What/how does compression ratio affect an engine?

No extra heat in high Octane. Same hydrocarbon structure is both. Same
BTUs. Only difference is the speed of combustion is controlled so it is
slower in the higher octane to prevent pre-ignition.
--
Cy Galley - Chair,
AirVenture Emergency Aircraft Repair
A 46 Year Service Project of Chapter 75
EAA Safety Programs Editor - TC
New address -
EAA Sport Pilot


"Scott" wrote in message
...
One thing I think "might" be a concern is that burning 100LL (can't get 80
octane avgas these days) in an engine built for 80 octane is the extra
heat. I think valves are most likely to be affected by burning the 100LL
instead of 80. Might be all wet on this, but that's what I've heard and
I'm NOT an engine mechanic...just a user You might try digging in the
Lycoming site and see what they say about 80 vs 100LL...

Scott


wrote:
OK, not cool to reply to my own post, I know. But I just found this
great resource which basically answers all my questions:

http://www.lycoming.textron.com/supp.../key-reprints/

"Lycoming provides helpful information in various publications,
including Lycoming Flyer Key Reprints. Lycoming's Key
Reprints is our effort to continually share our best practices,
key lessons and engines systems knowledge to empower
our customers."

Lower compression = lower chance of preignition = lower octane
required (ie. auto fuel)!
Yes, that would make a difference to the pocket book!

The issue of using auto fuel is addressed in this series also:

"Auto fuel is now being used as a substitute for Grade 80
aviation gasoline under STCs issued by the FAA. Most
major oil companies and engine manufacturers continue
to recommend that aircraft piston engines be operated
only on aviation gasoline. Deterioration of engine and fuel
system parts have been reported in aircraft using auto
fuel. Operators should consider the added risk of using
auto fuel in aircraft. Remember -- a pilot can't pull over
to the side of the road when fuel creates a problem with
the engine."



--
Scott
http://corbenflyer.tripod.com/
Gotta Fly or Gonna Die
Building RV-4 (Super Slow Build Version)

On Thu, 13 Dec 2007 04:00:58 GMT, "Cy Galley"
wrote:

No extra heat in high Octane. Same hydrocarbon structure is both. Same
BTUs. Only difference is the speed of combustion is controlled so it is
slower in the higher octane to prevent pre-ignition.


WAY off base, Cy.
On ALL counts, except the no extra heat and same BTU's.

--
Posted via a free Usenet account from http://www.teranews.com

On Dec 12, 9:08 pm, clare at snyder.on.ca wrote:
On Thu, 13 Dec 2007 04:00:58 GMT, "Cy Galley"
wrote:

No extra heat in high Octane. Same hydrocarbon structure is both. Same
BTUs. Only difference is the speed of combustion is controlled so it is
slower in the higher octane to prevent pre-ignition.

WAY off base, Cy.
On ALL counts, except the no extra heat and same BTU's.

--
Posted via a free Usenet account fromhttp://www.teranews.com

Higher-octane rated fuels have about the same flame front
speed as lower-octane fuels, at around 100 feet per second. It's their
resistance to detonation, which involves flame fronts speeds of 5000
feet per second or more, that makes them necessary in high-compression
engines. As the combustion process begins in the cylinder, the burning
raises the pressure through the entire air/fuel mix, and low-octane
rated fuels will break down under that increasing pressure and
spontaneously combine with the oxygen, igniting almost all at once
instead of *waiting* (key word) for the flame to set them off in a
controlled chain reaction.
Detonation therefore requires time to develop. Low RPM with
high MP is pro-detonation. Lean mixtures burn more slowly, so they're
pro-detonation. Big cylinders take more time for the flame front to
cross, so they suffer more from detonation.
Preignition is something else. It's ignition of the mix
during compression by some hot spot in the cylinder, perhaps a glowing
bit of carbon in the head or on the piston. The burn begins early,
before the sparkplug was scheduled to fire, and gets way ahead of
itself due to the still-increasing compression as well as the
combustion, and detonation might happen. The damage is about the same.
Engines that aren't leaned properly will develop more carbon to cause
preignition. Too much lead fouling can do it. An oil-burner will
carbon up, too.
Octane ratings are different than octane content. In the old
way, fuel under test was fed to a variable-compression test engine and
the compression was raised until detonation began to occur. Then that
fuel was shut off and a mix of octane and heptane was introduced,
engine still running, and the octane/heptane ratio was varied until
the detonation point was established. An 80-octane fuel had the same
detonation characteristics as a mix of 80% octane and 20% heptane,
hence the rating. 80/87 reflected the detonation resistance at lean
and rich settings.
Fuels with ratings above 100 obviously have to be rated using
some other method, since we can't have a fuel consisting of, say, 115%
octane.

