2 stroke thread (with occasional F1 relevance!)

[smoker250]

According to Graham White's Jan 2011 'Aeroplane' Crecy article ..

"One of the V-twin test engines still exists at Ricardo Consulting Engineers".

& S-250 needs to realize that propellers were also then an issue for very powerful aero-engines.
Especially for fighter aircraft, & jet thrust turbines leap-frogged this problematic area.

White continues on useful Crecy features..

"Piston cooling technology befitted high-performance diesels.
Most modern diesels use the Ricardo derived 'cocktail shaker'
idea for this critical function... ...it can be said that the Crecy was ahead of its time."

&,

R-R engineer Stuart Tresilian proposed a..

"9-litre 16-cylinder X-configured Crecy-derived engine.
This little screamer was calculated to produce 2,500hp at 7,000rpm."

R-R as a company, ( by contrast to Napier) then presented as none too receptive/successful with
cutting edge designs, doing better with the steady development of their conservative V12 mills..

Yes JAW, the Graham White article, perhaps you missed the paragraph describing the Crecys "almost insurmountable" problems, " Foremost were sleeves siezing in cylinders and piston failure owing to high crown temperature. White mentions the innovative oil cooling etc but concludes " Despite these efforts a definitive solution was elusive, piston failures still occurring at random". The Crecy was not ahead of its time , it was a flawed design, both mechanically and therodynamically. The simple proof of that is that neither Ricardo or anybody else even tried to develop the concept for any commercial use since then. Lord knows we could all use a 100kg 300 hp 3L V6 two-stroke turbo, but not if it carries a placard on the dashboard that says PISTON FAILURES MAY OCCUR AT RANDOM For every sound design that was never developed commercially, for example the Napier Nomad and the Rootes TS4, there are hundred crap designs that should never have seen the light of day.

[J.A.W.]

S-250.. did you not read the G.W. 'Aeroplane' article where it states Ricardo..

"... met his goal, Astoundingly he managed to coax 219hp/litre & a BMEP of 325lbs/in".
&,
"Finally, it can be said that the Crecy was ahead of its time."

Apparently not, since that directly contradicts your assertion..

I did actually put the 1st quote in a fairly recent post, but it seems you didn't get it..
Likewise the apropos comments on the Crecy oil system by Uniflow..

Why very large piston aero-engines have not been designed for decades - is pretty self evident..
& as previously stated, current technology would deal to the Crecy issues you claim as crushing design faults..

I suggest you spend a bit of time reading some of the real data in this thread prior..

Such as the ~1000-hp 2.3ltr 2-stroke turbo-compound V6 designed for NASA by Garrett as a helo mill..

[gruntguru]

JAW I don't think the Garret proposal incorporated sleeve valves which is one obstacle to removing heat from the Crecy piston. The Garrett engine and the Nomad were both diesel which is a totally different kettle of fish when it comes to piston and sleeve heating.

I also believe that bore diameter would be a threat to piston cooling on SI two strokes i.e. a smaller cylinder displacement version of the Crecy would be less problematic. e.g. I assume Ricardo's test engine was smaller bore than the Crecy?

[uniflow]

JAW I don't think the Garret proposal incorporated sleeve valves which one obstacle to removing heat from the Crecy piston. The Garrett engine and the Nomad were both diesel which is a totally different kettle of fish when it comes to piston and sleeve heating.

I also believe that bore diameter would be a threat to piston cooling on SI two strokes i.e. a smaller cylinder displacement version of the Crecy would be less problematic. e.g. I assume Ricardo's test engine was smaller bore than the Crecy?

No, same bore and stroke.

I imagine my smaller ( non mechanical supercharged ) engine might survive better.

[J.A.W.]

JAW I don't think the Garret proposal incorporated sleeve valves which one obstacle to removing heat from the Crecy piston. The Garrett engine and the Nomad were both diesel which is a totally different kettle of fish when it comes to piston and sleeve heating.

I also believe that bore diameter would be a threat to piston cooling on SI two strokes i.e. a smaller cylinder displacement version of the Crecy would be less problematic. e.g. I assume Ricardo's test engine was smaller bore than the Crecy?

G-G, the Garret design team did review sleeve valves in their design considerations,
& reckoned them to hold certain advantages - not to be dismissed - for future potential.

