Oddball engines and prototypes

[WilDun]

Don't get me wrong, good on the guy and some interesting thinking going on but to say it's balanced (or doesn't shake) can not be accurate. It's kind of like saying my twostroke parallel twin is balanced because the combustion forces bounce the piston back where it came from. My twostroke twin is not balanced and although from a distance it looks ok it's not fun to be around up close -- until I fitted the balance shaft.

No,no, I wasn't criticizing anybody (except the 4 stroke manufacturers), just talking in general about what might have been the reason for it not being fully developed by anyone and I guess it didn't get perfected by Bourke because it didn't come into being at the right time, also probably because Bourke was getting on (age wise) amongst other things but I do acknowledge that the vibration could have been a factor - and BTW a piston attached to a crankshaft is definitely not "free" either, as someone I think suggested!

[husaberg]

No,no, I wasn't criticizing anybody (except the 4 stroke manufacturers), just talking in general about what might have been the reason for it not being fully developed by anyone and I guess it didn't get perfected by Bourke because it didn't come into being at the right time, also probably because Bourke was getting on (age wise) amongst other things but I do acknowledge that the vibration could have been a factor - and BTW a piston attached to a crankshaft is definitely not "free" either, as someone I think suggested!

Those bourkes were designed for opposed piston design, the dwell appeals to me as it can be very useful in what is the most limiting factor of a 2T engine.
Unfortunalely it dewells in the wrong place
But thats just requires a rethink of the linkage
One car maker i think had it tied up but it didn't pan out.

This bit (below)is what drew me to it.
I don't know how many of the claims about it are true or just hype in regards to its extreme lean burn potential

The use of the Scotch Yoke reduces vibration from the motions of the connecting rod—for example, the peak acceleration in a Scotch yoke is 25% less than the acceleration in a conventional crank and slider arrangement. The piston movement and therefore vibration is sinusoidal so the engine could theoretically be perfectly counterbalanced, unlike a conventional engine which has harmonics in the piston movement courtesy of the lateral movement of the crankpin.
The Scotch Yoke makes the pistons dwell very slightly longer at top dead center, so the fuel burns more completely in a smaller volume.

plus

There was an Aussie crowd doing scotch yoke engines based on Subaru engines.
http://www.autospeed.com/cms/article...-Engine&A=0948



the thing is though the sleeve engine worked pretty much from the get go with little R&D time.
Go the Fletner sleeve engine

I just seen this


Plus this

[Pursang]

Sure. And that compression pressure presses alternately against the left-side head and the right-side head. Can you guess the result of that?

I've never seen a better description of a two-stroke twin

I'm sure Mr. Bourke & Mr. Newton would say: "Can't push a head one way, without pushing the piston back the other way".
It's the Law (3rd Law: Equal & Opposite forces, etc.) Is combustion pressure a factor in determining engine balance?
Bourke spent an awful long time developing his engine, perhaps he got some of it right.
A description by someone who attended a dyno test of a Bourke engine said that it rattled as the tuning & timing was adjusted. Noisy? sure, but No mention of shaking. He also identified an error in the the BSFC claim, due to a gearing issue between the engine & dyno.

The Guy that built the replica says that you must use Bourke's design & rules exactly or it can all turn to poop, very quickly.
In the video you can see the engine & dyno move dramatically when he pulls the starter cord.
If it was a real 'shaker' I would expect it to bounce around a bit as he runs it up to speed. My washing machine does.

Duel piston mono stroke was his description, not mine. He also had a bit of a 'thing' about people confusing strokes & cycles.
In those early years, Mr Scott's was probably the main 2cyl two-stroke of renown.
Bourke's engine had only 2 Moving Parts. Perhaps the description was a means of product differentiation.

I'm not supporting, promoting or attempting to sell anything or anyone. Just discussing an interesting engine.

Bourke built actual working engines, he developed a 400ci engine for AMC, their engineers tried to convert it to a low compression, regular engine, that failed and then discontinued the project.

We watched a video of a working replica, seem strange to discount its operation out of hand.

cheers, Daryl.

