LiquidPiston been featured many times and it always feels like a magical bullet. For some reason my BS meter overshoots. If it is that good, we would already seen it's mass adoption.
It seems that by using modern technologies and materials, they might have solved the problems of this type of engine, which despite what they say in their advertising is not at all new, but it is more than one hundred years old.
More than a half of century ago, several companies have experimented with it, including Wankel (NSU), Renault and Isuzu, but eventually they have abandoned it. Isuzu has even produced it commercially for some time around 1963.
I have read the main LiquidPiston patents and I do not know why they have been granted, because they do not seem to include any innovation over similar patents that are more than one hundred years older.
Nevertheless, LiquidPiston must have made some true innovations, because it seems that their engines work OK, at least for military applications in drones and portable electric generators, where high power to weight ratio and low noise and vibrations are likely to be the main advantages.
Whichever is that they have improved is not in the overall design of the engine, which was well known and described in the old literature, but in the details of parts like the combustion chambers or the intake and exhaust valves, or in the seals, or in the materials used and in the manufacturing methods.
Based on how the air intake/outtake works, it seems like it will be limited to a single "cylinder" for now so it's not a silver bullet that can replace a rotary engine in something like the RX8.
Edit: There are other features of this design that seem like they would limit how far it can scale. For example, the "crankshaft" is hollow to carry air for combustion. This surely limits how much torque it can handle vs a traditional solid shaft.
Still, this is very cool and I hope they can overcome these challenges.
Mass adoption doesn't happen overnight though. Things need to be proven to some degree to make big bets on them... especially in aerospace. Making generators and UAVs is a great way to do this; If a generator fails and it's 75% lighter than what it replaced, then just have two of them around... and now you have learned something for relatively cheap.
Right, the company started right around the same time as Achates Power, and their opposed piston design is already being tested in prototypes in a partnership with Cummins, one of the largest engine manufacturers. So either a large amount of BS, or some very, very rigid licensing and partnership...
Looks like liquid piston have some partnerships with the US Government, but targeting small, lightweight generators on drones to recharge batteries, not motive power for vehicles:
