CHTs too cold?

[GeeBee]

One thing missing in this entire discussion is this fact. The velocity of the piston and rings near the top of the stroke is.......zero or nearing zero. That means several things. One on a tapered barrel the rings are not only compressed to their maximum, they also stop hydrodynamic lubrication for a split second. You are entirely dependent upon the rings at their maximum compression (due to the taper) not penetrating the viscous surface of the oil. Now you might say colder is better because the oil will have more viscosity, but too much and the ring pushes the oil rather than riding up on it as it slows below hydrodynamic speed. Think of a powerboat coming off plane and you get the picture. That "boat" is coming off a plane every cycle of the piston and the only thing that keeps that ring from taking a bite out of the top of the cylinder, (assuming ring gaps are correct) is a film of viscous fluid under very high pressure with no hydrodynamic aid.

 

[carusoam]

Wow!

We’re going to need to announce today’s award...

Today’s award, the Rheology Prize... a prize that is in the sub category of tribology...  this highly revered award goes to GeeBee!

For simplifying how viscous liquids actually lubricate surfaces.... and made it really understandable with boat planing accross the surface example!

That could explain why a step forms in the cylinder wall when the pilot fails to follow the proper break-in procedure...   If he really goofs it up, the step is in the wrong place...  because.... due to momentum, the piston travels slightly differently at different rpms...

Next week, we will be discussing The Lubrication Approximation... the theory behind ground affect, and also what lifts the boat on plane... 

PP thoughts only, not a rheologist or theologian myself... (Siri suggested theologian... )

But, I can spread peanut butter on a piece of bread with amazing precision... using the doctor blade... aka butter knife.

Best regards,

-a-

[aviatoreb]

43 minutes ago, GeeBee said:

One thing missing in this entire discussion is this fact. The velocity of the piston and rings near the top of the stroke is.......zero or nearing zero. That means several things. One on a tapered barrel the rings are not only compressed to their maximum, they also stop hydrodynamic lubrication for a split second. You are entirely dependent upon the rings at their maximum compression (due to the taper) not penetrating the viscous surface of the oil. Now you might say colder is better because the oil will have more viscosity, but too much and the ring pushes the oil rather than riding up on it as it slows below hydrodynamic speed. Think of a powerboat coming off plane and you get the picture. That "boat" is coming off a plane every cycle of the piston and the only thing that keeps that ring from taking a bite out of the top of the cylinder, (assuming ring gaps are correct) is a film of viscous fluid under very high pressure with no hydrodynamic aid.

 

Beautiful.

What happens at idle and taxi when clearly the cht is not terribly hot.  Is it the cht or the oil temp that is key?  Or both?

[GeeBee]

11 hours ago, aviatoreb said:

Beautiful.

What happens at idle and taxi when clearly the cht is not terribly hot.  Is it the cht or the oil temp that is key?  Or both?

Both. Why do you think engine manufacturers tell us to avoid prolonged ground runs? Why do they tell us to preheat?  Is that for the oil or the cylinders? If you look at "quick pre-heat" systems like Reiff, where is the heat applied? That tells you the priority for a cold engine. They tell us to get the engine warmed up after start, especially oil temp for a variety of reasons, bypass issues as well as viscosity. But...they tell us to avoid prolonged ground running.  It is a delicate balance. Unless you have a high idle for Lycoming, 1300 rpm or more, you are actually starving cylinders of splash lubrication. The entire cylinder is running mostly on residual lubricant at low idle. I would assume Continentals are the same. 

All of this is why I prefer long term, forced air preheat and Muti viscosity oil (Multi viscosity is where I separate from Mike Busch). The long preheat heats both the heads and the sump. The multi-viscosity oil provides correct viscosity for the heads at below normal operating. temps.

Consider this. In the old days before advanced rings and bore machining there was "upper cylinder lubricant" systems. Something like Marvel Mystery Oil injected into the intake system. Was it a high viscosity oil or low viscosity? What it was was low viscosity, low residue lubricant that was continuously injected because after one wipe, it was gone.  

