Aviation gas

[weimedog]

Heviarti my 797 starts really easy with 100LL in the cold. Just have to give it 4-5 squirts with the carb primer. It fires on first or second pull with compression release...released. When things are warmer only 2-3 squirts. It also starts about as easy on pump gas. I run Mobil pump gas simply because the Mobil filling station we have here has a separate distributer & tank for each grade. Doesn't mix like the rest of the brands including Sunoco. But this is THIS particular gas station. Other places will have other brands where that is true. I don't like buying fuel for my sawswhere they have the same hose for different octanes. When I'm filling something as small as a five gallon can, the volumn of fuel in the hose from the LAST sale has some impact on my final mix. What if the last sale was 87 octane? And I wanted 93? By the way all the AV Gas I have purchased came from Accent Technology, a Phillips company. They also sell a 87 Octane "Mo-Gas". But as was mentioned in this thread, they all pull from one of three terminals up in my part of the world. One in Albany, Rochester, and Syracuse. If you want Alcohol enhanced fuel only the Rochester terminal can provide that. I wouldn't put that garbage in a plane or saw.

 

[heviarti]

Alas we have no amoco here. only conoco. I know all about 16:1. my 4-30 A runs it.

The whole saw is down for a full overhaul, but my super 44 does the same thing. and since gas piddles out the tank vent (my biggest mac pet-peeve) i'm willing to say the vent is clear.

 

[fishhuntcutwood]

I checked the manuals, as I told you I would, and pretty much all they gave me was specific weight, density at certain temps, weight per volume, flash point, military nomenclature, and the mention of certain additives (didn't say what they were for in particular) and detergents, and Prist when used in military aeronautical applications. I couldn't find much in the way of specifics on it in my A&P or FAA literature either. Sorry I couldn't give you more on the additives, but it seems to me this thread has taken off pretty well, and the info abounds. That, and it'd probably be found to be in error by somebody else anyway, so I'll just bow out...

That said, I asked a good friend of mine who used to log professionally, is now in the CG with me, and is extremely knowledgeable in matters of saw and timber, and he said a bunch of guys ran/run 100LL and they love it. He said a friend of his mills with it, and he can put his hand on the cylinder while the saw's running, it runs so cool.

Take care all,
Jeff

 

[DanMan1]

No, it will not contribute to exhaust valve erosion.

Actually It's the Exhaust valve seat that erodes first, which is part of the head, not the valve.
But enough of this boring factual stuff, Where's Macman?

 

[bwalker]

The reason avgas runs slightly cooler is also the reason that it makes slightly less power in most cases.

 

[Oregon_Native]

Av Gas

the only real reason i use av gas is the it dosnot absorb water as bad a pump gas it takes a year or so to breakdown to the point that ist performance starts dropping unlike pump gas that lasts a few weeks that an it burns a little cleaner and smells better.

 

[MacDaddy]

But enough of this boring factual stuff, Where's Macman?

I gave up my wicked ways Im not like that anymore (Clint Eastwood Unforgiven) I took some advise from a friend and Im cleaning up my act

 

[Crofter]

My friend had an experimental plane with a rotax. there was no stipulation to use Av Gas, but they warned about any alcohol. There was a test to check for content by mixing a measured amount of gasoline with a measured amount of water and see what the net sum was. 8 0z of each adds up to less than 16 if there is alcohol presence as it has a great affinity for water and somehow slips it into the mixture which leads to separation problems with the oil premix. The previous owner deadsticked, damaged and sold it. My friend had it quit twice on approach and dead sticked it sucessfully. Apparently long approach with forced windmilling with no load with closed throttle and little charge was leading to icing. It was a flying boat type hull and not too forgiving. It didnt like cool fall weather. Aviation gas might have been better. I had a few flights in it, but I dont care too much for the reliabilty of a snow machine engine in a plane. To make a long story short, gasoline is not all the same and if you are at a critical border for icing, seizing, freezing, or vapour lock, something different might be better medicine than cornerstore generic.

 

[jimbo1490]

Here are a few facts about toluene:

It has an octane rating of 114 (R+M/2)

Toluene has a lower 'octane sensitivity' (about14 points) than any of the fuel alcohols(20-30 points), meaning it is an ideal octane boost for a heavily loaded engine, as it's motor octane rating derades less under load than the alcohols.

