What kind of car do you have Phil? I think it is the latest trend.
I specifically asked Jim Mederer if the ECU controlled the pump pressure
on the RX8 and he said no. He could be wrong as there is no real way
of knowing unless you hook a scope to the pump wire feeding electrical
power to the pump. On the other hand Jim has considerable experience with
the RX8 engine on his dyno. He tells me the pressure regulator is built into
the pump.

In theory all you really need is a electronic pulse width controlled pump
for a constant dribble fuel injection system. No electronic injectors.
No pressure regulator. Probably work fine for an aircraft engine.
Less parts to fail.

Paul Lamar

A Ford Focus. I didn't know there was any difference, until I turbocharged my car. There's a controller next to the pump that adjusts the pulse width. I still have injectors though. I'm missing something...how do you eliminate the injectors?

   Phil Williamson

Ah So another Ford product.

There are two things you don't need in an aircraft system. Smog controls and good idle.
There are hundreds of thousands of airplane engines out there with a constant
mechanical dribble fuel injection system. More fuel speed up the pump. Less fuel slow
the pump. Based on RPM, manifold pressure and intake temp. The last two could
be manual (pilot) feed back from the EGT's.

Paul Lamar

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

So as the engine RPM comes up, the engine would smooth out? I take it this would mean no moving parts ('cept the fuel pump). If that's right, pretty damn simple...and reliable, I assume. :)

Phil Williamson

 
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