Heheheh,
I know this one- because the alternative is a VW engine! <grin>
Actually, the multiple transfer is because the heating of an internal
combustion engine is so uneven. The head, especially, builds up much of
the waste heat, and there's not much surface area there, or much oil.
Look at the finning on an air-cooled bike- the head's heavily finned,
and the cylinder's fins taper away as they approach the crank. So you
use a high-heat-transfer medium (water) and metal (aluminum) to get the
heat out of the head quickly.
This keeps hot-spots in the head cooler, and lets you run a higher
compression ratio. Air cooled VW's ran ratios on the order of 6:1 or
7:1- any higher, and you ran into detonation problems! Also, pollution
problems, as the low ratios were less efficient.
So the coolant was introduced as an efficient way to cool a small, hot
area quickly, and at the same time, even out the temperatures in the
head and cylinder.
Not a thermodynamicist, but I play one on the web,
Toby
pkort@cis.picker.com wrote:
So why are most
> automotive engines designed to transfer heat several time; metal block to
>liquid
> coolant to air combined with metal to oil to air or in some cases from metal
>to
> oil to coolant to air?
Paul
> OROC
|