Gami gas has arrived...

I'm curious. What piston engines need 100 octane? Turboed engines?
 
UngaWunga said:
I'm curious. What piston engines need 100 octane? Turboed engines?
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My normally aspirated IO-550 needs it. :dunno: Compression ratio, mag timing, lots of variables probably lead to it. Can we control those variables in other ways without requiring processes that aren't cost-effective is the other question...
 
flyingcheesehead said:
My normally aspirated IO-550 needs it. :dunno: Compression ratio, mag timing, lots of variables probably lead to it. Can we control those variables in other ways without requiring processes that aren't cost-effective is the other question...
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I think it has an 8.5:1 compression ratio, same as the high compression (160HP) Lyc O-320s. Those "need" 100LL because the only other choice back then was 80 octane, after 91 was phased out.
What's your mag timing? I recall it's 25 degrees on the O-320.
 
AV8R_87 said:
I think it has an 8.5:1 compression ratio, same as the high compression (160HP) Lyc O-320s. Those "need" 100LL because the only other choice back then was 80 octane, after 91 was phased out.
What's your mag timing? I recall it's 25 degrees on the O-320.
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Honestly, I don't know offhand. Looking at the TCDS, only the A and N models have a specified timing (22 degrees), my G is very similar to those but does not specify the timing.
 
My io-540 does as well.8.5:1, 25btdc.

Detonation is not so simple on these slow running, big bore engines. The io-360s in UNLs fleet are also 8.5:1 and 25btdc. They are rated for 91/96 fuel, so 94ul should work, but they experienced low level detonation on it that destroyed the valve seats. 8.5:1 and 25 degrees is most fuel injected engines.

It's easy to say, "well just turn the timing down a bit", but airplanes climb on the excess power above what's required to maintain level flight. A small decrease in power equals a huge decrease in performance. If an airplane uses 2/3 of it's power to maintain level flight, taking away 10% of the total power reduces power available to climb by 1/3.
 
Jim K said:
Detonation is not so simple on these slow running, big bore engines. The io-360s in UNLs fleet are also 8.5:1 and 25btdc. They are rated for 91/96 fuel, so 94ul should work, but they experienced low level detonation on it that destroyed the valve seats. 8.5:1 and 25 degrees is most fuel injected engines.
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Was it detonation? I only heard "valve seat regression", which some attributed to lack of lead as a lubricant.
 
Dana said:
Was it detonation? I only heard "valve seat regression", which some attributed to lack of lead as a lubricant.
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Yeah, short term, detonation (which only occurs when the valves are closed) is more likely to dish a piston. (Or worse.)
 
Dana said:
Was it detonation?
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Here is an old but still good article written by the late John Deakin explaining detonation in the context of aircraft piston engines:
www.avweb.com

Pelican's Perch #43:Detonation Myths

Before getting into this month's column, I'd like try and address one of the most common question I'm getting from readers of my series on piston engine
www.avweb.com www.avweb.com

In a nutshell, detonation refers to an acceleration (beyond what's normally happening) of the burning of the fuel/air mixture inside the cylinder at some point after the spark ignites the mixture. (As opposed to pre-ignition, which means burning starts BEFORE the spark.) That accelerated burn leads to higher-than-normal peak pressure inside the cylinder and also results in higher-than-normal CHTs.

Detonation is not a discrete all-or-nothing, but can range from light to heavy. (I understand "light detonation" may sound like a contradiction in terms, but it exists nonetheless.) Short occurrences of light detonation can probably be written off as nonevents, while sustained heave detonation can destroy an engine within a few minutes. The biggest problem with light detonation is that if undetected and unmitigated, the increase in CHTs it causes makes it more likely for detonation to continue and grow in magnitude. That's why it is a slippery slope to accept "just a little detonation" as something acceptable.

Now, if we accepted a lower-octane fuel in aviation, it would reduce detonation margins, meaning we should expect to sometimes see light detonation when there isn't any today, and heavy detonation when there's just light detonation today. Compression ratio, induction air temperature, fuel temperature, ignition timing, MP/power output all factor in on how often and how much that would happen.

