Determination and Scaling of Thermo Acoustic Characteristics of Premixed Flames

Abstract

The paper investigates the determination and the scaling of thermo acoustical characteristics of lean premixed flames as used in gas turbine combustion systems. In the first part, alternative methods to characterize experimentally the flame dynamics are outlined and are compared on the example of a scaled model of an industrial gas turbine burner. Transfer matrix results from the most general direct method are contrasted with data obtained from the hybrid method, which is based on Rankine-Hugoniot relations and the experimental flame transfer function obtained from OH*-chemiluminescence measurements. Also the new network model based regression method is assessed, which is based on a n − τ − σ dynamic flame model. The results indicate very good consistency between the three techniques, providing a global check of the methods/tools used for analyzing the thermo acoustic mechanisms of flames. In the second part, scaling rules are developed that allow to calculate the dynamic flame characteristics at different operation points. Towards this a geometric flame length model is formulated. Together with the other operational data of the flame it provides the dynamic flame model parameters at these points. The comparison between the measured and modeled flame lengths as well as the n − τ − σ parameters shows an excellent agreement. NOMENCLATURE

Modelling of Thermoacoustic Combustion Instabilities Phenomena: Application to an Experimental Test Rig

“…where α = A u /A d is the area ratio, ζ a pressure loss coefficient, which can be evaluated from the steady state incompressible Bernoulli equation [13] …”

Design for Thermo-Acoustic Stability: Modeling of Burner and Flame Dynamics

“…The second term describes the constructive and destructive interactions of swirl velocity induced and axial velocity induced vorticity fluctuations that become dominant in the high frequency range. Also the axial position of the peak heat release x OH,max is a known candidate parameter [12] of flame dynamics. These are given in Table 2.…”

“…In previous papers [11,12] we have reported our findings on the scaling rules necessary to correctly transfer the thermo-acoustic behavior determined in a single burner test rig to a multiburner annular combustor and validated a network model for the annular combustor. In previous papers [11,12] we have reported our findings on the scaling rules necessary to correctly transfer the thermo-acoustic behavior determined in a single burner test rig to a multiburner annular combustor and validated a network model for the annular combustor.…”

Non-linear behavior of the thermoacoustic oscillations in the LIMOUSINE combustor

“…In the last years, there have been many reports of FTF for a variety of geometries [4,21,[56][57][58][59][60][61][62][63][64], obtained from either practical or numerical experimentation. A slightly different approach to characterize the flame is the Transfer Matrix by [65,66] that uses the acoustic field as the output variable. This allows measuring the flame response at the upstream and downstream ends.…”

“…However for a qualitative treatment these measurements would be sufficient to characterize the flame and its stabilization behavior [103]. The convective time scale is defined as the delay time required for any perturbation in the flow at the point of fuel injection to travel to the location of the flame with effective mean convective speed [66]. This can be presented mathematically as…”