Frans,
Let's take this example:
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. The Rotax Install Manual provides the
pressure curve of the fuel pumps. According this curve, the pump is able
to supply 120 liters/hour at zero bar. This is what you get when the
engine is not running. However, if you need 0,92 bars (relative
pressure), the out put flow has to be restricted to 96 liters /hour.
I must admit that the 96 vs 120 liters per hour is not a so big
difference, but the fact is that the fuel flow through the filters is
reduced when you increase the power.
Remi
[quote:0fd8912cfa="air.guerner at orange.fr"]
The higher the fuel flow, the higher the pressure loss across the
filter. On the
914, when the engine is not running, there is of course no boost
pressure and
therefore the fully open fuel pressure regulator is sending all the fuel
back
to the tank. This is when the fuel flow across the filters is maximum.
However,
when the engine is running at max boost, more fuel pressure is required
and
the regulator sends a lot less fuel back to the tank. Therefore, at high
power,
the flow through the filters is greatly reduced and bubbles in the
filters
is less likely and possibly totally eliminated.
-----[/quote:0fd8912cfa]
Sorry, I don't get it. As far as I understand the fuel pump delivers a
constant
rate to the engine, and all the fuel not used by the engine is going
back to
the tank. At high power, still the same is being pumped to the engine,
but as
the engine is consuming more, less is being sent back to the tank. The
fuel filters
are however not in the return line, but in the line TO the engine, and
they
see a constant flow, independant of the actual fuel consumption of the
engine.
Correct me if I'm wrong.
Frans
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