2 stroke thread (with occasional F1 relevance!)

[johnny comelately]

Some relativity, the published figures on these are a fair way short, it is a good "preread" before posting
https://www.youtube.com/watch?v=XhkZetCyaNs

[johnny comelately]

"Most important" Manolis?

Important, to be sure, but really only an important parameter among many in the internal combustion mill..

Gas turbines for example, have had their combustion process worked out for decades, but the gas-pumping
/fluid work part of their function - has been a real struggle to achieve overall "efficiency" in fuel use terms.

The 'simple' 2T has, for over 60 years, been seen as an inexpensive method to harness a pulse-jet to shaft work.

& it is the overall cost-benefit ( notwithstanding the dreaded 'marketing' dept) which keeps interest going.

After all, automatic firearms have, for well over a century now, been an example of practicable 2T function.
A firing stroke does the 'work' & vents waste - while the recoil ( recip') recharges on the upstroke..
No one would now consider having an extra two non-productive strokes in a gun - to be anything but a waste.

Love the analogy to the gun

[J.A.W.]

The only thing to add is that there are quite a few 2Ts with poppet valves (including the RTA96C) - what is the point of adding that much complexity, friction, ruining the combustion chamber shape and increasing the discharge coefficients ?

Seems you are still not getting it Mudflap..
..sure Detroit Diesel 2Ts have been running a 4V (poppet) exhaust for ~80 years,
but they are slow-running workhorses, & ok, so you missed the point in the Ricardo study, too - that the
superior 2T torque output was cruelled at higher rpm - by the limitations of the "discharge coefficents".

But if you really are open to learning, you could look up the '24/7' concept - as it applies to new 2T designs,
& kindly, report back.

[Tommy Cookers]

Wartsila port sizes are doubly helped, by very low bore:stroke ratio and by design to piston speed not piston acceleration
this is fine when there is a cathedral-type space for the engine


all aircraft piston engines (not just those called compound) are compounds - the exhaust gas works for propulsion

the 6x (2:1) Merlin pre-1940 'ejector' exhaust stated as worth up 150 hp free thrust with a 1000 hp engine at 350 mph
the link re the (later) 130 Merlin stating 450 hp 'free thrust' says 12x 1 stub exhaust gives more thrust due to pulses
the reason other fighters had gone towards individual stubs
this preservation of pulses is surely analogous to race turbo and turbocompound exhaust system design

whether/why the 2 stroke has more energetic pulses than the 4 stroke is a question
is effective EVO just earlier in a 2 stroke because it must be ?

the physics of blowdown are due to Mach-related resistance not our conventional lower-speed view of flow resistance
ie blowdown is a choked process
if the EV was as big as the bore and opened instantaneously it would not change the necessary timing of EVO bbdc
(eg the rotary or 2 stroke is no better in this respect)

the physics of blowdown are improved by increasing the gas density and so reducing velocities
this gives increased thermodynamic reversibility and so increases available mechanically-useable energy downstream
maybe analogous to the argument (if there is one) for partial exhaust restriction in aircraft exhaust-jet propulsion

[johnny comelately]

on topic/ off topic whatever but you have to love this
https://www.youtube.com/watch?v=2nIbyezOUP0

[J.A.W.]

on topic/ off topic whatever but you have to love this
https://www.youtube.com/watch?v=2nIbyezOUP0

Sure do, Johnny - if only as a cogent example of why a practicable performance 4T chainsaw is a non-event..

[johnny comelately]

on topic/ off topic whatever but you have to love this
https://www.youtube.com/watch?v=2nIbyezOUP0

Sure do, Johnny - if only as a cogent example of why a practicable performance 4T chainsaw is a non-event..

Its amazing isnt it, as they say "only in America" but these days Scandinavia too -https://www.youtube.com/watch?v=tdIB-jUa6-E

off topic but

[J.A.W.]

Ok, back on topic, 'from Russia with love' - a basic 2T with 'Moore's law' injection-tech efficiency benefits..

http://www.aviamech.com

[J.A.W.]

