i am working on GE 9e turbine dln1. can you please
what is exactly combustion dynamics in Gas turbine? can someone please explain me about it. as it is very important for me to understand the combustion philosophy.
Because there is 1) so much air versus fuel in the primary combustion zone in Premix Steady-State combustion mode, and, 2) there is such a small diffusion flame in the secondary combustion zone when in Premix Steady-State Combustion mode the pressure in the combustors can fluctuate--so much so that the combustion liners and transition pieces vibrate causing 1) increased wear on the parts, and, 2) the diffusion flame can propagate back into the primary combustion zone and/or the diffusion flame in the secondary combustion zone can be extinguished.
When operating in Premix Steady-State combustion mode the stability of operation (the absence of diffusion flame in the Primary combustion zone and the presence of diffusion flame in the secondary combustion zone) is very low--so oscillating pressure in the combustors can cause both increased mechanical wear on parts and cause unstable combustion and primary zone reigniton or loss of secondary diffusion flame.
GE draws an imaginary four-sided box (diamond; parralellogram) to describe the small area that represents stable combustion and low emissions (the area inside the box). DLN combustion is a pretty precise science.
Standing near a heavy duty gas turbine one can feel vibrations on the walkway and even in the ground. Those are normal pressure oscillations of combustion, which is not an entirely smooth process. Many people mistakenly believe the normal vibration of combustion is the result of shaft rotation. When standing near a turbine when it trips while loaded, even though the turbine shaft is still rotating the vibrations on the walkway and the ground virtually disappear as the unit coasts down from rated speed. That's because there's no fuel combusting.
And when a unit has DLN combustors, the pressure oscillations--can have serious implications for mechanical wear and combustion stability, and also, emissions.
Hope this helps!