How dirty is a CONSTANT RPM 2-stroke with a Tune-Pipe?

[Logic]

I was thinking about light and simple so 2 stroke came up.

If the intake charge is escaping out the exhaust
except
when the tuned expansion pipe is kicking it 'all' back; how efficient would a constant and exact/optimal RPM, 2-stoke engine, turning a genset, be?
(We aren't discussing generator/alternator efficiency here)


Here's a nice read on the why and how of Tune-Pipes and some dyno graphs:
http://www.jawamania.info/Files/tech...ust_system.pdf

Here's emissions numbers of various engines doing the Euro Cycle. etc:
https://publications.jrc.ec.europa.e...%20%282%29.pdf

But no constant rpm with tuned expansion pipe research I could find yet.


Or
How efficient and clean is a 2-stroke with a variable Tune-Pipe?

Here's a study on a variable Tune-Pipe:
Improving the Performance of Two-stroke Motorcycle with
Tuned Adjustable Exhaust Pipe
https://maxwellsci.com/print/rjaset/(2)59-65.pdf
The tuned exhaust system was found to improve fuel economy of the engine by 12%.
The major engine-out emissions, HC and CO were reduced by a minimum of 27.8% and 10.7% respectively.
An improved power output of 15.8% increase was achieved.
As a bonus, it w as also found that the exhaust noise was reduced .

https://www.youtube.com/watch?v=0odVzSgufjk

https://www.tiktok.com/@europeanpowe...60752034729248

I'll do more research on this but if you have a moment to look at the graphs etc in the linked study, I would like the opinions of those who are more up to speed with the numbers in eco 4-strokes for HC, CO, etc plz so we can compare.
https://maxwellsci.com/print/rjaset/(2)59-65.pdf

Many of the papers also speak of cleaning up the exhaust.
I also have some ideas on cleaning up the exhaust.

[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.

[Logic]

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

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.

No it wouldn't. See this animation:

https://www.youtube.com/watch?v=HbqS3fz8EDA

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

[cRiPpLe_rOoStEr]

I have never seen any 2-stroke engine with EGR. But anyway, maybe picking the EGR flow further down the exhaust stream might lead to some natural cooling prior to the exhaust gasses being recirculated, which might be good.

[Logic]

Originally Posted by cRiPpLe_rOoStEr

I have never seen any 2-stroke engine with EGR. But anyway, maybe picking the EGR flow further down the exhaust stream might lead to some natural cooling prior to the exhaust gasses being recirculated, which might be good.

Yes very good. The colder the better, for timing advance / power.
For economy..?
But most all EGR systems have a cooler that might be skipped with enough open air EGR plumbing as would be the case on a motorbike or under a car.