Tetra-ethyl lead

[Ted]

And FWIW, at least by my reading your posts WRT Sunoco racing fuel came across more along the lines of "it will work, you don't know what you're talking about if you don't believe me" than "I'm suggesting that it might be an option" but that could just be me. I hope we can both agree that none of us know all there is to know on that subject.

That was my interpretation as well.

 

[Ted]

Did the Thielerts control the prop from the single lever? I've never seen one in person.

Yep. One lever controls everything.

 

[Cap'n Jack]

I respect your comments and need to respond. I am an up front guy, I DON'T sugarcoat anything. My marketing concept is ,I state all the advantages of my ideas and I also admit its flaws. All the data I spoke about is 100% correct.
Popular marketing used today is to promise the world, get a signed commitment and then deliver the least amount possible just shy of getting sued.. That ain't me. This all started when I suggested a brand of no lead fuel to use as an alternative to 100LL. Without exception that fact was beat down. No tests where done on this fuel to prove whether it would work or not. It was just my suggestion it might be a option. I even said that maybe Sunoco could reformulate it to raise the octane level a bit. I do apologize to Ted as I asked if he did any testing and since he didn't respond I took that as NO. My mistake. I don't need to market anything to anyone on POA as I am busier then I ever wanted to be so feel free to tell all your friends to stay away. I could use the break,.

What's the ol saying ?

You can please some of the people some of the time but you can't please all the people all the time............................

Life goes on.

Ps. I am still amazed I have not gotten the boot from the moderators yet for my unpopular views.

Cheers.
Ben.

I don't know what sales/marketing people you worked with in the past...but I have never worked for a company that used the practices you described. In my industry, the market is simply too small to stand such tactics; those companies that employ them are out of business and the people that used those tactics work in different industries.

I'm not sure why you think the mods will boot you off...you've made a poor job of arguing your point with the post below...but you haven't been that rude. Taking an unpopular position has never been AFAIK a reason for banning here.

All you guys make good points on flame propagation but it is all theory that someone read somewhere, heard from a friend, saw scribbled on a wall, overheard about it in a bar from the cocktail waitress etc. No one has done ANY testing to prove your ideas about this product or any other No Lead substitute so all your talk is just 'hearsay'. I have throughly and personally tested my set up. I didn't hire a test pilot or fancy, high priced engineers. I just set out a well defined scope of testing parameters, explored them and documented the results. I commend you on your great ability to wear blinders though. <G>

You guys keep buying prebuilt motors for your planes and hope to be able to buy fuel when 100LL dries up. I will keep building motors and flying my planes that have overcome that obstacle.. Over and out.

Tailwings guys and gals.

Ben.
[URL="http://www.haaspowerair.com"]www.haaspowerair.com[/URL]

On this board, there are prople with expertise in a number of fields- computer science, biotechnology, and closer to this thread, chemistry, engineering, physics, engines. That was a pretty broad brush to tar the group with. You simply don't know the expertise of people here...yet.

 

[kyleb]

Wow. Great attitude.

I say homebuilders are antisocial at best, and perhaps sociopathic, withdrawing from society into their little garage or hangar beavering away on their airplane because they can't trust anyone but themselves, whilst mumbling to themselves about all those pathetic passive people.

You called? ;-)

 

[Dan Thomas]

Wow. Great attitude.

I say homebuilders are antisocial at best, and perhaps sociopathic, withdrawing from society into their little garage or hangar beavering away on their airplane because they can't trust anyone but themselves, whilst mumbling to themselves about all those pathetic passive people.

When I lived in BC we had a homebuilder's club that was very social. Two years ago we had a reunion, a good time, and had a few laughs about how long some of these projects are taking. I've yet to meet a really antisocial homebuilder; maybe they're the guys who never join a local chapter.

And homebuilders, on the whole, tend to be fine craftsmen. Some of the machines they've created, especially if they're scratch-built, take a long time but are works of art and make the typical spam can look like a steam locomotive. In fact, many of the advances in recent years have shown up in the homebuilt world long before the certified aircraft manufacturers picked up on them. Composite construction, glass cockpits, geared engines: all developed by homebuilders. Synthetic vision has been available to homebuilders for a long time already, and most glass cockpits still don't have it. The new Cessnas are still using float-style fuel tank gauge senders, while homebuilders have been using uncertified but super-accurate capacitance gauges with none of the moving parts that make those float-types so troublesome. And some certified aircraft started life as homebuilt designs; the Cessna 400 is a development of the Lancair.

