At lunch the other day some one said that they have a new auto fuel on the east coast and it is supposed to be 130 unleaded. Have any of you heard such rumours?

130 octane would run like crap in most of our engines. The power level would be reduced dramatically I would think.

From Shell's website - http://www.shell.com/business-customers ... 71515.html

As you may be aware, Avgas contains Tetra Ethyl Lead (TEL) - the additive which has recently been banned in automotive forecourt fuels in the European Union for environmental reasons. Although the total fuel volume used in aviation is less than 0.5% of that used in the automotive sector in Europe, there is considerable pressure from Environmental Lobbyists to remove or replace TEL in Avgas and produce an unleaded grade.

To understand what is involved, we first need to look at what benefits TEL has. As you may know from the problems with Automotive fuels, Lead compounds from TEL form a protective layer on the valve seat and prevents the soft valve seats from eroding. Without TEL small areas of a soft metal valve seat will fuse to the valve and be 'plucked' from the face of the seat.

Once attached to the valve they form an abrasive surface which further damages the valve seat. This combination of actions is known as Valve Seat Recession (VSR) as the seat of the valve is worn away and recesses into the cylinder head. The solutions to this are to either use a VSR additive or fit hardened valve seats which are resistant to this action.

VSR additives are now commonly used in Lead Replacement Petrol on automotive forecourts, however for several reasons they are not yet approved for use in aviation engines. This means that the only current method of preventing Valve Seat Recession for aviation engines using unleaded fuels would be to fit hardened valve seats. This is common in new manufacture Avco Lycoming and Teledyne Continental engines, but some older engines would need modification.

The other more significant problem with unleaded fuels is that of Octane rating.

Octane rating is a measure of how resistant a fuel is to detonation or "pinking"; the higher the Octane rating, the more the fuel / air mixture can be compressed without detonation happening. To make this clear, octane rating is not a measure of the amount energy in the fuel, but is a measure of its resistance to detonation.

The advantage or higher octane fuels is that a higher compression ratio or supercharging ratio can be used, which then leads to a higher engine cycle efficiency, which in turn means more power output for a given fuel burn. However, to confuse things further, there are four principal ways to measure Octane rating, RON, MON, Lean Mixture and Rich Mixture ratings.

Road fuels tend to be measured on a RON scale, for which unleaded fuels tend to be 95 - 98 RON but are only 85 - 87 MON. Avgas is measured on Lean Mixture (similar to MON) but also has a Rich Mixture Octane rating.

The Lean Mixture rating is 100 octane (15 octane higher than the comparable 85 MON for unleaded Mogas) but Avgas also has a Rich Mixture rating of 130 which allows higher supercharger boost pressures to be used without detonation occurring. This is particularly a problem when using high power settings at low altitude, for example during take off.

As you can see TEL in Avgas makes a significant difference to the octane rating and without it Octane ratings would be back down to 80 - 85 Lean Mixture - the level for road fuels - instead of 100 / 130. This is not a problem for most typical modern normally aspirated engines as their compression ratios are quite modest and detonation would not be a problem with 80 - 85 Lean Mixture Octane fuel.

However, for those aeroplanes with supercharged or turbocharged engines the use of low octane unleaded fuels would not be suitable. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the supercharging and massively de-rate the engines. This de-rating would be so severe that many of the engines would no longer be powerful enough for the aeroplane in question.

Modern aviation unleaded fuels are currently being developed, such as 82UL in the United States. This is an 82 Octane Lean Mixture rating fuel and is approved for use in modern non turbo Avco Lycomings engines amongst others. However, it is not yet available in Europe but also not everyone can use it - your aircraft manufacturer must raise a Aircraft Modification document to approve its use.

Some new Cessnas are approved to use 82UL, but most aircraft types currently do not have manufacturer's approval. The potential quantity of Avgas piston engined aircraft world-wide that could use this grade is estimated to be around 60%, although some of these would probably need fuel system modifications prior to approval.

To date there are no additives available to replace TEL which increase the Octane rating - the additives used in automotive Lead Replacement Fuels only tackle the problem of valve seat recession and do not effect the Octane rating of the fuel. Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer raise a modification to replace their engine with either a turboprop or diesel engine.

Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer raise a modification to replace their engine with either a turboprop or diesel engine.

Not quite right, ethanol is around 113 octane and has been used in Brazil for years. Also, Texas Skyways has the STC to use AGE 85(88% ethanol) in a couple of their higher compression engines. Whatever happened to Swift Fuel we heard about a few years ago----it was unleaded and high octane?

