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

 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


This makes me wonder ... why hasn't Mazda already done this if it is
that obvious?????  They could make a 50 MPG Mazda 6.

SD

Me too. Back in the late 1940's, 1950's and 1960's over 9000 turbo
compound
aircraft engines were built. They reached a TBO of 3000 hours in airline
service.

As far as  turbo compound piston engines are concerned they  are very
hard on
exhaust valves and much energy is therefore lost in the exhaust valves.
Needless
to say the rotary has no exhaust valves so in theory it would be
significantly
more efficient.

Paul Lamar

What engines were turbo compounded in 1940-60's.

Van Vannoy

Allison, CW R3350, Napier Nomad. P&W did some TC R&D for the B36 R4360.

Paul Lamar
--

Hi, the low average power ~20hp in a car makes the potential improvment
from compounding too small to off set the increased weight and cost.  With
trucks it is a different story and some are now so equiped.  The tandem
cruise engine is an excellent idea.  I think Volvo had a show car years ago
with piston engines.

Murry I Rozansky

When gas becomes  $10 a gallon things change. We are now near that
in Europe. 100LL is over $10 a gallon  in Europe.

Compared to a hybrid there is way less increase in weight or cost.

Paul Lamar