Aviation gas

[pbtree]

Along with the "Dean" thread, and some 056 Kid threads, this may be one of the longest and most disputed threads ever!

It's been hashed to death!

Jeff

Amen! :bang: :spam:

 

[bvaught]

It's spelled toluene, pronounced tall-you-ween (sorry for the mis-spellings :^). You are talking about the two-stroke stone age when you mention the 60's. Purpose made two-stroke oil was uncommon back then. Mostly people used motor oil (four stroke, OK with lead) at a fairly rich ratio, like 16:1 as recommended, or castor oil. By the late 60's and into the 70's, purose-made two-stroke petroleum and synthetic oils were available, firstly to the boat insustry. At that time, Amoco developed a lead-free high octane fuel marketed primarily to the boat crowd. All the boat engine manufacturers recommended it. We used to call it 'Amoco white gas' as it had no dye color. With the exception that it's now 93 instead of 95 octane, that fuel is essentially Amoco Ultimate, which was always lead-free, even before gov't mandates.
It's worth mentioning that 100LL is rated for octane number by 'research octane' only while all auto fuels are rated by the average of research ond motor octane numbers. This makes the octane rating of 100LL 3-4 points higher than it would be if the R+M/2 method was used. So Amoco Ultimate is actually within a couple of points of 100LL, both measured by the same method.

Jimbo

This post is complete BS. 100LL is rated by MOTOR OCTANE NUMBER. It would totally blow Amoco Ultimate out of the water in terms of Research Octane Number and MON. The info about avgas is out there research ASTM D2700, this is the specification for AVGAS.

 

[bvaught]

Man I don't know whether to stick my finger in the fan blades here or not!

What the heck, you only live once......

first off, I'm a commercially rated pilot (single and multi) and also a certified flight instructor (18 years now I think), as well as being a certified master auto mechanic, and also worked at a Stihl dealership, though I'm not certified by them in any way. Oh yeah, also have co authored 2 books on automotive electronics and electrical systems. I don't say that to say my opinions are worth any more than someone elses, but that I have had a rather morbid relationship with both aviation and chainsaws over the past few decades. That and a buck can get me a cup of coffee, except at starbucks.....

I see a few things not discussed yet, the main one being the purpose of an octane rating. In a cylinder we want the fuel to burn and not detonate. Detonation occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture to autoignite. This produces multiple flame fronts within the combustion chamber instead of a single flame kernel that expands outward from the spark plug as designed. The Octane rating simply measures the resistance to detonation. In general, a lower octane fuel will have more energy than a higher octane fuel. You would not notice it in a saw but a car, everything else being equal, will get better mileage on 90 octance fuel than on 120 octane fuel.

Operating environments have nothing to do with it really, unless you either have poor design or physical blockage that allow cylinder head temp to go above design specs. If you want to get technical, the temperature drops by 4.5F every 1000 feet, so even at 10,000 feet it is only 45 degrees cooler than on the ground. (a kinda cool formula to use here, is when they give the dewpoint temperature during the weather broadcast, take the current temp, subtract the dewpoint, divide it by 4.5 and that gives you the height of the cloud bottoms outside in thousands of feet) .

Anyway, what I'm trying to say is that IMHO 100LL is one of the better fuels for 2 stroke engines, use it if you can get it. If you show up at an airport with a 5 gallon can and they don't want to sell it to you, go to the next airport because they are full of it. The ONLY objection someone can give is that since there has been no road tax applied to it, you cannot use it in a vehicle driven on the street. If you tell them it is for off road use only they cannot argue with you. As has been pointed out, a place to get it for free is from the line trucks that fuel planes, after they are done gassing up a plane they stick the fuel nozzle in a funnel, and eventually the sump fills up and they have to dispose of it. Be aware there will be water in this fuel! Let it sit in a can for a day at least, a few days is better, and either carefully decant the fuel or siphon it down to the last 6" or so. I'm a cheap bastard so I'll pour the last into glass 1 gallon jugs and always let it settle for a day at least, then you can see the water and you can carefully pour off the gas on top.

