2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

Big motor companies such Toyota, Ford, GM & Chrysler spent plenty on 're-inventing' 2-strokes ~20 years ago..

According the Kevin Cameron, who followed up their developments, they pretty much ignored all the time proven
methods of long-experienced manufacturers & designers.. .. to run up blind alleys.. of complexity & cost..

& so, increasing computing power was put into refinements of traditional 4-strokes, so that even an appliance
such as the once lowly Corolla has evolved - so as to have engine tech that 50 years ago was the province
of high end Euro-exotica, & boast powered creature comforts of which 1/2 a century ago - were Cadillac standard..

No doubt as diminishing marginal returns tightens matters, the inherent 2-stroke power density/mass/BMEP
advantages must again be re-examined - just as Manolis & Uniflow here have indicated the utility for flying..

F1 seems bent on complexity & faux 'green' efficiency credentials at the current time, & it is
noted that both F1 & Moto GP have had to specifically ban 2-strokes from competition..

Maybe A-G can seer-see Ferdinand Porsche's century old electromotive flights of fantasy - reach reality?
Certainly toting even hi-tech batteries around aint goin' anywhere fast..

[FW17]

Boat engine makers have put in some effort to develop 2 stroke engines

the latest Evinrude G2 300 hp is a 3.4 l v6 engine with a very flat torque curve

Any idea how it will perform against a 300 hp land based engine

[J.A.W.]

Some of the 4-stroke outboards are modified car mills.. & all are bulky/weighty/lazy by comparison..

I do note that the new Evinrude 200hp-to-300hp G2 share basic B X S dimensions..
& it is a matter of tune ( variable exhaust valves,& etc) that makes the power difference.

W-F1, could you post a link to the tech-specs?

Of course these machines are required to operate at maximum torque as efficiently as possible,
so - that is a bit F1 like, if on an everyday/regular-use longitudinal level..

[gruntguru]

Boat engine makers have put in some effort to develop 2 stroke engines

With a bit of help from Orbital Engine Company.

[J.A.W.]

Some such as Mercury 'Optimax' - do use the Orbital air-blast DFI, but Yamaha utilize their own high pressure DFI,
& BRP have 'voice-coil' type ETEC DFI for Evinrude.. .. it is also applied to Ski-Doo snowmobiles..

[FW17]

JWA

the basic spec was from Evinrude site http://www.evinrude.com/en-us/



The exhaust of the engine is something that I could not understand; it is common unit not individual pipes and chambers; but still the entire exhaust is tuned

[J.A.W.]

W-F1.. ..thanks for the link/vids..
..2-strokes which feature even firing multiples of 3 cylinders..
.. can run unitised exhaust collectors which utilize the synchronised blowdown timing overlap for torque tuning..
..however, for maximum output & where space permits, a discrete pulse chamber exhaust..
.. 1 per cylinder.. generally gives best H.P. results - where such applications are deemed worthwhile..

[smoker250]

Thanks Uniflow, I should have figured that out for myself. I dug up a little on the Crecy, "Ricardo used an open ended or expansion sleeve which relied on the fit of the sleeve in the cylinder for sealing. The sleeve clearance was to a certain extent self regulating because of the effect of thermal expansion" .
It is a fascinationg experiment you are doing, no-one has done as far as I can tell, I can't wait to see how it goes.

At the conclusion of the article on the Crecy it mentioned that in Dec 1944 a mechanically supercharged unit achieved 1798 hp, extrapolated to possible 2500hp turbocharged. By that stage in the war one of the latest variants of the Merlin was already certified for flight at 2340 hp.

[uniflow]

Thanks Uniflow, I should have figured that out for myself. I dug up a little on the Crecy, "Ricardo used an open ended or expansion sleeve which relied on the fit of the sleeve in the cylinder for sealing. The sleeve clearance was to a certain extent self regulating because of the effect of thermal expansion" .
It is a fascinationg experiment you are doing, no-one has done as far as I can tell, I can't wait to see how it goes.

At the conclusion of the article on the Crecy it mentioned that in Dec 1944 a mechanically supercharged unit achieved 1798 hp, extrapolated to possible 2500hp turbocharged. By that stage in the war one of the latest variants of the Merlin was already certified for flight at 2340 hp.

Smoker, I am a little slow on building the crank cases to suit this cylinder but I'm back on to the project again. I intend to try several different types of cylinder including a vairiant of Frits Overmars FOS cylinder.

[J.A.W.]

Smoker, R-R calculated that the full-power Crecy would be too potent for the Spitfire airframe..

Yet they'd also figured out that the Merlin was not enough & had fitted their scaled up V12 Griffon mill to the Spit..

Highest service rating achieved for the Merlin was ~2,200hp by the American V-1650-9 on ADI & 90in/Hg boost..

[J.A.W.]

Orbital's airblast DFI has been utilized for heavy fuel (diesel-type) use in SI 2-strokes..
..including for flight applications..

http://www.hirth-motoren.de/UAV/PDF/Hea ... tation.pdf

[FW17]

Crecy had more parts than a 4 stroke engine, the simplicity of a 2 stroke was totally lost and was quiet heavy too

[J.A.W.]

More parts?
Funny, the traditional R-R gear train driven SOHC 4 valve per cylinder - with associated rocker gear complex..
..& all that gear thrashing about.. ..above the piston....seems to be absent from your cartoon W-F1..

& yes, for sure.. ..high specific output mills do tend to require more beef.. ..to hack the pace, as it were..

The larger displacement German D-B 600 series units were comparatively lightly built, & lightly boosted too..

"Quiet" though, was one thing the Crecy could not be accused of being, by any manner of means..
..no shrinking violet, that one..

[autogyro]

Crecy had more parts than a 4 stroke engine, the simplicity of a 2 stroke was totally lost and was quiet heavy too

http://alternathistory.org.ua/files/use ... _Crecy.gif

I think the main restriction for use in modern use and F1 would be the relatively low rpm which limits the basic design to WW2 era aircraft and boats pre turbine applications.
This matched the requirements for an efficient 'low rpm' prop to make use of all that power which still needed rpm reduction gearing.

A modern version could use electromagnetic sleeve actuation to reduce the moving parts and increase reliability.
I do not know how well the piston-rings-sleeve- water jacket would behave however.
IMO a supercharged through scavenged opposed piston unit would work far better.

[FW17]

why is rpm a limiting factor?