Truck engine manufacturers are jumping on the TC band wagon.
     Pratt & Whitney Canada are trying to patent the turbo compound
     rotary so I would not be a bit surprised if they were not building
     some hardware to try it. At least I hope so.

     I find it interesting that Pratt & Whitney US and Pratt & Whitney Canada
     is allied with Rocketdyne.

     http://utc.com/

     Rocketdyne was rumored to be working on the TC rotary here in SoCal.

     Paul Lamar ...No rotor no motor.



     Paul,

     Was messing around with e-shaft direct-drive turbocompound concepts..

     Roughly what's the diameter of the flywheel on a 13b? At 6000rpm an 18
     inch wheel has a tip speed around 325mph and a 24 inch wheel has a tip
     speed around 450mph.


     Also, does anyone have some calcs for determining average flow velocity
     based on volume and pipe diameter? Need to figure out what diameter
     direct drive wheel would be required to interface well with the exhaust
     flow.

     Maybe a 2:1 planetary reduction - the tc turbine 2x the e-shaft speed
     would make the interface between the exhaust and the turbine more
     efficient.

     I wonder if a turbo compound could drive through a small automotive
     torque converter - ideally with an electric lockup. They seem pretty
     robust and there are lots of different versions out there.

     http://en.wikipedia.org/wiki/Torque_converter

     It occurs to me that the rotary engine might have a big advantage when
     considering a direct drive (or close ratio) turbo compound - high
     continuous RPM. This can make the size of the wheel smaller and yet
     still have the tip speed close to the flow speed of the exhaust.
     There's no way a direct drive would work on a big diesel.. Aircraft
     operations have it easier too - essentially one continuous RPM whereas
     road going applications require quite a bit of dynamic range. Even for
     a tractor-trailer engine which is mostly continuous operation.


     Matt-

     The ring gear is about 12 inches in diameter.

     Well you can start with the volume and speed of air going in as a start
     and knowing air temp of the exhaust you can figure the volume
     and speed of the air coming out. Assume the pipes are the same size.
     Then
     you add heat which increases the volume and speed coming out.

     V1 x T1 = V2 x T2 Temperature must be in Rankin. V is volume.

     Pressure is constant.

     T1 is 100 F or 560 Rankin

     (V1 x T1)/T2 = V2

     T2 is 1700 F or 2160 Rankin

     Speed of the air going in is V1/Area = Speed in.
     Speed coming out is V2/Area = Speed out.

     I suspect the mass flow is the same as matter can nether
     be created nor destroyed except by fission.

     A 13B pumps as much air as a 2.6 liter piston engine which is about
     230 CFM at 6000 RPM and a VE of 80%
     At a VE of 100% it would be about 275 CFM.
     With a p-port the VE is 120% so it would pump about 330 CFM.
     See the attached chart.

     Assume it is two 2 inch intake pipes so area would be 6.28 square inches
     or .0436 square feet. Speed going in would then be 7,568 feet per minute
     or 126 feet per second or 185 MPH going in.

     Coming out it would be 2160/560 x 126 FPS or 486 FPS.

     A turbine generates max HP when the blade velocity is half the
     flow velocity. That is because the turbine torque is max at zero RPM and
     zero at max flow velocity when the flow and the blade are both going
     the same speed. HP is the product of torque times RPM. See the attached
     chart.

     So size the turbine so the blades are going 243 FPS or 165 MPH.

     I'll leave the turbine diameter as an exercise for the student :)

     You can speed up the air coming out by necking the output pipe area down
     (at the expense of slight back pressure) and slow the air down by
     diverging
     the pipe area. Also you can use a variable nozzle like modern turbo
     chargers
     to tailor the best turbine HP to the e-shaft RPM and the turbine
     diameter.

     Check my arithmetic and physics. I could be wrong.

     Paul Lamar ...No rotor no motor.

     Paul,

     In the gas law Volume is inversely proportional to the temperature.

     PV=nRT

     or

     (P1 x V1) / T1 = (P2 x V2) / T2

     with a constant pressure

     V1 / T1 = V2 / T2    or    (V1 x T2) / T1 = V2

     Joel


I had (V1 x T1)/T2 = V2  My mistake.

I should have known that is what happens when you skip steps :)

Thanks for catching that Joel


Paul Lamar ...No rotor no motor.

Paul,
Mass flow out is higher because of the products of combustion.
You are adding fuel in the engine.

Bill Schertz

Thanks Bill.
True but it is 14 pounds of air to one pound of fuel.
When fully leaned it could be 18 pounds of air to one pound of fuel.
I did not consider that significant when determining the rough diameter
of the turbine.