Frans,
Sorry to confirm you are wrong!
The fuel pump is unable to supply 120 liters per hour and 15 PSI at the
same time. The pump performance curve suplied by Rotax (914 Install
Manual, paragraph 14.4.1, page 50) shows that the pump is able to
deliver only about 90 liters per hour at 15 PSI (relative pressure).
Should you need 1,5 bars/22 PSI (relative) then the flow would have to
be restricted to 55 liters per hour. Should you need 1,75 bars/26 PSI
(relative) then the flow would have to be restricted to 20 liters per
hour. 120 liters per hour can be delivered only with zero out put
pressure. Again this comes from the pump performance figures provided by
Rotax and this behaviour could be verified with any similar fuel pump.
In my previous example, assuming you are running on one pump, the flow
through the pump and the filter would be 96 liters per hour. The engine
would use about 30 liters per hour. The remaining 66 liters would go
back to the tank. Again, the conclusion is that the fuel flow through
the pump and filter is reduced when you push the power lever. I am
pretty sure you will be able to confirm this whenever you are ready to
run your engine. I would be curious to know your measured figures.
Remi
"You are flying at full power at 16000 feet, ISA conditions. According
to the Rotax
Manuals, the air box pressure (absolute pressure) is 1,2 bars. The fuel
pressure
at the carbs must be 0.25 bars above airbox pressure, that is 1,45 bars
absolute. Ambient pressure at 16000ft is 0,53 bars, so the fuel pressure
must
be 0,92 bars above ambient. The fuel pressure regulator adjusts the flow
back
to the tank so that the pump is able to supply the required pressure.
[/quote:6ba7d7472f]
I don't agree with that. The fuel pump delivers 120 liters, with 15 psi
or something
like that. The fuel pressure regulator simply opens a valve when the
pressure
exceeds a limit, so the excess fuel flows back to the tank.
If the engine consumes more, the pressure drops a bit, so the valve
closes a bit,
and less fuel is flowing back to the tank. Let's say that 96 liters flow
back
(your example). This means that the engine is using 24 liters per hour.
The
flow through the filter is 96 + 24 liters, still 120 liters per hour.
The ratio
may differ, but the total remains constant.
You can also see it like this: the pressure regulator does not
communicate with
the pump, so the pump does not know what is going on and always delivers
120
liters per hour, regardless whether the engine is running at full power,
or not
even running at all.
Anyway, as soon as I have the installation ready I can tell you for
sure, as I
have a fuel flow sensor in series with both the feed line and the return
line.
I will tell you how much flows through the filter with various power
settings.
Frans"
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