Now, the other thing to do is see if you can get the jet fuel, which is basically kerosene. The best use I have found is that it is the best fuel for salamander heaters, burns much cleaner than kero or diesel.

Anyway, my points again:

1) 100LL is good for saws
2) Will it give them "more power"? maybe, maybe not. Most likely not unless there were ignition issues with that individual saw.
3) Octane, to be blunt and crude, does not relate to "more power", it relates to "resistance to detonation". Ignition timing also relates to detonation and ignition can be advanced when using higher octane which may result in higher power output but that is not what is being discussed here.
4) You can legally buy aviation gas and use it for anything except a vehicle driven on a public road.


I think that's the end of my rant, here someone else take this dang soap box!...

Disclaimer- It is now 1am and I reserve the right to make corrections tomorrow if I read this and I look at something and wonder what the heck was I thinking when I wrote that!.......

Hip Hip Hooray for this well written post. Welcome to Arboristsite!!!

I havent been able to read this entire thread yet and plan to do a comprehensive post later (like it will do any good).

 

[bvaught]

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.

The 4 stroke rotax 912 prefers premium auto gas. You can run 100LL but you have to change the oil more often, Im not sure why but apparently it builds up in the oil and causes problems. Some experimental airplane owners that run highly modified car engines in their airplanes using 100LL, have had oil compatibility problems causing lead sludge to build up. It is interesting to note that the standard aviation oils have almost no antiwear or anticorrosion additives. The premium aviation oils have very expensive antiwear and anticorrosion additives that are designed to prevent harmful deposit buildup in the combustion area. I assume the aviations oils are designed to work well with lead as well. The last oil analysis ,from an airplane motor, I read indicated 1100 ppm of lead, which was 10X higher than anything else reported on the analysis sheet.

 

[no longer collecting]

plane fuel in chainsaw..

This is only my opinion....i've been fishing and hunting up north for 25 years using floatplanes for transportation. The outfitter uses floatplane fuel (100-102 octanes)for all the chainsaws,brushcutters he uses to clean the trails and the same fuel goes into all the outboard motors that are leased on site. Done that for a long time and used those many times. I think that the positive side of high octane is a more refined and cleaner gaz...less pollution as stated earlier when dropping fuel in the lake this gaz is very volatile....evaporates and limits the damage to environment to almost none....but i did not see any improvement on the equipment i used versus regular 94 octane fuel.........if you are talking about "jet fuel" this maybe another interresting topic if someone has ever used any in chainsaw??????

 

[Mr.]

"jet fuel" this maybe another interresting topic if someone has ever used any in chainsaw??????

I'll stick with my "Rocket fuel."

Fred

 

[rupedoggy]

Wood butcher, I thought the description you made of the mixture auto igniting was called pre-ignition not detonation. I learned detonation was caused by an octane that was too low, for the compression of the engine. Can you explain these terms for us? Thanks. Mike

 

[fishhuntcutwood]

Jet fuel, A and B is basically diesel, and there's a thread on diesel in saws floating around the board right now. If you're gonna do it, stick with avgas. Jet fuel and avgas are completely different things, and not interchangeable.


Jeff

 

[Mr.]

Jet fuel, A and B is basically diesel, and there's a thread on diesel in saws floating around the board right now. If you're gonna do it, stick with avgas. Jet fuel and avgas are completely different things, and not interchangeable.


Jeff

Cause, "I'm a rocketman burning........"

I think people get the two mixed rocket fuel and jet fuel.

Fred

 

[Wood Butcher]

Wood butcher, I thought the description you made of the mixture auto igniting was called pre-ignition not detonation. I learned detonation was caused by an octane that was too low, for the compression of the engine. Can you explain these terms for us? Thanks. Mike

OK I'll try. I'm going to put a big disclaimer here in that how I am describing things is more tailored towards 4 stroke engines, and there may be subtleties that I am not aware of in regards to 2 stroke engines, for example I have no idea how this "flame front" travels in a combustion chamber designed for loop scavenging.

