George,
In automotive fuel systems, Cost and Emission control are the
driving forces in design.
The recirculating system seems the best for aircraft application.
The regulator maintains a uniform pressure differential between the
rail and the plenum (intake manifold) because the regulator pressure
is also controlled by port vacuum. The resultant is a constant
pressure differential across the injector. This means that the
mixture is only controlled by the pulse width and pressure change is
not a factor.
A safety system used in automotive fuel systems is worth considering
in aircraft.
1. When the ignition is turned to run, the fuel pump is
activated for two seconds which is sufficient to bring the system to
operating pressure. Some fuel would have been returned to the fuel
tank by the heating and expansion of the fuel during the last engine
shutdown. V-8’s can rise to 245 degrees F 45 minutes after shutdown.
2. The pump relay is activated by a signal from the ignition
pulse indicating that the engine is either cranking or running. A
switch from the oil pressure sender can also be incorporated as a
secondary source of power to the fuel pump relay. Either one will
independently allow the engine to start and run. An engine
stoppage will cause both to turn off the pump.
3. Ford uses an inertia fuel shut off switch witch will
disengage the pump in the event of an impact. I understand that
Ford has had some problems with their switch.
Remember, a large amount of fuel can be pumped into the engine
compartment in the event of a line failure/crash.
Joel
Joel,
Thanks for that info!
One innovation from discussions, is the leak-down regulator by-pass, which I
think is a great idea in releasing undue pressure in the fuel rail/
injectors.
George (down under)
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