Dilution effects of CO2, Ar, N2 and He microjets on the combustion dynamic and emission characteristics of unsteady premixed flame

Abstract

To evaluate the control effectiveness of jet in cross flow on thermoacoustic instability of lean premixed flame, the dilution effects of CO2, Ar, N2 and He microjets on the dynamic and emission characteristics of premixed flame were experimentally studied in a laboratory-scale gas turbine combustor. Three factors of jet in cross flow were investigated—Injection flow rate, inner diameter of injector and injecting medium. CO2 performs better than other three gas medium in both combustion instability and NOx emissions control. Results denote that an optimal sound pressure damping ratio can be reached as 80.3% with injection flow rate of 3.5 L/min. And the damping ratio of heat release rate can be as high as 75%. NOx emissions concentration can be reduced to 15.9 ppm. The NOx emission damping ratio can be as high as 35.4%. Flame becomes dispersed and flat under microjets with high flow rate. The flame length is reduced to 54 mm when both the sound pressure amplitude and the NOx emission concentration are all at the bottom, Flame length after passive control only equals to 40% of the original. The results confirmed that suppression effectiveness of combustion instability is associated with the relative molecular masses of the jet in cross flow. However, the detailed triggering mechanism and the coupling of combustion instability with jet in cross flow still needs exploration. This study demonstrated that the passive control with microjets has the potential to be applied to combustion systems under combustion instability.