The Falco, made of wood:

Siers Barracuda, a design that must be over 30 years old but looks brand new:

And which of you wouldn't want to try the Bushby Midget Mustang?

Or an aerobatic biplane, the Stolp Starduster?

Dan

 

[flyersfan31]

You called? ;-)

You know I was kidding, right?

 

[dmccormack]

The Wright Brothers were home builders.

 

[Capt. Geoffrey Thorpe]

The Wright Brothers were home builders.

I thought they built bicycles and airplanes???

 

[dmccormack]

I thought they built bicycles and airplanes???

You're confusing HOUSE builder with the marketing schmuck "home builder."

 

[gismo]

The Wright Brothers were home builders.

True, and AFaIK, history shows they were fairly "antisocial".

But I do have to say that virtually every serious homebuilder I've ever encountered was very friendly and nice to know. Most (but not all) were fairly humble and many were pretty quiet until you got them talking about their project(s).

 

[Dan Thomas]

True, and AFaIK, history shows they were fairly "antisocial".

But I do have to say that virtually every serious homebuilder I've ever encountered was very friendly and nice to know. Most (but not all) were fairly humble and many were pretty quiet until you got them talking about their project(s).

The humility comes once you realize that your project will take every bit as long as your buddies took to make theirs, and that you're not quite as far above average as you thought. One of the most humble guys I know has been working on his airplane since 1968 and it ain't done yet. Beginning to wonder...

Dan

 

[jesse]

Sometimes you need to 'stir the pot' to get reactions from passive people. I see I was successful too. Passive people can't and won't build experimental planes as they take alot of self control and personal dedication to get something finished. Out of hundreds and maybe 1000 or more people who are signed onto this list I can count on one hand the ones who have completed a kit plane and flown it. Care to comment on why that is.

There are a lot of people on this forum that fly certified airplanes simply because there isn't an experimental option that makes more sense.

There are plenty of very smart people on here that are very capable of building an airplane. Some of them do - others probably will some day - people have busy schedules that don't make it easy. Building an airplane is not for everyone and one shouldn't look down on those that choose not to.

As to myself? I do not mind experimental aircraft and if I were to own I would prefer it be experimental. For me, it's just a matter of time before I do. When I do I'll certainly remember you and it won't be in a way that gives you money.

As for you not wanting to buy something from me.... well there is a 99.999999999999% chance your experimental wont get finished, or even started either so I don't lose any sleep over a lost sale that will never exist. Just my humble opinion.

That is an awfully poor short-sighted attitude for a business owner to have.

Ben ' fixin to get banned from POA' Haas.

Ps. I am still amazed I have not gotten the boot from the moderators yet for my unpopular views. .

You're not going to get banned for damaging your own business's reputation.

OTOH - we do ask that you treat folks with respect and adhere to our community's Rule of Conduct which is available here:
http://www.pilotsofamerica.com/forum/faq.php?faq=vb_faq#faq_faq_rules_of_conduct

 

[hindsight2020]

This topic fires me up. Let me get the flamesuit on and rant for a little.

I don't know why the certification nazis on here are so defensive about mogas use. This blind faith in 100LL is almost cultish. I sympathize with the experimental crowd. They got the right attitude. My only criticism of the builder side of that crowd is they are so infatuated with the activity of building they don't seem half as interested in flying, evidenced by the trend (IMO as a turn-key pilot) of building beautiful impressive aircraft with HORRIBLE cockpit layouts, as a collective. Other than that, I find them the only eventual answer to the survival of GA for the "little guy". Everybody running full AB towards accepting at face value the escalating operating costs of affording "the hobby of flying" are simply validating the attrition warfare doctrine that suggests flying is worthy only of those fortunate with higher disposable income thresholds. That elitist attitude makes no sense to me.

The level of misinformation about the thermodynamics of fuel combustion in old piston engines versus the legal artificialities introduced by the criminalizing of behavior (aircraft certification as a whole comes to mind) is something many on here get mixed up quite easily.

