LiquidPiston unveils quiet X Mini engine prototype

LiquidPiston unveils quiet X Mini engine prototype
Credit: Donal Boyd

LiquidPiston has a new X Mini engine which is a small 70 cubic centimeter gasoline powered "prototype. This is a quiet, four-stroke engine with near-zero vibration. The company said it can bring improvements to applications such as lawn equipment, small generators, mopeds, auxiliary power units for boats, and UAVs. The engine's improved noise, vibration and harshness (NVH) characteristics, said the company, will increase product performance, enhance operator comfort and prolong application life.

The X Mini is based on LiquidPiston's thermodynamic cycle and architecture; it can run steady state with air-cooling. With the X Mini, the company said they can now show that their engine technology can scale down in size and can be configured for spark-ignited operation to support both gasoline and diesel applications. The engine has only two primary moving parts, a shaft and rotor, a 4-pound core and fits in a 6.6" x 6.2" x 5.4" box. The company said tests showed high power density, producing 3.5 horsepower (indicated at 10,000 RPM).

"Except for ancillary parts such as injectors, fuel pumps, and oil pumps, there are no other moving parts," according to the company.

The president and co-founder, Dr. Alexander Shkolnik, said the team had plans to further optimize the engine for increased power (greater than 5 horsepower) and efficiency, and lower operational noise. According to the company release, "When mature, the engine is expected to weigh 3 pounds, produce over 5 horsepower at up to 15,000 RPM, and be over 30 percent smaller and lighter than comparable four-stroke piston engines."

While it is a rotary engine, the company points out that the X Engine is not a Wankel engine, as it has "a fundamentally different thermodynamic cycle, architecture and operation."

Shkolnik co-authored a paper, "Development of a Small Rotary SI/CI Combustion Engine," which described small rotary internal combustion engines developed to operate on the High Efficiency Hybrid Cycle (HEHC). "The cycle, which combines high compression ratio (CR), constant-volume (isochoric) combustion, and overexpansion, has a theoretical efficiency of 75 percent using air-standard assumptions and first-law analysis." Similar to the Wankel rotary engine, the 'X' engine has only two primary moving parts, they said, but unlike the Wankel, "the X engine is uniquely configured to adopt the HEHC cycle and its associated efficiency and low-noise benefits. The result is an engine which is compact, lightweight, low-vibration, quiet, and fuel-efficient."

LiquidPiston adopted the saying "Think Outside the Cylinder" as their philosophy, on the premise that by rethinking the engine, starting with basic scientific principles (e.g., thermodynamics), engines can be significantly improved on all parameters.

The company is upbeat that the X Mini may enable new applications not possible with current engine technology; early next year, they will host an open call for ideas about new applications with a cash prize for the most innovative submission.


Explore further

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More information: LiquidPiston Unveils Power-Dense, 70 Cubic Centimeter, Gasoline Powered "X Mini" Engine Prototype, PDF: liquidpiston.com/wp-content/up … Engine-Prototype.pdf

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Nov 21, 2014
Hummm lots of video and no real detail as to how it works. Why does this look like a scam?

Nov 21, 2014
Hummm lots of video and no real detail as to how it works. Why does this look like a scam?
@MR166
at first glance over the article, i assumed the same

there seems to be a great deal of info provided though (although the paper is paywalled)
see these links:
http://liquidpist...type.pdf
http://papers.sae...32-0104/

i think this is interesting
ATTN: SPECULATION COMING
i wonder if they could scale this up to a much higher horsepower output... and how it would be for speed, etc

i think i will ask an expert in thermodynamics on this one

PS. - the lack of detail could be a patent issue, especially regarding certain comments above, like the one
the company points out that the X Engine is not a Wankel engine, as it has "a fundamentally different thermodynamic cycle, architecture and operation."


Nov 21, 2014
Wonderful. An integrated generator and the ability to use locally-derived biofuels will free many third-worlders from labor and darkness. If it needs cooling, a water immersion or ebullient cooling can suffice in water-rich areas.

Nov 21, 2014
I am a big fan of 2 cycle engines. The have a crank and piston and virtually no other moving parts. Lots of HP little weight. Too bad their emissions are so high. I owned a car with a Wankel engine. Great from a HP to weight standpoint and very rugged but terrible gas mileage and it would put out a virtual smoke screen when started in cold weather.

