Hi Paul/Rolf;

I was taking another look at the chamber volume as a function of intake
close angle for porting.
I was using the formulas from the 1981 edition of the Rotary Engine and
my results do not appear to be correct.

Can someone run through the formula/calculation for an intake close
angle of say 45 degrees?
Assuming a 13b:
e=15mm
R=105mm
b=80mm

Thanks
Cary


What page number are you looking at Cary?

Sorry,
'81 Edition, page 14, Section 2.4.2, bottom right - formula 2.24
V=volume
e=eccentricity=15mm
R=Generating circle radius= 105mm
b=width of rotor housing= 80mm
alpha= degrees eshaft rotation
Vmin=minimum volume at TDC (long formula 2.25) =~  56.5cc or
in the case of a 9.4CR rotor 654/(9.4-1)= 77.9cc

V = Vmin + ( 3 * root(3)  / 3) * e * R * b ) * (1 - sin(2/3 * alpha +
pi/6) )

Formula makes more sense if you look at Figure 2.9 on page 15.  Shows
the chamber volume
changes as a sine wave based on eshaft rotation compared to a piston engine.

I just noticed the formula is different in the '71 edition.
3 * root(3) * e * R * b =~ 654cc (swept volume) - the  "/ 3" term
appears to be incorrect.
The "/ 2" in the '71 edition appears to be correct.

Still need to work out the intake close timing angle.  Not sure if the
alpha value can be replaced with the
degrees of eshaft rotation?

Thanks
Cary

There are errors every once in awhile in the book.
I am not sure I understand the goal here.
I have a lot of intake timing diagrams for both the side
ports and the P-ports verses VE.

Perhaps the angles are expressed in radians and not degrees.

Good  Stuff, Cary

I looked at it too and was contemplating if the chamber volume changes
linearly with the piston movement. That is, if the volume changes with
the simple sine function of the piston movement.
You just confirmed that. Here is my explanation:

Looking at the RX7 or RX8:

Dimensions are E=15, R= 105, b= 80,

Displacement is sqrt (27) * E * R * b = 654.7 cc,
Piston stroke = 2*E * 1.5 or simply 3*E = 3 * 15 = 45 mm,
(1.5 is the piston stroke factor caused by the housing moving away by 1*E).

Piston area = 145.5 cm^2, calculated R* sqrt (3) * b, Area = 105 * 1.732
* 80 /100 in cm^2

In the RPE we have piston travel form TDC to BDC say from 0 degrees to
180 degrees.
To do the same in the Wankel we have to deduct the piston rotation from
the crank shaft rotation. 270 – 90 = 180, or simply divide the crank
angle by 1.5.

Piston travel from TDC to BDC is (1- cos (alpha /1.5)) * E * 1.5; (1.5 =
piston stroke factor)
Where alpha is the crank angle of the e-shaft, E = 1.5 cm.

Volume at TC = displacement / (CR-1)

For a 9:1 CR, the volume at TDC is 654 / ( 9 – 1) = 81.8 cc,
Volume at BDC = 654.7 + 81.8 = 736.5 cc,

Volume at any crank angle =
Volume at TC + 145.5 cc * (1-cos (alpha / 1.5)) * 1.5 (r) * 1.5 (factor),
(alpha between 0 – 180°)


E.G. at 90 degrees e-shaft rotation, we have
81.8 + 145.5 * ( 1 – cos (60) )* 1.5 * 1.5 = 245.5 cc chamber volume.
The air taken in is of course just 245.5 – 81.8 = 163.7 cc.

Rolf


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