[tmo]

I had a car, and a motorcycle, that had the oil added straight to the fuel... No valves to stick, either

The Reaper's chainsaw likely works like that as well...

[aviatoreb]

57 minutes ago, GeeBee said:

Both. Why do you think engine manufacturers tell us to avoid prolonged ground runs? Why do they tell us to preheat?  Is that for the oil or the cylinders? If you look at "quick pre-heat" systems like Reiff, where is the heat applied? That tells you the priority for a cold engine. They tell us to get the engine warmed up after start, especially oil temp for a variety of reasons, bypass issues as well as viscosity. But...they tell us to avoid prolonged ground running.  It is a delicate balance. Unless you have a high idle for Lycoming, 1300 rpm or more, you are actually starving cylinders of splash lubrication. The entire cylinder is running mostly on residual lubricant at low idle. I would assume Continentals are the same. 

All of this is why I prefer long term, forced air preheat and Muti viscosity oil (Multi viscosity is where I separate from Mike Busch). The long preheat heats both the heads and the sump. The multi-viscosity oil provides correct viscosity for the heads at below normal operating. temps.

Consider this. In the old days before advanced rings and bore machining there was "upper cylinder lubricant" systems. Something like Marvel Mystery Oil injected into the intake system. Was it a high viscosity oil or low viscosity? What it was was low viscosity, low residue lubricant that was continuously injected because after one wipe, it was gone.  

What oil do you use?

[jlunseth]

1 hour ago, tmo said:

I had a car, and a motorcycle, that had the oil added straight to the fuel... No valves to stick, either

The Reaper's chainsaw likely works like that as well...

I have quite a few things around my place that run on 50:1. Whoever said force never solves anything simply has not applied enough.

[GeeBee]

1 hour ago, aviatoreb said:

What oil do you use?

I use Aeroshell 15W-50. Yeah, I know it is a synthetic blend and I have a small sump engine (IO-550). However I change the oil every 90 days or 35 hours whichever occurs first so I am not worried about sludging from a synthetic blend. The long chain polymers are a plus for upper cylinder lubrication as they do not break down under heat as easily as regular petroleum, and they do not coke on the valves. Again it is a balancing act. 

If we could get rid of leaded fuel, things would be much better for all of us as we could go full synthetic. 

 

 

[GeeBee]

2 hours ago, tmo said:

I had a car, and a motorcycle, that had the oil added straight to the fuel... No valves to stick, either

The Reaper's chainsaw likely works like that as well...

LOL! Let me guess. Was it a Trabant?

 

[tmo]

No sir, a Polish contraption - wish I still had one today, alas that shall never be.

[aviatoreb]

38 minutes ago, GeeBee said:

I use Aeroshell 15W-50. Yeah, I know it is a synthetic blend and I have a small sump engine (IO-550). However I change the oil every 90 days or 35 hours whichever occurs first so I am not worried about sludging from a synthetic blend. The long chain polymers are a plus for upper cylinder lubrication as they do not break down under heat as easily as regular petroleum, and they do not coke on the valves. Again it is a balancing act. 

If we could get rid of leaded fuel, things would be much better for all of us as we could go full synthetic. 

 

 

Thanks.

Yeah thanks also for the remark on leaded fuel.  It seems that if and when no-lead 100 octane aviation fuel finally comes, it will be more expensive per gallon.  But I am feeling like our per hour cost, including extended engine life, will actually be lower.

[Blue on Top]

11 minutes ago, aviatoreb said:

It seems that if and when no-lead 100 octane aviation fuel finally comes ...

100 No Lead fuel will never come (in my opinion).  There is a catch 22 between the lead, magnetos and high compression ratio engines.  

Magnetos don't have precision enough timing.  Electronic ignition has the capability, but the engines we have are not designed for them.  In addition, variable timing ignition does not guaranty a known horsepower output that is required for certification.  I still have hopes, though. 

