Comparison of flame transfer functions measured with locally resolved full-field-vibrometry and OH*-chemiluminescence

Information about heat release can be used to discuss the flame dynamics and stability behavior of turbulent combustion systems. The most common experimental approach to determine heat release fluctuations is the recording of OH*-chemiluminescence. Since there is a strong dependence of chemiluminescence on strain rate and mixture gradients, spatial information must be judged with care. As already shown in previous work, Laser Interferometric Vibrometry (LIV) directly detects the line-of-sight values of density fluctuations along the laser beam axis. Neglecting friction, losses of thermal radiation and conduction and assuming only small fluctuations of pressure in the reaction zone, heat release fluctuations can be calculated directly from density fluctuations. With available LIV techniques only pointwise scanning was feasible, resulting in time-consuming traversing of the flame to cover the whole flame field. A new camera-based full-field-LIV-system, developed at Technische Universität Dresden, is capable to simultaneously determine spatial information of heat release within the whole field with only one measurement, lasting a few minutes. This leads to a dramatical reduction of measurement time and furthermore reduces experimental efforts. Since the system is able to measure the complete flame at once, it is also possible to get information about the transient behavior of the combustion process. In this work the full-field-LIV system was applied for the first time on a swirl stabilized, lean and premixed methane flame. The results of this newly developed technique were checked against those of a commercially available single-beam LIV-system. Finally, the flame transfer function (FTF) was recorded with full-field-LIV and OH*-chemiluminescence and compared against each other.