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Old 11-21-2014, 11:19 PM   #1 (permalink)
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LiquidPiston X Mini 70cc Engine

This is another twist on a compact rotary engine design:

LiquidPiston unveils quiet X Mini engine prototype

http://www.greencarcongress.com/2014...41119-lpi.html

LiquidPiston X Mini 70 cc Gasoline Engine Early Prototype Demo on Vimeo

How It Works | LiquidPiston

The rotor is the valves and the combustion chamber all in one. It is a 4 stroke engine, but there are three combustion events per revolution of the rotor.

They have tested it at 3HP on the dynamometer For a 70cc engine.

http://liquidpiston.com/



An air cooled version and a water cooled version.

I think it would make a fabulous genset for a serial hybrid.

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Last edited by NeilBlanchard; 11-22-2014 at 09:31 AM.. Reason: Corrected information
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Old 11-21-2014, 11:36 PM   #2 (permalink)
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No- 3.5 hp now with hopefully 5+ with refinement.
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Old 11-22-2014, 04:07 AM   #3 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
No- 3.5 hp now with hopefully 5+ with refinement.
That's what I read too. Pretty cool, though, if the efficiency claims prove to be true.
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Old 11-22-2014, 08:59 AM   #4 (permalink)
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Felix Wankel Patented the "Rotary" engine, which is not really a rotary, in 1926, if my memory serves me properly, almost 90 years ago.

The basic flaws are the surface area of the combustion chambers and the problems with sealing the combustion chambers. I had one of the first RX2s and the fuel mileage was atrocious (13.5 MPG). The engine basically blew up at 13k miles and I got a replacement free, even though the car was salvaged.

The surface area and shape of the cumbustion chamber with flat surfaces on the sides means serious heat transfer issues and differential rates of expansion of those surfaces make sealing almost insurmountable, even after 90 years.

To keep the tip seals from melting you have to lubricate the tip seals with oil losses similar to a two stroke engine. Not quite that bad but bad enough that, in my opinion, it's dead end technology.

Many major manufacturers including Mercedes tried to overcome those design "defects" and not one of them has succeeded.

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Old 11-22-2014, 09:03 AM   #5 (permalink)
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My 50 year old Honda with a 50cc engine, about 3 cubic inches, produces 4.8 HP. As Neil mentioned the high specific power of rotaries is due to the 3 combustion events per revolution, same as a 6 cylinder conventional design.

The number of revolutions of the crankshaft is not the same as the number of revolutions of the rotor.

There are better solutions.

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Old 11-22-2014, 09:34 AM   #6 (permalink)
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The other advantage of this design is there is no valvetrain with it's "normal" parasitic loads. This is a big deal, I think.

Also, each power "stroke" directly accelerates the next compression stroke, with far less mass than a 6 cylinder engine. This reduces (eliminates?) the need for a flywheel.

They make a diesel version of the larger engine that is 70HP.
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Old 11-22-2014, 09:55 AM   #7 (permalink)
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Ever spun a camshaft with a wrench Neil? With all the valve train except the timing chain connected.

The reciprocation of the piston mass and a portion of the conn rod, means you are accelerating and decelerating each of those masses 8 times per combustion stroke (2 revs of the crank). Exponentially greater losses than valve actuation losses.

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Old 11-22-2014, 10:05 AM   #8 (permalink)
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Yup, that too! This engine probably has it's challenges (like sealing the rotor) but it has several big advantages over reciprocating piston engines.

Another HUGE advantage is the force vectors of the power stroke coming just after TDC means that the most power is available at an awkward position of the con rod and the crank journal. No need to compromise the geometry by shifting the crank center - which improves the power stroke, but hurts the compression stroke.
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Old 11-22-2014, 12:30 PM   #9 (permalink)
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Many of your arguments are correct.

Quote:
Originally Posted by Old Mechanic View Post
Felix Wankel Patented the "Rotary" engine, which is not really a rotary, in 1926, if my memory serves me properly, almost 90 years ago.

The basic flaws are the surface area of the combustion chambers and the problems with sealing the combustion chambers. I had one of the first RX2s and the fuel mileage was atrocious (13.5 MPG). The engine basically blew up at 13k miles and I got a replacement free, even though the car was salvaged.

The surface area and shape of the cumbustion chamber with flat surfaces on the sides means serious heat transfer issues and differential rates of expansion of those surfaces make sealing almost insurmountable, even after 90 years.

To keep the tip seals from melting you have to lubricate the tip seals with oil losses similar to a two stroke engine. Not quite that bad but bad enough that, in my opinion, it's dead end technology.

Many major manufacturers including Mercedes tried to overcome those design "defects" and not one of them has succeeded.

regards
mech
But, that was 30 years ago. Science and engineering does not stand still.

The sealing is much easier to deal with in this design than on the Wankel/Mazda rotaries. There, the seal was in a dynamic position on the fast moving lobe tips. Cooling was limited. Here, the seals are in a static position and can be provided with cooling more readily.

Heat losses due to surface area can be minimized by coatings. Many coatings are now available to us for just this purpose. In the last 10 years alone, the advances have been notable to reduce heat losses, friction losses and all at a price range that a well equipped garage inventor can use.

The base construction materials themselves are improving not just with coatings and alloys, but in combinations and with fabrication techniques that were not even possible 30 years ago.

Does this mean, this design is going to be successful? No. But, it is less of an issue than you think. The company seems reasonable in making their first markets the small, less restricted engine applications. Once they get their technology in production, incremental improvements may make this engine design more suitable for general transport applications.
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Old 11-22-2014, 03:02 PM   #10 (permalink)
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Even in the supplied 14 second video you can see where the combustion process creates pressure OPPOSING the pressure necessary to move the rotor in the desired location.

I call deal killer.

Compared to this:



Maybe some should consider it further. No valves, no con rods, no combustion pressure trying to reverse the rotational direction.

It all equals a physics based dead end as far as anything approaching a better engine design.

History has proven it. Refine it all you want, you may get a little better but the basics remain the same.

Maybe we would spend our time better defining the true sources of "pumping losses". What percentage would you attribute to cam and valve train operating losses?


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mech


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