
LiquidPiston: Efficient rotary engine - dgudkov
http://liquidpiston.com/
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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

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deelowe
They list the benefits here: [http://liquidpiston.com/technology/engine-
benefits/](http://liquidpiston.com/technology/engine-benefits/)

Last time this was discussed, the power density was listed at the most
interesting feature. Also that apex seals are in the casing instead of the
rotor, which I think some speculated could help with wear/maintenance.

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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](https://en.wikipedia.org/wiki/Atkinson_cycle)

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Derpdiherp
Previous posting of this:
[https://news.ycombinator.com/item?id=11908942](https://news.ycombinator.com/item?id=11908942)

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snarfy
It's like an inverse Wankel. The chamber is the triangular part and the rotor
is oval shaped.

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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.

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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.

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toss1
It even has disadvantages compared to the Wankel engine, in that the intake
and exhaust airflows are through the sides of the engine, so you can't even
stack them along the same crankshaft without seriously compromising the
airflow and packaging. Also, while it doesn't have the Wankel rotor tip seals
and their associated issues, they don't say much about sealing all their other
surfaces.

This is likely why they replaced the 6.5Hp motor in their demo go-kart with a
3Hp version of their own motor (if it was a real Wankel, they would have used
a two- or three-rotor stack and gotten almost the same or more power for ~1/4
the weight, which would have been a good demo. Instead, they look like they're
driving a go-kart at about 1/4 throttle.

Although they tout weight advantages, their power-weight ratio is actually
pretty bad compared to a variety of other engines, including Wankels and two-
strokes of similar sizes, e.g., for model airplane power plants.

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FiatLuxDave
I'm very confused why the name of the company is LiquidPiston, when their
primary product appears to be a rotary engine, not an actual liquid piston
engine. Was there a pivot or a previous product? Does anyone know?

For examples of actual liquid piston engines, see:

[https://en.wikipedia.org/wiki/Fluidyne_engine](https://en.wikipedia.org/wiki/Fluidyne_engine)

[https://en.wikipedia.org/wiki/Humphrey_pump](https://en.wikipedia.org/wiki/Humphrey_pump)

[https://en.wikipedia.org/wiki/Pulsometer_pump](https://en.wikipedia.org/wiki/Pulsometer_pump)

[http://www.google.com/patents/US5127369](http://www.google.com/patents/US5127369)

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willyt
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](http://www.hovercraft.org.uk)

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mveety
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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IgorPartola
I'll just leave this here: [http://thegarage.jalopnik.com/the-rotary-engine-
sucks-177317...](http://thegarage.jalopnik.com/the-rotary-engine-
sucks-1773174001)

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Aelinsaar
So it has all of the usual problems you'd find in your Mazda's Wankel. Neat.

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amelius
Somewhat disappointed that it isn't an electrical engine.

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passiveobserver
They've apparently created a
[https://en.wikipedia.org/wiki/Wankel_engine](https://en.wikipedia.org/wiki/Wankel_engine)

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milesokeefe
It is a rotary engine but it is distinct from the Wankel rotary engine.

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passiveobserver
How so? Looks the same to me.

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firmgently
__autoplaying video __(warning for those of us with a limited data allowance)

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firmgently
autoplaying video (for those of us on limited data allowances)

