Dynamics of lean blowout of a swirl-stabilized flame in a gas turbine model combustor

Abstract

Lean blowout (LBO) of a partially premixed swirl flame is studied using chemiluminescence imaging and simultaneous stereo-PIV and OH-PLIF measurements at repetition rates up to 5 kHz. The flame, which is operated with methane and air in a gas turbine model combustor at atmospheric pressure, features a pronounced precessing vortex core (PVC) at the inner shear layer. In the first part of the study, the stabilization mechanism of the flame close to LBO is investigated. The fields of velocity and OH show that near LBO there are essentially two regions where reaction takes place, namely the helical zone along the PVC and the flame root around the lower stagnation point. The zone along the PVC is favorable to the flame due to low strain rates in the vortex center and accelerated mixing of burned and fresh gas. The flame root, which is located close to the nozzle exit, is characterized by an opposed flow of hot burned gas and relatively fuel-rich fresh gas. Due to the presence of high strain rates, the flame root is inherently unstable near LBO, featuring frequent extinction and re-ignition. The blowout process, discussed in the second part of the study, starts when the extinction of the flame root persists over a critical length of time. Subsequently, the reaction in the helical zone can no longer be sustained and the flame finally blows out. The results highlight the crucial role of the flame root, and suggest that well-aimed modifications of flow field or mixture fraction in this region might shift the LBO limit to leaner conditions.

Lean blowout limits of a gas turbine combustor operated with aviation fuel and methane

“…However, the increase airflow of secondary swirler would also cause the decrease of FAR near the fuel injector. According to M. Stohr [20], the flame root located above the fuel injector is significant for the flame stability. The decrease of FAR near the fuel injector would lead to the failure of sustainment of flame root, thus result in the flame lean blowout.…”

Prediction of Global Extinction Conditions and Dynamics in Swirling Non-premixed Flames Using LES/CMC Modelling

“…With the high-speed PLIF and chemiluminescence technique applied for imaging reactive radicals two-dimensionally, it is possible to analyze transient and phenomenological characteristics of local extinction in turbulent non-premixed flames [6][7][8][9][10]. In particular, the turbulent non-premixed combustion in swirling flow fields also attracts lots of attention because of its significant practical applications, such as in gas turbine combustors [11][12][13][14][15]. The turbulence−chemistry interaction in unconfined swirl non-premixed flames with a range of swirl numbers was reviewed in Ref.…”

“…The blow-off duration was also quantified. Blow-off dynamics in a dual swirl combustor were related to the helical flame zone and the movement of the flame root [14] and it was concluded that the blow-out starts when the extinction state at the flame root lasts for a time exceeding a critical duration. Furthermore, re-ignition at the flame root was inhibited, which differs from what was observed by Cavaliere et al [15], in which the re-burning near the bluff body can be seen even at the last stage of blow-off transients.…”

Dynamic Data-Driven Prediction of Lean Blowout in a Swirl-Stabilized Combustor

“…They used photomultiplier tubes with CH chemiluminescence filters to capture the optical signal and characterized the signal in the vicinity of blowout. Chaudhuri et al [4] and Stohr et al [5] investigated LBO dynamics of premixed and partially premixed flames using combined particle image velocimetry/planar laserinduced fluorescence (PIV/PLIF)-based diagnostics. However, these works did not focus on developing strategies for mitigating LBO.…”