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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-616049@logan.com>
Subject: Re: [FlyRotary] Re: Pport/cold side injectors
Date: Fri, 21 Jan 2005 10:23:22 -0500
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Wow! Ok, Ernest

Certainly sounds plausible that long runners would contribute to the
separation of the wheat and chaff.  I wish I could remember what my
professors taught me in those long ago days. Perhaps if I had day dreamed
less and studied harder......Nah!!!

Thanks again, Ernest.  Glad my injectors are all within 2.5" (or less) of
the ports.

Ed A
----- Original Message -----
From: "Ernest Christley" <echristl@cisco.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, January 21, 2005 9:50 AM
Subject: [FlyRotary] Re: Pport/cold side injectors


> On Fri, 2005-01-21 at 09:12, Ed Anderson wrote:
> > The Swiss Mistral rotary folks reported that when they went to long
runners
> > that they believed they encountered  a "distillation" problem as Ernest
> > mentioned.  Due to this problem they believed that they encounter
detonation
> > with their turbo set up due to the "Low Octane" part being ingested at a
> > different time than the lighter high octane part of the fuel.  I am
> > certainly not enough of a chemist to even know if this even sounds
> > plausible.  However, the team did have a Chemist and that is what he
> > reported.
> >
> > I must admit I'm a little bit skeptical of this mode as it would seem
that
> > even if it happened you would have a continuos stream of light and heavy
> > elements intermixing between one injection period and the next.  But,
they
> > certainly had the resources and inclination to look into the problem and
> > that was their conclusion.
> >
> > Ed A
>
> It's entirely plausible, Ed.
>
> First consider gasoline.  Being a organic substance, it is not a nice
> even mixture of identical molecules.  It is a random and often chaotic
> mixture of carbon compounds.  These compounds are mostly chains of
> carbon atoms with hydrogen hanging off the unused bonds.  Sometimes the
> chains hook back on themselves, but mostly they just intertwine like
> strands in a cotton ball.  The shorter strands evaporate and burn easier
> and faster.  If I can get the order correct, the number of carbon atoms
> in each molecule goes:
>
> 1)methane
> 2)butane
> 3)propane
> .
> .
> 8)octane (this one's important)
> 12)hexane
>
> Now the way organic material burns is important.  When exposed to oxygen
> and energy (we usually use heat, but other methods are possible), the
> oxidation process removes a carborn from the END of the chain, reacts it
> with the oxygen to give up carbon dioxide and water.  It's very
> important to consider that the center carbons are safe till all the ends
> are burned off, and none will burn till the ends are exposed to oxygen.
>
> Now, how does that apply to us.
>
> First, liquid gas does not burn except for the very surface...the part
> exposed to oxygen.  In the few milliseconds that a molecule will be in
> the combustion chamber of an engine, it has to be exposed to air and
> burn completely.  If it has to wait for 1000 neighboring molecules to
> burn away first, it will be halfway down the exhaust before it can even
> get started.
>
> Second, if you let the gas distill, you seperate out the short chains
> from the long chains.  Think of dried wheat chaff, stick, and logs.  The
> chaff will flash and be gone.  The sticks will keep an nice fire going,
> and the logs will burn all night...IF you can get them lit.  For a nice
> campfire, you'd want some of all of it.  What Mistral experienced was
> the chaff getting sucked in quickly and being burned off with some of
> the sticks, and then the logs clumping up and being sucked in as a tree
> trunk.
>
> Third, the magical 'octane'.  The original test for octane was to
> compare the burning of a sample of a fuel in a calibrated engine.  The
> engine was calibrate with pure OCTANE, exactly 8 carbon atoms in every
> molecule.  You can burn any fuel in an internal combustion engine, you
> just have to get the mixture and spark timing correct.  If the fuel
> burns fast like propane, you want to spark later.  You'd want to spark
> diesel earlier.  A mixture that is either lean or rich of peak will want
> an earlier spark.  Higher compression calls for a later spark.  In all
> cases, what you're doing is compensating for how quickly the fuel burns
> so that you can get maximum pressure in the cylinder at the right time.
> The problem that was found with the long runners was that it screwed the
> mixture up.  Instead of a nice clean flame front that could be
> compensated for, you got a hodgepodge mixture of wheat chaff and oak
> tree trunks.
>
> This is courtesy of an overzealous organic chemistry professor from
> 1987.  I may have forgotten a thing or two since then.
>
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