Herbert Boks wrote:

Dear fellow rrrrrrrotarians,

I want to ask for your thoughts/comments on the following.

I am building a Cozy MK IV and will install a 3rd gen. 13B. I've spent

some

time trying to understand fuel systems for EFI engines, noting that with

2

main tanks, the need for return lines adds a lot of complexity to the
system. I'm thinking about electrically controlled fuel valves on the
firewall (2 valves and 1 solenoid or motor per tank). Since with EFI we
must have electricity to run the engine in the first place, the

inability

to switch tanks in case of a power outage is not really an issue. In my
opinion an EFI demands a backup electrical system in any case. I see

great

advantages in placing the fuel valves on the firewall:
- shorter fuel lines
- no need for a sump tank
- less fuel heat, because it runs back to the main tanks
- no fuel lines inside the cockpit

There is the added risk of not being able to shut the valves when power
fails due to engine fire. I'm not sure how to address that yet.

My understanding of EFI is rather superficial, so I may be overlooking
things. I may also be overlooking other side effects. What do you think?

Herbert

Building PH-CZY (Ch.10)
Cozy MK IV #0769

herbert@datamax.nl
The Netherlands

Ed Anderson wrote:

Hi Herbert,

    I faced the same challenge when putting a 2nd gen six port 13B in an
RV-6A.  I did not want to have to mess with return fuel lines and switches.
So I built a small rectangular (1 1/2x3x8 inches) aluminum tank out of
aluminum rectangular tubing by welding plates on both ends and AN- fittings
for fuel.  The high pressure EFI pumps (two) each have there own feed line
from the bottom of this tank.  The tanks is located low on the fire wall and
is fed from two wing tanks by a single selector which switches between them.

  The two EFI pumps pull fuel from this header tank for the injectors and
returns unused fuel via a pressure regulator to the top of this same header
tank.  Any fuel actually injected creates a partial vacuum in the header
tank which pulls the fuel from the wing tanks to replace the fuel used.
This partial vacuum is substantial and will pull fuel up at least 24".  I
also have a boost pump in the low pressure portion of the fuel line to the
header tank for take off and landing insurance.

It has worked fine for me.  The only two possible problems might be having
the header tank get too hot which could potentially create a vapor lock
(although turning on the boost pump should eliminate this problem should it
occur and of course placing the tank in some location other than the engine
compartment) and if you should have a leak in the tank then the partial
vacuum would suck air instead of fuel.  However pressure testing the welding
should remove that problem.

  I have 75 hours flying with this arrangement which requires no return
lines nor any multi port switches.

Best Regards

Ed Anderson
Matthews NC

 
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