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Engine downstream burning


Steve1300
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If an engine, in Low Speed Ground Idle, has the fire burning in the turbine area, how does that happen? It will start with low start TIT (750) and run in LSGI, but there is a fire in the turbine and the blades glow.

The fuel nozzles were flow checked and they were good. If the engine is sped up to NGI, the fire goes out and when shifted down again, the fire stays out.

I have never seen that before, and I don\'t really have an answer as to how it is happening. The only theory I can come up with is that, for some reason, the fire is not starting in one or more burner cans, so the fuel from that nozzle is making it back to the inlet guide vanes where it is igniting.

Anyone have an idea or theory to share?

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Never seen it before, but a quick thought would be that the flame transfer tube/s to the other cans are damaged/missing; or, that there is a burnt/cracked can. Also may have only one exiter firing.

Have you done a performance run?

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All of the information I have about the situations encountered with only one ignitor firing tell me to expect slower starts. I have nothing to indicate - if the flame propogates as designed - I should have downstream burning in the turbine.

By the way, both ignitors are firing.

A cracked can? If I have a cracked can, is it possible that the split is large enough to allow air to prevent the fuel stream from being ignited within the can?

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Depending on where the crack is, it may intitially tend to quench the flame instead of shape it. My thoughts however tend to the flame transfer tube. Some tubes have an insert joining the cans, while others are clamped without the insert. Maybe the clamp has broken, letting in air preventing initial ignition ..... only way to really find out is to pull the turbine off :( :(

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My initial assessment was that I have a can not burning. The fuel is hitting the thermocouples and cooling them off - giving me the cooler start temp.

We shipped the engine out to Miami Lakes to get checked. I hope they come up with something to go on. We don\'t pull our own hot sections here, so I have to depend on others to evaluate the problem. It should be on the test cell for run today.

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It sounds like you have a torching fuel nozzle. If your fuel nozzles are the duplex type, once the secondary nozzle kicks in, the spray pattern will change and voila! the problem goes away. It feels like a coking problem from here.

I know you have no way to do a spread check on individual thermocouples, but I would pull and them look.

I think you have may also a failed T/C, remember a failed T/C will drop the average across (what is it 16?) the harness assembly giving you a lower temperature.

But, is this temp issue only during start?If so, a torching nozzle could direct the flame pattern within the combustion chamber away from the T/C also giving you a lower temp.

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WE have a fuel nozzle tester which checks the patterns versus the spray pressures. All of them were good. The repair station where we sent the engine said that our actual flow quantities were slightly high on a couple of them, but the amount was only about 2%. I don\'t think that would cause the degree of troublw we were having.

I am trying to imagine what would give us unburnt fuel all the way back to the turbine and burn up the second stage. I\'m pretty sure that the fire is not taking place in the can, since the fuel is making it back into the turbine blades before burning.

When I do get some information as to the cause, I will remember to post it here for everyone. That is - if they ever actually give me the cause to report.

Thanks for the input, guys.

:)

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The engine overhaul facility has not reported finding any problem with the cans, but the second stage vanes were destroyed. I\'m afraid that we will never know what happened. Since our nozzle tester showed a good pattern, we are out of ideas. Hopefully, it will do well on their test cell and we\'ll get it back soon.

I really would have liked to have something to blame this problem on..... Drat!

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2nd stage vanes is very bizarre. Were they burned up in just one area? And the 1st stage turbine nozzle guide vanes were good!?! Those are the hottest vanes in the engine! Plus if you had my theoretical torching nozzle, a portion the first stage vanes would be toast.

(This makes me wonder if the vane classification was messed up and you had too much area. But you should have had high RPM and low torque when the engine ran.)

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Actually Lockheed says that downstream burning will cause most of the damage to the second stage of the turbine, and wonderful enough, the second stage is the only one you cant boreoscope.

The reason you wont see the turbine inlet stators burned is because the fuel is burning beyond them instead of lighting off in the cans and having the correct airflow around them to form the flame.

I used to have a source document but when I was medically grounded I pretty much dumped all my Lockheed manuals, books, handouts and everything, to maintain my sanity.

It may have been in a sup for the MC-130P -1 since we were having all kinds of inflight torching and they told us its normal!!!!! Wonder if they have started throwing turbines yet.

Maybe someone else here has something.

Good luck

Dan

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Our start times were still around 45 seconds. The second stage vanes were burned out in only one section as well, so that would be where the fuel fire was starting. A turbine like that will not necessarily give enough torque difference that folks would notice it right away. We also do not know how long those turbine fires were going on, but as I orignally said, it happened only in LSGI.

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