I have found a couple of references that say that the thermal efficiency of wankel rotaries gets better as the revs increase.

http://www.der-wankelmotor.de/Entwic...icklungen.html
(Hanns-Dieter) Paschke had early recognized that the thermal efficiency of the wankel engine with rising number of revolutions becomes better.

http://media.mazda.ch/dossiers/Wankel/Wankel%20E.pdf
Mazda sees it being used in automobiles. Because the rotary engine's thermal efficiency increases with increasing engine speed and the engine is vibration free, it is especially promising for installation in sports cars.

I believe Hanns-Dieter Paschke from the first link was one of the original Wankel engineers at NSU. The second link is from Mazda.

Does anybody know why a wankel's thermal efficiency would get better with higher revs?

Brian

 

i've racked my brain for and hour for every crazy concept i could think of, and none of them made a simidgin (sp?) of sense...

man oh man, cool beans TO THE MAX!!

 

If you don't know why, there is no way MOST of us could (I caped most because i don't wan't to offend anyone and get flamed for it).

 

It seems kind of hard to believe that the thermal efficiency would increase as revs increase but the quotes came staright from NSU and Mazda.

I'm no mechanical engineer or anything, perhaps a mechanical engineer or somebody else might know why?

The "swirl" of the intake charge might be greater at higher rpms (better combustion) but I would think that much more heat is lost at higher rpms also.

I know that previous rotaries had richer air/fuel ratios at low speeds because of overlap (less thermally efficient) but Mazda mentioned increased thermal efficiencies with higher revs while also mentioning how it relates to the renesis (which has no overlap).

 

i have no idea how an engine works, at least the details, even less about a rotory, 'cept that it uhhhhhhhhhhh spins a triangle around. Anyways, it might be due to the greater heat yeiling a slight expansion of the rotor itself causing less of 'X' to be loss through the seals due to the expansion. Also the centripital force of the quickly spinning rotor may have something to due with it, but because i know nothing of how one works, other than the spinning used to compress and ignite the air-gass mixture, i have nothing useful to offer lol.
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Lovely Wendie

 

Hi P00man,

Welcome to the forum. You might be on the right track with the basic concept. I could imagine that the centrifugal force of the rotors and apex seals could cause a little tighter sealing to the peripheral housings.

The slight thermal expansion of apex and side seals may help a little bit too?

Brian

 

Time. There is less time for heat to be lost to the rotor and housings.

 

Hi MikeW,

Are you saying that you think a smaller percentage of heat is lost at higher rpms because each "stroke" completes faster?

Don't forget that heat is produced much more quickly at higher rpms also. Let's say for example that the tachometer reads 9,999 (:D), your rotors will be revolving at 3,333 rpms and would be producing MUCH more heat than at idle (750 rpms on tach, rotors spinning at 250 rpms).

I remember that you didn't think that the rotors turned at 1/3 the speed of the eccentric shaft in a different thread. Do we agree now?

Brian

 

The bottom line is that the car is exquisite (perhaps a little to far?) and rotaries are possibly the greatest engines ever...except for that one that runs off of a thermal difference...what was it called?
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IPAD CASES

 

Stirling

 

Blahahahaha
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LovelyWendie

 

I was looking at the diagrams a bit wrong. (haven't owned a wankel engine car) The rotors spin 2/3 backward relative to the main shaft, hence 1/3 the forward angular velocity. Sorry about the misunderstanding.

The primary methods of heat transfer, conduction, convection, and radiation. Lets forget about convection, radiation is about the same-low or high engine speeds, so the conduction of heat to the rotor, rotor housings, and the side housings is of utmost importance. Maybe the surface coatings, in addition to low friction and high wear resistance, also thermally insulate the engine.

 

http://www.der-wankelmotor.de/Entwic...icklungen.html
(Hanns-Dieter) Paschke had early recognized that the thermal efficiency of the wankel engine with rising number of revolutions becomes better.

If only I hadn't a dropped out of German School.....

try this http://216.239.35.120/translate_c?hl...language_tools