the clean two-stroke thread

[ceci]

This forum brings together the two best systems used to inject into the commercial 2S (DiTech & TPI).
The solution may be found in a fusion of both?

[Niels Abildgaard]

A imoral combination of fuel injektor and exhaust valve

[WilDun]

All very good ideas of course and most are actual reality through 'in field' experimentation - all good so far.

Just a couple of questions from an armchair (wannabe) engineer, - Is it true that NOx is formed in the squish clearance gap between the head and piston of current two strokes??

When we say that the transfer charge going into the exhaust from the 'A' ports is pure, what about the oil in that air? - I'm always rabbiting on about it I know - but after all, this is the cause of two stroke smoke (which no one seems to think is important) and some point out that you don't see it when going at speed.

Racing isn't the problem, it's puttering around the streets and taking off from an idle where the problem lies! so I believe it is very important - that's mainly why the two stroke has become the enemy.
Just about everything it puts out will be opposed by the "Greenies" and the general public (whose opinion is very important in all this) will see smoke as being obnoxious and will back them up! - smoke from the exhaust is often perceived by some to be 'smelly', but (significally) it is highly visible and not a good look these days!

[Vannik]

NOxes are formed above a certain temperature which is what the squish is trying to avoid, to prevent detonation. This does lead to unburnt hydrocarbons.

With a modern controlled oiling system the low speed smoke can be almost eliminated by supplying the oil required by the load and not just a function of rpm.

[ceci]

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.

.

The TPI to be effective there has to be a strong countercurrent that vaporizes the spray (otherwise it only deposits in the crankcase) and this only occurs in the mid-high RPM zone.
The transfer & admission at low RPM is only a smooth movement of gaseous masses with few inertias.

I
A standard Ditech runs up to about 8,000 rpm and surprisingly, un restricted to about 10,000 which is good but I think about their limit. A single injector also limits things to 10,000 RPM or less. Simply because an injector small enough to allow good low speed tuning becomes to small to get things done in the limited "Time" available at higher RPM. .

This is an attempt to fix that problem you describe



What is suggested is to use the DiTech as a main jet and the TPI as a power jet

[TZ350]

What is suggested is to use the DiTech as a main jet and the TPI as a power jet

Yes, I like that idea.

[WilDun]

NOxes are formed above a certain temperature which is what the squish is trying to avoid, to prevent detonation. This does lead to unburnt hydrocarbons.

With a modern controlled oiling system the low speed smoke can be almost eliminated by supplying the oil required by the load and not just a function of rpm.

Thanks Vannik,
I lived and rode bikes from the early sixties and started using this wonderful new "ashless" two stroke oil - all designed in the interest of reducing smoke and pollution!
A little later (late sixties) I had a 250cc Suzuki twin - it had a pump oiling system with the oil guided into main and big end bearings (hailed as a breakthrough then), then it disappeared and only now (50 something years later) I have seen it being hailed as a breakthrough - in these pages!
The pump could be adjusted and was controlled from the throttle position - it still smoked like hell, no matter how you set it! and after moving away from bikes for around 40 years, I have come back to study them again and have found that not a helluva lot has changed except 'band aid' additions to prop up its failings! - any real improvement was biased toward improving the horsepower and levelling the torque curve! - this was all happening when the 2 stroke was disappearing fast from our roads! - so that is why I am very sceptical (yes that's how we spell it here ) about all the "new innovations"!

Perhaps I'm wrong, but I'm just not seeing any real moves toward a clean machine - I do hope there are some convincing attempts in the pipeline!

[Norman]

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.

That is quite an improvement! Up to 21%..same power. Much less fuel escapes out the exhaust.

BRP has a solution on their 850 ETEC machines with an extra "boost" injector at the inlet. I was thinking with two TPI injectors the DI injector could be made with smaller finer spray for low load up to "medium" rpm. And as mentioned above use the TPI as "power jet".

