2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Riff_raff.

You write:
"Seriously, only three moving parts? Have you actually considered just how you will assemble the counter-rotating, geared crank system? Or what will you do if more than one pair of pistons is required? The overhung crankpin will also present some problems."


The basic mechanism is used, among others, in the PatRoVa 4-stroke rotary valve prototype engine:



presented at http://www.pattakon.com/pattakonPatRoVa.htm

(see the youtube video at https://www.youtube.com/watch?v=6Q-EGdeS0ws )

It comprises only three moving parts and it runs reliably.

It was also used in a few harmonic engines like:



shown at http://www.pattakon.com/pattakonPPE.htm#harmonic

Quote from http://www.pattakon.com/pattakonEduc.htm about the harmonic prototype of the photos (75mm bore, 80mm stroke, 9,000rpm):
“An internal combustion engine having pure sinusoidal motion of its pistons. The balancing of the single cylinder prototype is so perfect that it can stand free on the ground operating from idling to top revs (24 m/sec mean piston speed) without any tend to leave its place.”

Here is a simple four-cylinder 2-stroke even firing :



having four moving parts in total.

Thanks
Manolis Pattakos

[OdinYggd]

Yeah, but that's a 2-stroke. It probably comes complete with the coughing and oil burning bad behavior that makes 2 strokes appear unfriendly as seen by environmental folks.

I've got a design in testing that accomplishes 2 power strokes per revolution from only 3 moving parts, yet it is a 4-stroke cycle. And where you still have the unbalanced reciprocating mass of your monolithic piston to deal with, my design does not have any unbalanced forces at any RPM assuming that all of the components are accurately manufactured.

Quite literally in my design, any vibrations produced are the direct result of manufacturing variation causing the components to not balance perfectly.

Oh and before anyone thinks I am talking about a wankel/rotary, I'm talking about a piston engine.

[wuzak]

I am always open to more information so if someone can dig up information on whether the Crecy was intercooled or not and whether it had iron sleeves in the aluminiuim block, or any other information that adds to the discussion. I did say at the beginning that it might have been better if he kept it as a diesel. Ricardo might have been clever but looking at the combustion chamber he used in the E65, if he used that in the Crecy then no wonder he had problems.

The Crecy had steel sleeves running in an aluminium block. Both were Rolls-Royce developed alloys.

RR/P and RR/D (the converted sleeve valve Kestrels running petrol and Diesel, repectively) also ran steel sleeves inside aluminium bores.

Some more information on the Crecy, OTOH:
Riccardo ran a single cylinder development engine, not a twin as has been stated earlier. It had a different bore and stroke to the Crecy.
Rolls-Royce built 6 "main" engines (V-12s) and at least 6 development twin cylinder units. The reason they built the twins was to be able to test the sleeve mechanism.
The piston construction was composite - ie made up of a few parts, rather than a single casting/forging.
Piston cooling was from oil sprayed on the inderside of the crown. The oil was fed through a gallery in the connecting rod. This proved unreliable and would have been replaced by a more conventional spray system mounted in the block, as per RR's V-12s.
There was no intercooling on the supercharger. It was not normal practice in RR single stage supercharged engines.
A very large proportion of the air from the supercharger was for scavenging purposes - it basically went straight out the exhaust ports.
The direct injection fuel pumps were from a captured German aircraft!
Best output of the Crecy was ~1800hp with open exhaust and ~2500hp with turbo-compounding.
The Crecy had very good specific fuel consumption - at wide open throttle. At part throttle it wasn't so fantastic - Rolls-Royce considered the Crecy to be a full throttle engine like the gas turbine.
The Crecy program proceeded slowly as it had only a few engineers working on it and the priority was low.
The Crecy's combustion chamber was designed for stratified charge, with a rich mixture near the plug and lean away from the plug. Not sure whether it was a feature of Riccardo's engine or a RR design.

[manolis]

Hello OdinYggd.

The PatTwo is a different 2-stroke.

A difference it brings is that it has “four-stoke-like” lubrication (see the oil scraper ring of the conventional PatTwo).

Another difference it brings is its “clean” / easy breathing.

I.e. it eliminates the coughing and the oil burning of the conventional 2-strokes.


