2 stroke thread (with occasional F1 relevance!)

[uniflow]

J.A.W, been peeking at ESE works tuner? Lots of interesting stuff happening there alright. (from time to time).

[J.A.W.]

J.A.W, been peeking at ESE works tuner? Lots of interesting stuff happening there alright. (from time to time).

Uniflow, you know it.. & inspite of it being a modest enough thread - sited on a basic bike forum - in far off New Zealand..
..somehow I suspect others, (KTM, Rotax/BRP, Polaris,Yamaha.. & other Euro 2T makers, perhaps) likely are, too..

[uniflow]

More than you might know James.

[J.A.W.]

A fairly basic BRP/Rotax presentation/offering - a test/results comparison - of current 2T fuel injection systems.
Here: http://www.a3ps.at/sites/default/files/ ... oxhall.pdf

[J.A.W.]

As a topical comparison aside, one which demonstrates the inherent efficacy of the 2T for G.P. racing..

At the Australian FIM G.P. at Phillip Island - last weekend, the Moto 2 class - CBR 600cc/4cyl Honda 4T powered (which replaced the pukka/pursang G.P. 250 bikes) - had a final* run at the fast-flowing track..

Miquel Olivera won in 39`25.9 - averaging 169.2 km/h - with a top speed of 285.2 km/h.
(Tito Rabat did quickest ever Moto 2 lap of 1`32.470, in 2014).

Back in 2008 on a 250cc 2T Gilera, Marco Simoncelli won in 39`02.5 - at an average speed of 170.9 km/h,
( quickest lap 1`32.075) & a top speed of 279.85 km/h.

Well, so much for progress then, huh..


* The modified production Hondas are to be phased out - replaced by 750+cc/3cyl Triumph units - in 2018.

[manolis]

Hello all.

Thanks J.A.W. for the Rotax/BRP link.

Here are some parts from it, with some text "underlined", and some "references" magnified to make it more "readable":




It seems that for the 600cc 2-cylinder test-engine (78KW (106bhp) / 8,200rpm) the ETEC is better than the LPDI (Low Pressure Direct Injection) only below 20Kw (27bhp), i.e. below 1/4 (one quarter) of the peak power.
Strange.
Rotax mentions that they have made, so far, more than 500,000 ETEC engines for marine use and for sleds; these engines operate, most of the time, above 50% of their peak power.
The SDI (or TPI of Rotax) was used from 2003 to 2009 in the Skidoo sleds.




High revs with the engine providing less than 50% of its peak power.
In the ETEC the injection ends more than 100 crank degrees before the ignition (to give time for the preparation of the air-fuel mixture), several degrees earlier than the closing of the exhaust port, which causes a substantial quantity of fuel to be lost in the exhaust.

According the Rotax, the substantially simpler - cheaper LPDI (Low Pressure Direct Injection) appears better that the famous ETEC.

Interesting the "Injection Port" of the LPDI. At heavy load / high revs a part of the injected fuel lands on the piston skirt and is lost to the exhaust during the next scavenging.




Here the engine operates at peak power (WOT, 8,200rpm).
Spot on the injection timing of the ETEC and of the LPDI.
In the ETEC, the exhaust pressure waves return only a part of the fuel (inertia of the fuel droplets); the rest is lost.
The LPDI appears substantially better in these revs / load.




According the Rotax, the optimum is the combination of the ETEC (at low revs, light loads) with the LPDI (at high revs, heavy loads).


In all cases the inevitably late (classic design) exhaust closing is the key problem and the key limitation.

In the PatATE:



the exhaust can close earlier; substantially earlier; which may prove a good solution of a long existing problem.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, & thanks for the well considered/presented post..

I'd note that the Rotax test unit was evidently of the basic porting/soft-tune type, given the output figures..

The latest high performance Ski-Doo units do already feature a dual-injection set-up,
& the most recent (& larger capacity) Evinrude HO (high output) engines now incorporate variable exhaust port timing.

Perhaps a variant of the current F1 DI system - can also be utilized to advantage - & no poppet valves to crowd in..

[J.A.W.]

