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/

http://bioage.typepad.com/.a/6a00d83...65f5970d-800wi

An air cooled version and a water cooled version.

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

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.

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

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.

regards
mech

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.

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.

regards
mech

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.

Many of your arguments are correct.
 

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.

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:

http://www.youtube.com/watch?v=2BQwBGKxShk

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?


regards
mech

Technically true, But the output shaft rotates at twice the speed of the rotor so it is actually still equivalent to a 3 cylinder engine. (3 combustion events every 2 revolutions). Still a nice idea. Could be great as a 2 rotor(6 cyl equivalent) for a regular car.

Bullets and pistons are round for a reason. Highest volume for surface area, mating surfaces expanding and contracting at the same rate. Easy to seal and long lasting.

Now get rid of the reciprocation costs, valve train costs and minimize the heat losses to the cylinder head and manifolds by using the exhaust to preheat the intake, combined with a single injector and inlet port for combustion events and you're speaking my language.

regards
mech

A Theoretically Ideal engine would likely be a expandable spherical chamber but I am not sure how that would work. Circles are easier to seal with a back up compression ring, but this engine doesn't seem to have the traditional problems of a wankel seal because the sides of the apex seal can butt up against the side walls of the housing.

Old Mechanic: Could you tell me which frame (or second) in the 14sec video you see the pressure opposing rotation? I'm pretty sure regular piston engines also ignite the mixture before TDC by about 30° of crank rotation which also tries to oppose the crank.

It's a bit ironic perhaps, but things that work tend to be invented once, things that don't however..

FYI ... AFAIK this is just the most recent 'version' prototype ... sense the company founded back around ~2004 ... They have had other prototypes of earlier versions... As I recall , there is a SAE paper from ~2010 on a 20HP 140cc prototype ( the "M2" )

Link
I'm wishing them the best for more improvements in the future.
:thumbup:

So, it lacks all the parasitic losses of a reciprocating engine with poppet valves, but it may be harder to seal.

We will have to see how they proceed from here.

I wouldn't really hold my breath for a rotary engine, but it could become a reasonable option for the general aviation if it can overcome the durability issues that have always plagued the Wankel design.

isn't rotary pretty reliable in constant-rpm applications?

The big difference with this and the Mazda one is the piston does not rotate it oscillates so much simpler to seal

Had them been reliable at all, don't you believe they would have taken over the stationary/industrial market already?

no

I doubt it's that simple.

There are numerous times a 'reliable' option .. sometimes even a more reliable option .. did not 'take over the market'.

Sure there might be "better" engine layouts that we don't have easy access owing either to an inherently higher overall cost or to political pressures, but the Wankel has proven itself not so dependable. Anyway, I'd still want to see how a similar engine employing the LiquidPiston configuration would fare in real-world driving conditions.

+1

I look forward to their continued development/improvement .. so it might someday be good enough to try in my own ride :D

As long as they overcome those apex seal issues that plagued most Wankel engines, this engine design would be quite competitive. BTW even though the water cooling seems to fare better due to a more accurate thermal management, the simple air-cooling layout might sound attractive for the general aviation market that still relies mostly on outdated designs.

I just saw this somewhere on Youtube or something and went through all their papers.

The concept looks decent. Apex seals in the housing instead of the rotor should make them more reliable I'm guessing.

Compression ratio can be pretty much as high as you want, that's good. Could set it at 18:1 expansion, 12:1 effective compression for similar VE to a Mazda Skyactiv-G.

Increased dwell actually isn't good for low speed given the surface area to volume ratio is still poor, but you can just run the engine at high speed only as a generator or something.

Since you have most of the combustion chamber in a quench/squish zone and a tiny pocket to ignite most of the fuel, combustion speed is not a problem. Then again, combustion speed is less important if you have a really big expansion ratio.

Now the bad:
XMv3 indicates 18% peak efficiency, 5 bar IMEP, 4 bar BMEP without Atkinson cycle intake "timing". That is BAD. A similar sized Wankel from AIE gets almost 7 bar BMEP: https://www.aieuk.com/40s-5bhp-wankel-rotary-engine/ The sealing must not be working, or something. A dyno chart would make it easier to figure out what's wrong.

The rotor has a similar problem to the Wankel: one side has the exhaust constantly going through it, the other side goes through intake/compression/expansion. There's definitely going to be a big temperature difference, which might contribute to poor sealing. Since you can't liquid cool the rotor, this is probably a big problem, since even if you're using inconel, the exhaust side would expand by several thousandths, that's going to create some bad vibration for the apex seals. A carbon ceramic rotor with dry lubricant ceramic seals might work, at very high expense. Another idea is to use intake air to cool the rotor, but that reduces power density and WOT efficiency.

It looks like the rotor air cooling blows out the exhaust? That can't work for any emissions controlled engine, can't be mixing fresh air into the exhaust.

I'd like to see what happens with a bigger sized demonstrator if they ever come out with one. The bigger size alone would make sealing, cooling loss, and pumping loss less of a problem.

Most likely it could serve the purpose of a hybrid, or being matched to a CVT.

They've been awarded a military research contract to make a very compact generator for howitzers:

https://newatlas.com/military/liquid...rmy-generator/

This posting has a nice summary of the advantages over a standard wankel
https://tech.slashdot.org/comments.p...0&cid=60840426

Like it or not, as long as the military gets involved, a ground-breaking tech becomes more likely to succeed and eventually appealing to the average Joe at a later stage. Just look at how the Jeep CJ and the Wrangler evolved.

It's been a while, and LiquidPiston even tried a 2-stroke Diesel prototype, still based on its inverted Wankel design. Sure trying to sell such engines for military applications, not only gensets but also UAVs and eventually outboard motors too, might generate a spontaneous marketing just like the Jeep after WWII, but LiquidPiston is wasting time not making some 2-rotor and 3-rotor engines which could cater to the Mazda fanbase as a crate engine, and for general aviation to compete with those flat-4 and flat-6 gassers too.