Swirler effects on combustion instabilities analyzed with measured FDFs, injector impedances and damping rates

Comparison of Flame Describing Functions Measured in Single and Multiple Injector Configurations

“…1 (c)). In a previous study carried out with the same type of injectors [30], the spray flames considered here did not show any significant spatial inhomogeneities of equivalence ratio during flow modulation in the frequency range of interest. This is because a large part of the spray is directed towards the conical wall of the terminal plate (see Fig.…”

“…This configuration is shown in Fig. 1(b) and described in detail in [30]. The inner diameter of the flame tube is 69 mm, which corresponds to the area of a single sector of the annular chamber.…”

Do flame describing functions suitably represent combustion dynamics under self-sustained oscillations?

“…An estimate of heat release rate (HRR) integrated over the flame volume is obtained by measuring the OH * chemiluminescence (with a 10 nm filter centered at 308 nm) from the flame using a photomultiplier tube. The validity of using OH * chemiluminescence as HRR indicator has been systematically validated in the current configuration in [63]. The spray flame considered in this study is found to operate in a quasipremixed fashion due to the recessed position of the atomizer in the injector.…”

“…The equivalence ratio fluctuations therefore remain low at the injector outlet compared to the velocity fluctuations and there is no significant spatial stratification in the flame zone. The readers are referred to [63] for the detailed analysis. Additionally a PI-MAX intensified CCD camera from Princeton Instruments is used to obtain the flame images.…”

“…This defines a condition for determining the reference position for velocity measurements; one must choose a location at the exit of the injector where the relative velocity fluctuation coincides with the relative volumetric flow rate fluctuation. The measurements and the subsequent determination of this location are detailed in [63]. For the swirler 716, the reference position for the measurement of velocity is located at a distance of r = 4 mm from the center of the injector and at a height of h = 2.5 mm from the backplane.…”