vjaqua wrote:

For those of you that would like to consider a direct drive Wankel - The 2 stroke version
would be ideal. With double the number of power strokes the torque and horsepowe at the
lower RPM ranges would be roughly doubled. Paul is undoubtedly corect in indicating
that the port area  is probalbly somewhat restricted, but this is not as much of an issue
at the direct drive rpm point. External scavanging would be required, so an electric
assisted turbocharger would be apropriate (like Turbodyne). The motor section could
be run as a generator or alternater once the engine "bootstraps", and this would eliminate
one of the major accessory drives. Just think with modest boost pressure 200 bhp
at 3000 rpm - Vance

The two stroke wankel is in the category called cross scavenged.
In other words the intake is on one side of the rotor and the exhaust
is on the other. Most piston based cross scavenged two cycle engines
have a lump in the piston that directs the intake flow upward into
the chamber and the exhaust flow downward on the other side of the 
chamber and out the exhaust port. This is not possible with the geometry
of the wankel rotor so the scavenging efficiency will be low, the 
fuel consumption high and the power output way less than expected.
This is because highly undesirable mixing of spent exhaust gases and
fresh charge takes place.

Even in two cycle  piston engine cross scavenging is the least
efficient. It is however widely used in model airplane engines.
Uniflow scavenging is the most efficient. Air is taken
in on one end of the cylinder and exhaust let out on the other end. Almost
all successful two cycle diesel engines in trucks, ships and other industrial
use have uniflow scavenging. The Continental and Junkers Jumo aircraft 
diesels among them. I see no way of implementing uniflow scavenging 
in a wankel.

The means of supplying the charge air is irrelevant to scavenging 
efficiency. A roots blower would be the simplest. The power required 
of a pure electric blower makes it impractical. A turbo charger would  
use up the least amount of HP providing some way of starting the 
engine is devised.

BTW an electric assisted turbo charger is mainly useful to reduce emissions 
when the throttle is opened rapidly. This is so because the power
in a diesel is controlled by the amount of fuel injected and not
by throttling the intake pipes. When more power is needed more fuel
is injected... excessively and temporarily richening the mixture
beyond the optimum until the engine RPM can speed up and pump more air. 
That is why you see black smoke coming out of trucks from time to time.
This is the why of electric assisted turbo chargers.
They might however be used as Vance suggested... to start a two
cycle turbo charged two stroke engine.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org