Dan

On Thu, 13 Dec 2007 04:00:58 GMT, "Cy Galley"
wrote:

No extra heat in high Octane. Same hydrocarbon structure is both. Same
BTUs. Only difference is the speed of combustion is controlled so it is
slower in the higher octane to prevent pre-ignition.



Cy

I'm on your side. See my prior post.

Lot of people are using different words to describe the same thing
which may be part of the problem.

Big John

On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
wrote:

If you're flying a homebuilt you can burn whatever you want - but the
alcohol restriction wasn't put there at random, it increases vapor
lock problems dramatically,

How do the planes which do fly on ethanol handle that problem,
pressurized tanks?

and is incompatable with many of the
materials commonly used in aircraft fuel systems.

The sealant sloshed in the tanks is one, I think ...

Do automobiles with flex-fuel capability do anything to minimize the
vapor lock issues? I'm sure the materials were selected to be ok.

On Dec 10, 11:06 am, GeorgeB wrote:
On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley

wrote:
If you're flying a homebuilt you can burn whatever you want - but the
alcohol restriction wasn't put there at random, it increases vapor
lock problems dramatically,

How do the planes which do fly on ethanol handle that problem,
pressurized tanks?

and is incompatable with many of the
materials commonly used in aircraft fuel systems.

The sealant sloshed in the tanks is one, I think ...

Do automobiles with flex-fuel capability do anything to minimize the
vapor lock issues? I'm sure the materials were selected to be ok.

Most autos use electric in-tank fuel pumps now. When the
fuel is pushed to the engine there's little vapor-lock risk. Aircraft
still often use pumps on the engines that pull the fuel, so that the
pressure on the fuel in the lines drops and the vapor pressure of the
fuel will cause vapor lock under the right conditions. Low-wing
airplanes that have the tanks in the wings will have boost pumps
somewhere low in the system, but when they're turned off after takeoff
the risk of vapor lock rises with autofuels.
Remember the old high-school science demonstration of water
boiling at room temperature when a bell jar is placed over a bowl of
it and the air sucked out of the jar? The lowered atmospheric pressure
lowers the boiling point of the water. Gasoline has a higher vapor
pressure than water, so lowering the pressure on it will make it give
off vapors quickly, and those vapors displace the fuel in the lines
and prevent the fuel flow. The pump will be quite happy to pump
vapors, but carburetors and fuel injectors don't deal with vapors very
well, and the engine gets hungry and goes on strike.
A pump that sucks the fuel to lift it from the tank lowers the
fuel pressure between the tank and pump. A pump that pushes it upward
from the tank avoids that.


Dan

"GeorgeB" wrote in message
...
On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
wrote:

If you're flying a homebuilt you can burn whatever you want - but the
alcohol restriction wasn't put there at random, it increases vapor
lock problems dramatically,

How do the planes which do fly on ethanol handle that problem,
pressurized tanks?

The vapor pressure of ethanol alone (or gasoline alone) is less than a
gasoline ethanol mix. The maximum vapor pressure comes from about 10% to 20%
ethanol and 80% to 90% gasoline. I don't recall why - just what is.


and is incompatable with many of the
materials commonly used in aircraft fuel systems.

The sealant sloshed in the tanks is one, I think ...

Do automobiles with flex-fuel capability do anything to minimize the
vapor lock issues? I'm sure the materials were selected to be ok.

