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

[Andyman]

Originally Posted by Logic

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.

...

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..?

I'm not sure that Aerohead disapproved of this subject. I think his point was that the legal requirements could be difficult to satisfy for new two stroke engine products in the US. I thought that the information he gave us was useful. If a new two stoke engine could meet the emission requirements it may be accepted. With the recent changes at the EPA, that might be easier. I hope we are not going to be breathing more pollution soon, but we probably will because of the large amount of fuel being used or burned up in wars. If we can clean up old two stroke engines, it would be a step in the right direction.

I do have an idea. I suggest wrapping the expansion chamber (tune-pipe) in insulation so the exhaust gas will be hot enough for the catalyst. The centrifuge may not be needed if the two stroke oil burns cleanly. I think it would be useful to add valves to the transfer and exhaust ports. They could be rotory valves so they can operate quickly. That could improve engine efficiency by delaying the opening of the exhaust port. The transfer port opening could also be delayed until after the piston reaches the bottom of the stroke to allow enough time for most of the exhaust to leave the cylinder before the new fuel mixture starts to go in. This might work better if a reed valve is added to the bottom of the transfer port and the volume of the transfer port is increased.

[Logic]

Originally Posted by Andyman

I'm not sure that Aerohead disapproved of this subject. I think his point was that the legal requirements could be difficult to satisfy for new two stroke engine products in the US. I thought that the information he gave us was useful. If a new two stoke engine could meet the emission requirements it may be accepted. With the recent changes at the EPA, that might be easier. I hope we are not going to be breathing more pollution soon. If we can clean up old two stroke engines, it would be a step in the right direction.

I do have an idea. I suggest wrapping the expansion chamber (tune-pipe) in insulation so the exhaust gas will be hot enough for the catalyst. The centrifuge may not be needed if the two stroke oil burns cleanly. I think it would be useful to add valves to the transfer and exhaust ports. They could be rotory valves so they can operate quickly. That could improve engine efficiency by delaying the opening of the exhaust port. The transfer port opening could also be delayed until after the piston reaches the bottom of the stroke to allow enough time for most of the exhaust to leave the cylinder before the new fuel mixture starts to go in. This might work better if a reed valve is added to the bottom of the transfer port and the volume of the transfer port is increased.

People make the mistake of liking to think that electricity, EVs and even 4-Strokes are clean Andyman. They are not:


https://en.wikipedia.org/wiki/World_...nd_consumption

Wind blows.
We all of us, anywhere, breath in an air molecule that's been in for eg: Marilyn Monroe's lungs, once every 30 years IIRC.
And she exhaled what? A millionth of what a car or power plant does in a day!?

Then consider that city driving, which is 98% of all driving worldwide means accelerating WEIGHT from robot to robot etc, and that, that accounts for 68% of fuel used!
(vs 14% for aero)

So ye; the lighter we can make vehicles...
and 2-strokes win here, as far as available engines go.
(Better would be Linear Generators, but that's not going anywhere fast atm)

The other thing to consider is that this clean 2-stroke is a ~250cc CONSTANT rpm engine to replace the average load of around 20kw of a normal, variable rpm engine, in a series hybrid.
This lowers the expensive, weighty battery requirements dramatically and makes optimizing the engine (of any sort) far-far cheaper and simpler.

ie: There is no need for fancy, expensive valves and direct injection etc, that clean up the emissions from a variable rpm engine:
The ports (and tune pipe etc) can all be optimized to open at the optimal/desired crank angle/rpm... easily and cheaply!

I LIKE the wrapped tune pipe idea though! Thx!
If it's designed fort the extra volume; that's good thinking (of a simple solution!) and can be extended to any centrifuge too, for very little in extra weight.

[cRiPpLe_rOoStEr]

Originally Posted by Andyman

If a new two stoke engine could meet the emission requirements it may be accepted. With the recent changes at the EPA, that might be easier.

In fact it is possible to make an emissions-compliant 2-stroke engine, yet it would be harder to justify from a marketing standpoint after some countries effectively banned the imports of new 2-stroke motorcycles around 2008, and some of those countries in fact have a larger motorcycle market than the United States. Not to mention the latest successful 2-stroke engines became more concentrated around lower displacement brackets.

[Logic]

Originally Posted by Andyman

... I think it would be useful to add valves to the transfer and exhaust ports. They could be rotory valves so they can operate quickly. That could improve engine efficiency by delaying the opening of the exhaust port. ...

