The annual operation data of an F-class gas turbine generator set revealed that the duration of the startup process accounts for about 8.5% of the whole operation process. The three combustion models of a DLN2.0+ combustor demonstrated higher NOx emissions than the premixed mode under normal load during the startup process. In order to evaluate the scale of NOx emissions at this stage, numerical simulation was carried out for the startup process to discern the NOx emission pattern. Typical simulation conditions for each season were established to calculate the total annual NOx emissions at the initial stage based on operating data. On this basis, the characteristics of NOx emissions influenced by changes in the atmospheric environment were studied in depth. The results of this study provide referential data for evaluating the pollution characteristics and combustion adjustment of a ground gas turbine during startup.

In this paper, the effect of the swirler scheme on combustion instability is studied. Through the proper orthogonal decomposition (POD) of flame images, Abel inverse transform and other methods, the influence of swirl intensity on the characteristic frequency of combustion instability was emphatically studied. Based on the low order thermoacoustic network (LOTAN) of the combustor, the flame transfer function (FTF) under different swirl schemes was obtained by the optimization method. The experimental results show that the stable combustion equivalence ratio boundary of the system decreases monotonously with the decrease in swirl intensity, while the characteristic frequency of unstable combustion is not monotonous with the swirl intensity (the oscillating frequency of swirler A with the largest swirl intensity is approximately 319 Hz, swirler B is approximately 280 Hz, swirler C with the smallest swirl intensity is approximately 290 Hz). The optimization results of FTF can easily introduce this non monotonic phenomenon. The swirl intensity mainly affects the hysteresis time of the system (the lag time of swirlers A, B and C are 5.98 ms, 6.82 ms and 6.20 ms, respectively), which is mainly caused by affecting the flame structure and convection velocity. At the same time, the FTF obtained by optimization reflects the same trend with the experimental results, and there is no significant difference in value, which proves the rationality of the optimization method. This work emphasizes the importance of FTF for combustion instability analysis.

In order to study the characteristics of pressure fluctuation during unstable combustion, experimental studies had been conducted on the mechanism model of the swirl combustor and the industrial swirl combustor. The signal of dynamic pressure, heat release rate, and the high-speed flame image in the two combustors were synchronously collected by using dynamic pressure sensors, a photoelectric sensor, and a high-speed camera under normal temperature and pressure. After empirical mode decomposition of the dynamic pressure signal, several intrinsic mode functions were obtained. It was found that the pressure pulsation energy is concentrated in the first three order intrinsic mode function. Through fast Fourier transform spectrum calculation, it was found that the first three order intrinsic mode function pulsation can characterize the changes of heat release rate and air flow pulsation under cold state and flame instability. It showed that the decomposition of the dynamic pressure in the combustor by this method can obtain the main physical processes in its connotation, and provide data processing methods for the induction mechanism of oscillating combustion and combustion diagnosis in an industrial combustor test.