What/how does compression ratio affect an engine?

"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