[Frits Overmars]

the peak acceleration in a Scotch yoke is 25% less than the acceleration in a conventional crank and slider arrangement.

I'm always sceptical when reading such claims, so I did some comparative calculating with an engine where the con rod length is a conservative twice the stroke size, and an engine with an infinite con rod length, aka a Scotch Yoke geometry.

The piston acceleration extrema in the normal engine were
63000 m/s² in TDC; 38100 m/s² in BDC

For the Scotch Yoke these values were
50600 m/s² in TDC; 50600 m/s² in BDC

So the claim of 25% less peak acceleration for the Scotch Yoke seems about correct:
63000 / 50600 = 1,245

But that is not the whole story. For an optimal comparison with the Scotch Yoke let's look at a normal flat twin with both con rods on the same big end pin.

When one piston is in TDC, the other one is in BDC, so the total force on the big end pin is:
63000 * piston mass + 38100 * piston mass = 101100 * piston mass

For the Scotch Yoke the total force on the big end pin is:
50600 * piston mass + 50600 * piston mass = 101200 * piston mass

This seems to be even a fraction more than the total forces in the normal engine, but that stems from the different acceleration profiles over one crankshaft rotation.
If we integrate the acceleration values per crank degree, the normal engine and the Scotch Yoke show identical total values.

So the claim of 25% less peak acceleration in the Scotch Yoke is correct, but irrelevant.

What is relevant, are the lighter pistons that can be used with the Scotch Yoke, although the slot construction around its big end pin may cancel out this advantage.
In the animation shown above there is only a line contact between the big end bearing and the slot, but that will have insufficient load carrying capacity.
An auxiliary sliding construction in the slot will add both mass and friction, and a roller bearing construction will do away with most of the friction there, but add even more mass.
Summary: the Scotch yoke will prevent friction-causing trust forces acting on the piston skirts, and it offers effective under-piston pumping.

[Pursang]

- and BTW a piston attached to a crankshaft is definitely not "free" either, as someone I think suggested!

That was Russell Bourke's claim. After much reading & thought, I think the explanation is this.

In operation, the Bourke crankshaft does not (need to) impart any energy to the engine to complete a cycle.

In a regular engine, flywheel inertia is required to push the piston through the non-power parts of the cycle.

In a running Bourke engine, the power stroke of one piston pushes the other one through those parts, the crankshaft is not required.

He claims that the crank just captures energy from the process.

In Burke's words: You might guess that the engine would shake from piston action but it does not, because the twin piston assembly is free as it can't transmit its reciprocating forces to the body of the engine, and also absorbs those forces within itself. It is simply thrown back and forth, explosion forces reacting against momentum forces so that things are cancelled out, as in a free piston engine, which it is.

The Bourke engine has a 'formula' that Must be followed. Perhaps there is a specific combination of dimensions: bore, stroke, combustion volume, mass of Piston Assy, mass of housing etc. that produce the harmony.

Instead of a crank & scotch yoke, the engine could have a lever & ratchet to capture the energy or a linear generator with coils & magnets producing electricity. i.e. A Free Piston Engine.

Like this:


Which (sadly) brings my thoughts back to Pit-side Battery Chargers for Electric racing machines.

Cheers, Daryl

[WilDun]

In operation, the Bourke crankshaft does not (need to) impart any energy to the engine to complete a cycle.

In a running Bourke engine, the power stroke of one piston pushes the other one through those parts, the crankshaft is not required.

Instead of a crank & scotch yoke, the engine could have a lever & ratchet to capture the energy or a linear generator with coils & magnets producing electricity. i.e. A Free Piston Engine.

Cheers, Daryl

Duh!..... yeah it's all beginning to filter through to me now!

[Pursang]

In the animation shown above there is only a line contact between the big end bearing and the slot, but that will have insufficient load carrying capacity.

Which bit Frits? The Bearing or the Slot or the single line of contact?

Bourke developed a 3 layer, hydraulic slipper bearing to manage the load and speed of the engine.
description here:




An actual Bourke yoke assembly is a bit more substantial than the animation.
(As you said, negating any lightweight piston advantage).



