Calculating fuel flow through an orifice

[Johansson]

I am getting more and more frustrated at the moment, I have searched "everywhere" after the calculations for liquid flow with no success at all.

I know the fuel pressure, density of the fuel and area of the injector hole and I want to know the flow through it, the fuel lines etc are frictionless for the sake of simplicity.

All I can find are page after page on calculating flow in water lines and so on, but no formula where I can select a feed pressure.

//Anders

[Viv]

Hi Anders

Here http://www.spiraxsarco.com/resources/st ... ustion.asp

Look under oil burners

Hope that helps if not let me know as I have some other links i could probably find for you

Viv

[Johansson]

Thanks, but I don´t know if that link straightened any question marks for me.

Varying the pressure of the fuel oil immediately before the orifice (nozzle) controls the flowrate of fuel from the burner.

However, the relationship between pressure (P) and flow (F) has a square root characteristic, √P∝F, or knowing the flowrate P∝F2.

For example if:
F2 = 0.5 F1
P2 = (0.5)2 P1
P2 = 0.25 P1

If the fuel flowrate is reduced to 50%, the energy for atomisation is reduced to 25%.

Which other links do you have that could be of interest?

[Viv]

Hi Anders

Here's one that has helped me out in the past

http://www.martindalecenter.com/Calculators.html

I will see what others I can find

Viv

[Johansson]

Great link, it contained more calculators than I though was possible.

The strange thing is that I haven´t found a single one that calculates flow from pressure and flow area.

If someone knows the calculations I would prefer them instead of a calculator since I want to understand how it is done. It is quite strange that it is easier to find an "Interplanetary Dust" calculator than one that tells me how much liquid a 4mm hole with 3 bar feed pressure flows...

[Mark]

I bought a couple of the PJ series nozzles in stainless steel. This supplier has size, flow rate, and PSI conversions for product selection. Perhaps knowing the specific gravity of your fuel and some of these other factors you can extrapolate a formula. ha
http://services.bete.com/scripts/cgiip. ... r?capplic=
http://services.bete.com/scripts/cgiip. ... pplic=99.9
I guess you would need a formula for how long the diameter of your orifice is too and the transition tubing, transition angle, viscosity, what kind of spray pattern you want, and on and on. Maybe some of this stuff will provide a few crumbs of information if you look it over.

Flow Rate (GPM) = K ⎯√⎯P⎯S⎯I (see bottom of the chart)
http://www.bete.com/pdfs/BETE_PJ.pdf

Metric chart.
http://www.bete.com/pdfs/BETE_PJ-metric.pdf

[WebPilot]

 Hi Anders. This is a complicated calculation but this may help.

 The general relation between flow rate and pressure requirement is expressed by

     ΔP = R·S·Q²
where

• ΔP is the pressure loss
•  R is a measure of the total resistance
•  S is the specific gravity, weight or density
•  Q is the volume flow rate

NOTE: A consistent set of units needs to be utilized.

 Usually charts are consulted where one knows the type of orifice, diameter, and pressure drop and one merely reads the flow rate.

[Johansson]

Thanks guys, what seemed like a relatively simple calculation turned out to be quite advanced. The flow chart for the fog nozzle might give some indication since one with a 1mm orifice flows 0.9L/min at 2 bar, but I guess that it will be easiest to flow test one of the injectors and draw up a chart myself.