2 stroke thread (with occasional F1 relevance!)

[Pinger]

.
Here is a progressive power tuning article of a 2T triple, & shows the gains of 3-3, over 3-1..

I've never disputed that single pipe per cylinder yields best power.
However, I'm not in denial that expansions wreck torque in the first 2/3rds of the rev range making them unsuitable but for a handful of applications. All the graphs posted begin in the upper third of the rev range - ignoring how poor the engine is on those pipes lower down.

Here is plot unashamedly showing power produced over the entire rev range as there is nothing to hide here.

[J.A.W.]

regarding firing 2 or 3 or 4 cylinders simultaneously
the crankcase is of course common for each set of cylinders - saving much bulk and weight and bearing etc friction

If minimising the number of expansion chambers was of high importance, you could just about justify sharing with cylinders firing 180 degrees apart also. How the chamber volume (assuming it has to be sized for adequate flow) affects the reflection of pulses is a bit of an unknown at this point - though alluded to in J.A.W.'s thread he linked to.

Simultaneous firing cylinders could be horizontally opposed with 180 deg pin phasing - if the crankcase is large enough to accept enough charge to feed two cylinders. All dependent on the rules imposed by the FIA (eg, swept volume, etc).

The prospect of 2T in F1 is an interesting one. I'd prefer to see it pursued without the hybridisation (2T neither needs or responds as well to forced induction) and with a dramatically reduced weight limit. More representative of how it would be competing with heavier more complex and expensive technologies in road use.

P, check out the Konig flat 4 2T, it 'migrated' from a boat via a clever Kiwi, to finish 2nd in the `73 500cc World Championships,
& it featured shared 180' phased pipes, something that Kevin Cameron also applied to the early TZ 750 Yamaha,
..quite effectively - when the 4 factory pipes, which were formed into oblong sections to 'gang' together to fit
the allowable space under the chassis, broke up under the sonic pulse/metal fatigue effects..

www.odd-bike.com/2013/04/konig-500-gp-o ... erdog.html

[J.A.W.]

.
Here is a progressive power tuning article of a 2T triple, & shows the gains of 3-3, over 3-1..

I've never disputed that single pipe per cylinder yields best power.
However, I'm not in denial that expansions wreck torque in the first 2/3rds of the rev range making them unsuitable but for a handful of applications. All the graphs posted begin in the upper third of the rev range - ignoring how poor the engine is on those pipes lower down.

Here is plot unashamedly showing power produced over the entire rev range as there is nothing to hide here.http://evinrude.i.lithium.com/t5/image/ ... B13D?v=1.0

Yeah, P, that is a 2T VS 4T chart.. 'apples & oranges'.. though it does show the 2T advantage.

Compare the linked charts of the tuned Kawasaki 750 on the dyno.. of 3-1 VS 3-3, its the same bike..

What you seem to have difficulty with - is that the tuning potential of a fixed pipe shape may well be forced
right up high, for racing purposes, or for lower rpm range TQ, back-to-back testing shows that the only real
advantage of the 3-1 pipe is in packaging/cost.. & not power-performance, anywhere in the 'powerband'..

Even with the staid ol' GT 750, Suzuki deleted the 'balance pipe' that ran across the headers, when they 'tuned' it up
somewhat - in its later models ( albeit keeping that ludicrous faux 4 pipe set-up).

[Pinger]

Yeah, P, that is a 2T VS 4T chart.. 'apples & oranges'.. though it does show the 2T advantage.

The 4t curve is irrelevant - the point is that the entire 2T rev range is shown.

Compare the linked charts of the tuned Kawasaki 750 on the dyno.. of 3-1 VS 3-3, its the same bike..

I know, and as I acknowledge, for absolute power, the expansion wins.

What you seem to have difficulty with - is that the tuning potential of a fixed pipe shape may well be forced
right up high, for racing purposes, or for lower rpm range TQ, back-to-back testing shows that the only real
advantage of the 3-1 pipe is in packaging/cost.. & not power-performance, anywhere in the 'powerband'..

Fair enough, if we take my KTM 500 as an example, yes it has an expansion and torque right across the rev range - at least partly due to gentle chamber geometry. But at circa 100hp/litre it isn't gaining that much on 75hp/litre multis with cross-charging manifolds (which with porting and bigger carbs could yield higher outputs). Obviously though the KTM as a single cannot employ a manifold.
But if you were running a multi with a rpm ceiling of 6000 rpm there's not going to be that much more benefit from single pipe per cylinder and against the space and (radiated) noise concerns of exp's, the manifold arrangement has enough going for it to be considered.
The Kawa 3-1 though. The headers are way too long to be cross-charging. So space saving is all they are achieving. For that application I'd go straight to individual pipes.
My thinking is admittedly skewed toward auto use - where acceptance of expansions will be vetoed in a nano-second due to radiated noise. Packaging them and dealing with radiated heat will seal their fate.

