Big Dave has hinted that this design of engine is old and is based on the 1940s Junkers Jumo aircraft engine. In fact, the opposed piston diesel engine is much older than that. The Jumo is probably the most famous opposed piston diesel worldwide, but there are plenty more about, and some predate the Jumo by a good few years.
One was built by Junkers as a stationary plant, light marine and automotive engine and mirrors the design of the OPOC very closely, except that it has two cylinders inline instead of two opposed pistons, but both are operated from the same crank with the upper piston on a crosshead (its not a skotch yoke as described above, the skotch yoke is a crankshaft & rod arrangement designed to keep the con ron in line with the cylinder at all times). Another well known engine that uses the same single crank and crosshead arrangement is the Doxford ship engine. This is a very large engine designed to propell large ships and was first built in the 1930's. Again, its a vertical engine (about 3 storeys tall!) but differs from the Doxford and OPOC in having crossheads half way along the con rods so they are effectively in two parts (very common for large ship engines). Info on the Doxford can be found
here.
Another engine that had only one crank was the Rootes/Commer TS3. This engine was based on an earlier Sulzer design and had the crankshaft located centrally below the cylinders with large rockers linking the pistons to the crankshaft via two con rods each. A very strange looking unit, but actually very effective and used extensively in Commer trucks during the late 1940's until the early 1970's. It was a pretty powerful unit for its time. From just 3.3 litres (203ci) it developed 120bhp at 2400rpm, which for a truck engine was pretty impressive. The nearest equivalent 4 stroke truck engines of that power were closer to 8 litres (450ci). More info
here.
The Junkers Jumo had, as was stated, two crankshafts, one for each piston, geared together to keep them in sync and deliver the power from both to the aircrafts propellor. It is not the only opposed piston engine with multiple crankshafts. Probably the most exceptional opposed piston diesel is the Napier Deltic, which is an extremely compact, extremely powerful engine designed for marine, and later, rail locomotive use. It consists of three 'banks' of opposed pistons arranged to form a triangle. Think of it a bit like forming a V engine with opposed pistons, the putting another bank across the top. Each corner of the triangle had a crankshaft for the pistons in the two banks coming together at that point. In its standard 18 cylinder form (each bank having 6 cylinders) it was an 88.9 litre engine (5425ci) and delivered approximately 4000 horespower in its most powerful version. However, it was not as big or heavy as a conventional 4000 horsepower engine. In fact, it was less than half the size and weight. You can get an idea what this engine was about
here.
It is also interesting to note that in the UK an opposed piston diesel has already been used by the British army for a tank. The engine was built by Leyland (the truck maker) and featured 6 cylinders and looked like a horizontal version of the Junkers engine or one bank of a Deltic.
So, as you can see the new OPOC engine isn't really that new either. Also, many of the technical issues mentioned in the video were overcome around 50 years ago. As for the engine being perfectly balanced, frankly its not. He has forgotten that the very long rods for the outer pistons change and very short rods for the inner pistons mean they don't move in perfect unison. The outer piston will have relatively even movement, whilst the inner piston will tend to move very rapidly around TDC but very slowly at BDC, meaning the pistons won't balance each other perfectly. Also, to achieve the port timing he demonstrated, the inner and outer pistons are not working on exactly opposed crankpins. The crankpin for the inner pistons will be advanced compared with the pins for the outer pistons, which again affects balance. The result is that, whilst the engine has reasonably good balance, it is far from the perfectly balanced machine claimed, and thus will suffer from the same vibration problems experienced with more conventional engine designs.
In terms of emmissions, most 2 stroke diesels failed to meet the new regulations because they were relatively old designs running traditional mechanical fuel injection and had received minimimal development work. As a result, combustion was generally poorer than the 4 stroke that had been gradually developed over the years whilst the 2 stroke pretty much stood still. If the same development is applied to a modern 2 stroke diesel and is coupled with modern electronically controlled common rail or unit injector technologies, there is no reason why a 2 stroke could not run as clean, if not cleaner than a 4 stroke diesel. More importantly, if done right the 2 stroke has the potential to be more fuel efficient than a 4 stroke of the same output.