Automotive

LiquidPiston unveils X Mini engine

Two views of the X Mini
Two views of the X Mini
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A backpack blower engine and the X Mini
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A backpack blower engine and the X Mini
A 40 bhp moped engine and the X Mini
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A 40 bhp moped engine and the X Mini
The X Mini is air cooled
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The X Mini is air cooled
The X Mini is 30 percent lighter than a comparable engine
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The X Mini is 30 percent lighter than a comparable engine
The X Mini has only two movin gparts
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The X Mini has only two movin gparts
An iPhone and the X Mini
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An iPhone and the X Mini
Two views of the X Mini
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Two views of the X Mini

Back in 2012, Gizmag looked at LiquidPiston’s X2 rotary engine. The compact, low-vibration, high-efficiency 70 bhp and 40 bhp compression ignition engine was something of a sensation. Now the company is back with the 70 cc X Mini engine, which LiquidPiston’s President and Co-Founder, Dr Alexander Shkolnik unveiled on Wednesday at the SAE International/JSAE 2014 Small Engine Technology Conference in Pisa, Italy.

In a telephone interview with Gizmag, Shkolnik tells us that the decision to concentrate on smaller engines was based on public feedback and that over the past two years, LiquidPiston has been improving this technology. He says that the power-dense rotary four-stroke engine prototype’s basic architecture is pretty much the same as that of the X2, which shows the scalability of the engines.

The X Mini has a 4 lb (1.8 kg) core, is 30 percent smaller and lighter than a comparable engine, fits in a 6.6 in x 6.2 in x 5.4 in (16.7 x 15.7 x 13.7 cm) box, and has only two moving parts. According to Shkolnik, the X Mini is spark ignited because it suits a petrol engine of this size better than compression ignition used in the X2. Despite its size, the X Mini puts out 3.5 bhp and when fully developed could punch 5 bhp with a weight of only 3 lb (1.3 kg).

Shkolnik says that despite its size, the X Mini has improved noise, vibration and harshness (NVH) properties. It's extremely quiet due to its lack of poppet valves and its use of three chambers versus cylinders which means that vibrations cancel one another out, and the overexpansion cycle of the combination Otto, Diesel, Rankine, and Atkinson principles contribute to the lack of noise.

An iPhone and the X Mini
An iPhone and the X Mini

LiquidPiston sees the X Mini as having a wide range of applications. Its main focus is handheld power gear, such as lawn and garden equipment, but it can also be applied to portable generators, mopeds, unmanned aerial vehicles, robots, as a range extender for hybrids, and as an auxiliary power system for other vehicles.

Shkolnik says that the X Mini’s next development cycle will focus on emissions and the company expects it to be much cleaner than similar power plants. In addition, early next year, LiquidPiston will offer a cash prize for the best ideas for employing the new technology.

"We are currently in discussions with interested industry partners looking to enhance their existing product lines," reveals Shkolnik. "The X Mini is an incredible breakthrough, and we expect to further optimize the engine for increased power (greater than 5 horsepower) and efficiency, and even lower operational noise."

According to Shkolnik, the X Mini could be on the market in two or three years.

LiquidPiston’s paper Development of a Small Rotary SI/CI Combustion Engine is available at SAE International.

Source: LiquidPiston (PDF)

21 comments
Mel Tisdale
For a more detailed analysis of this engine it is worth following the link in the opening line to the earlier (2012) Gizmag article. The comments are also very informative. For the record, I think those of Pikeman and Sleat just about nail it. I suppose there must be some credibility to the design seeing as it clearly has not disappeared into vapourware heaven - yet.
Josh Coray
Very interested in this motor, it is a good application for a small concept we were looking at. Might have to pick one up.
Slowburn
A compress to ignition in a homogeneous fuel air mixture using a high octane fuel offers the same advantages without having to totally retool the factories. or salve the seal problems.
Hovnimrsk Prdelac
@ Mel Tsdale - the main complaints of Sleat at the previous article was a missing animation or detailed picture of the engine in work. That's no more the case - very clear videos are now available in Youtube and I wonder why they were not presented in the article, because they are indeed quite interesting. For example this one: https://www.youtube.com/watch?v=0e785YnDmq0
LowFlyerXX
Very interesting. I wonder, why are not such small yet efficient motors used for Hybrid applications.. Or, as article suggests, lawnmowers, home electro-power generators, etc. Thousands of uses!! @Hovnimrsk Prdelac - quite fascinating nick
MG127
so it is a modified Wankel engine? while Wankel has 2 pockets for combustion, this has 3 and a different design for the center part.
Paulinator
Very interesting design, but it still retains several compromises that may prove fatal to the concept: 1/ The rotor has an enormous circumference and travels at 2/3 crankshaft speed. That means that the seals will have to function at stratospheric pressure velocities. 2/ The combustion chamber shape is awful. 3/ Some of the expansion forces are working on the wrong side of the crankshaft. 4/ The rotor is being heated from both sides. The result will certainly be poor specific fuel consumption, eye-blistering emissions and marginal service life at peak rpm and output. Perfect for low-cost and disposable ISIS attack-drones though.
mhenriday
But just how efficient is this engine, i e, what is its thermal efficiency ? The larger X2 was reported to boast an efficiency of 75 % ; is that the case also for this scaled-down version ?... Henri
Illini_Rob
So lets see if I have this right. This company has been in operation for 11 years and has managed to produce two test engines. This particular engine currently has a TBO of 3 hours and BSFC of 545 g/kW*hr -- (15% efficiency). They *claim* that they will get to TBO 1000hrs and 30% effeciency .. but I can't find any evidence that either of them has designed or built a production engine before. Meanwhile small, light, mass produced strato-combustion engines can do 400g/kW*hr all day long -- with greatly reduced emissions relative to old-school ported 2-strokes.. Hrmmm looks like more Ph-Ds running a professional grant-hunting business.
Horst
This is amazing, in my working live I worked a lot with liquid ring compressors, sometimes called liquid piston compressors. Never did I think that one could turn that principle around to change it from a driven machine to a driving machine. Well, that's life.