8 ms·

Efficient Rotary Engine Lands Million-Dollar Darpa Contract

76 points by craigjb 11y ago

raverbashing 11y ago
A better chance at Darpa than selling it to the doofuses at the big motor companies, where it would certainly be shelved.
mattlutze 11y ago
The benefit and trouble with rotary engines is their reliability -- fewer moving parts means they'll generally fail less during their life cycle, and running them under higher loads / higher output, within their specifications, will generally not reduce the life expectancy (as in, run a 100HP rotary continually at 30 or 100, nearly the same running life). But they will have a shorter overall lifespan. That large moving inner chamber and the outer chamber walls around it will wear down, and when they fail you replace a significant amount of that combustion chamber (or just junk the entire motor). It's a neat application of the technology, and particularly in contexts where either the motor is going to run for long periods at a specific speed or not be used all the time, it could make a great option for power generation.
- busterarm 11y ago
  2nd Generation Turbo RX7 owner here. Rebuilt 13B engines before. The reliability of the engine itself is way misunderstood. They aren't more or less reliable than any other engine (okay, they're way more reliable than Subaru engines...). The problems are with heat and lubrication. The early RX8s had a flawed design. 2nd and 3rd Gen RX7s had problems with their OMPs and terrible electrical problems. 2nd gens have really weak alternators stock. Turbos usually fail before engines do. Honestly the engine itself is awesome. Yes, if you lose a seal it will screw your engine (but usually the housings & rotors are salvageable). Piston engines throw rods and screw your whole car. If you bypass the OMP and run premix and actually do proper maintenance on your car, they will last. My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. I still am on the stock OMP (it's an S4).
  - caboteria 11y ago
    Glad to see their longevity is improved. I had a '74 RX-4 and the conventional wisdom at the time was that you'd get 70-80k miles before you'd lose compression on one of your tip seals. My dad got 80k on the first motor so we weren't too bummed. We changed the motor for a new one and it was still going strong when the body rusted away so badly it wasn't worth fixing. Fun car, though.
  - mattlutze 11y ago
    This book[1] on the Wankel history considered 150k miles the life expectancy for the 13B, less than for previous motors. They're really cool motors, I'm in that boat with you. How they work means forced-induction doesn't necessarily impact engine life the same way FI on piston/crankshaft motors. That the piston motor is just going to last longer not needing or before it needs major restoration. A mildly interesting point is that heat isn't an easily mitigated factor, unless we're talking the exact use cases in the OP article -- generators, which run in a very controlled RPM band. Same when we talk about UAV engines or other electricity-generation applications. So, you can engineer the motor to be efficient at those rotation speeds WRT heat management and fuel efficiency. 1: https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=PA117&dq=wankel+life+expectancy&source=bl&ots=_3t9jAEzs5&sig=Ymz3dkAEy-ibxmTPrVJmLh_CKYs&hl=en&sa=X&ei=yDc6VfnFCsuwsQGVxoGoBg&ved=0CDsQ6AEwAw#v=onepage&q=wankel%20life%20expectancy&f=false https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=P...
  - yason 11y ago
    My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. That's really low. I don't think I've ever bought a car with only 110k miles on it...
    - snowwindwaves 11y ago
      in canada it is unusual to see cars with more than 300,000 km on them, so a vehicle with 176,000 km is more than half way to being really well used, not "really low" mileage. I had a toyota land cruiser with 365,000km on rebuilt engine and 800,000 km on the body though. Where do you live that 110k miles is low mileage? How many miles is a lot to you? How/why are people driving that much?
dietrichepp 11y ago
The efficiency is mentioned, but I don't see any numbers telling how efficient it is, which is what I really wanted to hear. (Just numbers about how small it is.)
- Aoyagi 11y ago
