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Retractable spark plugs in Frame 5 GE gas turbines
  | Posted by Raza Haider  on 2 June, 2012 - 10:07 am |
Please explain the phenomena how retractable spark plugs come out of combustion chambers at 50% speed of gas turbine
|
May seem to simple, but the answer is air pressure.
| Posted by CSA  on 3 June, 2012 - 11:47 am |
> May seem to simple, but the answer is air pressure.
To expand on CuriousOne's "simple" explanation, the spark plugs used on non-DLN combustors have a spring inside them that causes the plug tip to be inserted into the combustion liner when the unit is shutting down and axial compressor discharge pressure is low. Since the fuel nozzle is in the center of the combustion liner the spark plug tip needs to be close to the fuel nozzle during firing when the turbine is being started.
During acceleration after flame has been established axial compressor discharge pressure increases as speed increases. Increasing CPD overcomes the tension of the spring and pushes the plug tip out of the combustion liner to prevent the tip from being burned by the hot combustion gases/flame ball.
The Speedtronic does not have any control over when the spark plug is inserted or pushed out, nor does it have any indication of the position of the spark plug tip.
The sliding surfaces of the spark plugs can become worn and/or galled causing them to stick--usually in the out position. But that rarely happens to both spark plugs at the same time, which is one of the reasons there are two spark plugs.
When the unit is shut down, one can manually pull the plug out to check the friction of the sliding surfaces. DO NOT let go of the plug and let it slam into the combustion liner! There is a ceramic insulator in the plug which can be broken. (Actually, this is a favorite pastime of many mechanics when they learn the plug is spring-loaded.... Of course, since it has a wire connected to it it's meant to be damaged by mechanics during a maintenance outage. And, of course, they didn't know they could damage the spark plug with their little fun and games with their new-found toy.)
To expand on CuriousOne's "simple" explanation, the spark plugs used on non-DLN combustors have a spring inside them that causes the plug tip to be inserted into the combustion liner when the unit is shutting down and axial compressor discharge pressure is low. Since the fuel nozzle is in the center of the combustion liner the spark plug tip needs to be close to the fuel nozzle during firing when the turbine is being started.
During acceleration after flame has been established axial compressor discharge pressure increases as speed increases. Increasing CPD overcomes the tension of the spring and pushes the plug tip out of the combustion liner to prevent the tip from being burned by the hot combustion gases/flame ball.
The Speedtronic does not have any control over when the spark plug is inserted or pushed out, nor does it have any indication of the position of the spark plug tip.
The sliding surfaces of the spark plugs can become worn and/or galled causing them to stick--usually in the out position. But that rarely happens to both spark plugs at the same time, which is one of the reasons there are two spark plugs.
When the unit is shut down, one can manually pull the plug out to check the friction of the sliding surfaces. DO NOT let go of the plug and let it slam into the combustion liner! There is a ceramic insulator in the plug which can be broken. (Actually, this is a favorite pastime of many mechanics when they learn the plug is spring-loaded.... Of course, since it has a wire connected to it it's meant to be damaged by mechanics during a maintenance outage. And, of course, they didn't know they could damage the spark plug with their little fun and games with their new-found toy.)
| Posted by CSA on 3 June, 2012 - 11:35 pm |
Just to clarify one point, the fuel nozzle "sprays" fuel into the center of the combustion liner. The spark plugs needs to be closer to the center of the combustion liner during firing when starting.
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