Liquid Piston engines? Better than 2-stroke someday?

Can someone with more experience take a look at Liquid Piston, , which came across on my Facebook feed a few days ago. They claim some pretty interesting numbers, though they have few (maybe two?) engines, neither of which are on the market. The thing spins really fast – 10,000 RPM claimed, so add the weight and complexity of a belt or gear reduction unit. They appear to be a long way from their projection of a 4 pound engine (dry) that generates 5 HP at 14,000 RPM. Is there anything to this? Thanks!

1 Like

I think it will be very interesting to see where this engine goes. The idea is to have a rotary engine but instead of being a Wankel style where a triangle rotor spins in an oval casing, it is an oval rotor spinning in a triangle casing. This design creates many advantages over the Wankel engine. Possibly the biggest advantage is that unlike the Wankel, it allows the designers to choose the exact combustion chamber shape which greatly improves efficiency. Other advantages include the use of stationary seals, higher possible compression ratios, much better distributed engine temperatures, piston wears instead of casing(MUCH easier to rebuild), slightly more efficient scavenging, and a much higher overall efficiency. Sadly there are some disadvantages compared to a Wankel engine. These include the use of 3 combustion chambers instead of 1 which also comes with a more complex ignition system, more complex rotor, less compact, inconvenient exhaust and intake location, and difficult to scale up (very hard to make a multi-rotor version).

If they make a 16-30hp version it could be an excellent alternative to the current 2 and 4-stroke engines paramotor engines, but I doubt they will ever see production. They have held on longer than most companies do that have never sold any products, but unless they change something fast, they will end up just the companies who made the wave disk engine, turbine on a chip, tesla pulse detonation engine, Duke engine, and dozens of others. All these were revolutionary engines capable of changing the world, but the company ended up being built around designing the engine rather than actually producing the engine and after a few years when people and governments realized they would never produce anything, they lost all funding and disappeared. Liquid piston is currently at the point where they are starting to loose funding. This year they received about half the government funding they did for last year and about a third the funding of two years ago, and they are having less investors than ever before. My prediction is they will be completely gone within two years. I really hope I am wrong, but I have seen it happen too many times and they are on the exact same path as all the other companies that have died.

1 Like

Basically it all comes down to a few questions when you think about really flying any time soon:

  • Is if suitable for our needs (e.g. weight to power ratio, noise, fuel consumption, responsiveness, …)?
  • Can you actually buy it (if your are not the DARPA or the US military, etc)?
  • Is it affordable?
  • Is it reliable?
  • Can you get spare parts without too much of a delay and in several years as well (without a major support contract)?

While the projects from Liquid Piston look great (+1 for investing in thermal engine innovation!) and might be a fit for PPG, the answers to all other questions are either “no” or “unknown” on the first glance. Hopefully that will change some day.