Acoustic and Optical Investigations of the Flame Dynamics of Rich and Lean Kerosene Flames in the Primary Zone of an Air-Staged Combustion Test-Rig

In this study, the thermoacoustic behavior of nonpremixed kerosene flames from rich to lean combustion conditions is investigated. Flame-transfer-functions (FTF) measured purely acoustically are compared with results based on flame chemiluminescence. $OH*, CH*, C2*$⁠, and $CO2*$ were selected as potential measures for representing steady and fluctuating heat release when burning nonpremixed kerosene. In addition, their ability for the quantification of equivalence ratio fluctuations will be highlighted. The measurements were performed in the primary zone of an atmospheric rich-quench-lean (RQL) combustion test-rig. The new experimental approach allows a characterization of the primary zone independent of the secondary zone. Rich and lean operating points were analyzed by fueling an aero-engine prototype injector with and without acoustic excitation. To improve the quality of the acoustic wavefield reconstruction a thermocouple correction method was implemented. The flame dynamics determined with the multimicrophone method (MMM) exhibit a frequency and equivalence ratio depending effect of rich combustion conditions. The results for the steady behavior of the chosen radicals by altering equivalence ratio and thermal power indicate proportionality of the chemiluminescence to thermal power. Furthermore, the $CH*/C2*$ ratio is found to be a promising indicator for the global equivalence ratio in the combustion chamber. The flame-transfer-functions based on chemiluminescence show a good qualitative agreement with the multimicrophone method. Based on the experimental findings a calibration curve for the different radicals to obtain quantitatively correct flame-transfer-functions from chemiluminescence is presented.