, but now I'm really interested in it!:D

I'm learning about what happens after the refinery process. There's a lot more things you can do to the fuel, so to alter its flashpoint and make it lighter, etc.
I assume that the different types of fuels are generally named for those kinds of properties, but I'm still not sure of the different catalouges used.
I'm also still not sure what an octane is. Does it have something to do with the number of hydrocarbons?

[peter_4059]

Sophie,

Octane rating is a test that is done on an experimental engine (a bit like a small car engine but in a lab). The fuel being tested is compared to a standard fuel (iso-octane). The engine is adjusted to measure the point where "knocking" takes place (I think it is the ignition timing that is adjusted but would need to check). The octane number is a measure of how likely the fuel is to cause knocking - higher octane means the fuel is less likely to cause knocking.

If you are interested in refining get into chemical engineering.

Peter

[RobF]

What's the course/level of study Sophie?

Last time I heard this much about crude oil refining was in Grade 10 I think..... :P

[Shnoz]

The octane rating seems pretty straight forward. I would assume a higher octane is used in jets than in cars, otherwise there may be some unwanted side effects.:D
I'm in senior school now, we get to do much more interesting things than in junior school! Although I think it's a problem when you have so much homework there's no time to learn.:lol:

[Gerald Sargent]

I recall back in the 50's at the Esso laboratories in UK watching octane
measure being made on an internal combustion engine with an adjustable
compression ration ( the cylinder could be moved up and down) and using
a standar fuel to calibrate, the octane rating was then determined at the
compression at which audible knocking was heard. Gerald.

[peter_4059]

Sophie - the engine in a jet (turbine) is different to a car's internal combustion engine so octane rating is not measured for jet fuels. Jet has other specifications to ensure it is suitable.

[multiweb]

That's a one way trip :lol:

[Barrykgerdes]

Distillation of gasoline these days is quite a sophisticated procedure.
In the old days when petrol was required for the evolving motor car petrol was obtained by a fairly simple process of fractional distallation.

This basic petrol had elements of the fuel that ignited (flash point) over a range of temperatures. With the lower compression of the early cars the compressed gas to be ignited by a spark did not reach the flash temperature so combustion was quite smooth. However as the compression of engines was increased to improve efficiency a problem arose where elements of the fuel reached flash point before proper ignition. This caused pinking (a nasty knocking sound in the engine) as the uncontrolled ignition of the gas took over.

By further refining of the petrol these volatile elements were removed (improving the octane rating) particularly for aviation engines that needed the higher efficiency of higher compression ratios. This of course led to an increase in the cost of refining so many experiments were carried out to find a way of making a higher octane without the expense of re-refining. Quite by accident it was found that lead (in one of its forms) stopped the pinking so the tetra-ethyl-lead company came into production and made zillions regardless of the lead pollution it caused. Another way to improve octane was by water alcohol injectors that cooled the mixture so that combustion temperature was reached later in the stroke.

As development of the internal combustion engine continued there was also development in the refining industry and catalyctic cracking came into being where the lighter elements that caused the problem were made to combine into heavier elements by use of a catalyst so creating a higher octane. Improvements in the refining process produced more and more petrol of a higher octane rating to the point where the government was able to say "no more lead". Of course the manufacturer of lead for gasoline was not very happy because it cut out a "nice little earner" but that is progress.

Barry