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LiquidPiston: Efficient rotary engine

liquidpiston.com

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Re: LiquidPiston: Efficient rotary engine

#2

Post by vlehto »

Nah.

It has almost all the problems of Wankel. Low torque, difficult sealing, weirdly shaped expansion chamber (where part of the burn happens at high RPM, this might get you impurities in the burn). This seems to be kinda "sleeve valve" type valves. Poppets dominate for couple of reasons: A quick open and close and B self sealing. Both features that these things necessarily lack. The balance of the thing seems horrible. You could get good balance if you put four of these on single crankshaft. But then you have 12 incredibly small burn volumes for given size of engine -> even less torque.

"A dwell near top-dead-center forces combustion to occur at nearly constant-volume conditions." If you increase chamber pressure in regular engine during top dead center, you risk breaking the crankshaft. It's likely this thing can only do it because of low HP and no crankshaft. Which in turn fucks the balance.

I'd pick rotary Atkinson over this. https://en.wikipedia.org/wiki/Atkinson_cycle

Re: LiquidPiston: Efficient rotary engine

#4

Post by wscott »

The website says "efficient" all over the place, but did anyone see where they quantified that?

It doesn't look like it would be efficient at a car-sized scale.

But even a comparison to typical lawnmower-sized engines would be helpful.

Re: LiquidPiston: Efficient rotary engine

#5

Post by Artlav »

Huh, "patented thermodynamic cycle" sound like a big red flag.

I can't quite figure out how they can manage to seal this contraption - plenty of rotating and sliding gaps in there.

Manufacturing of some of the shown parts look tricky as well.

It looks more like some cool gadget that you design for a movie than a practical machine.

Re: LiquidPiston: Efficient rotary engine

#7

Post by dsfyu404ed »

The way the shape of the combustion area changes to include long thin areas as the rotor is moved looks like an emissions nightmare. Deep and/or wedge shaped combustion chambers went away in the 1960s because of that.

Emissions speculation aside, what part of this is superior to a Wankel?

I can see the three chamber design having merit for compression ignition apps because you can better spread the combustion force around the block and reduce the amount of material needed for a particular power level or part life. With some creativity off-highway diesel could probably be used a the lubricant(highway diesel is ultra low sulfer and doesn't lubricate well at all) in low power (portable equipment) applications. All the simplicity and light weight of a two stroke gas engine but with far less idle fuel consumption, no worrying about forgetting to premix or forgetting that you already premixed and doubling the oil and you can refill it by siphoning off your tractor (and don't have to worry about fuel going stale over the winter). This is just wishful thinking though.

With a little reworking the three small chambers per rotor would probably be pretty nice for an air compressor application. More of a smooth hum and less of a drone.

The only possible thing I can think of is

Re: LiquidPiston: Efficient rotary engine

#10

Post by mveety »

willyt wrote: post #9

Good power to weight ratio and high speed running with low torque would be excellent for Hovercraft racing! (and light aircraft) http://www.hovercraft.org.uk

Light aircraft engines actually run at relatively low rpm and have a surprising amount of torque for their weight and size. The Cessna I fly operates around 2400 to 2600 rpm, compared to my car which is limited to 9000 or a motorbike which might go up to 14000.
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