26 replies to this topic

[TDIMeister]

http://newsoffice.mi...S0TmTE.linkedin

 

Discuss!

[desmo]

Trolling for investors/marks I presume like all alt-engine schemes.  You want to raise money?  Build the damn things and sell them, even if it's low volume. Oh and in the meantime, stfu.

[MatsNorway]

http://liquidpiston....-mini-gasoline/

Edited by MatsNorway, 21 December 2014 - 16:15.

[imaginesix]

Seems like a tiny Wankel would make a lot of sense as a portable power unit, so a better Wankel should be an easy winner. Not convinced about "no vibration at all" though.

[Canuck]

Power density doesn't scale particularly well is my understanding.

[TDIMeister]

Power density doesn't scale particularly well is my understanding.

Never does for any type of internal combustion engine.

[Canuck]

My point exactly. I'm too brief for my own good.

[Kelpiecross]

By the standards of most "new" engine layouts I would think that this engine is fairly promising. I wouldn't be surprised to see it actually in production for some specialised use.

Why do they call it "LiquidPiston"? I was expecting to see something like those 19th. Century water pumps that used an oscillating column of water as the piston.

[gruntguru]

19th century company name?

[Lee Nicolle]

Seems like a tiny Wankel would make a lot of sense as a portable power unit, so a better Wankel should be an easy winner. Not convinced about "no vibration at all" though.

As a volounteer firey decades ago we had a Wankel engine on a pump. It worked well and was fairly quiet. And started easily.

Otherwise I remember very little about it!

[bigleagueslider]

This Wankel concept has been making the rounds for several years now. When all said and done it is no better than a modern 4-cycle recip piston engine.

[MatsNorway]

Depends on what you want to use the wankel for.

 

High hp, low weight? -> wankel

 

durability, low weight and simplicity? - > two stroke

 

etc

Edited by MatsNorway, 22 December 2014 - 10:56.

[GVera]

They claim 1000 hours between overhaul for the 70 cc engine in the final commercial version, doesn't seem too long lasting

[Greg Locock]

compared with an aircraft engine or a motorbike engine that's pretty good.

[Kelpiecross]

I think the main problem with rotary engines like this one is that the rotor turns at the output speed meaning that the tip seals (which presumably are on the casing) are subjected to very high rubbing speeds. I assume that this is why the company is only suggesting making very small engines rather than a full-sized car engine - to keep the rubbing speed down.
In comparison, the apparently similar Wankel has much lower seal rubbing speeds.

If you ignore seal speeds it is not hard to come up with various schemes for rotary engines - even something like a vane pump layout would work in theory.

[Catalina Park]

compared with an aircraft engine or a motorbike engine that's pretty good.

We start to worry when a Cummins gets to 12,000 hours. Though some of the previous versions used to get to 30,000 hours.

1000 hours is still a fairly long life for a small engine. It is 41 Le-Mans races!

[bigleagueslider]

compared with an aircraft engine or a motorbike engine that's pretty good.

There is no way that 70cc A/C rotary will survive 1000 hrs running at 10,000 rpm. And why would this 3.5hp 10K rpm rotary be any better than the typical 3.5hp loop-scav two-stroke recip engine that costs far less? The vibration of a modern 3.5hp 2T recip chainsaw engine is not that bad. Their claims for efficiency and durability of a large diesel engine design based on this concept were disproved many times by the rotary projects of John Deere, Rolls-Royce, Daimler Benz, etc.

[manolis]

Hello TDIMeister.

Here is an explanatory gif animation:



(at http://www.pattakon....an/Wankel_L.exe is the relative windows exe controllable program).

It explains, among others, how the Wankel rotor envelope can be defined.


And here:



are some basic claims of LiquidPiston (and it seems MIT agrees with these claims).


Regarding the low compression ratio of the Wankel:

The visual basic exe program at http://www.pattakon....ssion_ratio.exe calculates the maximum compression ratio of the Wankel with respect to the selected geometry.
A typical Wankel geometry can operate with a compression ratio near 18:1, which is higher than the compression ratio used in the typical modern engine. By increasing the three pockets around the triangular rotor, the compression ratio drops as much as required.

