Half a croissant, on a plate, with a sign in front of it saying '50c'
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Alternate Wankel Pocket

A non-symmetrical pocket for rotors, with a scoop
  [vote for,

Now, I'm not sure if this will work, so it may very well add to my already-impressive collection of bad ideas. But bear with me.

Rotary (or Wankel) engines, as part of their design, have a small pocket in each of the three rotor faces, which acts to give additional volume to the space created by the rotor in its motion. This is a benefit in that it adds to the amount of fuel/air mixture that can be exploded in one rotation, but it also decreases the maximmum possible compression of the gases prior to ignition.

Part of the downside, as I see it, is that the pocket is symmetrical across its long axis (see link for complete description of rotary engines). This creates a simpler design, but also means that an ignition creates a force that is equal forwards and backwards, so the engine must rely on its natural momentum to continue to push the rotor in the correct direction immediately after ignition.

As such, I propose that the pocket in the face be changed to a scoop design (one short deep face on the forward end, tapering to a shallow face on the "back" side), with the same volume as the current pocket in the rotor face. See basic art for cross-sections.

Now, this would alter the dynamics a bit.

First off, this would create a sharp volume increase, and therefore stronger vacuum, in the intake chamber of the rotor chamber at the beginning of the rotation. This would cause the engine to starve itself unless fuel line pressure were increased, but I don't see that being a problem with modern fuel pumps.

Secondly, I hope (*this is the reason for the idea*), it would create a side of the dimple for ignited gases to "push" against, adding to the force already created by the expansion of the gases to power the rotor around. Currently, spark plugs are placed equidistant from the edge of the face and the center, dividing the ignition pocket into thirds...the plugs would have to be shifted forward a bit (downward in howstuffworks's illustrations) to have the same positions relative to the center of the pocket's volume. Alternatively, a third spark plug could be added just past the lower one, although you might have too much spark and not enough fuel.

Thirdly, and this is the tough part, the exhaust chamber would have a vortex in it (caused by the altered pressures of the new dimple shape) that would probably cause exhaust bleeding - some exhaust gases would remain in the pocket for the next cycle, which would interfere with the combustion, and cause the engine to lose power after the first cycle.

So....a rolling teflon "exhaust scoop" mounted on a spring would be added to the system. Just beyond the upper lip of the exhaust vent, the scoop would be spring-loaded to quickly dip into the pocket on the rotor face and act as a method of quickly decreasing the volume of the gas, forcing more of it out and into the exhaust system.

Now, the addition of moving parts does sort of work against the whole idea of rotary engines, even if they are simple plastic rollers and springs. And I'm sure that, given my fairly weak knowledge of fluid dynamics, I've missed something hugely important here...so I'm posting this out of curiosity, partly.

shapu, Aug 10 2004

Basics of Rotary Engines http://travel.howst...m/rotary-engine.htm
How Stuff Work's rotary engine education. [shapu, Oct 04 2004, last modified Oct 05 2004]

Current rotary face (cross-section) http://www.imgmag.c...Halfbaked/Face1.gif
[shapu, Oct 04 2004, last modified Oct 05 2004]

My proposed alternate pocket shape http://www.imgmag.c...Halfbaked/Face2.gif
[shapu, Oct 04 2004, last modified Oct 05 2004]

The basic workings of the "scoop" http://www.imgmag.c...alfbaked/Face2a.gif
[shapu, Oct 04 2004, last modified Oct 05 2004]

Comparison of Wankel and Quasiturbine http://quasiturbine...yQTVersusWankel.htm
[Willie333, Sep 29 2005]


       misreading of ti.. no, I'm not even going to go there.
RayfordSteele, Aug 10 2004

       In that link, the picture of a pocket that I see *IS* assymerical. Did you look at it closely?   

       As such, there's only one part of this idea that's really unique, and that's the exhaust scoop, which isn't a bad idea because as near as I can tell, even a wankel rotor with a symmetrical pocket would have the problem of "recycled air".   

       So, the initial concept is baked, but there's an extra extension that's new and possibly good. [+-]
5th Earth, Aug 10 2004

       What Rayford said.   

       "Hey Beavis, this guy wants us to..."
wagster, Aug 11 2004

       Is that an alternative wankel pocket in your trousers or are you just pleased to see me?
goff, Aug 11 2004

       It's asymmetrically shaped across the short axis, you're right. In my old wankel rotor that I have lying around (please, don't ask), it's a perfectly uniform cut. Damn Mazda.   

       That said, I was really more interested in depth change - even in the picture, if you ignore the shape across the long axis, the rate of change of DEPTH is the same in front and back.   

       Glad you like the scoop, though.
shapu, Aug 11 2004

       Recycled exhaust gas is used to keep combusdtion temps lower to reduce oxides of nitrogen (NOx) emissions. I'm sure Mazda engineers took this into consideration in the design of that pocket. Rotaries run a little "dirty" anyway, needing a thermal reactor or catalytic converter to clean up the exhaust- again, this was taken into consideration in the design process.
whlanteigne, Oct 25 2004

       I'm impressed with two things: 1) You knew that. 2) You dug this out of the lost-idea graveyard.
shapu, Oct 25 2004

       I'm pretty sure this violates the laws of physics, regarding fluid dynamics. Off the top of my head, I think that any change you make in the pocket shape to change the amount of any unit area projected on a rearward axis (i.e. change the rear of the pocket to a long tail) will be precisely balanced by an equivalent but opposite increase in total numbers of unit area, giving you the same total rearward-projected area, on which the total force projected by the psi in the chamber is independent of anything else; thereby giving you the same rearward force.   

       Otherwise you could just dispense with the actual internal combustion, put one of your shaped pockets in a rotor, put some pressure into the space between the rotor and the housing permanently, and let the pressure push the rotor around forever because of the imbalance between the shape of the front of the pocket and that of the rear.
gzuckier, Mar 22 2005

       The quasiturbine seems to be a better design to devote your energies to. It is easy to see the design flaw of a wankel by gluing three toothpicks into a triangle and pushing them inside a cardboard circle. If you exhert pressure on the middle of one of the toothpicks it tends to leak at the edges and not remain sealed well.
Willie333, Sep 29 2005


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