Taking the Pulse of Combustion

In the last 30 years, there has been significant regulatory pressure for gas turbine manufacturers and users to reduce nitrogen oxide (NOx) emissions. In response to these regulatory initiatives, gas turbine manufacturers initially turned to water and steam injections (Wet Low Emission technology) during the combustion process as the methodology for achieving the necessary reductions. However, as low emission requirements continue to increase, manufacturers have had to turn to alternative reduction methodologies, the two most popular of which have been lean-burn and dry low NOx designs.

While lean fuel technology leads to single digit NOx emissions, the low fuel-to-air ratio also leaves these turbines more prone to coupled acoustic/heat release pressure oscillations as a result of minor operational instabilities. While the magnitude of these oscillations may be low, even small fluctuations less than 1 psi (0.069 bar) can cause structural vibrations that result in high cycle fatigue in metal parts downstream of the combustors such as nozzles, baskets, transition pieces, and blades.

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