180Marty wrote:

Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer raise a modification to replace their engine with either a turboprop or diesel engine.

Not quite right, ethanol is around 113 octane and has been used in Brazil for years. Also, Texas Skyways has the STC to use AGE 85(88% ethanol) in a couple of their higher compression engines. Whatever happened to Swift Fuel we heard about a few years ago----it was unleaded and high octane?

Swift UL94 is now available at a few airports. Mostly in the upper midwest.

https://swiftfuels.com/ul94-map/

Ethanol is just plain bad news. Between vapor lock, dissolving rubber, mixing with water and going stale in record time, it is useless in aircraft. Might work in some vehicles that are driven everyday in optimal conditions and traded off every three years, but that's about it. Dig or pump our fuel out of the ground and leave the fields for food crops thanks.

Looks like GAMI down in Oklahoma may be getting close to a 100LL replacement.

http://www.gami.com/g100ul/abs201701.pdf

BTW when I say "close" I mean 2-3 more years at the rate the FAA moves.

Those GAMI folks are a top notch crew.

Ethanol is just plain bad news.

Not in my experience. I have a 1992 Toyota 4x4 that has had 30 to 50% ethanol in the tank since 2001 and still runs great!!!!! Also, everything else I own with a sparkplug gets at least 10% ethanol. If you notice the AGE85 is 88% ethanol because ethanol has a Very Low Reid Vapor pressure of around 2. It needs very volatile Pentane to light the fire. I have a Ford that uses E85 and in the winter they drop the percentage to around 70% ethanol because it needs the more volatile gasoline to get started. You need to get your facts straight.

Another problem with Ethanol, is that it contains quite a bit less energy per gallon. I loved E85 in a couple of high boost / high power street cars I built, but it's not great when you only have so much capacity for fuel, and fuel weight etc. It requires approx 30% more fuel when running an 85% ethanol blend. Pure Ethanol is worse. Ethanol does burn cooler though, so the lower EGTs are very nice! But I just don't see it as worth it for these issues and others mentioned above personally.

Ethanol gets a lot of hate by people that don't understand it. It's a great fuel, high resistance to detonation but yes, does contain less energy by volume so it takes more to make the same power. This can end up being not such a bad thing as the extra volume in flow helps cooling considerably. The higher volume/BTU is a really good argument though as to why it shouldn't be used in aviation, it really starts to reduce range as the ethanol content increases, around 30% for E85.

Some people complain about it "gumming up the carb", it's hygroscopic so it will pull moisture from the air, but it also suspends that moisture better (compared to gasoline) so as long as you don't leave it sit for 6 months the moisture shouldn't separate, its when the moisture separates and sinks that the metal parts (float bowl, fuel tank) now sitting in the water will begin to corrode. Don't let it sit through winter, run a tank of pure gasoline or mix an additive before storage and the moisture won't get sucked in. The shelf life is only a little over 3 months for ethanol so it shouldn't sit that long anyway.

I'm not advocating it's use in aviation, just saying it's not the devil some people say it is.

We had a presentation from the NRC (National Research Council) on their progress towards a replacement for 100LL. As confirmed earlier in this thread, they stated the challenges and standards criteria were suitability for turbo/supercharged piston engines at 20,000+ feet. At that point I lost interest, as the replacement will be just as esoteric as the current fuel and inevitably more expensive that anything my car uses. For the majority of our backcountry airplanes operating below 20,000', I want to burn whatever the snowmobile parked under my wing burns, or the outboard motor tied up at the float beside me. The Rotax can even do it with a turbocharged motor.

It is a mistake to tie our GA fuel standard to an upward cost spiral to serve a tiny sliver of mainly commercial aviation.

Mike Busch just did and EAA webinar and mentioned the FAAs efforts on a 100ll replacement fuel. Out of 17 initial candidates two still remain, Swift and Shell. Both are around 105 octane. Apparently testing should be complete early 2018 and the fuel should be on the market late 2018 or 2019.

So ethanol can work ok. But, uses a super volatile substance to light it, very poor shelf life, less energy per gallon. How many more millions, probably billions, of gallons gets dumped on the ground every year by average people because it went stale compared to ethanol free fuel? Won't find any statistics on that. Lots of conventional crude oil available - so why waste time with a subpar fuel? So much false environmentalism these days....Don't even get me started about urea, dpf filters and regen cycles.....

