My initial reaction is that 150mpg is at best optimistic
. My VW 4 cyl diesel averaging 70mph over 500 miles gets roughly 50mpg. An engine with an equivalent of 32 pistons will offer greater surface area (about 4 times) for the same displacement to loose heat. If 20% heat loss is through the radiator of my VW, then a very quick calc indictes that this would go up to about 50% heat loss - so 50mpg becomes approx 31.25mpg...
Large displacement iron block 6-cyl truck engines are not a fair comparison for mass either, since they are designed for 15'000 cost effective hours of extreme conditions before overhaul. A better package, especially for small displacement, would be two large diam pistons per arm (or whatever it is called). That crank mech looks relatively complicated too, so the only weight saving i see is in the block/head casting mass (worth considering though).
The main problem with this type of design is always emissions. Like a uniflow scavenge 2-stroke, you need to keep the rings oiled. This means that there is a steady leakage of oil from the exhaust valve. 4-stroke poppet valves are a compromise, but they do work.
I notice the demo video showed that this "diesel" engine was spark ignited
. You would need a ring of diesel injectors for good fuel/air distribution. Getting the right fuel spray pattern and air swirl is feasible, but would take development.
The main point worth considering is that turbo charging offers a good way to improve power/weight of a conventional engine. A gas turbine can be seen as a big pistonless turbodiesel
, giving an idea of power/weight possibilities. The limit to this boost is normally combustion initiation, with various alternate methods currently being investigated.
I suspect that a range of more compact turbodiesels, with improved crank mechanisms and combustion mechanisms will now start to appear. The main limitation for more conventional designs is always cost and durability, and i'm afraid a demo with a load of compressed air
doesn't do it for me...
Mart