Study on the Impact of Fuel Staging on Flame Structure and Thermoacoustic Oscillation in a Diesel Multi-Nozzle Combustor

Abstract Modern gas turbine combustors usually adopt multinozzle lean premixed and pre-evaporated (LPP) combustion technology to reduce emissions. However, the thermoacoustic oscillation of this design poses a significant threat to the safe operation of gas turbines. This paper conducts experiments and numerical calculation studies on a diesel multinozzle LPP combustor under atmospheric pressure with inlet temperature near 380 °C to investigate the influence of its fuel staging ratio (FSR) on the flame structure and thermoacoustic oscillation. In the experiment, the pressure fluctuation and the self-luminescence images of OH* were measured simultaneously. The flow field and flame structure were obtained by RANS calculation. The results show that for the diesel multinozzle LPP combustor, increasing the FSR can suppress the thermoacoustic oscillation of the combustor, and the oscillation amplitude is reduced by up to 60%. When the pilot stage is not ignited, the oscillation mode is double-period limit cycle oscillation, while after the pilot stage is ignited, the oscillation is single-period limit loop oscillation. The proper orthogonal decomposition mode shows that the main energy of the oscillation is concentrated in the global axial synchronous oscillation. The Rayleigh index and numerical calculation results indicate that the change of FSR alters the flame distribution in the combustor. The increase of FSR causes the flame to develop from the interference zone between the wall and the main stage to that between the main stage and the pilot stage. The change of flame structure is the main reason for the suppression of thermoacoustic oscillation.