REFLECTOR: The definitive answer on octane and av-gas

[dandemitchell at earthlink.net]

What ever happened to this thread? I have nothing past this date.

As I was informed during flight school, the reason for the dual ignition,
other than safety, was it could handle a multitude of octane fuels. The
reason was that the flame front is originating from two different positions
and thus the total time to burn the fuel was reduced. I was told the longer
burn time of a single plug cylinder could lead to higher combustion chamber
pressures thus causing pre-ignition where the flame had not yet reached.
The dual plug design allowed later firing, less kick-back (fixed firing
point), and quicker fuel burning. This reduced the cylinder pressures
during the burn cycle and thus the potential of pre-ignition at high power
settings. Note I did not talk about chemistry etc., I know nothing there
except to keep di-hydrogon monoxide out of the fuel/oil. (if that is that
is the correct formula)

Ed Mitchell



> [Original Message]
> From: John Dibble <aminetech at bluefrog.com>
> To: <Jim_Agnew_2 at yahoo.com>; Velocity Aircraft Owners and Builders list
<reflector at tvbf.org>
> Date: 2/13/2005 9:55:52 AM
> Subject: Re: REFLECTOR: The definitive answer on octane and av-gas
>
> My understanding is that the dual ignition did not compromise power. 
Another,
> simplier solution which I used was to remove the cylinders and add 2
additional base
> gaskets which lowered the compression ratio.  This did reduce power which
was only
> noticeable during rapid acceleration.  Again, the benefit of dual
ignition for
> mototcycles, may not apply to aircraft engine, but I would like to
explore it.
>
> John
>
> Jim Agnew wrote:
>
> > I suspect that the dual ignition allowed for a retarded spark timing to
allow
> > for the lower octane fuel.  It will work up to a point, however the
engine will
> > produce less power.
> >
>
>
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