Roger DeCoster, multiple World MX Champion, & with a life-career in the sport, reckons: "Two-strokes are good for the sport."

See here: http://www.mxlarge.com/2017/10/28/decos ... -2-strokes

[J.A.W.]

Uniflow, this YZ 345 article might be of interest, given your own efforts in this area..

http://www.dirtbikemagazine.com/two-str ... ries-yz345

[manolis]

Hello J.A.W.

You write:
"The latest high performance Ski-Doo units do already feature a dual-injection set-up,"


This is the new 850ETEC of Rotax / Skidoo for sleds:



Besides the typical ETEC on the cylinder head, it has additional booster injectors before the reed valves.

I can't see how this arrangement can solve the HC emissions problem of the ETEC at high revs / heavy loads, as Rotax describes it in the following plot (the red area is where the ETEC is better, the green area is where the LPDI is better):



With the booster injectors of the 850ETEC actuated, the crankcase is no longer fed with clean air, but with air-fuel mixture (just like the old 2-strokes, nothing to do with the TPI), which means the scavenging is realized with air-fuel mixture and not with clean air.

And as Rotax notes: the exhaust pressure waves can return to the cylinder some of the unburnt fuel passed to the exhaust, but not all.

According the recent (September 2015) presentation of Rotax at http://www.a3ps.at/sites/default/files/ ... oxhall.pdf ,
a LPDI (Low Pressure Direct Injection) combined with the ETEC could really improve things.




You also write:
"& the most recent (& larger capacity) Evinrude HO (high output) engines now incorporate variable exhaust port timing."


I can't get it.

The problem of the ETEC, as Rotax explains it, is the operation at higher revs / heavier loads, wherein the LPDI appears substantially better.

I can't see how the variable exhaust port timing can soften / solve this (HC emissions) problem of the ETEC.

At higher revs / heavier loads (wherein the exhaust port has to be kept fully opened) the late injection reduces the time for preparation of the air-fuel mixture before the ignition (worsening the combustion efficiency and the emissions), while the early injection enables a quantity of the injected fuel to pass directly to the exhaust and be lost.

Focusing on the HC emissions, the variable timing of the exhaust port would be really beneficial for the LPDI 2-strokes, because it would spread the (green in the Rotax Plot) area wherein the LPDI is better.

Thanks
Manolis Pattakos

[uniflow]

Manolis I'll say it again, a twostroke without the ability to process this exhaust return pressure wave is a lawnmower.
Better to master the TPI system, mark two version not shown yet I belive is the answer. More power AND better emmission control, I have an interested party so can say nothing yet about it yet.
Haha, not KTM

[manolis]

Hello Uniflow.

You write:
"a twostroke without the ability to process this exhaust return pressure wave is a lawnmower."


Quote from https://www.f1technical.net/forum/viewt ... start=2170 (3pages ago):

Since the lawn mower engine



is the favourite reference here, let's see how it handles the charge.

The exhaust port opens early, otherwise the crankcase, when the piston opens the transfer port, will fill with burnt gas.
After the end of the transfer, the still wide open exhaust port provides a "free way" to the fresh mixture to escape. Say as the Atkinson - Miller cycle does in the 4-strokes, but here anything that leaves the cylinder is lost and pollutes.
At the end of the exhaust, a good part of the entered air or air-fuel-mixture is not in the cylinder, and the torque drops dramatically.


And here is how things work in the PatATE:

The exhaust can open later; the rate the exhaust opens is substantially higher than in a conventional allowing the faster blow-down even with substantially later exhaust opening.
From the beginning the PatATE has a gain (on thermal efficiency and on torque) due to the extended expansion allowed by the later exhaust opening.

At the end of the blow-down the transfer opens and the scavenging starts.
The air / air-fuel mixture from the crankcase gathers progressively speed and inertia (as happens during the overlap of the sport/racing 4-strokes, article of David Vizard), with the pressure in the crankcase dropping progressively.
The entering air-mixture expels the burnt gas out of the cylinder.

Then the exhaust closes. The exhaust can close more than 50 crank degrees earlier than in the conventional lawn mower 2-stroke engine.