I have a C-150 with a mogas STC. I use 87 octane exclusively. The price differential between 87 octane mogas and 100LL is NOT arbitrary to me. $2.75 versus $4.00 and upwards of $6.00 at x-c destination type airfields. That's north of a 50% delta. No preventive maintenance/mod would offset such a direct operating cost savings. So pushing for the introduction of cost-saving fuel measures is something that not only do I patronize, but support and keep an open mind about, unlike a lot of the replies I read on here. My engine was not designed for the amount of lead introduced by 100LL, nor can it take advantage of the higher octane. The use of mogas benefits my engine at annual as evidenced by no lead fouling problems and better plug shape year to year. Should I pay a prohibitive premium because the sight of the carting of 5-gallon cans back and forth my aircraft amongst your "garmin 430 WAAS-as-a-necessity-laden hobby" causes you discomfort? The looks I get imply my "kind" is somehow undeserving of being on that side of the fence. Yet I'm not the one gearing-up my Bo every other week, driving insurance off the roof for everybody. If I didn't know better I'd think they're bellying up on purpose My impetus is to keep aviation acessible to my future children, not to keep lyco in business and the GA market cornered with 60-year old engine specs and an LSA market designed to allow those people previously accustomed to pricing out the peanut gallery on certified aircraft to continue to do so with a glorified kite. Vapor lock vapor sclock....

As to the alluded differences between old-spec piston engines and modern water-cooled ECU-driven auto engines, the differences here are duly noted, but are quite overstated. There's nothing magical that happens between 7:1 and 8.5+:1. Nothing. Most mogas application questions arise out of the fuel pressure delivery systems and line designs in these old aircraft, than simple thermodynamics as it pertains to CR. Simply stated, 87 octane will run fine in many aircraft originally certified for 91/96 avgas.

I spoke with Petersen specifically about the O-320 series and the 160HP upgrade attained by 8.5:1 pistons. From the horse's mouth? Nothing happened with the introduction of 87 octane in this configuration. Granted, just like their fuel plumbing modifications on the PA-28 series calls for, issues with these STCs have more to do with poor fuel system design than the bona fide suitability of mogas inside of the combustion chamber. As such, the tests we discussed were accomplished on the Cessna 1xx series, which obviously benefits from an organic positive pressure delivery system, and largely mitigates the vapor lock issues. No variable timing ECUs, spark retardation and anti-knock sensors needed. None. Just a sticker. The reason the FAA told Petersen to go pound sand with 87 and 89 octane on 8.5:1 jugs had to do with the usual fear-mongering and liability spiel endemic to GA. They told them "placard it at 91 [effectively mimicking the original avgas certificiation] or you lose all that R&D expense". Petersen said OK and now they sell it to you as gospel. The only way I was even able to get them to cough up that factoid out was by cub-scout swearing my inquiry was largely academic and that after our conversation was over I'd continue to view the STC stated limitations as the word of God handed down from the Heavens itself (sure...). So let's not confuse the criminalizing of behavior as contributing in any shape or form to the physical and thermodynamical realities of such fuel applications.

I can only conclude that such insistence on the anti-mogas crowd to dismiss the viability of automotive gasoline stems more from the implicit litmus test that if you can't afford $6.00/gal of juice you're unworthy of participation in american aviation, than a real concern on the part of the aforementioned for the safety and lives of ordinary people with a dream and fascination for the activity of flying. They really should quit staring, it almost makes it look like I have moonshine and this is 1920.

 

[kyleb]

This topic fires me up. Let me get the flamesuit on and rant for a little.

<snip>

I can only conclude that such insistence on the anti-mogas crowd to dismiss the viability of automotive gasoline stems more from the implicit litmus test that if you can't afford $6.00/gal of juice you're unworthy of participation in american aviation, than a real concern on the part of the aforementioned for the safety and lives of ordinary people with a dream and fascination for the activity of flying. They really should quit staring, it almost makes it look like I have moonshine and this is 1920.

I've never found anyone who is/was anti-mogas. However, there are plenty of realists out there who understand the limitations of mogas (from volitility issues to fuel system material compatability issues to octane issues). Those issues mean mogas is not a one size fits all solution. That alone creates a distribution problem, because many (most?) FBO's lack the resources to dispense Jet A, Mogas, and whatever the fuel is for piston types which cannot use Mogas.

That's why the entire industry is holding out for a single commercially available fuel which works in all piston types. Right now, the only one is 100LL.

 

[dmccormack]

That's why the entire industry is holding out for a single commercially available fuel which works in all piston types. Right now, the only one is 100LL.

Ummm... sorta.

The plug fouling caused by 100LL in many engines means 100LL doesn't necessarily "work."

 

[gismo]

Ummm... sorta.

The plug fouling caused by 100LL in many engines means 100LL doesn't necessarily "work."

