REFLECTOR: Fuel Flow Sensor

[Al Gietzen]

Kurt;

 

Thanks for the clarification, and my concern is relieved.  I over reacted
based on too little information, and should know by now that you think
things through carefully.  I assumed it was the more typical automotive
electronic FI (such as I have) with a fuel rail feeding injectors at the
intake manifold, and much more line in the engine compartment.  

 

 We've had considerable discussion of vapor lock issue on the rotary engine
list, where most use mogas (rotary actually performs better on mogas), and
there have been problems.  Your system should be fine.  And I guess I'd
agree that if there is nowhere downstream from the pump to put the flow
meter, it wouldn't be a huge factor to put it upstream.  What is the "drive"
mechanism in the flow meter?

 

Al

 

Subject: Re: REFLECTOR: Fuel Flow Sensor

 

Al, and all....

 

I am most concerned about vapor locking as well. Perhaps I did not describe
the fuel system well enough. 

 

The fuel does not flow THRU the fuel rail and back in to the system. This is
an Airflow Performance Fuel Injection unit. The pumps are also from Airflow
Performance and are rotary-type pumps (Not the solenoid type pumps that can
heat the fuel all by themselves).

 I am also planning on using Avgas.

 

When I talked to Airflow Performance Fuel Injection, he specifically asked
me if I had any fuel lines, pumps, etc., in the engine bay. I said NO. The
only thing in the bay is the 6" fuel line that runs to the servo, and the
injector lines themselves. I specifically talked to them about the return
line. I initially had planned to return it to the sump, and asked them about
the return flow and pressure. When they finished questioning me and
determined that the lines were not flowing thru the engine bay, they
informed me to just "T" it back into the pump inlet line.

 

I have a friend with an RV-6 that has the same pump and recirculation
plumbing that I am working on. This is the way the people at Airflow
Performance said to plumb it. So far, after 3 years of flying it works fine.
(although their flowmeter is downstream of the pumps).

 

The pumps in my setup do have to "suck" the fuel through the flowmeter, then
the screen filter that sits under the gear leg, then through the pumps (that
are mounted on the bottom of the gear hoop bay, between the firewall and
gear bulkhead). Then they push the fuel up to the top and to the engine.

 

The "recirculation line (probably better named a bleed off line) is
completely inside the gear bay area. 

The pumps, flowmeter and plumbing are even or below the top of my sump tank.
The filter just above that. So, everything in the system except the actual
engine feed line is well below the "bottom of the main tanks" level.  In
addition, I do have a screen-type racing filter in each main tank-to sump
tank 

supply line. 

 

I appreciate the concern and information on this issue. Considering the way
my system is plumbed, and that fuel does not recirculate through the engine
bay, I had hoped that I  alleviated most of the areas for a vapor lock to
take place. Of course, one can never be too safe when it comes to this
issue, it usually shows up at the worst time. 

 

Keep up the good info and critiques, 

 

Kurt 

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