How it works: https://www.liquidpiston.com/how-it-works
I still don't understand how it seals better than a Wankel. I understand how it's turned inside out, and it's very clever, but it seems like it would have the same problem with seals.
Yes. However, the apex seals of the Wankel are the most troublesome, from what I've read about the RX-7/8.
This design has a smooth surface against the seals at all times, and they can be lubricated directly.
What you're describing is a challenge on peripheral port (race) engines where very large intake and exhaust ports must be bridged by the apex seals, and in the pursuit of performance their radius is often less than ideal making the transition onto and out of the port area more abrupt.
The spark plug hole however is relatively small and circular.
High-mileage Mazda Wankels typically require overhauling because the side seals become seized in a compressed state (their springs are meager segments of ~sinusoidal wire, and the motor burns oil by design causing excess carbon/coking clogging them up), resulting in excess blow-by and unintended oil burning. Once the side seals go, the combustion gases start reaching the oil control rings, baking their soft interior seals into brittle plastic and it's all downhill from there.
source: former rx-7 enthusiast with multiple diy engine rebuilds in his past.
Edit:
BTW something that's often misunderstood about Wankels is that the rotor turns lazily at 1/3rd the engine RPM. So despite it being a "high revving" engine, there isn't actually that much centrifugal force acting on the apex seals at conventional engine speeds. The pain point in this department is the stationary gears responsible for converting that 3X eccentric shaft speed into a mix of orbital and rotational motion at the rotors.
1000+Hp Turbo 4rotor AWD [All-Wheel-Drive]
https://m.youtube.com/results?search_query=4rotor+turbo+1200... There's definitely a market for rotary engines, time will tell how this new form takes shape.
http://what-when-how.com/automobile/wankel-engines-automobil...
See also Pengaru's comment about problems with side seals, specifically:
I'm curious what the emissions look like. And I'm not sure if the apex seals actually change how much distance they rub over (though stationary may be enough to make them easier to deal with, and probably cheaper to replace the rotor rather than the housing if it gets scratched).
Both intake and exhaust is done via two separate ports in the rotor. Due to their positioning, there are separate intake and exhaust strokes.
> a one rotor X engine behaves like a 3-cylinder 4-stroke
I don't expect emissions to be any good since it's fundamentally a 2-stroke, which is perfect for non-road based applications. I don't think we'll see this on the road... ever.
> https://www.liquidpiston.com/how-it-works
At 53 seconds, it shows the intake cycle beginning. In the same lobe, the exhaust & the intake ports are both open or "connected" at the same time, which is the 2-stroke cycle.
They need to be 100% isolated and it's not super obvious that they are.
I'm pretty in awe of the cleverness. Hope it works out.
Does this design require oil in the fuel? Certainly in the case of burning diesel I would expect that alone is a good enough lubricant.
It's very small and lightweight, so it could serve as a range extender running a generator in an electric vehicle.
2 strokes have to go oil-sump + direct injection with supercharger to be able to match a 4 stroke when it comes to maintaining thermal efficiency, match power density while meeting emission standards.
All that complexity and the 4 stroke atkinson's cycle looks really attractive again. A huge benefit in of the Atkinson's setup is it can switch back to the Otto seamlesssly and directly drive the car for additional power (i.e Hybrid vehciles)
If you can parse through the noise of Quora posts, this highlights above[0].
Tesla won't use it gasoline for range extension - it's against their religion - which I subscribe to.
[0] https://www.quora.com/Why-arent-2-stroke-engines-used-in-car...
It's lighter, so less power is required to move the whole car, so it's fine if it provides less power than a regular diesel.
It is also easier and cheaper to make.
Is durability and maintenance the real issue?
So using it for constant RPM applications such as a generator can make sense. Using it as the prime mover where a wide power band is needed is a bad choice.
To make a 2 stroke meet emissions while maintaining its primary gain - thermal efficiency, and matching the power density a lot of complexity is needed.
This quora post[0] largely sums that up, but quora is only so trustworthy.
[0] https://www.quora.com/Why-arent-2-stroke-engines-used-in-car...
That's actually quite clever -- increase the capacity, without increasing the size.
The new piston design looks to have a much larger sealing area against the walls of the block, and the lack of distinct edges -- the ever-so-fragile apex seals -- should increase longevity, although IANAME, so have your salt-shaker ready for action.
These look fairly simple to build as well.