Regards,
Martin
 
Jim K said:
but they experienced low level detonation on it that destroyed the valve seats.
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It's strange that all the people running mogas in their O-320s and O-360s with 8:5:1 compression (STC requires 91AKI and approves the use of UL94) haven't reported any valve issues. UND is doing something different.
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Jim K said:
It's easy to say, "well just turn the timing down a bit", but airplanes climb on the excess power above what's required to maintain level flight. A small decrease in power equals a huge decrease in performance. If an airplane uses 2/3 of it's power to maintain level flight, taking away 10% of the total power reduces power available to climb by 1/3.
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True, it would have to be something that maintains as much of the rated take-off power as possible.
Maybe someone will get an STC for a methanol-water injection system for takeoff and use UL94 instead of 100LL.
 
Dana said:
Was it detonation? I only heard "valve seat regression", which some attributed to lack of lead as a lubricant.
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The best explanation I've seen is very light detonation causing micro-welding of the valve to the seat. Then when the valve opens it rips that weld apart and a little bit flakes off. After a few hundred hours the seat wears away. Lead is not a lubricant, but deposits on the valve prevent the metal- metal contact that creates the problem.

Mike Busch did a great webinar on the subject:

The most relevant part starts around 22min, but the whole thing is great. I recommend 1.5x speed.

George Braly also did a lot of testing with UL94 and found light detonation under the conditions UND was running. He gave a seminar on this at either sun n fun or osh.... Martin might even have it on his channel.

AV8R_87 said:
It's strange that all the people running mogas in their O-320s and O-360s with 8:5:1 compression (STC requires 91AKI and approves the use of UL94) haven't reported any valve issues. UND is doing something different.
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Agreed. My uneducated guess(es) would be:
(a) most people running auto fuel don't run peak egt like UND does (per the poh). Id be willing to bet most of them run full rich most of the time.
(B) they also run 100ll some of the time, so there's some level of deposits on the valves
(C) most of the mogas stcs are on the lower power models
(D) a lot of them haven't flown enough to have an issue
(E) no one is looking. I've heard rumors about mogas "ruining valves" but I've never heard of anyone checking dry tappet clearances over time like und was doing.

AV8R_87 said:
True, it would have to be something that maintains as much of the rated take-off power as possible.
Maybe someone will get an STC for a methanol-water injection system for takeoff and use UL94 instead of 100LL.
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I don't know so I'll ask, how much fluid does a system like that consume?

I really don't want to give up my payload or my performance. Given the choice, I'd prefer to run my engine on paint stripper. Changing some o-rings is much less of a problem than giving up performance.

I have a hard time believing g100ul is as bad as is being presented. I have to wonder how much of this is being ginned up by Swift.
 
UngaWunga said:
I'm curious. What piston engines need 100 octane? Turboed engines?
Click to expand...

My rule of thumb used to be a line drawn around 230hp, those and above generally need 100LL. I don't know if that's still true lately, the fuel game seems unsettled.

The 225hp motors I know that can run mogas are the IO-470J/K used in the Beech Debonairs.

I think there are a few 250hp exceptions to my rule of thumb, but I don't recall them offhand.
 
Jim K said:
I don't know so I'll ask, how much fluid does a system like that consume?

I really don't want to give up my payload or my performance.
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People doing that on turbocharged cars running pump gas seem to be using between 10-20% of fuel flow of additional 50/50 methanol and water. So averaging it at 15%, for an engine that used 20gph on takeoff you'd need 3gph of methanol/water mix. If we assume 5 minutes of takeoff power where that would be needed, that's a quart of fluid. I'd probably think that a 1 gal tank would be a good amount to have. All ballpark stuff on a napkin. A good option to have if we can't get this fuel situation sorted out.
 
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AV8R_87 said:
Maybe someone will get an STC for a methanol-water injection system for takeoff and use UL94 instead of 100LL.
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Member of the must run 100LL club (200 hp - io-360) checking in. A new system with multiple failure modes introduced at a critical phase of flight (aren’t they all?) is not high on my list of wants.

But I’d be interested if engineer @Ted had thoughts into the future fuel situation with our engines.
 
