2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Even if using non-moving mechanical parts, there are ways & means, inc' perhaps by
managing flow energies, & coiling the linear pipe-work into a space-convenient helical shape.

See below a drawing of a patent expired double-cone system:

[manolis]

Hello J.A.W.

You write:
“Hi Manolis, no designer who is serious about improving the high-performance S.I. 2T,
can blithely ignore the tremendous effects on power/efficiency of a tuned exhaust.”


If it has to do with conventional 2-strokes, yes.
If it has to do with heavily unconventional 2-strokes, not necessarily.

Here is the PatATE and its ports timing plot:





Obviously it is a 2-stroke.
However its port timing is “closer” to a racing 4-stroke than to a conventional 2-stroke.
Its transfer closes substantially later than the exhaust.
A tuned exhaust can’t make big difference (as it does in a conventional 2-stroke).
The geometry allows the trapping of more fresh charge: after the closing of the exhaust there is plenty of transfer port-time-area for the transfer to complete, making the breathing heavily un-conventional.
And if a compressor (or turbocharger) is used, it can make lots of power (without tuned exhaust).



Similarly, the OPRE Tilting of the Portable Flyer has a substantially unconventional breathing which focuses not in the tune exhaust, but on the tuned intake-transfer.





When the transfer ports open, the fresh charge at the transfer pipe and in the scavenge pump is well compressed augmenting the beginning of the scavenging and the sweeping of the cylinder. Later the transfer-intake path “opens” and the scavenging continues “tuned”.

A tuned exhaust doesn’t seem necessary. At least, not yet.

The OPRE Tilting fits well with the Portable Flyer: lightweight (for its capacity), two “direct” power output shafts (the two counter-rotating shafts), true vibration-free, can be reliable at high revs (for the same rpm, the mean piston speed is less than half than that of a typical 2-stroke), its specific lube consumption can be lower than the conventional 2-stroke, etc, etc.

For its capacity, the weight of the OPRE Tilting is small, as well as its external dimensions and the distance of its two crankshafts (opposed piston, easy and rid-of-load synchronization).
Instead of using a tuned exhaust, its capacity can be increased with lower “penalty” on the weight and cost.

I prefer to increase the capacity of the two OPRE Tilting engines of the Portable Flyer than to carry a pair of tuned exhausts above my back-shoulders.

The current design uses a pair of OPRE Tilting engines, 350cc each, i.e. 700cc in total. They will run between 7,000 and 9,500rpm (7 to 9.5m/sec mean piston speed).
In comparison, the KTM 300 EXC TPI running at “only” 8,000rpm has 19m/sec mean piston speed.

So, there is reasoning behind the choice of not using tuned exhaust.



You also write:
“Even if using non-moving mechanical parts, there are ways & means, inc' perhaps by
managing flow energies, & coiling the linear pipe-work into a space-convenient helical shape.
See below a drawing of a patent expired double-cone system:”


Here is the “double cone” complete patent document from the US-PTO:

https://www.pattakon.com/tilting/Double ... 701960.pdf

The space below the rotors of the Portable Flyer needs to be as rid-of-obstacles as possible:



Deflecting the downwash of the propellers, the pilot controls the flight.

If you could make a sketch of how you imagine the use of the "double cone" exhaust in the OPRE Tilting, it would help.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, certainly a thoughtfully designed 2T exhaust system which will both
'earn its keep' in power gains to offset its weight, with acceptable output levels
of sound/gas emissions - yet also not be too bulky - is for sure, a needful task.

Here are a couple of ideas in image form, one from the past, & a current one from Rotax.

[J.A.W.]

& perhaps add some dimensional inspiration from the Klein bottle?

[manolis]

Thanks J.A.W.

If, without tuned exhaust, the power of the OPRE Tilting engine proves inadequate for the Portable Flyer, then tuned exhausts will be added.



KLEIN BOTTLE, MOBIUS STRIP etc.

Here is a non-Mobious (two-sided, with two boundaries) toothed belt:



and here the same non-Mobious toothed belt stereoscopically:



More at https://www.pattakon.com/pattakonPatBelt.htm


Here is a Mobious strip:



A Mobius strip is a one-sided nonorientable surface having a boundary.


And here is “your” Klein bottle: a one-sided nonorientable surface without boundary. While the Klein bottle has no boundary, it cannot help "hitting" itself; it is the "curve / intersection" where the “neck” (from right bottom) gets into the “main bottle”:



Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, I'd have to suggest that a properly designed exhaust is a must nowadays in 2021, since
surely no one ought to suffer the needless addition of noxious noise & gas levels from an open exhaust
blasting all over them, while concentrating on mastering the requirements of a novel flying machine.