I think you'll find that the FAA's definition of "work" WRT avgas substitutes relates to maintaining detonation margins, avoiding fuel system component degradation, and no reduction in power output. Increased plug fouling frequency wasn't and isn't on their radar since it can be mitigated by more frequent plug maintenance.

 

[ebetancourt]

Here is what my engine manual says: "high grade aviation gasoline should be used at all times. ... ... Aviation gasoline with a minimum knock rating of 80 octane should be used... ... Fuels containing a minimum of lead content are preferred.":smile:

Sure wish the fuel injection STC didn't require aviation gasoline.
:smile::smile::smile:

Ernie

 

[dmccormack]

I think you'll find that the FAA's definition of "work" WRT avgas substitutes relates to maintaining detonation margins, avoiding fuel system component degradation, and no reduction in power output. Increased plug fouling frequency wasn't and isn't on their radar since it can be mitigated by more frequent plug maintenance.

• Low compression engines don't have detonation problems
• fuel system degradation is due to ethanol additives -- doesn't happen with straight mogas
• "Reduction in power" -- how?

 

[Ted]

• Low compression engines don't have detonation problems
• fuel system degradation is due to ethanol additives -- doesn't happen with straight mogas
• "Reduction in power" -- how?

1) Your O-145 doesn't have detonation problems on 100LL, but it will still detonate with the wrong fuel. Of course, on your engine the "wrong" fuel has as an extremely low RON/MON value. A GTSIO-520-H or TIO-540-J2BD, however, will have detonation issues unless operated properly with the right fuel. A Navajo burns more fuel in one hour than your Chief does in 8 hours, and they tend to fly more. As was already said, most FBOs have zero interest in carrying more than one type of piston fuel. I need to fly 4 hours in my Aztec to burn as much fuel as a King Air in 1 hour. Guess which one they make more money off of. So when you then look at how little fuel the engines that can run off of 80 will burn, is it much of a wonder why they don't want to keep a separate fuel around for your engine? They could keep 80 around, which is optimized for your engine, and Navajos and 421s would be throwing cylinders before the gear even came up.

2) Correct

3) Fuels have different energy contents. If you have a fuel with lower BTU/gallon, you will have a reduction in power. Ethanol has fewer BTU/gallon than standard gasoline. However since it has a higher RON/MON, if your vehicle is optimized for it you can extract more of that energy and put it to work making horsepower (higher compression, etc.)

 

[dmccormack]

1) Your O-145 doesn't have detonation problems on 100LL, but it will still detonate with the wrong fuel. Of course, on your engine the "wrong" fuel has as an extremely low RON/MON value. A GTSIO-520-H or TIO-540-J2BD, however, will have detonation issues unless operated properly with the right fuel. A Navajo burns more fuel in one hour than your Chief does in 8 hours, and they tend to fly more. As was already said, most FBOs have zero interest in carrying more than one type of piston fuel. I need to fly 4 hours in my Aztec to burn as much fuel as a King Air in 1 hour. Guess which one they make more money off of. So when you then look at how little fuel the engines that can run off of 80 will burn, is it much of a wonder why they don't want to keep a separate fuel around for your engine? They could keep 80 around, which is optimized for your engine, and Navajos and 421s would be throwing cylinders before the gear even came up.

2) Correct

3) Fuels have different energy contents. If you have a fuel with lower BTU/gallon, you will have a reduction in power. Ethanol has fewer BTU/gallon than standard gasoline. However since it has a higher RON/MON, if your vehicle is optimized for it you can extract more of that energy and put it to work making horsepower (higher compression, etc.)

I agree with the issues about distribution -- different problem.

But the FAA's approach to mogas is over-blown. MANY airplanes have STC's available for mogas use, and the changes are minimal (fuel lines, metering, etc).

87 octane pure mogas (no ethanol) is and should be a suitable replacement fuel for many piston airplanes in the GA fleet.

 

[Ted]

87 octane pure mogas (no ethanol) is and should be a suitable replacement fuel for many piston airplanes in the GA fleet.

Many number, small percentage of the AvGas consumed (which is already a small percentage of total fuel consumed, in fact it's a fraction of a percent).

 

[dmccormack]

Many number, small percentage of the AvGas consumed (which is already a small percentage of total fuel consumed, in fact it's a fraction of a percent).

In the US, GA burns as much 100LL in a year as US cars burn mogas in a day.

