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LiquidPiston unveils 40-bhp X2 rotary engine with 75 percent thermal efficiency


October 21, 2012

The LiquidPiston X2 rotary engine boasts a thermal efficiency of 75 percent

The LiquidPiston X2 rotary engine boasts a thermal efficiency of 75 percent

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The internal combustion engine (ICE) has had a remarkably successful century and a half. Unfortunately, it’s notoriously inefficient, wasting anywhere from 30 to 99 percent of the energy it produces and spewing unburned fuel into the air. Last week, Gizmag interviewed Dr. Alexander Shkolnik, President and CEO of LiquidPiston, Inc. about the company's LiquidPiston X2 – a 40-bhp rotary engine that burns a variety of fuels and requires no valves, cooling systems, radiators or mufflers, yet promises a thermodynamic efficiency of 75 percent. (Update: The engine has a goal of achieving a 57 percent brake efficiency.)

Co-founder of LiquidPiston with his father Nikolay, Dr. Shkolnik believes that the internal combustion engine is at the end of its development cycle. According to Shkolnik, after 150 years the ICE has made as many incremental improvements as it can. Many varieties of ICE, such as the Otto cycle used by petrol engines and the Diesel cycle, have had their successful points, but all fall short of being as efficient at they could be. Even what seem like very efficient engines, like the diesel, aren't as good as they might appear.

“Everyone would say at first glance that the diesel engine is more efficient (than the petrol engine). The truth is that if you had both engines at the same compression ratio, the spark-ignited engine has a faster combustion process and a more efficient process. In practice, it’s limited to a lower compression ratio otherwise you get spontaneous ignition.”

LiquidPiston’s approach to the problem was to go back to the basics of thermodynamics and work forward to develop what Shkolnik calls the “High Efficiency Hybrid Cycle” (HEHC), which combines the features of the Otto, Diesel, Rankine, and Atkinson cycles.

The idea is to compress the air in the LiquidPiston X2 engine to a very high ratio as in the diesel cycle and then isolating it in a constant volume chamber. When fuel is injected, it’s allowed to mix with the air and it auto-ignites as in a diesel engine, but the fuel/air mixture isn’t allowed to expand. Instead, it’s kept compressed in a constant volume so it can burn over an extended period, as in the Otto cycle. When the burning fuel/air mix is allowed to expand, it’s then overexpanded to near-atmospheric pressure. In this way, all the fuel is burned and almost all of the energy released is captured as work. Shkolnik calls this use of constant volume combustion “the holy grail of automotive engineering.”

Constant volume combustion and overexpansion provide an HEHC engine like the X2 with a number of benefits. Shkolnik points out that the X2 engine is exceptionally quiet because it burns all of its fuel. In current ICE engines, an alarming amount of fuel goes out the tailpipe. This not only cuts down on fuel efficiency and pollutes the air, it also makes the engine noisy. Since the X2 engine burns its fuel completely, there’s no need for complicated silencing apparatus. (Update: The engine runs quietly due to not needing poppet valves.)

The overexpansion used in the cycle also means that there is very little waste heat. An ICE only converts only 30 percent of its heat into work while the X2 engine has a thermal efficiency of 75 percent, so a water cooling system isn’t necessary. Water may be injected into an HEHC engine during compression or expansion for cooling, but doing so also helps to lubricate and seal the chamber and as the water cools the engine it converts into superheated steam, which boosts engine efficiency.

Shkolnik says that the X2 engine is a rotary because piston engines aren’t suitable for the HEHC and a rotary engine provides much more flexibility. Also, the use of a rotary design greatly simplifies the engine with only three moving parts and 13 major components required. That allows the X2 to be one-tenth the size of a comparable diesel engine.

When asked whether the X2 engine isn’t just an updated Wankel, Shkolnik pointed out that though both are rotary engines, the Wankel is very different. For one thing, it uses a straightforward Otto cycle like a piston engine and operates at a much lower compression rate than the X2. In comparison, the X2 engine is almost the opposite of a Wankel. “It’s almost like the Wankel engine flipped inside-out,” said Shkolnik.

