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AutoBlog: EcoMotors: Opposed piston, opposed cylinder engine ups power density

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People have been predicting the death of the internal combustion engine for at least 50 years. Thing is, most of the folks making the predictions has themselves died, or been silenced by A) ICE is still here B) it's better than ever. Still, the technology could be improved. All that sound and all that heat is just inefficient waste. And what about parasitic losses, like power steering pumps and valve train? Well, some OEMs (like Ford) are switching to mileage boosting electronic steering to save some MPG. However, electric valves are a long ways off. Not only would they be infinitely variable, but removing the chains, rods and springs needed to run conventional valves would increase mileage by 20%, at least. And that's just one route.

Another is the EcoMotors International (EM) opoc engine, aka open piston, opposed cylinder. Here's how it works. Instead of an I or a V pattern, EM's opoc is layed out like a two-cylinder boxer engine. However, each cylinder contains two pistons, and they are facing each other. This gives you four rods turning the crankshaft, with no cylinder heads and no valve train (for the record, we're not sure how fuel/air enters and exits). The opoc engine is also a two-stroke, guaranteeing lots of quick torque, but it "runs as a fully balanced 4-cylinder 4-stroke engine."

Shrinky-dinkying the engine has a whole host of other benefits that EM lumps together under the banner, "power density." They include: lower weight and smaller size, fewer materials, less friction, higher MPG, lower missions and less heat rejection. And as the engine is working against itself, there's plenty of built in noise cancellation. Power? Burning diesel, two 100 mm cylinders produce 325 hp and 664 lb-ft of torque @ 2,100 rpm. Nice. And thanks to Eugene for the tip!

[source: EcoMotors]

EcoMotors: Opposed piston, opposed cylinder engine ups power density originally appeared on Autoblog on Sun, 02 Aug 2009 12:36:00 EST. Please see our terms for use of feeds.

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It's a new interpretation of an old idea. Opposed piston 2-strokes are not new....

Today, we find them in medium sized marine/industrial diesels. In fact, all the back up generators on US Navy Nuclear Attack Submarines and many diesel locomotives use the Fairbanks-Morse 38ND8 1/2 opposed piston diesel engine.

In the 1930s, Junkers-Jumo produced a series of opposed piston aero-engines for use on high endurance float planes and other long ranged aircrafts. The use of diesel fuel and the 2-stroke cycle allows for a good combination of fuel efficient and decent power density. The models were 204, 205, 206, 207, 208, 218 and 223. Of these the 205 was most widely used, seeing service in aircrafts such as the Dornier Do26.

Usually, opposed piston engines have two crankshafts linked together by a chain or gear drive. Their advantage over traditional 2-stroke designs is that intake and exhaust can enter on opposite ends of the cylinder. The cross flow aspiration dramatically improves the completness of scavenging, improving power and greatly reducing emissions. Emissions is not a concern in the 1930s, but fuel efficiency and power density were. This new concept uses a single crankshaft with long/short connecting rods. In this respect, it is rather innovative. However, one of the traditional virtues of opposed piston designs is that they are very strong and robust. I am not sure if the long, skinny connecting rod of this new design will share that attribute.

Fairbanks-Morse Opposed Piston Engine (Cutaway)


Fairbanks-Morse Opposed Piston Engine (10-cylinder version)


Junkers-Jumo 205 Opposed Piston Aircraft Engine (6-cylinder, 12-piston)


Edited by dwightlooi
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I always wondered what made the Fairbanks Morse diesels so much more powerful than their GM or Alco counterparts. When I read that it was opposed piston, I pictured in my head an H layout like a Subaru, Porsche, or Corvair... an impression inflated by the fact that all FM road switchers had the prefix "H" in their model number. I couldn't figure out why that would make the engine that much more powerful.

Thanks for this Dwightlooi.

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