There's plenty of mogas, it's cheaper, and it works.

 

[TMetzinger]

Well, first - ethanol free mogas is not plentiful, since the ethanol is added far up the pipeline.

Second, what I _think_ Ted was trying to say was that if you took all the avgas consumed in a year and built a big lake of it, then drained out all of it that was consumed by engines that could NOT safely run on mogas, there would be a comparatively small pond left. So, given that the small pond is all the mogas that could safely be sold to the GA fleet, it's not cost-effective to put the infrastructure in to sell it.

It's almost like the "run your diesel on old vegetable oil" problem in reverse - it certainly works, but the economics of doing it large scale don't pan out unless you get rid of all the non-diesel engines.

 

[Ted]

In the US, GA burns as much 100LL in a year as US cars burn mogas in a day.

There's plenty of mogas, it's cheaper, and it works.

You're missing the point. If you could fly your plane into the local Sam's Club gas station and just pump in your 87 that would be one thing (this is ignoring the ethanol issues), but airports that don't sell gas to people driving cars will have no motivation to create an extra set of tanks to support selling fuel that nobody wants to buy. I know precisely one airport that sells MoGas in my area, and he's having a really hard time selling it. What's the point for him to do it again?

 

[dmccormack]

Well, first - ethanol free mogas is not plentiful, since the ethanol is added far up the pipeline.

Second, what I _think_ Ted was trying to say was that if you took all the avgas consumed in a year and built a big lake of it, then drained out all of it that was consumed by engines that could NOT safely run on mogas, there would be a comparatively small pond left. So, given that the small pond is all the mogas that could safely be sold to the GA fleet, it's not cost-effective to put the infrastructure in to sell it.

It's almost like the "run your diesel on old vegetable oil" problem in reverse - it certainly works, but the economics of doing it large scale don't pan out unless you get rid of all the non-diesel engines.

Got it -- understand all the implications of distribution, etc (although I think ethanol is added fairly far down the line -- usually at retail).

My point is that there are many airplanes that would run fine on mogas (even with ethanol, if corrosive and water retention issues were addressed), there's an established, widepsread distribution channel, and automobile fuel is already unleaded.

It's that last mile from the local JiffyMart to the ramp that's missing.

 

[dmccormack]

I know precisely one airport that sells MoGas in my area, and he's having a really hard time selling it. What's the point for him to do it again?

Likely because few owners have access to, or will spend what's required for the STC.

 

[TMetzinger]

If 100LL is outlawed and replaced by a fuel that costs a lot more, then the economics may change to the point where mogas becomes much more attractive to folks - which will drive them buying the STC, pestering their FBO for fuel, etc.

But absent a change like that, there's nothing sufficiently attractive about mogas.

 

[dmccormack]

If 100LL is outlawed and replaced by a fuel that costs a lot more, then the economics may change to the point where mogas becomes much more attractive to folks - which will drive them buying the STC, pestering their FBO for fuel, etc.

But absent a change like that, there's nothing sufficiently attractive about mogas.

At root of my argument is that the eventual (inevitable?) removal of "lead" from any fuel means GA will need another fuel. It would seem most economical and realistic to modify GA aircraft powerplants to use mogas than to use some new, as-yet untested replacement fuel.

 

[Capt. Geoffrey Thorpe]

Got it -- understand all the implications of distribution, etc (although I think ethanol is added fairly far down the line -- usually at retail).

My point is that there are many airplanes that would run fine on mogas (even with ethanol, if corrosive and water retention issues were addressed), there's an established, widepsread distribution channel, and automobile fuel is already unleaded.

It's that last mile from the local JiffyMart to the ramp that's missing.

As I understand it, it is added at the terminal after it comes out of the pipe line. Dunno if it is added before /after /while it goes into the tanker truck.

Swap out your Lycontinental for a Jabiru - they don't have a problem with ethanol. (Might still be an issue in your aluminum tank)

http://www.usjabiru.com/images/pdf/JSL007-3 Alcohol - Lead - Fuel Ratings.pdf

 

[dmccormack]

Swap out your Lycontinental for a Jabiru - they don't have a problem with ethanol. (Might still be an issue in your aluminum tank)

That's most likley where the GA fleet is headed, once lead becomes next in the enviro-crosshairs.

 

[COFlyBoy]

At root of my argument is that the eventual (inevitable?) removal of "lead" from any fuel means GA will need another fuel. It would seem most economical and realistic to modify GA aircraft powerplants to use mogas than to use some new, as-yet untested replacement fuel.

