Max Advance

[Eric Fahlgren]

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
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