tesseract

http://auto.howstuffworks.com/rotary-engine.htm

Wisconsin S2k

I understand how a rotary works and what it is. i've read plenty of technical breifs on it, from its design, history, function, etc.

The way it was explained to me is this:

Basically during 1 cycle on an engine, it makes power once during that cycle, and displaces whatever size engine it's displacement is.

A rotary makes power twice during 1 cycle, however, it also displaces twice the volume of it's engine during that cycle, so although the engine displaces 1.3 liters per "stroke" it technically does this twice during it's entire cycle.

So. to calculate volumetric efficiency (volume of actual displacement vs power made) you essentially have to double it's displacement to make it an equal comparison.


This is the way it was explained to me, and in fact, I want to say ultimate lurker was the one who said it a LONG time ago. (UL correct me if I'm wrong)

tesseract

i was talking power/physical displacement (or size), not volumetric efficiency. it's pretty widely known that rotaries are not all that efficient, just look at the poor fuel economy. but the actual physical size of the engine is very small for the power it makes.

how about the vol. eff. of an electric engine? is the power stroke at the apex between the magnets (or whatever is generating the field)?

Uber-s2k

IMO this is the general formula to launch the S as quick as possible.

Let out the clutch fast (no need honestly for a real 'dump' or 'sidesteep'), apply throtle. Not being sarcastic keep reading

When you get full traction (no tire spin), be at 6k RPM(>'04) and WOT.

Variances that make it different everytime -

tire presure
tire temp
tire tread left
surface condition
surface temp

What RPM you need to acomplish this changes based on the above factors. IMO generally 4.5-6.5k RPM.

Wisconsin S2k

[quote name='tesseract' date='Feb 5 2005, 03:10 PM'] i was talking power/physical displacement (or size), not volumetric efficiency.

Wisconsin S2k

Here's a formula how to caculate the volume of such engine...
It follows : Excentricity X Radius X Width X 5.196.
Excentricity about how much the excentricity is on the central shaft.. Lets say 15mm...
Radius is the distance from the centre of the rotor. lets that one is 105mm . Width is the width of a rotor.That's let say 80mm.. (actual these are from the mazda 787B engine ) Calculate all measurements in cm!
1.5cm X 10.5cm X 8cm X 5.196 = 654.7ccm...
Per Rotor chamber that is..
Since the displacement formula equals to the formula how to calculate the power of that engine, that is how it follow for calculating the power of an rotary engine... Although, it might only be an estimate of how much it produces. You still have to concider the compression-ratio and intake/exhaust size (and timing for creating the prevered power-curve..)..
Displacement X presure per square cm. X central shaft Rotation per Second! The out come must be devided by ten, or alse you have an ten time more powerfull engine out come in theory.
Lets say : 8.7kg/cm (for a compr.rat. of about 9 to one)X 654,7 X116.6rotations per second / 10 = 66343Watts!!! Is about 66,3kW@7000revs/minute(90HP).
Note : per Rotor... If you have a two-rotor engine you have, obviosly, multiply by the number of rotors the engine has..

Wisconsin S2k

4-stroke BMEP = (HP * (6500 / .5)) / (L * RPM)
2-stroke BMEP = (HP * (6500 / 1.0)) / (L * RPM)
Wankel Rotary BMEP (HP * (6500 / 3)) / (L * RPM)

cause
4-stroke have 1 combustion every 2 revolution 720

Wisconsin S2k

And here is an article right off of rx7.com about the 13B 1.3 liter rotary engine.

The key for comparing the displacement between the 4-cycle engine and the rotary engine is in studying the degrees of rotation for a thermodynamic cycle to occur. For a 4-cycle engine to complete every thermodynamic cycle, the engine must rotate 720

tesseract

you're right, the comparison is bunk. but if you put both engines on a table in your living room, which would take up more space? pretend they are solid blocks of lead for this...

Wisconsin S2k

from a size standpoint, I'd think the rotary will be smaller.

but we aren't talking size. we are talking displacement. 2 very different things.

please dont think im trying to knock the rotary engine. for what it is, i think it is quite an engineering marvel.