[m_ter_berg]

In the 1940's, the Germans had the Jumo 223 diesel (2 pistons per cylinder, 2 stroke, supercharged).

Has anybody considered parallel cylinders joined at the top to accomplish the same thing?

The idea would be to have only one crankshaft and no valves, but excellent scavenging. For a simple 2 cylinder engine, there could be an intake port on one cylinder and an exhaust port on the other cylinder (each cylinder has a piston on a common crank).
The joining at the top between the cylinders could allow for a swirl for better combustion efficiency.
Maybe scavenging would be better too.
You could have the efficiency of the Jumo 223 diesel, but with only one crank case (and easier maintenance).

What do you think?
(advantages, disadvantages?)

- Mark

[ebaines]

I'm having a hard time visualizing what you mean by this:

Has anybody considered parallel cylinders joined at the top

Can you describe this a little more clearly? Do you mean in-line cylinders, like on a flat-six? Or perhaps you're thinking of something like in the attached photo, using levers to connect each piston to a single crank shaft?

[m_ter_berg]

This is a reply to ebaines to help visualize the engine concept:

Imagine an old 2 cylinder, 2 stroke (Yamaha RD400 motorcycle engine).
Now cover the exhaust ports on one cylinder and cover the intake ports on the other cylinder. Drill a hole between the cylinders at their top so that gases can move between the cylinders. Put a supercharger on to the intake port.

The intent is to work as a single piston 2 stroke engine, but with maximum scavenging efficiency and more complete combustion.

Does this help?

- Mark

[ebaines]

So the cylinder that has its intake port covered gets its fuel/air mixture through a pipe that comes from the other cylinder? Are the two pistons in phase? If so - I don't see the advantage over simply using a single larger diameter piston. If they're working 180 degrees out of phase like in the attached sketch then the second cylinder's fuel/air mixture intake consists of the exhaust of the first cylinder, so would have too little unburned fuel in it to make much power. You must have something else in mind - what am I missing?

Attachment 46391

[m_ter_berg]

Getting closer.. .
The 2 pistons would move in phase.
The port between the top of the 2 cylinders would allow gases to move from one cylinder to the other.
The intended advantage of this is to minimize any chance of unburned mixture escaping out the exhaust port.
This was one of the advantages of the Jumo 223, but I am suggesting this may be accomplished with only 1 crank, no valves (just ports), and much simpler than the Simpson 2 stroke engine you have in the diagram.

There is an efficiency advantage in 2 stroke diesel engines that have exhaust ports and intake ports 'controlled' by separate pistons.

Have a look at the first 2 engine concepts in this website.. .
Hybrid Opposite Piston Engine - HOPE & Portable Range Extender / State of the art

[joypulv]

I don't know a tenth of what you two know.
I just remember 2 cylinder 2 strokes as vibrating all to pieces.

[m_ter_berg]

After some snooping around on the Internet, I found the concept I had in mind.
It is called a "split piston"design. Have a look.. .

http://www.odd-bike.com/2014/02/dkw-...force-fed.html

[ebaines]

Very interesting - the idea of a common combustion chamber for the two cylinders is what I was missing. Also the pistons are not quite in phase with each other, as one leads the other by an amount to optimize scavenging.