Why are cooling systems necessary ?

[Guest]

The temperature reached by combustion can easily exceed 2,000 F. An aluminum piston would melt. So would an aluminum head. Even iron would lose a lot of it's structural strength.

I'm taking a mechanics of materials class right now, and this would be the greatest factor of engine failure. As the temperature gets closer to the melting point of the material, the material will reach a point where it looses it's elasticity and does not return back to the shape it was before. I believe at this point the mechanical parts will fail because they will be so distorted that they will no longer fit. The pistions ring lands are usually the first to go, due to the heat generated by friction.

Also, of course, the oil would've broken down by then too, making the friction astronomically high. Everything would melt in a very short amount of time.

[Guest]

I always wondered how on earth they managed to get an AIR COOLED flat six to cool properly.

Especially when its mounted in the back. I mean in the font...lots of nice cold air, in the back...no such luxuary!

I know they have a big 'scoop' on the bottom of the car to suck in air flowing under the car. Then the engine driven fan (power robbing) blows it out the top of the back into the low pressure zone there.

[manchild]

Well, the most exposed parts are outlet valves. Their edges can heat up and than burn out or break off when they hit the valve seat. It usually happens only on one part of the valve or piston and than expands. Piston head can heat on one spot and get small hole while the rings and the rest of the piston can look pretty much ok.



http://www.kb-silvolite.com/feature.php ... ad&F_id=47

[Guest]

I checked out the site you just linked. I love 'becomes pasty':

Lack of clearance can be excluded as cause of damage since, in spite of the high temperature due to the piston head scorching, no scuffing occurs in the initial stages. However, the piston head becomes so severely over-heated in the squish zone that material in the top land and behind the rings down to the oil ring groove becomes pasty and is removed by a combination of inertia forces and the ever increasing penetration of combustion gases into the growing scorch zone.

[Guest]

The Keith Black site is great.

I found this:

When detonation occurs cylinder pressure can see a 500% increase to 5000 PSI.

Using my Honda's 81mm Piston as reference, that's 40,000lbs of pressure. Wow!