[J.A.W.]

The 4t curve is irrelevant - the point is that the entire 2T rev range is shown...

...I acknowledge, for absolute power, the expansion wins...

Fair enough, if we take my KTM 500 as an example, yes it has an expansion and torque right across the rev range - at least partly due to gentle chamber geometry. But at circa 100hp/litre it isn't gaining that much on 75hp/litre multis with cross-charging manifolds (which with porting and bigger carbs could yield higher outputs). Obviously though the KTM as a single cannot employ a manifold.
But if you were running a multi with a rpm ceiling of 6000 rpm there's not going to be that much more benefit from single pipe per cylinder and against the space and (radiated) noise concerns of exp's, the manifold arrangement has enough going for it to be considered.
The Kawa 3-1 though. The headers are way too long to be cross-charging. So space saving is all they are achieving. For that application I'd go straight to individual pipes.
My thinking is admittedly skewed toward auto use - where acceptance of expansions will be vetoed in a nano-second due to radiated noise. Packaging them and dealing with radiated heat will seal their fate.

Ok P, you still seem stuck on the usage characteristics..

..that 2T TQ hit is what pumps the boat 'out of the hole', & allows it to stay on the plane with moderate power settings..

The snowmobile will automatically 'spool-up' via its CVT.. & thus the dyno charts must reflect this..

I'd have thought your KTM 500 ought be closer to 60-65hp, although it is also a very basic 'punchy TQ' 2T design..
The current ( & obviously more highly developed) KTM 250 2T MX is good for 50 RWHP..

Obviously with regular 'car' usage, a engine will be both built down to a price, & tuned for economy/durability,
whereby the virtues of the 3-1 make themselves self-evident.. but you must accept, it is a convenient 'palliative',
rather than the technical optimum vs 3-3, regardless of the rpm range..

& that Kawasaki 3-1 chart does clearly show the wave form of the cross-charging effect, since even with long headers, the rapidity of the consecutive sonic pulses do still demonstrate a harmonic synergy pattern..

[Pinger]

Ok P, you still seem stuck on the usage characteristics..

Yep. Engines are to be used! Whatever best facilitates that.

The snowmobile will automatically 'spool-up' via its CVT.. & thus the dyno charts must reflect this..

It will pull in lowest ratio until it hits a torque peak before shifting out. Otherwise no dyno plot possible - just a single figure at one engine speed.

Obviously with regular 'car' usage, a engine will be both built down to a price, & tuned for economy/durability,
whereby the virtues of the 3-1 make themselves self-evident.. but you must accept, it is a convenient 'palliative',
rather than the technical optimum vs 3-3, regardless of the rpm range..

One man's 'palliative' is another man's solution. Horses for courses and all that...

& that Kawasaki 3-1 chart does clearly show the wave form of the cross-charging effect, since even with long headers, the rapidity of the consecutive sonic pulses do still demonstrate a harmonic synergy pattern..

Say, ex port opens at 90deg BBDC. 10 deg to establish pulse so opening cylinder/piston is at 80deg BBDC when pulse sets off. 120 deg further round, is 40deg ABDC. Which gives the pulse 10 CAdeg to traverse manifold to required cylinder (for optimum 40deg before ex closure). At 9000 rpm that is 0.2ms. At 500m/s (speed of sound at 600C) 93mm can be travelled in 0.2ms. Those headers ain't cross-charging.(Maybe at lower rpm they are).

[Pinger]

talking of cars I see that a suggested cause of the Ford Orbital 2 stroke failure was inadequate ring life

That sounds familiar - in that I seem to recall it being said at the time.
Re-reading Orbital's paper on the 5million km trial it says no ring problems providing the ports were properly chamfered.
Even if ring wear is deemed excessive - are detachable cylinders not acceptable with a view to treating rings as service items? It would require reasonable access to the engine but sled motors seem to survive well enough without casting the block and upper crankcase in one piece.
It may be that ring wear is too high a price to pay for loop scavenging.

[Muniix]

Hybrid intergration with the ZeroShift on a 7 ratio gearbox is made so much simpler. One can improve its shift performance even further, the emmisions improvement​ is also better.
Aprilia use it in their​ MotoGP bike.

