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Abstract
Stratified swirled flame is widely used in gas turbines and aero engines to achieve low emissions. However, the limitation of implementing laser diagnostic in real combustors acquires more accurate measurements of field information in the flame, especially the unsteady heat release, which relates to a lot of important phenomena, such as combustion instability and blow-off. The present study employs large eddy simulation (LES) combined with a detailed OH* chemiluminescence reaction mechanism to validate the chemiluminescent image of OH* in a stratified swirled flame at the atmosphere condition. 10 kHz particle image velocimetry images and OH* filtered images are recorded during the experiment. The heat release and flow structure of the stratified swirled flame at two different fuel stratification ratios show distinguished flame shapes. In general, the velocity results of LES have good agreement with the measurement. The numerical OH* and heat release comparison reveals a strong dependence on the local strain rate and turbulence level of OH* emissions. It is also noticed that the wrong flame shapes may be deduced from the Abel inversed OH* image since the signals are weak in the outer recirculation zone. This indicates that the strain rate in different regions of stratified swirl flame has a significant impact on OH* signal distribution. The results provide insight into the ability of chemiluminescent emissions, such as OH*, to indicate heat release in more complex industrial flames.
Highlights
Stratified swirled flames are commonly used in lean premixed prevaporized (LPP) combustors for gas turbines or aero engines.1 The concentrically staged fuel/oxidizer fields achieve flexible operation conditions and low emissions
The height of the combustion section is 200 mm, and the width is 105 mm. It consists of two opposed observation windows with an area of 100 × 150 mm2 [see Fig. 1(c)]. 10 kHz Particle Image Velocimetry (PIV) was implemented by using a QuasiModo (Spectral Energies) diode-pumped Nd: YAG laser with a maximum power output of about 600 mJ per pulse at 532 nm
The outer recirculation zone (ORZ) lies at the corner under the outer shear layer (OSL). These flow structures have been widely studied for their stabilization of flame
Summary
Stratified swirled flames are commonly used in lean premixed prevaporized (LPP) combustors for gas turbines or aero engines. The concentrically staged fuel/oxidizer fields achieve flexible operation conditions and low emissions. It is correlated with many unsteady phenomena, such as combustion instability and flame flashback.4–8 In both cases, the heat release rate of the flame has to be measured. The direct measurement of the heat release rate is not accessible In many cases, it is indirectly measured through the chemiluminescent species CH∗ and OH∗.9–12. Since chemiluminescence originates from the reaction zone of the flame, it is commonly assumed to characterize the heat release rate of flames. Bedard employed detailed kinetics including the emitting species to simulate the combustion instability and compared that to experimental spectral measurements in a practical high-pressure rocket combustor. This paper uses the detailed GRI 3.0 mechanism combined with the OH∗ chemiluminescence reaction mechanism to simulate a stratified swirled methane/air flame at the atmosphere condition. Based on the numerical simulation and experimental results, it allowed us to gain a deeper understanding of the chemiluminescence mechanism in different fuel stratification ratios of flame
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