[Pursang]

Firstly, good on you Haufen for creating this page.......

........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.….

Ken, your pursuit of Squishband Reed transfer is sound too, for the same reason. This is the ideal place for an update...Please!

Cheers, Daryl.

[Flettner]

That is quite an improvement! Up to 21%..same power. Much less fuel escapes out the exhaust.
".

The 21% was achieved on a very tight slow trail ride track with bugger all on pipe work. That appears to be where the worst area is for a carburetor bike. Even though the transfer steams aren't high inertia, the B port injector placement and timing have a big part to play in TPI efficiency.

[husaberg]

it may have been discussed but why not let time and overlap be your friend rather than enemy
why do we need a bike that revs to 14000 RPM?
We are not talking competition here where a engine of 125cc or whatever is ran to the extreme.

What about an extreme long stroke engine.
say 65mm bore and 105mm strioke
For no better reason than this gives 350cc and arround about 25ms at a max of 7000rpm

a 4T dirt bike of around that size would be 30-35 HP at the wheel.
As a KTM300 is more than fast enough for a non expert they make about 50HP
40 is likely what a CR500 made.

So somewhere in between maybe 40HP
if someone plugs in these bore and stroke into the Sim
with 180 duration a very mild pipe 30mm carb and a RGV250 reed valve
What does it look like?
With a long stroke and little little overlap i am picking it would be pretty clean.
Also with a low rev ceiling it would have the time to run DI.

Neils Sleeve i wager could be very clean if it was tuned for it

[Pursang]

it may have been discussed but why not let time and overlap be your friend rather than enemy.......

.......if someone plugs in these bore and stroke into the Sim
with 180 duration a very mild pipe 30mm carb and a RGV250 reed valve
What does it look like?
With a long stroke and little little overlap i am picking it would be pretty clean.
Also with a low rev ceiling it would have the time to run DI.

Ah Ha!, the KISS approach......maybe add in a big 'step' at the exhaust port and work on the A transfers for shortcut proofing rather than Max HP.

Cheers, Daryl.

[husaberg]

Ah Ha!, the KISS approach......maybe add in a big 'step' at the exhaust port and work on the A transfers for shortcut proofing rather than Max HP.

Cheers, Daryl.

A ex dam yes
a Deflector piston well i would not rule that out either
But yes.

The long stroke does give some obvious advantages if not chasing the nth degree of performance.

If i was being serious the CRM250 would be the starting point i guess.
Anyone ever rode or seen one.
I have posted the trapping valve before which was something Lotus were believe working on maybe for GM

[WilDun]

Husa, you are seeing things from the right perspective rather than from a competition/racing perspective only and that's refreshing!
I also do think we should rewind a little!

Toyota (and maybe others) did that - ie they made their bore/stroke 'under square' way back in the late eighties - they were four strokes of course but reaped great benefits with torque - they were good or better in that department than engines with fancy VVT etc and perfectly good for the average guy on the roads!

I feel that with the old 'split single' two strokes (championed by Puch) there was a great opportunity to keep the charges separate, but I felt that 'squish' and it's problems might be an obstacle there
However, Haufen indicated that it is probably not the problem I believed it might be - so I'll listen to him and consider the split single.

[Pursang]

a Deflector piston well i would not rule that out either

I'm impressed by Mr Scott's solution to creating efficient, compact combustion chamber(s), with squish, while using a deflector piston.

He did this over 100 years ago! A modern update of this configuration would not be difficult!

Maybe 3 or 4 chambers with 10mm plugs instead of the 19's or 22's that Scotty used. But, he could change the compression ratio by changing the plug reach!:

Note the decompressor valve 1/2 way up the cylinder wall (above Ex port). Similar one in the 490 Maico I'm working on (but in the back wall).
Kick starting with it engaged is like kicking over a 175! Thank Goodness!

Fact: Scott patented the Kickstarter (as we know it) in 1908

Cheers, Daryl