Hi all

 I worked from 1968 to 1993 on Rotary Engine

 One item always eluded me and that was working out the CR and for purely
 academic reason I would like to complete this program, I would be
 grateful
 if you could give me some worked examples data.
 R'=R+a : e : B : Radial flank clearance : Width clearance & finally
 rotor
 pocket volume.

 In my worked example based on the Norton Rotary

 R'= 71.5 mm e= 11.6 mm : B=68.2 mm : Flank Clearance = 0.5 mm : side
 clearance = 0.15 mm , the compression ratio's ranged from 7.5 to 1 &
 9.2 to
 1 do you have any examples that also include combustion pocket size, or
 could you please measure the rotor pocket volume, and tell me the
 alleged
 CR.

 We used to measure this for D.Garside and I would give him the volume
 of a
 Plasticine by filling pocket, scrape around the flank with a steel
 rule, and
 then measuring the fluid displacement,



 It is possible that no two formulae give the same results.

 I have worked out the flank clearance Volume, but just need some actual
 rotor pocket volume, and the R'=R+a : e : B= width and the : posted CR

 Example R'= 10.5 cm : e=1.5 cm : B or width 7 cm

 Raw CR = Best possible ie, no combustion pocket or flank clearance =CR
 18.29 to 1

 Flank Clearance = 0.050 cm = CR = 15.41 to 1

 As above but with volume in rotor pocket = 35 cm = CR = 8.66 to 1

 If flank clearance set to zero and pocket volume = 35 cm = CR = 9.41
 to 1

 But you should include for the pocket volume and the spark plug/s
 recess and
 also the Land clearance, sometimes called top land clearance in piston
 engines.

 And the only way to test the program is by having as many types of
 engine
 data and Chamber Volume and CR

 Bob Rowley

 Tamworth

 UK

 The volume varies with the year. A rotor I have
 here in my office is 10 mm deep. Mean width is 48
 mm and it is about 77 mm long. CR is roughly 9.6.
 Housing width is 80 mm.

 You can download Kenichi Yamamoto's book "Rotary Engine" from this
 web site. It contains most of the dimensions on the Mazda rotary.

 http://foxed.ca/foxed/index.php?page=rx7manual

 Here are a couple of excerpts.

 Other info is scattered throughout the tech papers on our site.

 Paul Lamar

 Hi Bob;

 Be wary of formulas errors in both the '71 and '81 editions of KY's
 Rotary Engine books.
 Here is an old email on the error in the volume formula.

 '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.
 Hi Paul;

 When I originally did port timing for the Pport I had to estimate.
 Stock port timing are available at:
  http://www.yawpower.com/dectech.html

 I have seen some of the Pport intake timing diagrams vs VE from some
 of the old Mazda tech papers
 posted here occasionally - don't recall seeing the diagrams for the
 side ports.

 I wanted to confirm what the upper limit was for intake port close
 angle that intake inertia has to overcome
 before compression in the chamber starts pushing it back out when the
 intake port is still open.

 Had to work backwards to get the degrees of eshaft rotation. Values
 look reasonable, I think?
 Intake BDC Vmax = 77.9cc + 654.7cc = 732.6cc

 30 ABDC - V = 711.8, Vmax/V = 1.029 (6 port 2ndary IC)
 45 ABDC - V = 687.2, Vmax/V = 1.066 (40,50 approx side port IC)
 60 ABDC - V = 654.1, Vmax/V = 1.120 (RB street port IC)
 70 ABDC - V = 627.7, Vmax/V = 1.167 (6port Aux high speed side port,
 RB JBridge)
 75 ABDC - V = 613.4, Vmax/V = 1.194 (Mazda Factory PPort)

 Does anyone happen to know the location of the 13b oil injection port
 in degrees ABDC?
 Might be useful as a manifold pressure gauge tap.

 Cheers
 Cary

 We are already using it for the manifold pressure for Tracy's EFI
system.
 Works great. I have some nicely machined metric fittings for sale for
 that use.
 I don't know what the timing is but it clears the welded p-port by
 about 1/4 inch. Hint Le Mans timing.

 Paul Lamar


Hello Bob,

Regarding the calculations for the CR, here is an example of how to go
about it.

Definition of the CR = (displacement + volume at TDC) / volume at TDC,

Mostly known is the displacement calculation = 27^0.5 R e b

For the small volume at TDC we first calculate a rotor with flat flanks
(straight lines between centre point of apex seal contact)
Here is the calc for the small volume at TDC with straight flanks:
Small volume = [Pi ((e/R)^2 + 1/3) -- 3^1/2 /4 (1 + 6 (e/R))] * R^2 *b
    = [Pi * ((e/R)^2 + 1/3) -- 0.433 * (1 + 6
(e/R))] * R^2 * b

_Example:_ RX8, e = 1.5 cm, R = 10.5 cm, b = 8 cm,
e/R = 0.14286

Displacement = 27^1/2 * 10.5 * 1.5 * 8 = 654.7 cm3

Small volume = [ 3.1416 *(.14286)^2 + 1/3) - .433 * (1 + 6 * .14286)]*
10.5^2 * 8 cm
    = [ 1.1113 - .8042 ] * 110.25 * 8 = 270.9 cm3
(flat flanks)

CR = (654.7 + 270.9) / 270.9 = 3.42 having flat flanks,

Reducing the volume at TDC increases the CR.
E.G. 270.9 - 180 = 90.9 thus: CR = (654.7 + 90.9) / 90.9 = 8.2:1,(-190
cm3 = 9.1:1)

We now add a radius to the flank to obtain the additional volume needed
for the selected CR.

