Experimental investigation on flame appearance and emission characteristics of LPG inverse diffusion flame with swirl

The flame appearance and emission characteristics of a LPG inverse diffusion flame (IDF) are studied experimentally in a coaxial burner. Flame length, CO and NOx emissions are examined at different equivalence ratio and swirler vane angle. The flame length of non-swirling IDFs steadily increases with increase in the fuel jet velocity. A reduced flame length is observed with the increasing air jet velocity. The IDFs with swirl are wider, shorter and stable compared to the IDFs without swirl due to the generation of internal recirculation zone (IRZ). The soot formation in the IDF is qualitatively estimated with the soot free length fraction (SFLF). The SFLF increases with an increased air jet velocity due to the effective entrainment of the fuel, which leads to an improved premixing of the fuel and air to produce an elongated blue zone of the IDF. The IDFs with swirl are wider, shorter and stable compared to the IDFs without swirl. IDFs with the 30° swirler have comparable characteristics of the CO and NOx emission with that of non-swirling IDFs. The adequate entrainment and the swirl effect for vane angle of 30° produce favourable environment corresponding to low CO and NOx emission.