Pietenpol-List: MOGAS

[matronics]

Original Posted By: "John McNarry"
Someone on another list I subscribe to asked about using motor gas inA-65's. I took the time to write out a response and thought it might be ofinterest here as well.I am not a fuels expert, however I recently took a 3-day class by ASTM onaviation fuel. After much complaining at work about not having anytechnical training (and also having far too much training in the managementor quality concept of the moment) management selected a class forpowerplants engineers. I don't have any idea how they picked the class out,but I suspect it was either the cheapest one offered or it sounded soboreing that nobody would ever complain about the lack of technical trainingagain. It was fascinating (go figure).I wasted a lot of the classes time asking questions to learn about yourexact question. Here is a summary:To start with, fuel is very weird. It is too complicated to manufacture anexact chemical compound that does what fuel does. In fact different barrelsof crude from different parts of the world mix up differently. As a resultfuel is not specified by what it is, it is specified by how it performs. Inshort the industry has a number of performance tests, time has shown thatthey are pretty good and fuel that passes those tests is acceptable for usealthough the exact chemical makeup will vary widely.The next part of the process is that the fuel is predominately distributedby pipeline. Apparently there are several pipelines that stretch across theU.S. For instance one pipeline (the colonial) stretches from Texas toeither New York or Chicago (I forget which.) Fuel is put into it at anumber of different places and taken out at another group of places. Theonly reason it works is the fuel is constantly flowing through the pipe (itonly goes one way.) The strange part is multiple different fuels are in thepipe at once (Jet-A, motor gas of different grades, home heating oil,diesel, etc.) Imagine it as a convoy of different products going down aroad. Basically they have big slugs of each and they don't mix too much aslong as you keep the whole thing constantly moving. They are sequenced sosimilar products are next to each other to make it less troublesome when theinevitable fuel on the edge of each slug mixes with the fuel in the nextslug (no spacers, its just the next thing in the tube.) So imagine a slugof cheap motor gas, then a slug of medium motor gas then a slug of expensivemotor gasoline then the medium stuff than the cheap stuff then somethinglike jet-A followed by kerosene and so on in a rotation that they find workswell. Here is the kicker, when a specific company puts fuel in that is ofa certain grade they put it into the middle of a slug (they wait until theslug they want to add to comes by and then start adding fuel to the pipe.)When they want to take out they wait until what they want comes by and theytake out of the middle. Thus, when a specific oil company puts fuel in atone end, they have no way of getting their fuel out at the other end. Itworks because they put stuff in that meets a specific spec and take stuffout that meets the same spec. However the fuel that Texaco refines may verywell end up at the Exxon gas station. Hence the industries emphasis onadditives (i.e. Techron), they cant say their fuel is better due torefining, because they cant sell you the stuff they refine. They can claimits better cause they dumped some powder or a quart of something into thetank though. If when they take the cheap grade gas out it tests too low onoctane they just mix in some of the stuff from the premium batch to bring itup to the minimum levels.100LL does not flow through the pipeline because the quantities are toosmall. It is however shipped or barged around and mixed up in much the sameway. So when you buy gas, the important thing in my opinion is turnover(you don't want some stuff that has been sitting around gathering water andcontamination) not brandname. Also, be aware that as a result of thisprocess the people you are buying gas from have little control over thecomposition of their product.Now for octane, 'isooctane isn't something that it is put in the gas. It isa fuel that is run in a test engine (a goofy 1 cylinder engine that isn'tvery much like your engine, but its a really old and established test so itwont change.) Thus 100 octane is the test engine running 100% isooctane.Ratings above 100 are measured different, but lets leave that alone as itisn't important for a typical light aircraft. What it means is the fuel youare using behaves like this test fuel with respect to knock. Think of it asa knock index. You may know knock better as 'detonation', its the samething and is bad for your engine. Each engine requires a certain knockindex if you will, or else it will detonate. Anything above that doesnothing to add to the performance, in fact it may make the fuel morevolatile. They test the fuel for this characteristic because it isimportant that the engine not detonate. Now, as long as your not detonatingyou have enough 'octane' in the fuel. How much is required varies fromengine to engine. High compression ratio's and turbochargers require a muchhigher octane than other fuels. The A-65 was invented long ago when fuelwas much lower octane than today's 100LL. 100LL is however required forhigh compression turbocharged engines such as the TIO-540 (lest theydetonate.) Because airports don't want to add another fuel system (trucks,tanks, etc) they force the recips to all use the same fuel.High octane fuels did not come along until the late 30's. They weredeveloped for the raceplanes and the military. Primarily they allowed forus to get a lot more power out of the same size engine than other countrieswere able to extract. This development definitely had a lot to do withAmerica's success in the second world war.From the point of view of an old fashioned engine the high octane is totallywasted. What you do gain by purchasing 100LL is a fuel that has a verystrict quality system in place (have you ever heard of the service stationdown the street filtering or sumping their fuel?) Aviation gasoline goesthrough filters as it is delivered to the airport to remove contaminates andagain on the truck. The fuel in the storage tanks/truck/etc is sumpedregularly. The filters are for both particles and for entrained water.Entrained water (water suspended in the fuel) is a concern as it cancondense out rapidly if the temperature drops (i.e. weather changes or youclimb to altitude.) The reason for the concern about alcohol is it ishydroscopic (it really likes water) and will hold a much greater amount ofentrained water than gasoline without it. The STC the EAA got on motor fuelrequires you to be sure you don't have any alcohol in the fuel you use (notexactly a reasonable requirement as you can see from the description of thedistribution system described above.) This quality system and assured lackof alcohol is what you gain by buying 100LL. It is about a lot more thanoctane.One other benefit of 100LL is the lead. it can help with the lubrication.100LL has about 4 times the lead the old 80 octane stuff the A-65 wasdesigned for. So, it would be a good idea to fuel up with 100LL everyfourth tank or so. If you go anywhere with your airplane you are bound tobuy some 100LL so this will probably take care of itself very nicely.Thus, if you want to use motor gas it can be made to work. However if youwant a similar level of safety you will need a pretty sophisticated setupfor filtering and sumping the fuel. My recommendation is if you want to usemotor gas you need to do it in a big way: get yourself an epoxy lined drum,put a sump in it, let it sit for a while before using it to allow anyentrained water to precipitate out and sump it religiously, and filter thestuff coming out of it. Be aware that you have a higher risk of problemswith entrained water than if you are using aviation gasoline so be cognizantof changes in temperature. The filter they airport uses to get out theentrained water is fairly sophisticated and extremely expensive so yourhome-made set up will probably lack this feature. If you keep your airplaneat an airport with fuel this is probably more work than it is worth.However if their is no fuel on the field this may be worth the effort forthe convenience.To answer your question I would not use additives in motor gas, however Iwould take great pains to develop a good distribution/filtering system.Additives are not regulated or tested. They do not have any associatedperformance standards. So more or less, who knows what they will do for orto you. This is not completely true for several jet fuel additives thatserve very important purposes for people that have very specific problems oroperational requirements, but once again that isn't a Pietenpol issueeither.I hope this was not more detail than you wanted. Once again, this is not asubject that I am an expert in so evaluate it's merits for yourself.Best Regards,Kevin Holcombhttp://www.angelfire.com/va2/aerodrome/_______ ... __________

