F-16.net

Newbie Joined: Mar 17, 2005 Posts: 1 Status: Offline

I'm a former 16 CC, now a mechanical engineering student. I'm wondering what percentage of the total work out of the engine is used to turn the compressor.

F-16.net Sponsor

If you have had Thermodynamics, get a Temperature-Entropy diagram of an engine and compare the compressor temperature delta (out (t2) minus in (t1)) to the temperature delta from the combustor exit (t3)to the nozzle exit (t4). A rough approximation of the compressor work fraction is (t2-t1)/(t3-t4). This is simplistic, but maybe useful to you. The fraction will be different for different throttle settings, speeds, and altitudes.

With your practical experience and and ME degree, you will have a good career ahead of you.

Last edited by VarkVet on May 31, 2008 - 02:56 AM; edited 1 time in total

kicoombs wrote:

I'm a former 16 CC, now a mechanical engineering student. I'm wondering what percentage of the total work out of the engine is used to turn the compressor.

I’m still a crew chief and think that’s a stupid question.

Work = Force. Distance

Since the compressor is part of the engine producing the work (connected by shaft to heat section of motor where energy/power is produced)… the question should be. How much work is used to turn the gearbox or ADG. Or

How much work is lost supplying bleed air to the ancillaries.

So I thik the formula is 1 X 1 = 1

Make sense?

Edit: I’m sorry, I guess it takes some work for N2 to power up N1 Doh

Newbie Joined: Nov 07, 2007 Posts: 14 Status: Offline

Wow, last post was interesting. I think what you are getting at is how much horsepower is required to turn the N1 and N2 compressors. This gets complicated fast and is was beyond me. The HPC is driven by the HPT that part is simple but it gets weird since the HPC is also being assisted by the Inlet Fan (three stages) and would require horsepower from the LPT in this process. On a straight turboshaft I have always been told that they are about 50 percent efficient so if the engine made 40,000 horsepower the turbine would actually have to extract 80,000 hp from the expanding gases to produce it's thrust rating and stay self-sustaining (drive the compressor). On a duel spool engine the numbers would change at all power settings. Someone smart will chime in soon and save the day.

Yes the turbines "extract" horsepower to turn the compressors and everything attached to the gearbox and ADG.

Quote:

Turbine - Noun - Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder.

So when a jet engine operates the turbine extracts horsepower to turn the compressors (N1 & N2), the engine gearbox/accessories, and the airframe gearbox/accessories. The power remaining in the exhaust stream is what provides thrust.

Until a jet engine reaches "self-sustaining RPM" the turbines are not extracting enough power to keep the compressor turning. The engine will die back out. Above that RPM the engine starts to develop thrust that can be used to propel the aircraft.

In a turbojet/turbofan engine the ratio wouldn't be near 2X, as it has a much different cycle than a turboshaft.

Figure the F100-PW-229 is using 254 pounds of air per second and compressing it 32:1, while turning fuel/oil pumps and a DC generator, AND the AC/DC generator of the aircraft and it's hydraulic pumps.

I don't even know where to start doing math to figure that one out. But rest assured the N1/N2 compressors and all those gears/accessories take A LOT of horsepower to turn.

NOTE - The JFS makes 210HP just to start a GE F110 or PW F100. At MIL power it must be a large factor of that as it does not even power them all the way to IDLE thrust.

F-16.net

Forum: F-16 Design & Construction

Back work ratio of F110-GE-100 Engine