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LiquidPiston's “inside-out” rotary X-Engine wins Army research contract
- verdverm 6y agoHow it works: https://www.liquidpiston.com/how-it-works https://www.liquidpiston.com/how-it-works
- tsomctl 6y agoA picture is worth a thousand words. (Well, video in this case) 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.
- wffurr 6y agoThey claim the seals are stationary and can be lubricated from the housing, which "solves" the durability and emissions problems with Wankels.
- prsutherland 6y agoA Wankel has seals attached to the rotor that rub against the wall of the chamber. This engine only has three points on the chamber wall that touch the rotor, so the seals can be installed on the chamber wall and it is significant easier to cool and lubricate a fixed seal rather than a rotating seal.
- dv_dt 6y agoWouldn't there also be seals on the two faces of the rotor too?
- ansible 6y ago> Wouldn't there also be seals on the two faces of the rotor too? Yes. However, the apex seals of the Wankel are the most troublesome, from what I've read about the RX-7/8.
- sitharus 6y agoAs I understand it from friends who're in to rotary engines, the biggest problem is the spark plug hole. The seal - which is being forced outwards by rotation - will fall in to the hole slightly and then wear against the edges of the hole as it rotates past. This gradually increases blow-by and reduces efficiency until it no longer seals at all. This design has a smooth surface against the seals at all times, and they can be lubricated directly.
- pengaru 6y agoThat is not the primary source of wear problems on Mazda Wankels. 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.
- smokelegend 6y agoInsane power 1000+Hp Turbo 4rotor AWD [All-Wheel-Drive] https://m.youtube.com/results?search_query=4rotor+turbo+1200hours+awd 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.
- deelowe 6y agoThe same seal that contacts the rotor likely seals the face as well. That's how wankels work.
- mannykannot 6y agoThe 'seals' section in this article suggests that wankels need separate apex and side seals: http://what-when-how.com/automobile/wankel-engines-automobile/ http://what-when-how.com/automobile/wankel-engines-automobil... See also Pengaru's comment about problems with side seals, specifically: https://news.ycombinator.com/item?id=25451923 https://news.ycombinator.com/item?id=25451923
- tsomctl 6y agoSo what, you have oiling or cooling passages immediately behind the seal?
- Groxx 6y agoHuh. So it's basically a rotary 2-stroke engine? 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).
- irjustin 6y agoThe thing that makes this so interesting is that it's a 2-stroke, 3-lobe engine. The traditional wankel being a 4-stroke, 1-lobe. 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.
- SamBam 6y agoCould you explain that last part further?
- irjustin 6y agoReally small 2 strokes (like leaf blowers) use mixed oil-fuel which is absolutely terrible for emissions. 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-cars https://www.quora.com/Why-arent-2-stroke-engines-used-in-car...
- topspin 6y ago> I don't think we'll see this on the road... ever. It's very small and lightweight, so it could serve as a range extender running a generator in an electric vehicle.
- irjustin 6y agoThe primary limiting factor is emissions for road cars and 2-strokes. 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-cars https://www.quora.com/Why-arent-2-stroke-engines-used-in-car...
- ksec 6y agoIs this not the same / similar design as the new Mazda Rotary ?
- donw 6y agoIt looks like the rotor design is quite different -- much more rounded and oblong, as opposed to triangular, with the combustion happening inside the rotor. 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.
- fastball 6y agoIntake/exhaust is happening through the rotor, not the combustion.
- flubert 6y agoNot an actual liquid piston engine. https://en.wikipedia.org/wiki/Fluidyne_engine https://en.wikipedia.org/wiki/Fluidyne_engine https://archive.org/details/liquidpistonstir00west https://archive.org/details/liquidpistonstir00west
- deleted 6y ago[deleted]
- dkarp 6y agoApple isn't an actual apple ;) Just the name of the company
- adrianmonk 6y agoStill an interesting comment, though, because while most people know that regular apples exist, not as many people know that liquid piston engines exist.
- 0xFFFE 6y agoWankel Engines are not new. May be these engines have better lifespan.
