Frans Veldman a crit :
> Furthermore the engine can safely be operated at a higher
> temperature, which is good for performance. (This is not so obvious, but
> think about it this way: we ignite the fuel to get heat. Heat is what
> drives our engines. All heat taken away from the engine is a loss of
> energy. We should not cool any more than necessary to keep the engine
> from melting.)
Frans and all,
Please pardon me for jumping in. I would like to point out that running
an engine hotter implies *greater* heat rejection, all other things
being equal, since heat rejection is a direct funtion of the the
temperature difference between metal and coolant.
Also in a liquid cooled engine, some degree of local boiling (nucleate
boiling) *does* occur. It is this local boiling that insures protection
---From hot spot, due to boiling removing enormously more heat than just
heating liquid. Naturally we are speaking of an adequate flow of coolant
which removes the bubbles and let them collapse in the general flow.
Several thorough NACA reports have been published on the subject
((TN-1498, TN-2049). Some info (mostly in French I'm afraid) at
http://contrails.free.fr/engine_liquide_refroid.php.
Bottom line, no need to be afraid of some internal boiling, and
everybody will agree that 50/50 coolant is better, and water is best
(but it can freeze).
Best regards,
--
Gilles
http://contrails.free.fr
|