Distance d from short axis point to flat rotor flank:
d = (R-e) -- (e+ R/2) = R/2 - 2e
d = R/2 -- 2e = 105/2 -2*15 = 22.5

Select clearance to = .5 mm, h = d -- clr, h = 22.5 -.5 = 22 mm
Length of ½ flank s = cos 30 * R = .866 * 105 = 90.93 mm

Note : if the clearance is selected differently one must recalculate the
radius and the volume of the circle segment.
Also note that the radius will not have a constant distance to the apex
of the small axis as the rotor turns. In other words, the flank may be
constructed as a curve instead of a radius to minimize the clearance
volume. However, the difference is small.

Radius of arc R1 = (s^2 + h^2 )/ 2h = (90.93^2 + 22^2 ) / (2*22) =
198.92 mm, = 19.89 cm
½ angle = Asin (90.93/198.92) = 27.2 degrees,

Circle sector = R1^2 * pi * 27.2° / 180° = 187.85 cm^2
Area triangle = (R1^2 -- s^2 )^0.5 * s = 160.85 cm^2
Circle segment area = 27.0 cm^2
Volume circle segment = area * b = 27 * 8 = 216 cm^3

CR without a pocket and with .5 mm clearance radius:
Small volume at TDC = (270.9 -- 216) = 54.9 cm3
CR = (654.7 + 54.9) / 54.9 = 12.93 :1

For CR = 9.1 : 1 we need 190 cm^3 , where we require a pocket of 216 --
190 = 26 cm^3
If the pocket is 0.8 cm deep and 4.5 cm wide on average, it will be 7.2
cm long, or use any other combination to make up the 26 cm^3 .

For a CR = 8.2:1 we need a pocket of 216 -- 180 = 36 cm^3 using above
radius and 0.5 mm clearance.

_Select CR = 10:1_. To find the clearance volume : Displacement / (CR--
1),
Volume = 654.7 / (10-1) = 72.75 cm^3 , [(654.7 + 72.75 ) / 72.75 =10
: 1]

_Pocket size CR 10:1_ = 270.9 -- 72.75 = 198.15, and 216 -- 198.15 =
17.85 cm^3
Or: 216 -- 270.9 + 72.75 = 17.85 cm^3
Or: 72.75 - 54.9 = 17.85 cm^3

Regards
Rolf Pfeiffer

BTW Rolf used to work for NSU back when.
Paul Lamar


Rolf--Over the years we've reference data from various engine builders
and
manufactures including NSU regarding intake and exhaust port timing.
Given
your personal experience with these engines at NSU, do you have a
recommended method that you could share with us that is both simple and
relatively accurate for measuring port timing?

Steve Beckham


Steve

In a peripheral port engine like the RX7 you simply use the formula for
the trochoide:

X = e * cos (3 alp) + R * cos (alp)
Y = e * sin (3 alp) + R * sin (alp)

Here we are only concerned with the dimension X from centreline of the
trochoide.

Remember, angle (alp) refers to the angle of R, and the angle of the
eccentric shaft is (3 alp). When you compare the port timing of the
Rotary with the that of the RPE, the ratio is 3/2.
In other words, if the inlet at the rotary opens at 60 degrees BTDC, it
would be equivalent to the RPE of 40 degrees BTDC.

For a chamber to be at TDC position the angle alp for R is 30°, and for
e = 90° (3*30)

I we assume that the inlet opens at (alp) 55° BTDC, (3 alp) would be
165°.
The opening edge of the port from center would be:

X = 15 * cos (165) + 105 * cos (55) = 45.74 mm from center of the
trochoide.

The timing with reference to e would be 165° - 90° = 75° BTDC.
In terms of the RPE that would be 50° BTDC.

We can simply double the angle (alp) for the equivalent RPE timing, (55
-- 30)*2 = 50°


The BDC position of a chamber occurs at (alp) = 60° and (3 alp) = 180°.

Say the inlet closes at (alp) = 40°, (3 alp) for e would be 120°.
(All with reference to the original shape calculation of the trochoide).

The timing with reference to e would be 120° - 60° = 60° ABDC.
In terms of the RPE that would be 40° ABDC.

X = 15 * cos (120) + 105 * cos (40) = 72.94 mm from center of the
trochoide.

The port would be 72.94 -- 45.74 = 27.2 mm wide measured along the
x-coordinate.

The same calculation works for the exhaust port in reverse rotation.

For some reason In feel that nobody cares about that. One can't change
the porting anyway.

Regards
Rolf Pfeiffer