Engine Fuel Pressure Options

[sprint3]

Was wondering if anyone knew what the fuelpressure is when injected into the burners in a jet.

[rjb4000]

Was wondering if anyone knew what the fuelpressure is when injected into the burners in a jet.

Fuel pressure? How is this pressure measured? Where is this pressure measured? What units? What temperature? What atmosphere? What type of jet? Who makes the jet? How much thrust? What power setting?

[velocityflier16]

RJB's right. It depends on the type of jet, the altitude of the jet, the atmospheric conditions, and power setting. I would recommend doing some research on google.

[Aspiring Boeing ...]

Or on the engine manufacturers website if you can find it in the website or pdf doc.

The fuel pressure could also depend on whether the EPR limiter is set and at which setting (which is kind of tied into what velocity said about the power setting).

Regards,
Chris

[Piltdown Man]

Forgive me, but what is an EPR limiter and how is it set?

Here are the numbers for an Allison 250C20. "In normal operations, fuel from the tank is delivered to the EDP by electric boost pumps at a pressure of about 15 to 20 pounds per square inch (psi). The EDP then increases the fuel pressure for delivery to the fuel nozzle in the combustion chamber. A minimum operating pressure of 30 psi is required to open the metering valve in the nozzle to initiate a primary flow condition for starting, a minimum pressure of 150 psi is required to open the valve to a secondary flow position for idle and flight power, and the maximum pressure required at full throttle is about 600 psi."

But I'm sure every engine will be slightly different.

PM

[velocityflier16]

PMD, EPR is the Engine Pressure Ratio. The engine pressure ratio (EPR) is defined to be the total pressure ratio across the engine. Here is an awesome diagram that I found just for you. Hope this helps!

http://www.grc.nasa.gov/WWW/K-12/airplane/epr.html

[rjb4000]

PMD, EPR is the Engine Pressure Ratio. The engine pressure ratio (EPR) is defined to be the total pressure ratio across the engine. Here is an awesome diagram that I found just for you. Hope this helps!

http://www.grc.nasa.gov/WWW/K-12/airplane/epr.html

I think the power in the aircraft that PM flies are set by EPR, and he was just commenting on the previous poster's lack of a real contribution to the topic.

Also, setting a power limit really has nothing to do with fuel pressure.

[Piltdown Man]

Thanks rjb, you are right. And as if by magic!

PM

[velocityflier16]

Is that in the F100?

[Piltdown Man]

70 actually, but identical in layout - just 20 or so fewer seats behind you.

PM

[Saltman66]

Good question. Don't know the answer but I'm guessing it would'nt have to be excessive since once the fuel reaches the exhaust gases, it's going to burn regardless of the pressure used to get it there.

[rjb4000]

it's going to burn regardless of the pressure used to get it there.

You sure about that?

[Ranger]

it's going to burn regardless of the pressure used to get it there.

I don't think that I'd bet on that. The fuel has to reach the cans and ingitor plugs in the proper FORM as well. I'm not a mechanic so I'm not good at using the proper terms. But, the fuel doesn't reach the burner cans in a liquid state. Prior to reaching the cans it is mixed with air and atomizes into a vapor. It's the vapor that actuall reaches the cans. In the cans the ignitors ignite the fuel/air mixture and that is what makes the fire burn and the engine produce thrust.

Fluffdoc, help us out here! (Good luck with the cards!)

[Piltdown Man]

I've just got out my "Boys Book of Jet Engines". Eventually, I find the following nuggets:

The form of the fuel is critical to its burning. At low pressures, a "bubble" is satisfactory with a "tulip" at intermediate pressures. At high pressures a finely atomised spray is required. This is because the combustion chamber is so short, you have to burn the fuel quickly. To assist with atomisation, Ranger is bang on when he suggests that fuel is mixed with air but this book suggests that this occurs right at the very tip of the nozzle using bleed air. This air also prevents carbon form forming on the orifice.

As for the pressures: "A single fuel pump can deliver fuel at the rate of 100 to 2,000 gallons (real English ones) per hour at a maximum pressure of about 2,000 psi. To drive this pump, as much as 60 HP may be required".

There we have it. I'm more edjermacted.

PM

Boys Book of Jet Engines = The Jet Engine, Rolls Royce. ISBN 0 902121 04 9