Inlet temperature impact on combustion instability in a centrally staged combustor

The present study investigates the effects of inlet temperature on combustion instability in a lean premixed pre-vaporized (LPP) centrally staged combustor. Experiments are conducted with varying injection heights to examine how inlet temperature influences spray field, combustion instability, and flame dynamics. As the inlet temperature rises from 400 K to 700 K, significant improvements in fuel evaporation are observed, leading to enhanced fuel-air mixing. Therefore, it is observed that the flame distributes along shear layers and within recirculation zones at low inlet temperature, while only along shear layers at high inlet temperature. Besides, the inlet temperature also plays a crucial role in influencing combustion instability, but this effect varies depending on the injection heights. In general, an increase in inlet temperature leads to a reduction in oscillation amplitude. However, in the two cases with low injection heights, the amplitude exhibits a fluctuating decline. Furthermore, elevated inlet temperatures could induce a transition in oscillation modes, with a significant change occurring around 500 K. Dynamic Mode Decomposition results present the coherent structure of the two modes. Coupling analysis of heat release fluctuations and pressure fluctuations indicates that the phase difference between them markedly decreases as the inlet temperature rises. Finally, the local Rayleigh index integration reveals distinct driving regions of thermoacoustic coupling under the two modes. Through the above analysis, our study elucidates the effects of inlet temperature on spray characteristics, flame structure, and, particularly, combustion instability in a centrally staged combustor, which may offer guidance for the design of aero-engine combustors.