SoonerAviator said:
It's hard because for decades they've been trying to make a fuel that will meet the established fuel standard while doing so without lead. It's hard to meet a fuel spec that doesn't necessarily dictate the only way aviation engines can be run, however it is what is used for FAA certification of those engines. So you have a situation where you're trying to meet a standard that everything is based off of, despite it not being the only potential "standard" capable of meeting the needs of piston aircraft engines. FAA stepping on its own johnson, so-to-speak.
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Thanks for the reply. I don't understand it - maybe its all the Nyquil I've been taking for the last whatever number of days laying in bed (what year is it?).

1) Does / will it work without stripping paint or other bad things?
2) Will it play well with 100 LL; "Fungible" and all of that.
3) Net net, is really not a matter of having something that works, but just a matter of how it fits with regulations and standards?
 
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I can live with not running my mooney at 100% when temps are 110degs and cylinder heads are 500 degs. plus the poh says 96octane is good
 
schmookeeg said:
My rule of thumb used to be a line drawn around 230hp, those and above generally need 100LL. I don't know if that's still true lately, the fuel game seems unsettled.

The 225hp motors I know that can run mogas are the IO-470J/K used in the Beech Debonairs.

I think there are a few 250hp exceptions to my rule of thumb, but I don't recall them offhand.
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My 215hp should not run mogas...
 
No matter what is chosen for the final fuel it will be interesting to see what happens after folks run it for a few hundred hours. Any time you change something of this nature there are bound to be issues.
 
WDD said:
Almost as if they need to a test and control. Sell 100LL but say it’s 100UL and see how many new issues are attributed to it.
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Blind study. I agree. We see how things take on a life of their own. Drones, killer clowns, paint stripper fuel...
 
Based on the drama surrounding this fuel on, ahem, other fora, I am hoping to move to something Jet-A motivated before my hand gets forced by the assortment of fed and state mandates against 100LL

I'm also trying to fly the hell outta my 6-pot leaded death cookies while I still can :D
 
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WDD said:
Almost as if they need to a test and control. Sell 100LL but say it’s 100UL and see how many new issues are attributed to it.
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Yeah, kind of funny, but you'd be surprised what problems will be reported just because of what people think something is.

True story. Many, many years ago I did market research for the auto industry. There was a car that was built by Toyota that was sold by both Toyota and Chevy. When Chevy sold it, it was the "Prism". Same car, same parts, same assembly line, etc. The Chevy had more reported problems than the same car with the Toyota badge on it.
 
Dixiebluesky said:
So if the av gas spec they are trying to work within was pushed aside, how hard would it be to formulate a fuel using the modern manufacturing process that met our needs?
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Indeed, that's exactly what Swift, GAMI, and Lyondell/VP-Racing have had to do... but the FAA insisted on leading the unleaded avgas effort, and from 1991 to around 2010 they insisted that D910 without lead was the way it had to be done. Swift departed that paradigm early in the 2000's; GAMI came on board in 2009, with a non-D910 approach. Lyondell is working through the PAFI process, and the FAA didn't figure out the need for a new spec until about 2015... so only 24 years wasted effort, at a cost of 100's of millions of dollars. Sigh.

AV8R_87 said:
could any of the engines that "need" 100LL operate in a safe and satisfactory manner, maybe with some minor operational procedure changes, on 94UL?
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The basis of the 70/30 evaluation AOPA did over a decade ago now was based on all the factors that affect engine certification. The late Cesar Gonzales of Cessna summarized this all pretty well in his presentations at Oshkosh over the years. Sure... the 30% of the engines that need 100 octane could be made to operate on less octane, but it raises huge certification issues... some aircraft could go through a costly recert program, with test flying and generation of new performance tables... but others will fail the balked landing (single) or single-engine (twin) certification standards. Modifications to control CHT, oil temperature, manifold pressure, timing at less than current restrictions would have to be developed... and certified, and deployed to the fleet.

And who will pay the bill? Most folks are going to line up to buy an STC to reduce their aircraft performance, if there's an alternative... at least, an investor would wonder about spending money that way. And timing?