Well..!
My apologies for not putting more thought into your suggestion/s Andyman.
I was fighting with aerohead at the time and ...er... hot headed.
(Wish I could call it a debate, but that involves deduction and responding to the points/questions posed by your contender)

https://www.youtube.com/watch?v=5czHDU6pK8E

That's very clever for being simple and great for a wide rpm range.
But for constant rpm it's still unnecessarily complex and the supercharger adds weight and takes up space doing the work that the existing crankcase was/is doing.

[Logic]

"The engine of our dreams" above:
Well it comes out of someone else's DIY garage.
Not the 1st time this kind of thing has happened.

https://www.youtube.com/watch?v=MC3wNFApaKE

[cRiPpLe_rOoStEr]

Originally Posted by Logic

That's very clever for being simple and great for a wide rpm range.
But for constant rpm it's still unnecessarily complex and the supercharger adds weight and takes up space doing the work that the existing crankcase was/is doing.

It might be quite hard to provide oiling for a turbocharger to operate with a conventional 2-stroke, but it's not undoable at all. BRP now uses turbochargers on some of its snowmobiles. Sure a turbocharger might not be so dumproof at all, but it has the advantage of usign waste energy from the exhaust stream instead of increasing drag to the engine like a supercharger.

[Ecky]

This is peripheral to your idea, Logic, but Mazda is using the rotary again in nearly the exact way described - as part of a serial hybrid. Rotaries have many of the same characteristics (and drawbacks) of two strokes, and even have similar power density.

Best I recall, Mazda managed to greatly improve the rotary efficiency and emissions by coupling the rotor to a small motor, which actually slows down and speeds up the rotor during small parts of its revolution, to achieve different combustion chamber characteristics. One could similarly do this with a reciprocating piston engine, for example changing the dwell time or speeding the piston up as it approaches TDC.

I don't see why a two stroke could not be made extremely clean or efficient as long as it did not need to operate in a wide range of conditions. It's just a matter of implementation. However it would almost certainly need to be paired with a relatively large battery, given that the compromises of running outside its ideal conditions would be much more severe, and extra buffer would be needed to prevent that.

[Logic]

Originally Posted by Ecky

This is peripheral to your idea, Logic, but Mazda is using the rotary again in nearly the exact way described - as part of a serial hybrid. Rotaries have many of the same characteristics (and drawbacks) of two strokes, and even have similar power density.

Best I recall, Mazda managed to greatly improve the rotary efficiency and emissions by coupling the rotor to a small motor, which actually slows down and speeds up the rotor during small parts of its revolution, to achieve different combustion chamber characteristics. One could similarly do this with a reciprocating piston engine, for example changing the dwell time or speeding the piston up as it approaches TDC.

I don't see why a two stroke could not be made extremely clean or efficient as long as it did not need to operate in a wide range of conditions. It's just a matter of implementation. However it would almost certainly need to be paired with a relatively large battery, given that the compromises of running outside its ideal conditions would be much more severe, and extra buffer would be needed to prevent that.

Thx Ecky.
Yep I have been looking at rotaries for power density and wondering about their efficiencies etc at constant rpm.
The Mazda Iconic SP is both a beautiful car and interesting in that the plan is use a 2 rotor in a PHEV.

It looks to be pretty aero too!
NB the different left and right, mirrored mags that look like they suck some air out from under the car.



I NB that any engine designed and optimized for constant rpm is not only more efficient but a hell of a lot cheaper!
ie: A carburetor and old school ignition, properly tuned, is fine for constant rpm.
(Then tuned length intake and exhaust plumbing is always optimal and cuts down on emissions)

I have not looked into how large the battery needs to be to avoid varying loads on the 'genset' as the trend seems to be to make them large enough to cover the average trip distance with the engine off and a wall charge and that looks to be more than enough to avoid varying engine loads.

If one were to also use ram air to help induction and the vacuum behind vehicles to help extract exhaust and fill the vacuum, airspeed is the only variable, but a decrease in pumping losses should only require a decrease in fuel (leaning out) to keep keep rpm constant.

[cRiPpLe_rOoStEr]

Wankels are cool, but 2-strokes seem to remain somewhat more dumbproof. OK, a Wankel is also meant to have fewer parts than a 4-stroke, which would in theory make it easier to work on them, but they require a more specific knowledge to assemble and mantain them properly...