If the return fuel enters the top of the tank (under a little pressure) and
expands
while falling to the level of fuel in the tank, would that not cool and therefor
not evaporate?
This also does away with any need for a second fuel valve and it's weight and
complexity
in an emergency.
Kevin
On Apr 26, 2012, at 5:20 PM, Frans Veldman <frans@privatepilots.nl> wrote:
>
> On 04/26/2012 08:11 PM, Raimo Toivio wrote:
>> I have two guestions:
>> 1) would it be wise to have a 2nd fuel valve in a fuel return line also
>> to get an ability to close it or one-way-valve in the case of emergency?
>
> I have a one-way valve in the return line for exactly this reason.
>
>> 2) why this line is connected to the fuel outlet which locates in the
>> bottom of the tank? Why not to the upper corner of the (reserve side) tank?
>
> This fuel might be quite warm. Imagine when your tank is half empty. The
> hot fuel will have to make a free fall before it reaches the pool of
> fuel, and it will probably evaporate before it even gets there. No big
> deal as the tank will vent it away, but you might find that your fuel
> consumption is a tad high. It is better that the return fuel immediately
> enters the cold fuel in the tank, so even when some fuel has already
> evaporated and produced bubbles, it will condensate back into useful
> fuel when it contacts the cold fuel. So the bottom of the tank is the
> correct position, and so it is depicted in the build manual anyway.
>
>> So, I have noticed no problems to use my engine with return line which
>> is off-line. There are also many Rotax aplications with no plans for
>> return lines in use. What is a main reason we should have a fuel return
>> line? To get more fresh cool fuel or what?
>
> I can't say this for the 912, but for the 914 it is to avoid vapor lock,
> so yes, to get cold fuel all the time and to avoid keeping it longer
> than necessarily in the hot engine compartment.
>
> Frans
>
>
>
>
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