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

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. :)

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.

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

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

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.

' two-stroke engines '
 

Two-stroke engines were banned in the United States, starting around 1991.
Orbital Engine's 2-stroke, of much interest in the automotive industry, was finally abandoned, after unsuccessful attempts to bring them into compliance for tailpipe emissions.
Today, in the United States, the only 2-strokes allowed to be sold, are under 50cc in displacement, and mostly for powered yard-care products and chainsaws.
They're 'filthy' and will be superannuated by electric replacements.

I'm going to pretend we actually read each others posts with the intent to understand,
rather than immediately rushing to engage in some insane game of intellectual one-upmanship to satisfy a need to be considered cleverest and for the pure joy of a good argument.

ie: This reply is not actually for aerohead, as he wont read it with the intent to understand it, but for others reading this thread.


Whether they are banned in the USA or not is NOT the question.

The question is:
How clean can you make a 2-stroke
IF
it runs at a constant rpm..?
(as is the case in a serial hybrid)

So if a 2-stroke is run at a constant rpm we can get most of the charge that is otherwise lost out the exhaust to return to the combustion chamber, with a Tune-Pipe.

But not all as there will be some dilution in the tune pipe.

If a tiny reed valve is added to the TRANSFER port;
then the first bit of lost to exhaust charge is not in fact charge but air.
The first bit to be lost is the last bit to be returned by the tune pipe.
So any dilution in the tune pipe is more with plain air than charge.
Meaning more to all charge is returned to the cylinder, by the tune-pipe before the exhaust port closes.

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

ie: in the video that 1st bit of green to escape, which is the last bit of green to be returned is plain air and any dilution is no longer a problem.

The other place where there is a problem is with the power stroke only being around half a downward stroke, vs a 4-stroke's full stroke, before the exhaust port opens.
This means that there is way less time for a complete and clean burn of all the charge.

If one were to add hydrogen; the burn is speeded up dramatically, making that initial exhaust escaping down the pipe cleaner.

Here some sort of onboard hydrogen or HHO/Hydroxy cell could be used.
NOT for economy, but for improved emissions...
( Do NB MIT etc's plasmatrons that are in fact efficient at onboard hydrogen production however)

That leaves the lubricating oil and soot as an issue.
They are MUCH heavier than the gasses in the exhaust.
So a centrifuge after the tune-pipe would be efficient at separating these particulates in the exhaust from the gasses, whence they could be returned to the intake.

( I suspect a centrifuge may also be a very effective muffler. Especially with some thought in that direction put into it's design.
I also NB the effectiveness of Helmholtz and /or Quarter Wave Resonators on fixed rpm exhaust etc noise )

The last step, if still required after adding hydrogen, would be an exhaust catalyst.
They need the high temperature one sees in the exhaust just after the engine, to work.
So they would have to be before the tune-pipe.

That simply doesn't work.
Leaving the placement of the catalyst after the tune-pipe and centrifuge as the last remaining problem to be solved before light and simple, fixed rpm 2-strokes might be unbanned.

Any ideas?
One does not want to waste fuel to re heat a damn catalyst..?

Aren't direct-injection outboard motors and snowmobiles still allowed there? And what about some motorcycles fitted with that transfer port injection (TPI) used by KTM and Husqvarna?

Clean at any rpm by injecting fuel directly into the cylinder AFTER the exhaust port is closed:
Aprilia's direct injection two-stroke engine concept

https://www.cycleworld.com/resizer/U...5JN7RELZYA.jpg

There a shaft driven air compressor involved and a lot of complexity.
Compare that to the simplicity and cost of Constant rpm 2-stroke.

That TPI system used by KTM and Husqvarna is not the same as direct injection, as the fuel is injected through the transfer ports instead of through the cylinder head. AFAIK the TPI doesn't rely on the compressor to provide a spray-guided injection similar to what Orbital Engines developed (and which seems to be what Aprilia was trying).