Liquid Piston Rotary Engine - Yet Another Engine That Changes Everything?
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2023-11-19に共有
So today we will take an in-depth look at this engine, we will analyze its benefits, its drawbacks, we will compare it with traditional piston engines and Wankel rotary engines to measure it’s potential to change everything.
If we observe the animation of the engine in operation we can observe that the Non-Wankel X engine which has a fundamentally different thermodynamic cycle, architecture and operation completes three combustion events for a single rotation of the rotor and does intake, compression, combustion and exhaust. Just like a Wankel engine.
Is this nonsense? It’s not and that’s because the inverted geometry of the x-engine enables it to overcome a major limiting factor of the Wankel engine. Kenichi Yamamoto is the father of Mazda’s Wankel engine, he is the man behind Mazda’s inspirational endeavor to make Wankel engines viable for mass production and in 1981 Mr. Yamamoto wrote a book called the Rotary engine. In this book he discusses and calculates the compression ratio for Wankel engine. And it turns out that the practical compression ratio limit for a Wankel engine is around 12:1. This limit is a consequence of the geometry of the Rotary Wankel and the resulting shape of the combustion chambers. This compression ratio limit also limits the maximum efficiency of the Wankel engine and it also makes a diesel Wankel rotary unfeasible. Yamamoto’s calculations stand as correct more than 40 years later because Mazda’s latest and only currently produced rotary engine which is used as a range extender in the MX30-REV has a compression ratio of 11.9:1
But the different geometry of the liquid piston engine means that it does not have a compression ratio limit which means that a diesel version is possible and that’s exactly what the liquid piston has done with their XTS-210 engine, which is a compression ignition version of their design.
But the unique geometry of liquid piston engines enables another benefit, which is the main source of the engine’s potential for improved efficiency. And that is a piston-less implementation of the Atkinson cycle, Liquid piston calls this a High Efficiency Hybrid Cycle, because obviously this sounds far more sexy for marketing and investor attracting purposes. But in reality it is a pistonless Atkinson cycle.
The entire premise of the Atkinson cycle is to have a greater expansion or combustion stroke and a smaller compression stroke. A compression stroke saps power whereas a combustion stroke generates power. So if we create a greater combustion or expansion stroke than we give the engine the possibility to extract as much energy from the combustion as possible which means reduced energy losses and improved efficiency.
Liquid piston engines have resolved the compression ratio limitation of rotary engines but they have not resolved the apex seals. The x-engine still has apex seals they have simply changed location. Instead of being in the rotor they are now in the housing. Liquid piston claims that this is a significant benefit because the seals no longer have to withstand centrifugal forces. According to a technical paper they wrote their models show a blowby reduction of 35% over a traditional Wankel however liquid piston believes that ultimately they can achieve around 65% blowby reduction compared to a Wankel. This simply is not enough for a truly widespread application in many different markets.
But the real problem with lubrication is with the crankshaft. Because air comes into the engine through the crankshaft it means that we cannot expose the crankshaft to a constant oil bath or even pressurized oil. Instead, as we can see from their how it’s made video, the engine uses sealed bearings instead of lubricated journal or ball bearings. In terms of longevity this is an inferior solution and this together with the apex seals is the reason why even the mature design of the engine is only expected to last 1000 hours between rebuilds.
So overall, this is no doubt a very clever design and I genuinely like the reverse Wankel idea of the Liquid Piston Rotary Engine. I’m also sympathetic of the fact that new engine designs need to claim very widespread potential applications to attract investors but outside of a few niche applications, where this engine will likely excel and offer genuine benefits, I personally don’t see a lot of potential for widespread use.
A special thank you to my patrons:
Daniel
Pepe
Brian Alvarez
Peter Della Flora
Dave Westwood
Joe C
Zwoa Meda Beda
Toma Marini
Cole Philips
#d4a
00:00 Working principle
03:06 Rotary Diesel
05:27 Pistonless Atkinson
08:07 Power density
09:53 Apex seals
11:11 Lubrication issues
14:08 Efficiency
15:52 Torque and VVT
17:18 You're in the Army Now
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コメント (21)
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I’m a big fan of rotary engines and the Liquid Piston engine intrigues me for being a clever way of putting the Atkinson cycle into practice but I agree with you, it still needs improvements to become something that is universally better than the piston engine.
