EXPERIMENTAL INVESTIGATION ON LIFT-OFF, BLOWOUT, AND DROP-BACK IN PARTIALLY PREMIXED LPG OPEN FLAMES IN TUBULAR BURNER

The higher pollutant level in non-premixed combustion and safety issues pertaining to premixed combustion can be counteracted by partially-premixed mode of combustion. The partially premixed flames exhibit the benefits of both premixed and non-premixed flames. Partially premixed flames enhances complete combustion leading to reduced soot formation and hence lower emission. However, the equivalence ratio plays an important role in the stability of such flames. This paper reports the experimental investigation on the flame characteristics and stability of partially premixed LPG-air flames in tubular burner. The stability curve obtained for the base case without any secondary flow shows that the velocity at lift-off, drop-back, and blowout increases with increasing equivalence ratio. In the presence of secondary co-flow air, the lift-off and blow off velocity decreases compared to base case indicating poor stability due to extensive flame stretch leading to aerodynamic quenching. The experimental results show that the velocity of flow at lift-off, blowout, and drop-back are higher in the presence of secondary swirl air than the base case. Co-swirl air increases the stability due to better mixing at the flame base with increased residence time. Flame stability deteriorates with co-flow air as co-flow strains the flame boundary due to flame stretch.