The inverse jet diffusion flames: A systematic review

The gaseous Inverse Jet Diffusion Flame (IJDF) is a unique nonpremixed flame that can be established in a simple coaxial burner when central air jet surrounded by annular fuel jet is ignited. The active research on laminar IJDF was initiated in the early 1980's, with a primary focus on its sooting characteristics. The soot formation, evolution and morphology in inverse jet diffusion flame differ fundamentally from that of the normal jet diffusion flame (NJDF) due to its distinct reactant delivery mode and fluid dynamics. The unique feature of the IJDF configuration is its reduced soot formation as compared to the NJDF configuration, particularly at higher air-fuel velocity ratio, even for hydrocarbon fuels. The literature has reported six types of laminar IJDF based on visual appearance and air-fuel velocity ratio. Furthermore, laminar IJDF is mainly utilized as a lab-scale flame by various researchers for the fundamental investigation of soot evolution in nonpremixed flames. Unlike normal jet diffusion flame, which is established with the fuel jet enveloped by an oxidizer jet, the post-flame emissions and the flame stability aspects of turbulent IJDF are relatively less understood. From a global perspective, coherence in the research on inverse jet diffusion flame is lacking and there is a need for an extensive investigation to understand this special type of nonpremixed flame. The present review identifies different emerging areas related to IJDF that the combustion researchers can pursue in the future.

Various aspects of laminar and turbulent IJDF, such as flame structure, soot formation, flame height, flame stability, thermal and emission characteristics are discussed in this review. This review may serve as a reference that contributes to the research perspectives on laminar and turbulent inverse jet diffusion flames for adapting the favourable aspects of this flame configuration in a wide range of industrial and domestic applications.