<snip>

Shoot, I'm still lost!  : )  I guess I don't understand the "dribble"
part. Time to search the internet.

Phil Williamson

The constant dribble term is kind of a joke among aircraft people.
It refers to the super simple nature of the typical AC mechanical
fuel injection system.

In a four cycle engine the intake valve is open only 1/4  of
the time. With most automotive electronic injection systems
the fuel injector is open only during the time the intake valve is
open. That is called timed injection.

With a constant dribble system fuel is dribbled into the
intake runner ALL of the time. At high power and high RPM the engine
can hardly tell the difference. All it cares about is getting enough
fuel. A simple electric fuel pump can supply the fuel to injectors
fed by a pipe spider with small holes that are open all of the time.
Speed up the pump more fuel. Slow it down less fuel. High pressure
and tiny injector holes atomize the fuel.


Paul Lamar

Paul,

Why not use K-jet injectors with the above set up. Then you don't have the
dribble problem and flooding when you shut the engine off. I have often
thought this would simplify the fuel injection system greatly. You could
even use an engine driven pump like Kinsler, but that gets prohibitively
expensive in a hurry. Kinsler/Hilborn injection is not cheap. It is also a
pain to adjust with different sizes of restrictors etc.

If you use electronic control with the speed density method and a pulse
width control on the fuel pump it makes things nice and simple, plus
relatively inexpensive. Two pumps for safety, one line to the fuel manifold,
and a couple check valves.You can use a switch like Tracy for cold
enrichment, and a pot for fine tuning the mixture in cruise with the EGT. It
is still possible to totalize the fuel if you use a calibrated positive
displacement pump. SIMPLE!!! Just requires some programming, testing and
assembly. Only one gotcha I can think of, what does the motor curve look
like? Is it going to be linear? You might have to adjust for the pump motor
curve, and who knows if it will work well at the lower speed range of Idle.
How consistent are the pump curves? Testing would tell the story.

Monty

I agree. Probably cheaper, more reliable and less current draw in the bargain.
Less current draw and the airplane will fly further with a dead alternator.
How much are those K-jet injectors?

You could also use staged PWM fuel pumps to get a wider dynamic range.

Paul Lamar
 
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