Not only does the X2 engine work on a different principle from the Wankel, but it doesn't suffer from the same limitations. The X2 engine has a better surface to volume ratio, it doesn’t have the thermodynamic limitations of the Otto cycle and it doesn't have the emissions problems of the Wankel. The Wankel has apex seals that are carried around with the rotor and need to be lubricated. To do this, oil has to be sprayed on them, which means that the Wankel is burning oil as it runs, resulting in the high emissions that have recently curtailed its use. The X2 engine, on the other hand, moves the seals from the rotor to the housing, so no special lubrication is required.

Another way that the X2 engine differs from the Wankel is that Shkolnik has no intention of it sharing the same fate as the Wankel, which turned into an automotive also-ran when put head to head with the ICE or hybrid electrics to power motor cars, (though he admits that the X2 engine would be an excellent range extender for hybrids). Instead, he plans to go after niche markets that can use the X2’s peculiar strengths.

One place where the X2 engine may have an advantage is in auxiliary power units (APUs). Shkolnik said that an enormous amount of diesel fuel is wasted by lorry drivers for “hotel” purposes. That is, when they stop overnight they leave their engines idling to provide power for the living amenities of their long-distance rigs. Small, lightweight diesel power units with high fuel efficiency, he believes, would be particularly attractive.

Another area is military applications. The U.S. military has a need for APUs that can run on heavy fuels, which the X2 engine can. Also, the Pentagon is very keen on developing robots. According to Shkolnik, “you can do amazing things with robots, but ask a robot to carry this giant engine and there’s problems.” He believes that the X2 engine may be the answer to these problems. In addition, the military has need of APUs for tanks, which suffer from extremely bad fuel efficiency from idling to run electronics.

Currently, LiquidPiston is running its original X1 engine in tests, which has been built after only a year from its first design concept. This month, the company unveiled the X2, which is a more fully integrated engine with a simpler construction, at the DEER Conference in Dearborn, Michigan. Shkolnik says that the X2 will be available for partner tests in 2013 as a new round of financing is launched and he hopes to have a preproduction prototype by 2014.

Source: LiquidPiston


The story has been modified in some places to clarify some technical points.
About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past. All articles by David Szondy

is there a way that one can buy a stake in any of these emerging tech. like a normal investment. i seriously feel stuff like this would suit our lower power requirements down here in africa


It is small and lightweight but I could not see any message on fuel efficiency. Regarding the thermodynamic figures, it should be very fuel efficient but we need evidence from the designer/builder. If fuel efficient and able to use multifuel, this is the engine of the future! Just think about to conserve engine space in todays' automobiles.. wow..

Ali Şerbetci

I have heard far too many times about new wonder engines to be anything but sceptical.

William Blackburn

Great story of an exciting design. I'd like to know why this couldn't be adopted on a wide scale in place of the ICE? What limitations rule it out? Imagine our cars running with this level of efficiency gains. 70-80MPG for the average car woulkd be brilliant for the environment, our wallets and the future as oil reserves become scarcer. Perhaps, as Shkolnik said, the future is best positioned for the wide-spread adoption of electric cars with this tech powering them as an efficient range extender.


Good luck! I want one for my Powered Paraglider. Sounds like a great engine, but they rarely get past the concept phase...

Travis Tarr

My suspicions are roused by the blatant nonsense that unburnt fuel in the exhaust makes ICE noisy instead of the venting of high pressure gas.

I also suspect that the engine does not respond well to throttle changes.


Another well written article that is easy for the lay-man to understand. This sounds like a great development with only on drawback that I can see; it should have happened 50 years ago. We really should be out of any sort of combustion by now, its the most ancient technology available

Gerard Meehan

I think the lack of certain information is more telling...

"...markets that can use the X2’s peculiar strengths" and can cope with its weaknesses...

This is clearly only ever going to be a constant load auxilary power unit.

Tim Read

Hate to be skeptical.. but these promising new engines never seen to make it to the market.. there are tons of applications for these kinds.. the auto rickshaws that ply Bombay's streets can easily use this kind of an engine...or something else can.. but that will never happen..

Mihir Panchal

@Pikeman: "I also suspect that the engine does not respond well to throttle changes." That seems to be tacitly acknowledged by the company when saying that it would make a great range extender or APU, both of which operate within a narrow power/rpm range.