The metallurgical/tribology issue of sleeves has hardly been addressed by current technology,
& is unlikely to present many horrors given heat transfer/friction reduction advances in the last 70 years..

As U pointed out, Ricardo did get his full-size cylinders really pumping..

[manolis]

Hello.

Does anybody know how the Crecy seals the sleeve? At the inner side the piston it seems as having conventional piston rings. What happens at the external side of the sleeve valve?

Also, isn’t obvious the reason of the overheating?
If you trap 1/3 of the exhaust gas into the cylinder, the initial temperature of the charge when the ports close is high. Also, isn’t reasonable that during combustion a small(?) part of very hot gas will find the way, around the upper end of the sleeve valve (through the space between the sleeve valve and the cylinder liner) towards the exhaust ports?

Would the temperature increase or drop in case the long sleeves of the Bristol 4-stroke Radials were used in the Crecy?
I think it would drop a lot because the exhaust ports would be located at the top of the cylinder, allowing more efficient scavenging, leaving way less hot burnt gas into the cylinder and needing less cooling from the cylinder head.
With the sleeve extending inside the cylinder head (and with stationary rings for its sealing, as in the Bristol Radials) the upper side of the sleeve runs much colder.

Instead of arguing about what have been said, many years ago, about the Crecy engine and its potential, isn’t it better to strictly technical examine / evaluate Crecy’s arrangement?

Thanks
Manolis Pattakos

[J.A.W.]

Rings of course do - as you correctly point out Manolis - serve as a major heat conduction path..

Bristol did put huge efforts into getting their sleeve-valves working well,
& grudgingly assisted (under wartime compulsion reg's) Napier with getting theirs sorted too..

[gruntguru]

Manolis
Although it is many years since I read "The High Speed Internal Combustion Engine" I recall Ricardo evaluated all those options and found the plain sleeve using its top edge to uncover the exhaust ports was the best option. There were no seals, just a lubricated cylinder in cylinder fit. Heat flow from the cylinder maintained the clearance. Differential expansion closed the gap until heat transfer was sufficient for delta T to reach equilibrium.

The Ricardo 2 stroke / Crecey certainly did not trap 1/3 of the exhaust gas in the cylinder. There was a substantial scavenge ratio IIRC.

[manolis]

Hello Gruntugu.

I think the same method is used in the pinnacle engine (a four-cycle Opposed Piston with two crankshafts): they use an intake sleeve valve at one side of the cylinder and an exhaust sleeve valve at the other side of the cylinder, each opening and closing ports disposed near the middle of the cylinder.

They claim their system works fine.

The next reasonable question: if the sealing with the ring-less sleeve valve is good and the relative friction/wear low, why this technology was never used to eliminate the piston rings in normal size engines?


For the high quantity of residual gas: in order the fresh gas to escape out of the cylinder, the shortest way is obvious (short circuit of transfer / exhaust ports). In the giant 2-stroke marine engines a lot of effort is given in the reduction of the residual gas. Is there something special in the design of Crecy that forces the hot gas in the “cave” above the exhaust ports to exit from the cylinder?

Thanks
Manolis Pattakos

[smoker250]

JAW I don't think the Garret proposal incorporated sleeve valves which one obstacle to removing heat from the Crecy piston. The Garrett engine and the Nomad were both diesel which is a totally different kettle of fish when it comes to piston and sleeve heating.

I also believe that bore diameter would be a threat to piston cooling on SI two strokes i.e. a smaller cylinder displacement version of the Crecy would be less problematic. e.g. I assume Ricardo's test engine was smaller bore than the Crecy?

No, same bore and stroke.

I imagine my smaller ( non mechanical supercharged ) engine might survive better.

Definitely would I think Uniflow. Surface to volume ratio improves as bore gets smaller and that benefits both breathing area and cooling. Relatively cool scavenging air would also help instead of the red hot air coming out of a mechanical supercharger, (I dont think the Crecy was intercooled for some reason, but open to correction on that) Piston alloys vastly improved since then, better hot strength, and better combustion(squish bands and higher C/R etc)should lower exhaust temperature and heat flux. Getting the thermal expansion sealing right may take a bit of experimentation, thats all .

[smoker250]

S-250.. did you not read the G.W. 'Aeroplane' article where it states Ricardo..