Paul
 
UngaWunga said:
What piston engines need 100 octane? Turboed engines?
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Certainly most turbo'd engines. And almost all engines with 8.7:1 compression ratio or greater. And a goodly number of engines with 8.5:1 compression ratios. It depends on the allowed operating envelope as well, since detonation is dependent on 8 factors (according to Cessna's Cesar Gonzales) including red-line CHT, red-line oil temperature, red-line manifold pressure, engine timing, etc.
AV8R_87 said:
8.5:1 compression ratio, same as the high compression (160HP) Lyc O-320s. Those "need" 100LL because the only other choice back then was 80 octane, after 91 was phased out.
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Some 8.5:1 compression ratio engines can operate safely on less than 100 octane. Others can't. See above.
AV8R_87 said:
all the people running mogas in their O-320s and O-360s with 8:5:1 compression (STC requires 91AKI and approves the use of UL94) haven't reported any valve issues.
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How would we know?
AV8R_87 said:
Maybe someone will get an STC for a methanol-water injection system for takeoff and use UL94 instead of 100LL.
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There is such an STC for the turbo C210. I think it's no longer available because it wasn't selling. Not only needed for takeoff, but sometimes in turbo cruise in the flight levels as well... about 6 gallons per flight IIRC.

MackMooney said:
I can live with not running my mooney at 100% when temps are 110degs and cylinder heads are 500 degs. plus the poh says 96octane is good
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That's an odd octane. On which scale, automotive motor, automotive research, R+M/2, or aviation octane?

schmookeeg said:
My rule of thumb used to be a line drawn around 230hp, those and above generally need 100LL.
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Total horsepower really doesn't enter in to it... it's the operating conditions inside the cylinder that matter. Remember that Lycoming introduced an IO580 based on the IO390 cylinder, for Cessna's restart 206, to allow it to operate on lower octane fuel? So lots of horsepower, but lower compression ratio in that case... still, the engines blew the heads off the cylinders and did not continue to market. So a large engine under mild conditions won't detonate, but even an O200 under severe conditions (high compression pistons, etc.) will.

Paul
 
The issue should have been worked out with the engines instead of the fuel. A pathway to more modern engine development could have been put in place 20-30 years ago and today we would be using more robust modern tech. A well laid out and easily understandable path to certification would have done wonders. All of the caterwauling was never about real solutions it was just talking points aimed at feelings.
 
Dixiebluesky said:
The issue should have been worked out with the engines instead of the fuel. A pathway to more modern engine development could have been put in place 20-30 years ago and today we would be using more robust modern tech. ….
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That’s what Rotax did and the various diesels tried.

How you retrofit a 160hp Rotax to a Bonanza?
 
PaulMillner said:
There is such an STC for the turbo C210. I think it's no longer available because it wasn't selling.
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It would probably sell a lot better if there was no alternative for 100LL. Same reason I don't have the STC for 94UL - I have another option, priced the same (or less), and available at my home field, instead of something that I have to fly to another airport to get.
 
Dana said:
Was it detonation? I only heard "valve seat regression", which some attributed to lack of lead as a lubricant.
Click to expand...

Yes, GAMI has duplicated the issue on their dyno.

FAA did testing at their lab in Atlantic City showing NO issues with unleaded fuels and valve seats, as long as you keep the cylinder pressures under control (no detonation).
 
Pinecone said:
Yes, GAMI has duplicated the issue on their dyno.

FAA did testing at their lab in Atlantic City showing NO issues with unleaded fuels and valve seats, as long as you keep the cylinder pressures under control (no detonation).
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Well, I know I'm being silly, but I'd kinda like to see that confirmed by an independant lab doing a blind test. One competitor testing another competitor's fuel raises too many doubts.
 
flyingcheesehead said:
Ah, I got tripped up by the "FAA did testing" part in between, and I didn't know what GAMI had tested.
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Didn't GAMI test the Swift fuel on behalf of the FAA or maybe it was Lycoming?

Apparently they've got the most advanced test stand. For such things.
 
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Pinecone said:
FAA did testing at their lab in Atlantic City showing NO issues with unleaded fuels and valve seats, as long as you keep the cylinder pressures under control (no detonation).
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So, what was UND doing? Running lean of peak at 75% power or more?
 
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