2 cycle rotary valve engine

[PRiggs78]

Older mechanical designs are cool for their mechanical engineering approach to two stroke.

I like the idea of computer controlled direct injection and lubrication. This would be a feat on a tiny model engine.

 

[Steamchick]

I have not sketched-out the idea, but as a configuration for a disc-valve twin (180 degree crank) I wonder if there could be a "nice" layout with an enclosed lubricated central bearing on the crank, with the annulus being a chamber with a disc either side so a single carburettor could feed 2 cylinders.... Must get to a drawing board while the neurons are activated!...
K

 

[PRiggs78]

A twin may get by with a shared crankcase too space. Provided the case volume isn't too high negating any vacuum draw. There are plenty of twins out there that do this.

 

[Steamchick]

Hi PRiggs, But surely that would have to be a 360 crank twin? - effectively a split single?
K

 

[Peter Twissell]

It depends whether it's a parallel or boxer twin. A boxer with a 180 degree crank or a parallel with a 360 crank can share the crankcase volume.

A split single is something else - two cylinders are each offset from a single throw crank, so that the pistons hit TDC at maybe 30 degrees separation. They share a common combustion chamber. One cylinder has intake ports and the other has the exhaust ports. The design allows for a 2 stroke with asymmetric port timing.

 

[Kasey]

Are there any 2 strokes with 4 stroke style lubrication?

 

[Peter Twissell]

There has been considerable research into this area. Some years back, I saw a design which had oil fed bearings which were scavenged through a second set of oil passageways in the crankshaft, with seals keeping the oil from mixing with the fuel in the crankcase. Ceramic coatings eliminated the need for cylinder lubrication.
Large marine diesels use 4 stroke type lubrication, but don't use crankcase induction. They have supercharger type induction.
See also the Commer TS3 engine.

 

[Steamchick]

PRiggs: Great information: When I commented on a 360degree configuration, I was referring to a parallel twin, as I have never seen a 2 stroke "boxer" - and agree a 180 crank would suit that!
Peter Twissell: I also remember a crank made up with direct lubrication and a host of seals.... - maybe something Yamaha were working on in the 70s with a view to "cleaner" 2-strokes achieving the California emission laws of that era? Having worked on cars' emissions since the late 1980s, more closely post 2000, I am sure that piston ported engines are too limited to meet current laws and have practical power bands, as they rely so much on the gas dynamics for their best (most efficient?) fueling, combustion, heat transfer and scavenging. However, there may be a means of varying the port timing to produce a cleaner 2-stroke of the appropriate size for motorcycles? But 4-strokes have taken a lead that is probably not commercially practical for anyone to try and achieve with 2-strokes. Money makes a lot of decisions!
Fortunately, we can make models outside of the road vehicles laws...
K

 

[Peter Twissell]

If the 2 stroke has any future in the automotive world, it might be as a range extender. In that application, the engine can operate at constant RPM and load, so it may be possible to optimise porting, exhaust geometry and gas flow for that one, narrow set of conditions.

 

[Steamchick]

Thanks Peter. Good one!
But there are perhaps millions of 2-strokes produced every year for "micro-power" hand tools, garden tools, etc. But even these are now being superceded by re-chargable battery appliances...
Ho hum... Progress?
A good job "us modellers" record history in our models!
K