  The cycle, which combines high compression ratio (CR), constant-volume (isochoric) combustion, and overexpansion, has a theoretical efficiency of 75% using air-standard assumptions and first-law analysis. This innovative rotary engine architecture shows a potential indicated efficiency of 60% and brake efficiency of >50%. From http://liquidpiston.com/technology/technical-papers/ http://liquidpiston.com/technology/technical-papers/
- aidenn0 11y ago
  Linked PM article has liquid piston targeting mid-50%s for their first engine.
digitalzombie 11y ago
Did they fix the reliability and oil consumption for Rotary? The rx8 ate a lot of oil cause the oil lubricating it evaporates. Also the Rx7 rubber hoses tends to wear down over time. While the rotary did won Le Man 24 hr endurance race, it is still plagues with problem. These problems isn't because Pistons are better but because Pistons had tons of time refining it. Rotary so far have been neglected and it seems like EV/battery technology will be the future while hybrid is just an intermediate step between oil and electric. Another interesting engine that GM tried was Turbine, jet engine for cars. It sound like a vacuum cleaner.
- brc 11y ago
  Mazda rotary engines are designed with oil injection to lubricate the seals - they are designed to consume oil. Rotaries, properly cared for, are a reliable engine with fantastic power delivery and small size. It's a shame they are plagued with high fuel consumption which limits their usefulness in anything but sports and racing applications. If you read the article this is not a conventional wankel rotary - the rotor design looks like a wankel housing, so it's flipped around.
  - watmough 11y ago
    Reputedly, if you own an RX-7 or RX-8, you should spin the engine up to 9k revs at least once every trip... lest carbon deposits build up and wreak havoc. I can't imagine a technology like this is that well suited to constant and relatively low power delivery.
    - busterarm 11y ago
      Not entirely accurate. The 5th and 6th ports don't open up until 3800 and ideally you want to slightly redline it for a few seconds, but you definitely want to at least open up those ports. You can also get away with not doing it for a while, but you shouldn't. on a pre-89 that (factory) redline is at 7k, 8k on 89-. RX8s you have to hit 9k. This does make it hard not to speed in an RX7, especially if you've done a little bit of work to it - not so much in the RX8.
    - 11y ago
aidenn0 11y ago
I know the intent for this engine isn't for road-legal cars, but... This runs on Diesel, and advertises a low-temperature exhaust; can someone who knows more tell me if diesel's need hot exhaust for emissions reduction? I know that they tend to use EGR for NOx, but every car with a diesel I've seen still has a catalytic converter to do something.
negativity 11y ago
This is a version of a Wankel Engine, right? https://en.wikipedia.org/wiki/Wankel_engine https://en.wikipedia.org/wiki/Wankel_engine Originally invented and patented way back in 1929.
- jccooper 11y ago
  Similar concept, different geometry. It's almost like an inverse Wankel. Perhaps this geometry is easier to handle wrt seals and lubrication. The points of the Wankel triangular rotor have always been difficult.
- tim333 11y ago
  Not a Wankel: http://pop.h-cdn.co/assets/cm/15/05/54caf9230d439_-_liquidpiston-02-1012-de.jpg http://pop.h-cdn.co/assets/cm/15/05/54caf9230d439_-_liquidpi...
x0054 11y ago
From Another Article: The compact design of LiquidPiston's lab engine currently tips the scales at 80 lbs for the 40-hp model. It would weigh less than 50 lbs in production, the company claims, far less than a comparable 40-hp diesel that would tip the scale at around 400 lbs. [1] How on earth do you get a 400lb diesel engine that ONLY produces 40HP. First, when comparing engines for power production, you should really talk about kW production capability, not HP. Engine's HP is only half the story, you also have to talk about it's torque. I know rotary engines are a cool technology, but something about this smells like BS. [1]http://www.popularmechanics.com/cars/a8174/liquidpistons-hyper-efficient-engine-turning-the-rotary-inside-out-13817971/ http://www.popularmechanics.com/cars/a8174/liquidpistons-hyp... Edit: citation added
- NickNameNick 11y ago
  If they're talking about a generator that's expected to run at its peak power all the time, then I'd expect it to be heavier than an automotive engine that only hits peak power intermittently. and 40 hp is 29.8kW. they're both measures of power. you don't need to know the torque to make the conversion.