During the closing of the exhaust, the rotary valve of the PatATE opens the intake port (without a reed valve to delay the beginning of the intake stream).

The vacuum created in the crankcase due to the inertia of the air / mixture going from the crankcase to the cylinder, suctions new air /mixture into the crankcase through the open intake port. Like a supercharger, but for free.

When the transfer port finally closes, the quantity of air /mixture trapped into the cylinder for compression / combustion / expansion has nothing to do with a lawn mower.

According the previous analysis, the quantity of air /mixture that can be trapped into the cylinder of the 2-stroke PatATE (or, differently, the volumetric efficiency) is comparable with the quantity of air /mixture trapped in the cylinder of the sport-racing 4-strokes, like the Ducati Panigale.
And if you double the specific torque of the Panigale (because the PatATE is a 2-stroke), the expected specific torque becomes more than 30% higher than in the green KTM EXC250TPI / 2018.


Where is the mistake or the trick?

Does the PatATE design fit with lawn mower engines or with green super-2-strokes?

End of Quote




I got no justified answers, yet.

The fact that, so far, the 2-strokes were/are strongly based on the exhaust pressure waves to achieve high peak power (and a BMEP not too much lower than the BMEP of the 4-strokes) is making it a common practice, not a "law".

On a similar thinking, according the common practice the 2-strokes could not even "dream" complying with the euro4 emission standards; however KTM, with their EXC250/300TPI models of 2018, changed it.




You also write:
"the TPI system, mark two version not shown yet I belive is the answer. More power AND better emission control, I have an interested party so can say nothing yet about it yet.
Haha, not KTM "

This time do apply for a patent first, to protect your invention / idea; otherwise KTM and the rest engine makers will have "the last laugh".

And if you need any help (for free) for the formalities of the patent application, just email me.

Thanks
Manolis Pattakos

[Pinger]

The exhaust can open later; the rate the exhaust opens is substantially higher than in a conventional allowing the faster blow-down even with substantially later exhaust opening.
From the beginning the PatATE has a gain (on thermal efficiency and on torque) due to the extended expansion allowed by the later exhaust opening.

If the above is such an advantage, Mercury, Evinrude, et all must rue shifting from cross-flow scavenging to loop, as with cross-flow scavenging they enjoyed an exhaust port width that easily matches yours.

At the end of the blow-down the transfer opens and the scavenging starts.
The air / air-fuel mixture from the crankcase gathers progressively speed and inertia (as happens during the overlap of the sport/racing 4-strokes, article of David Vizard), with the pressure in the crankcase dropping progressively.
The entering air-mixture expels the burnt gas out of the cylinder.

Inertia in a short arduously contoured duct that compares favourably with the inertia obtained by deploying a very long unobstructed and essentially straight tract? And that isn't even factoring in the 4T pumping element that initiates the flow or the extended time frame relative to the 2T that enables it.

The vacuum created in the crankcase due to the inertia of the air / mixture going from the crankcase to the cylinder, suctions new air /mixture into the crankcase through the open intake port. Like a supercharger, but for free.

Well if that is so effective why do all the 2Ts that operate at higher than 4bar BMEP employ a returned -ve pulse to achieve that effect?
Didn't read up on exactly where the pumping losses in a 2T occur - did you?

[uniflow]

Just wander out to your shed Manolis and build this engine of yours. No amount of talk here is going to convince you, do some experiments with and without a tuned exhaust, see for yourself. The energy recovered from the exhaust system on a twostroke is way more than a little gas inertia in a transfer port, anyway a rotary valve induction already utilises this small transfer advantage. Different trapping valve arrangements in the exhaust port have been tried many times by different people, I don't see it in production yet (Subaru come to mind)
As for the rotary drum inlet (that is what we are looking at) its opening and closing is too slow as compared to a large dia rotary disc valve inlet. Rotary drums were abandoned in the 1930's, DKW did a lot of work on these but all eventually ended up rotary disc valve, then these days we have the reedvalve sideshow, rotory disc engines still make more ultimate power. With the variable dics valve housing I have developed we can have the best of all timing worlds. Good strong low end with early valve closing and then strong top end with the servo adjusted late valve closing. All built tested and in most cases entered and competing in real race events. Good race results would require a much better rider though

[manolis]

Hello Pinger.

