Wankel stroke question
#1
Wankel stroke question
I am still trying to learn the fundamentals of what all occurs inside the rotary engine, and sorry if this has been asked before...
But in my searching today, I came across this pic:
![](https://upload.wikimedia.org/wikipedia/commons/b/b0/Wankel-Airco.jpg)
It looks like long sides of the cylinder come in a bit on each side at the midsection, is this an optical illusion or are they doing this? Are all wankel motors shaped this way? I was under the impression that they were perfectly oval shaped. And if the latter is the case, what is the purpose of this?Larger combustion chamber?'
Thanks for any help
But in my searching today, I came across this pic:
![](https://upload.wikimedia.org/wikipedia/commons/b/b0/Wankel-Airco.jpg)
It looks like long sides of the cylinder come in a bit on each side at the midsection, is this an optical illusion or are they doing this? Are all wankel motors shaped this way? I was under the impression that they were perfectly oval shaped. And if the latter is the case, what is the purpose of this?Larger combustion chamber?'
Thanks for any help
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#5
Registered Zoom Zoomer
iTrader: (2)
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There's allot of math in the workings of the rotary engine. Really interesting stuff, ultimately producing incredible output per volume and very smooth turbine-like operation.
Many of us got RX-8's primarily due to its Wankel-based engine. Good to see your 'how it works' interest.
Many of us got RX-8's primarily due to its Wankel-based engine. Good to see your 'how it works' interest.
#6
So far I am guessing I have stumped you... Can anyone supply a valid answer? I know the basics of how a rotary works, the vids werent much help, although I did stumble onto this pretty cool vid of a 4 rotor making 1600 Hp. It got pretty cool when at the 2 minute mark teh exhaust manifold got so hot it burst into flames. http://www.youtube.com/watch?v=0BGGB...eature=related
But still no one able to answer the question...
But still no one able to answer the question...
#7
There's allot of math in the workings of the rotary engine. Really interesting stuff, ultimately producing incredible output per volume and very smooth turbine-like operation.
Many of us got RX-8's primarily due to its Wankel-based engine. Good to see your 'how it works' interest.
Many of us got RX-8's primarily due to its Wankel-based engine. Good to see your 'how it works' interest.
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#8
So far I am guessing I have stumped you... Can anyone supply a valid answer? I know the basics of how a rotary works, the vids werent much help, although I did stumble onto this pretty cool vid of a 4 rotor making 1600 Hp. It got pretty cool when at the 2 minute mark teh exhaust manifold got so hot it burst into flames. http://www.youtube.com/watch?v=0BGGB...eature=related
But still no one able to answer the question...
But still no one able to answer the question...
i'm no expert and I may be wrong, but a perfect oval would yield no compression. Seals would not be in contact at all times, as it does with an epitrochoid.
#9
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#10
Administrator
what was your question? it seemed to be "are they all shaped like this?" which was answered by stealth.
was your question "why are they shaped like this?"
if so then its because that is the path traced by the tips of the rotor as it revolves around the eccentric shaft. if it wasn't shaped that way the tips would not be able to keep in contact with the wall for sealing the chambers.
was your question "why are they shaped like this?"
if so then its because that is the path traced by the tips of the rotor as it revolves around the eccentric shaft. if it wasn't shaped that way the tips would not be able to keep in contact with the wall for sealing the chambers.
#12
Registered
It looks like long sides of the cylinder come in a bit on each side at the midsection, is this an optical illusion or are they doing this? Are all wankel motors shaped this way? I was under the impression that they were perfectly oval shaped. And if the latter is the case, what is the purpose of this?Larger combustion chamber?'
Thanks for any help![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
Thanks for any help
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
Edit: Here it is:
https://netfiles.uiuc.edu/ro/www/Soc...elgeometry.pdf
Last edited by robrecht; 02-25-2009 at 01:59 PM.
#13
Pretty interesting information
. On an unrelated note, what is the limiting factor for a rotary engine as far as RPM's are involved? Is it simply the rotational inertia of the rotor? It seems like it wouldnt have any or many parts really limiting it from having a nearly endless redline, unlike a traditional motor which is limited by the connecting members and valves.
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#15
Registered
Pretty interesting information
. On an unrelated note, what is the limiting factor for a rotary engine as far as RPM's are involved? Is it simply the rotational inertia of the rotor? It seems like it wouldnt have any or many parts really limiting it from having a nearly endless redline, unlike a traditional motor which is limited by the connecting members and valves.
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#16
Registered Zoom Zoomer
iTrader: (2)
Pretty much yes. Inertia vs. strength of materials.
Keep in mind that the 9k rpm redline is as shaft measured. The rotors themselves are only going 1/3 that speed (3k).
btw: the rotors are steel and the combustion housings aluminum, so impossible to seize the engine, which is a nice innate-materials advantage.
The upcoming 16X (1.6L vs. current 1.3L) has a slightly different rotor "orbit" in its housing, due to a physically larger internal capacity (same external size) , to facilitate a larger combustion chamber and thereby greater power. It will also have aluminum end housings (current iron) to maintain the same weight as the current engine at that greater power. Brilliant!
