[SS_Dave]

I have a buddy that told me that jet engines didn't have fuel pumps.
After I got done laughing, he said that they had them, but they are only used
to start the engine. After that the compressor provided the pressure to move the fuel. I am still laughing. Is there anybody here that is a bonified jet engine mechanic, engineer, or point me to some proof positive that the pumps run all the time? I got a 100 dollar bet going here, but I need absolute proof.

Also, the same buddy says that on a fuel oil furnace, the ignitor runs all the time. I say it shuts off after the flame is detected by the flame sensor. Can anybody verify that? I got 50 bucks on this one.
Yes, beer was involved. :beers:



thanks

 

[BillsCamino]

I think the guy that supplies the correct answer needs to get half...

 

[quikss]

As for the jet engine, you are both right. It depends on which type of jet engine you are talking about. If its a pulsejet, it doesn't need a fuelpump at all if you are using the aspiration method.

Want proof:http://www.aardvark.co.nz/pjet/starting.shtml

aspiration
This is when the fuel is drawn into the engine through an atomizer by the air which enters through the intake. This has the advantage that it is very simple and requires no fuel pump or other ancilliary equipment.

Jeff

 

[cobra2411]

But on a typical commercial jet there is a pump... Many actually, pumps in the tanks to move fuel, then one on the engine to feed the engine.

Don't know about the igniter on the furnace. On a plane the igniters are used to start, and take off, but are off most of the flight...

David

BTW I have my FAA A&P license...

 

[SS_Dave]

As for the jet engine, you are both right. It depends on which type of jet engine you are talking about. If its a pulsejet, it doesn't need a fuelpump at all if you are using the aspiration method.

Want proof:http://www.aardvark.co.nz/pjet/starting.shtml

aspiration
This is when the fuel is drawn into the engine through an atomizer by the air which enters through the intake. This has the advantage that it is very simple and requires no fuel pump or other ancilliary equipment.

Jeff

Jeff, we were talking about modern passenger jet engines.
I did tell him about the ramjet or pulse jet not needing a pump.
V-II rockets from hitler were pulse jets.

OK, Bill, If I collect I'll split the dough.

I have a feeling I may never see the cash though.

 

[quikss]

Ah, I see. I figured you meant jet engines in general. But as far as I know, all modern jet planes use a fuel pump.

Now the real question is, does a jet engined plane need a fuel pump if it is on a conveyor belt?

Jeff

 

[SS_Dave]

Now the real question is, does a jet engined plane need a fuel pump if it is on a conveyor belt?

Jeff

Oh No, not that again!
No conveyors involved here. OK?


I know the engines have pumps, the bet is, do they run all the time?
I say yes.

I thought there were some airline mechanics on this site?

 

[Motorhead62]

OK Guys,

Here is the deal on Fighter Jet Engines:

1) Inside the internal fuel tanks there are electrical transfer pumps that supply fuel from the tanks to the fuel supply manifolds, BIG fuel lines.
(External tanks are force fed to the internal tanks via pneumatic bleed air)

2) At the ends of the fuel supply manifolds are electric fuel boost pumps that supply pressurized fuel to the engine supply manifolds.

3) After the engine supply manifolds are engine driven high pressure fuel pumps that supply fuel to the fuel controls.

4) The fuel controls meter fuel to the combustion manifolds.

5) The combustion manifolds supply fuel to the injectors/spray bars inside the engine.

I hope that is enough clarification!

Go Air Force!!! :thumbsup:

 

[SleeperBBC]

Ill shoot at the fuel furnace. Im assuming a waste oil furnace works the same. We had one at a shop and it didnt even have an ignitor. You used paper kindling to ignite the oil and switch on a small piston pump that would drip the waste oil onto a pedistal where the flame was controlled. So if it did have an ignitor, I would assume it would not say on all of the time on that style, but I would bet there are different styles that the ignitor stays on.

 

[Randy Mosier]

Oh, there are pumps allright. And a fuel controller which controls the fuel to the nozzles in the combustion chamber according to the demands of the engine. I've changed plenty of them. As was mentioned earlier, there are boost pumps in the tanks and a pump on the engine to supply fuel to the nozzles under high pressure, which is regulated by the fuel controller. Most turbine engines intergrate the engine pump and fuel controller into one unit.

He may be thinking of the ignitors. The ignitors are used to start the engine and are then shut off after the engines are up to operating speed. The principle is the same a cutting torch. The fuel is ignited at the nozzles and and the flame is maintained by the pressure of the fuel coming through the nozzles in much the same way the flame is maintained on a common cutting torch. However, under certain conditions, the ignitors are left on as a precaution; when flying through heavy rain or snow or sleet, and during takeoff.