76 points by craigjb 11y ago

A better chance at Darpa than selling it to the doofuses at the big motor companies, where it would certainly be shelved.

mattlutze 11y ago

The benefit and trouble with rotary engines is their reliability -- fewer moving parts means they'll generally fail less during their life cycle, and running them under higher loads / higher output, within their specifications, will generally not reduce the life expectancy (as in, run a 100HP rotary continually at 30 or 100, nearly the same running life). But they will have a shorter overall lifespan. That large moving inner chamber and the outer chamber walls around it will wear down, and when they fail you replace a significant amount of that combustion chamber (or just junk the entire motor). It's a neat application of the technology, and particularly in contexts where either the motor is going to run for long periods at a specific speed or not be used all the time, it could make a great option for power generation.

busterarm 11y ago
2nd Generation Turbo RX7 owner here. Rebuilt 13B engines before. The reliability of the engine itself is way misunderstood. They aren't more or less reliable than any other engine (okay, they're way more reliable than Subaru engines...). The problems are with heat and lubrication. The early RX8s had a flawed design. 2nd and 3rd Gen RX7s had problems with their OMPs and terrible electrical problems. 2nd gens have really weak alternators stock. Turbos usually fail before engines do. Honestly the engine itself is awesome. Yes, if you lose a seal it will screw your engine (but usually the housings & rotors are salvageable). Piston engines throw rods and screw your whole car. If you bypass the OMP and run premix and actually do proper maintenance on your car, they will last. My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. I still am on the stock OMP (it's an S4).
- caboteria 11y ago
  Glad to see their longevity is improved. I had a '74 RX-4 and the conventional wisdom at the time was that you'd get 70-80k miles before you'd lose compression on one of your tip seals. My dad got 80k on the first motor so we weren't too bummed. We changed the motor for a new one and it was still going strong when the body rusted away so badly it wasn't worth fixing. Fun car, though.
- mattlutze 11y ago
  This book[1] on the Wankel history considered 150k miles the life expectancy for the 13B, less than for previous motors. They're really cool motors, I'm in that boat with you. How they work means forced-induction doesn't necessarily impact engine life the same way FI on piston/crankshaft motors. That the piston motor is just going to last longer not needing or before it needs major restoration. A mildly interesting point is that heat isn't an easily mitigated factor, unless we're talking the exact use cases in the OP article -- generators, which run in a very controlled RPM band. Same when we talk about UAV engines or other electricity-generation applications. So, you can engineer the motor to be efficient at those rotation speeds WRT heat management and fuel efficiency. 1: https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=PA117&dq=wankel+life+expectancy&source=bl&ots=_3t9jAEzs5&sig=Ymz3dkAEy-ibxmTPrVJmLh_CKYs&hl=en&sa=X&ei=yDc6VfnFCsuwsQGVxoGoBg&ved=0CDsQ6AEwAw#v=onepage&q=wankel%20life%20expectancy&f=false https://books.google.de/books?id=IB2lMFqTTl8C&pg=PA117&lpg=P...
- yason 11y ago
  My 10AE has over 110k miles on it and has not blown up yet -- probably has another another 40k on it before it'll be ready for a rebuild. That's really low. I don't think I've ever bought a car with only 110k miles on it...
  - snowwindwaves 11y ago
    in canada it is unusual to see cars with more than 300,000 km on them, so a vehicle with 176,000 km is more than half way to being really well used, not "really low" mileage. I had a toyota land cruiser with 365,000km on rebuilt engine and 800,000 km on the body though. Where do you live that 110k miles is low mileage? How many miles is a lot to you? How/why are people driving that much?

dietrichepp 11y ago

The efficiency is mentioned, but I don't see any numbers telling how efficient it is, which is what I really wanted to hear. (Just numbers about how small it is.)