Nov 21, 2014
I think an afterburner is needed, but how to harness or reclaim that lost energy? Thermoelectric puts out so little.

Nov 21, 2014
The afterburner commnent regarded 2 stroke engines, not the one discussed.

Nov 21, 2014
I think an afterburner is needed, but how to harness or reclaim that lost energy? Thermoelectric puts out so little.


Organic rankine cycle. Uses a liquid other than water, such as butane for the working fluid.

BMW proposed to use one for cars in the 90's, and made some prototypes, but declined because of cost and weight added to the car with the technology at the time.

EWH
Nov 21, 2014
From the linked abstract:
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%. As this engine does not have poppet valves and the gas is fully expanded before the exhaust stroke starts, the engine has potential to be quiet. ...Two prototype engines are discussed. The first engine is the larger X1 engine (70hp), which operates on the HEHC with compression-ignition (CI) of diesel fuel. A second engine, the XMv3, is a scaled down X engine (70cc / 3HP) which operates with spark-ignition (SI) of gasoline fuel.

Nov 21, 2014
BMW proposed to use one for cars in the 90's, and made some prototypes, but declined because of cost and weight added to the car with the technology at the time.
---------------------------------------------------------

Which means it may be more amenable for stationary loads. Letting some engines run dirty and efficient, and cleaning up with another process has been used before. The nature of alternative energy leads to integration, since many are simply extensions of natural processes, harnessing the available power. Natural process cascade down to the lower energy levels, getting maximum benefit.

By using our waste as inputs to other processes we mimic nature and reap substantial benefits using already-proven integration.

EWH
Nov 21, 2014
Also see this article from two years ago on the diesel version, with engine diagrams and thermodynamic cycle plots: http://www.gizmag...y/24623/

Nov 21, 2014
Which means it may be more amenable for stationary loads.


It usually is.

But, the combined cycle idea has surfaced and re-surfaced time and time again with engines, and it's always failed with the issue of cost.

It makes sense at the very large scale, slightly in the middle, but not at the very small scale because the heat loss from a small engine is usually very large even before any recuperator can take effect. The temperature is low, therefore the recovery efficiency is low and the cost of adding the system is more than the savings in fuel cost.

And even if it does cost less, an engine such as a car engine is usually designed to run for approx. 5000 hours (~300,000 mi) which means it has to recover its own cost within a limited number of hours, which is rather difficult to do.

Nov 21, 2014
The afterburner commnent regarded 2 stroke engines, not the one discussed.


Wrt. 2-stroke engines and stationary applications, nearly every large stationary engine is actually operating as a two-stroke, both diesel and spark ingited, because there's no practical reason why they can't have a scavenging blower to replace the induction and exhaust stroke. It's more efficient and doubles the power density.

Nov 21, 2014
Yeah, there's no hope at all. We should just give up.

But developers already know whatever you suppose and more. If they continue it they may know something you do not. And every development is another arrow in our quiver, another tool we can integrate into a system for synergy.

Nov 21, 2014
Yeah, there's no hope at all. We should just give up.


That's weakness of spirit.

Accepting that something isn't necessarily perfect doesn't mean the improvements so far aren't important. It just means you need to keep a wider perspective on where to go after you run out of room to improve.

After all, if the engine really can be taken anywhere near the 75% theoretical maximum, it's already astoundingly efficient for an internal combustion engine of its size, and frankly much better than any internal combustion engine. The question of waste heat recovery is rather secondary to that.

Nov 21, 2014
Certainly you knew that remark was in mild sarcasm.

Waste heat becomes more important when it comes to competing with the other technologies. Integration is the key.

Nov 21, 2014
We are all more together in thinking than many realize. We are just coming at it from different directions, loaded with different notions and ideas, . . and biases. We agree on the importance of technological improvement, of development, on the integration of all this together, which is what this is really all about.

Most of you seem to worry about the potential and the costs. I try to show you the overall costs to society will be much lower than we have now.

Nov 21, 2014

Waste heat becomes more important when it comes to competing with the other technologies. Integration is the key


That's a rather sweeping statement.

For starters, a heat engine technology that is more than 50% efficient stands to gain less and less out of waste heat recovery in proportion to what it's already making because the available efficiency margin is narrow. It's not necessarily sensible to squeeze the last few percentage points out of it.

