Opposed Piston Engines

[Charles LamontParticipant @charleslamont71117]

The red engine in Jason’s post #812827. This ingenious and remarkably compact arrangement was devised by John Ericsson. An example of the type was used in the famous Monitor.

There are two separate cylinders back to back.

Looking at the top photo, the first clue is if there is a single piston, why on earth would you connect it to the crankshaft twice? Next, the connecting rods are at about 90° to one another. The starboard side is fully in, and the port side at about mid-stroke. If both sides were connected to a single piston the mechanism linkage could not move. In fact, that 90° angle determines the phasing of the two pistons. So (another clue) no flywheel is needed, because there are no dead centres.

A small disadvantage is that a large diameter gland is required to accomodate the rocking link to the bell crank arm. This will cause quite bit of friction and makes the areas on each side of the piston rather unequal.

[JasonBModerator @jasonb]

That would explain the two eccentrics and presumably two valves. It would be quite a nice one to model which is why I have kept the images, I like it’s simplicity a lot more than the Monitor.

Interestingly the Patent model seems to have “normal” size piston rods. It makes use of a crosshead and guide at each end and I assume there is a vertical slot to allow for the up/down movement of the lever as it describes an arc. No valve detail.

[Howard LewisParticipant @howardlewis46836]

The Commer TS3 (Made in the Tilling Stevens factory in Maidenhead) was a three cylinder, scavenge blown, opposed piston two stroke diesel.

Supposedly,a lot of inspiration came from the Junkers Jumo

Each piston drove to a rocking lever, the lower end of which had another con rod on the crankshaft which was below the cylinders.

There was talk of a TS4 for the Admiralty, but don’t think that it ever came to fruition.

The Admiralty did use conventional Foden FD6 blown two strokes in some vessels.

And, of course, they used the Napier Deltic (An 18 cylinder two stroke with three 6 cylinder banks arranged in triangular form around the crankshaft)

As used to power the Deltic locomotives, two, each producing 1,650 bhp, were used.

The Rolls Royce K series engines, in 4, 5 and 6 cylinder forms were opposed piston two strokes.

The two crankshafts were connected by a train of gears. They were known as the “Peanut Butter Engines” because reputedly, they would run on it! The intention was that by disengaging one of the gears, one crankshaft could be moved relative to the other to adjust the compression ratio. (No doubt, this would also change the port timings).  In this way the engine could run on whatever fuel could be found on the battlefield. (A M O D specification for the engines)

The test “bed” was a Dennis tractor unit used with its trailer to deliver parts, overnight from Crewe to Hythe Road in London. The transmission was a three speed Allison torque converter. Talking to the driver, they only ever used one ratio. “What’s it like on hills?”  “What’s a hill?” (With 250 bhp available, no wonder) Reputedly, unladen, it could out accelerate a Jaguar from 0 – 30!

Being a scavenge blown two stroke, they were NOISY!

There is one in the Rolls Royce Heritage collection.

The larger Leyland L60 was a similar engine, intended for tanks.

Howard

[Howard Lewis]

On Howard Lewis Said:

There was talk of a TS4 for the Admiralty, but don’t think that it ever came to fruition.

 

YouTube video here, with the people involved talking about it, and a sight of the thing itself:

[Howard LewisParticipant @howardlewis46836]

Thank You Andy, for that.

The engine was far more developed than first thought.

Interesting about cushioning the drive to the scavenge blower on the Stage 2 engine.

The TS3 used a long quill shaft to drive the blower. They were prone to breakage. (I have the remains of one in a drawer in the workshop, waiting to find a use after MANY years!)

The problem with all superchargers was the inertia when the engine was accelerating, and the need for some flexibility in the drive.

The TS3 initially used an in line injection pump, but later used a DPA.  The governor development engineers at C A V were slightly in awe of the TS3. Like the R-R C range, it had a huge rate of acceleration (circa 5,000 rpm/sec/sec).

It was said that if you were alongside the engine on a test bed and it got out of control, you had less than 5 seconds (That long?) to do something (Run being the safest!) before you were joined by bits of hot metal!

Driven hard for long periods, the oil needed to be of high quality if crankcase explosions were to be avoided. Embarrassing, to say the least, since the air compressor, for the brakes, was mounted on one of the side covers, driven off one the rocker levers.

Rolls Royce Oil Engine Division use three different versions of the “compounder” drive to the supercharger, before arriving at a satisfactory, reliable compact system.

In a mixed fleet, used to conventional 4 stroke engines, the problem was that drivers did not know to keep a blown two stroke spinning (Lacking the low speed speed torque of the 4 stroke.Very little torque was available below 1600 rpm). Often that resulted in the wet liners moving and coolant going into the sump.

The Foden FD4 and FD6 were similar, needing their 4 speed plus 3 speed range change gearboxes, to enable the revs to be kept up.

Kept revving, the TS3 sounded like a Triumph TR2 and went like one. Rated speed was 2500 rpm

Once I saw 2300 rpm, in 5th gear, down hill. The speedo graduations stopped at 70 mph, but the needle was over the watch at the bottom of the dial, at 6:30! The only car to overtake was a Lotus Cortina!

Howard

 

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