Flight school teaches basic pre-flight fuel inspection techniques but not fuel storage techniques. This exercise has been an eye-opener - at the very least taught me not to take the responsibility for granted. If you decide to own and operate your own bowser, you'd better learn all about fuel storage techniques (and fuel characteristics, fuel testing, fuel transportation, regulations, etc.).
I think we could do with some further "Farmyard Investigation" on this, Sunday just gone was a very good fine and sunny day with only a slight breeze where I live, I was doing the normal sorts of chores, washing the pots, vacuuming the carpets , feeding the tribe and mowing the lawn, so I thought "AH" I'll put some 95 octane petrol in a clean clear jar to see what happens.
4 hours later, 95 Octane all gone leaving only a very fine feel of oiliness, but none of the "White powder" observed in the sample I saw in the jar at the LZ adjacent to the home of Gaseous.
So question is, Is the White powder part of the Dye used in the Ident of 100LL, or is it some other sort of additive that is put there by the manufacturer when refining and mixing this Aviation Fuel, and if an additive what is it?
Thanks Peter, The final piece of the puzzle just dropped in!
The precipitate is most likely Lead bromide - the stuff that makes your exhaust white. I evaporated some avgas in the dark and got no precipitate so the precipitation is caused by sunlight. What Avgas has got that 95 octane hasn't, and is photosensitive, is tetra ethyl lead and ethylene dibromide.
A little research yielded this: (URLs on machine at work so don't have them now)
Ethylene dibromide, a clear liquid, decomposes under the influence of light to form ethylene glycol and free bromide ions which are pretty reactive.
Tetra ethyl lead, another clear liquid, decomposes under light to give ethylene(I think) and free lead.
Lead atoms plus bromide ions react readily to produce lead bromide which is a white solid at normal temperature. This is the reaction that also happens in your combustion chamber where it does its magic. It then goes down your exhaust to make it white.
It seems sunlight is mimicing the conditions in the combustion chamber which activate the lead chemistry to give the precipitate in the fuel.
The identifier dye turns the white powder pale blue.
It doesn't happen with 95 octane as they use heavier benzene or its derivatives to increase the knock rating - ? the oily residue you got, Peter.
Any real chemists out there confirm this?
Last edited by Gaseous : 25th April 2005 at 22:19.
Well, water detection tablets with the diddy syringe thing for the Jet A1 bowser, but a swill in a jar and a "Bright and Clear" check for the AVGAS.
I believe it's something to do with the lower tolerance for dissolved water in Jet A1 that the burners don't like, whereas a 1930's carburetor
and Champion's finest can still make a bang with a higher ppm of dissolved water.
The Shell man tests both fuels for water with his kit but as users we do as above. Should we be using tablets on the AVGAS?
Seems to be you wearing the White coat,..... so Ethelene Glycol was, and I think still is a liquid used as a coolant in big A/c piston engines....It was also injected along with water into the fuel stream of the Rolls Royce Griffon engine when at full throttle and full supercharged boost to give I believe more bang to the fuel.
Then, if it is present in the 100LL of today, is this done for the same reason to make a Low Lead fuel more explosive upon compression/ignition, seems the more we dig the wider the hole is appearing! but I am sure we are near the answer, despite the Farmyard Experiments!
Ethylene dibromide is present in avgas to scavenge the lead and prevent it fouling your plugs. Ethlene glycol is a product of photoinitiated decomposition and is not as far as I know a constituent of healthy avgas.
In the combustion chamber ethylene dibromide will decompose during the burn to hydrogen, carbon and bromide ions, it being too hot for ethylene glycol to exist, let alone form. The hydrogen and carbon then just burn with the rest.
Water is not miscible with healthy avgas to an extent that is problem. It separates out and can be drained off safely. Water will only mix if avgas is contaminated with surfactants. If water is left in avgas for a long time microbial growth is possible, but not likely due to fuel toxicity, at the water/fuel interface.
Summary of what I have learned about avgas form this thread.
Keep it clean, keep it dark and cool, keep the storage tank clean and preferably insulated. Drain off water and don't keep it for more than a year. Check it regularly. Filter it properly on the way to your aircraft. If its not clear and blue, or you are not sure about it, dont burn it in your aircraft.
Last edited by Gaseous : 27th April 2005 at 00:42.
Cross eyed,
just a suggestion. if you resize your pictures to 800*600 or less before posting them we dont end up with threads that have to be scrolled horizontally.
it makes them easier to read.
good thread.
Linear Mode
