NOx emission performance of triple flames

Abstract

A numerical study was performed to address the NOx characteristics of both normal and inverse triple flames in comparison with non-premixed and partially premixed flames. The cross-flow was found to shorten the triple flames and to raise the combustion efficiency of normal and inverse triple flames by about 12.1 and 7.2 per cent, respectively. With a cross-flow, the inverse triple flames experienced shorter flame lengths and subsequent lower NOx concentrations than those produced by either partially premixed or non-premixed flames. For inverse triple flames, increasing the lean mixture momentum and decreasing the rich mixture jet velocity together with increasing its premixing degree led to a reduction in the flame length and in both thermal and prompt NOx emissions. The increase in the lean equivalence ratio or its diffusive area split the flame high NOx concentration region and reduced the peak concentration, while increasing the radial inward entrainment reduced the NOx concentrations further. The results were experimentally verified using a slot burner, whereby the flame lengths and NOx emissions were fairly reproduced. The results indicated that triple flames can be widely used in industrial burners at various operating conditions.