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Was optimistic about this engine for a while, but just like Achates Power, they unfortunately seem to have become one of the countless entities that promised to "change everything" but ultimately delivered little or nothing.
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I very much appreciate how you talk about both the ups and downs, instead of focusing on one or the other. Whenever I hear of a new engine technology, I'm always excited to hear your views on it because of your balanced and fair analysis.
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Finally, an analysis of this engine that doesn’t feel like paid marketing, nor is a video just crapping all over it because it’s different. It was great to see someone actually gather all the numbers together and go through them in a comprehensive video. I’ve followed this engine for a while and knew something had to be up with the engine for LPI to have been stuck in ‘development’ for so long. Thanks for pointing out the longevity and efficiency figures as well as the most glaring weakness in the crankshaft.
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One added benefit over the Wankel engine that I don't think you addressed is that it heats up more evenly. One of the problems with the Wankel is that it only fires on one side and will shift and deform because of that.
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The diesel may be better in a uav due to higher efficiency resulting in longer loiter time, and not having to shield electrical noise from the ignition system.
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This channel is so important. No shilling. Just factual observation and simple technical translation in a consistent manner with no fluff.
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Interesting thing to note: this basic layout of engine actually appears in one of wankle's papers demonstrating possible configurations of rotary engine, the reason being that both setups actually use the same math just applied to the case vs rotor. This means that if they wanted to pretty much anyone could build an engine of the same layout as the x-engine so long as they use a different rotor design.
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This the most comprehensive and realistic explanation of this engine. In the end, the same core defficiencies will doom it to the wankel’s fate. At this point, it is diificult for any “new” internal combustion design to out perform existing ic technology that has the benefit of over 100 years of progress.
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As always, spot on. Great explanation. I am a mech designer, with some hobby affinity with engines. For my dad it was his life. He would have enjoyed this a lot! It is an art in itself to explain complicated things simply. You 've got it!
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I'm into paramotoring, ultralight form of aviation where we carry the motor in our back. What we want: absolute most power out of least amount of mass and space. Also, as we have "a lawnmower" in attached in our backs, it is nice if it does not vibrate that much. The drawbacks of the liquid piston would not be problems in this sport: - Longevity: Our current two stroke engines last ~300h anyways before full rebuild. Something like 1000h would be a dream - Torque: Propeller does not need it - Difficult to mass produce: Our current motors are hand crafted and expensive anyways. - Poor emissions: Haha lol, not on list of priorities :D. The paramotor is practically a large fan that blows the fumes away from self anyways
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First time I've listen to one of your videos and I must say that I am impressed by the in depth coverage as well as the pros/cons presentation.
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Thank you for the well prepared video ! Big kudos for having also very committed community who are willing to watch 20 minutes with enthusiasm and a lot of comments 😊
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This is the best video I've seen yet on the X-Engine, bravo! I was not aware that they were trying to shove air through the crankshaft, I had just assumed there was a divider in the center of the rotor so they could push air in one side and let exhaust out the other. That seems like something they're going to need to fix before they can make much progress on commercialization. I understand the amount of rotor surface area that's exposed to combustion poses a big heat management problem and makes it challenging to turbocharge. Of course if you could turbocharge one of these then the power/weight would be up into the turbine realm and even 30% efficiency would be a huge win for aviation.
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Great tear down and analyses of these engines. Just love clear language and no annoying back ground audio. Thanks, 5 Stars.
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This channel has taught me a lot, I am proud of the fact that when they said the crankshaft supplied the air mixure my first thought was "that's not gonna mix well with lubrication".
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Thank you for a very level-headed breakfown of something that the media tends to oversell. Really love the work and the good engineering approach to these subjects.
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I think it's my standard comment at your vids: 'When I think I know it all, something clever and new comes up." How interesting and what a clear explanation again. Thanks!
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I love watching your videos. Your way to explain complicated things with all the graphics is just awesomme. It helped me a lot. Thank you!
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For the (sealed) Crankshaft Support Bearings, you would hope that these Bearings have been filled with High Temperature Grease - when operating at those temperatures. The 'normal' grease in many bearings would simply 'run-out' very quickly, leaving little or no lubrication. Mind-Blowing how this guy can study all engines in complete depth, and even their shortcomings in design. I'd like to know what car he drives.....because it has probably got the best-designed Engine!! Greetings from Australia