Anyway, back to the subject, let's start the moment the spark plug fires....

When that happens, a burning wall of fire called a "flame front" expands outward until it fills the chamber. To give an example of this I am going to refere to the late late night TV show when the evil contractor, after trying all other methods to force the orphanage to move out of the ground where he is going to build the new shopping mall, goes and pours gasoline everywhere while all the kids are out at the movies (remember you thought it was fishy that EVERYONE in the orphanage got a free movie ticket in the mail). Anyway, he pours gas everywhere, walks to the door, and right before he leaves he lights a match and drops it. Now remember how the flame looks racing across the room! That is a real life example of what a flame front looks like. Virtually all gasoline engines are designed to use this. I'm pulling this number out of my rapidly decomposing brain cells, but if I remember correctly the front travels in the neighborhood of 300-400 feet per second.

I'll talk about detonation in a minute, but there is one more thing we need to talk about, ignition timing. This Flame front obviously needs a certain amount of time to fill the chamber and develop pressure, so the faster the RPM's are the sooner in terms of crankshaft rotation the fuel has to start burning.

Now detonation happens when the fuel, for a variety of reasons, burns faster than designed and the pressure spikes. This causes the remaining unburned fuel to explode rather than burn and is where you get bent rods and broken pistons, etc. Think of it as when the van full of orphans pulls up to their burning building and the bad guy is spinning out of the lot in a cloud of dust and the hero driving the van starts chasing him down the mountain road and the bad guy goes over the cliff at the hairpin turn, remember what happens when the car hits the bottom of the ravine? Thats what detonation is like.

In answer to the question- Pre-ignition, as the term suggests, is the ignition of the fuel-air mixture before the regular ignition spark from the spark plug. If the regular spark occurs shortly after the pre-ignition, the colliding of the two flame fronts will cause a pinging noise in an automobile engine. This usually happens from a "hot spot", which can either be a glowing piece of carbon stuck in the head somewhere, or an edge of a gasket or other sharp edge protruding too far in the cylinder, or the wrong heat range spark plug on occasion. A loose spark plug will not transfer heat correctly to the head and can give the same symptoms of a too hot one as well.

I should have mentioned this earlier, but what we want to have happen is the burning fuel to give a gentle push, which has to start before top dead center and developing peak pressure a couple degrees after TDC (IIRC), and detonation will give a more or less instantaneous shock-laden jolt while the piston is still moving up.

I hope that somewhat explains the difference between the two. I've left out other factors such as heat, air/fuel ratio, lugging an engine, etc. Sorry for the long-windedness but I'm making it brief as possible and still cover the basics!

 

[Chris11]

Detonation is simply diesel engine operation. You need low octane fuel and/or high compression ratios. Look how rugged a normal diesel engine is built and you get an idea about the forces. Typical peak pressure is about 3x of a gas engine. Flame front speeds are usually slower than in gas engines and with it you have lower peak rpms.

Best regards
Christian

 

[bwalker]

Detonation is simply diesel engine operation.

Its not. A diesel engine uses compression to ignite the fuel air mixture. The resulting combustion is not detonation.

 

[Crofter]

Ah! there is some quibbling room in those couple previous statements, better get the definitions down pat.

 

[Joseph]

Jet fuel, A and B is basically diesel, and there's a thread on diesel in saws floating around the board right now. If you're gonna do it, stick with avgas. Jet fuel and avgas are completely different things, and not interchangeable.

Jeff

Commercial jet fuel, known as Jet-A, is pure kerosene.

Regards

Joseph

 

[bwalker]

I do not think that Kerosene and Jet "A" are identical. I base this on the fact that they smell and look differant from what I have seen.
Jet A, Kero, and #1 diesel are all simular, but not the same.

