Maximum advance

Walter Sherwin wsherwin at home.com
Thu Jul 12 21:16:03 GMT 2001




> > programmatically combine the pressure transducer data together with the
> > crank angle data, to create a pressure-volume (PV) diagram for a given
> > cylinder.  Then you would have a good visual representation of the
entire
> > cylinder experience, including peak combustion pressures and phasing of
> > same.  The number of things you can deduce from a PV diagram are
endless.
>
> Are there other useful diagrams of this sort?  I'm thinking of a
> (just made this up) PQ diagram where
>
>    Q = cos(a) * sin(b)
>    a = angle between rod and bore centerline, as the rod aligns
>        with the bore, this goes to 1.0
>    b = angle between rod and crank throw, as the rod/crank angle
>        goes to 90d this goes to 1.0
>
> which describes the vector component of the pressure that is
> actually doing useful work (or so it seems to me).  The Q term
> is interesting in and of itself, so I think I'll write a little
> plotter that produces a bunch of curves for various rod/stroke
> ratios (and maybe with bore offsets, too).
>
> --
> Eric Fahlgren                            Mechanical Dynamics, Inc
> efahl at adams.com                          Ann Arbor, Michigan, USA
> --------------------------------------------------------------------------
--



Yup, that's the beauty of modern DAQ's and computers.  Provided you have the
right input data signals in the first place, you can interrogate their
meaning in umpteen different ways and formats without too much grief.  The
PV diagram will expose pumping efficiencies and pressure consequences.  Your
PQ diagram idea could help with the relative phasing of combustion/expansion
pressures WRT the reciprocating engine geometry for max power & torque at
all times.  I'm sure there are many other equally valid diagrams that could
also be pondered so as to focus one a given aspect.  Maybe even more than
just two variables at once....

Walt.

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