If you cannot reveal your engine design, how can we talk about it?
Apply for a patent (to protect your idea / your intellectual property) and then open it to the public.

Thanks
Manolis Pattakos

[OdinYggd]

If you cannot reveal your engine design, how can we talk about it?
Apply for a patent (to protect your idea / your intellectual property) and then open it to the public.

Thanks
Manolis Pattakos

I wish I could afford to. Patents are insanely expensive to get and maintain, and based on what I know about the process are quite literally more than I can afford.

And yet the design shows signs of life, breathing fire off the header when tested despite my somewhat inexperienced machining of the components and the use of whatever materials I could get instead of carefully selected alloys.

Its even leaking- and quite badly, giving only 45 PSI compression when my spreadsheet says it should have around 180 PSI.

There's a good chance it will run anyway despite the sealing issue if given a properly functioning ignition system. The one on it right now vibrates noticably at cranking RPM and is likely not igniting as often as it should be.

[manolis]

Hello OdinYggd

To apply for a patent in the UK-IPO (Great Britain Intellectual Property Office) and so to put your idea in the “patent pending” condition is not expensive.

If you file it electronically, the initial cost is 20 pounds.

Then, you have 12 months to pay another 210 pounds for the Search and the Examination in the UK-IPO (or your application is abandoned).

If before the end of the 12 months period you decide to proceed with the protection of your idea in other countries, you can use your initial application in the UK-IPO as the “priority”. You have also the option of the WIPO/PCT.

If you want to ask anything, please do.

Thanks
Manolis Pattakos

[J.A.W.]

Thanks for the interesting & informative new posts Manolis..

& perhaps O-Y - even if shy - can explain how he intends to get a "4-stroke" - providing 2-stroke BMEP values?

[OdinYggd]

Its quite clever how I figured it out, and each cylinder fires twice per revolution while maintaining a 4-stroke cycle. Plus it is possible to make it modular, allowing assemblies to be simply tacked on to build up composite units of a required capacity up to the maximum torque capabilities of the output shaft.

The equations I was able to find in old engine books place it at a theoretical max output of 29 horsepower at 3600 RPM from a package roughly the size of a 2-liter bottle, although I doubt the initial prototype will achieve it because a few of the tolerances are too loose and it doesn't make its full compression pressure. Yes this is not just a design on my computer, I already built one and have been tinkering with it for a couple of years trying to get it running.

Made almost entirely of steel, it weighs 26 pounds not counting the ignition system or carburetor- for a theoretical power to weight ratio exceeding 1:1 out of an all-steel block.

If I use aluminum as much as possible instead of steel, the block weight is reduced to only 17 pounds and I get 1.7 horsepower per pound from it assuming that the manifold flow doesn't choke and all components can tolerate the strain. It probably could run at even higher RPM too because it can be almost perfectly balanced.

Looking at the US Patent Office info though, I'd be to the tune of $1500 USD just to even have a shot at getting a patent issued by the time all is said and done with applications and prior art searches. I just plain can't afford that- in fact the most expensive single component on this thing is the ignition coil at $60. Sucks so much for me sometimes that I end up with some really interesting ideas and just plain can't afford to develop short of building as much of it as possible from scratch out of whatever I can find.

[riff_raff]

Thanks for the reply Manolis. While the single cylinder using the harmonic crank mechanism shown in your photos seems like it can be assembled without too much trouble, I would still imagine your 4-cyl concept would require multi-piece crankshafts.

I also don't think your engine would have acceptable reliability with the overhung crankshaft rod journal. The only engines I have seen where this arrangement was used successfully were small displacement or lightly loaded applications.

[J.A.W.]

See the cut-away drawing of the Ariel Square-4 with overhang-type big-ends in this link..

http://www.thevintagent.blogspot.com.au ... andit.html

[wuzak]

By 1940 Ricardo had 5 2 stroke test engines.

There were two E.65 single cylinder engines, using the open ended sleeve.
There was a Rolls-Royce Crecy V-2 development engine, being run in single cylinder form (known at Ricardo as the RR/4).
There was a single cylinder development based on the E.65 but with a junkhead being developed by Napiers.
And the E.54, which was a single cylinder built by Ricardo with Crecy stroke and bore.