[aviatoreb]

34 minutes ago, Blue on Top said:

100 No Lead fuel will never come (in my opinion).  There is a catch 22 between the lead, magnetos and high compression ratio engines.  

Magnetos don't have precision enough timing.  Electronic ignition has the capability, but the engines we have are not designed for them.  In addition, variable timing ignition does not guaranty a known horsepower output that is required for certification.  I still have hopes, though. 

I thought they had it pretty much figured out but its too expensive and not yet certified.  So boutique laboratory grade fuel but not mass production.  What do I know...

Anyway - above my pay grade and I keep buying the stuff available at the pump.

E

[N201MKTurbo]

You could use this:

https://www.sigmaaldrich.com/catalog/product/sial/360066?lang=en&region=US
 

It is 100 octane. It has no lead. It is $400/gallon.

[N201MKTurbo]

We could easily re-certify our engines to run on unleaded fuel. You would lose about 10% of your takeoff power. 
 

No reason to lose any cruise power, those are strength and heat limits. Granted when you are MP limited you would lose cruise power. There is nothing electronic FI or ignition can do to change that.

[aviatoreb]

1 minute ago, N201MKTurbo said:

We could easily re-certify our engines to run on unleaded fuel. You would lose about 10% of your takeoff power. 
 

No reason to lose any cruise power, those are strength and heat limits. Granted when you are MP limited you would lose cruise power. There is nothing electronic FI or ignition can do to change that.

Even our turbo charged engines?  My TSIO520NB could operate on unleaded car fuel if the power were downrated 10%. Even at altitude for detonation margins?

[jaylw314]

1 hour ago, aviatoreb said:

Thanks.

Yeah thanks also for the remark on leaded fuel.  It seems that if and when no-lead 100 octane aviation fuel finally comes, it will be more expensive per gallon.  But I am feeling like our per hour cost, including extended engine life, will actually be lower.

IIRC, the Swift 100 fuel was also a little more energy dense per gallon.  But AFAIK, they abandoned the FAA's program and are just going the traditional STC route, so I doubt we'll ever really get any data on it.

https://www.aviationconsumer.com/uncategorized/whither-100ul-tested-fuels-fall-short/

[tmo]

1 hour ago, Blue on Top said:

high compression ratio engines

Is 8.5:1 (Lycoming O-360A1A, first from the list of Lycoming O-360 variants on Wikipedia) really high compression ratio? I know it's apples to oranges, but Mazda gasoline engines are 14:1; yes, not supercharged, with direct injection, and a clean sheet design, of course, but I thought 8.5:1 was average at best, even in the heyday of GA.

The Auto Fuel STC lists many engines, from Lycoming O-235 to O-540, including a bunch of O-360's. Even Lycoming themselves list automotive fuels as acceptable for many engines in their SI1070 - admittedly just the normally aspirated ones (but even the AEIO-540-D).

I understood the bigger issue was with the fuel delivery system and the difficulty to prove vapor lock would not happen.

I am purposefully ignoring the subject of ethanol in car gas; there are unleaded aviation fuels, like the HJELMCO 91/96 UL listed in the Lycoming SI, just not 100 octane. They are not popular, I'll grant you that, but if 100LL suddenly doubled in price...

On a total thread drift - how much lead is in leaded automotive fuels, as compared to 100LL? Enough to wonder about bringing them back (which I realize will not happen, but still)?

[N201MKTurbo]

59 minutes ago, tmo said:

Is 8.5:1 (Lycoming O-360A1A, first from the list of Lycoming O-360 variants on Wikipedia) really high compression ratio? I know it's apples to oranges, but Mazda gasoline engines are 14:1; yes, not supercharged, with direct injection, and a clean sheet design, of course, but I thought 8.5:1 was average at best, even in the heyday of GA.