So whoever said they are no more is clearly .. espousing opinions as is normal.

This is official, verified and approved by me and Not an opinion.

[manolis]

Hello Pinger

You write:
“My understanding is that at low (throttled) loads the 2T barely suffers from throttling losses, it is the 4T that is hamstrung by them.
Compare the 'pumps' in question. One operates at between 1.4:1 - 1.6:1 (at best), the other circa 10:1 compression ratios. Hence the difference.”


Quote from http://www.jhis.co.uk/ICE/Help/ICEHelpWebMain.html :





It is for a model engine (0.211cubic inches) at high revs (18,000rpm) and full load (1.6:1 primary compression ratio).



In the following plot (from http://www.pattakon.com/pattakonPatTwo.htm )



the blue curve is indicative for a PatTwo at light load, the green curve is indicative for a conventional 2-stroke at light load, the red curve is indicative for full load in either case.

The lower “loop” (or side) of the each curve relates with the space underside the piston crown (it is the upper section in the case of the PatTwo; it is the crankcase in the case of a conventional 2-stroke), while the upper “loop” (or side) of each curve relates with the combustion chamber (the cylinder).

The Ex and Tr are where the exhaust and the transfer ports open, respectively.




The pumping losses in a 4-stroke and in a 2-stroke are not proportional to the “relative” compression ratios.

With 10:1 compression ratio the 4-stroke may have lower pumping loss than a similar capacity 2-stroke having 1.6:1 primary compression ratio (the one “pumps” per crankshaft rotation, the other per second crankshaft rotation).

The pressure in the crankcase of the 2-stroke with the 1.6:1 primary compression drops near 0.5bar, while the pressure in the cylinder of the 4-stroke with the 10:1 compression ratio cannot drop below, say, 0.3bar.


Things get more complicated as the “fresh charge” is heated by the surrounding walls:

Quote from http://www.pattakon.com/pattakonHydro.htm :

“After the intake valve closing, the piston continues to move towards the BDC. The charge (air or mixture) inside the cylinder undergoes an expansion. The expansion causes the charge temperature to drop increasing the heat absorption from the hotter walls (cylinder, piston crown, cylinder head, intake and exhaust valves). After the BDC the piston compresses a hotter charge and restores less mechanical energy than the mechanical energy consumed to expand the charge. “


Thanks
Manolis Pattakos

[Tommy Cookers]

[quote=Muniix post]
Hybrid intergration with the ZeroShift on a 7 ratio gearbox is made so much simpler. One can improve its shift performance even further, the emmisions improvement​ is also better.
Aprilia use it in their​ MotoGP bike.[/quote]

well I tend to say that F1s shift performance is not any better with the K on the scene than it would be otherwise
though a more road engine's shift would be improved
and what are Aprilia using ?

[Muniix]

I was thinking that with current 2T designs they have 3 seperate pressure wave tuned and interacting ports, intake, transfer and exhaust. With a pressure wave engine one could reduce this complexity to two. Integration possibilities? Just me thinking outside the box.

In regards physical issues related to exhaust systems that TJI improves the situation with cooler exhaust allowing greater selection in materials being used and on meeting emmisions, less NOx and other nasty species like OH-.

Kevin Cameron has a physics degree so that always helps​ him ignore opinions​ to come up with superior designs.

Knowledge trumping opinions everytime.

My friends niece is at Qld University doing Physics and Maths on the Scramjet research. Interesting research even if it's hypersonic they still have to deal with and understand fully subsonic.

[J.A.W.]

Anyone who has access to a 2T motorcycle ( not with CVT ) can test the low 2T 'pumping losses'..
..per the overt characteristic of very little apparent 'engine braking' - as the give-away, but if you kill the ignition..
..then open the the throttle, you will suddenly develop 'engine braking'..

The lack of friction from not driving cams/valve gear/large capacity-high pressure oil pumps-scraper rings & the like too.

Here, yet another approach to exploiting the 2T fundamentals: https://www.pureburnengines.co.uk/two-s ... pplication

& some further blurb/data on the recent TFI KTM:

www.motocrossactionmag.com/home-page/in ... oke-engine

& Pinger, a dyno actually measures the TQ, & calculates the HP - TQ/RPM.. ( 5252).
..if you read the 3-1 on the H2 test, it matched the 45 y/o standard 3-3 pipes for output..
..but not the more recent, & carefully researched 3-3 pipes.. anywhere in the rpm range..

