the clean two-stroke thread

[Haufen]

As our beloved two-strokes are likely to disappear in the not so distant future, this thread shall serve as pool a for anything clean two-stroke related.


The goal of this thread is to provide information, share the latest news and publications on two-stroke technology and discuss possible ways and technologies which would make for a clean yet still rather simple engine, especially:

- found an interesting link or engine or new tech on a two-stroke? Post it here.

- basics: why are two-strokes 'dirty' in comparison to four strokes (no, it's not the oil burning)

- brainstorming: what would a clean two-stroke ideally look like? Which technology / features would it use?

- bonus: if we find our brainstorming to be successful and maybe worth looking at more indepth, we might as well forward and / or publish our ideas or just build something by ourselves.

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Basics:
why two-strokes are 'dirty' and most four strokes are not that clean either. An excursion into emissions and legislation.

This is a work in progress, I will fill in further bits soon and try to keep it as compact as possible.

1) there are different kinds of emissions
NOx, CO2, HC, PPM etc. --> what is it, where does it come from and do we really need to know all of this?

2) main reason why two-strokes are referred to as 'dirty' (still not the oil burning)

3) legislation --> how clean do you need to be?

4) let me know if there is a special topic of interest you would like me to focus on, also. I have accompanied the development of a clean two-stroke engine in the past where I was responsible for performance and emissions. Due to an NDA I can not get too specific on that particular engine, but there are many general aspects which can be focused on.

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I am looking forward to many interesting discussions!

[ceci]

I do not know if it is a mistake of mine or the less gray smoke I see coming out the more flame comes out when the lighter close

[Flettner]

Uniflow block, opposed piston, 640cc. Differential piston sizing, larger transfer piston, smaller exhaust piston. Utilizes squish as a cosiquence of these differnt piston diameters. Two plugs per cylinder. I might have gone a bit too extreme on this one I think.

[Flettner]

I guess Im allowed to insert this image?

[WilDun]

Good to see you have this thread under way and I hope it brings a lot of ideas online! - I won't launch into any big discussions (just yet).

As you no doubt know, I believe the "visible" pollution ('smoke') as seen by the general public (consumers) has a huge impact on sales these days - I acknowledge they are only seeing the tip of the iceberg of course, but that alone will contribute to a change in course, (ie using four strokes instead) to keep consumers happy! - the smoke alone is a bad look today and (rightly or wrongly) it is seen as the culprit and puts people off two strokes!

Good luck and thanks for starting the thread Haufen.

[ceci]

Good to see you have this thread under way and I hope it brings a lot of ideas online! - I won't launch into any big discussions (just yet).

As you no doubt know, I believe the "visible" pollution, seen as 'smoke' by the general public (consumers) has a huge impact on sales these days - I acknowledge they are only seeing the tip of the iceberg of course, but that alone is/has contributed to a change of course, to keep the consumers happy!.

Good luck and thanks for starting the thread.

The double rule of the game allows these types of solutions, which are only commercial solutions.
With them the Euro4 homologation standards are met and the majority of the population that demands that they are met is satisfied.
And the owner is allowed, if he wishes, to manipulate the system according to his own criteria.

[BMWST?]

a good portion of the new intake charge is lost out the ehaust port.One of the most promising ideas in my mind would be a fuel injected two stroke where the fuel is injected AFTER the exhaust port is closed

[Pursang]

a good portion of the new intake charge is lost out the ehaust port.One of the most promising ideas in my mind would be a fuel injected two stroke where the fuel is injected AFTER the exhaust port is closed

Sounds Simple doesn't it?

Issues include the need for a fully vaporized fuel air mixture, before ignition.
One of the advantages of crankcase induction is that the mixture enters at say 20C. then thrashes around in there for around 15 cycles, absorbing heat from the crank & rod & bearings & Piston & cylinder wall, to finally be transferred to the cylinder at up to 100C. Hopefully thoroughly mixed and no longer Wet and hard to completely burn. (Not guaranteed, in my experience).

Some of the Direct Injection techniques include Very High pressure, to maximise atomisation, or injecting fuel pre-mixed with air.
Mahle's "new" process with pre-combustion in a pre-injection chamber will need to prove to be commercially successful in Automobiles (again) before it ever gets applied to 2 Strokes.

Flettners TPI uses injection against the transfer air flow to good effect, but afaik, this is not timed to EPC.

Another technical/mechanical problem is the very short time period available between EPC & ignition as rpm increases.

Cheers, Daryl

[Niels Abildgaard]

Make a side-exhaust valve and inject fuel directly on valve

[WilDun]

As our beloved two-strokes are likely to disappear in the not so distant future, this thread shall serve as pool a for anything clean two-stroke related.................
- bonus: if we find our brainstorming to be successful and maybe worth looking at more indepth, we might as well forward and / or publish our ideas or just build something by ourselves.

-----------------

Basics:
why two-strokes are 'dirty' and most four strokes are not that clean either. An excursion into emissions and legislation .......

