Opposed Piston Engine-3 cyl.

[Shannow]

As to the packaging of the engine...look at the ford V-8...

Look where the head gasket part line is, which is the end of the piston stroke, and look how much head there is...nearly another block/crank's worth.

Nothing says the opposed piston engine needs two pistons of equal stroke, at the limit of short stroke for the second crank, it can be functioning mainly as a valve mechanism, less as a power piston (still power there, 'though).

* Mount the bottom crank to the gearbox, and have a slanted 3 cylinder (like one bank of the V-8 shown).
* make it flat, and obtain the drive off an intermediate timing gear between the two cranks (have read a few papers on investigating primary transmission drive off camshafts, so it's not out there).

 

[Cujet]

Originally Posted By: Shannow
Originally Posted By: Cujet
I have to wonder how the computational fluid dynamics aspect plays into greater efficiency.


My engineering thesis was two part...one was flow of air and fuel in a simulated inlet manifold, wet floor, mixing, film speeds etc. Part 2 was to develop a glass cylinder that could take cylinder heads from the J-Car (1.3 to 2.2, SOHC, and DOHC, Cosworth DFV, and the rotary valve head that AE Bishop's were designing for the J Car).

Was for flow visualisation, and to be fitted with an instrumented flow straighter to MEASURE swirl and tumble.

That was 1990... CFD at the time at the University was cutting edge, but extremely low resolution and inertial effects.

Nowadays, with the power of CFD, that test rig would be totally unnecessary.

For the engine in question, they mention piston tops for an effective combustion chamber shape, but would also give them all the information that they need on purging the cylinder without over-purging, "egr" tuning by cylinder residuals, swirl, and what happens to that sworl when the combustion chamber is formed in that last little bit of piston movement.


I understand that we can model all sorts of things accurately today. But sometimes it's hard to significantly beat 70 years of refinement. I suspect the engineers that built the previous generations of opposed piston diesels understood what worked and why.

In my world, the aviation world, we have all manner of "super smart" engineers, many of whom have trouble achieving what has been achieved in the past, not to mention exceeding it. Piston engine efficiency is a great example. The Lycoming engine in my lowly Cessna 177RG can achieve a BSFC number of 0.42 (pounds fuel per HP produced, per hour) in it's stock configuration, and 0.38 with the simple addition of electronic ignition. A efficiency number only recently matched by Toyota in it's Prius. NOTE: There have been many who have tried to build a better aviation piston engine, many of us are still waiting for that success....

 

[A_Harman]

Originally Posted By: Cujet
Originally Posted By: Shannow
Originally Posted By: Cujet
I have to wonder how the computational fluid dynamics aspect plays into greater efficiency.


My engineering thesis was two part...one was flow of air and fuel in a simulated inlet manifold, wet floor, mixing, film speeds etc. Part 2 was to develop a glass cylinder that could take cylinder heads from the J-Car (1.3 to 2.2, SOHC, and DOHC, Cosworth DFV, and the rotary valve head that AE Bishop's were designing for the J Car).

Was for flow visualisation, and to be fitted with an instrumented flow straighter to MEASURE swirl and tumble.

That was 1990... CFD at the time at the University was cutting edge, but extremely low resolution and inertial effects.

Nowadays, with the power of CFD, that test rig would be totally unnecessary.

For the engine in question, they mention piston tops for an effective combustion chamber shape, but would also give them all the information that they need on purging the cylinder without over-purging, "egr" tuning by cylinder residuals, swirl, and what happens to that sworl when the combustion chamber is formed in that last little bit of piston movement.


I understand that we can model all sorts of things accurately today. But sometimes it's hard to significantly beat 70 years of refinement. I suspect the engineers that built the previous generations of opposed piston diesels understood what worked and why.

In my world, the aviation world, we have all manner of "super smart" engineers, many of whom have trouble achieving what has been achieved in the past, not to mention exceeding it. Piston engine efficiency is a great example. The Lycoming engine in my lowly Cessna 177RG can achieve a BSFC number of 0.42 (pounds fuel per HP produced, per hour) in it's stock configuration, and 0.38 with the simple addition of electronic ignition. A efficiency number only recently matched by Toyota in it's Prius. NOTE: There have been many who have tried to build a better aviation piston engine, many of us are still waiting for that success....


In the case of the OP engine, it went out of production in the '70's and '80's, and therefore missed out on the CAE revolution. Achates has been smart in recognizing the advantages of that engine type and has systematically applied modern technology to advance its performance. Another major factor in the rebirth of the OP has to be advances made in diesel fuel injection. Modern common-rail systems operating at 30kpsi and injecting up to 7 times per power stroke would greatly improve the control of air-fuel mixing during combustion.

 

[Cujet]

Interesting:

This design has been around in various forms for a very long time. I'd love to see one in action someday.

 

[Silk]

That's the Commer TS3. Here's one running. Here's a bit of history of the engine. He wonders what it would've developed into if Chrysler hadn't shut the Rootes engine plant down. There is a TS4 in NZ, and have seen a video of it running...somewhere on the web.

http://www.commer.co.nz/history

 

[PeterPolyol]

Originally Posted By: Cujet
Interesting:

This design has been around in various forms for a very long time. I'd love to see one in action someday.

Smokes, that's a whole lotta reciprocating mass!

Got to peep some of the Achates videos with the staff talking about their problem-solving approach; it's impressive the tenacity they've adopted to sort the inherent drawbacks, particularly the oil consumption and the triple-duty ring sealing. It's the first time hearing of a "fuel specific oil consumption" metric- their testing method using sulfur species as a marker is pretty cool. The teams done a great job

 

[Shannow]

 

[Cujet]

I certainly hope they are successful. I believe there are a wide range of modern technologies that could be used to manage the engine. Including computer controlled, electrically driven scavenging instead of both a supercharger and turbocharger.

There are many variations on two stroke diesels. Some are quite impressive.

Here is a very interesting and efficient design.