[Diy_efi] The Hunt effect

[Adam Wade]

--- 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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