Lifted flames have been investigated in the past years for their benefits in terms of NO~x~ emissions reduction. 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. This aspect helps to avoid local equivalence ratio close to the unity, hence the nitrogen oxides promoted by high temperatures. As a further advantage, here a dedicated device for the air-fuel premixing is not required, since this process occurs directly inside the combustion chamber, notably reducing flashback risks. The distance between the flame front and the nozzle exit is called *lift-off height* (LOH) and it represents the main parameter that characterized this type of flame.

In the present work, a low swirl lifted flames from air-methane mixture is investigated through numerical simulation. Indeed, even if lifted jet flames have been widely investigated in the literature, there are only a few examples of lifted partially premixed flames at low swirl conditions. Nevertheless, this kind of flames revests an important role considering a current gas turbine (GT) applications, since their benefits in terms of staibility and low pollutant emissions.  
This study has been performed within the ANSYS Fluent CFD suite and the numerical results are compared with experimental data coming from a dedicated campaign held at Engler-Bunte-Institute (EBI) of Karlsruher Institute für Technologie (KIT). The combustion model here employed is the Flamelet Generated Manifold (FGM), while the reaction mechanism is the GRIMECH 3.0. However, the usual FGM model is not able to predict correctly the LOH of the flame, since a complex mechanism involving local quenching due to heat losses and aerodynamical stain effects should be taken into account. Indeed, investigations point out that the LOH is therefore determinated by such effects, since the flame experienced a global quench next to the nozzle exit and stabilized downstream of this zone.

Quenching effects have been introduced into the combustion model thanks to a correction of the source term in the progress variable equation within the FGM model developed at TuM and described in open litereature. The comparison between numerical results and experimental data have been performed in terms of LOH and OH\* chemilumionescence maps, showing a quite good agreement. This points out the  capability of the numerical model in the representation of lifted flames, allowing further investigations of the flame structure otherwise not available from experimental techiniques.


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

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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