- pjc50 6y agoThey are keen to claim that it's not a wankel engine.
- lvs 6y agoYeah, but it basically is. The most important difference, as it appears, is they've ported the intake and exhaust through the piston rather than through the block. I don't quite understand the claim that it has a different thermodynamic cycle...
- fastball 6y agoHere is their diagram[1] of the cycle. Wankel engine uses the otto cycle (blue), theirs is what they are calling the High Efficiency Hybrid Cycle, or HEHC (in red). In terms of shape they do seem approx. the same, so when LiquidPiston says theirs is different I think they are just saying it is a more efficient cycle, not fundamentally different in terms of stages. [1] https://uploads-ssl.webflow.com/5f6086e9bbbabd41a20f2984/5f7d7a4ab14f906c57d07892_cycles-1024x676-1-768x507.jpg https://uploads-ssl.webflow.com/5f6086e9bbbabd41a20f2984/5f7...
- lvs 6y agoThanks, that is quite obviously the identical thermodynamic cycle between the two engines.
- cardiffspaceman 6y agoThe rotor in the center of the LiquidMotion device is shaped more like an oval (or race track) while the Wankel rotor is shaped like a bowed-out triangle. The LiquidMotion rotor has volume within that is carries gases, while the Wankel rotor is solid (or at least if it's hollow the volume inside isn't used). I don't recall ever seeing a counterweight on a Wankel but then I'm not even a little acquainted with Wankels in the field so it could be that Mazda forgot to tell me. There is of course the possibility that this is a Wankel as far as patents would say. As different from a Wankel as a true Hemi is from a regular V8.
- jiggawatts 6y agoLooks like it would be useful as a compact engine for small planes or drones. The "through" flow of air and exhaust would be easy to ingrate into an airframe.
- busterarm 6y agoWankels are already sorta popular in small planes.
- VBprogrammer 6y agoI know there is a niche of homebuilders in the US fitting Wankel engines. I'm not sure that could be described as popular though. Is there something I'm missing?
- fastball 6y agoSeems like it would also be pretty good for lawnmowers and such.
- darig 6y agoVery smart to add the secondary electric motor so you can completely cut off the X-Engine and fly slightly quieter so innocent wedding guests can't run away before you murder them from across the globe.
- THE_PUN_STOPS 6y agoI worked there! Very interesting technology. Engine development is hard.
- tomcam 6y agoOk, we need to hear more!
- THE_PUN_STOPS 6y agoIt was just like any startup really, a great team of really smart and dedicated folks trying to disrupt an entrenched industry using new ideas. Lots of simulation, lots of practical prototyping, lots of test rig time. We spent so, so many hours in test chambers observing how a particular engine type behaved with incremental changes to its design, changes which were backed up by simulation. The resulting data was used to strengthen the simulation and we repeated this loop many times. The challenge with this is that there are seemingly infinite different parameters to observe and control in each loop in both the physical and simulated engines, which must be done with high fidelity to learn things. My understanding of thermodynamics was routinely humbled by my coworkers. I remember one time rolling into the office in the morning to find my coworker twirling with excitement and saying something like "I had a realization at 3AM and came to the office and figured out my enthalpy problem!" Working with your buddies to create a working engine from scratch that is unlike any engine that has ever been created before it is a real rush. I recommend it for anyone. Here's a slo-mo video of combustion inside an LP engine. We bolted a thick piece of quartz onto the engine instead of one of the side pieces. https://vimeo.com/111796558 https://vimeo.com/111796558
- layoutIfNeeded 6y agoWouldn’t this have the same problems as Wankel engines, that is suboptimal combustion due to the weird crescent-shaped combustion chambers?
- mlyle 6y agoRead the article. >..."they have a triangular rotor inside a peanut-shaped housing. We have the opposite, a peanut-shaped rotor in a tri-lobed housing. So take everything you know about the Wankel and turn it literally inside out. They have a long, skinny, moving combustion chamber, we have a stationary combustion chamber that's nice and round...