They can run higher fuel pressures and/or increase the injector pulsewidth
as a function of measured or inferred fuel rail temperature. Another helpful
option is to have a system that returns excess fuel back to the tank which
tends to purge out any vapor bubbles.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote in message
news:KP6dnV86MLVlRcDanZ2dnUVZ_vmlnZ2d@wideopenwest .com...
"GeorgeB" wrote in message
...
On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
wrote:

If you're flying a homebuilt you can burn whatever you want - but the
alcohol restriction wasn't put there at random, it increases vapor
lock problems dramatically,

How do the planes which do fly on ethanol handle that problem,
pressurized tanks?

The vapor pressure of ethanol alone (or gasoline alone) is less than a
gasoline ethanol mix. The maximum vapor pressure comes from about 10% to
20% ethanol and 80% to 90% gasoline. I don't recall why - just what is.


and is incompatable with many of the
materials commonly used in aircraft fuel systems.

The sealant sloshed in the tanks is one, I think ...

Do automobiles with flex-fuel capability do anything to minimize the
vapor lock issues? I'm sure the materials were selected to be ok.

They can run higher fuel pressures and/or increase the injector pulsewidth
as a function of measured or inferred fuel rail temperature. Another
helpful option is to have a system that returns excess fuel back to the
tank which tends to purge out any vapor bubbles.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

I'm not sure, and also not qualified; but enough others are weighing in...

So, IIRC, the real issue with the STC is whether the fuel in question can be
reasonably asserted to conform to the same ASTM specification as the fuel
which was used for the test program for certification of the STC.

In the case of automobiles, the decision was made by governmental edict to
simply treat E10 the same as "pure" gasoline for automotive purposes.
However, that was not made applicable to certified aircraft engines; so all
of the testing would need to be done again to obtain a new STC. Speaking
only for myself, I would be reluctant to invest much effort or funding in
such a venture because the formulation of the fuel could be a moving
target--for example, next year mogas could magically become E15.

As to whether any, or all, of the other concerns are valid, I really don't
know. But, I do recall reading that the original specification regarding
vapor presure, which was indeed written to minimize vapor lock, may have
been written in error--shortly after WWI!

So, everyone else's guess is probably at least as good as mine.

Peter
Just my $0.02

As far as cars are concerned, for quite some time now, most vehicles have
had returnless systems where the pressure regulator and pump are in the
tank. The reason that fuel is not returned to the tank is that the fuel,
having made the trip to the fuel rail and back, has picked up heat. This
heat is released in the fuel tank, heating the fuel and increasing the fuel
tank pressure. This wrecks havoc with the evaporative emission systems
ability to detect leaks smaller than the current spec of 0.020".

Now with an aircraft, this shouldn't be a problem as there are now emission
systems on them...yet.

Dale Alexander


They can run higher fuel pressures and/or increase the injector pulsewidth
as a function of measured or inferred fuel rail temperature. Another
helpful option is to have a system that returns excess fuel back to the
tank which tends to purge out any vapor bubbles.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

On Mon, 10 Dec 2007 19:25:31 -0500, "Capt. Geoffrey Thorpe" The Sea
Hawk at wow way d0t com wrote:

"GeorgeB" wrote in message
.. .
On Mon, 10 Dec 2007 09:23:52 -0800, Richard Riley
wrote:

If you're flying a homebuilt you can burn whatever you want - but the
alcohol restriction wasn't put there at random, it increases vapor
lock problems dramatically,

How do the planes which do fly on ethanol handle that problem,
pressurized tanks?

The vapor pressure of ethanol alone (or gasoline alone) is less than a
gasoline ethanol mix. The maximum vapor pressure comes from about 10% to 20%
ethanol and 80% to 90% gasoline. I don't recall why - just what is.


and is incompatable with many of the
materials commonly used in aircraft fuel systems.

The sealant sloshed in the tanks is one, I think ...

Do automobiles with flex-fuel capability do anything to minimize the
vapor lock issues? I'm sure the materials were selected to be ok.

They can run higher fuel pressures and/or increase the injector pulsewidth
as a function of measured or inferred fuel rail temperature. Another helpful
option is to have a system that returns excess fuel back to the tank which
tends to purge out any vapor bubbles.

Not only purges bubbles but also cools the lines. The pump moves
multiple quantities of fuel compared to what the engine actually
consumes (on some vehicles as much as TEN TIMES.- but most closer to
3)

--
Posted via a free Usenet account from http://www.teranews.com