It excites me as it seems very promising.

Bruce Hudson

I agree with Tim Read in that it sounds most appropriate for a constant load power unit, but that could be more important than now as that's what we need for an electric range extender for autos. Also small, light weight, quiet. Most important metric, though, is cost.


Any process that produces carbon nanoparticles will banned because of genetic pollution. Let me know if this engine does. A quick death to the I.C.E. is predicted.

Stewart Mitchell

Excellent. No cooling system and lubricated with water sure sounds intriguing. If this invention delivers what promised we sure can expect changes in the way we think about transportation. An engine that continiously delivers 40 BHP actually is enough for the vast majority of cars that travel on our roads today. Occasionally you might need some more to accellerate but that is seldom done for longer time than 30 sec and then you are back att using 30 BHP. Sure hope this will fly.

Conny Söre

The newly re-designed Thorium LFTR reactors from China by 2017 will flood the world with cheap electric power, replace the oil idiom, and alter means of transportation for all mankind. This diesel effort. a very 20th century effort will be lost in the myriad of new and effective fully electric systems. An \America hungry for domestic energy sources will willingly convert tot he new electric paradigm, featuring Chinese styled electric bullet trains, short hop rechargeable cars, and an astounding re-arrangement of lifestyles dispensing with the "McMansion in the burbs" syndrome. This small diesel will have to find niche markets, if it proves to work as efficiently as predicted, and may fond a spot as an emergency charger for battery cars. Even as the American interests turn from Diesel to natural gas, this little buzz bomb engine is unlikely to find large markets.

Bruce Miller

While its burn cycle is different than a Wankel engine, its basic mechanical design is very similar. The issue with the Wankel engine has always been one of poor wear and not meeting emissions standards because oil is burned in the combustion since it is being used to seal the "cylinders" and lubricate them. Using water to seal and lubricate is talked about in the article. But water lubrication has its own issue and these are not talked about in the article. If they can make this engine with water lubrication to cut down emissions and make changing the seals in the engine a simple, fast procedure they may have a winner. I wish them luck. With the glut of Natural gas on the market they should look at using this fuel also.....


A constant load engine would be just the ticket for replacing diesel engines on locomotives. Also it would lend itself nicely to replace the ice in the Chevy Volt. Though, as others have mentioned, most of these are reported with glowing articles and then never heard of again.


It looks like a great improvement, but it really means we will still be burning fossil fuels, which is our actual biggest concern. It is time to go for new, clean technologies, not extending old, non-efficient ones. Zero emissions should be the starting point. No more fuel-dependent economies and policies should be a main part of the beginning of mankind's new era. We must change our minds....now!

Charlie Channels

No comments at all at the major failures of rotary engines like Wankel's: bad reliability and low torque.

Samer Helmy

Some of the hyperbole regarding the deficiencies of ICE vs. this latest wunderkind make me a bit skeptical. Sealing challenges may be the biggest hurdle. Still, if a limited-rpm engine could be used for an APU, or as a range-extender, or even coupled with a CVT (like the one I've been tinkering with) in a conventional auto, then maybe there is hope. We shall see how it all shakes out after they have put some significant hours on a real unit.

Bruce H. Anderson

Looks like perfect engine for hydrogen on demand. HHO is known for long time and was presented as holly grail. According to my experience is only Oxy-Hydrogen and water vapors with traces og Hydrogen Peroxide. As much Hydrogen Peroxide as better. Oxy-Hydrogen will trigger decomposition of H2O2 and that engine will extract maximum from super steam formed. Theoretically is possible a close loop. I will follow that subject! Thank you for posting it! Nice article!


I don't see where this can avoid heat losses from so much surface area and time which will make this unit likely not as eff as a diesel.


I am thinking that the narrow power band and lack of throttle response problems could be addressed with a constant velocity transmission.. The traction drive planetary transmission that is used in the NuVinci bicycle hub and by Rotrex in their superchargers would be a good place to start...

Warner DeFord

As a fan of the rotary and compressed air the missing fuel is air. A supercharger which makes a Wankel dangerous is the part of the rotary engine principle which Di Pietro has been driving airport vehicles on compressed air, the fuel of the future won't pollute the air we have. What about the Aussie's "dirt air bike" O2 porpellant is actually nitrogen.