Toluene has more energy per unit volume than gasoline, unlike additives like MTBE, have have less energy density than gas.

Chevron's published composition of 100LL shows that toluene comprises up to 14% alone and is the predominant aromatic hydrocarbon. (Unfortunately composition specifications for automotive gasoline is harder to pin down due to constantly changing requirements.)

Toluene is no harder on gaskets and seals than any of the other aromatics contained in gasoline within the limits of ASTM spec ASTM D4814, which provides the technical properties for todays gasoline. A 5 or 10% increase in the aromatic content of gas will most likely be well within the refining specs of gasoline defined by ASTM D4814, which specify an aromatic content of between 20% and 45% (except in CA where its 35%), a pretty wide lattitude, really. What this means is that if the 93 octane gas had an aromatic content of about 30% and you increased it by 10% by adding toluene, the resulting mix would contain 40% aromatics, a mix that's still within the industry definition of gasoline.

About the only down side is that toluene does not vaporizes quite as easily as gasoline owing to it's lower volatility, so it may make cold starting a little harder, especiallay in cold weather.<p>
Why some on this forum are so opposed to using this cheap, unregulated and readily available octane booster is beyond me and furthermore, completely unsupported by any facts. Those same folks will then tell you to go ahead and use racing fuel, which is LOADED with toluene !!??

'nuff said

 

[Luke]

ignition advance/compression

I have read several dyno test on car engines that attempted to clear up octane requirements. As I remember them, you only want as much octane as your compression and chamber shape require. At a given "dynamic" compression, octane, and chamber shape (flame front length, turbulance, reversion...) all engines have a sweet spot. More octane than you need is not necessarily bad, but it will burn slower. More advance than you need costs power and I don't mean through detonation. On saws I would think that if you have some advance opportunities and serious compression it might help. If you have a stocker, might not see anything, possibly a slight loss of power. I also have been told that building true "dynamic", as opposed to static, compression is always a challenge in two cycles. Makes sense. But on the flip side, saws do have very short flame fronts relative to plane and car engines. I think that this could only be determined on a dyno or very controlled timed cuts.

 

[bwalker]

About the only down side is that toluene does not vaporizes quite as easily as gasoline owing to it's lower volatility, so it may make cold starting a little harder, especiallay in cold weather.

How do you expect tolulene to enhance to octane of the charge in your combustion chamber when it is unlikely to change to a combustable state? Admitingly it might cure a case of deto by causing chamber temp to fall, but it will also have a performance loss as well. Think of the effect that all those liquid droplets passing through the motor unburnt have on combustion chamber temp and you will understand. Also of note is the fact that the tolulene bought at the paint store is really inconsistant and full of trash. Doesnt stop the tight wads from using it though.
As for armatics in race gas. Most of the high quality(phillips,elf,etc) race gases have very little aromatics.

 

[Crofter]

Ben Remember another post when you were talking about all the heat absorbed by the premix oil being vaporised and burned and now you are claiming that toluene is going to go through the combustion process in the form of unburnt droplets.. Are we to conclude that toluene is less volatile and more resistant to combustion than premix oil.

 

[bwalker]

Pre mix oil isnt a octane booster or a fuel. Tolulene would be more volatile on average than the premix oil, but consider the concentration involved. Pump gas already contains around 35% according to Jimbo. add another 15% and almost half your fuel is tolulene.
In summation both pull heat from the chamber. Tolulene has a negative effect because of the amounts involved.

 

[heviarti]

thought we cleared up that this is toluene and not tolulene?

 

[jimbo1490]

BWalker:
I researched the technical specs for several race fuels and found that indeed, the highest grade racing fuels are highly parrafinic, low volatile content fuels. Before you crow victoriously, be aware that these fuels were all over 115 R+M/2 octane rated, and contained TEL levels "at or near the highest allowed presently by the US Surgeon General". These fuels are NOT recommended for use in any air cooled engine, but were for 'Pro Gas', F1 and the like.