- deleted 6y ago[deleted]
- layoutIfNeeded 6y agoCan you point me to a timestamp where you see a “nice and round” combustion chamber in the video? I still see a crescent shaped one.
- crote 6y agoLook at the red areas in this image: https://uploads-ssl.webflow.com/5f6086e9bbbabd41a20f2984/5f6086e9bbbabd8f300f29a9_engine.png https://uploads-ssl.webflow.com/5f6086e9bbbabd41a20f2984/5f6... Left is a Wankel engine, right is the LiquidPiston engine. The red areas on both sides are the combustion chambers during ignition. The chamber is clearly a lot rounder.
- nabla9 6y ago>We're running engines for tens of hours, dozens of hours, we're not yet in the hundreds of hours where we want to be. Durability and reliability and maintenance are the issues with these type engines. For some military applications that's not an issue. If you want to build large number of cheap lightweight drones for high intensity warfare, durability is secondary. They will be shot down eventually anyway. Operating smaller number for training purposes during peacetime is not that expensive.
- aidenn0 6y agoThe edge-seals can be externally lubricated in this engine; that will at least improve maintenance.
- bsder 6y agoYeah, that was the first thing I looked for: https://youtu.be/8vbQjlzvaO8?t=58 https://youtu.be/8vbQjlzvaO8?t=58 I presume that having those seals on the non-moving part is a big win.
- busterarm 6y agoI have a turbo'd rotary engine in a mostly-unmodified car that's at 140k miles without an engine rebuild. I've had to replace numerous things under the hood due to the heat output though (wiring harness, everything rubber) or otherwise poorly designed (the weak alternators...). If you discount design flaws in the early RX-8s wrt lubrication, turbo timing issues in the FDs, the oil metering pumps in FCs & FDs, the engines are pretty solid. Almost all of the blown engines I've seen start wth people trying to increase boost. The problem is that you can modify the car little by little and every way you do this puts stress on the engine. You have to modify the car a lot (fuel pump, injectors, engine porting, turbo wastegate modification, new exhaust, bigger alternator, ecu chipping/megasquirt, cooling upgrades) before the car can really handle the new power that it has without tearing itself apart.
- SoSoRoCoCo 6y agoHave you ever owned an RX-7? It was pretty dang solid.
- syntaxing 6y agoPretty neat. Seems like a “pseudo” four cycle engine in a two cycle form. I can definitely see this being used in a drone/aerospace application. Even without the efficiency benefit of four cycle vs two, not having piston heads is already a huge plus (moving parts are a pain when you have nothing to ground to but the air). Though I would guess the engine will have to run at a much higher rpm since the air displaced seems lower.
- young_unixer 6y agoMaybe this "inside-out" engine inspires someone to create middle-out compression based on the same idea.
- daly 6y agoand put it in a "Piper Cub" airplane, calling it "the Pied Piper"?
- smokelegend 6y ago"This guy fucks"
- ehwhyreally 6y agoThey mentioned it being quiet, Rotaries are far from quiet.
- aidenn0 6y agoIf it's compact enough to compete with 2-strokes, it's likely way quieter than that. In theory a rotary would be quieter than a similarly powerful spoark-ignited engine due to reduced vibrations, but I don't suspect it's a huge difference.
- dmix 6y agoKnow what's really quiet? High loitering kamikazi drone and gliding that last while: ie: https://www.youtube.com/watch?v=zzzOH5fBAqw https://www.youtube.com/watch?v=zzzOH5fBAqw
- ogre_codes 6y agoYou can hear it in the video and it is pretty quiet. They've also developed a system where you can shut off the motor and cruise on battery power for short bursts for stealth type applications.
- mleonhard 6y ago
- mrpaulgraham 6y agorotaries are far from quite, my friend
- bilegeek 6y agoFound this awhile ago when researching if there were any diesel wankel engines. Glad to see it's got some updates. On a related note, does anybody know of DARPA-funded projects that eventually become consumer-grade? It seems that cool stuff like this never makes it out of the military due to the classified nature, which is sad.
