Hi Paul,

  Here I go with that thinking stuff again.:-)) If you were doing a turbo
  compound system on your RX8, would you also change the rear axle
  ratio to something taller? On a car the higher gear ratio would put
  more load on the engine to maintain cruise speed, resulting in the
  throttle being more open. That reduces pumping losses and more hot
  air to apply force on the turbine. That should then add slightly
  more advantage from the turbo compound system. With that in mind,
  what gear would you chose instead of the 4.44:1 they have?

  Dale Davies

  Lets assume the car has a frontal area of 20 square feet.
  The rule of thumb is 80% of the height times the width estimates
  the frontal area. Lets say 6 feet wide and 4 feet high.
  Or 5.5 feet wide and 4.4 feet high.

  Lets also assume the C sub d of .3! Typical for a Prius. Drag would
  then be 20 x .3 x 75 x 75 x .0026 or 88 pounds at 75 MPH. 75 MPH is
  110 FPS. So required HP is then drag x FPS or 8250 pound foot per
  second or 15 HP. Double that for tire rolling resistance and you get
  30 HP needed to maintain 75 MPH on a level road at sea level.

  Automotive turbo compound is a real challenge. 90% of the time a car
  cruises on the freeway or autobahn at 30 HP while the engine may be
  rated at 400 HP. In order to make that highly efficient you need a
  small engine running at about 75% of it's max power at best torque
  RPM. This is the rational for shutting of some of the cylinders in a
  piston engine.

  The rear axle ratio could be the same as the current RX8 at around
  3.5:1 for acceleration and hill climbing reasons.

  What would be great is a 2.5 rotor Wankel engine. In other words 2
  rotors for acceleration and hill climbing and a smaller one rotor
  for cruise. The unique configuration of the e-shaft makes that possible.


http://www.rotaryeng.net/RX8-**TC-eng3.html<http://www.rotaryeng.net/RX8-TC-eng3.html

  The small one rotor engine would have a tiny turbine to get the
  BSFC below .36! Diesel range or below.  The fuel burn would then be
  about 10.8 pounds per hour or about 1.7 gallons an hour. At 75 MPH
  the MPG would then be about 44 MPG.

  The advantage over a hybrid is less extra weight and cost for
  electric motor and battery. Not to mention the limited availability
  of lithium. The advantage over the diesel is better acceleration and
  less cost and weight. No carcinogenic black smoke problems either.

  Paul Lamar

Ok. How would you propose to couple and decouple the "main" engine when
 needed?  The trick will be to do it seamlessly.  With cylinder deactivation
 and drive by wire this is fairly simple.  When engaging a whole other
 engine would be difficult.  The rotary has low rotational braking forces.
 It would likely be easier to build a 3 rotor with one rotor being 50 or
 60mm wide for full time use.  The advantage would be that current machining
 equipment can be used.  Then the cut rotors need lube while reducing air
 intake to reduce pumping loses.  An R100 size rotor should be around 125HP
 with Renesis end housings.  If narrowed to 40 or 50mm the power would be
 reduced and a larger throttle position required.


 I welcome your thoughts,

 Dale Davies

 One way clutch. AKA  Sprag clutch.

 Paul Lamar

Paul   Just wondering.  These large radial engines only turn 1/3 the RPM of
our engines so it would seem to need three times the  RPM reduction from the
turbine speed to the engine shaft. Looking at the posted images there
doesn't seem to be a lot of reduction  in the gearing  (posibly 12 to 1?)
Does the exhaust turbine operate at a much lower speed or is the fluid
coupling a torque converter with a very high lock up speed. Are we
investigating the traction drive in order to use a more efficient recovery
turbine that runs at a higher speed or is there some other reason?

george grimes

The R3350 turbines were turning 16,000 RPM at cruise and 19,000 at take off.

A turbo charger size turbine would have to run upwards of 80,000 RPM.

If you make the turbine about the size of the rotary you may get
sufficient HP recovery direct drive. No gear box. Here are some old 3D's.

When a light weight rotor is developed (not the current cast iron) a 16,000 RPM version of the Mazda rotary will become possible.

Paul Lamar