Emar,

Previous ignitors used by GE in their heavy duty gas turbines were either retractable or stationary. This was because the tips of the ignitors would be damaged if they were in or near the flame (conventional flame or DLN "flame"). So, the early ignitors (called "spark plugs") were retractable and as pressure in the combustor increased the tip of the ignitor would be pushed out of the combustor. Later high-energy ignitors, used with most DLN (Dry Low NOx) combustors were stationary with the tips placed just at the very inside edge of the combustion liner to keep them out of the intense heat of combustion to make them last longer.

This "torch" ignitor would seem to be another way of igniting the fuel in the combustor by "blowing" a small stream of some kind of flammable gas into the combustor when the ignition phase of start-up is happening. It's still and ignition source--a source of heat, and the tip of the tube doesn't have to be inside the combustion chamber because the flame can be blown into the combustor. (Note that a "spark plug" is STILL used to ignite the flammable gas being used to ignite the fuel in the combustor...!)

Personally, I've always disliked the term "spark plug" used for ignitors of gas turbines. It implies that, as in an automobile engine, the spark plug is going to constantly periodically spark to keep the fuel in the gas turbine combustor burning--and that's simple NOT true in a gas turbine where the fuel flow is constant, not periodic as in a piston-driven internal combustion engine. The "spark plug" ignitors of gas turbines are only necessary to establish flame, and because the flow of fuel into the combustor is continuous, as long as there is sufficient air and fuel, the flame will burn continuously WITHOUT the need for a spark to keep it burning. In a typical GE-design heavy duty gas turbine the ignitors ("spark plugs") are only energized for about 60 seconds or so to help establish flame and to ensure that during that 60 second period the flame doesn't flicker or go out because of low fuel flow or impurities in the fuel. If flame is detected after than 60 second period the ignitors ("spark plugs") are de-energized; their job of establishing flame is complete.

It's also not desirable to have an ignition source in the combustor at all times during operation because if for some reason (problems with fuel flow or excessive air causing flame to be momentarily lost) the concentration of fuel inside the combustor can increase and if re-ignited it can cause a big/large explosion inside the combustor--which is NOT desirable for many reasons.

So, the ignitors of a gas turbine are usually only energized ("working") for a brief time during the ignition sequence and are then turned off.

 

Emar,

Previous ignitors used by GE in their heavy duty gas turbines were either retractable or stationary. This was because the tips of the ignitors would be damaged if they were in or near the flame (conventional flame or DLN "flame"). So, the early ignitors (called "spark plugs") were retractable and as pressure in the combustor increased the tip of the ignitor would be pushed out of the combustor. Later high-energy ignitors, used with most DLN (Dry Low NOx) combustors were stationary with the tips placed just at the very inside edge of the combustion liner to keep them out of the intense heat of combustion to make them last longer.

This "torch" ignitor would seem to be another way of igniting the fuel in the combustor by "blowing" a small stream of some kind of flammable gas into the combustor when the ignition phase of start-up is happening. It's still and ignition source--a source of heat, and the tip of the tube doesn't have to be inside the combustion chamber because the flame can be blown into the combustor. (Note that a "spark plug" is STILL used to ignite the flammable gas being used to ignite the fuel in the combustor...!)

Personally, I've always disliked the term "spark plug" used for ignitors of gas turbines. It implies that, as in an automobile engine, the spark plug is going to constantly periodically spark to keep the fuel in the gas turbine combustor burning--and that's simple NOT true in a gas turbine where the fuel flow is constant, not periodic as in a piston-driven internal combustion engine. The "spark plug" ignitors of gas turbines are only necessary to establish flame, and because the flow of fuel into the combustor is continuous, as long as there is sufficient air and fuel, the flame will burn continuously WITHOUT the need for a spark to keep it burning. In a typical GE-design heavy duty gas turbine the ignitors ("spark plugs") are only energized for about 60 seconds or so to help establish flame and to ensure that during that 60 second period the flame doesn't flicker or go out because of low fuel flow or impurities in the fuel. If flame is detected after than 60 second period the ignitors ("spark plugs") are de-energized; their job of establishing flame is complete.

It's also not desirable to have an ignition source in the combustor at all times during operation because if for some reason (problems with fuel flow or excessive air causing flame to be momentarily lost) the concentration of fuel inside the combustor can increase and if re-ignited it can cause a big/large explosion inside the combustor--which is NOT desirable for many reasons.

So, the ignitors of a gas turbine are usually only energized ("working") for a brief time during the ignition sequence and are then turned off.

Dear WTF?

I respect your considerate reply and your time. You articulated precisely what I would have guessed on my own, and after reading your reply, I came to the same conclusion. In the future, keep responding in the same way.
Regards
EMAR