As for the Klein bottle example, do compare the previous drawings, those of dual opposed cones,
a flattened expansion chamber wound coil-like & the blind-end Rotax curved multi-cone turbo-pipe.

The Klein bottle serves as an inspiration for spatial conservation, so given adapted geometrics/bleed
vents in actual use as a functional 'shaped-charge' 2T exhaust, & a practicable approach utilizing
such features as shown in the drawings - might be incorporated, all with due regard to seeking efficacy
in sonic wave propagation while containing/conveying/quelling emissions - yet still being light/compact.

[Pinger]

Nicely made engine block you got there!

Another project i came across (again) is this guy working on a 50cc engine with oval exhaust port at 100% of cylinder bore width. Radical transfers, head, exhaust channel. Well basically everything
Was

https://youtu.be/c92CQuHdP1Q

What is he using as piston rings?

[J.A.W.]

Nicely made engine block you got there!

Another project i came across (again) is this guy working on a 50cc engine with oval exhaust port at 100% of cylinder bore width. Radical transfers, head, exhaust channel. Well basically everything
Was

https://youtu.be/c92CQuHdP1Q

What is he using as piston rings?

Trapped L-shaped ring in screw-together piston, & it proved ah, problematic...

[Pinger]

Cheers J.A.W.
Either of us could have saved him three years of his life....

[Brake Horse Power]

No one said it was easy. I like his over ambitious ideas. The piston is cool as well. Curious to see how it will run with the bridge installed. Would be good to get that running first with the whole new intake

Next plan also here. [media] [/media]

[gruntguru]

Disc valve exhaust port - Oh dear. I know Yamaha have EXUP but that is a long way from the port.

If you wanted to supercharge a 2 stroke, Manolis has lots of ideas for assymetric port timings. Or you can just turbocharge it.

[J.A.W.]

Disc valve exhaust port - Oh dear. I know Yamaha have EXUP but that is a long way from the port.

If you wanted to supercharge a 2 stroke, Manolis has lots of ideas for assymetric port timings. Or you can just turbocharge it.

Actually gg, Yamaha did in fact develop their 4T EXUP regulatory system via their YPVS 2T
rotary-drum exhaust valve set-up, which sat astride the 2T's exhaust ports, as timing control.

& if not constrained by rules over use of 'atmo' pressure-boost, a forced scavenge via additional
pump is 'old school' 2T tech, & one which does not preclude an exhaust energy turbo, as well...

[Pinger]

No one said it was easy. I like his over ambitious ideas. The piston is cool as well. Curious to see how it will run with the bridge installed. Would be good to get that running first with the whole new intake

He'll very likely find the same problem with the exhaust bridge that everyone else has.

Next plan also here. https://youtu.be/Q_48YIOSedc

He'll probably make the big power he expects but acceptance of an engine spewing fresh mixture out the exhaust port will not happen.
There are several other flaws in his design that make it not worth pursuing.

[J.A.W.]

Curiously enough, doyen of performance motoring Kevin Cameron commented on the 2T
external scavenge-pump set-up in his Cycle-World blog: 'Ask Kevin'; just a few weeks back:

https://www.cycleworld.com/story/blogs/ ... cavenging/

His view was that an external pump was fine, & duly noted a Toyota effort to convert a DOHC 4V
4T engine to run as a 2-cycle by doing so.

I think Kevin has perhaps conflated the Detroit Diesel 4V (wherein all 4 poppets are exhaust valves,
yet inlet ports are cut into the cylinder liner, per typical 2T usage) since AFAIR, Toyota's experimental
attempt failed, (unlike the many decades of D.D. service - still supported as NATO milspec inventory).

Toyota's efforts fell over due to running their ordinary 4T valve train at crank rpm, (twice the 4T ratio),
& accordingly suffered from insufficient port-area/time, plus problematic poppet valve tech-issues.

[Pinger]

KC misses that the ocean going ships now employ turbochargers and there was a step change in thermal efficiency when the change from Roots blowers occurred.

He's right though, nothing new with blower scavenging. Blair spent time outlining the need for adequate blowdown when using a blower (to avoid losses at the blower). Our man with the big plan appears not to have read Blair.

Interesting points as to why 2T development was abandoned by the OEMs. They still got shafted being forced to electrify but because of the cheating with their diesels (clearly a wrong choice pursuing only it, a high NOx emitter) they were left voiceless at the table. If they had more efficient 2T to offer perhaps we would have a viable alternative to electrification which many are going to struggle to afford and loss of personal mobility is a real threat here. Well done the bean counters - open minds and purse strings could have saved us from this pending electrification debacle.