 

[fatrat70]

On the modern aircraft ie... Boeing 737,757 etc... there is a minimum of 2 depending on model and designation. One being a low pressure engine driven pump, and a high pressure engine driven pump. All with at least 1 electrical low pressure pump. I look at them at least 5 days a week. Continental line maintenance mechanic.

 

[BillsCamino]

You guys are killing me here...I was holding out for some $$$!

 

[BarefootDave]

Randy & FatRat are right on. The jets I fly use a low pressure pump to provide fuel to the engine for start and to supply the high pressure pump once the engine has started. The engines can suction feed up to 25,000 ft but require what we call "motive flow" produced by a jet pump (no moving parts, just bernoulli's principle) fuel above that altitude. The low pressure electric pump can be used in place of "motive flow" belowe 25,000 ft but will not provide enough pressure to the high pressure pump to keep the engine running above that. I've been a pilot since 1982 and an A&P mechanic since 1985.

 

[79943]

you have received some good info here. i work for a company that has made fuel nozzles, spray bars and manifolds for a number of years. not real familiar with what goes on from the fuel control back but know a little bit about the rest of the fuel delivery system. in most cases the fuel is fed into the nozzles under very closely controlled pressure. as was stated the pressue is from pumps and the fuel controller. the pressure determines the amount of fuel being delivered not just from the normal ratio of pressure to volume but also because the pressure strokes a valve in the nozzle (sometimes) that opens under pressure and controls the fuel flow curve. the angle of the spray and atomization are very critical to a good clean burning charge. spraybars on the other hand are only used on military jets and they dump fuel into the afterburner. fuel distribution is still critical on those but as a general rule atomization is not as critical. you should see the nozzles that are used in power generation type gas turbine engines. i could literally take one of the aircraft nozzles and drop it into one of the inlets on one of those suckers. a typical aircraft fuel nozzle would easily fit in your hand, some would fit in the palm of your hand. some power gen nozzles on the other hand are close to 5 feet long.

 

[Hal_396]

The jets I work on work like this: Fuel goes through the fuel flow transmitter and on to the fuel control unit by electrical fuel pumps in the tanks. They will run on gravity/suction feed also. I know because I started one the other day and forgot to turn on the electrical boost pumps and the engine still ran just fine. So technically, your friend is right.

As you may recall, its one of these pumps that they suspect caused the demise of TWA's flt 800.

 

[SS_Dave]

The jets I work on work like this: Fuel goes through the fuel flow transmitter and on to the fuel control unit by electrical fuel pumps in the tanks. They will run on gravity/suction feed also. I know because I started one the other day and forgot to turn on the electrical boost pumps and the engine still ran just fine. So technically, your friend is right.

As you may recall, its one of these pumps that they suspect caused the demise of TWA's flt 800.

AW KRAP!

Hey Bill, can I borrow some money?

Did the engine spool up ok?
It sounds like there are at least a couple configurations.
Can I say that we are both right?

Edit:
Hal, I gotta go with Pat and Randy and the rest of the crowd.
I knew I could count on you guys.
I'll print this thread out and show him.

thanks! :beers:

 

[Hal_396]

Oops, I stand corrected. My training manual states:

The fuel pump consists of a centrifugal boost stage and a gear drive stage. Normal flow capacity is 14,500 pounds per hour at a pump discharge pressure of 100psi. (Jet fuel weighs approx 6.7 lbs per gallon). A pressure regulating valve maintains a maximum pressure increase across the main stage of 950 psi. A full flow by-passing type micronic fuel filter is integral with the fuel pump.

So you are correct!!!!!!!!

BTW, A jet engine (JT8D) normally burns around 3000 to 3500 lbs per hour at cruise. Thats like 475 to 500 gallons per hour!!!!!!!!!!!!!!

 

[docs427]

as for the oil burner the ignitor is on all the time

 

[SS_Dave]

Alright!

Thanks Hal and everyone else too!
Looks like I would have to share with about 6 guys.
That would be something like 16 bucks apiece.
Hey, its a twelve pack.



docs427: are you sure?


Why would they need to keep igniting a ball of fire?
Doesn't make sense.

 

[SS_Dave]

Hey, looky what I found.

http://www.enginecontrols.goodrich.com/small/products/pumps.shtml

aint the internet great!


I searched for about a half hour before I posted this, but didn't
find anything. go figure.