The Auto Fuel STC lists many engines, from Lycoming O-235 to O-540, including a bunch of O-360's. Even Lycoming themselves list automotive fuels as acceptable for many engines in their SI1070 - admittedly just the normally aspirated ones (but even the AEIO-540-D).

I understood the bigger issue was with the fuel delivery system and the difficulty to prove vapor lock would not happen.

I am purposefully ignoring the subject of ethanol in car gas; there are unleaded aviation fuels, like the HJELMCO 91/96 UL listed in the Lycoming SI, just not 100 octane. They are not popular, I'll grant you that, but if 100LL suddenly doubled in price...

On a total thread drift - how much lead is in leaded automotive fuels, as compared to 100LL? Enough to wonder about bringing them back (which I realize will not happen, but still)?

I think they have backed off on how much TEL is in 100LL. I recall it was originally 4gm/gal. The last leaded auto gas was 0.1 gm/gal.

There is a difference on how the test engines are set up for measuring the octane for auto fuel and aviation fuel, so the octane numbers are not exactly apples to apples. It has to do with the timing and mixture used to do the testing. The 95 octane auto fuel would test lower using the aviation settings.

[N201MKTurbo]

2 hours ago, aviatoreb said:

Even our turbo charged engines?  My TSIO520NB could operate on unleaded car fuel if the power were downrated 10%. Even at altitude for detonation margins?

With a turbo engine, you should be able to get 75% of the current power in cruise even with a de-tuned engine. The detonation events are going to happen at full power. You would need more MP to get the same cruise power, but it should still make it.

I think if an unleaded aviation fuel was widely available, these STCs would probably happen.

 

Everybody here wants to hot rod their engines, not de-tune them....

Edited December 23, 2020 by N201MKTurbo

[tmo]

Yes, I know about the difference between RON (research octane number - the one displayed on pumps in Europe) and MON (motor octane number), which I believe is the difference you're referencing. And AKI = ( RON + MON) / 2 so that's that - if memory serves, this is what the US pumps display.

Aviation fuel ratings are yet different, but the Lycoming SI takes that into account, and still allows 88 MON / 98 RON automotive unleaded fuels to be used.

[GeeBee]

They do, but in aviation you have a lean octane number and a rich octane number. While they still use R+M to obtain an index they also do so rich and lean. In reality,  100LL is 100 lean, 130 full rich.

 

[PT20J]

@GeeBee is correct. A couple of years ago I got into a discussion with one of the other pilots at the museum about reduced power takeoffs in the DC-3 (which I don't think is a good idea) and his counter was that the 100LL (blue) gas isn't as good as the old 100/130 (green) that the engines were built for. So I did some research: Same stuff.

Skip

The difference between 100_130 and 100LL — General Aviation News.pdf

AvGas_100LL_specs_--_ASTMD910.pdf

 

[Blue on Top]

The last I knew about 100NL was a forum that one of the major petroleum makers gave at Sun-N-Fun 2019.  They were going after a magnesium additive instead of lead.  They assured all of us that there would be no cost increase, no EPA worries and no problem getting it certified ... soon.  Hummmmmm.

In a piston single, the only FAA-approved performance is takeoff and landing over an obstacle.  Landing is not an issue (no thrust involved there ... there is drag, though .  Takeoff on the other hand requires a known horsepower.  If the engine automatically pulls back to protect from detonation, the consequences could be fatal ... and put the OEM out of business in the ensuing lawsuit.  There HAS to be a good solution.

[N201MKTurbo]

So, any STC to detune an engine to use lower octane fuel would require new performance charts to account for the reduced takeoff power.

None of the electronic ignition systems out there now advance the timing more than the fixed timing we now have at full power.

They all seem to have fixed maps, so they shouldn't reduce the timing spontaneously. Any system that has a knock sensor, ion current sensor, or cylinder pressure sensors, could automatically reduce the engine power to maintain detonation margins. 

On the flip side if the engine was certified with low octane fuel, and had electronic timing with detonation detection, It could cause your engine to make more power than certified if you put 100LL in it.