Opposing Piston Engines 10

[Painterman]

Hello to all,

I keep on noticing favorable comments about opposing piston engines, i.e., Junkers and Napier Deltics. If they are so good, then why aren't they used more widely? That is to say, these engines must have a problem or a shortfall. Can anybody say what the problem is? Also, what about their efficiencies?

Any other would be appreciated.
Kind thanks & best regards
Painterman (DFD)

 

[tbuelna]

clasdauskas,

The Jumo OP 2-stroke diesels had decent BSFC for the 1930's. But it is nothing in comparison to a modern, production class 8 truck diesel engine, which typically achieve BTE's close to 50% with a TBO exceeding 1/2 million miles, while meeting tough EPA emissions standards and being produced and sold at a profit.

Sadly, most people don't appreciate how absolutely well engineered most production engines really are.

Regards,
Terry

 

[Marquis]

"Pat Primmer said:The lack of a cylinder head should increase thermal efficiency due to reduced surface area at the same bore and stroke.

Regards"

The other thermo dynamic efficiency gain comes from the speed of compression of two opposed pistons - at low speeds it's the abundance of Real time which is the reason why much more heat loss occurs at low engine rpms.
With the faster compression there should be less low rpm heat loss and it could possibly negate the need for a glow plug

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[Nemesis4]

There has been a lot of interest in this topic (judging by the 63 replies). It has occurred to me that it would be possible to actually build an experimental opposed piston engine using two VW flat four engines side-by-side. Lopping off (and blanking off) the outer cylinders, connecting the flywheels by chain and either adapting the existing inner cylinder barrels or making up new ones. It would still be a big job but much simpler than building an OP engine from scratch. I am not saying that the engine would be better than a conventional petrol engine just that it would be interesting to experiment with it. I would not be surprised if it could be made to run quite well without a blower for scavenging.

 

[patprimmer]

If it were as simple as arranging cylinders opposite each other you could use any pair of inline engines bolted together at the deck surface.

Ports, con rods, crank rockers and crankcase are just a few problems that you have glossed over.

Regards
Pat
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[Nemesis4]

True to some extent. But - the VW's have their sumps in the right place so the oil system would be OK. No crank rockers - this is a "Jumo"-type layout -two cranks only. The existing crankcases should be OK.
Being air cooled would allow the ports etc. to be made more easily than with a water jacket etc.
Two Subaru flat-fours could also be used - with possible problems of making the ports through the water jacket. I didn't say it would be easy (nothing is easy), - just simpler than building from scratch.

 

[patprimmer]

I was thinking the Commer Knocker configuration which is the only opposed engine I have actually seen.

I agree a pair of VW engines could be used as the basis for a twin crank arrangement, but so could.

I also think two inline engines could also be used. Some simple sheet metal work would fix the sump and oil pickup. The VW would also require some closing ff of the crankcase. Crank phasing might also be an issue with modifytin existing engine pairs.

There is still a major effort required to create an induction and exhaust system no mater what you use as basic raw materials.

The real question is why would you bother.

Regards
Pat
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