Experimental investigation of soot formation in inverse diffusion flames of CO₂ and N₂ addition: Isolation of dilution and thermal effects

ABSTRACT

This experimental study compares the flame structure, temperature, and soot formation characteristics of normal (NDFs) and inverse diffusion flames (IDFs), evaluates the effect of CO₂ addition, and isolates the thermal and dilution effects of CO₂ and N₂ addition on soot formation in IDFs. A hyperspectral imager using the TR-GSVD algorithm measures IDFs with different CO₂ addition (X_D) in the oxidant, with N₂ addition as the comparison. In contrast to NDFs, IDFs have an opened tip, and the visible flame height and flame width decrease as X_D grows. IDFs have a higher peak temperature than NDFs, but their peak soot volume fraction is substantially lower. Compared with N₂ addition at the same X_D, CO₂ addition narrows IDFs and makes the reaction zone visible, and the peak temperature of CO₂ addition is 350 K lower than that of N₂ addition. The suppression effect of CO₂ on soot formation is more potent than N₂, with a soot formation rate of 30% that of N₂ addition and a soot loading of 20–60%. The activation energy of soot formation reaction with CO₂ addition is higher than N₂ addition. The isolating results reveal that the thermal effect contributes to the main suppression effect of CO₂ addition on soot formation, while the dilution effect of N₂ addition is stronger than its thermal effect.

KEYWORDS:

• Inverse diffusion flame
• soot formation
• CO₂ addition
• dilution effect
• thermal effect

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00102202.2022.2095205

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51827808].