 

[Joseph]

I do not think that Kerosene and Jet "A" are identical. I base this on the fact that they smell and look differant from what I have seen.
Jet A, Kero, and #1 diesel are all simular, but not the same.

...Cut and Paste....

"The most common fuel worldwide is a kerosene-based fuel classified as JET A-1. JET A-1 is produced to an internationally standardized set of specifications, and has a flash point of 38°C and a freezing point maximum of -47°C.

A version of JET A-1 known as JET A is available only in the United States. It is similar, except for its higher freezing point of -40°C. The only other jet fuel that is commonly used in civilian aviation is called JET B. JET B is a fuel in the naptha-kerosene region that is used for its enhanced cold-weather performance. However, JET B's lighter composition makes it more dangerous to handle, and it is thus restricted only to areas where its cold-weather characteristics are absolutely neccesary.

Both JET A and JET B can contain a number of additives:

* Tetra-ethyl lead (TEL) to increase the fuel's flash point;
* Antioxidants to prevent gumming, usually based on alkylated phenols, eg. AO-30, AO-31, or AO-37;
* antistatic agents, to dissipate static electricity and prevent sparking; Stadis 450, with dinonylnaphthylsulfonic acid (DINNSA) as the active ingredient, is an example
* Corrosion inhibitors, eg. DCI-4A used for civilian and military fuels, and DCI-6A used for military fuels;
* Fuel System Icing Inhibitor (FSII) agents, eg. Di-EGME; FSII is often mixed at the point-of-sale so that users with heated fuel lines do not have to pay the extra expense;
* Biocide additives.

Jet fuels are sometimes classified as kerosene or naphtha-type. Kerosene-type fuels include Jet A, Jet A1, JP-5 and JP-8. Naphtha-type jets fuels include Jet B and JP-4.

Jet A

Jet A is the standard jet fuel type in the U.S. since 1950's. Jet A has a fairly high flash point of min. 38°C, with an autoignition temperature of over 425°C. Jet A can be identified in trucks and storage facilities by the fuel code 1863. Jet A trucks, storage tanks and pipes that carry Jet A will be marked with a black sticker with a white "JET A" written over it, next to another black stripe. Jet A will have a clear to straw color if it is clean and free of contamination. Water is heavier that Jet A, and will collect on the bottom of a tank. Jet A storage tanks must be sumped on a regular basis to check for water contamination. It is possible for water particles to become suspended in Jet A, which can be found by performing a "Clear and Bright" test. A hazy appearance can indicate water contamination beyond the acceptable limit of 30ppm (parts per million).

Jet A1 is a version of Jet A with freezing point of -47 °C instead of -40 °C.

The U.S. commercial fuels are not required by law to contain antistatic additives, and generally do not contain them."

...End of Cut and Paste...

Kerosene and Jet "A" are Identical.

BP is the largest producer, If You "do not think so" contact BP Customer Service Department.

I have a Fire Pump{a P250] that uses Jet "A" / Kerosene , the engine is a OMC 55 HP.

Regards

Joseph

 

[fishhuntcutwood]

"The most common fuel worldwide is a kerosene-based fuel classified as JET A-1.

The fact that is says "kerosene-based" and not just "kerosene" would be indicative that they're not identical. They are very similar, so much so that I'd say that they're basically the same, but not identical. You can run a diesel truck on JP5/8 (don't ask me how I know) but you have to add ATF because JP5/8 doesn't have the lubricative properites that diesel does. Again, they similar, but not identical. Aviation fuels are highly regulated, and are reguired to have several additives to make them airworthy, whereas kerosene doesn't.

They're different enough so that if you try to burn JP5 in your kerosene heater, it'll smoke you out. Again, don't ask me how I know.

Jeff

 

[bwalker]

The fact that is says "kerosene-based" and not just "kerosene" would be indicative that they're not identical.

Exactly.