Patrick McGean

Why do people keep assuming that it will only run on fossil fuels and thus keep us dependent on them? It seems that this engine is flexible enough to run on alternative fuels such as ethanol or biodiesel (although it would have been nice if they were explicitly mentioned). If proven, I do believe this type of engine would be the best interim solution for range extending electric vehicles until battery technolgy improves so that charging times are on par with current ICE refueling times. I would love to know what the estimated cost targetof the X2 is.

Knowledge Thirsty

I know very little about this topic and I'm hoping one of you experts can help me understand. When the author states that the relatively low number of moving parts allows the X2 to be one-tenth the size of a comparable diesel ICE, does he mean a comparison of power output - i.e. BHP? If so, how does scalability factor into possible applications? What I mean is, how adaptable is the design from very small to very large?


@Samer Helmy: You need to update your knowledge.

For starters you may wanna look up what won the 24h Le Mans 1991 and afterwards you could look up how rotary engines have done well on both the street and on race tracks. Take for instance the RX-8's in the Grand Am series where they have been both fast and reliable for years.

@Ali Tan Şerbetci: The 75% thermal efficiency tells you about the fuel efficiency - most combustion engines are around 40% efficient and to find anything much better than that you'll have to look at HUGE ship engines the size of buildings.


No noise? Runs? Where's the video? No video and only drawings means, to me, that it's a paper tiger looking for VC money.


O.K. One more time. How the hell does it work? No cooling system needed, Contained combustion (75%) "Over expansion to nearly atmospheric pressure" which seems to mean a slight vacuum, noiseless due to complete containment which means evidently vibration free also, Please, someone, (Steveastrouk preferably) explain this Magic to me in Layman's' (Idiots) terms. No exhaust noise, no exhaust, wtf? What actually moves, turns, slides, etc....



Commendable, but too little too late, in my opinion. This is, more or less, a solution looking for a problem, but the problem they seek to solve isn't going to be with us long enough for this development to be worth the investment that it will clearly need. Yet another engineering cul-de-sac, I fear.

Mike Hallett

All of the claims seem to depend upon that 'magic' 75% efficiency claim. With some of the modern materials now available this engine could be running at a higher overall temperature raising the theoretical efficiency somewhat. The rankine cycle effects of the total loss water injection will likely be offset by having to keep large quantities of water on board as the steam produced goes out the exhaust. That adds to the weight and volume this engine requires. I for one, don't know if complete combustion can be effected in a constant volume however some mixing might be happening by sliding surfaces to make this happen. It does seem that in this design combustion occurs rather equally spaced keeping the engine's outer section at a thermal equilibrium while the core gets cooled by passage of gasses in much the way that a turbine does. But perhaps because it passes much less gas volume, it cannot carry away enough of the 25% waste heat it still generates. It could end up very dependent upon ambient conditions.

If it does indeed have 75% peak efficiency it surpasses all other thermal engine systems including combined cycle stationary generators. If it sounds too good to be true, it probably is.

Paul Gracey

2 good 2 B true I fear


It sounds like a perfect engine except for one small flaw...it burns fuel! Burning fuels are killing off the human race. It's time now to stop the burning.

The engines of the (very near) future will not burn fuel, but will be plasma-based instead. The efficiencies will be in the thousands of percent more efficient than current chemical burning processes...no matter how much improved they become.


"The internal combustion engine (ICE) has had a remarkably successful century and a half. Unfortunately, it’s notoriously inefficient, wasting anywhere from 30 to 99 percent of the energy it produces and spewing unburned fuel into the air."

Looks like someone is still living in 1970, believing that all engines are like 400+ cubic inch big blocks with carburetors having venturis the size of toilet bowls.