The LiquidPiston arrangement can go to even higher compression ratios; the question is: do they really need (or can they handle) compression ratios higher than 18:1 ?

The more compact combustion chamber (the three stationary pockets) at the TDC is an advantage of the LiquidPiston, but soon after the TDC the surface of the surrounding walls to the volume ratio is substantially bigger than in the conventional Wankel (see the GIF animation), which is already bad as compared to the surface to volume ratio of the conventional engines.


Regarding the “constant volume combustion”

With reference to the GIF animation:
Keeping stationary the red part, you have the conventional Wankel.
Keeping stationary the triangular rotor and the casing, you have the LiquidPiston version.
Looking carefully, you can see that the volume increase at a "leaf" of the LiquidPiston equals to the volume decrease of the one chamber of the conventional Wankel.
And because the "Volume change vs power shaft angle" of the Wankel is symmetrical (which means that the rate of volume increase after the TDC equals to the volume decrease before the BDC), the "Constant Volume combustion" claimed by LiquidPiston / MIT is wrong.
Both engines offer the same "Constant Volume combustion".


As for the claim that the Wankel rotary cannot operate with “over expansion”, this claim is wrong, too:
all it takes is the proper arrangement of the intake ports (to allow a big part of the air / mixture to return back to the intake manifold before the begining of the compression).


Regarding the cooling:

A big problem of the Wankel Rotary was always the cooling of the stationary casing, around the spark plugs area wherein the combustion takes place. The engine compartment is very hot as compared to that of a conventional engine of similar power.
An advantage of the Wankel rotary is that each side of its triangular rotor participates alternatively in all phases of the cycle, so the cool air/mixture during the intake cycle cools its surface.

In comparison the biggest problem of the LiquidPiston engine seems to be that the one lobe of the rotor is dedicated to compression-combustion-expansion (which means serious problems with its cooling) while the other lobe of the rotor (which comprises ports) is dedicated to the intake and the exhaust.
It requires a lot of coolant inside the moving piston.
It is like the engine of Scuderi, wherein other pistons are dedicated to the intake and the compression (so they operate cool), and others are dedicated to the combustion, to the expansion and to the exhaust (so they are problematic).


PS.
TDIMeister, in case you are familiar with patenting in Germany, please e-mail me.

Thanks
Manolis Pattakos

[bigleagueslider]

Manolis- You are correct that the LP rotary engine is not technically a Wankel rotary engine. But the basic kinematic arrangement of the two engines are similar with the way they use a crankshaft and phasing gears to produce the desired motion of the rotor. Your point about the advantage of the LP engine's fixed combustion chamber versus the Wankel engine's moving combustion chamber in the rotor face is valid. The practical CR limit for a Wankel is closer to 13:1 than the 16:1 you noted. And the Wankel's moving combustion chamber does not work with a fixed diesel DI injector located in the housing wall. However, the LP design suffers from some of the same problems the Wankel does. One is the peripheral sealing arrangement required between the housing and rotor. This has always been an issue with Wankels, and from what I can see the housing mounted tip seals used by the LP engine don't really resolve the problem. The LP engine also suffers from the Wankel's same large surface area/volume in the working space, which is not helpful for thermal efficiency.

 

Lastly, I looked at some of the claims LP makes for their engine. This one particular statement in a press release caught my attention: "Efficiency - The  HEHC  cycle  increases  average  efficiency  over  conventional  diesel  engines  from  less  than  20%  to  more  than  50%  under  typical  operating  modes,  reducing  fuel  consumption  by  as  much  as  threefold  over  conventional  diesel engines." Seriously, there is no modern diesel engine that has an average BTE below 20%. And I doubt their 40hp concept engine gets anywhere close to an average 50% BTE (with a claimed peak BTE of 58%!).

[manolis]

Hello Bigleagueslider.

