The Bucket Foundry

[WilDun]

Yes, old style pattern making is still king! - and probably a lot less frustrating! - but I do like Fusion 360 now and again and 3D printing can be fun as well! - good for manipulating and fine tuning a design.

BTW have you heard that Fusion 360 is now offering the full deal for around $350/year (permanently.) ie if you buy it now and $450/year after September - that is instead of $1,500 !! for the full program! ........ all subject to you renewing it every year! - That will be USD of course!
The free version for hobbyists and students remains the same! - that's easily good enough for me of course! - great program really!

[Vannik]

Thanks for your thoughts, everyone. I'm still thinking about some transfer options. I found a CFD study of scavenging with different crankshaft phase angles, but nothing about scavenging port angles. Trying to fit the long transfers around the exhaust along with cooling flow has been challenging, especially in Fusion 360.

Lohring Miller

How about two scavenging plenums around the cylinder, one above the other, each connected to a crankcase by one or two ducts, use the one chamber for swirl flow and the other for column flow?

[lohring]

Let me play around with fitting the transfer passages. It's tough to get them around the exhaust and intake ducts. I tried a run in EngMod, but the outputs don't make sense. When I get further along I'll send you a pack file with the passage drawings.

Lohring Miller

[lohring]

I found two papers on opposed piston scavenging. They used CFD to investigate the flows. The first paper looks at crank radius to rod and crankshaft phase ratios. The second looks at two intake flows with flat topped pistons and tumble flow with pistons dished on one side. Their engine scavenged best with uniform, swirling intake flow. However, a symmetrically dished piston wasn't tested. Does the tumble from symmetrical dishing scavenge the center of the cylinder? Does it do better with swirl added? Below are chamber pictures. The double squish chamber should create the tumble I'm talking about. I couldn't attach the papers.

Lohring Miller

[Frits Overmars]

I found two papers on opposed piston scavenging. They used CFD to investigate the flows. The first paper looks at crank radius to rod and crankshaft phase ratios. The second looks at two intake flows with flat topped pistons and tumble flow with pistons dished on one side. Their engine scavenged best with uniform, swirling intake flow. However, a symmetrically dished piston wasn't tested. Does the tumble from symmetrical dishing scavenge the center of the cylinder? Does it do better with swirl added? Below are chamber pictures. The double squish chamber should create the tumble I'm talking about. I couldn't attach the papers.

Lohring, where those engines scavenged with air or with mixture?

[lohring]

I believe they used air for the CFD simulations. Below are the links:

https://journals.sagepub.com/doi/ful...87814015581569
https://www.mdpi.com/1996-1073/8/6/5866/htm

Building an opposed piston engine should be easy, right? Just take two stock engines and put a cylinder in the middle. So far I've spent days trying to fit all the passages around each other limited by ring pin location and stock piston skirt configuration. We'll see how it ends up.

Lohring Miller

[Niels Abildgaard]

I believe they used air for the CFD simulations. Below are the links:

https://journals.sagepub.com/doi/ful...87814015581569
https://www.mdpi.com/1996-1073/8/6/5866/htm

Building an opposed piston engine should be easy, right? Just take two stock engines and put a cylinder in the middle. So far I've spent days trying to fit all the passages around each other limited by ring pin location and stock piston skirt configuration. We'll see how it ends up.

Lohring Miller

Thank you for the links.
Another bunch of academians having fun with CFD and going nowhere.
Opposed piston engines have one problem and that is getting power from the two pistons to the user(s) and keeping the pistons in step.
The lasting solution was first seen by me in 1994 and that was to put an AC generator on each shaft and let them rotate in opposite directions to cancel out torque reactions.
Modern electric maschines can transform up to 15kW/kg with less in pipe.
Bye,bye gears in boxes
What the world now needs is a way to put sparkplugs in center of pistons.

https://web.archive.org/web/20080501...c2/junkers.htm
.

[Flettner]

I'll say again Neils, there is no problem joining the cranks on OP engines, or at least the ones I've built.
Central spark plug? Why have a spark plug? Not talking diesel either.

[WilDun]

I'll say again Neils, there is no problem joining the cranks on OP engines, or at least the ones I've built.
Central spark plug? Why have a spark plug? Not talking diesel either.

Yes, now that we know that other types of fuel can be used without spark plugs:-
CC shape is now irrelevant.
Cylinder heads - no cylinder heads or associated attachments, (gaskets and fasteners etc.) - expensive to manufacture with high assembly and disassembly costs).
Spark plugs, - not normally required ..... (however they could still possibly be useful as a starting aid or a combustion timing device).

