Paul,

I've made some big improvements to the turbo sizing spreadsheet.

The big problem with the previous version was that it allowed the user
to input values for both air-fuel ratio and BSFC. This can result in
unrealistic results for mass flow and horsepower.

In this version, the user can input only air-fuel ratio and desired
horsepower. the BSFC is calculated based on the inputs.

There is also a barometric pressure input, so users can enter an
"altimeter" setting and see how this affects power.

I have added a couple of larger Garret turbo maps and also a larger
Rotrex supercharger map. The Rotrex superchargers are very efficient and
are a real alternative for someone who wants a boosted engine for
altitude performance, but doesn't want the heat or installation issues
of a turbo.

The Rotrex uses a traction drive gearbox like Paul and Doug are
implementing on their turbo compound engines.

I have also added a second data point on each map that shows mass flow
corrected for evaporative cooling effect. I have used a very
conservative factor of 0.5 for evaporative cooling effect, because a lot
depends on the individual configuration, placement of nozzles etc.

The ethanol gives a very large evaporative cooling effect, but with gas
the effect is much smaller.

I have also used a very conservative mass flow per horsepower factor. If
you enter the values for a 550 cubic inch piston engine turning 2700 rpm
and a volumetric efficiency of .85, you will get only 244 hp.

The input example shows a rotary engine turning 8000 rpm and making
nearly 300 hp. This is obviously a P-port engine with a VE of 1.2. But
it is based on the same power equations as the piston engine.

If you enter ethanol as fuel you will see more power. Ethanol contains
quite a bit of oxygen so it gives a natural supercharging effect -- you
get more power at a given mass flow. But ethanol has less net heat
energy so, you must run a richer mixture and will see lower BSFC.

However, a rotary should allow fairly lean mixtures with either gasoline
or ethanol. Even a turbo rotary will allow leaner mixtures than a turbo
piston engine because the exhaust valve in a piston engine has a hard
time coping with the high heat of boosted engine.

The spreadsheet can be used to enter conditions for all phases of
flight, from takeoff power and full-rich mixture, to cruise at altitudes
up to 20,000 feet.


Regards,

Gordon.


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