Combustion and NO_x emission characteristics of dual-stage lean premixed flame

Premixed flames have shown different behaviors while operating with inhomogeneous equivalence ratio. This property can be used to improve the performance of premixed flames. Present work proposed the idea of dual-stage lean premixed (DLP) combustion, which constructs lean premixed flames with equivalence ratio staged radially. Laminar DLP flames were built in a coaxial jet burner. The combustion and NO_x emission characteristics of DLP flames were analyzed and compared to the homogeneous cases. Results showed the arrangement of DLP combustion allows more heat to support the ignition of secondary premixed gas, which is located in periphery and has a lower equivalence ratio. So, the DLP flames can reach a fairly low global equivalence ratio compared to homogeneous cases. Besides, the secondary flame can produce a certain number of intermediate products during combustion, which will reduce NO_x into N₂, helping limit the NO_x emissions of the overall combustion. In short, the idea of DLP combustion may provide new thinking for the development of clean combustion.