Mazdatrix built this 350 HP turbo two rotor RX8 engine with
three exhaust ports per rotor. Both side and peripheral exhaust
ports are used. That power is generated at only 8000 RPM.
The waste gate opens at that point. The pressure in
the combustion 1.3 L chambers (there are two of course. Total
displacement is 2.6 L or 158 ci) are rather high. Well over 2 HP
per cubic inch so the stock 8 mm tension bolts are increase
to a 1/2 inch diameter. These act like 17 dowel pins holding
the expansion of the aluminum rotor housing. If you don't do this
the cast iron end housings can crack around the top dowel
pins.

This engine is irrelevant to most aircraft use unless you
want to race at Reno. The fuel burn would be enormous at around
30 gallons an hour and you would have to have a low drag high
speed airplane  to get reasonable mpg. Of course you could use
the power for short takeoff in an STOL aircraft.


snipss....

Paul Lamar


Just wondering, what kind of power and fuel burn
at 6000 rpm could we expect from a 2-rotor that
uses p-port and side ports for intake AND exhaust?
The follow-on question is:  [assuming cleanly-designed
lightweight manifolds could be fabricated] if there is
not that much difference, then why bother to close up
the side ports when p-porting?

Gene Kahn

There is  fundamental difference between intake ports and
exhaust ports. Intake ports are far more configuration sensitive
because the pressure differences are slight. An exhaust port
is basically releasing high pressure while an intake
port is drawing in air. I hesitate to call it sucking
in air but many engines work like that including side
ports.

In a p-port there is a strong effect from organ pipe
tuning and that is why the engine can get 20% more air
in than its displacement would indicate. In other words the
volumetric efficiency (VE) of a p-port is 120%. That is partially
due to the fact there are no intake valves to get in the way.

Aerodynamically speaking it is conceivable  a side port could
interfere with this. One has air coming in from three directions
90 degrees apart instead of only one. Air in an intake
system can be moving as fast as mach .4.

Richard Sohn tried it on one of his single rotor engines
and he found no benefit.

Fuel burn is a minor function of breathing losses.
In other words when the VE is high and the pressure
drop across the exhaust port is low the power generated
per pound of fuel burned is the best. Torque is also
highest at that point. HP is the product of RPM and
Torque so HP does not peak until some higher RPM.

The rule of thumb for any rotary up to this point
is a BFSC of .47 while a Lycoming aircraft engines
are slightly better at about .45. The BSFC in my
230 HP Contnental O-470 in my C182 is .52.

BFSC is given in pounds of fuel burned per HP generated
in one hour. Mazda now claims their new rotary is more
efficient than their piston engines.

Some gasoline engines approach .40 and some
diesels, at low to medium power, claim .35. Mostly
due to a much higher compression ratio and wide open
throttle all the time. In other words good
breathing. When a gasoline engine is wide
open throttle its fuel burn gets much closer
to a diesel's fuel burn with both near max power.

The diesel engine works best at low to half max
power where cars and trucks spend most of their
time. Aircraft engines spend most of the time
from half power to max power. Historically diesel
have not made successful aircraft engines but
hope springs eternal :)

The downside with high compression ratio is
the engine must be much stronger to contain the high
pressures and therefor the power to weight ratio
of a diesel engine suffers.

Did I cover everything? This is turning into
another book. Speaking of books I highly recommend
a few.  Download this list from:
http://www.rotaryeng.net/books10.html

Paul Lamar