Gregg Eshelman

OK, a specific volume of fuel be it diesel fuel or gasoline or natural gas or corn oil or alcohol has a certain number of BTUs of heat energy contained in it. Burning that fuel with the oxygen in the air at its stoichiometric ratio will release all of those BTUs. This of course is not taking into account the latent heat of evaporation for each fuel used as that's not the point I am trying to make here. If you obtain a certain amount of BTUs of stored heat energy from any given quantity of fuel, then you have to dissipate a certain amount of heat energy into the environment or the device will melt down into a pile of junk. How can a mechanical device possibly be able to convert all of that chemically released heat energy into useful work? That's what i want to know. That heat energy MUST go somewhere, and if it's not going into the environment, then it will melt the engine down. This could be a good engine for airplanes or torpedoes or trains, but cars? I don't think so. Unless it's used to power a generator which then charges up a battery bank and an electric motor is run off of that at varying RPM and loads.


Expanded Viewpoint

what are the torque values ?; usually these engines produce low figures unless spun to high rpm !

Wayne Day

This is the second time I've read about a rotary diesel auxiliary truck power source. The first time was many years ago, and they vanished into obscurity.

The only other neat rotary engine out there never sells to the public - they're exclusively for UAV's and other military stuff.

I strongly suspect this engine is headed the same way - to be snapped up by warmongers, and never see any commercial light of day.

If the inventors are reading this - GUYS - beware - the levels of theft and corruption within many military establishments is staggering: watch your back!, and ignore the comparably honest civil sector at your own peril!

I wish them best of luck - I've been wanting something like this for a decade or more...


It sounds like the fuel is burnt in a static central chamber and the resulting compressed gases are used to rotate the piston like a rotary compressed air engine. I would think the static chamber could get quite hot, which may be why they are using water injection. Creation of steam would harvest waste heat and add more compressed gas - increasing the thermal efficiency as well as lubricating etc. Expansion to near-atmosphere could be achieved by using the piston's momentum and appropriate valve positioning.

i would expect a fairly narrow power band, which could be compensated for by a CVT.

if this is the case the claims of fuel efficiency and fuel flexibility are possible, although probably a bit optimistic.

sounds like there is a working prototype. will be interested to see where this leads.

Stu Fletcher

Awesome. Just think of a 80hp twin engine jet ski running on 2 of these little rippers, all that would be needed would be some engine synchronisation kits and maybe even some fly by wire steering. I wonder if it will put out as much torqe as the Revetec engine. Revetec just updated the news on there Diesel and it should be assembled in 2 weeks time.

Spriscilla the Queen of the Ocean

The article doesn't really cover how the engine works. Google it and read the PDF white paper from a 2005 ASME conference. It actually has a lot more in common with the dual piston motor (intake - compressor / expander - exhaust) than with a Wankel. They already have a working test model. This is the announcement of the first iteration of it, not theoretical vaporware.


YAWN. another wonder-engine messiah. I'm with the sceptics on this one!


Aren't you embarrassed to accept uncritically an efficiency claim that any one-semester Thermodynamics undergraduate could tell you is physically impossible? And how about the rest of the article, saying ICEs waste "30 to 99 percent" of the energy consumed. The former figure is far too low - no simple-cycle engine is going to do better than 45%, leaving 55% wasted - and the latter too high, as even the most miserable engine that I know of gets 15% efficiency.


Not only am I skeptical, I'm really surprised at the vagueness of the presentation here. Gizmag has some vague pictures that don't seem to be on the website, and even the website pictures are vague!

There is even a "movie" on the website (that gizmag didn't bother to include) that contains ~30 seconds of still image! How strange.

Do the principals of Liquid Piston care that even the patents describing their work can't be viewed (broken link?)? Do they mind that even the theoretical papers describing their work are behind a rather steep paywall?

Assuming this engine is real, and actually functions, wouldn't there be at least an animation of the mechanical theory-of-operation available? Or do you have to supply venture-capital funding to see that?

Is everyone else reading this so mechanically adept that they can grock the whole mechanical idea with a single-frame illustration, a few external mechanism photos, and a hopelessly blurry "operating sequence" illustration that looks like it was badly assembled from an Autodesk animation?

Why not include sequential images that are at least hi-res enough to read the captions? Is the author of the article even interested in how it works?

If somebody's adept enough to build a revolutionary ICE from scratch, why can't they make a video of it running? Why can't they take the top cover off and crank it through one cycle? One can literally make an average production quality (but high image quality) smartphone youtube of the mechanical operation of something in 10 minutes. Why not here?