Apparently a report by Ricardo in 1941 indicated that there were issues with the junkhead arrangement with failure of the sealing rings. Napier's scheme was for an H-24 of similar layout to teh Sabre, but 2 stroke and 3000hp target. Napiers abandoned their work in 1942 to concentrate on the Sabre.

The E.65 particulars were:
Sleeve Bore: 4.81" (122.174mm)
Cylinder Bore (Sleeve OD): 5.01" (127.254mm)
Stroke: 5.5" (139.7mm)
Sleeve Stroke: 1.5" (38.1mm)
Swept Volume: 99.9cid (1.64l)

The E.54 specs were:
Sleeve Bore: 5.10" (129.54mm)
Cylinder Bore (Sleeve OD): 5.34" (135.636mm)
Stroke: 6.5" (165.1mm)
Sleeve Stroke: 1.75" (44.45mm)
Swept Volume: 132.8cid (2.18l)

The Crecy specifications were:
Sleeve Bore: 5.10" (129.54mm)
Cylinder Bore (Sleeve OD): 5.34" (135.636mm)
Stroke: 6.5" (165.1mm)
Sleeve Stroke: 1.95" (49.53mm)
Swept Volume: 1593cid (26.11l)
Supercharger Diameter: 11.7" (297.18mm)
Supercharger Gear Ratio: 8.77:1 (originally 7.65:1)
Boost: +18psi
Sleeve Material: KE.965 (later NMC)
Cylinder Material: RR.50
Dry Weight: 1650lb (748.4kg)
Dry Weight with turbine: 1800lb (816.5kg)
Dry Weight with turbine and CR props: 1900lb (861.8kg)

The Crecy was around the same weight as a 2-stage Merlin. The supercharger was smaller than the 1st stage in a 2 stage Merlin (12"for most models) but larger than the 2nd stage (10.1").

KE.965 Special Valve Steel | Flight Archive
Hiduminium R.R. Alloys | Flight Archive
I can't find anything on the NMC steel as yet.

Ratings (without Turbine)
Combat and Take-off: 1768hp, 2750rpm, +15psi boost, 323lb exhaust thrust
Max Climb: 1605hp, 2750rpm, +12psi boost, 315lb exhaust thrust, @5,000ft
Max Cruise: 1422hp, 2500rpm, +10psi boost, 285lb exhaust thrust, @10,000ft
Economy Cruise: 1125hp, 2500rpm, +10psi boost, 229lb exhaust thrust, @10,000ft

Ratings (with Turbine)
Take-off: 2729hp, 3000rpm, +24psi boost, 287lb exhaust thrust
Max Climb: 2513hp, 3000rpm, +20psi boost, 322lb exhaust thrust, @10,000ft
Max Cruise: 2070hp, 2750rpm, +15psi boost, 238lb exhaust thrust, @10,000ft
Economy Cruise: 1827hp, 2750rpm, +15psi boost, 226lb exhaust thrust, @10,000ft

There were 8 V-2 engines constructed. No.1 and No.2 were Compression Ignition (CI) types, the remainder were Petrol Injection (PI) types. No.2 was converted to PI a some point in its life. No.4 went to Ricardo, No.6 went to the RAE for altitude testing (must have had an altitude chamber).

There were 6 main (V-12) engines numbered 2, 4, 6, 8, 10 & 12.

2 and 4 were built as Mk Is. 2 was converted to Mk II by early 1943 (started testing in that configuration on 26 February 1943).

6, 8, 10 & 12 were built as Mk IIs.

Total running time on all 6 engines was 1705.28 hours.

The Crecy I had integral cylinder block and head. There were problems with this arrangment, so the Crecy II was evolved with seprate cylinder heads - 1 for each cylinder.

The turbine used for exhaust energy recovery was a 50% scale version of that used in the Whittle jets being developed at the time at Rolls-Royce. It was geared to the crankshaft, bt I'm not sure if it was a fixed ratio or variable speed.

Data is from Nahum, Forster-Pegg and Birch, The Rolls-Royce Crecy, Rolls-Royce Heritage Trust, Historical Series No 21.