"... met his goal, Astoundingly he managed to coax 219hp/litre & a BMEP of 325lbs/in".
&,
"Finally, it can be said that the Crecy was ahead of its time."

Apparently not, since that directly contradicts your assertion..

I did actually put the 1st quote in a fairly recent post, but it seems you didn't get it..
Likewise the apropos comments on the Crecy oil system by Uniflow..

Why very large piston aero-engines have not been designed for decades - is pretty self evident..
& as previously stated, current technology would deal to the Crecy issues you claim as crushing design faults..

I suggest you spend a bit of time reading some of the real data in this thread prior..

Such as the ~1000-hp 2.3ltr 2-stroke turbo-compound V6 designed for NASA by Garrett as a helo mill..

Just because someone designed it doesnt mean it was ever built and made to work or ever could have. Nasa gave up their G.A.P. general aviation propolsion program in the 90s after they realized they were even worse at designing aircraft engines than they were at designing space shuttles. Mention a 2.3 litre 1000hp 2 stroke to any engineer in the automotive or aviation field today and he will probably ask you politely to take your hand out of your pants.

TCM announced in August their TD 300, a 310 hp 3l V6 255kg 4 stroke turbodiesel. On the way to being certified at probably 2000 hrs TBO. These guys know what theyre doing, thats why one of China's biggest aeropace companies, Avica, bought them out a couple of years ago. There are a few of 2-stroke aviation diesels being developed, Zoche, deltahawke, Wilksch, and theres a theres a flat six uniflow 2-stroke from Italy but I cant remember the name. They may be lighter than a foursroke but don't have either the reliability or the fuel efficiency.

[smoker250]

To give the Crecy design what credit its due, a Ricardo diesel sleeve valve conversion of a RR Kestrel was used by George Eyston to break the workd speed record for diesel cars in 1936 at 159 mph, which stood till 1953. So all those millions of pounds and thousands of man hours wern't wasred after all.

[J.A.W.]

Definitely would I think Uniflow.

S-250, you could actually read the cited ( & linked) article, then you would know.. ..for sure..
..rather than relying on what you "think".. ..a few links/cited articles to go with your flaky opinions too - perhaps?
..since it seems your credibility factor is off to a bit of a shaky start.. so far...

& don't of course ignore..
..Ricardo's contribution to the tens of thousands of sleeve valve aero engines that were produced & flown..

[J.A.W.]

Hello Gruntugu.

I think the same method is used in the pinnacle engine (a four-cycle Opposed Piston with two crankshafts): they use an intake sleeve valve at one side of the cylinder and an exhaust sleeve valve at the other side of the cylinder, each opening and closing ports disposed near the middle of the cylinder.

They claim their system works fine.

The next reasonable question: if the sealing with the ring-less sleeve valve is good and the relative friction/wear low, why this technology was never used to eliminate the piston rings in normal size engines?


For the high quantity of residual gas: in order the fresh gas to escape out of the cylinder, the shortest way is obvious (short circuit of transfer / exhaust ports). In the giant 2-stroke marine engines a lot of effort is given in the reduction of the residual gas. Is there something special in the design of Crecy that forces the hot gas in the “cave” above the exhaust ports to exit from the cylinder?

Thanks
Manolis Pattakos

Manolis,

The Bristol & Napier sleeves which extended higher than those used by the Crecy,
had rings to seal against the junk head ( & perform heat transfer),
& their sleeves also move in a wrist like rotational as well as vertical plane..
..at 1/2 the speed of the Crecy sleeves - being 4-strokes..

The Crecy was referred to as a "Sprint" engine, for use in high speed fighter aircraft,
& was fairly energetically blown, indeed its exhaust jet thrust efflux was a to be a
considerable contribution to the design speed of the aircraft it powered..

[uniflow]

Yes, what was Harry thinking ideed. One of the V twin test engines I belive did 1000 hours without burning pistons or sleeves. It was found later ( after the war ) that the Crecy had an oil feed problem to the center part of the engine ( I think you will find it was the center pistons that failed ). The test engines showed it was possible to produce this kind of power safely.

Without going to my book shelf and finding the RR Crecy book ( and then the right page ), I think this 1000 hour test was at something like 350 BMEP as well. A LOT of heat.
For those that doubt, these facts are from real tests, not speculation or dubious calculations.