Chamber volume is 650 cc. At 6000 rpm it takes .01 sec between the beginning of the intake
strokes. The duration of intake is however over 270 degrees of crankshaft rotation, or over
.0075 seconds.
Flow is volume over time or 650 cc / .01 sec = 65000 cc/s or 65 l/s. (650 / .0075 = 87000
cc/s)
One cc is .061 cubic inch.
87000 cc/sec is 5.31 cubic inch per second or 318 cubic inches per minute or .18
cubic feet per minute.
The actual flow volume needed for a NA engine of 1.3L two cycle or 2.6 L four
cycle is 310 cubic feet per minute. This looks like a problem.
The chart attached below from Macinnes book is corrected for
100% vol. eff. Typical of the rotary engine giving 310 cubic feet of air
required per minute. Not .18 cubic foot. PL
Paul,
87000 cc/ sec is 1000 times more or 5310 cu inch per second. That is 318,000 cubic inches per
minute or roughly 180 cubic feet per minute (not .18 cubic feet per minute).
Your calculation above is for two rotors I am only talking one rotor. One inlet runner for one
rotor.
I am not sure how you get the 310 cuft per minute. We know that 1.3 Liter / 2.6 Liter engine is
equal to ~40 cubic inches per chamber.
40 cubic inches / 1728 * 6000 rpm = 139 cubic feet per minute per rotor, or 278 cfm for two rotors,
which is not too far off from your number of 310 cfm.
Regarding air volume sucked in per unit time, which is the basis for the air velocity travelling in
the intake runner, one must also consider that this value of 278 cfm for both runners is averaged
out over the 360 degree crankshaft rotation, when in fact the air is drawn in over only 270 degrees
of crankshaft rotation, consequnetly the mean air velocity is larger by a factor of 360 / 270.
(After the 270 degree intake stroke there is a 90 degree crankshaft rotation where no suction takes
place.)
Calculating the velocity, we get 139 cfm divided by the cross-section of the 1.5" pipe in square
feet.
Cross-sectional area = 1.5 * 1.5 *.7854 / 144 = .012272 square feet.
Velocity = 139 / .012272 = 11,300 fpm. * 360 / 270 = 15,000 fpm, as I had before.
The area of the 1.5" ID pipe is 11.4 cm2.
Velocity is Flow over area or 65,000 cc/s / 11.4 cm2 = 5700 cm/s or 57 m/s.
Using 0.0075 sec: 86666 cc/s / 11.4 cm2 = 7600 cm/s or 76 m/s.
Both velocities are well within accepted intake air velocities (absolute maximum is about
120 m/s).
Imperial:
Chamber volume is 40 cuin.
Flow is 40 / .01 = 4000 cuin/sec. (40 / .0075 = 5333 cuin /sec)
Area of 1.5 ID pipe = 1.5 * 1.5 * 7854 = 1.767 in2.
Velocity = 4000 cuin / 1.767 in2 = 2265 in /s or 188 fps or 11,300 fpm.
Using .0075 sec: 5333 / 1.767 = 3000 in / s or 250 fps or 15,000 fpm.
We are in agreement on this fps number for a 1.5 inch pipe. I got only
210 FPS but that is in the same ball park. PL
Regards
Rolf
This is how I got it.
Paul Lamar
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