On Mon, 08 Dec 2003 22:34:01 GMT, "Lawrence James"
wrote:

Cutting off the air supply is a good choice. It was not one we were
presented with in the original post. Cutting off the fuel is often hard to
do quickly.

Firing a co2 extinguisher is also ok. Lets talk about the physics involved.
Even presuming your co2 stays cold enough to have an effect which I will
allow you. The moving parts in the engine are the ones that have to most
difficulty transfering heat energy. This is because the have small
lubricated contact surfaces to the non-moving parts. The ones that your
cold slug of co2 are going to encounter are the valves and the pistons.
Valves exchange heat through the valve guides, the valve springs, and the
oil. Normally excessive heat is being transfered from the valves to these
other items. But in this case we will allow that the co2 has cooled the
valve below normal operating temp. The cooled valve will contract. This
will increase the clearance in the valve guide and shorten the valve stem.
Neither of these is going to result in damage. Next stop is the combustion
chamber and the top of the piston. Again the moving part, in this case the
piston, is going to have the most problems with heat transfer. Pistons are
only able to transfer heat through the rings, the wrist pin, and the oil.
Again allowing that your co2 has cooled the piston lower than normal
operating temp. The piston will contract increasing the clearance between
the piston and the cylinder wall. This is not going to cause any damage
either. The head and block are simply going to contain far far too much
heat energy for your co2 to have a noticable effect. And the head and block
also have smaller contraction and expansion rates for the same temp change
as the valves and pistons. Even bringing other parts into the mix you are
always going to have a situation where you have cooled the moving part and
increased the clearances. And you simply are not going to be able to cool
anything down enough to result in a loss of material strength. This is why
you can't damage an engine with co2.


Excellent analysis Lawrence. Let's also remember that the CO2 will
likely encounter a heated intake charge coming from a turbo/blower,
further reducing the "shock."

Back to the nitrous comparison - hence the saying, "turbos and
nitrous love each other." The cooling effect of nitrous on the
intake charge is more pronounced on a forced induction engine...