[Tommy Cookers]

See the cut-away drawing of the Ariel Square-4 with overhang-type big-ends in this link..
http://www.thevintagent.blogspot.com.au ... andit.html

the overhung crank was eliminated c.1936 when the engine was enlarged and completely redesigned
ie a conventional crank was used thereafter in all engines till production was stopped in 1958

@ wuzak
sorry, our posts seem to have crossed
imo there's a spread of opinion in the book even over some facts (one top RR achiever said the Crecy was the work of the B team)
the bore:stroke ratio is low as always with sleeve valve engines
(at this time conventional engines went to higher b:s ratios, but sleeve valve port areas would not support this)

[wuzak]

@wuzak
surely the Crecy was not actually rated at the levels you suggest ?
ie your quoted values are for predicted performance far greater than was ever demonstrable in sustained running ?
yes, I have the book

I doubt that they did the actual tests required for an official rating.

So I'm not suure if they are predicted or real measured values. I would have to read the book again, rather than just picking out data.

[J.A.W.]

the bore:stroke ratio is low as always with sleeve valve engines
(at this time conventional engines went to higher b:s ratios, but sleeve valve port areas would not support this)

Ah, not necessarily.. T-C.. ..the Napier Sabre was over-square ( 127mm X 121mm)..
..as were the 24 cyl R-R Eagle & Pennine mills.. ..but unlike the long-stroke R-R V12s..

& the sleeve port time/area breathing advantage is listed by Fedden..
" d. Improved volumetric efficiency due to greater effective port areas."
..as amongst the positive attributes of his sleeve valve design..

I have previously posted Ricardo-Crecy test data (via G. White) of post R-R development which shows..
..significant increases in specific output..

As W has noted, the Crecy was port optimised for a narrow 'powerband',
& current variable port/duct flow tech could certainly show improvement there..

[Tommy Cookers]

I do not believe the interest in sleeve valves was motivated by the problems with poppet valves. Sleeve valves give a far higher potential for better gas flow.
Loop scavenged two strokes are probably unbeatable in this respect.

The interest in sleeve valves was based on Ricardo's finding that sleeve valves ran cooler than poppet valves, this improvement wrt detonation enabled much higher mep (supercharged) with the low compression ratios envisaged with 1920s fuel (a skewed comparison, like so many). That apparent advantage largely disappeared with the sudden improvement in fuel quality that followed.
Once Heron's internally cooled exhaust valves were fully developed (in the USA, handily before WW2), the sleeve valve was redundant. The huge US sleeve valve engine programs were abandoned early in WW2

If RR had known to silver-plate the bigend faces of the Vulture (like Wright etc) the Sabre would not have appeared in numbers. The Sabre was a reserve engine, resulting from a policy of having technical reserves.

C.F.Taylor said that the usual (eg Sabre) type of sleeve valve was lacking in port area. I think this was why Ricardo's interest turned to the 2 stroke open sleeve as realised in the Crecy.

All cylinder ported engines are relatively starved of port area as larger bore:stroke ratios are used (for higher power via higher revs). This is broadly a historical trend, associated with broad historical progress in fuel quality.

Poppet valves are advantageously aligned wrt gas flow and size, and to use overlap. Crucially, poppet valves areas are relatively larger at larger bore:stroke ratios. F1 uses this to great advantage, now that valve action is so improved via pneumatic springs. F1 b:s ratios are now around 2.4:1 (this is startlingly large)

Poppet valves are used in some 2 strokes ?


Would the 2 stroke prevail in current F1 ?

GP motorcycle 2 strokes always had relatively low bore:stroke ratios to allow sufficient port depths (a fraction of stroke). Shortening the stroke for more revs and power wouldn't work because the port areas would not increase. All these engines had b:s ratios close to 1

GP motorcycle noise limits introduced about 35 years ago were very hard on the 4 stroke, the last ever (flat 4, never raced) MV Agusta failed the noise test at full rpm when producing no power (driven electrically) ! The last MVs that actually raced made as much noise as a grid full of 2 strokes. They were competitive, having a stroke short enough to rev about 40% higher than the 2 strokes

.... easier for me to bump this (than to think out what I had in mind)