rocketbob

rocketbob

Well Known Member
Can anyone point me out to the calculation for a given orifice size, what the fuel flow would be thru that orifice at a given pressure?

Ex.:

0.040" orifice, fuel at 3psi...what would the fuel flow be in GPH thru the orifice?
 
Bob,
I do know it was higher than I expected :eek:

A design I tried back in the begining as a fuel purge was to use a Van's restricted orifice constantly flowing fuel back to the tank via a return line. At just 4 psi that .030 hole (I think that's what it is) was flowing about 4-5 gph which was way more than my FF gauge could factor out so I ditched that design for that reason. I was quite surprised by the high fuel flow reading from such a small orifice.
 
I built the engine monitor I'm using in my rocket, so I do have the luxury of making the proper calculations to correct for the return line. I haven't settled on the size of the vapor return orifice but want to do it empirically. Rather than introducing a second EI cube hampster wheel, since pressure is known at the orfice it should be simple to calculate the flow at a given point in time.

I had seen the Orifice plate wiki entry but came to a quick conclusion that a calculation with a constant might be close enough. :)
 
Fuel flow

Bob,

Not scientific but tried and tested in my RV-8 with constant fuel return line.
#68 drill size at 30 lb pressure returns 9 GPH.
I used only one flow meter, installed just before entering the fuel controler.
The return line was tee'd off the engine driven fuel pump and does not affect fuel flow readings.
Not sure if this helps.
 
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