Flame Stability Characteristics of Two-Dimensional Trapped Vortex Combustor

Abstract

ABSTRACTFlame stability characteristics of a two-dimensional (2D) trapped-vortex combustor (TVC) are investigated experimentally by considering two injection strategies, namely: (i) Inj-1 and (ii) Inj-2, for certain operating conditions. Injection strategy 1 (Inj-1) reinforces the shear driven stream-wise vortex flow structure within the cavity, whereas for Inj-2, a counter stream-wise vortex is established within the cavity. The study indicates that for a particular injection strategy, mainstream Reynolds number (Rems) and mainstream equivalence ratio (Φms), the cavity fuel-flow rates have to be increased with the primary airflow rate for sustaining cavity flame. Besides this, for the same operating condition, Inj-1 has a wider flame stability limit as compared to that of the Inj-2 case. For the Inj-1 case, fuel-air distribution within the cavity is almost near stoichiometric; however, for the Inj-2 case, the cavity region is found to be fuel lean. Analysis of this result also indicates that cavity equivalence ratio (Φc) at the flame blowout condition increases with MFR up to a critical value, beyond which it drops down. This critical MFR value demarcates two physical situations, namely: (i) non-merged and (ii) merged cavity flames. Besides this, an attempt has been made to bring out the phenomenology of flame blowout by analyzing the natural luminosity images near blowout condition. Furthermore, a plausible mechanism for flame blowout is proposed for 2D TVC. A semi-empirical correlation for the flame blowout data in terms of Da and MFR is obtained in this work, which can be useful for the design and development of TVC in the future.