Re: Work output - back to ceramic EM - somewhat long

["Doug Johnson" <ur-quattro@msn.com>]

Isn't the "ideal gas law" applicable only to isentropic processes, where no
energy is transferred in or out of the system?  Sure, no energy is
transferred in or out of the "entire" turbocharger system, but you can't
look only at the turbine or the compressor when using this law (i.e., the
system perimeter would encompass all four gas pipes leading into and out of
the turbo).  Also, need to account for energy of the gasses themselves,
going into and out of the "system").  You will need to account for the loss
associated with higher exhaust gas discharge temperature as it leave the
turbo.  Sh*t, this is more complicated that can be done with text; it
deserves two detailed diagrams to completely understand the changes being
proposed with ceramic coating.  Where am I in error on this one?

FWIW,

 - Doug

----- Original Message -----
From: The Murphy-Fahlgren Family <efhome@master.adams.com>

> > I wrote:
> > >Does
> > >the ideal gas law (or an approximation) work ok [in these conditions]?
> >
> > Bob responded:
> > More or less.  The conditions will be quite a way from those at which
> > "ideal" seems to apply.  Much closer here, though, that in that tank of
N2O
> > of infamy.
> >
> > >If so, then
> > >I can see where pv is constant (pressure goes down proportional
> > >to volume going up), and hence T remains more-or-less constant
> > >as the gas passes the exhaust turbine.
> >
> > Subject to conduction losses from the EM, yes.
> >
> > >It follows then, that maintaining the temperature in the EM would
> > >be accompanied by a proportional increase in pressure.  Does the
> > >following seem reasonable?
> >
> > Seems that way to me.  You reduce the heat loss (make it more nearly
> > adiabatic) with the ceramic coating then the pressure should increase
some.
> >
> > > Io = original (no ceramic) EM gas temp, deg F
> > > Ic = new (ceramic) EM gas temp
> > > dP = improvement in ressure differential across exhaust turbine
> > >
> > >      Ic + 460
> > > dP = --------
> > >      Io + 460
> > >
> > >Increasing dP in itself will not increase HP (in fact may hurt, since
> > >the exhaust turbine may now be "too small," increasing back pressure
> > >and reducing efficiency).  But, by resizing the exhaust turbine,
> > >we could improve the spin up of the turbo (a direct result of dP > 1),
> > >while concurrently improving its high flow efficiency (a result of
> > >putting in an exhaust turbine with a higher A/R ratio).
> > >
> > >If we can believe the marketing literature published by the coating
> > >vendors, the temperature in the EM is increased by 200-250 deg F.
> > >Let's assume that means that Io = 1000 and Ic = 1200.  We have
> > >thus realized an improved pressure gradient of almost 14%, which
> > >seems not too shabby (I always consider engineering improvements
> > >in terms of salary increases, it puts things in perspective for
> > >management types :).
> >
> > Bottom line econonics, huh?  :-)
> >
> > >My off-the-cuff calculations seem to indicate that $20 spent on
> > >ceramic coatings in the EM is money well spent, _if_ they are part
> > >of a bigger picture rework.  Am I missing something here that flaws
> > >my logic?
> >
> > If so, I'm missing it too. ...
>
> If we really want to extract that last little bit of energy out
> of the exhaust stream, we would put a deLaval nozzle on the turbo
> outlet and point it towards the back of the car.  Hmmm, if we put
> on an afterburner...
>
> Hoping this spurs further conversation,
> Eric Fahlgren
> --
> The Murphy-Fahlgren Family            Try to take over the world.
> efhome@adams.com                                  Canton, MI, USA
>