- ChuckMcM 6y agoFWIW lots of DARPA stuff becomes commercial/consumer grade. Exhibit A is probably the entire Internet but close behind would be high bypass turbofan engines, LiDAR systems, laser range finders, "space" blankets, etc. There is a long line of these things.
- drjasonharrison 6y agoGPS
- hobby-coder-guy 6y ago“Close behind” Not really
- kirse 6y agoExhibit A-1 would be Siri on every Apple phone, originally a DARPA AI project.
- Tor3 6y agoSiri I never touch, internet I use all the time. The latter came way earlier too. So no.
- mattkrause 6y agoIt's intentional too. Many programs start with basic research, but also have specific milestones related to commercialization. For example, a biomedical program might have specific timelines for filing patents, meeting with the FDA for Investigational New Drug/Device Exemptions and thence clinical trials. This is rather different from the NIH and NSF, which tend to want smaller, self-contained projects from individual labs rather than a consortium that'll take a single idea from end-to-end.
- kylesteger 6y agoAbout 4 years ago some friends and I were taking an Uber out in the Hartford area. The driver had a sweet BMW 535 wagon. He worked for this company and we got to talking about how performant and efficient it was. Really cool to see the technology making big waves!
- LoSboccacc 6y ago> 40-lb (18-kg), 6.5-hp engine out of the go-kart in the video above, and replaced it with a 4.5-lb (2-kg) X-Engine making 3 hp. This is a completely flawed comparison power and weight don't interchange linearly as cooling requirements and seam inefficiencies drive size up and power down as power grows.
- deleted 6y ago[deleted]
- tfolbrecht 6y agoCould be an interesting powerplant for ICE powered robots like Boston Dynamics BigDog.
- elihu 6y agoVery interesting. No mention in the article if this has better fuel efficiency than existing rotaries, though their FAQ blames the poor efficiency and emissions issues of the Wankel on the weird shape of the combustion chamber[1], so if this design resolves those issues maybe we'll see these in cars eventually. (They'd better act quick if they want to get in on that market; I expect it'll be essentially all electric sooner than most people think.) They seem to think the apex seal wear issue will be better with the apex seals stationary. In addition to that, I wonder if it might also be possible to design the engine such that you can just slide the apex seals out sideways through a slot in the engine housing (sealed off in normal operation) without disassembling the whole engine? That by itself could be a pretty big improvement even if the seals wear down the same as they do in other rotaries. I also wonder if they have a good solution to having more than two rotors? Mazda made a 3-rotor but due to the way the engine fits together the eccentric shaft had to be in two pieces that bolt together. I hope as soon as this company makes a car-sized engine someone swaps one into a Mazda RX-7 or RX-8 just for fun. Maybe see if they can beat these guy's record [2] for longest RX-8 trip on a single tank of gas. Or swap one into one of the old Mazda rotary pickups. [1] https://www.liquidpiston.com/faq https://www.liquidpiston.com/faq [2] https://www.youtube.com/watch?v=PfiQu3XH2Pg https://www.youtube.com/watch?v=PfiQu3XH2Pg
- hwillis 6y agoSliding friction is an issue with efficiency, I suspect. The flat sides of the rotor are holding back hot, compressed, abrasive gas. That means the faces need to be very flat and very rigid. Unlike the face of an engine block, you can't get away with a gasket to mask imperfections. You need a hard, smooth bearing surface. That means expensive materials, which makes them even harder to flatten. Then you need the actual sealing elements, and they'll be at the worst spots possible- far away from the shaft. The sealed edge is in fact the fastest-moving part of the engine. Bearing surfaces are rated on their PV- pressure times velocity. Both pressure and velocity create heat, and the life of a bearing surface is very roughly inversely proportional to the 4th power of the PV it's run at. Naturally, you want to put bearings as close to the shaft as possible. > They seem to think the apex seal wear issue will be better with the apex seals stationary. They're almost certainly right, although the actual details of implementing the seal are very complicated. They have to seal the corners as well as the sliding edge, so you need multi-part seals that are cut so that spring tension pushes them all outwards, and they still have to seal against each other[1]. They also need to be pressed sideways into their groove and kept from being dragged diagonally. However, normal Wankels burn oil to keep the seals lubricated. Since these are stationary, they can be fed from oil in the crankcase. They can also be fenced in with scraper rings like a normal piston has, which keeps oil on the bearing surface and prevents it from being burnt off. Normal Wankel rotors lift off too much to keep the oil contained. [1]: https://i.ebayimg.com/images/g/gRYAAOSw8-tWVSxv/s-l1600.jpg https://i.ebayimg.com/images/g/gRYAAOSw8-tWVSxv/s-l1600.jpg > I also wonder if they have a good solution to having more than two rotors? Mazda made a 3-rotor but due to the way the engine fits together the eccentric shaft had to be in two pieces that bolt together. IIRC they'll have pretty bad second-order vibration, but either way the exhaust/intake is in the way to a significant degree.
