[Diy_efi] Peak cylinder pressure timing

[Hugh Keir]

Steve, Erik, Rod, Phil

If you can display the data out as degrees after top dead centre over
various RPM's, it will then be easy to add or subtract values from the
various ignition timing tables in your ECU for best performance. It sure
would be great for detonation warning as well.

I am sure it will be a bit of a moving target as you play with air fuel
ratio to maximise cylinder pressure at your assumed 14° or so after TDC and
the changing air fuel ratio ( weaker is I believe slower to ignite ) alters
the speed of combustion.

To go closed loop on the spark timing is more advanced than any of the
current breed of available ECU's can cope with, although I believe Autronic
are playing with the idea of offering this function on their next generation
ECU.

I believe you are correct in your assumption on how to calculate torque
although the pressure deteriorates rapidly and it must be linked to the area
under the curve.

Hugh

----- Original Message -----
From: "steve ravet" <sravet at arm.com>
To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
Sent: Wednesday, March 05, 2003 7:17 PM
Subject: Re: [Diy_efi] Peak cylinder pressure timing


> Phil Lamovie wrote:
> > Lets say we log lots of incremental values into a table;
> > say pressure vs degrees crank.
> >
> > The issue then becomes one of how to use the data acquired.
>
> There's a thesis that's been posted before from a graduate student using
> ion sensing to determine the peak pressure point, one of his
> applications was to use that as feedback for ignition timing so that the
> peak pressure was always at the "best" crank angle.  That wouldn't
> require any fancy math, and would eliminate the "spark tables" current
> used.
>
> > If you can do fast samples with an FFT function the area under
> > the curve (torque) becomes apparent.
>
> Instant torque is cylinder pressure times piston area times the
> "horizontal" component of the crank arm, right?  Average torque is the
> integral of that, also no fancy math required.  I'm not sure what use
> average torque would be other than display it for the user -- maybe
> traction control?
>
> --steve
>
> --
> Steve Ravet
> steve.ravet at arm.com
> ARM,Inc.
> www.arm.com
>
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