Forum: Technology

Orangeburst wrote:

When you mentioned IGV's, I assume these are Inlet guide vanes? So there are internal moving parts to the inlet?

On the F100 they are called CIVV (Compressor Inlet Variable Vanes) for the 1st stage N1 (Low Rotor or Fan) blades, they limit the amount of air ingested by the engine. (GE calls them IGVs, but same concept) The first 3 stages are variable in the N2 (High Rotor or Core) compressor, they are RCVV (Rear Compressor Variable Vanes) and vary the amount of compression. The CIVV and RCVV are scheduled by the engine control system for the optimal compressor performance curve, while keeping it from touching the stall margin curve.

Orangeburst wrote:

If I understand correctly, aviation engines are 7-stage on the compression side.

The F100 is a 13 stage compressor, 3 N1 and 10 N2, driven by a 2 stage N2 turbine (High Pressure) and 2 stage N1 turbine (Low Pressure). F110s use a 3/9 compressor and 1/2 turbine; F119s use 3/6 compressor with 1/1 turbine; the F135 a 3/6 driven by a 1/2, and the F136 (if produced) 3/5 by 1/3.

As you can see, each engine has a unique configuration of compressor and turbine stages.

Orangeburst wrote:

What kind of discharge pressures are we talking?

F100-PW-229 = 32.4/1
F110-GE-129 = 30.7/1
F119-PW-100 = "OPR in the 35/1 'class'"
F135-PW-100/400 /-600 = 28/1 or 29/1 during "powered lift" of -600
F136-GE-??? = "OPR 35+"

The thing to remember is the massive amounts of air being pressurized though; using the 'public' figures of the F100 and F110; The F100 uses 254lbs/sec at MIL while the F110 uses 270lbs/sec. Then pressurizing it over 30/1 into the combustion chamber! Shocked

We getting off topic here?
Then again, when talking 'inlets' to an 'engine guy', we're talking engine inlet or station 2; the compressor inlet. (First engine readings are PS2, & TT2) We have inlets even when the motors aren't installed!

I'll let you guys do the math on flow vs volume vs pressure... Doh

TEG

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Thank you TEG..Looks like the efficiency of these motors has really improved over the years with less number of stages and that has to be tremendous in reduced maintenance, although each upgraded stage works harder and hotter I assume.

Did a little crunching but I do not know the inlet pressure referenced in the 30:1 pressure ratio. I would assume it to be represented about SL 14.7 psia. Looks like about 190,000+ ICFM @ 450 PSIG after the final stage. Man that is some serious air flow. No doubt these motors are technical marvels and it is simply amazing how much work can be done in such a small package.

Just as a comparison, an air compressor allows for max. 5 ICFM/HP @ 125 psig, which would require a 40,000 HP electric motor. Throw in another 300+ psi and this is off the charts. The only one I know that large is actually at AEDC AFB (your cousins) in Tullahoma, TN. It is 60,000HP unit and is used in some deep aeronautical science and analysis. The only reason I brought up air compressors is my factory craftsmen used to be a part of the aviation engine union before they closed it and moved overseas. I was always curious about the similarities. All in all the only things that look similar are the science, they have rotors (impellers)and they are compressors Doh

Appreciate it TEG

I have a question on egnine tech. Why is it that the US is pushing OPR up while EJ has lowered it to 25?

Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

shingen wrote:

I have a question on egnine tech. Why is it that the US is pushing OPR up while EJ has lowered it to 25?

OPR is a rule of thumb for overall engine efficiency. The higher the ratio, the more power you're extracting from a given amount of fuel. TEG can speak to this much better, but the trade offs in higher OPR include increased weight, higher cost due to more exotic materials and/or shortened part lifespans.

Guysmiley wrote:

OPR is a rule of thumb for overall engine efficiency. The higher the ratio, the more power you're extracting from a given amount of fuel. TEG can speak to this much better, but the trade offs in higher OPR include increased weight, higher cost due to more exotic materials and/or shortened part lifespans.

What GS says... I'll elaborate a bit.. Cheers

More pressure is better, just like higher compression in a gasoline or diesel engine. (Why do you think they use turbos or super-chargers?)

