What/how does compression ratio affect an engine?

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

Let me reccomend a book. It's very old but packed with aero engine
knowledge. It's historically significant and a good read. Read it and
you'll know more about airplane piston engines than you could imagine there
was to know.

"The High Speed Internal Combustion Engine" by Sir Harry Ricardo.
See: http://www.ricardo.com/ricardoStore/...t.asp?P_ID=149 (1968)

(In this case, "High Speed" refers to MPH and not neccessarilly RPM.)

Sir Harry was a British mechanical engineer whose most significant work was
between WW1 and WW2. He championed the sleeve valve engines that were
developed into the Bristol Centurion but his most historic work was on the
Rolls Royce Merlin. He also worked on the last generation of high power
piston engines like the Napier Nomad and consulted with all the US engine
manufacturers. He is a towering figure in the history of airplane piston
engine development.

His work with high octane fuels, supercharging and high compression ratios
is has been acknowledged as a major contribution to the Allied victory in
WW2.

Bill Daniels

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

"Morgans" wrote:
"Jim Logajan" wrote
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.

It wasn't intended to address that specific aspect. It was an analogy,
maybe a lousy one, but it's not like I get paid to do them!

:-)