Opposed Piston Diesel Engines Are Crazy Efficient

hello everyone and welcome in this video we're going to be discussing the rather unique opposed-piston engine that Achates power is developing which has shown to have pretty impressive efficiency figures now the first opposed piston engines date back to the late 1800s and they've seen use in ships airplanes submarines tanks trains and other forms of transportation ever since rolls-royce even developed an opposed piston engine for use in military applications in the 1950s having a look at the engine you'll see that two Pistons move towards one another meaning at top dead center where combustion then occurs these engines operate as two-stroke engines meaning every single time the Pistons join in the center the power stroke occurs unlike four-stroke engines the basics of how this engine works is fairly straightforward when the Pistons reach bottom dead center fresh air is pumped in through ports on the bottom of the cylinder while the exhaust is pumped out through ports on the top of the cylinder the two Pistons then move towards one another and just before meeting in the center diesel fuel is injected directly into the cylinder there are two injectors for each cylinder both facing one another on opposite sides combustion occurs pushing the cylinders back out and then the cycle repeats itself the top Pistons and bottom Pistons each rotate an individual crankshaft and these two crank shafts are then geared together to supply power to a single output shaft now while having to crank shafts may seem like an additional complexity this engine has no valvetrain meaning no camshafts rocker arms valves valve springs and even no cylinder head this particular engine we're looking at is the achates power 2.7 liter 3-cylinder engine which is good for 270 horsepower and 480 pound-feet of torque what makes this design efficient well with the lack of a cylinder head the amount of surface area that the combustion is exposed to relative to the volume of the combustion chamber is significantly reduced instead of transferring heat to a cylinder head that heat is sent to an opposing piston so more heat is used to generate useful work also by splitting the total stroke length between two Pistons you're able to have a very high stroke-to-bore ratio without super high piston speeds helping to extract as much useful work as possible it's also possible to create an ideal combustion chamber with both piston tops helping to create a fast-moving mixture and quick combustion the two-stroke engine is supercharged to control intake air pressure and it's also turbocharged the intake and exhaust ports are designed to optimize air flow scavenging the exhaust ports are open first allowing higher pressure exhaust gases to begin to exit once pressure has dropped the intake ports are exposed and fresh air flows in while the remaining exhaust gases are pushed out both ports are closed off as the Pistons move towards the center and a small amount of residual exhaust gas is left behind you might be wondering why the engine has specifically three cylinders from an efficiency standpoint this is found to be the ideal setup with just two cylinders there are gaps in exhaust delivery to the turbocharger which reduces overall efficiency especially at low loads and low engine speeds when you're not producing much exhaust with four cylinders there is too much overlap between the exhaust ports opening and one cylinder and the intake ports opening on a different cylinder this results in additional residual gas being left behind decreasing scavenging efficiency which reduces overall efficiency now that's not to say that the engine can't be used in other layouts two three four and five cylinder options are all acceptable and Achates power has worked on developing a 4 cylinder engine for combat purposes but from an efficiency standpoint three cylinders remains ideal speaking of efficiency test results show brake thermal efficiency remaining above 40 percent across a wide variety of loads in rpm peaking as high as 46 percent indicated thermal efficiency doesn't dip beneath 51 percent for the various loadings tested so the advantage here isn't just that the engine is super efficient but that it remains efficient across a wide range of rpm and loading now these efficiency numbers were achieved in 2012 studies published in SAE as recent as 2017 have shown that brake thermal efficiencies as high as 55 percent are possible using three cylinder opposed piston diesel engines so the next and most obvious question will we ever see these engines in production vehicles obviously adopting new engine technologies can certainly be a risk but we just might see them in the near future as reports from the 2017 Detroit Auto Show indicate that nine automakers have signed on as development partners and at least one of them has started to implement tooling for producing an opposed piston engine and greater volumes I'd love to hear your thoughts on this engine in the comments below what do you think is good about it and what flaws does this design have what do you think is holding it back from mass production currently also if you're interested in other unique engine technologies I'll include links in the video description as well as additional information about this engine if you guys have any questions or comments feel free to leave them below thanks for watching

Channel: Engineering Explained

Views: 4,763,798

Rating: 4.9260321 out of 5

Keywords: efficient engine, engines, achates power, opposed piston engines, two stroke engines, diesel, diesel engine, 3 cylinder, turbocharged, supercharged, supercharger, turbocharger, two stroke, two-stroke diesel, new engine, ford f150, engineering explained

Id: UF5j1DvC954

Length: 5min 2sec (302 seconds)

Published: Sun Jul 22 2018

Reddit Comments

[u/CookieMan0]

The question is why these aren't in vehicles. Here are my guesses:

• High complexity and external dimensions for given displacement

• Low volumetric efficiency

• Large size means cylinder counts are normally kept small, and small engines aren't smooth

• Probably needs a really heavy-duty start to turn two crankshafts

[u/Tom555]

I'm not as knowledgeable as far a engine efficiency goes but as far as packaging wouldn't this have limitations?

Perhaps it sits in the bay flat like a boxer engine, it seems like this would be difficult to fit. Sure it doesn't have value covers like a boxer but an extra crank shaft is sure to take up some space with presumably an extra method for keeping it oiled.

You would think this would also limit it to larger/taller vehicles when mounted length ways. Interesting to see if they are able to keep the displacement down for it to fit inside and eco hatch etc. If they can do that it might have potential.

[u/mj7602]

2 stroke AND diesel? I can’t see this meeting any stringent emissions regulations.

[u/techexengineering]

More mechanical complexity (more crankshafts, more gears, more friction) and the absolut necessity of having a supercharger and turbo to expell exhaust gases even though not completely. What about reliability and maintenance. Does it make up? Maybe.

[u/gabbagool]

well one reason is that they're diesel. and just when they were making a comeback here the automakers had to fuck it up.