Trying to fit spark plugs between almost touching pistons? - difficult and unnecessary!

Thank you for the links.
Another bunch of academians having fun with CFD and going nowhere.
Opposed piston engines have one problem and that is getting power from the two pistons to the user(s) and keeping the pistons in step.
The lasting solution was first seen by me in 1994 and that was to put an AC generator on each shaft and let them rotate in opposite directions to cancel out torque reactions.
Modern electric maschines can transform up to 15kW/kg with less in pipe.
Bye,bye gears in boxes
What the world now needs is a way to put sparkplugs in center of pistons.

https://web.archive.org/web/20080501...c2/junkers.htm
.

Niels,
I don't want you to think I am ignoring your efforts in this area (speaking for myself) but I'm sure it's the same thing for the rest of the people here.
All that research is totally relevant and I would be keen to know more about the connection method for the cranks - perhaps I missed something and should have read it properly.
So I will do that, but I'm not totally sold on the idea of an engine without gears as yet!

[lohring]

So far this is what I've come up with for a racing opposed piston twin. It's piston ported with Walbro carbs, just like most of the other engines we run. I tried really hard to use all off the shelf parts. This means some crazy ports and passages to accommodate the stock piston ring pins and cut away skirts. I applied flat tops on the domed pistons, a standard mod. In this case it should give some squish. I could dish the pistons as well.

The long transfers have a straight in flow with a 5 degree up angle. The short transfers have a 15 degree horizontal swirl angle with a 20 degree up angle. I tried to keep all the passages close to symmetrical while maintaining clearance. The tit in the intake port supports the ring gap as do all the dividers above it. The intake width is limited by the skirt width.

Below are the pictures:



I appreciate everyone's thoughts.

Lohring Miller

[lohring]

This picture gives an idea of the problems involved with fitting everything in:



Lohring Miller

[Pursang]

The lasting solution was first seen by me in 1994 and that was to put an AC generator on each shaft and let them rotate in opposite directions to cancel out torque reactions.
Modern electric machines can transform up to 15kW/kg with less in pipe.
Bye,bye gears in boxes.

Niels, do you have more info on that development?

Connecting the cranks of an O/P engine with synchronised motor/alternators could create a Very compact, high efficiency, generator unit.

Electronic management of the piston phasing might also be used to extend the operating power band, say, for vehicle use.

The next stage is then to eliminate the mechanical, rotary cranks and replace them with linear coils.

This ones a boxer not an O/P, but you'll get the drift.
Perhaps it would be called an opposed free piston engine.



Cheers, Daryl

[Niels Abildgaard]

The next stage is then to eliminate the mechanical, rotary cranks and replace them with linear coils.

This ones a boxer not an O/P, but you'll get the drift.
Perhaps it would be called an opposed free piston engine.



Cheers, Daryl

It is not my cup of tea.
Unbalanced and low efficiency.

[Frits Overmars]

So far this is what I've come up with for a racing opposed piston twin. It's piston ported with Walbro carbs, just like most of the other engines we run. I tried really hard to use all off the shelf parts. This means some crazy ports and passages to accommodate the stock piston ring pins and cut away skirts.

Lohring, I'd love to see how that engine would look without the restrictions forced upon you by the stock pistons. Did you design something like that?

Connecting the cranks of an O/P engine with synchronised motor/alternators could create a Very compact, high efficiency, generator unit. Electronic management of the piston phasing might also be used to extend the operating power band, say, for vehicle use. The next stage is then to eliminate the mechanical, rotary cranks and replace them with linear coils.
This ones a boxer not an O/P, but you'll get the drift.Perhaps it would be called an opposed free piston enginel

Daryl, what you show us is neither a boxer nor an opposed piston engine. But let's forget the semantics; something like it has already been running (and shaking like hell).
Now the builders are concentrating again on an opposed free piston engine with the combustion chamber in the center where it belongs (right Neil?) and coils around the cylinder.

[ken seeber]

Frits is so correct, it'd be a shaker.

The central combustion chamber, classic opposed piston would be the go. One would think that this could be crankless. With a suitable encoder, or more correctly an axial position transducer, would enable the linear generator to act as an motor to both start the unit and maintain a movement relationship between the two pistons. Some DMG CNC milling machines use this for movements, rather than screw actuators. This would allow for compression ratio control as well as adjustable phasing. Throw in a couple of MOSFETS, an ECU, the battery and you’re away.

Unfortunately beyond me.