High Speed Imaging of Flame Structure and Dynamic Processes in Swirl Stabilized Prevaporized Liquid Fuel Flames

Abstract

Detailed optical measurements with high spatio-temporal resolution were carried out in a gas turbine model combustor (GTMC) at atmospheric pressure using prevaporized ethanol as fuel. The GTMC features co-annular swirl nozzles with separate air plenums for the inner and outer air streams, allowing control of the air split ratio L between the nozzles. In the current study, the air split ratio was fixed at L = 1.6, which resulted in equal pressure drop across both nozzles. The total air mass flow rate was fixed at 400 g/min and flames with different fuel flow rates-resulting in thermal powers between 10.9 kW and 16.9 kW and corresponding global equivalence ratios between φ = 0.55 and φ = 0.85-were studied. Air, fuel, and all supply lines, were preheated to >100°C in order to avoid fuel condensation within the supply lines or the fuel plenum. The flow field was measured with stereoscopic particle image velocimetry (S-PIV), the distribution of the OH radical within the combustion chamber was measured using planar laser-induced fluorescence (OH PLIF) and the overall flame shape and flame dynamics were imaged using OH* chemiluminescence (OH* CL). All measurements were performed at a sustained repetition rate of 10 kHz. In addition, pressure fluctuations in both air plenums and in the combustion chamber were recorded at a sampling rate of 100 kHz using calibrated microphone probes. All studied flames stabilized within the inner air nozzle, with the main reaction zone being lifted off the burner nozzle. Dominant frequencies for the examined operating conditions were studied by means of fft-analysis of the pressure and heat release rate fluctuations. Furthermore, spatially resolved fft-analysis of the OH PLIF signal allowed to identify the regions were specific modes are dominant.

Flame Extinction and Re-Ignition in a Swirl Stabilized Prevaporized Liquid Fuel Flame Close to Lean Blow-Out

“…The LBO is also dependent on the reactivity of the flow, and can be influenced by the injection of pilot fuel/air [19], or by the preheat temperature [16]. In the current study, a gas turbine model combustor (GTMC) was adapted and set-up for the study of prevaporized single component fuels [20]. Prevaporized ethanol was supplied to the combustor using a direct evaporizer.…”

Influence of Fuel Staging on Thermo-Acoustic Oscillations in a Premixed Stratified Dual-Swirl Gas Turbine Model Combustor

“…The burner features two concentric corotating swirlers, each supplied by a separate plenum, allowing to feed each of the two concentric flows with premixed mixtures of different equivalence ratios. This GTMC has been studied previously with focus on technically premixed methane flames (Arndt et al 2015(Arndt et al , 2017Meier et al 2015) and prevaporized liquid fuel flames (Arndt et al 2019(Arndt et al , 2020. A nearly identical setup is available for liquid fuels (Bärow et al 2013).…”