5 ms·

LiquidPiston: Efficient rotary engine

87 points by dgudkov 10y ago

vlehto 10y ago
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
snarfy 10y ago
It's like an inverse Wankel. The chamber is the triangular part and the rotor is oval shaped.
wscott 10y ago
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.
Artlav 10y ago
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.
Derpdiherp 10y ago
Previous posting of this: https://news.ycombinator.com/item?id=11908942 https://news.ycombinator.com/item?id=11908942
dsfyu404ed 10y ago
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
- deelowe 10y ago
  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.
- en4bz 10y ago
  Since combustion happens on the three corners of the engine the heat distribution will be much more even compared to a Wankel where there is a heat differential between the combustion and compression side of the engine. Since there is better heat distribution the tolerances may be able to be smaller reducing the sealing issues.
passiveobserver 10y ago
They've apparently created a https://en.wikipedia.org/wiki/Wankel_engine https://en.wikipedia.org/wiki/Wankel_engine
- milesokeefe 10y ago
  It is a rotary engine but it is distinct from the Wankel rotary engine.
  - passiveobserver 10y ago
    How so? Looks the same to me.
willyt 10y ago
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
- mveety 10y ago
  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.
deleted 10y ago
[deleted]
amelius 10y ago
Somewhat disappointed that it isn't an electrical engine.
firmgently 10y ago
autoplaying video (for those of us on limited data allowances)
firmgently 10y ago
autoplaying video (warning for those of us with a limited data allowance)
Aelinsaar 10y ago
So it has all of the usual problems you'd find in your Mazda's Wankel. Neat.
IgorPartola 10y ago
I'll just leave this here: http://thegarage.jalopnik.com/the-rotary-engine-sucks-1773174001 http://thegarage.jalopnik.com/the-rotary-engine-sucks-177317...
toss1 10y ago
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.
FiatLuxDave 10y ago
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

87 points by dgudkov 10y ago

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

snarfy 10y ago

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

wscott 10y ago

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.

Artlav 10y ago

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.

Derpdiherp 10y ago

Previous posting of this: https://news.ycombinator.com/item?id=11908942 https://news.ycombinator.com/item?id=11908942

dsfyu404ed 10y ago

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

deelowe 10y ago
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.
en4bz 10y ago
Since combustion happens on the three corners of the engine the heat distribution will be much more even compared to a Wankel where there is a heat differential between the combustion and compression side of the engine. Since there is better heat distribution the tolerances may be able to be smaller reducing the sealing issues.

passiveobserver 10y ago

They've apparently created a https://en.wikipedia.org/wiki/Wankel_engine https://en.wikipedia.org/wiki/Wankel_engine

milesokeefe 10y ago
It is a rotary engine but it is distinct from the Wankel rotary engine.
- passiveobserver 10y ago
  How so? Looks the same to me.

willyt 10y ago

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

mveety 10y ago
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.

deleted 10y ago

[deleted]

amelius 10y ago

Somewhat disappointed that it isn't an electrical engine.

firmgently 10y ago

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

firmgently 10y ago

autoplaying video (warning for those of us with a limited data allowance)

Aelinsaar 10y ago

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

IgorPartola 10y ago

I'll just leave this here: http://thegarage.jalopnik.com/the-rotary-engine-sucks-1773174001 http://thegarage.jalopnik.com/the-rotary-engine-sucks-177317...

toss1 10y ago

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.

FiatLuxDave 10y ago

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