Originally posted by PacerX
A small amount of mass (unmeasureable in terms of standard chemistry practices) is converted to energy during combustion.

If you look at things in an Einsteinian way, instead of Newtonian, it works.

"Mass is not created nor destroyed."

Depends on what you call "destroyed" or "created" as mass and energy are interchangeable.


In fusion or fission, a MUCH larger amount of mass is expended... i.e. turned into energy.

Originally posted by DOOM Master
This is correct, even though the amount of mass that is converted into energy via an internal combustion engine is only measurable on the atomic scale. And actually, mass can be created out of quantum flucuations of the space-time continum in the form of matter-antimatter particles. Isn't quatum theory grand?

Originally posted by PacerX
Nobody else answered it, but here's the short explanation for why the exhaust valves can be smaller:

Hot gases, such as those in the cylinder, have residual energy after forcing the piston down the bore, not much mass has been lost by combustion (very little), but they are occupying the same volume as they did previously, but at a much higher temperature and therefore pressure.

The difference in pressure between the exhaust manifold and the cylinder helps force the spent gases in the cylinder out, kind of like when you shake up a bottle of pop and open the top.

Because this difference in pressure is working in favor of the motor in this case, so the exhaust valve can be much smaller than the intake valve and still efficiently flow the exhaust gases out.

Originally posted by 92RS shearn
lol, yeah guys you are right though I think this goes a little outside the topic of the basic operation of an ICE.
I think that the newtonian theory is more than adequate for this. It is adequate for all of my thermodynamic classes and all of the related industires (Power generation, HVAC, Jet propulsion, etc.).