Quote:
Originally Posted by serialk11r
I think that gets a bit complicated, the exhaust gas expanding into the exhaust pipe would produce...a wave? And then as the piston rises what happens is affected by how that wave behaves.
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Well we have two things happening, the pressure wave exiting at whatever the speed of sound in the exhaust pipe is (~1500 ft/sec) but that's moving through whatever gas/atmosphere is already in the pipe. There is also the left-over exhaust gas from the combustion that is exiting at whatever speed it does (that formula, I've heard 300 ft/sec estimates).
The formula I posted seems to be only for the piston 'pushing' the gas out. But in a situation where we open the exhaust early (before BDC, modern performance engine) there is left-over pressure that isn't really doing anything to push the piston anymore. And the idea is that the pressure of the gas pushes itself out (well moves to the lower pressure pipe) so there is less work for the piston to do on the up stroke. But does that pressure difference affect the speed of the exiting gas?
(remember physics is my big weakness...)