Aoyagi 11y ago
The cycle, which combines high compression ratio (CR), constant-volume (isochoric) combustion, and overexpansion, has a theoretical efficiency of 75% using air-standard assumptions and first-law analysis. This innovative rotary engine architecture shows a potential indicated efficiency of 60% and brake efficiency of >50%. From http://liquidpiston.com/technology/technical-papers/ http://liquidpiston.com/technology/technical-papers/
aidenn0 11y ago
Linked PM article has liquid piston targeting mid-50%s for their first engine.

digitalzombie 11y ago

Did they fix the reliability and oil consumption for Rotary? The rx8 ate a lot of oil cause the oil lubricating it evaporates. Also the Rx7 rubber hoses tends to wear down over time. While the rotary did won Le Man 24 hr endurance race, it is still plagues with problem. These problems isn't because Pistons are better but because Pistons had tons of time refining it. Rotary so far have been neglected and it seems like EV/battery technology will be the future while hybrid is just an intermediate step between oil and electric. Another interesting engine that GM tried was Turbine, jet engine for cars. It sound like a vacuum cleaner.

brc 11y ago
Mazda rotary engines are designed with oil injection to lubricate the seals - they are designed to consume oil. Rotaries, properly cared for, are a reliable engine with fantastic power delivery and small size. It's a shame they are plagued with high fuel consumption which limits their usefulness in anything but sports and racing applications. If you read the article this is not a conventional wankel rotary - the rotor design looks like a wankel housing, so it's flipped around.
- watmough 11y ago
  Reputedly, if you own an RX-7 or RX-8, you should spin the engine up to 9k revs at least once every trip... lest carbon deposits build up and wreak havoc. I can't imagine a technology like this is that well suited to constant and relatively low power delivery.
  - busterarm 11y ago
    Not entirely accurate. The 5th and 6th ports don't open up until 3800 and ideally you want to slightly redline it for a few seconds, but you definitely want to at least open up those ports. You can also get away with not doing it for a while, but you shouldn't. on a pre-89 that (factory) redline is at 7k, 8k on 89-. RX8s you have to hit 9k. This does make it hard not to speed in an RX7, especially if you've done a little bit of work to it - not so much in the RX8.
  - 11y ago

aidenn0 11y ago

I know the intent for this engine isn't for road-legal cars, but... This runs on Diesel, and advertises a low-temperature exhaust; can someone who knows more tell me if diesel's need hot exhaust for emissions reduction? I know that they tend to use EGR for NOx, but every car with a diesel I've seen still has a catalytic converter to do something.

negativity 11y ago

This is a version of a Wankel Engine, right? https://en.wikipedia.org/wiki/Wankel_engine https://en.wikipedia.org/wiki/Wankel_engine Originally invented and patented way back in 1929.

jccooper 11y ago
Similar concept, different geometry. It's almost like an inverse Wankel. Perhaps this geometry is easier to handle wrt seals and lubrication. The points of the Wankel triangular rotor have always been difficult.
tim333 11y ago
Not a Wankel: http://pop.h-cdn.co/assets/cm/15/05/54caf9230d439_-_liquidpiston-02-1012-de.jpg http://pop.h-cdn.co/assets/cm/15/05/54caf9230d439_-_liquidpi...

x0054 11y ago

From Another Article: The compact design of LiquidPiston's lab engine currently tips the scales at 80 lbs for the 40-hp model. It would weigh less than 50 lbs in production, the company claims, far less than a comparable 40-hp diesel that would tip the scale at around 400 lbs. [1] How on earth do you get a 400lb diesel engine that ONLY produces 40HP. First, when comparing engines for power production, you should really talk about kW production capability, not HP. Engine's HP is only half the story, you also have to talk about it's torque. I know rotary engines are a cool technology, but something about this smells like BS. [1]http://www.popularmechanics.com/cars/a8174/liquidpistons-hyper-efficient-engine-turning-the-rotary-inside-out-13817971/ http://www.popularmechanics.com/cars/a8174/liquidpistons-hyp... Edit: citation added

NickNameNick 11y ago
If they're talking about a generator that's expected to run at its peak power all the time, then I'd expect it to be heavier than an automotive engine that only hits peak power intermittently. and 40 hp is 29.8kW. they're both measures of power. you don't need to know the torque to make the conversion.