Most of you seem to worry about the potential and the costs.


Cost is nearly always translatable to energy, because money requires trade, which ultimately means the consumption of physical goods, which represent a use of energy. When something costs money, it almost certainly costs energy, and if it ends up being worth less in money than it costs, it represents a net loss.

By that heuristic, one can estimate that means of production that cost more money reduce living standards no matter who ends up paying it

Nov 21, 2014
Eikka, look up what Yogi Berra, American Philosopher, said about theory versus practice.

Okay, okay, . . I'll do it for you:

"In theory there is no difference between theory and practice.

In practice there is."

Nov 21, 2014
theory versus practice


Theory, as it describes the limitations of physic, mathematics, logic, economics, etc. is a boundary to practice.

That's the point of theory. One cannot overcome a theoretical Carnot heat engine because, as far as anyone knows and can prove, it is at the limit that our environment permits. Breaking the limit would lead to paradoxes and contradictions in physics, like getting something out of nothing.

Nov 21, 2014
In other words, "theory" is synonymous to being optimistic given all what is currently known.

Practice is trying to live up to that optimum.

Magical thinking is pretending that you can ignore theory and just do something in hopes that it will lead to better results, because you don't like what the theory predicts.

Nov 21, 2014
Please just take the lesson.

I say that without sarcasm but to remind you in life things rarely can be predicted or analyzed and controlled.

Nov 21, 2014
i think this is interesting
...
i wonder if they could scale this up to a much higher horsepower output... and how it would be for speed, etc
...
the lack of detail could be a patent issue


@Captain
Go to http://patft1.usp...-adv.htm
Enter "an/liquidpiston" and click search
This shows 8 issued US patents assigned to liquidpiston, and they all look like they are on this engine.
The same search on http://appft.uspt...adv.html
shows 9 published patent applications assigned to liquipiston.
There is some overlap as it takes a while for published applications to be removed after a patent issues, but that's still a lot of information if you are curious.

Nov 22, 2014
Wouldn't the ends of the rotor need to be sealed so that high pressure gases would not leak in to the other chambers?

Nov 22, 2014
It's obvious who failed Thermodynamics on the way to his Master's.

Nov 22, 2014
Looks like a downscaled version of a Wankel engine and seems to work pretty much in the same way.

Nov 22, 2014
For more info:
https://www.youtu...85YnDmq0
As or how efficient and quiet it actually is: The market for generators, go karts and lawn mowers will tell- Unless they can scale it up or else put 3 'cylinders' on one shaft to balance it better.

JRi
Nov 22, 2014
In the case of vehicles, at 75% efficiency the waste heat is almost all used for heating the interior and keeping the windshield from fogging up during winter times.

I wonder what are the weak points of this motor concept. It does sound pretty promising.

Nov 22, 2014
I say that without sarcasm but to remind you in life things rarely can be predicted or analyzed and controlled.


Well, you can keep running head first into a wall because solid objects being solid is "only a theory" and "practice is different".


Nov 22, 2014
If anybody ask what's wrong with this engine and why it will not ever succeed -
The mechanical solution choosen for this so called High Efficiency Hybrid Cycle will never offer the presumed adavantages, as not did it for Wankel.
Also, at 30-33% efficiency it's far worse than best ICE. Any improvement will be done, won't change the efficiency, merelly make these types of engines (HECH vs. ICE) equals.
A Carnot or a Rankine cycle, not relevant as choice.
The real "choice in the matter" is the mechanic solution and materials involved for a cheaper, economical and greener engine.


Nov 22, 2014
that's still a lot of information if you are curious
@RealScience
Thank you for the information. I appreciate it!

I will be looking into it!

Nov 22, 2014
In time this will be replaced by electricity.

Nov 22, 2014
My electricity prediction was not a one-off statement, it was a prediction. We are learning how to use the world's most versatile fuel, electricity. The delight lies in the reactance, the dual nature of electromagnetism. We do not just get 10,000 degree temperatures from it, we can use the dual properties for almost anything, light, prime movers, communications, electronics, it keeps on expanding with our knowledge.

Where would we be without the ability to use magnetic fields to move electrons?

