Numerical Modeling of Gaseous Partially Premixed Low-Swirl Lifted Flame at Elevated Pressure

Abstract

Lifted flames have been investigated in the past years for their benefits in terms of NOx emissions reduction for gas turbine applications. In a lifted flame, the flame front stabilized on a position that is significantly detached from the nozzle exit, improving the premixing process before the reaction zone. The distance between the flame front and the nozzle exit is called liftoff height and it represents the main parameter that characterize this type of flame. In the present work, a partially premixed lifted flame employing air-methane mixture is investigated through numerical simulation. Indeed, even if lifted jet flames have been widely studied in the literature, there are only a few examples of lifted partially premixed flames. Nevertheless, this kind of flames assumes an important role considering the current gas turbine applications, since their benefits in terms of stability and low pollutant emissions. This study has been performed with LES calculations using a commercial software suite and the numerical results are compared with experimental data coming from a dedicated campaign held at Karlsruher Institute für Technologie (KIT) on a novel low-swirl injector nozzle. Quenching effects due

Numerical Modeling of Lean Spray Lifted Flames in Inclined Multi-Burner Arrangements

“…Still considering the previous analysis, the main reaction zones again appear at the side of the swirling jet, but a not trivial behaviour is present con- cerning the most reactive side. Although the limits pointed out in the previous paragraph concerning the position of these zones, it could be concluded that these regions are related to the outer shear layer between swirling jet and ORZ, as already pointed out in the previous studies for this type of flame on the single sector both experimentally [15] and numerically [28]. This fact could be observed from the axial velocity maps, where the black isolines identify the production formation rate.…”

“…3 (inner and outlet inlets), a target mass flow rate corresponding to the conditions of Tab.1 has been imposed. This boundary condition consists of an adapted radial profile derived from previously Large Eddy Simulations (LES) carried out on the same nozzle with a smaller effective area [28]. Here, it is assumed that the trend in the radial direction concerning mass flow distribution and turbulent quantities are the same for the two nozzles.…”

Assessment of Thickened Flame Model Coupled With Flamelet Generated Manifold on a Low-Swirl Partially Premixed Gaseous Lifted Flame

“…In the previous works by the authors, the effects of heat losses were included within the FGM model through a correction factor applied by scaling the reaction rate [17,18]: outcomes have shown a discrepancy with the experimental measurements, resulting in a short flame stabilized low in the flame tube. A possible explanation for such behaviour could be incorrect modelling of the heat loss effects on the reaction, due to this simplistic approach, as described in [35].…”

“…On the other hand, the limitations of a priori regime assumption and chemistry tabulation could strongly impact the final prediction [13], and nowadays many research efforts are devoted to compare finite rate methods with and flamelets-based ones for describing turbulent combustion [14,15]. Considering the numerical works carried out so far on the KIT-EBI's flame [16,17], turbulent combustion has been initially modeled with flamelets based approaches as (or very similar to) the Flamelet Generated Manifold (FGM). This model however has shown to overpredict the reaction rate, leading to a flame stabilized too low and short with respect to the experimental finding.…”

“…This model however has shown to overpredict the reaction rate, leading to a flame stabilized too low and short with respect to the experimental finding. The prediction can be improved when the FGM model is modified to take into account the effects of local stretch and heat loss on the global reactivity, referred as FGM-EXT in [17]. Further works from the authors [18] carried out a comparison among the previously mentioned models and the Thickened Flame (TF) model [19]: indeed, the use of the TF approach resulted in a better description of the flame lift-off and shape of the reaction zone.…”