Fuel injection return fuel line.

[innovator]

I would like opinions of where the return fuel line from my injection set up should go, either the fuel tank or collector pot.

I have a 35 litre fuel tank with a 3 litre internal collector. There are 2 low pressure pumps feeding the high pressure unit in the collector.

If I put the return into the collector I will be able to maximise fuel usage but will I encounter problems with foul fuel. What would these problems be?

How is it best to feed the return fuel into the collector? At the top, bottom, against the side, down a coil or spiral of pipe?

The vehicle is for road, hillclimb and track day use.

Thank you

John

 

[patdaly]

For my money, I send it back to the fuel tank. The logic is that the fuel is heated during the pumping process, and if you return it back to the main tank, the hot fuel gets mixed back into a larger volume, thus slightly limiting the rise in fuel temperature.

 

[TheBlacksmith]

I'll second patdaly's comment. You risk eventual vapor lock if you short circuit the fuel loop.

Blacksmith

 

[innovator]

Thank you for the advice, the fuel return will go into the tank.

Can any body expand on the problems of foul fuel in an injection system?

What happens to the fuel (apart from getting warm) and why does it damage fuel lines?

John

 

[schmidtj86]

I guess I'd have to disagree with the pumping process heating the fuel. The main heating comes from the engine bay temperatures itself. Let's suppose compressing a liquid raised its temperature, then expanding it through the regulator would reduce it right back, but this doesn't happen, unless it changes states, or you count the electric pump's friction and windings as enough to heat the fuel.
One argument for not pumping it back to the tank is that it would eventually heat all of the fuel, and the tank would be forced to vent the vapors. Not a strong argument, at least if you aren't concerned with emissions.
Another argument, that since you are in hill climbing and stuff is that if the low pressure pumps are both uncovered, then, the reservoir would be drained sooner without the return fed to it.
I would recommend using two identical high pressure pumps in the system - one feeding the swirl pot, one feeding the fuel rail. And run the return to the reservoir swirl pot. And run a return line to the tank from the swirl pot.

Jeremy
Injection Logic

 

[ivymike]

The electrical pumps that I've played with the most (wiper pumps, fish tank pumps) rely on heat transfer to the pumped fluid for cooling. Even the small pumps get very hot, very quickly, if the fluid is recirculated. A fuel system has a bit more surface area for the fluid to lose excess heat than do the systems I've experimented with, but I wouldn't discount the heat transfer from the pump out of hand.

 

[innovator]

My collector is actually inside my tank. There are 2 low pressure pumps feeding this and when the collector is full it will over flow into the main body of the tank. The high pressure pump is mounted in the collector.

I intend to insulate the hoses and fuel rail in the engine bay.

My hose supplier (Aeroquip distributor) says the act of injection causes oxidisation in the fuel. I can not understand how this happens because it is not the injected fuel that is recirculated.

I have also discovered that the only hose recommended for in tank use is teflon.

John

 

[kimbo1]

I disagree with using two high pressure pumps for fear of starving of fuel - that is why you have a 3 litre collection pot for in the first place, and you could probably do the whole race on that!
I used to run the return fuel to the collector pot but reading the above points re heating I probably won't anymore

 

[fuelstat]

To Innovator RE Foul Fuel and fuel line damage: May I suggest you get a copy of SAE J1645. The fuel line damage if your not using E-10 or other oxgenated fuel comes from a small physics problem called Charge Separation/Static electricity generated in the flowing fuel. Both Ford and Ricardo have blown pin holes in fuel lines in testing in their labs.