[Rupert S]

quick question about avgas, as the subject implies. What does the 100 or 100LL stand for? As far as I've been able to find out it's something to do with the octane levels but if so, what is this relative to? (100 moles of octane per litre, maybe?)

[Steve Morley]

No idea what an octane is, but 100ll stands for 100 octane, low lead

[Russell]

Seek, and ye shall find.

http://www.mgcars.org.uk/mgcc/sf/000403.htm

Interesting discussion about 100LL, MON, RON etc.

Just ignore his whining about TAX, which is obviously wrong.

[Tony2]

From what I remember, I think octane level basically is a measure of the fuels resistance to premature ignition (no jokes please). Therefore in high compression engines where the fuel/air mixture reaches a higher temp on the compression stroke the fuel must not self-ignite before it is required to.

[Rupert S]

I realise the omportance of octane levels and that the 100 does refer to the octane level but I don't understand what the volume of the sample is that the rating of 100 is taken from. I would guess it is something like 100 moles of octane per dm cubed of avgas.

[Steve Morley]

Whay ya gonna do when you find out?

[Rupert S]

Not that I want to distill my own AVGAS, I'm doing a rather detailed analysis of AVGAS and the gasoline fraction of north sea crude oil for Chem AS.

[Jane]

So why not contact the various companies that stick their pipes under the north sea. whilst I try to remember the book that I have which details the structure of 100 octane fuel. Had one motorbike decompressioned a bit so that it wouldn't matter where we went and it would be OK on such fuel as 86 octane or lower. Makes higher compression engines run rough, hot and not much power. Learnt that long time ago when it was explained by a Romanian speaking Romanian motorcyclist to me as a non-Romanian speaking motorcyclist - but similar interests made us comprehend each other as we compared bikes.

[Andy Lees]

The octane rating is a measure of the character of the explosion in the cylinder.The desired explosion should take place slowly to give a strong, smooth push to the piston. Iso- Octane (8 carbon atom,
branched alkane or paraffin) does this very nicely and is rated 100.
Heptane (7 Carbon atom, straight chain alkane) produces a sudden
explosion, similar to thumping the piston with a sledge- hammer.
A violent explosion produces "knocking". Heptane is rated zero.
Any given fuel can be tested for it's tendency to produce knocking, against known mixtures of heptane and iso-octane. Petrol used in cars has an octane rating of approximately 80. That is, it has the same tendency to produce knocking as a mixture of 20 volumes of heptane and 80 volumes of iso-octane. The addition of tetra-ethyl lead slows the burn rate and boosts the "octane rating" of a fuel.
So 100LL means that you' ve got a high quality fuel with minimal production of knocking, similar to iso-octane, and only a small amount of tetra-ethyl lead has been added to achieve this. Hence
the LL-- low lead. Must knock off now.

[Steve Morley]

I reckon you've bin reading about the Welsh who are making diesel out of cooking oil and avoiding tax. You'll never get away with it!!

[Chris Scholfield]

More to the point is the question of how much longer 100LL will be produced. As you know the old leaded 4 star (for cars) has been greatly reduced in output with the result that a litre costs

[Steve Morley]

Where do they put it when they remove it? Or where did they get it from to put it in?
You must be able to get it a a bargain. We should stock up then we can clean up when they ban it.

[Rupert S]

Actually, and even better than cooking oil, alot of people in rural france have their cars converted to run off camping gas (everything that comes off crude as a gas - mostly methane and butane) very cheap, no tax and very efficient. I wonder if anyone has a camping gas engine in a mircrolight. But back to 100LL, i've managed to find out that the 100 does indeed refer to to moles of octane. the only thing is I don't know how much gasoline that is relative to.

[Steve Morley]

Methane. Hmmm... It'll take a lot of beans but I have an idea.

[Rupert S]

Seeing as how pedantic some of us can be here, I though I'd correct myself... camping gas is not a mixture of methane and butane. It's a mixture of mostly methane and ethene - the fact that it's a mixture of alkanes and alkenes makes the methane combust much more quickly when it has a spark put to it, so I would imagine it's mixed with quite alot of air before it reaches the engine... Wouldn't it be great to have a gas for fuel. You could have fuel to full capacity and still put on that 20 lbs!