The Toyota Prius (Miller / overexpansion) has a 13:1 compression ratio.
The Mazda SkyActiveG (Miller / overexpansion) has a 14:1 compression ratio.
The Mazda SkyActiveD di Diesel has also 14:1 compression ratio.
With the poor sealing (the “apex” rings of the Wankel and the relative rings of the LiquidPiston are single rings and have line – instead of surface – contact with the surfaces they slide on) any further increase of the compression ratio seems meaningless.

Mazda phased out the Wankel Rotary long ago because they could not make it competitive (low mileage, high emissions).

The disadvantages of the conventional Wankel (extreme surface to volume ratio, poor sealing, low BTE, emissions etc) have not been addressed by the LiquidPiston version.
Some of them get worse.
For instance, for the cooling it is required a lot of coolant per second to circulate between the stationary radiator and the hot lobe of the moving piston. The strange motion the piston performs makes the flow of the coolant (and the required sealing) a difficult problem.


The degree of “constant volume combustion” is identical for the conventional Wankel Rotary and for the LiquidPiston engine.
Unless I am wrong, the calculation of the volume change of the chamber shows that in both cases the volume varies in a pure sinusoidal way, like V(f)=A*sin(f)+B (wherein A and B are constants):

The following Wankel Volume Change plot is the volume of the chamber of the Wankel rotary (as well as of the LiquidPiston) vs the rotation angle.
Each small red circle is the calculated volume at the specific angle (horizontal axis), while the white continues line is a pure sinusoidal curve:



The few lines of code required for the above calculation are at: http://www.pattakon....lume_Change.txt
If there is interest, I can further explain how this code (and geometry) works.


It’s a pity that MIT did not advice LiquidPiston the obvious, i.e. that the figures they claim for their engine (BTE etc) are, by far, unrealistic and that the Wankel Rotary is not as bad as they think.

Thanks
Manolis Pattakos

Edited by manolis, 01 February 2015 - 07:45.

[bigleagueslider]

Thanks for the response Manolis. I agree that MIT should be more careful about what they promote. At one time MIT actually had one of the finest engine research labs in the world. If you check the bios of the LP founders, it looks like they have some connections with MIT.

 

One of the more interesting recent applications of a Wankel is Pratt & Whitney's EnduroCore compound engine concept.

[MatsNorway]

Just got info on it again from a collegue. Via. a news site. 

 

They are still going

 

http://liquidpiston....engines-diesel/

Edited by MatsNorway, 09 June 2016 - 10:40.

[MatsNorway]

http://jalopnik.com/...dium=socialflow

 

Here it is again. This time in a Go-kart.

 

In other news. (for you Lee) here is a timelapse of a ford flathead rebuild.. A engine that can rev and does not use rubber clamp/hoses to mount the exhausts..

http://thegarage.jal...rebu-1781952963

Edited by MatsNorway, 15 June 2016 - 07:14.

[blkirk]

Wired also wrote about the go-kart.

 

https://www.wired.co...-electric-cars/

[mariner]

Some more up to date info here

 

http://www.enginelab...gine-on-go-kart

[malbear]

Trolling for investors/marks I presume like all alt-engine schemes.  You want to raise money?  Build the damn things and sell them, even if it's low volume. Oh and in the meantime, stfu.

Ok I have a product that I would like to sell . I chose the Speedway market where there are only two manufacturers GM Italy and Jawa .http://www.gmengines...roduct_info.htm       http://shop.jawa.cz/...r=cms&id_lang=4

 

what is the market size  any idea . is there room for a start up or would it be better to approach one of the manufacturers .

would the speedway racing governing body instantly reject my engine as it may not conform to their traditional layout.

Bore 112 mm stroke 51 mm  head design propriety and subject to new IP.

do I test the water with only one engine or produce say 1000 to reduce set up costs 

[E1pix]

Not sure if I'm on topic here, so sorry if not, but a friend's been importing a 48-hp karting rotary for a decade:
http://engines4racin...php?page=rotary

Yes, it's a beast!