Potential of Expansion Chamber Exhaust Pipes for Two-Stroke Powered Tools
by
Porsche Engineering Services
"...using expansion chambers, power of the series production engine can be raised by 40 percent while still offering an advantage in emissions of 34 percent.
Tuning an expansion chamber for the same peak horsepower as the box silencer gives an advantage in emissions by 62 percent..."
https://sci-hub.ru/10.4271/2010-32-0011
Quote:
Originally Posted by freebeard
Not the expert your looking for; but wouldn't the tune-pipe reduce exhaust gas [effectively] recirculation? Which comes on all new motors?
The percentages you report are impressive.
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No it wouldn't. See this animation:
At the optimal rpm the Tune-Pipe is just making it so 'all' the escaped air/fuel mixture is forced back into the cylinder just before the exhaust port closes.
That's what negates the BIG negative of the 2-Stroke.
Also NB that with a small reed valve to intake a bit of plain air into the transfer port above; the 1st bit of air would not contain any fuel and thus not waste/pollute as much.
If you wanted to do EGR, you would do it after the Tune-Pipe on that last bit of pipe where the muffler is placed.
You also want a very fast burn so that it's all done before the exhaust port opens.
The extra (very turbulent) time the charge spends below the piston likely helps tremendously, but 2-strokes do seem to benefit from hydrogen addition more than 4-strokes do.
I'm NOT saying you get more energy out than you put in, just that it helps with emissions.
https://www.sciencedirect.com/scienc...05844024026288