G100UL

[larrynimmo]

Now approved for use with 611 different engines….however….

does not include most IO (fuel injected engines)

[GeeBee]

If you look at the list, they approved most engines that use 80 and 91 octane by their TCDS but I notice none that require 100. It looks like they want to examine that data closely.

 

[KSMooniac]

It will come sooner or later. Lots of their testing was in TN Cirrus and Bo aircraft with high compression pistons.

Sent from my LM-V405 using Tapatalk

[OR75]

the higher the compression ratio, the more difficult it will be.  most fuel injected are high compression  

Edited October 29, 2021 by OR75

[EricJ]

The AOPA published an article yesterday with a link to a new AML with "hundreds" of engines approved for G100UL.   There are a number of Lycoming O-360 variants included, so some vintage Mooneys may be covered, but only a couple Lycoming IO-360 variants that I don't think are relevant to Mooneys.  Likewise there are a couple Continental IO-360 models, but I don't think they're pertinent, either.

AOPA article:
https://www.aopa.org/news-and-media/all-news/2021/october/28/faa-approves-hundreds-more-engines-to-use-unleaded-avgas

New AML:   https://download.aopa.org/advocacy/2021/SE01966WI_AML-Amd1.pdf

[OR75]

6 hours ago, 1980Mooney said:

Perhaps you should say "higher" compression as compared to carbureted.  I don't consider 8.5 in a TCM IO-550 or 8.7 in a Lycoming IO-540 to be particularly "high" - especially when compared to automotive IC engines (2020 Corvette 11.5 compression ratio and 2020 Toyota Corolla 2.0 Liter 13.0 comp ratio).  Of course true high compression automotive IC engines don't run wide open for significant periods or even at 65-85% for long constant cruise.

I would think that the big Continental and Lycoming turbocharged engines in each airframe application will need extensive testing.  That is because, although with a 7.5 compression ratio in Continental and 7.3 in Lycoming, the boost of the specific application could create the regime of detonation that is different from time tested experience with 100LL Avgas.  I bet a lot of this will be learned the hard way (like Mobil One...) and there will be many lawsuits.

Ok 

[A64Pilot]

Over the years I’ve read over and over that it’s only the big bore turbo motors used in higher performance twins that can’t safely run on 94UL, which is what you get if you take the lead out of 100LL

I suppose of course that includes the same motor in a single.

They could of course run well if boost was limited, but that would impact useful load and I assume min single engine speed etc pretty badly.

Same articles also point out that majority of fuel is burned by the minority of aircraft, those high power twins.

[N201MKTurbo]

Our IO 360 make the same HP/cylinder as the biggest engines out there. But there are only 4 of them. A 6 cylinder version would be a 300 HP engine. Brice’s T310R has three times the cylinders as my Mooney and uses exactly 3 times the fuel.

Actually he runs it pretty easy most of the time and it only uses 2.5 times the fuel.

Edited October 30, 2021 by N201MKTurbo

[A64Pilot]

I understand the 50 hp per cyl. However when you turbocharge those cylinders that of course increases peak cylinder pressure, that is the point of turbocharging.

So a turbo motor requires higher octane, than a NA motor, even I believe a turbo normalized motor as it’s intake air is significantly hotter then a NA motor.

I know back in the 70’s that University of Tennessee ran a twin Cessna on what was then called “Gasahol” for quite a lot of hours with no issue.

They only ran one motor on Gasahol and the other on Aviation fuel of course, and I’m unaware of what mods if any they did to the motor run on Gasahol.

‘I assume timing reduction and restricting manifold pressure and cyl head temps, but you know what assume means, maybe they didn’t do anything?

So it can be done, not legally of course and that’s the hurdle. My supposition is that it can be done, but you won’t have the required detonation margin to pass. Accidentally take off with the cowl flaps closed and you may have an engine failure for example

Edited November 2, 2021 by A64Pilot

[OR75]

49 minutes ago, A64Pilot said:

I understand the 50 hp per cyl. However when you turbocharge those cylinders that of course increases peak cylinder pressure, that is the point of turbocharging.

So a turbo motor requires higher octane, than a NA motor, even I believe a turbo normalized motor as it’s intake air is significantly hotter then a NA motor.

I know back in the 70’s that University of Tennessee ran a twin Cessna on what was then called “Gasahol” for quite a lot of hours with no issue.

They only ran one motor on Gasahol and the other on Aviation fuel of course, and I’m unaware of what mods if any they did to the motor run on Gasahol.

‘I assume timing reduction and restricting manifold pressure and cyl head temps, but you know what assume means, maybe they didn’t do anything?

So it can be done, not legally of course and that’s the hurdle. My supposition is that it can be done, but you won’t have the required detonation margin to pass. Accidentally take off with the cowl flaps closed and you may have an engine failure for example

I am not familiar with that specific test but alcohol is actually an octane booster so that in itself probably prevented detonation and they may not have made any modification.

alcohol on the other hand does have impact on seals , rubber hoses,  deposits in the combustion, etc ....

 

[N201MKTurbo]

49 minutes ago, OR75 said:

I am not familiar with that specific test but alcohol is actually an octane booster so that in itself probably prevented detonation and they may not have made any modification.

alcohol on the other hand does have impact on seals , rubber hoses,  deposits in the combustion, etc ....

 

Alcohol works almost as well as MEK for stripping our tank sealant.

[Tim Jodice]

I forgot why but I know bore size has a lot to do with detonation limits. Most aircraft engines are around a 5 inch bore while cars are around 3-3.5 bore.

Maybe someone he smarter than me can explain it. 

[A64Pilot]

31 minutes ago, Tim Jodice said:

I forgot why but I know bore size has a lot to do with detonation limits. Most aircraft engines are around a 5 inch bore while cars are around 3-3.5 bore.