You could get much of the advantages the LiquidPiston is offering by getting a very high ratio diesel, lining the combustion chamber with high refractive material, opening the exhaust valve during the early part f the compression cycle, and if using the engine for constant load applications using gasoline as fuel.


This new mix of design for a high efficiency (75%) rotary engine might be promising. I think the usual seal issues will turn up especially if the manufacturing is lower quality .

David P Flynn

I would have loved taking on this challenge myself, if I thought rotary engines were worth the effort and if it was a new idea. Over 100 years ago a gentleman named Umpleby invented this and he was inspired by another gentleman named Cooley who tried this as a steam engine. It will probably have the same seal problems as the Wankel and I suspect it will have worse vibration. I don't think it does anything better than a Wankel.

I think my engine would do it better. (Hossack Engine)


I agree with piolenc, anybody who has ever looked into thermodynamics at all knows the concept of Carnot efficiency, the maximum theoretically attainable efficiency of any mechanical heat engine. Carnot Efficiency n = 1 - Tc/Th where Tc is the cold temperature (usually ambient, about 300K) and Th is the hot temperature (usually limited by the materials the engine is made from). Any practical engine has efficiency far less than Carnot efficiency, car engines are at most 35% and are practically more often at 25% or less.

Did you know that fuel cells, being non-mechanical, are capable of exceeding Carnot efficiency? In other words, no matter how good this engine ever could possibly be, a fuel cell can most likely be made more efficient. If I was a truck driver, I would much rather idle a fuel cell for "hotel power" than any mechanical engine.


re; Grunchy

Expensive, fragile, and requiring expensive special fuel that's the ticket all right.


APUs on trucks are becoming increasingly irrelevant as truck stops are now offering in cab climate controlled air, auxiliary power, and entertainment at prices lower than the energy can be generated by the truck.


Sounds good.... except for....As the name implies, combustion engines are thermal engines. They apply most of the power immeadiately following ignition when peak pressure develops. Logic would dictate that NOT taking advantage of this energy AT THAT TIME allows the ignited fuel mixture to begin cooling BEFORE this energy can be exploited, thus DECREASING efficiency. Another issue I have is if you contain the charge and it does begin to cool, the laws of conservation of energy demand that the heat be transfered to the case MORE completely, having more time to do so, again decreasing efficiency. I will say this about the Wankel and other devices that are known for "suboptimal" throttle response: used as the Primary Mover in a hybrid arrangement eleviates this issue as the battery provides buffering between power supply and load demand. I would not be so foolish as to dismiss something sight unseen but it does sound like another Venture Capital scam. Hope I'm wrong though. As far as saving fuel costs go, if the world suddenly became twice as efficient, the cost of fuel would be twice the price. Fact is, the major economies are moving toward a Natural Gas/Electric economy. The hangup? Distribution and the Btu content of gasoline and diesel are really impressive and thus far unbeatable. Some even venture that modern steam engines will emerge as the closed loop systems work fairly well. throttle response? Back to that whole hybrid thing...


I know this can be done, but to reach the market place for consumers who would love to buy it, only that is unrealistic. The developers should go to China, where the government would love to help kick start it, and it would be manufactured by the millions and exported throughout the world.

Dawar Saify

How long will the seals last on the engine wall? How easy will it be to replace all three?

I assume you can galley slave multiple rotors for an higher HP output engine?

Powell Gammill

sleat, Oct 23/12 has nailed the host of problems precisely! No matter who comes up with winning technology and a feasible, workable design, if the idea in any manner, undercuts the ability of the financiers who rely on the current fossil fuel designs to power the world, - rest assured, it is destined to never see the light of day! J. P. Morgan personally saw to it, that Nicola Tesla, a futuristic electrical Genius, could not continue his work and experiments! Allowing Tesla to do so, would be counter-productive to J.P's aspirations! Tesla demonstrated one of his innovations through replacing a Pearce-Arrow's I.C.E with a 80 HP electric Motor, powered without batteries or cable connections, - in the same manner as radio signals are transmitted, - from a broadcast central power source! Don't believe that? - do the research, and find out for yourselves!

Robert Gillis

If this technology is anywhere near real it should be on a fast track to replace the onboard ICE generators currently used to recharge EVs like the Chevy Volt.

