59941 - Investigation of Adjacent Lifted Flames Interaction in an Inline and Inclined Multi-Burner Arrangement 

The reduction of pollutant emissions from aircraft engines has  received extensive attention in the recent decade in order to comply with more stringent emission regulations. Long term goals were set by the Advisory Council for Aviation and Research in Europe (ACARE) for the year 2050, i.e. NOx emissions reduction by 90% with respect to year 2000.

The main objective of this research is to assess an innovative, low emission combustor concept, which is developed in the frame of the European research project CHAIRLIFT (Compact Helical Arranged combustoRs with lean LIFTed flames) and has the potential to meet the long term targets. Lean lifted flames and its very low NOx emissions are combined with an inclination of burners in annular combustor for improved lean blow out limits. The lean lifted spray flames (with low swirl) feature a high degree of premixing and consequently significantly reduced NOx emission. A combustor with a tilting of the axis of the burners/flames relative to the axis of the turbine in an annular combustor is called Short Helical Combustor (SHC). The stability of the flames is increased by the interaction of the inclined adjacent flames, which has the advantage that no extra pilot flame is required, which may produce additional NO_x emissions. Additional benefits of SHC concept are the reduced length of the combustor, a lower required turning angle of the nozzle guide vanes  (NGV) resulting into a smaller number of NGV combined with reduced cooling air requirement.

In the presented work, a multi-burner array test rig consisting of up to five modular burners  will be presented, which allows investigating multiple lifted spray flames in an innovative burner arrangement at a realistic geometrical scale. A series of tests were conducted for different burner inclination angles (0 and 45^o) at  different air fuel equivalence ratios and relative pressure drop at ambient pressure. The lean blow out limits (LBO) were determined in order to study the effect of burner inclination angle on flame stability at  different operating conditions. Generally, a  significant stability improvement by  the inclined burner arrangement was observed compared to the conventional inline  arrangement. Moreover, the flame chemiluminescence (OH*) measurements were used to provide a qualitative  characterisation of the flame structure and lift-off length at those conditions. Complementary numerical investigations were carried out using different numbers of burners  in order to evaluate if the center flames of the five-burner array are influenced by the  walls attached to the last and first burner. The numerical results indicate, that the middle flames of a 5 burner setup behave similar compared to a arrangement  with infinite numbers of burners (periodic boundary conditions), proving that the selected  setup is suitable as experimental reference case at laboratory scale for such burner concept.