Quote:
Originally Posted by aerohead
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.
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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.
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..?