- iforgetti 6y agoAnyone know where there is more complete description of the power cycle? From the article: >>> According to co-founder and CEO Alec Schkolnik, the X Engine design combines the high compression ratio and direct injection of a diesel engine with the constant volume combustion process of an Otto cycle engine and the over-expansion abilities of an Atkinson cycle engine, while solving the lubrication and sealing issues of the Wankel rotary engine and delivering huge power and efficiency
- twic 6y agoIt's shown in the video verdverm posted: https://www.liquidpiston.com/how-it-works https://www.liquidpiston.com/how-it-works 1. air flows in as the chamber is expanding 2. fuel is injected when it is at maximum size 3. the chamber contracts to a tiny size to compress the fuel-air mix 4. combustion occurs, and runs to completion, in the tiny chamber 5. the chamber expands to extract work from the high-pressure gas 6. the chamber contracts to exhaust the waste gas, The video makes the geometry clear. The way that the chamber contracts down to a tiny nub gives you the high compression ratio. The nubs being fixed in the stator lets you have injection. The fact that the combustion happens while the tip of the rotor is sliding over the nub gives you constant-volume combustion. I suppose the rotor being asymmetric lets you have overexpansion.
- steerablesafe 6y agoI wonder if it's literally an inverted Wankel engine, as in taking the geometry of the Wankel engine, applying inversion with respect to a circle[1] then fixing the frame of reference to the outer geometry, which was originally the rotor in the Wankel engine. [1] https://en.wikipedia.org/wiki/Inversive_geometry https://en.wikipedia.org/wiki/Inversive_geometry edit: on second though this would probably be too simple to be true.
- lrissman 6y agoI wondered that too and then saw this from tfa: “ "If you recall the Wankel," says Schkolnik, "they have a triangular rotor inside a peanut-shaped housing. We have the opposite, a peanut-shaped rotor in a tri-lobed housing. So take everything you know about the Wankel and turn it literally inside out. They have a long, skinny, moving combustion chamber, we have a stationary combustion chamber that's nice and round. You can drive it to a high compression, just by making the chamber smaller. And because it's stationary, we can directly inject fuel where the Wankel could not. So those are the two key advantages of the diesel: high compression ratio and direct injection.”
- steerablesafe 6y agoI'm just wondering if there is a strong mathematical link between the two. Like flipping the sign somewhere in the description of the geometry of the Wankel engine results in this. I did some crude geometric measurement on the geometry based on the video and the chamber doesn't seem to have the shape of an Wankel rotor inverted with respect to a circle.
- 8draco8 6y agoBut what does that change? Major flaw of Wankel engines, apex seals are still there, only now they are fixed in place not on the piston. I think "flipping" the design allows for smaller engine but reliability seems to stay the same. Please correct me if I'm wrong.
- ppf 6y agoInteresting idea - is there a technological reason why this design is possible now, or did the designers of the orignal rotary engine just not consider this layout?
- hedora 6y agoTheir demo generator is hoping to be 5KW and 100lbs vs an existing 764lb 5KW model. A 5.5kw generator from tractor supply runs $650 and weighs ~150lbs. I’m sure this engine has some big advantages, but lbs/steady state watt doesn’t seem to be one. What am I missing?