Calculating Fuel Pressure

[mjm333]

mjm333 (Mechanical) Feb 14, 2008
Can anyone please let me know how I can calculate the fuel pressure before a diesel generator fuel pump from a gravity feed daily service tank.

The tank measures 2450mm wide x 1520 long x 1520 high and is sat on a stand 600 mm high.

The steel pipe out of the bottom outlet of the tank is 12 mm OD and runs for about 9 metres to the generator, with 5 bends in the pipe run.

Thanks for any help given

 

[Artisi]

The pressure at the pump is the height between the fuel level in the tank and the inlet point to your fuel pump which must be corrected for the S.G. of the fuel.

What height is the fuel pump inlet in relation to the tank?

 

[Bribyk]

If you know the properties of the fuel and the flowrate, your pressure at the pump can be solved using Bernoulli's equation with friction losses.

 

[Artisi]

"Bribyk (Mechanical) 14 Feb 08 17:46
If you know the properties of the fuel and the flowrate, your pressure at the pump can be solved using Bernoulli's equation with friction losses. "

I think that using Bernoulli's formula is a bit over the top for this particular installation since there is probably less than 2m of static head available with a full day tank and maybe 1 metre as the tank nears low level, and assuming for the sake of it the flow rate of fuel is 1 litre/sec,the friction loss might be a couple of mm. - at best you could assume a pressure of 1.5m and at worst less than 1m at the pump.

I think the O/P is confusing tank volume with pressure.

 

[mjm333]

Hi Artisi/Bribyk, first off thanks for replying. OK, the fuel tank and generator are on the same level, and the fuel pump is approximatly 400 mm above ground level. Fuel is standard gas oil so dependent on temprature (tank/set both outside)the SG will be about 0.83.

I dont know the flowrate of the fuel with the set running i'm afarid.

The problem I have is that the set has a base tank which the fuel pump draws from. The tank is now not complient with pollution regs here in the uk. I would like to supply the set with fuel direct from the bulk tank which is complient. The engine manufacturer has specified that maximum fuel flow to injection pump is 54 US gph/202 lts/hr.

So I need to know what would be the maximum fuel flow from the bulk tank,with the tank full,and what pressure can i expect at the pump.

 

[Artisi]

Must be a big engine with a fuel demand of 200 l/hr or 0.9 USgpm.

Lets assume that the I.D. of your fuel line is the same as 3/8" steel pipe and from water friction tables the head loss for 1 USgpm is approx 4.3 ft per 100 ft.

You have approx 30 ft of pipe + 5 bends maybe equals to 40 ft total pipe run, this equals 40/100 x 4.3 /3.28 = 0.5 m head loss thru the pipe at 200 l/hr.

Provided you maintain approx 0.5 metre fuel level in the day tank you won't have any problem.

If unsure, increase the pipe line to 1/2" I.D., the head loss becomes approx 0.2 m.

Trust this helps

 

[Bribyk]

Correct me if I'm wrong but, isn't a diesel injection pump a positive displacement piston-type pump? Your flowrate will be: # of pump strokes per minute * displacement of pump (gal/stroke) = gpm.