Keep in mind that the 9k rpm redline is as shaft measured. The rotors themselves are only going 1/3 that speed (3k).
btw: the rotors are steel and the combustion housings aluminum, so impossible to seize the engine, which is a nice innate-materials advantage.
The upcoming 16X (1.6L vs. current 1.3L) has a slightly different rotor "orbit" in its housing, due to a physically larger internal capacity (same external size) , to facilitate a larger combustion chamber and thereby greater power. It will also have aluminum end housings (current iron) to maintain the same weight as the current engine at that greater power. Brilliant!
Pretty interesting information
. On an unrelated note, what is the limiting factor for a rotary engine as far as RPM's are involved? Is it simply the rotational inertia of the rotor? It seems like it wouldnt have any or many parts really limiting it from having a nearly endless redline, unlike a traditional motor which is limited by the connecting members and valves.
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
Last edited by Huey52; 02-25-2009 at 02:40 PM.
#17
Pretty much yes. Inertia vs. strength of materials.
Keep in mind that the 9k rpm redline is as shaft measured. The rotors themselves are only going 1/3 that speed (3k).
btw: the rotors are steel and the combustion housings aluminum, so impossible to seize the engine, which is a nice innate-materials advantage.
The upcoming 16X (1.6L vs. current 1.3L) has a slightly different rotor "orbit" in its housing, due to a physically larger internal capacity (same external size) , to facilitate a larger combustion chamber and thereby greater power. It will also have aluminum end housings (current iron) to maintain the same weight as the current engine at that greater power. Brilliant!
Keep in mind that the 9k rpm redline is as shaft measured. The rotors themselves are only going 1/3 that speed (3k).
btw: the rotors are steel and the combustion housings aluminum, so impossible to seize the engine, which is a nice innate-materials advantage.
The upcoming 16X (1.6L vs. current 1.3L) has a slightly different rotor "orbit" in its housing, due to a physically larger internal capacity (same external size) , to facilitate a larger combustion chamber and thereby greater power. It will also have aluminum end housings (current iron) to maintain the same weight as the current engine at that greater power. Brilliant!
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#18
Registered
Not long after I asked that, I remembered reading somewhere that the motor stops "breathing" after about 7500 RPM. This is something else I dont quite understand... I am guessing that after reaching a certain rotational speed it isnt able to efficiently expel the spent gasses and inhale the needed combustibles?
I was confused at first about the shaft rotational speed and the pistons rotational speed, but got that sorted out after seeing a few vids
. I would be interested to see the components of the 16X compared to the 13B to see how the orbit is different.
I was confused at first about the shaft rotational speed and the pistons rotational speed, but got that sorted out after seeing a few vids
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#19
Lubricious
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Pretty interesting information
. On an unrelated note, what is the limiting factor for a rotary engine as far as RPM's are involved? Is it simply the rotational inertia of the rotor? It seems like it wouldnt have any or many parts really limiting it from having a nearly endless redline, unlike a traditional motor which is limited by the connecting members and valves.
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
The flame-front issue makes wankel RPM largely dependent on the physical size of the engine. Large rotaries were made to power natural-gas pumps, with rotors 1 meter in diameter. These were limited to 1200 rpm precisely because of the flame-front issue. Likewise, very small wankel engines could run at much higher rpm.
http://www.me.berkeley.edu/~liepmann...02.IMECE01.pdf
#20
That is another aspect that I had not thought about ![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
Interesting info in here. Thanks for all the help
. I am sure I will come up with some more questions, but I think my brain is full for now haha.
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
Interesting info in here. Thanks for all the help
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#21
Registered Zoom Zoomer
iTrader: (2)
http://www.mazda.com/mazdaspirit/rotary/16x/
They're rotors, not pistons. Using the term "pistons" around here is a no no!!![Wink](https://www.rx8club.com/images/smilies/wink.gif)
They're rotors, not pistons. Using the term "pistons" around here is a no no!!
![Wink](https://www.rx8club.com/images/smilies/wink.gif)
Not long after I asked that, I remembered reading somewhere that the motor stops "breathing" after about 7500 RPM. This is something else I dont quite understand... I am guessing that after reaching a certain rotational speed it isnt able to efficiently expel the spent gasses and inhale the needed combustibles?
I was confused at first about the shaft rotational speed and the pistons rotational speed, but got that sorted out after seeing a few vids
. I would be interested to see the components of the 16X compared to the 13B to see how the orbit is different.
I was confused at first about the shaft rotational speed and the pistons rotational speed, but got that sorted out after seeing a few vids
![Smilie](https://www.rx8club.com/images/smilies/smile.gif)
#22
Registered
http://www.mazda.com/mazdaspirit/rotary/16x/
They're rotors, not pistons. Using the term "pistons" around here is a no no!!![Wink](https://www.rx8club.com/images/smilies/wink.gif)
They're rotors, not pistons. Using the term "pistons" around here is a no no!!
![Wink](https://www.rx8club.com/images/smilies/wink.gif)