[Diy_efi] The Hunt effect

[dh at busb.com]

The octane can't be taken out of gasoline and still be gasoline.  There's
even some in diesel, how about that!  The octane equivalence is for
alternative fuels and blended fuels.  So, yes and no and maybe.

You say apple and I say oranges, for a given flame speed smaller distance is
less time.  The answer is that fruity blend either way.

Yep, turbulence is better in some engines than others.  But, consider the
change in shape, especially with a true hemi between piston down (cylinder)
and piston up (drooping pancake.)  When the piston is down the turbulence is
one direction and when the piston is up that same turbulence is quite
different.

I believe that the only true hemi is by Toyota these days.  The dodge
version suffered greatly from the dome on the piston to keep compression up.
That's why the only real application for those monster is extremely low
compression ratio motors, say, top fuel.

dh

----- Original Message ----- 
From: "Adam Wade" <espresso_doppio at yahoo.com>
To: <diy_efi at diy-efi.org>
Sent: Thursday, October 06, 2005 2:09 AM
Subject: RE: [Diy_efi] The Hunt effect


> --- John Gross <jogross3 at hotmail.com> wrote:
>
> > Flame front speed is the rate of burn of the fuel
> > air mixture itself, and is determined SOLELY by the
> > chemical composition of the fuel.  The Octane
> > content makes a negligible difference in this
> > value.
>
> There is no octane in pump gas.  The octane number
> represents the detonation resistance of a given fuel
> compared to a cetane/octane blend, IIRC.  So there is
> no "octane content" in fuel -- changes in octane
> rating are due to -- different composition of the
> fuel.  So the above is contradicting itself, it would
> appear.
>
> > Twin plug heads burn faster simply because you're
> > starting the burn from multiple locations, so the
> > flame front has less distance to cover to consume
> > the volume in the chamber.
>
> And here I thought it was because two kernels
> increased volume at twice the rate until they merged,
> and further that this doubling of burn rate raised
> pressure sharply over the rate in a single-plug head
> and engine of otherwise identical design, intake
> configuration, and rpm.  Increasing pressure in a gas
> increases temperature, thus making it easier for the
> flame front to propagate over its entire surface.
>
> > Dynamic compression adds to the rate of burn because
> > it increases the intensity of the turbulence.
>
> Hm, I'd always thought that it was the increase in
> density and temperature of the mixture that made that
> difference.  What about a high-compression engine with
> an open hemispherical combustion chamber?  By your
> description, as long as the cc is the same shape and
> volume, there shouldn't be any notable difference in
> burn rate.
>
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>
>
>
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