h a l f b a k e r yIt's as much a hovercraft as a pancake is a waffle.
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A Wankel where the erstwhile "rotor", now containing all the plumbing that used to be in the outer shell, is stationary and the housing rotates.
Requires spark plugs and intake and exhaust valves on each of the three faces of the hypotrochoid (triangle thingy) instead of just one set on the inside
of the epitrochoid (housing) but, of course, the components will last that much longer.
Maintenance would be pretty annoying, but the apices sweep along an unbroken surface, which mitigates Wankels' Achilles heel: keeping a tight seal between each apex and the casing.
Animations of :Wankel DKM 54 / KKM 57 / Mazda(KKM based)
http://www.der-wank...KKM/dkm_vs_kkm.html
[FlyingToaster, Oct 11 2015, last modified Oct 24 2015]
Wankel "rotary" engine
https://en.wikipedi.../wiki/Wankel_engine
[FlyingToaster, Oct 23 2015]
Early 1900's "rotary" engine.
https://en.wikipedi.../wiki/Rotary_engine
the most well known manufacturers were Gnome and LeRhone. [FlyingToaster, Oct 23 2015]
[link]
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One of the major problems with the Gnome and its relatives is the gyroscopic force engendered by the large spinning mass. |
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Also, they're usually 2-strokes with total-loss lubrication. Castor oil was the favoured product. |
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Contrarotating pairs might help, but there are still going to be some vicious forces on the "crankshaft". |
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Valves operated by hydraulic tappets, presumably ? |
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I wrote the post assuming a 4-stroke, but it'd make a great 2-stroke : uniflow without oil loss, the intake is right infront of the exhaust pipe for easy turboscavenging, and it gets rid of that pesky thermal expansion disparity 4-stroke Wankels suffer from. |
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Yeah, pretty vicious wobble (I think; I'm still trying to visualize the housing's path) but bear in mind that the housing is only a bare aluminium shell, and its speed is just half that of the crankshaft. |
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Oil loss would be restricted to combusted oil: more loss than a regular piston-engine but less than a crankcase scavenged 2-stroke, or regular Wankel, which both toss unburnt oil out the exhaust ports. |
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//tappets// the cam motions are 1:1 with the housing, so it would be built right in. |
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// its speed is just half that of the crankshaft // |
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You mean the rotor ? The crankshaft will have to be fixed, the rotor floating on the sprocket, and the casing being driven. |
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What's the advantage over a gas turbine ? |
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Rotation ratios (<link> for animations of the first two): |
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Original Wankel DKM 54 (the original Felix Wankel design)
epitrochoid: 3
hypotrochoid: 2
shaft: 3 |
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Mazda Wankel (KKM 57, designed by Wankel's coworker and the name coopted)
epitrochoid: 0
hypotrochoid: 1 (eccentric)
shaft: 3 |
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Proposed...
epitrochoid: -1 (eccentric)
hypotrochoid: 0
shaft: 2 (it's held by the hypo, but run, geared off the epi) |
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the proposed one is actually closer to the original engine (which was never produced in any number) than it is to the Mazda version, except the triangle thing is static so all the plumbing can be included without bother which, unfortunately, causes the eccentricity in the casing's movement. |
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Or, to answer your question, it's the "rotor" that's fixed. |
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Compared with a gas turbine ? Nothing you wouldn't expect, though with variable valve timing the power band would be wider. |
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Can a hamster live in one? It would then be the Hamster
Wankel Rotary Rotary Engine |
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I have almost no idea what you're talking about. I love it. |
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^ Take a look at the 2nd or 3rd animation on the first link. That's a normal (Mazda) Wankel engine. |
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Proposed in this idea is that we turn it on its head, put all the valves/plugs/injectors inside the rotor, making the housing an unbroken trough, and spin the housing instead of the rotor. Imagine the aforementioned animations with the rotor stationary and the housing rotating. |
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Upsides
- the plumbing, since it's on the sides of the triangle, never scrapes the corners of the rotor, which increases the efficiency of the sealing.
- since all the stuff is in the middle, any heat transfers or turbocharging can be done very efficiently. |
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Downsides
- you have to take the engine apart to change the spark plugs (though the engine is much easier to take apart).
- the engine vibrates more, since the housing, which is larger and heavier, is doing the wobbling, not the rotor. |
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Of course, what I find really neat (thanks HB) is that Wankel originally designed the rotary with no vibrations whatsoever, having both rotor and housing rotating (that's the first animation in the link "DKM54"). Later a cow orker changed it to the stationary-housing design (KKM57), which rotor vibrates, that became the Mazda engine. |
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Thank you very much, [Toaster]! I have quite a bit better understanding now. |
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After long thought I have decided that I'll never have the
mechanical acumen to properly judge this idea. I am
therefore awarding 1 (one) bun in recognition. |
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But, since I'm willing to go to great lengths to defend the clever double-homonym title, which part don't you get ? |
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It's a wankel rotary <link> but, in a fashion vaguely similar to the famous WWI-era engine also called a "rotary" <link>, the crankcase is the bit that spins around, not the crankshaft (which is attached to the body frame). |
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And, because having valves, spark plugs and injectors spinning around is a pain in the ass, we've moved them into the non-spinny bit in the middle. Not having them on the crankcase means the apex seals (located on the points of the triangle, they're the equivalent of piston rings) don't keep scraping over the valves, spark-plug cutouts, et cetera, which means they should last longer and provide a better seal. |
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