This is not to state that for certain applications, the synergystic grouping of 3 is not useful, indeed..
& for exploiting 'exhaust nozzle throttle control' - it may well be advantageous in marine/aero-engine duties..

[Muniix]

Another issue with rotary valve systems is with the 'window' communicating with the combustion chamber. The flow coefficient must be optimised through its geometry to match that of the inlet and exhaust runners, no physical limitations i.e. dimensions, the crank angle duration to fully opened and closed be minimised and preferably the whole system matched to piston motion.

This provides the best fluid flow efficiency for cylinder filling and effective exhaust gas extraction for optimal engine pumping efficiency and throughput. Creating the ideal situation for combustion in the process, additionally use of exhaust gas energy recovery in a exhaust gas turbine or pressure wave device can be optimised. Being able to match delivery ratios to cylinder volume changing is important.

Fluid flow simulations with models that work with compressible gas need to be performed to validate and optimise a design as is standard practice in any IC engine.

The sealing issues​ are well described by in the Bishop patents, are complex and why Bishop have many patents on good and not so to protect the world from poor Implementations as is Bishops standard practice on all their IP. This is why using the patent process to protect IP is actually expensive in reality. Anyone can lodge a patent, it only means something when it is returning revenue or profits​and protecting your business strategy, hostile behaviour can be effectively dealt with.

Like a book arranging standard words it is in the whole process that makes it valuable.

[manolis]

Hello J.A.W.

Here is the KTM250 TPI of 2018 from your link:




According the DIRTBIKE TEST / Jimmy Lewis ( http://dirtbiketest.com/fresh-dirt/ktm- ... dG5bwpu.97 ) :

KTM says there will be, “considerable benefits over carbureted models including drastically reduced fuel consumption while also no-longer having the need to pre-mix fuel or alter the machines’ jetting.”
Called TPI (Transfer Port Injection) the biggest difference from current off-road four-stroke fuel injection systems is the placement of the injectors in the transfer ports and not in the throttle body or in the air boot (from what we can see).




Question for all:

With the exhaust port remaining open for several (20? 25?) crankshaft degrees after the end of the transfer (i.e. with all the fuel into the cylinder), what stops a part of the fuel from escaping unburned to the exhaust?

We talk for an engine operating in a wide range of revs and loads.



In comparison, here is a PatATeco 2-stroke design which, either carbureted (the carburetor connects to the left / lower port):





or injected:



keeps the fuel in the cylinder:

the transfer starts with air from the crankcase, it continues with rich air-fuel mixture from the space underside the piston crown and ends with air coming from the crankcase and passing though the piston and the asymmetric transfer ports.

The rich air-fuel mixture can enter into the cylinder even after the closing of the exhaust.

In the same design the intake is highly asymmetrical without reed valves and without disk or drum valves.

More at http://www.pattakon.com/pattakonPatATeco.htm

Thanks
Manolis Pattakos

[J.A.W.]

Hello Pinger

You write:
“My understanding is that at low (throttled) loads the 2T barely suffers from throttling losses, it is the 4T that is hamstrung by them.
Compare the 'pumps' in question. One operates at between 1.4:1 - 1.6:1 (at best), the other circa 10:1 compression ratios. Hence the difference.”

Quote from http://www.jhis.co.uk/ICE/Help/ICEHelpWebMain.html :

http://www.jhis.co.uk/ICE/Help/images/D21DSPVDiag.png

http://www.jhis.co.uk/ICE/Help/images/D21DSBHP.png

It is for a model engine (0.211cubic inches) at high revs (18,000rpm) and full load (1.6:1 primary compression ratio).

The pumping losses in a 4-stroke and in a 2-stroke are not proportional to the “relative” compression ratios.

With 10:1 compression ratio the 4-stroke may have lower pumping loss than a similar capacity 2-stroke having 1.6:1 primary compression ratio (the one “pumps” per crankshaft rotation, the other per second crankshaft rotation).

The pressure in the crankcase of the 2-stroke with the 1.6:1 primary compression drops near 0.5bar, while the pressure in the cylinder of the 4-stroke with the 10:1 compression ratio cannot drop below, say, 0.3bar.

Things get more complicated as the “fresh charge” is heated by the surrounding walls...

Thanks
Manolis Pattakos

To be fair Manolis, I note that minuscule motor was sans exhaust pipe.. & that's a integral part of real-world 2T function..

This would surely tend to 'colour' the results of the test outcome.. somewhat significantly..

& P, I thought you'd find this project - to be of interest..www.2strokesdownunder.com/viewtopic.php?f=7&t=107