All of the other race fuels for which I could find published distillation fractions(including the ones you mentioned) showed aromatic contents in the usual 30-50% range, with the balance of the blending stock being paraffinics. This is exactly as we would expect, since without TEL additive, the octane rating of the basic blending stocks will be greatly reduced. It is generally undesirable to add large amounts of oxygenates as a sole octane improver since the energy density of the fuel will suffer excessively. The only logical choice is to increase the aromatics.

All the unleaded racing fuels were of the high-aromatic type blend. It should be noted that a few years back, F1 racers all used a standard fuel blend of 86% toluene and the balance a filler stock with no appreciable octane rating. These engines would have run fine on 100% toluene, if the rules had allowed it.
If you read up on the refining process, you will discover that various aromatic species (primarily toluene) are desirable by-products released from "heavy" gasoline during catalytic cracking. These aromatics cause a dramatic increase in the octane reserve of the raw fuel stock. It takes further refining (and expense)to remove this aromatic content, and doing so reduces both the octane rating and energy density of the resulting fuel. Currently only the US seems to be in the business of removing aromatics from fuels, even though the majority of Americans breath cleaner air than they did even 20 years ago. Canada and most of Europe have actually increased the allowable aromatics in their gasolines. Canada and Europe allow about 50% aromatics.

To compensate for the resulting increase in HC and CO emissions that accompany this increase in aromatics (again, one of a only a few downsides), Canada has permitted the use of certain organo-metallics of manganese, long banned (since 1978) here because they contain heavy metals and are almost as toxic as TEL. Europe is still in the process of phasing out TEL and will probably follow Canada with alternate organo-metallics rather than the US EPA model.

The approach adopted here is to add so-called "oxygenates" which are nothing more than partially burned hydrocarbons. As I mentioned in an earlier post, these reduce energy density, but have the advantage of making the fuel burn faster and more completely. This facilitated burning results in a net increase in anti-knock properties. Note that available heat energy is inevitably reduced, though.

Toluene got a bad name as a fuel additive when some dishonest fuel wholesalers began adding a low grade (waste product of other industrial processes) toluene which is usually used in paint factories as a thinner. This was done to save money during the late 70's and early 80's when crude oil prices were at historic highs.This lower grade of Toluene contained a lot of 'junk' isomers that were hard on BuNa rubber. Engines at the time still had many seals made of Butadiene-Acrylonitrile (BuNa) rubber which worked well with the lower volatility fuels of the 70's, since aromatic content did not need to be as high. TEL was still allowed then and TEL is still the most efficient anti-knock additive available. But since the early 80's engines of all types have all come equipped with fluoroelastomer (Viton) fuel wetted seals making this a non-issue. I doubt you could even buy a kit for a Walbro or Tillotson that did not have Viton seals, where applicable. It's now a Viton world.

It should be noted that this is NOT the type of toluene sold to consumers as paint thinner. Since this low grade toluene blends poorly with resins, it blends best under mechanical power agitation, else it will may come out of solution. For this reason, consumers are sold standard industrial toluene which blends much more reliably, and is a close match for what was in gasoline originally.

The very modest decrease in volatility that I referred to in an earlier post is nowhere near severe enough to cause the wholesale precipitation/evaporation you described in your previous post; at worst it could mean harder cold starts, especially in cold weather. It will not be an issue in a warm engine whatsoever, especially given that the mixtures recommended will still be within the ASTM definition of gasoline. Anyway, isn't it true that So-called 'power enrichment' in a piston engine generally increases engine power output over stoichiometric mixtures by evaporative cooling? It does so by reducing peak combustion temp thus delaying the onset of detonation which in turn allows more ignition advance. It does not take a rocket scientist to understand that some fuel in a mixture which is over stoichiometric is not going to burn (oxidize) since there is not sufficient oxygen available to burn it. Therefore it must be increasing power some other way, like evaporative cooling.

My point that the octane of 100LL is over-rated by 2-3 point compared with auto gas still stands, irrespective of the fact that I was unaware of the exact method used to rate its octane. For that reason, it will still be cheaper to get 97-98 octane gas (equal of 100LL) by blending 93 with toluene than by buying avgas, which is approaching $4 a gallon. The difficulty for most folks of obtaining 100LL just puts an exclamation point on it.