Nov 22, 2014
Eyenstien thanks for the video link. This engine looks to very powerful for its size due to 3 firings per revolution. But it also looks to have the same shortcomings as the Wankel IE ring sealing problems and high oil consumption. Also obvious marketing phrases like " High Efficiency Hybrid Cycle (HEHC)" make me very suspicious. 75% efficiency is another huge red flag as it violates the laws of physics. Did anyone notice how there is no provision for cooling other than a few fins? I know from experience that Wankels needed a lot of cooling. My guess is that this engine will have a great HP/weight ratio and little else.

My vote is that this is a hoax and just a ploy to separate investors from their money. I am sure that the engine runs and could be useful in a niche market but don't expect it to be powering your next automobile. As a racing engine it could be fantastic as are Wankels.


Nov 22, 2014
Also, as a last little comment, there seems to be a huge temperature differential within the rotor. One section continuously is subjected to high temperature exhaust gasses while the other section is subjected to cold intake temperatures. Is this a potential problem?

Nov 22, 2014
Also, as a last little comment, there seems to be a huge temperature differential within the rotor. One section continuously is subjected to high temperature exhaust gasses while the other section is subjected to cold intake temperatures. Is this a potential problem?

Yes, it causes uneven wearing and frictional losses. It's why the Wankel is considered the worst engine on the market for cars.

Nov 22, 2014
Also, as my "last" plus 1 comment, exactly what part of this "LiquidPiston" engine is liquid????????????

Nov 22, 2014
Perhaps it is an allusion to the fluid motion of non-reciprocating rotary engines.

Maybe they originally had a hydraulic coupling between detonation and shaft.

Is it "fudging" by the promoters and businessmen?

Nov 22, 2014
I think the MYT engine is better. It gives 40 times the power of ICE with same engine size.

Nov 22, 2014
The US used to have a railroad commonly called "the Frisco".
------------------------------------------

I remember seeing it on the boxcars, in just those words. It was probably in the late '40's, or about the time the Santa Fe went to diesel-electrics.

JRi
Nov 23, 2014
"LiquidPiston" is the name of the company, but may not have anything to do with the actual mechanics.


Maybe the guys started their company by researching the use of amorphous metal alloys in some motor parts. A bit like Liquidmetal company does for all kind of stuff. Just a wild guess.

Nov 23, 2014
Also, as a last little comment, there seems to be a huge temperature differential within the rotor. One section continuously is subjected to high temperature exhaust gasses while the other section is subjected to cold intake temperatures. Is this a potential problem?

Yes, it causes uneven wearing and frictional losses. It's why the Wankel is considered the worst engine on the market for cars.


High pressure applied on seals too. These problems were wisely solved by this 4 edges desing (instead of 3, wankel) http://quasiturbi...ndex.htm

Nov 23, 2014
It now qualifies to go head to head (sorry bad pun with no pistons) against the shock wave rotary disk engine:- http://www.shocke...rks.com/
Competing on low weight, high speed, high efficiency and underfunded obscurity.
Though the rotary shock wave engine had a $2.5M grant and Michigan State University behind it and still remained obscure- so its hard to beat.

Nov 24, 2014
Looking in detail at the cycle of this engine design:-
https://www.youtu...85YnDmq0
The entire high pressure section of the cycle (burn plus exhaust) is forcing the rotor towards the cusp on the opposite side of the rotor housing: This will be an extreme wear zone, especially as its a high compression engine and there is a fragile seal embedded in that cusp.
They will have to redesign the bearings to protect the cusp. And that seal will give reliability problems, especially as it separates high pressure exhaust from fuel gasses.

Nov 24, 2014
Just compare it to the wankel design: The wankel rotor tip seals are not physically opposite to the high pressure parts of the cycle as the housing cusp seals are on this design. Also the wankel only has a single 4 stroke cycle per rotation, not three x 4-strokes as in this design: So the wankel seal doesn't have to partition hot high pressure exhaust from fuel mixture due to 3x the rotational gap between power strokes.
Yes its a clever design, give the guy his degree, but it will be even less reliable than the wankel is.
It could indeed make a great compact lawn mower or kids go-kart engine.

Nov 24, 2014
You can mostly ignore my last post as the wankel does have three power strokes per rotation as this new design does.
But this video link below shows the wear near the wankel rotor tip seals, which would be worse on the housing cusp seals of this new design.
https://www.youtu...YSDZukwQ

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