Pressure Influence on the Flame Transfer Function of a Premixed Swirling Flame

Abstract

In order to assess the stability of gas turbine combustors measured flame transfer functions are frequently used in thermoacoustic network models. Although many combustion systems operate at high pressure, the measurement of flame transfer functions was essentially limited to atmospheric conditions in the past. With the test rig employed in the study presented in the paper transfer function measurements were made for a wide range of combustor pressures. The results show similarities of the amplitude response in the entire pressure range investigated. However, the increase of the pressure leads to a considerable amplitude gain at higher frequencies. In the low frequency regime the phase is also independent of pressure, whereas above this region the pressure increase results in a considerably smaller phase lag. These observations are particularly important when evaluating Rayleigh’s criterion: Interestingly, the choice of the operating pressure can render a system stable or unstable, so that the common procedure of applying flame transfer functions measured at ambient pressure for the high pressure engine case may not always be appropriate. The detailed analysis of high speed camera images, which were recorded to get locally resolved information on the flame response reveal different regions of activity within the flame that change in strength, size and location with changing operating conditions. The observed transfer function phase behavior is explained by the interaction of those regions and it is shown that the region of highest dynamic activity dominates the phase.

Further Characterization of the Disturbance Field in a Transversely Excited Swirl-Stabilized Flame

“…1. This superposition manifests in the flame response both locally and globally [27,32,34,35,[41][42][43][44][45]. The experimentally observed oscillation in the flame transfer function with frequency is attributed to constructive and destructive interference between disturbances at different parts of the flame.…”

Comparison of the flame dynamics of a premixed dual fuel burner for kerosene and natural gas

“…For low oscillation amplitudes, the overall heat release rate fluctuation can be expressed as a linear combination of the two effects:with being the response to acoustic perturbations and an equivalence-ratio dependent function . 27 Under the assumption of a stiff fuel supply which means that the fuel flow rate does not react to acoustic perturbations, the equivalence ratio fluctuations are directly related to the acoustic velocity perturbations and thus both contributions can be formulated as functions of : 28 Applying this relation allows to incorporate all potential effects in one FTF measurement which is the precondition for the later applied decomposition of the measured FTF into different mechanisms that originate from either equivalence or acoustic velocity fluctuations.…”

Determination of the Heat Release Distribution in Turbulent Flames by a Model Based Correction of OH* Chemiluminescence

“…For lean premixed combustion, the knowledge of the local heat release rate is particularly important to understand, predict, and control unstable combustion states, such as thermoacoustic instabilities [1][2][3] and flame flashback [4,5], Also in partially premixed and nonpremixed combustion systems, the heat release rate distribution is an important parameter in current research; for example, for phenomena like combustion noise [6,7], combustor design, and pollutant emission. However, the experimental determination of turbulent flame heat release rate is problematic, because available temporally and spatially resolved measurement techniques, like heat release imaging [8], are too complex to be applied to research fields like thermoacoustics [9].…”