What/how does compression ratio affect an engine?

"Matt Whiting" wrote in message
...
... Some believe that higher octane gasoline burns more slowly and thus
can
put more fire past the exhaust valve. However, most of my reading on the
subject suggests that this is a myth and there is no substantial
difference in burn rate as a function of octane.

Matt

Burn rates are essentially the same.

There are problems (in automobiles) with some premium auto fuels since the
changes in the chemistry to get higher octane can result in slower
evaporation which can cause an engine to stumble when you first step on the
gas.

--
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.

Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

"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.

See my other post and clue me in to why they sell 100 octane valves for
A-65s and C-85s. Are they a waste of money?

Scott


RST Engineering wrote:

Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim


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

On Dec 10, 4:22 pm, Scott wrote:
See my other post and clue me in to why they sell 100 octane valves for
A-65s and C-85s. Are they a waste of money?

See http://www.fsv2000.at/woche/2001_10/conti_sb_m77_3.pdf for a
TCM Service Bulletin about alternate valves for those engines. They
say that erosion problems have been encountered with the high lead
content of 100LL. It's not because the fuel burns hotter; it's a
corrosion issue. If the fuel burned hotter, I would see both higher
CHTs and more power out of my A-65. But I don't. You need to do some
research on Octane Ratings and Detonation. Google those.

Dan

On Dec 10, 2:32 pm, "RST Engineering" wrote:
Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim
----------------------------------------------------------------------------------------------

Gee, Jim... that can't be right. Because if it IS, it means 99 &
44/100% of the 'experts' out there are WRONG...

:-)

wrote:

On Dec 10, 2:32 pm, "RST Engineering" wrote:

Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim
----------------------------------------------------------------------------------------------


Gee, Jim... that can't be right. Because if it IS, it means 99 &
44/100% of the 'experts' out there are WRONG...

:-)


That's just about right...

Only if they are Ivory and it is Snowing

{;-)

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

wrote in message
...
On Dec 10, 2:32 pm, "RST Engineering" wrote:
Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT
GENERATED
BY A HIGHER OCTANE FUEL.

Jim
----------------------------------------------------------------------------------------------

Gee, Jim... that can't be right. Because if it IS, it means 99 &
44/100% of the 'experts' out there are WRONG...

:-)

"RST Engineering" wrote:
Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT
GENERATED BY A HIGHER OCTANE FUEL.

My understanding is that you are correct, yet not fully correct. At the end
of the combustion phase of the cycle there is no significant difference in
the amount of heat released between a high octane and low octane fuel.

BUT - one is more likely to burn unevenly and/or more quickly (i.e.
"knocking" or "pinging") which leads either to unplanned overpressures or
localized hot-spots (i.e. _high heat concentrations_). So sure - no _final_
difference in released energy, but time and space concentrations can result
in metal melting or breaking in one case and not the other.

I suppose one analogy would be to consider the difference between what a
bullet does to the human body versus what eating a large meal does. The
bullet may have about as much energy as the large meal (probably even less
than the meal), but the bullet will do a lot more damage to you than the
meal. ;-) It's all in how quickly the energy is released and the manner of
the release.

"Jim Logajan" wrote

BUT - one is more likely to burn unevenly and/or more quickly (i.e.
"knocking" or "pinging") which leads either to unplanned overpressures or
localized hot-spots (i.e. _high heat concentrations_). So sure - no
_final_
difference in released energy, but time and space concentrations can
result
in metal melting or breaking in one case and not the other.

So, in your example, the high octane would be the cooler burning fuel,
because it burns more evenly, and slowly, so it prevents knocking.

Other scientific data showes that the higher octane fuel, the lower the /btu
content. That's fact. Not a lot of difference, but a difference, none the
less.

I suppose one analogy would be to consider the difference between what a
bullet does to the human body versus what eating a large meal does. The
bullet may have about as much energy as the large meal (probably even less
than the meal), but the bullet will do a lot more damage to you than the
meal. ;-) It's all in how quickly the energy is released and the manner of
the release.

I don't see your analogy having anything to do with the discussion of octane
and valve differences.
--
Jim in NC

On Mon, 10 Dec 2007 14:32:55 -0800, "RST Engineering"
wrote:

Oh, not this old wive's tale again. THERE IS NO ADDITIONAL HEAT GENERATED
BY A HIGHER OCTANE FUEL.

Jim
And, by default, high octane gasoline is NOT slower burning. SOME high
octane fuels MAY burn slower, but others WILL burn faster. The
air/fuel ratio has a more predictable effect on burn speed.

--
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