This is not exactly what we are looking for but there are
some clues here.
This is from SAE paper 821149 "The Effects of Turbocharger Design
and Installation on Gasoline Vehicles Transient Response" I provided
some of the instrumentation on the R&D reported in this paper.
Note the 20 HP loss in the overall steady state engine net HP out going
from a .63 to a .38 A/R. This is a T3 turbo charger. R, the radius
of the turbine, is fixed and A, the area of the nozzles, is changing.
Basically what is going on here is more back pressure and net HP loss
is being being generated by the smaller nozzle.
Just like electric motors you can get the same HP from a
turbine if you make a small one running at high RPM or a large
one running at low RPM. In this case the weight penalty is less
severe in the over all scheme of things. The larger turbine
will have the same HP loss with the same nozzle area but the
RPM will be less and the turbine torque higher. Consequently turbine
power will be nearly the same. Turbine power is the bottom line
for turbo compounding.
Paul Lamar
Paul
Please correct me if I am off base here. For turbocompounding I am assuming
the NET turbine HP (at the same comparative mid rpm ranges) would be greater
out of a REN (Renesis) high power version then a 13B because..
Increased back pressure would affect the amount of exhaust gases brought
into the next intake cycle less in the REN than then in the 13B. Renesis
exhaust gases brought into the next cycle are almost completely eliminated
but conversely even though the REN engine has a larger exhaust port area the
energy needed to pump the gases out might be larger. Why ?? no open inlet
valve for some of the pressure to escape from. I think however that is good
thing as more kinetic energy is directed out towards the turbine. The
pressure and volume of gases should be greater in the REN as well.
This situation also seems analogous to a high head Pelton hydro systems.
The liquid is water. The inlets orifices are sized for to handle the
pressure and flow obtain the best rpms. Pelton wheel size determines torque
range.
So if want lower turbine rpm with good torque we will have to go up turbine
wheel and injector opening size at our limited volume. Right? Then what
about heat? Slowing the transit of hot gases through the housing will cause
the unit to heat up as will increasing the pressure.
Seriously........ time for an expert turbo advisor on this project just to
size the turbine huh?
What is used to drive a turbo for testing? Propane burner:)
Doug in Japan
Back pressure effect is more or less independent of the timing and type
of port. As soon as the exhaust port opens the engine must pump the exhaust gases
out so the back pressure in the exhaust system works against that.
For a given engine net HP the HP in the exhaust will be pretty much
proportional regardless of the type of exhaust port. I suspect at
high power the heat balance of an RX8 engine is pretty close to that
of a 13B. If it were significantly different at aircraft power levels
we would see a significant difference in the BSFC and we are not.
To drive the turbo for testing you will need a rotary engine that will
generate the exhaust gas mass flow and temperature.
That is 200 HP worth of energy in the exhaust. More or less the
same amount of HP that comes out of the e-shaft. Our goal is to recover
20 percent of that or 40 HP. The same amount CW achieved with the
R3350 TC.
Paul Lamar
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