Glad to hear Swift might happen before too many more years. Here's my real life experience with my 2017 Ford Focus with Direct Injection,Variable Valve Timing and 12 to 1 compression ratio. On E85 driving 65 to 75 it gets 30 mpg. On a recent trip to Virginia from Iowa I had to blend down once to about 30 percent ethanol and the mileage went up to about 40. I should try a test with 87 octane pure gasoline that is still available in Iowa and see if it gets 50mpg--- I bet not. Maybe with the 91 octane E0 that costs 70 cents a gallon more. E30 has been proven to be the best in tests since it has 100 octane characteristics and not that much less energy per gallon. Nano sized particles (they get stuck in your lungs) out the tail pipe are greatly reduced compared to gasoline. The high octane components of gasoline are also the ones that cause cancer. PS when I'm at the airport, I try not to breathe 100LL exhaust fumes even though they don't smell bad. And Mark, you must not be old enough to remember the 1973 oil embargo that put everybody on their knees just because oil companies could.

180Marty wrote:If you notice the AGE85 is 88% ethanol because ethanol has a Very Low Reid Vapor pressure...

This is true. As you add alcohol to a gasoline mixture, the vapor pressure rapidly rises until around 10% ethanol, and then the vapor pressure of ethanol begins to reduce until it is roughly the same as the parent gasoline at 50% ethanol, and it continues to reduce to roughly 1/3 or less of the vapor pressure of gasoline at 100% ethanol. While not exactly intuitive, it does mean that high alcohol blends are not a vapor lock risk compared to gasoline.

Alcohol combustion at a given compression ratio is not as efficient as gasoline combustion. The fuel vaporization cools the mixture to a much lower temperature than with gasoline, and this reduces the thermal efficiency of the engine. Higher compression ratios yield higher thermal efficiency. Luckily, alcohol is highly resistant to knocking and can be burnt in a conventional Otto cycle at compression ratios that offset the losses from vaporization. In fact, the compression ratio can be increased to offer 5% or even more thermal efficiency with alcohol. An engine that uses the same compression ratio for both gas and ethanol blends will only suffer a loss in efficiency, however. And alcohol requires a lot more volume of alcohol per volume of air, which lowers the power output of these engines at a given compression ratio and manifold pressure.

Lead is terrible. MTBE is terrible. Alcohol in avgas is a real bummer for a number of reasons. But aviation is 1930's technology with some 60's technology scabbed together along the way. It isn't very attractive compared to what else is available in the everyday auto world.

No, not old enough to remember that embargo. A year before i was born. Lol Between the US and Canada's potential for production, there is no need for Saudi oil anyway. Just a political game that ethanol would not change anyway. We have lots of oil for sale here in Northern Alberta, just let us know where to connect into the keystone....

StampCreek wrote:......Modern aviation unleaded fuels are currently being developed, such as 82UL in the United States. This is an 82 Octane Lean Mixture rating fuel and is approved for use in modern non turbo Avco Lycomings engines amongst others. However, it is not yet available in Europe but also not everyone can use it - your aircraft manufacturer must raise a Aircraft Modification document to approve its use. Some new Cessnas are approved to use 82UL, but most aircraft types currently do not have manufacturer's approval......

A number of years ago, 82UL was gonna be the next big thing.
EAA & Peterson even had their mogas STC's amended and their stickers changed to reflect "approved for 82UL aviation fuel".
However, that next big thing never seemed to materialize.
Has anyone ever even seen this "82UL" for sale at a US airport?
I never have.

180Marty wrote:

Therefore if Avgas 100LL were to disappear, the only other option currently available to owners with turbo or supercharged engines would be for the aircraft manufacturer raise a modification to replace their engine with either a turboprop or diesel engine.

Not quite right, ethanol is around 113 octane and has been used in Brazil for years. Also, Texas Skyways has the STC to use AGE 85(88% ethanol) in a couple of their higher compression engines. Whatever happened to Swift Fuel we heard about a few years ago----it was unleaded and high octane?

They only have the STC for the carbuerated 470U. The O-470 is not a very high compression engine...

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180Marty wrote:I should try a test with 87 octane pure gasoline that is still available in Iowa and see if it gets 50mpg--- I bet not. Maybe with the 91 octane E0 that costs 70 cents a gallon more.

Actually, probably not. Higher octane fuel has a slightly lower BTU content than lower octane fuel. If you don’t need it for detonation resistance then adding octane shouldn’t increase your engine efficiency.