Fritz Menzel

Firstly if they had this running there would be a video on youtube to boost their shareprice I suspect.

I can't tell much from the illustrations provided but this is evident:

In order to achieve constant volume combustion without valving between the compression/expansion volume and the combustion volume the rotor would need to stop at the minimum volume point of its rotation.

This isn't practical as it would mean stops during other cycles in adjacent volumes, would require complex mechanics, and would also restrict maximum rpm HEAVILY.

Therefore a valve system to a separated combustion chamber would need to be the employed method. As the compression and expansion ratio are claimed to be separated so significantly this must mean the constant volume separated combustion section is in fact a transfer port between two rotors, one acting as intake/compressor and the other as expansion/exhaust.

This appears to be the case as the brown squares in the housing loosely resemble the rotary transfer valve systems employed in split-cycle or non-continuous Brayton cycle engines being developed elsewhere.

Such a combustion technology would provide exactly the same benefits to a piston engine as it would a rotary. Therefore, anyone developing such would be foolish indeed to develop it alongside a modified rotary compressor which are mechanisms that have been plagued with problems since their inception and have finally been retired for their inability to meet emission standards.

Moving the apex seals from the rotor to the housing has the advantage that they no longer need to run over the port openings but it does not remove the need for lubrication. Secondly the reduced heat load on the intake/compression rotors seals will be passed to the expansion/exhaust ones causing problems there. Thirdly a similar seal arrangement to the wankel working at well over twice the pressure will take some serious work. Lastly the seals will no longer be subject to centripetal acceleration outwards against the housing causing sealing problems at anything above low rpm.

I'm not saying it can't be made to work, it is a nice design, the rotary should also offer some benefits like reduced friction, this geometry doesn't suffer the compression ratio restrictions of the "wankel" and moving the seals to the housing certainly has some potential but I am a realist that doesn't see much potential if a prototype can't be made to run for 5 minutes on a dyno already, and the basic mechanism/geometry is hardly new.

Conclusion: this is a split cycle engine like the piston ones that have been in development for the past century, it's a good idea which would be nice to see but the rotary aspect feels tacked on. If you feel like investing in the split-cycle race (and aren't worried about the handicap of additional problems to solve) there are also gerotor and other rotary-based variants out there besides the piston ones. At any rate if any have success with the combustion system I'd expect it to arrive in piston form first.

Additionally if anyone really wants to invest in a technology I expect to be required for this and most other such engines in development I have my own project in the works, however, even more than this one you won't find out any details at all without signing some serious paperwork!

I hope this better explains it in a little more detail and a little more realistically.

Rohan Neilson

Keep in mind, if lubricants are necessary, gasoline and diesel will always be by-products, like the resins used in plastics. The fossil fuels will have to be burned somewhere. If less people want to burn it, the increasing supply of unused fossil fuels will cause the price to drop. Does it seem likely that oil companies will waste the fuel, and let the price of the lubricants escalate?

J Scott Schaffer

Pikeman's "suspicions roused by the blatant nonsense that unburnt fuel in the exhaust makes ICE noisy (...)" is exactly what I feel. And the Otto cycle is by no means "burning over an extended period", it is burning isochoric. The whole thing defies a number of laws of nature as well as one's logical reasoning, and the article is made up from countless distortions of facts. Too bad, as some of the principles applied might really make sense. But a conventional piston with piston rings is difficult to beat, as Felix Wankel already had to experience.


Neat technology...a revival of the rotary engine....this could be a game changer.

Larry Carson

in 1908!!!!!

The UMPLEB Y ENGINE was an attempt to adapt the Cooley rotary steam engine to four-stroke IC operation. It is often cited as the first rotary IC engine, but as you can see above,there were certainly earlier patents, if not earlier working engines.

Facts are in short supply but Umpleby appears to have made little progess with the engine

this engine was invented by Cooley .


We'll it sounds like increasing efficiency from 57% to higher numbers would require the hot air and gas that isn't burnt all the way in combustion, would have to be reintroduced into the compression/combustion. Kinda like how the turbo in an engine does, by using exhaust(wasted gases) back into the motor to increase compression. Maybe this design has a potential to change aviation reciprocating engines as well.

Ikeleaka Kaluva
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