Max Advance

[Brian Michalk]

While at the big EAA flyin at Oshkosh last year, I visited as many technical
forums as possible.  One of the most novel developments was a system by
GAMI, a company well known for its injector technology.  Well, what they did
was develop a system that used modified spark plugs to sense cylinder
pressure, and then servoed the ignition timing appropriately.  Their
research was based on some SAE papers, and their own experience; and they
found the best performance with a peak pressure pulse between 13 and 15
degrees ATDC.

The system is so elegant, as it behaves like a proper feedback loop should
behave.  It automatically accounts for air mass, fuel quality and other
variables.  As an added bonus, if the pressure is integrated over the crank
cycle, and then a baseline subtracted, it will show total shaft horsepower
that's accurate within a few percent.

I've been looking for a similar spark plug sensor.  The one from Optrand
sure looks a lot like the one being resold by GAMI.

> -----Original Message-----
> From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
> Behalf Of Eric Fahlgren
> Sent: Thursday, July 12, 2001 6:50 AM
> To: diy_efi at diy-efi.org
> Subject: Re: Max Advance
>
>
> Roy wrote:
>
> > Basically the time a cylinder needs for complete
> > combustion of the fuel is constant, you want max
> > pressure developed on the piston (BMEP) just after TDC
> > and therefore as the engine speed increases you need
> > to start combustion earlier so as this can be
> > achieved.  This is a very simple explanation of why
> > you need to use ignition advance.
>
> Well, it's not quite so simple.  What you really want to do is
> maximize the integral of the PQ curve (see my mail from 10 minutes
> ago), however you can.  After running a couple of thought simulations
> using the old meat computer, I think this means that you _probably_
> want the pressure in the cylinder at maximum when the rod-to-crank
> angle is about 90d for engines with big L (rod/stroke ratio), but
> probably a little earlier in the stroke as L gets smaller.
>
> (You can tell by all the "probablys" and "I thinks" that I'm
> sure about this. :)
>
> --
> Eric Fahlgren                            Mechanical Dynamics, Inc
> efahl at adams.com                          Ann Arbor, Michigan, USA
> ------------------------------------------------------------------
> ----------
> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without
> the quotes)
> in the body of a message (not the subject) to majordomo at lists.diy-efi.org
>

----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org