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jimmydasaint
Post  Post subject: What is the Advantage of a Rotary Engine?  |  Posted: Sat Nov 12, 2011 1:23 am
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Over a meal with an acquaintance, our conversation turned to the genius of the Mazda engineers who were using a Wankel (rotary) engine in the Mazda RX 8. He claimed that the efficiency was far too low due to the loss of energy and fuel during the rotary cycle. However, if it has been used successfully instead of a piston-driven engine what are the possible advantages? http://en.wikipedia.org/wiki/Wankel_engine




A piston-driven engine is shown below:


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marnixR
Post  Post subject: Re: What is the Advantage of a Rotary Engine?  |  Posted: Sat Nov 12, 2011 9:24 am
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call me a luddite, but all i feel that i want to know about a car is : will it reliably bring me from A to B on time at a reasonable cost ? i had no idea the Mazda RX8 had a Wankel engine + would not know in what way this affects the driving experience

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jimmydasaint
Post  Post subject: Re: What is the Advantage of a Rotary Engine?  |  Posted: Sat Nov 12, 2011 6:55 pm
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I did a little bit of searching and found the following:

Quote:
Wankel engines are considerably lighter, simpler, and contain far fewer moving parts than piston engines of equivalent power output. For instance, because valving is accomplished by simple ports cut into the walls of the rotor or side housings, they have no valves or complex valve trains; in addition, since the rotor rides directly on a large bearing on the output shaft, there are no connecting rods and there is no crankshaft. The elimination of reciprocating mass and the elimination of the most highly stressed and failure prone parts of piston engines gives the Wankel engine high reliability, a smoother flow of power, and a high power-to-weight ratio.



http://en.wikipedia.org/wiki/Wankel_engine#Advantages

Note that there is an advantage of the rotary driving movement as opposed to the use of pistons. However, efficiency is not mentioned here. However, if you can afford a Mazda RX-8, then looks matter better than the functionality.

Image

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imp
Post  Post subject: Re: What is the Advantage of a Rotary Engine?  |  Posted: Fri Aug 02, 2013 4:07 am

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In 1965, I worked for a company which obtained for testing, one of the newly introduced NSU "Spyder" autos, having a Wankel rotary engine, the design still proprietary to the German manufacturer.

We took the engine apart, our business being that of manufacturing sealing products. Obviously, one of the design's stumbling blocks was the means of sealing the tips of the rotor within it's "trochoidal" chamber. I believe then, thin carbon strips were in use, surely supplanted by newer technology.

It ran amazingly quietly and absolutely free of vibration. "Multiple decking" of rotors was in the works for future design, to obtain more power without increasing the rotor's size. See below article and pic.

http://www.jaylenosgarage.com/at-the-ga ... su-spider/

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Peter Dow
Post  Post subject: Mathematics of the Wankel Engine shapes  |  Posted: Thu May 29, 2014 12:03 am
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Regarding the mathematics of the unusual shape and profile of the Wankel engine triangular rotor and combustion chamber housing, I'm reviewing a mathematics demonstration I have just come across but which has been on the internet for a few years but, like me, you may not have come across it before now.
 
"Wankel Rotary Engine: Epitrochoidal Envelopes" by Tony Kelman on the Wolfram Demonstrations Project.
 


You cannot post a link within your first post!
Please remove the link(s) from your post and try again.
 
Quote:
This Demonstration gives an animation of an epitrochoid and associated planetary-motion envelope curve. The configuration shown has applications in the internal combustion engines invented by Felix Wankel and popularized by Mazda in RX-7 and RX-8 cars

 
 
Review by Peter Dow
 
If you think this video looks interesting, I highly recommend that you download the Wolfram CDF player software so that you can experiment with the features of Tony Kelman's demonstration. To quote Tony

Quote:
"The "eccentricity ratio" changes the shapes of the curves. The "reference frame" determines what is held stationary in the animation: either the epitrochoid (blue), the envelope curve (purple), or the centers of rotation of both curves. The "inner" envelope is the triangular rotor shape used in place of a piston in a Wankel rotary engine, whereas the "outer" envelope is the continuation of the envelope curve along the opposite extreme of motion."

 
So selecting reference frame = epitrochoid allows the display of the familiar KKM Wankel engine and selecting reference frame = fixed centers shows Wankel's original DKM engine with rotating housing.
 
You can slow the rotation animation down as well..

Looking at eccentricity ratios widely different from what we see in real Wankel engines is quite a revelation too.
 
As if all that wasn't enough, you also get to download and look at Tony's open source code and in particular the maths equations he uses to generate the curves.

Tony suggests some extensions to his demonstration. Well I have ideas of my own - I'd like to see computations of the areas between the curves representing the combustion chambers and a calculation of compression ratios for example.
 
Unfortunately, I don't have the Mathematica developers software package which, unlike the free player I got to view the demo, you have to pay - A LOT - for.

Excellent demonstration! Can't praise it highly enough!


Last edited by Peter Dow on Thu May 29, 2014 12:06 am, edited 1 time in total.


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Peter Dow
Post  Post subject: Re: Mathematics of the Wankel Engine shapes  |  Posted: Thu May 29, 2014 12:05 am
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Since this is my second post, I may now be able to link to the demonstration site.

http://demonstrations.wolfram.com/WankelRotaryEngineEpitrochoidalEnvelopes


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Peter Dow
Post  Post subject: Mathematics of the Wankel rotary-engine shapes - my webpage  |  Posted: Thu Jun 12, 2014 6:50 pm
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After I started this topic, I have since found another trochoids interactive demonstration webpage, this time by Christopher J. Henrich. His code is in Javascript which means it is pretty much open source, can run on most modern web browsers and therefore is ideal for me to modify.

So I've made a start and I'm publishing a webpage today which partially performs some of what Tony Kelman's demonstration does. I've a lot more to do yet but if you want to see how far I've got and monitor my progress, then click to my webpage using the following link.

My page includes links back to Christopher J. Henrich's original webpage and he is OK with me publishing this link. Anyway see for yourself.
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