Hybrid Car – More Fun with Less Gas

better mileage with higher octane? - Page 12

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Posted by Dan_Thomas_nospam on January 4, 2007, 4:15 pm
 



Solar Flare wrote:

  Mustn't confuse detonation with normal combustion. The fuel/air
mixture should burn across the chamber at about 100 feet per second.
Detonation is a different process and flame fronts can reach 5000 fps
or more. The enormous pressure spikes and abrupt release of heat does
plenty of damage.
      Detonation happens when the complex fuel molecules, under the
rising pressure ahead of the flame front of normal combustion, begin to
break down into simpler structures that can autoignite; they don't wait
for the flame front to set them off in a normal chain reaction. The
whole works might go off at once just becuse they're being squeezed and
their temp is rising.
      Detonation requires time for those molecules to break down, so
low RPM is a problem, large combustion chambers (which require more
flame-travel time) are a problem, lean mixtures (which burn more slowly
due to the distance between molcules) are a problem.
       Normal combustion is not an explosion; it's a controlled burn.
Detonation is an explosion, totally uncontrolled, and higher octane
fuels were designed to increase the capability of handling the higher
pressures and temps without breaking down into autoignitable
components.
        In aircraft we're still using leaded fuels because the engine
technology is stuck in the 1950s. Some avgas grades have large amounts
of lead in them, and sparkplug fouling is a big problem, even in the
heat of an aircooled engine. Those amounts of TEL are necessary for the
big cylinders found on aircraft engines, their low operating RPM, and
the higher operating temps (cylinder head temps to 550F, depending on
the engine).
        We've been promised unleaded avgas for some time now but
haven't seen it yet.

        Dan


Posted by clare at snyder.on.ca on January 4, 2007, 5:38 pm
 


On 4 Jan 2007 08:15:31 -0800, Dan_Thomas_nospam@yahoo.com wrote:


Right on Dan,
So much misinformation flying around about Octane - good to see there
are a few others who understand it. (Are you a Canuk? Member of RAA?
Perhaps read my artical the other month?)

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


Posted by Dan_Thomas_nospam on January 4, 2007, 7:32 pm
 


clare wrote:


        Canuck. Flight Instructor. Aircraft Maintenance Engineer.
Aircraft Systems instructor. Former member of EAA (1972-1992). Member
of COPA. Fly my Jodel D-11 when I have the time. Building a Hummelbird.
Should join RAA, but spend so much time working in aviation that by the
time I get home I don't want to read any more about it. Barely have
time for the H-Bird.

          Dan


Posted by clare at snyder.on.ca on January 4, 2007, 7:48 pm
 On 4 Jan 2007 11:32:49 -0800, Dan_Thomas_nospam@yahoo.com wrote:


Wherere you located?

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


Posted by Dan_Thomas_nospam on January 4, 2007, 11:15 pm
 
clare wrote:

 Three Hills, Alberta.


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