Ignition Timings

[Tracy S. Cummings]

the timing is constant because flame propagation is relatively constant (I
know that there are a lot of variables that affect this but for this
conversation they are not to critical). If our goal is to have combustion
pressure at its most effective point when the piston and connecting rod are
at the point of having the best mechanical advantage over the crank shaft
then we must ignite the fuel at some point "x" time in advance. this point
"X" is based on the burn rate of the fuel, gasoline is a popular fuel
because it burns relatively quickly, in the past kerosene was a popular fuel
but kerosene burns slowly, so slowly that it really limits the max rpm. the
faster the fuel burns the shorter the duration "x" can be. unfortunately
fuels with short burn times are also known as explosives. To sum this all up
as rpm's increase the ignition event starts at the same point of time "X" in
advance of tdc, but this is not easy to measure so degrees before tdc was
chosen because of the ease in measurment. they are the same thing when you
correct for the increasing rotational velocity.
john cummings
----- Original Message -----
From: Diehl, Jeffrey <jdiehl at sandia.gov>
To: <diy_efi at diy-efi.org>
Sent: Monday, May 22, 2000 3:18 PM
Subject: RE: Ignition Timings


> I didn't see any replies to this but find it very interesting.  If there
> were any follow-ups, forgive me.  So, why do we think this timing is
> constant?  Is it simply the amount of time it takes for the plugs to fire?
> It clearly isn't related to piston position.
>
> Inquiring minds...
>
> Mike Diehl,
> MR-2, '87na
>
>
> > -----Original Message-----
> > From: Corner Paul [mailto:Paul.Corner at icl.com]
> > Sent: May 17, 2000 3:34 AM
> > To: 'diy_efi at diy-efi.org'
> > Subject: Ignition Timings
> >
> >
> >
> > Hi All
> >
> > I've been messing about with the ignition side of my ECU,
> > writing new code
> > and grafting it to the fuelling software....
> > Working out the initial advance tables from the original
> > advance curves. I
> > noticed that when the data is converted from degrees/RPM to
> > mSec before TDC,
> > it remains fairly constant from tickover to 4500 RPM.
> > Question is - can I use this time constant up to, say 6500
> > RPM, rather than
> > messing around with look up tables etc. Perhaps, at a later
> > stage, when the
> > engine is running and the hardware has been tested, the
> > software can be
> > rewritten to use look up tables. It really depends on how
> > much advance is
> > required above 4500 RPM.
> >
> > Regards, Paul.
> >
> >
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