More pressure is tighter tolerances in blades/seals/stages/cases, etc. It is thicker cases and supports to deal with burst pressure and weight.

More pressure is hotter air into the combustion chamber and into the turbine. (Also later stages of compression) Advanced metallurgy, coatings, machining, and cooling are needed to off-set high CC or Turbine Inlet Temperatures (TIT) Hotter means more power, but also accelerated wear/tear/corrosion of hot components.

More pressure is harder to control surge/stall. Requires more advanced controls. Every ounce of energy must be squeezed from the engine, less room for error or 'wear'. Engines age faster and faster as they accumulate hours and wear. (Snowballing as they age)

Look at the F135 engine; PW actually lowered the OPR from PW-229/F119 levels. It is even below that of the latest USAF F100 or F110 engines. Somewhere between the previous generation's PW-220 and GE-100 OPRs. The name of the game here is low life-cycle costs, reduced part count, and reliability. (IE cheaper is better for the JSF program) On the other hand, IMO, PW could be keeping the OPR lower today to give a growth in thrust for future models. GE on the other hand is already saying the F136 has an OPR of "35+", which is pushing edge tech.

Keep 'em flyin' Thumb

TEG

shingen wrote:

I have a question on egnine tech. Why is it that the US is pushing OPR up while EJ has lowered it to 25?

To summarize what TEG said, it's a very deliberate emphasis on operating costs. Pretty much the same reason for lack of oomph in the RB199 in the Tornado. It's a European thing, you could say.

TEG, I've heard nothing about the F135 engine being less fuel efficient than the F119 or F100. Where did you read this?

lampshade111 wrote:

TEG, I've heard nothing about the F135 engine being less fuel efficient than the F119 or F100. Where did you read this?

The topic was OPR, who said anything about 'less fuel efficient'

The F135 has a publicly stated OPR of 29/1
The PW-229 has a publicaly stated OPR of 32/1
The F119 has publicaly stated OPR "in the 35/1 class"

One has to remember, a higher OPR is a more efficient burn of the air available. If one has two engines, with the same airflow, similar design, similar thrust, etc, the higher OPR will be a lower SFC, BUT...

The F135 has a much larger fan and BPR than the PW-229 or F119. So while the larger fan is moving more air, it does so with less compression than the fan of the F119 to which it shares a core.

While the OPR of the F135 is lower than the OPR of the F119, the F135 has a larger airflow. So while the F135 is moving say 25% more air with 10% less efficiency it makes more power and yields a lower SFC. Lower SFC is more efficient.

This is because the F135 has a higher fan (lower pressure) thrust component of the exhaust total. This is also why the F135 engine is not considered to be a 'super-cruise' engine. It has a higher thrust lapse due to having lower specific thrust than it's F119 father. (That has a very low BPR like that of it's PW-229 grandfather...)

You guys have to remember there are MANY variables to gas-turbine aviation engines. OPR, SFC, TIT, Air-flow, BPR, EPR, etc... (just to name a few) The F135 is larger than the F119, the F119 is larger than the F100. (wider but shorter)..... You can't just say the OPR is 2 or 3 less so it will burn more fuel!?!

Follow? Shrug

TEG

Last edited by Orangeburst on Aug 13, 2010 - 04:45 AM; edited 1 time in total

I may be way off base in my simplistic world, but the higher air compression allows for a more efficient lean fuel/air mixture, which increases combustible thrust and lowers SFC, but increases heat in the compression stages.

This may be dumb, but does the high air flow of the F135 (and other lower OPR motors) have excess air that is not burned and is part of the thrust component..ie are all motors compressed air jets (non consumed air) to some extent? Laughing

I know there are bypasses (like in my world), but not sure if they are pre or post compression (or at some stage of compression).

TEG needs compensation Smile

.

Bypass air by definition doesn't participate in combustion unless the afterburner is engaged. Some of the oxygen passing through the core is consumed but not all. Look up "stoichiometric engine".

Pictures are worth a thousand words right? Here is 2K worth. Perhaps a Moderator could spit this side-topic into a new thread?

TEG

That_Engine_Guy wrote:

Perhaps a Moderator could spit this side-topic into a new thread?

Agree and done.

Forum: Technology

Engine Technology