BS ENGINES

[Ed Lansinger]

Clint Corbin wrote:

>Aluminum pistons being flame proof?!  Aluminum melts at around 1100F (used to
>work in an aluminum foundry).  Flame temp inside an IC engine is around 1600F.
>[snip]
>If you increase the amount of energy being generated in the combustion chamber 
>(say by turbocharging or just increasing the breathing of the engine) enough,
>the piston will not be able to dump the extra energy to the cylinder and bam,
>you melt a nice hole in the piston.
>[snip]
>All in all, aluminum is not the best material for a piston.

Geez, Clint, that's an awfully harsh statement considering aluminum is the preferred 
material for production and many racing pistons these days, *including* turbocharged
and supercharged engines.  Aluminum being a more expensive material than steel, there 
must be a good reason that the OEMs use it.

Actually, _exhaust gas temperature_ is around 1600F, flame temp in the combustion 
chamber is more like 3000F.  Iron and steel are already starting to get rather weak 
around 1600F;  3000F will melt either.  So piston durability must be a more complicated 
issue than simply one of material selection.

As you allude, heat transfer is very important.  Aluminum is a nice material from that 
standpoint, much nicer than steel.  It's not clear to me that simply redoing the same 
aluminum design in steel will improve durability - strength at the same temperature goes 
up, but the piston temperature goes up because it can't transfer heat as quickly through 
itself to the walls, wrist pin, oil, intake air, etc., plus you have much greater 
stresses from the greater mass you are throwing around.

Obviously, I'm not a piston designer.

I have heard of people having lots of success with aluminum pistons and heads that use a 
(ceramic) thermal barrier coating.  Maybe this would be a good solution to the original 
question (which I missed).

Ed Lansinger
GM Powertrain Premium V (Northstar/Aurora) Software & Calibration Group