贫燃预混旋流火焰的模态转换燃烧不稳定特性分析

In order to study the combustion instability characteristics of combustion chamber, the combustion instability of mode switching on lean-premixed swirl flame was investigated by experiments. The experiments were about methane-air lean-premixed swirling flame. The dynamic pressure of flame field was measured by dynamic pressure sensor, and the chemiluminescence of CH* was captured by photomultiplier tube. High speed images with acquisition frequency of 4kHz were recorded to catch flame structure. The experimental results show that when the equivalent ratio of flame increases to 0.72, the combustion has mode switching. During the switching, the pulsating main frequency changes from 264Hz to 187Hz, and significant increase in amplitude. A proper orthogonal decomposition (POD) procedure is used to extract the spatial distributions of modes. The time distribution characteristics of flow can be obtained by Fast Fourier Transform (FFT) analysis of modal coefficients. The results show that the average flame is horn-shaped before mode switching and "M" after that. The modal switching is closely related to vortex shedding mode.