1) there are different kinds of emissions
NOx, CO2, HC, PPM etc. --> what is it, where does it come from and do we really need to know all of this?

2) main reason why two-strokes are referred to as 'dirty' (still not the oil burning)

3) legislation --> how clean do you need to be?

4) let me know if there is a special topic of interest you would like me to focus on, .......

---------------

I am looking forward to many interesting discussions!

We understand that you will be a little restricted and not be able to disclose specific things - but hopefully you will still be able to provide some interesting stuff here (otherwise you wouldn't have started the thread) - patents are a totally separate subject and tend to take away a lot of pleasure from those people who just like to invent things, but unfortunately they are reality!

A slightly modified excerpt from a post I made on "Oddball" thread ;-
In a road going machine it has to cope with constantly being used throughout the rev range from idle to full revs ( it is not good at doing that!) - it prefers to be efficient at a certain part of the rev range! I'm not a fan of chambers as some of you might know, but ironical as it might be, expansion chambers could possibly be excellent in that rev band!! - however I still see the mixing of incoming and outgoing gases as a problem and this will cancel out its usefulness - that, along with both the Schneurle transfer system and squish combustion chambers!

Burning oil emissions, although apparently not the real culprit, still needs to be addressed though, it is highly visible and it matters to the general public who, no matter what, will still percieve it as being bad and go for a four stroke instead - and they are the potential customers who can keep it all going!

O.P. engines using HCCI style combustion and the use of hybrid type transmission (without huge battery packs) could help to cure many of the above problems .....but of course, they do have their drawbacks as well! - All this may be only my theory, but I believe in it, and will do till someone proves me wrong!

[Norman]

I guess Im allowed to insert this image?

Flettner, do you have an idea how good the TPI system is to avoid fuel short cutting out the exhaust? That is to lower emissions. Is there a need for a Direct Injector in addition to the TPI to optimize for emissions you think?

[Flettner]

Flettner, do you have an idea how good the TPI system is to avoid fuel short cutting out the exhaust? That is to lower emissions. Is there a need for a Direct Injector in addition to the TPI to optimize for emissions you think?

Well, this TPI bike delivered 14 / 21 % fuel savings over my carburetor YZ, depending on how much 'on pipe' work. Same day, same track, alternating riders. Over many events. Dyno test showed similar top end power between the two bikes.
DI is a sledge hammer to crack a nut, expensive and complicated.
All this just because the exhaust port is too close to the transfers. Thats why my new engine devlopment has gone back to opposed piston. I believe I could get similar or better emmissions using a carburetor (with uniflow) as a DI engine. In saying that I will be using a form of TPI on my new Uniflow.

[Murray]

The big come back

https://www.stuff.co.nz/motoring/122...be-coming-back

[TZ350]

Flettners TPI uses injection against the transfer air flow to good effect, but afaik, this is not timed to EPC

A lot of the air that short circuits out a two strokes exhaust port comes from the A transfer ports.

With the injectors in the B ports you lose mostly clean air through short circuiting. The injectors should be timed to finish somewhere between BDC and TPC where the pipe should be sucking its hardest.

Not all the air transferred gets fuel injected into it. Some is lost to the exhaust system. Hopefully mostly clean air from the A ports. It is the last bit of air drawn into the cylinder around BDC and before TPC is what we hope to keep trapped in the cylinder. Hopefully most of the air from the B ports with the fuel in it.

This end point timing can also minimize the amount of fuel expelled back out through the carburetor. Proper timing of the injection end point can noticeably help with fuel efficiency and exhaust cleanliness.

Well, this TPI bike delivered 14 / 21 % fuel savings over my carburetor YZ, depending on how much 'on pipe' work. Same day, same track, alternating riders. Over many events. Dyno test showed similar top end power between the two bikes.

[ken seeber]

Firstly, good on you Haufen for creating this page.

Ceci, that’s beautiful. At Orbital we used FID (flame ionization detection) instruments (Beckman and Horiba) for HC detection. Lots of explanations of these, here’s just one: https://www.youtube.com/watch?v=BJzqdzLY2KU The one in the vid is a superb example of the issue, unburnt HC’s aplenty.

This confirms the main issue with 2 strokes: unburnt HCs.

NOx levels are inherently low. These are created by high pressures and temperatures. A 4 stroke only fires every second rev, so, power for power, its pressures and temps are higher. A win for 2 strokes.

Norman suggested fuel injection after EPC. Getting the fuel into the cylinder before EPC and therefore mechanically prevent fuel loss out the exhaust was exactly what Orbital and ETEC were doing. Mind you, certainly the Orbital system injected well before EPC at high speeds and loads, but this took into account the transportation time of the fuel charge.

Neil’s pursuance of the OP principle is sound, essentially putting the fuel charge into the working chamber some distance away from the exhaust port(s).

The goal of getting 2 strokes to be clean is to complete the combustion process within the engine, not in the exhaust or never.….