The assessment of the stability characteristics of kerosene-fueled, lean direct injection flames is an important issue for the design of low-emission aircraft engine combustion systems. To achieve this task, acoustic network models are widely used. In the present work, this technique is applied to determine the stability behavior of a liquid-fueled, lean direct injection combustor. The required transfer matrices have been measured in an atmospheric combustion test rig. The burner transfer matrix as well as the upstream and downstream reflection coefficients are obtained by using the multi-microphone method. Since the measurement of flame transfer functions for liquid-fueled flames is a complex task, two techniques are applied and compared. First, the flame response to loudspeaker forcing is measured with the multi-microphone technique. Second, a technique based on the simultaneous acquisition of different chemiluminescence signals is applied. The chemiluminescence response at four different wavelengths (310 nm, 407 nm, 431 nm, and 515 nm), corresponding to the species OH*, CH*, CO2* and C2*, respectively, are measured using photomultiplier tubes. With a calibration measurement at different operating conditions, it is possible to calculate the instantaneous heat release rate. Flame transfer functions and matrices are measured in the test rig with the two techniques. Additionally, all acoustically measured transfer matrices and optically measured transfer functions are used to predict possible unstable modes in the test rig. The experimental results and the stability analysis employing the measured flame transfer functions are in good agreement and demonstrate validity of the method.

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