ICE dead, not so fast
 

The ancient opposed piston layout may come back and fight on.
The lighter, lesser friction surfaces and simpler design do not need the typical four-stroke engine valvetrain, intake and exhaust ports, and complexity of synchronized camshafts and valves.
Electronic control now allows the optimum metering of air and fuel precisely and could take advantage of the design's inherent simplicity and efficiencies.

Opposed-Piston - Achates

https://www.youtube.com/watch?v=_QTfvIfsjJw

https://www.youtube.com/watch?v=Ov73-okhkG0

They say about 4 years from being put in a car. Is this the Elio motor?

It would be interesting to see more technical data on the engine. It obviously has some benefits and I'm sure some drawbacks.

"Simpler design" should have a disclaimer. It's interesting that you could possibly do away with camshafts, but without additional hardware you now have a fixed valve timing engine. I foresee most solutions to this being more complicated and potentially more failure prone than a balanced rotating shaft.

Plug-in hybrids (or EVs with "range extenders) are certainly one solution to battery limitations, but ICEs today are large and complicated, and take up a significant portion of a vehicle. Anything that can downsize the footprint without sacrificing efficiency would be great.

The only 2 stroke engine I have seen that even have a shot at possibly meeting emissions in the US use exhaust valves.

With direct injection and a cat you shouldn't need them, only issue is you would have to run "lean" to burn the oil blow by or have a trap of some sort

Modern snow mobiles run oil injection separate from the fuel.
The exhaust valve engines appeared to allow for more power at full throttle and delay the exhaust rejection to allow more time for better fuel burn at part throttle.

The part throttle or variable valve issues could be solved by teaming it with an electic propulsion and running the motor at max power just to recharge batteries. A setup like that should be allowed to have higher emissions while it's running because maybe it only needs to run 1/2 or 1/3 of the time.

Achates, Cummins and US Army
 

Gasoline and diesel (possible multi-fuel) Achates engines for the foundation of Future Fighting Vehicle for the US Army.

Achates Power Wins $14 Million Military Engine Project

us-army-awards-contracts-for-future-fighting-vehicle-designs

Different opposed piston engine designs
 

Opposed piston engine in a hybrid setup.

https://www.youtube.com/watch?v=jA0DZXpkQV0

Another engineering group and their opposed piston/opposed cylinder setup.

https://www.youtube.com/watch?v=9Gcaoel6QFY

Even weirder, a rotating opposed piston engine!

https://www.youtube.com/watch?v=kHXKNpXoQUo

? 1 cylinder opposed cylinder engine???

cylinder is the space for the piston.

Two pistons in one cylinder

Some years ago, a British magazine did a test with an old Commer truck with the TS3 "Knocker" engine and Euro-3 versions of the Isuzu NPR, Mercedes-Benz Sprinter (IIRC it was a 413CDI) and a Fiat Ducato, and almost all the emissions from the Commer were lower than its counterparts, its only disadvantage was the higher particulate matter emission. Anyway, some opposed-piston Diesel engines would be great for general aviation.

The free piston linear generator looks to be the perfect solution for a range extended EV.

Personally, I would like to see a terrhoidal engine... (The MYT) engine was an equivalent 800ci with a 15" diameter engine that weighed 150#... If it could be made to work, that is...

Even though some "revolutionary" designs are highlighted once in a while, I wouldn't hold my breath for the free-piston or for any rotary engine by now. Apart from the ressurging of the opposed-piston layout, which had been highly favored by German aircraft manufacturers during the interwar period, there are other concepts such as the real Atkinson cycle and the Scuderi cycle that might become more relevant in the next years.

The OP design claims it is 20% better than diesels - that is over 50% !! And they claim is is 50%+ better than the best gasoline, which is about 57% - which is clearly impossible; given the Carnot limit.

You're talking about the linear generator? I suppose they could twist it to mean those percentages if they are talking the comparable electrical output. Either way, this is a brilliant design if nothing more than the packaging.

This thing won't die

Now coming up under 37 mpg full size pickup.

Spec seems to be a 7 liter turbo motor.

Achates already claims that at least one manufacturer is setting up the tooling to make an engine that follows its concept. I'd just hope they get a gear-driven compressor (or crankshaft-driven like the one fitted to the old Rootes TS3) instead of belt-driven in a production version.
At Least One Automaker Plans to Produce an Opposed-Piston Engine - Motor Trend

lol, should get a block of iron and couple two cheap chainsaw engines, and link them to a opposed-piston configuration, then make some kind of a head/ combustion chamber for the spark plug :D
then attach the crank outputs with chains

I'd rather use gears instead of a chain to synchronize the crankshafts. Could eventually use the gears to provide power take-offs for the alternator, oil and fuel pumps and other accessories. I also like the single-crankshaft setup used in the Rootes TS3 engine.

this was more of an idea for some testin'. the best results indeed is achieved with gears.