That's All

Jimbo

 

[glens]

Anybody who takes that much care with spelling and punctuation will get my nod every time over the other participant who does not show they care so much about what they're trying to say in a discussion about which I know little.

 

[TimberMcPherson]

I used to run avgas in my 2 stroke bikes when I raced Formula 3.
I started racing on normal pump gas as I didnt have my race licence. I used to race against a guy who had a near identical bike to mine, if we got on the straight together we didnt loose or gain on each other unless one of us made a misschange. I got my hands on some av, ran colder plugs and at the next meeting down the main straight I was a walking pace faster than him for 3 more meetings until he did the same. Also ran it 50/50 with pump gas in my celica and skyline, they ran alot better with it.

Toululene or however you spell it was used by a few guys, but it can be hard on rubbers once the concentrations get a bit high. Sorry I dont have the scientific stuff on it, just seat of the pants comparisions.

 

[Crofter]

Thanks Jimbo!

 

[njforestfire]

For the amount of gas one uses thru their saws in comparison to the price one would pay for the av gas or higher octane gas, it makes more sense ($$$) to run straight pump gas. I like to put more of the money i make back into my saws - not thru them.

 

[bwalker]

thought we cleared up that this is toluene and not tolulene?

Technicaly it is toluene, but AKA methyl benzene, and tolulene. Toluol is a mix of toluene and xylene.
Does this satisfy the spelling nazis? FWIW its sold as tolulene in the painmt stotre near my house.

All of the other race fuels for which I could find published distillation fractions(including the ones you mentioned) showed aromatic contents in the usual 30-50% range, with the balance of the blending stock being paraffinics. This is exactly as we would expect, since without TEL additive, the octane rating of the basic blending stocks will be greatly reduced.

here is one that does not have any Toluene in it althought it does have another aromatic(xylene).
http://www.cpchem.com/msds_unsecured/Import_434260_MSDS_O_ENGLISH_A_ENGLISH_A_N.pdf
here is a MSDS of phillips pump fuel. notice the toluene level is between 1-10%.
http://seweb2.phillips66.com/hes/msds.nsf/MSDSID/US731678/$file/30017958.pdf
Here is one for phillips avgas. It is also between 1-10%.
http://seweb2.phillips66.com/hes/msds.nsf/MSDSID/US001769/$file/001769.pdf
See a trend here. High quality fuels have 10% or less toluene and instead rely on high alkalate blends stock to boost octane levels. Aromatics are the bane of RFG gasoline and clean combustion.

F1 racers all used a standard fuel blend of 86% toluene and the balance a filler stock with no appreciable octane rating.

I am aware they did. Shell actually blended a fuel for Honda that was almost pure tolulene. What works well in F1 doesnt transfer over to two strokes though. Kind of like comparing a butter knife to a samarai sword.

All the unleaded racing fuels were of the high-aromatic type blend

Thats not true as many of phillips unleaded fuels do not have much if any toluene in them. see below.
http://www.cpchem.com/msds_unsecured/Import_434260_MSDS_O_ENGLISH_A_ENGLISH_A_N.pdf

Canada has permitted the use of certain organo-metallics of manganese, long banned (since 1978) here because they contain heavy metals and are almost as toxic as TEL.

This isnt true either. MMT isnt toxic and is legal for use in the USA. The EPA was sued by Ethyl corp and it was proven in court to be a safe lead sustitute.

The approach adopted here is to add so-called "oxygenates" which are nothing more than partially burned hydrocarbons. As I mentioned in an earlier post, these reduce energy density, but have the advantage of making the fuel burn faster and more completely. This facilitated burning results in a net increase in anti-knock properties. Note that available heat energy is inevitably reduced, though.

I dont know what you mean by partially bunrt HC's. MTBE and ETBE are made from virgin sources. While they do reduce energy density the also boost octane WITHOUT BEING A HINDERANCE TO COMBUSTION like aromatics. By haveing more oxygen in a fuel it also causes older carb engines to run cleaner. The newer FI adjust fuel mapping accordingly.
Good thread BTW. Lets keep it going so we all can learn.