In this photo you can see the telescoping section extended to its
full length.
I
have attached a larger scale drawing of the total induction system for those who
want to make their own determination of the intake length. If the
telescoping portion is fully extended then it appears that the rest of the
length is approx 1.75 the length of the telescoping section as best as I could
determine by relative scaling.
Example
Calculation
I
measured the diameter of the rotor housing (smallest dimension) and found it to
be 7 1/8". I then took a circle and made it the same diameter and then
used that from one end of the extended intake to the combustion
chamber entrance and came up with 3.5 diameters or 3.5 * 7.125 = 24.9
inches or say 25inches. That figure does not appear unreasonable just looking at
the relative length of the extended tube length in the
photo.
So if the telescoping section is fully extended at 6000 rpm then the
total induction length is approx 25 inches.
if 25 inches then a pulse generated by the opening of the intake port
traveling to the entrance of the intake and reflected back to the intake port
(to aid in stuffing the combustion chamber) would need to travel twice that
distance or 50 inches. 50 inches is 4.167 ft which traveling at
the velocity of sound at sea level of 1100 ft/sec would need 41.6/ 1100 =
0.00378 seconds to make the round trip. Assuming the pulse is generated by
the opening of the intake port which causes the trapped remant exhaust gas to
burst forth into the intake thereby generating a shockwave/pulse and you want it
to arrive back as the port is closing.
Here
are the PP port timings as found on Paul Yaws excellent web site on the rotary
engine.
Mazda Factory Peripheral Port
IO 86° BTDC
IC 75° ABDC
EO 73° BBDC
EC 65° ATDC
This site is meant to give information
Don't know if this is the port opening on the R26B engine but the
only thing I could find.
So 86 BTDC opening (pulse goes out) and 75 ABDC (Pulse arrives back),
so total rotation from opening to closing is 86 + 75 = 181 deg, now it will be
somewhat less than this as it takes some finite time for the pulse to be fully
generated and you want it to arrive back probably 15-20 deg before the port
closes.
But for the moment lets ignore those realities and see what we get.
So 180 / 0.00378 = 47520 deg/sec of rotation speed
required. 47520 /360 = 132 revs/sec *60 = 7920 rpm which is a bit
high.
If we now adjust from some realities such as time it takes to
generate the pulse and having it arrive back before closing. Somewhere I
found some data in an engine book that indicates it would probably take
around 5-10 % of open time to generate the pulse peak. So taking 7.5
% opening time = 13.75 deg, so taking 14 Deg that and lets say 15 % of
total open period arrival before port closes. 0.20 * 181 =
27.2 deg before closing, we have 181 - (14+27.2)
= 139.9 deg total rotation travel time for the pulse to
transverse the intake.