Rolf Pfeiffer wrote:
cut
Rolf, I am not sure 0.5 mach is the upper limit for a rotary engine.
The Taylor data we have here is all for piston engines with poppet valves
unless you have something else. Note the VE's are all
way less than 100% while the P-Port rotary typically runs at 120% VE.
As I said before IMHO the ultimate configuration will be both side and
peripheral intake ports such as Richard Sohn is working on. Side ports
for cruise and P-ports for top HP.
Also the NSU RO80 had two peripheral ports for each rotor. A large high
speed and a small low speed. Then again it used carbs that need strong signals.
Paul Lamar
Paul, I am referring to SAE paper 790484, entitled An Analysis of the Volumetric
Efficiency Characteristics of 4-Stroke Cycle Engines using the Mean Inlet Mach
Number Mim.
Authored by Itaru Fukutami and Eiichi Watanabe. The Institute for Vocational
Training (Japan)
The data was obtained on both, the reciprocating engine and in Appendix C on the
Rotary engine.
The key here is a different definition of the Mach index.
Usually, the inlet Mach index Ms is used that considers displacement alone, while
the Mim index accounts for valve timing as well. To spare the formulae, Ms and Mim
are equal if the valve-opening period is 180 degrees of crank rotation and VE is
100%.
Mim (%) = 180 *VE / ( (IC - IO in degrees) *100) * Ms
It says, valve timing can easily vary between 210 and 340 degrees, which has now
been accounted for.
To look at his graphs, it is quite amazing how similar the VE curves are when using
the Mim number instead of Ms, even for widely different engines.
In the Rotary engine with side ports, the paper concludes that Min is about 0,55
Mach up 10% from the Recips. However, this conclusion is based on the artificially
smaller ports for the tests. The curve for the largeset port is discontinued after
0,25 Mach but it seems to lead into the other curves limited by 0.55 Mach.
Unfortunately, there is no data for peripheral ports. One can only assume that
peripheral ports may allow an even higher velocity before choking occurs, perhaps
as high as 0.6 Mach, but that is strictly speculation.
All tests are made without any intake or outlet manifolds, in order to avoid the
effect of such ducting.
One point I found particularly interesting is the peak of VE in the Recip to be
near about 2000 rpm, while in the Rotary there is a slight valley near 2000 rpm at
~ 87% and a levelling off to ~94% near 5000 to 6000 rpm. That is at large ports.
Using a reduced port sizes will yield a similar curve to the Recips. The increase
in the Rotary is likely caused by the ram effect. In the Rotary, each chamber
follows the next, perhaps with a 90-degree delay between suction strokes, while in
a recip the inlet valve is closed for nearly three quarter of the time during two
shaft rotations where the air column needs to be accelerated with each inlet valve
opening. Of course, in the Rotary, one can argue that exhaust gases push against
the intake, bringing the air column also to a complete stop, where renewed
acceleration is needed. However, it seems to me more likely that the pressure of
the exhaust will push some residuals into the chamber during intake, thereby
increasing VE. Since the last portion of the chamber is not fully burned, the gases
contain O2 and possibly fuel as well and thereby aid VE.
Jerry. With reference to the comment by Bill Jepson, he is of course right. A too
wide port reduces the support for the apex seal. But 45 to max 50 mm width should
be ok. From 80mm, 15 mm remain at each side at width 50, which should be good. Some
curvature is needed for the port closing side for either port for a gradual
reseating of the seal.
Rolf
Can you scan some of that paper in and send it to us Rolf.
Also copy it and mail it to me?
Paul Lamar
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