[matronics]

Original Posted By: owner-pietenpol-list-server(at)matronics.com
Thanks KevinA very good description of fuels.John Mc-----Original Message-----

[matronics]

Original Posted By: "Kevin Holcomb"
----- Original Message -----

[matronics]

Original Posted By: owner-pietenpol-list-server(at)matronics.com
Thanks, Kevin. A very good explanation of fuels.Here in North Carolina, at least in my county, all winter long thecommercial mogas contains 10% ethanol to help reduce ozone. This can be badfor airplanes in other ways than entrained moisture. Most aircraft fuelsystems uses buna-n rubber for the seals (gascolator, fule selector valves,etc.). Stromberg Carburetors use neoprene valve seats on their needlevalves. These rubbers are attacked by alcohol and they will disintegrate ina few weeks. I had a J-3 Cub back in the late 70's and early '80's, and Iregularly put car gas in it, thinking that since the A-65 specified aminimum octane of 73, the car gas would be better for the engine than allthe lead of 100 octane (the airport where I was based didn't have 100LL,just 100/130, which has 10 times the lead of 80/87). I nearly lost theairplane when the needle valve seat in the carb disintegrated, allowing asuper rich mixture into the intake manifold. I eventually replaced theneedle valve seat with a stainless steel one and solved the problem, but atthe time I never attributed it to the use of car gas. It was years later,after I sold the airplane, that I found out the alcohol in the car gas hadcaused the problem.As they say on AvWeb, Y'all be careful up there.Jack -----Original Message-----

[matronics]

Original Posted By: raymond smith