Converted wankel?

[ctrl_07]

I'm a bug fan of the wankel rotary engine, and I've just disovered
stirling power recently.

If stirling pistons are 90deg out of phase, and wankel rotors are
180deg out of phase, (180 = 90*2) it would seem to me that the
hot/cool gases can simply be ported to a 90 degree postion in the
rotor's sweeping motion, and quite naturally too.

In a two rotor setup the front rotor could be the hot side, with the
rear rotor being the cold side, with internal porting back and forth
going through the intermiediate housing. (perhaps containing a
regenerating material)

For introducing heat/cooling my thoughts were to modify the rotor
housing's water jackets, One liquid cooled, the other fire fed.

The benefits I can imagine are: 3 moving parts, conservation of
momentum, nil vibration, and the ability to oil the rotors and
ecentric shaft without leaking oil into the working chambers.

Has this been attempted or discussed before?

[stan.hornbaker]

Mike: As far as I know this had not been attempted as the Wankel configuration is not easily adapted to operate as a Stirling engine nor as any variations of Hot Air Engine.

A Wankel might be adapted as an air compressor or as an air engine but the mechanical friction losses and extra cost would make it non-competitive with normal compressors and air motors.

[bptdude___2569]

If you search, you WILL find a number of rotrary Stirling engine concepts. They may be streching the definition, but are still very cool and would answer some of your questions about rotary engine.

[ctrl_07]

@ Joe, I've tried googling that, but invariably as soon as you enter in "wankel" (with anything) it tops the results list with no mention of a stirling conversion. Info-overload heavy on wankel's only...

If you you have any links saved I'd be much obliged.

@William

I don't know the math but I could envision how the rotor gears and the stationary gear could induce more friction than a standard crank/bearing setup. On the other hand, conservation of motion is far superior to any back/forth/dead-stop action. Can one outweigh the other?

Ever driven a modifed rx-7? I've owned 3. Power for pound it murders any conventional engine of the same displacement. The reason isn't fuel efficiency! LOL :( It's mechanical efficiency. Every engine is an airpump of some manner and nothing yet beats a rotary at breathing.

The porting I have in my mind would be 90 degrees forward, so that the incoming volume of gas is accelerated into the next working chamber with the incoming rush of air helping to push that rotor around. That is to say, so velocity and preasure work together in the same direction.

I've read in the past the arguments against a rotary steam engine, and the problems tended to boil down to clearances and leakage crippling efficiency.

On the other hand, I do believe the wankel could have something quite suited to a stirling engine built right into it by design.

A stirling engine is a temperature differential engine yes? The hotter on one side and the colder on the other, the more work produced?

A wankel rotary have many more degrees of rotor sweep or "stroke" than a piston engine. This can allow for a more efficient engine since there is more time to heat and cool, thus more energy to be extracted.

Or so goes my theory...

[ctrl_07]

Actually, now that I think of it, parasitic loss could be furter reduced by dumping the flywheel. The weight and tumble of the rotors themselves should be enough.

[ctrl_07]

It just hit me! Eureka! I know how I can try this. :)

There is a lot of inefficiency in trying to take a gas, ram it through a small port (backpreasure = loss) to another rotor. Moreover since they are only spaced about 2 inches apart space for a decent regen is mil.

Even if I could do it, converting a mazda 12a/13b would be a crappy design.

You could say that the problem exists because the rotors are lined up and the intermediate housing is the bottleneck.

The answer is the peripheral port. Better breathing.

With a normal mazda rotary intake is accomplished through the side/end/front housings. In the rx-8 exhaust is side exited too. In a peripheral port engine, there are no ports in the end/front/mid housings used.

Here's what I have in mind. Have 2 rotors housed with end plates. The rotor housings are placed side by side, peripheral ports facing each other. If I had one hot rotor housing and one cool rotor housing it gives me an awful lof of time to heat and cool the gas as the since the working gas has to take almost a full rotation before it can exit again.

Such a simple design precludes a regenerator, in the typical sense, since the airflow would be an oval not back and forth, but if the two pipes between the rotor housings were encased in a heat conductive fluid, partial recover is possible.

[bptdude___2569]

You just needed to search for rotary displacer Stirling.

Here is a link to a working model:
http://www.bekkoame.ne.jp/~khirata/english/mk_rot.htm
http://www.bekkoame.ne.jp/~khirata/english/rotarye.htm

Here is a patent description:
http://www.freepatentsonline.com/3984981.html

Another patent description:
http://www.wipo.int/pctdb/en/wo.jsp?wo=2005083255

Here is one you might like because it is about the Wankel:
http://www-ifkm.mach.uni-karlsruhe.de/Html-e/Project/Stirling/stirling.html

And, my favorite source of cool stuff for the Stirling, YouTube:
http://www.youtube.com/watch?v=dzdtcSJwUrA&feature=related
This shows a small model rotary Stirling in action.

The principal is the same, just used in a continious circle motion instead of a back-and-forth traditional setup. I like the YouTube one because it shows not only a rotary engine, but a Stirling with a liquid working fluid.

[ctrl_07]

Thank's for the links. I was rather expecting that wankel related link to provide a long list of reasons why it can't work, but was happy to see so much in its favour, at least in theory.

[bptdude___2569]

Well, I don't know about converting a Wankel, but it has occurred to me that since the heat and cold on the outside are being supplied at a constant level, the best Stirling may in fact be some form of continous "burn" rotary displacement model. Another note put in the back of the idea book! :)

[ctrl_07]

I've already come up with three designs. :) With my luck none would work but that wont stop me from trying. :D

Design 1... http://69.46.29.93/design1.jpg

A typical linear rotor housing arangement,one in front of the other. To do this with two rotors 90 deg apart, when a balanced rotating assembly requires 180 deg would required big parasitic counter-weights. It would be better to simply use a 4 rotor setup like Mazda's R26B engine to do the balancing and increase the working fluid too.

Design 2: http://69.46.29.93/design2.jpg

A side by side rotor configuration. Note the yellow curve where the spark plugs would be. This would be a port or trench in the "hump" so that compression is not built up when it serves no purpose to. The fluid could be sent from one working volume (intake) to the other (exhaust) without undue backpreasure. Otherwise that compression would be just a power robbing.

Design 3: http://69.46.29.93/design3.jpg

More or less like design 2, but regen not shown, or prehaps not wanted to decrease deadspace and increase compression. In this design, to deal with the unwanted compression the machine would extract some usefull out of the hot cycle while still hot, and from the cold cycle while still cold.

Thoughs?