Maximum advance

[Bernd Felsche]

Greg Hermann tapped away at the keyboard with:

> At 9:30 AM 7/13/01, Bernd Felsche wrote:
> >Greg Hermann tapped away at the keyboard with:

> >Let's keep the computation fluid thermodynamics out of this. Heat
> >transfer to the walls is a small factor; as is heat transfer to
> >end-gas. The compression of the end-gas, and hence its increase in
> >energy, should be taken into account.

> I agree that I was being a bit of a smart *ss, sometimes that's fun to do!

Better to be paid to be one. :-)

> BUT--heat transfer to the piston crown and chamber walls, both
> convective and radiative, is, in fact, _quite_ significant,
> especially while near TDC.  I would hazard a guess that it can
> account for somewhere between 10 and 20% of the total heat input
> value of the fuel. Which is precisely why piston and chamber
> polishing and thermal barrier coatings make a significant
> difference in performance--both in terms of torque/power output
> and BSFC (fuel efficiency).

The theoretical peak pressure and temperature, assuming adiabatic
expansion, will be higher than that in practice. They therefore
provide a ceiling for conditions.

The greatest simplifying assumption in the proposed model is that
the temperature remains a constant behind the flame front - partly
because I don't have any idea at all _how_ this varies, even though
I understand that it varies and have some ideas as to why...

I'm not disputing that the non-adiabatic effects occur. It just
doesn't help to tell us what we want to know; the effect of timing
on torque.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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