Dan thanks for clarifying your point. (I was having trouble figuring out what you were getting at.)

I think the FAA/engine manufacturers need to come out with some better direction on how to determine which fuels are acceptable in an engine.

The PA-32-260 (O-540E)is placarded to use 100(LL) only. Though, in the Lycoming SI, it indicates that the engine was originally certified for 91/96. It does state that 94UL is an acceptable alternative, but it does not indicate if 91 octane MOGAS would be OK. If so, an STC would pay for itself pretty quickly at ~$5/gal Avgas and <$3/gal high-octane MOGAS.

 

[dmccormack]

Dan thanks for clarifying your point. (I was having trouble figuring out what you were getting at.)

I think the FAA/engine manufacturers need to come out with some better direction on how to determine which fuels are acceptable in an engine.

The PA-32-260 (O-540E)is placarded to use 100(LL) only. Though, in the Lycoming SI, it indicates that the engine was originally certified for 91/96. It does state that 94UL is an acceptable alternative, but it does not indicate if 91 octane MOGAS would be OK. If so, an STC would pay for itself pretty quickly at ~$5/gal Avgas and <$3/gal high-octane MOGAS.

It's been a long, long thread....

The mogas STC numbers are compelling. But you need to fly around with 5 gal gas cans.

 

[Ted]

My point is that there are many airplanes that would run fine on mogas (even with ethanol, if corrosive and water retention issues were addressed), there's an established, widepsread distribution channel, and automobile fuel is already unleaded.

Looking strictly at the anti-knock properties alone (leaving out ethanol , etc.) then there is probably a decent number (but still a small amount of fuel burned) that could run on MoGas.

Likely because few owners have access to, or will spend what's required for the STC.

It's a bit of a chicken/egg thing. If more owners had the STC and there was a higher demand, more places might go for it. Places won't go for it until there is a demand. However, the real thing comes down to the fact that, even if all available owners had the STC, the demand would not be all that high. One fill-up of a Navajo that needs 100LL will account for 10 fill-ups in planes that could use MoGas.

If 100LL is outlawed and replaced by a fuel that costs a lot more, then the economics may change to the point where mogas becomes much more attractive to folks - which will drive them buying the STC, pestering their FBO for fuel, etc.

If the cost of a replacement fuel is much higher than 100LL, that will have a significant negative effect on the rest of GA.

But absent a change like that, there's nothing sufficiently attractive about mogas.

Other than the reduced lead fouling for people who have engines designed for 80.

 

[dmccormack]

Looking strictly at the anti-knock properties alone (leaving out ethanol , etc.) then there is probably a decent number (but still a small amount of fuel burned) that could run on MoGas.

I know there's a difference in how octane is compted for avgas and mogas, but how is unleaded fuel boosted to 91 or 93 octane? Is that boosting sufficient to achieve the required octane to meet 100ll engine tolerances?

 

[Capt. Geoffrey Thorpe]

I know there's a difference in how octane is compted for avgas and mogas, but how is unleaded fuel boosted to 91 or 93 octane? Is that boosting sufficient to achieve the required octane to meet 100ll engine tolerances?

Working from memory (never a good thing) - more compact molecules with benzene rings, smaller molecules are generally good things. Long chain molecules are generally not. So it's a matter of adjusting the chemistry of the mix.

 

[Ted]

I know there's a difference in how octane is compted for avgas and mogas, but how is unleaded fuel boosted to 91 or 93 octane? Is that boosting sufficient to achieve the required octane to meet 100ll engine tolerances?

There are a number of anti-knock indices (frequently referred to as "octane" although that's the incorrect term). However the unleaded fuel isn't "boosted" to 91 or 93 (which is as we know it in this country at our gas pumps, which I believe is done using the (RON + MON) / 2 method), it's simply different parts of the crude oil (very oversimplified here).

The answer as to whether that's sufficient to meet 100LL spec: no, it's not. Everyone wishes the answer was simple.

 

[dmccormack]

There are a number of anti-knock indices (frequently referred to as "octane" although that's the incorrect term). However the unleaded fuel isn't "boosted" to 91 or 93 (which is as we know it in this country at our gas pumps, which I believe is done using the (RON + MON) / 2 method), it's simply different parts of the crude oil (very oversimplified here).

The answer as to whether that's sufficient to meet 100LL spec: no, it's not. Everyone wishes the answer was simple.

