Quote:
Originally Posted by setasai
... true but I'm unsure of the point of your post
The end result is fuel cooler "closed loop" vs return to the tank as the "cooler" is essentially the same thing since the tank (where all fuel ultimately goes back to regardless of system) is vented to atmosphere. Pressure should be EXACTLY the same inside vs outside and the difference in temperature is going to be negligible.
I mean really? If you're concerned about hot climates, get a white tank and insulate it with a layer of foam because if there were problems with temperature, we'd have FI bikes breaking down and exploding all over the place.  |
The problem is that the fuel pump adds a non-negligible amount of heat to the fuel on a return-type system. Pumping any liquid adds heat to it, significant amounts depending on the principle used. One effect of this can be that hot fuel vaporizes in the fuel rail, which means the injectors will be spraying vapor rather than liquid fuel. The result is a mixture that is too far off to fire properly, if at all. Another possible issue is fuel density. If the fuel temperature varies enough the density change can cause the amount of actual fuel sprayed (since fuel is sprayed by volume and not by mass) to vary enough to alter the mixture.
In a true returnless system (in the automotive technology that I'm familiar with, anyway) the fuel pump is cycled on and off such that it only delivers the amount of fuel needed by the injectors. Any other system is a return system, whether the fuel returns to the tank or returns to the fuel pump inlet. In return systems heat can be an issue if the circuit is too small to allow adequate heat rejection. On a car with fuel lines that are many feet long there's enough area to reject lots of heat. On a bike with fuel lines measured in inches that's not necessarily the case.
Oh, and the fuel tank will get hot, that pump heat has to go somewhere on a return system that runs back to the tank.