This dyno chart shows what a 'backyard tuner' has obtained from a real basic ( 45 y/o!) Kawasaki 750cc 2T roadbike engine..

https://www.tapatalk.com/groups/kawasak ... C-0776.JPG


& for contrast, this - 'Ronax VS Suter' - vid shows a pair of 'big bucks' 2T G.P. race-replica track bikes doin' their stuff..

https://www.youtube.com/watch?v=CPw5ZfnR2GM

[johnny comelately]

This dyno chart shows what a 'backyard tuner' has obtained from a real basic ( 45 y/o!) Kawasaki 750cc 2T roadbike engine..

https://www.tapatalk.com/groups/kawasak ... C-0776.JPG


& for contrast, this - 'Ronax VS Suter' - vid shows a pair of 'big bucks' 2T G.P. race-replica track bikes doin' their stuff..

https://www.youtube.com/watch?v=CPw5ZfnR2GM

on the 750 a good example of when the pulses sync and not

[J.A.W.]

Yeah Johnny, & bear in mind that's Jorgen's road-riding machine, not a peaky-tune dragster.

& back in the day, TKA tuner Nev Doyle had to rev his H2R racebikes out past 10,000rpm - to get ~25hp less..

[Pinger]

I'd also remind you, that lubrication systems are neither 2T, or 4T in themselves, being independent
of whether every piston down-stroke is a power-stroke, or not. Many smaller 4Ts to this day, run on
a 'splash' of lube, & some even use a fuel/oil mix

J.A.W. - the last of the above, 4T running on fuel/oil mix - presumably that is the Stihl 4mix and similar you are referring to. Where? In your home country (Australia?)?

I've read about their development in American documents but no one in the UK knows anything about them. I suspect they weren't marketed in Europe (strat charge being the preference). Other than the USA, where were they sold? Why not in UK (Europe?) and why chosen rather than strat charge? Any ideas anyone?

[johnny comelately]

Hi Manolis, surely - the term "best" is ah, best applied - via technical qualifiers..

The mammoth marine 2T's are very slow-revving so the single poppet valve is a convenience,
whereas in smaller scale, the faster operating Detroit Diesel required 4 poppets, & when Toyota
tried running one of their high rpm DOHC 4V SI engines in 2T mode, even 4 poppets proved inadequate.

I'd also remind you, that lubrication systems are neither 2T, or 4T in themselves, being independent
of whether every piston down-stroke is a power-stroke, or not. Many smaller 4Ts to this day, run on
a 'splash' of lube, & some even use a fuel/oil mix



And a few 1600cc 4T are using a 'splash' of lube too

[J.A.W.]

I'd also remind you, that lubrication systems are neither 2T, or 4T in themselves, being independent
of whether every piston down-stroke is a power-stroke, or not. Many smaller 4Ts to this day, run on
a 'splash' of lube, & some even use a fuel/oil mix

J.A.W. - the last of the above, 4T running on fuel/oil mix - presumably that is the Stihl 4mix and similar you are referring to. Where? In your home country (Australia?)?

I've read about their development in American documents but no one in the UK knows anything about them. I suspect they weren't marketed in Europe (strat charge being the preference). Other than the USA, where were they sold? Why not in UK (Europe?) and why chosen rather than strat charge? Any ideas anyone?

Yeah P, its about 'good lugging power' apparently, but that's not much good for a chainsaw.. strat charge is..

https://www.stihl.com.au/4-mix-engine-l ... power.aspx

[Pinger]

Yeah P, its about 'good lugging power' apparently, but that's not much good for a chainsaw.. strat charge is..

https://www.stihl.com.au/4-mix-engine-l ... power.aspx

Is there an echo here J.A.W.?
Just back from chatting to a guy who runs a garden tool shop and that's exactly what he said - the low down torque is its strongest feature. Strange though, as earlier 4T strimmers are criticised by golf course greenkeepers as lacking torque. All in the state of tune I guess. The other selling point it seems is less noise - or easier-on-the-ear to most people noise.
Also confirmed was the use of fully synthetic oil supposedly to reduce carbonisation of the exhaust valve which they are prone to.Overlooking the lack of HC content.....
First one I'd seen in the UK though and the feeling was that they exist not for emissions reasons but for the aforementioned benefits (the power of marketing!) - and to avoid having to pay Honda for its oiling system.
All agreed on the chainsaw - 45mins from the electric ones apparently. You'd go cold in winter at that.

Don't have the strat charge figures at hand but I don't think they reduce emissions by as much as some imagine.
Charge loss I think is in two stages. The first eruption of charge into the cylinder sees some immediate short circuiting to exhaust and the remainder that loops the cylinder and arrives first at the exhaust port can get lost also. Strat charge permits that air only is lost during the above.
It can't though, do much to prevent the charge loss at the other end of the gas exchange process when the ascending piston shoves mixture out before the exhaust port is closed (especially between transfer closing and ex closing). Can't see how strat charge can help then.