You write:
“If the above is such an advantage, Mercury, Evinrude, et all must rue shifting from cross-flow scavenging to loop, as with cross-flow scavenging they enjoyed an exhaust port width that easily matches yours.”


They could shift to cross-flow to achieve a faster blow-down.
But the side effects of the cross-flow scavenging make it a worse solution.

On the other hand, with the classic loop scavenging the exhaust port can be larger and larger (in expense of transfer port area and of short-circuiting) to give a faster blow-down at higher revs.


Quote from page 133, https://www.f1technical.net/forum/viewt ... start=1982 :

Here is the port map of the famous Aprilia RS250 of 1999 (two cylinders in V90, oversquare design with 56mm bore and 50.6mm stroke):



The porting is focused on the faster blowdown: the “peak” (?) exhaust duration is 209.3 degrees and the “typical” (?) exhaust duration is 193.4 degrees, while the duration for the side transfer ports is only 129.6 degrees and the duration for the boost port is only 127.3 degrees.

The transfer is not only 64 degrees narrower than the exhaust, but its maximum (at the BDC) is not bigger than the maximum of the exhaust.

The above way of presenting the porting of a 2-stroke does not fit with the asymmetrical porting of the PatATE.

Here is a different presentation of the porting of a, say, modified to PatATE Aprilia RS 250:



The ports of the Aprilia RS250 are shown by black line.

The red triangular is the exhaust of the PatATE RS250, the blue triangular is the transfer of the PatATE RS250.

Going from top to bottom:

The exhaust of the PatATE starts opening substantially later (at, say, 87 degrees before the BDC) than the exhaust of the original RS250 (which opens at 105 / 97 degrees before the BDC).

The (red) exhaust opens at a higher rate than in the RS250.
Soon the exhaust area of the PatATE gets larger than the exhaust area of the RS250 (and as mentioned before, the Aprilia RS250 is focused on a larger exhaust area for the sake of a faster blowdown).

Some 20 degrees later the transfer (blue) of the PatATE starts opening at a very slow rate, giving time to the blowdown to complete. At the angle wherein all the transfer ports of the original RS250 open, the area of the transfer of the PatATE is still quite small, with a substantially smaller rate of increase.

At the BDC the rate of exhaust closing and the rate of transfer opening of the “PatATE” are about the same.
At the BDC the area of the exhaust port is still larger than the area of the original RS250 exhaust port.

As the piston moves towards the next (lower in the diagram, see the beige arrows) TDC, the transfer of the PatATE strengthens and the exhaust weakens / reduces until it closes completely.

For another 20, or so, degrees the transfer of the PatATE remains open to complete the transfer, while the exhaust is closed.

According the plot, the transfer remains open several degrees later than the transfer of the original RS250; also the exhaust of the RS250 remains open several degrees after the closing of the transfer of the PatATE.

On the same diagram, going from left to right is like moving along the periphery of the cylinder, with the zero angle being at the center / middle of the exhaust ports.

The exhaust of the RS250 covers, at maximum, about 120 degrees on the periphery of the cylinder, the transfer of the RS250 covers the rest cylinder but has, necessarily, substantially shorter height.

The exhaust and the transfer of the PatATE extend, each, for some 180 degrees along the periphery of the cylinder, but they are substantially asymmetrical relative to the BDC: the exhaust is significant before the BDC (blowdown, upped half of the plot) while the transfer is significant after the BDC (filling of the cylinder by the compressed gas in the crankcase, lower half of the plot).
The height of the transfer and the height of the exhaust are equal.

End of Quote




You also write:
“Well if that is so effective why do all the 2Ts that operate at higher than 4bar BMEP employ a returned -ve pulse to achieve that effect?
Didn't read up on exactly where the pumping losses in a 2T occur - did you?”


In the following post - reply to Uniflow - the BMEP of the OS18TZ is well above 10bar.
And, unless I am wrong, it is not based on a tuned exhaust.

Thanks
Manolis Pattakos