Is it intentional obfuscation? After all, some high-end cars require higher octane rating unleaded mogas (which may or may not contain enthanol), presumably to reduce detonation ("knock" in cars).

 

[Cap'n Jack]

I know there's a difference in how octane is compted for avgas and mogas, but how is unleaded fuel boosted to 91 or 93 octane? Is that boosting sufficient to achieve the required octane to meet 100ll engine tolerances?

Working from memory (never a good thing) - more compact molecules with benzene rings, smaller molecules are generally good things. Long chain molecules are generally not. So it's a matter of adjusting the chemistry of the mix.

Ring compounds (they don't have to be aromatic, like benzene) or branched compounds have higher knock resistance. Octane is really a molecule that is 5 carbons long, but with branches to make a total of 8 carbons. Google "isooctane".

There are a number of anti-knock indices (frequently referred to as "octane" although that's the incorrect term). However the unleaded fuel isn't "boosted" to 91 or 93 (which is as we know it in this country at our gas pumps, which I believe is done using the (RON + MON) / 2 method), it's simply different parts of the crude oil (very oversimplified here).

The answer as to whether that's sufficient to meet 100LL spec: no, it's not. Everyone wishes the answer was simple.

This is one way of boosting octane. Additives such as benzene (as Cap'n Thorpe suggested), methyl tert-butyl ether (MTBE, generally not used any more), ethanol, and others are also used to increase octane. Most gasoline is broken down from larger molecures ("cracked"). Petroleum itself doesn't contain enough straight-run gasoline for world demand.

As for additives, they have to reduce knocking under the conditions the engine will run, remain soluble in cold temperatures, and not cause vapor lock at high temperatures (reasonably low vapor pressure). They should not attract or hold contaminants (such as water), and not damage the engine, fuel tank, and other parts of the fuel system. If the fuel is contaminated with water, the water should be able to be removed without changing the properties of the fuel.

That's a lot of demands to meet and that's why this problem isn't so easily solved.

 

[dmccormack]

That's a lot of demands to meet and that's why this problem isn't so easily solved.

I'm not arguing that it's simple -- just trying to understand.

Assume that 100LL will be outlawed, so far the only arguments in favor of 100LL over mogas rest on distribution and requirements of higher-compression engines.

Can't mogas can meet all the other requirements, given the use of auto fuel in a wide variety of climatic conditions and even certain a/c engines?

 

[Capt. Geoffrey Thorpe]

Is it intentional obfuscation? After all, some high-end cars require higher octane rating unleaded mogas (which may or may not contain enthanol), presumably to reduce detonation ("knock" in cars).

Just history. Back in the olden days gasoline was used as a cleaning solvent, then some guy got the idea to use it in cars... The original engines were very low compression and everything was good. But as demand for performance ramped up, compression ratios crept up and the demand for knock resistant fuel was created.

The problem is - how do you measure the resistance to knock. A couple methods won out for the most part for cars (the "Research" and "Motor" methods). Both use the same variable compression engine (CFR - cooperative fuel research), and both compare the test fuel to a mixture of isooctane and normal heptane. The difference between the two methods include the speed and load at which the engine is operated. But the idea was you test your fuel and find the knock limit. Then you test various mixtures of the octane / heptane to find the same level of knock. If you fuel knocked at the same point as a 90% octane / 10% heptane mix, it had an octane rating of 90. Of course, that system will only work up to 100% octane. The ratio of the RON / MON numbers was referred to as the fuel sensitivity.

For aircraft applications, the engine manufactures wanted to push beyond "typical" auto gas for more performance - particularly for air transport / military applications. But how do you measure the "octane" of a fuel that is better than 100% isooctane? A new test was developed that came up with a "Performance Number" (PN). I don't recall the details, but I believe it compares the knock limited maximum performance from a fuel to the performance from isooctane. So a performance number of 115 would be 115% better than octane under some specified conditions. I think that the numbers like 80/87 refer to the performance under two different operating conditions but I have reached the end of my memory...

And, in the end, the anti-knock capability of various fuels in your particular engine under particular conditions will be somewhat variable even if they have the same ratings.

The auto companies design engines to match available fuels. A lot of time is spend discussing particular applications and if they should be designed for regular or (higher octane) premium fuel. If you have a "Premium recommended" car, it likely has sensors that detect knock and retard the spark timing (or limit boost if you have a turbo) when you use regular fuel.