Here's an interesting description of the Bourke crank/yoke process;

"Looks like a crankshaft, functions as a camshaft. A high speed, reverse, roller camshaft".

Careful Buddy...Them's four-strokin' words!!



Cheers, Daryl.

[WilDun]

In Burke's words: You might guess that the engine would shake from piston action but it does not, because the twin piston assembly is free as it can't transmit its reciprocating forces to the body of the engine, and also absorbs those forces within itself. It is simply thrown back and forth, explosion forces reacting against momentum forces so that things are cancelled out, as in a free piston engine, which it is.
Cheers, Daryl

Not meaning to be a smartass, but I'd hate to see it misfire with no crank - The forces would be transmitted to the body then! Especially if there was a squish gap to maintain!
But then what I am saying is irrelevant really (perhaps I am just being a smartass! }.

[Flettner]

Hum, but what? has to weigh nothing but turn straight line into rotational, perhaps back to the epicycloid crank. I did order some more 7075 yesterday enough to build two rods (just in case the anodizers bugger it up again)
Need to think of something soon as the cylinder to go on this crank is not too far off being cast. I'd like to have a big cylinder 'cast up' before Christmas.

[Grumph]

Looking at Bourke's "multi layer" bearing, I have to wonder if he ever owned a Royal Enfield...

[husaberg]

Looking at Bourke's "multi layer" bearing, I have to wonder if he ever owned a Royal Enfield...

Royal Enfield not very long ago brought Harris Performance.
ie Suzuki superbike team and former Yamaha YZR500 frame makers
RE have a huge push on with the aim of producing some "new Sports bikes" in the Modern Triumph mould.

[WilDun]

Looking at Bourke's "multi layer" bearing, I have to wonder if he ever owned a Royal Enfield...

Yes Grumph, I think I know what you are thinking of, ie the white metal coated floating bush in the big end as opposed to the usual rollers of the day, I used to own a Model G and those never did give much trouble at least not in a road going bike.

[husaberg]

Yes Grumph, I think I know what you are thinking of, ie the white metal coated floating bush in the big end as opposed to the usual rollers of the day, I used to own a Model G and those never did give much trouble at least not in a road going bike.

RE would have is said to have used them as they were cheaper than Alloy cadged or not rivotd one piece big end cadges, which were not mass produced at the time.
Triumph (speedtwin)at the time ran its Al Alloy rods directly on the crankpin with no bearing at all.
There are MMC rods that do the same now. Reputed to last a whole MX season as well.

[Pursang]

Not meaning to be a smartass, but I'd hate to see it misfire with no crank - The forces would be transmitted to the body then! Especially if there was a squish gap to maintain!
But then what I am saying is irrelevant really (perhaps I am just being a smartass! }.

Someone needs to be as 'Smart as'.
I really don't understand how it works, that doesn't mean it can't.

I can sort of accept the free piston concept, when the engine has no load.
But, in my (sad, tortured) mind, a loaded over-run would put the crank/yoke/bearing hard against the piston action, allowing forces to be transferred to the case.

But, then again: Maybe the rate of gas expansion allows the 'following' piston to catch up with the yoke and counteract the 'over-runs' attempt to push on the 'leading' piston through the yoke (or visa versa). Hard to think about, hard to explain, hard to visualise. End result, as long as there are compressions & expansions the piston system remains free......Or not?

And that might apply to misfires too?

Don't know if there is any actual squish, compression ratio is high (up to 24:1) But combustion can start at 90deg. BTDC.
Dwell at top and bottom near 45deg.

It's hard to consider in normal terms.

cheers, Daryl,

[Pursang]

Hum, but what? has to weigh nothing but turn straight line into rotational.....

Ask and you shall receive.

Not quite nothing, but Very light and in both directions too!

https://mtc.cdn.vine.co/r/videos/245...Qqg0PSwPuWrY6V

Probably pay to be a bit tougher with the specifications when it comes to your Christmas presents.

Cheers, Daryl