FI Fuel Return Circuit

[Skippydiesel]

Well, yes,

But I was reluctant to suggest this- there is this deltaT thing!

In moderately warm summers a fuel cooler could perhaps be useful, but if you have something really hot like the more than 100F’s experienced a lot of places, the fuel cooler could turn into a fuel heater.

You would have to run a lot of tests before you have enough data to thrust its reliability and usefulness.

Naa - not going to happen. If your fuel has been heated, due to high pressurisation, it will likely be above ambient - can only be cooled down. You will not get the fuel temperature to rise above ambiently using a cooling device and lets face it if you are dedicated/crazy enough to be flying in 40C or above temperatures you will already have warm/hot fuel in your tank.

In the Australian summer (up to 47C in the shad last summer), I plan all my long flights to commence near first light (cool of the dawn). Stop for a wee break about 2 hrs later - late morning. May fly again, if cool enough but will not take off above 35C - wait until mid afternoon and fly for another 2-3 hrs.

[lakespookie]

Kai,

Do you have any pics of your installation i am curious as i plan on flying behind an EFI engine and have not really considered how i will solve the return line problem.

[Kai]

Hm…

You need to be cautious here: all efi systems are not created equal!

Mine is an Edge system- as long as the return fuel is dumped back into the tank above fuel level, there is no need for any oneway valve in the return line. How this is with other systems, I have no idea.

With the Edge system, fuel is returned from the pressure regulator in a ø3/8in (AN6) line to the top of the tank filler neck- there is perhaps a liquid column of 12in rise in there. All lines in the comlplete efi system are fire sleeved.

I go into the tank filler neck from the underside of the protective box. The connection is made by drilling a 3/8 hole through the top of the filler neck, through the box, and attaches to the fuel line. A pipe is angled 90 degs down into the tank (fuel), and has a collar/gasket silver brazed onto it just before the bend to prevent fuel leaks out of the tank. The line fitting I had to make myself, as I could not find a proper bulkhead fitting to my liking.

Works like a charm, perhaps a little crude and on the heavy side- but it has been sitting here since 2011.

[Kai]

Naa - not going to happen. If your fuel has been heated, due to high pressurisation, it will likely be above ambient - can only be cooled down. You will not get the fuel temperature to rise above ambiently using a cooling device and lets face it if you are dedicated/crazy enough to be flying in 40C or above temperatures you will already have warm/hot fuel in your tank.

In the Australian summer (up to 47C in the shad last summer), I plan all my long flights to commence near first light (cool of the dawn). Stop for a wee break about 2 hrs later - late morning. May fly again, if cool enough but will not take off above 35C - wait until mid afternoon and fly for another 2-3 hrs.

Yes- good point!

I am glad I don´t have to try out flying in temperatures like that myself. A couple of years back down south in Wagga Wagga I experienced 49C- the soles of my shoes were sticking to the asphalt!

Hot fuel in an efi system becomes a problem on the pump suction size. Any significant pressure drop here and fuel vapour will form in the line- rail fuel pressure will drop. The ecu will react as it always does when it detects an anomaly: more fuel! A lot of it! A typical pump will circulate something like 160 l/hr, so make sure the feed lines are of sufficient diameter, and have only long radius elbows.