Maybe someone he smarter than me can explain it. 

I believe it has to do with flame front propagation speed, the flame front travels at a set speed, smaller bores have the entire charge ignited in less time than a large bore as there is less distance to travel.

But also what has a tremendous effect is combustion chamber shape, the Hemi whose most airplanes have isn’t very good for detonation and is actually a very antiquated design.

Multiple plugs help a good deal though, more than one ignition source gets the flame front across the whole area faster.

The larger the bore the more spark advance is required, and increasing timing of course may lead to detonation,so big ole bore motors tend to be lower RPM due to higher RPM equals less time to ignite the whole charge, that is why ignition is usually advanced with RPM, because the flame travel is a fixed speed.

But airplane motors are often direct drive and therefore very RPM limited so big bores work well

Aircraft usually run fixed timing as we don’t usually vary RPM much, we wouldn’t benefit as much as say an automobile if we have variable timing.

Edited November 2, 2021 by A64Pilot

[dzeleski]

34 minutes ago, Tim Jodice said:

I forgot why but I know bore size has a lot to do with detonation limits. Most aircraft engines are around a 5 inch bore while cars are around 3-3.5 bore.

Maybe someone he smarter than me can explain it. 

A smaller bore size for a given cc has less distance to travel from the spark (ignition) to the cylinder wall, as well as within the head chamber for the flame front to actually travel across the volume of compressed air. The smaller the area the less of a chance for a second flame front to start.

Most smaller bore engines run shorter rod/stroke ratio, which means the piston is at TDC for less time. This also means that the piston will allow faster gas expansion without detonation since the stroke is longer.

In plain English: A bigger piston has more surface area for a flame to travel across and requires more advanced timing. Which means there is a higher probability of detonation.

Head and piston designs can drastically change these behaviors by changing the pressure gradient within the chamber. We used to not be able to run more then 8:1 compression NA on older engines with pump gas, now we can run 10-13:1 AND use boost with pump gas.

V10 F1 engines were 3.0l! tiny pistons, and allowed minimal detonation risk (among other things).

[A64Pilot]

2 hours ago, N201MKTurbo said:

Alcohol works almost as well as MEK for stripping our tank sealant.

I didn’t know that, I wonder what it does to bladders?

[EricJ]

Just now, dzeleski said:

V10 F1 engines were 3.0l! tiny pistons, and allowed minimal detonation risk (among other things).

Light weight so that they could spin them fast and make a lot of power with little torque.

[N201MKTurbo]

39 minutes ago, A64Pilot said:

I didn’t know that, I wonder what it does to bladders?

I had a friend help with a tank repair once. I sent him home with all the cover plates and he was going to clean them all up. I sent him home with some MEK. He said the MEK was too nasty, so he tried some denatured alcohol, He said it worked better than the MEK. The panels were squeaky clean when I got them back. I tried the alcohol the next day to do some sealant removal. I didn't think it worked as well as the MEK, but it was almost as good.

[N201MKTurbo]

46 minutes ago, A64Pilot said:

I didn’t know that, I wonder what it does to bladders?

I just looked and it says that ethanol is not recommended for nitrile rubber.

[A64Pilot]

I know ETH ate up a lot of fiberglass boat gas tanks, I wouldn’t have expected that either.

[carusoam]

You guys have done a great job of bringing up technical detail not covered often around here…

Deep discussion on cylinder geometry and detonation….

Inviting @Shadrach to the conversation….  Some of his favorite topics….

Best regards,

-a-

[Shadrach]

19 hours ago, N201MKTurbo said:

I had a friend help with a tank repair once. I sent him home with all the cover plates and he was going to clean them all up. I sent him home with some MEK. He said the MEK was too nasty, so he tried some denatured alcohol, He said it worked better than the MEK. The panels were squeaky clean when I got them back. I tried the alcohol the next day to do some sealant removal. I didn't think it worked as well as the MEK, but it was almost as good.

This does not match my experience in any way. MEK does a much, much, better job of breaking down sealant in the short term.  Denatured Alcohol has little effect. However, I’ve never soaked it over an extended period of time. Which may work much better. 

[dzeleski]

My point in bringing up F1 engines wasnt to compare it to aviation engines or how long they need to last for. It was simply to use as an example as to why race engines aim to have the smallest piston they can get away with. The new v6 hybrids are 1.6 liter engines which is something like 80mm pistons (3 inches). This also has to do with rotating mass but the topic of discussion was detonation which bore size, stroke, and head design matter.

[N201MKTurbo]

All that matters for detonation is mixture, pressure and temperature. Of course as you increase the pressure during compression it raises the temperature and when the spark ignites the charge, it further compresses the unburned fuel/air mixture and raises the temperature. When detonation starts it is that last little bit of unburned fuel that detonates with little explosive power. the further you get into it the larger the unburned fuel charge, so the more there is to explode. 

[Dave Morris]

On 10/29/2021 at 4:23 PM, EricJ said:

The AOPA published an article yesterday with a link to a new AML with "hundreds" of engines approved for G100UL.   There are a number of Lycoming O-360 variants included, so some vintage Mooneys may be covered, but only a couple Lycoming IO-360 variants that I don't think are relevant to Mooneys.  Likewise there are a couple Continental IO-360 models, but I don't think they're pertinent, either.

AOPA article:
https://www.aopa.org/news-and-media/all-news/2021/october/28/faa-approves-hundreds-more-engines-to-use-unleaded-avgas

New AML:   https://download.aopa.org/advocacy/2021/SE01966WI_AML-Amd1.pdf

However, the O-360-A1A and A1D are NOT included, so the entire line of M20A through M20C are excluded from this list, the way I read it.