On the Effects of Carbon Dioxide as a Diluent on Precursor Nanoparticles and Soot in Axi-symmetric Laminar Coflow Diffusion Flames

ABSTRACT

The impact on the use of carbon dioxide (CO₂) as a diluent in the fuel and oxidizer streams on the formation and evolution of precursor nanoparticles and soot in axisymmetric ethylene laminar coflow diffusion flames is experimentally explored using optical diagnostics in this paper. The optical diagnostics employed are based on temporally and spectrally resolved point measurements of laser-induced fluorescence, elastic scattering, and laser-induced incandescence. The measurements provide insight to indicative structure and concentration of precursor nanoparticles, and enable the determination of volume fraction and mean diameter of soot. Previous studies have indicated that the use of CO₂ as a diluent compared to nitrogen can reduce soot formation through both chemical and thermal effects. However, the effect of CO₂ addition on precursor nanoparticles’ concentrations and structure is not well understood, hence exploring the impact of CO₂ on precursor nanoparticles is one of the primary aims of this study. Flames with CO₂ as a diluent in the jet only, coflow only, and both streams are identified and investigated. For the flames studied with respect to the replacement of N₂ with CO₂: i), the soot volume fraction and mean soot diameter is reduced, and ii) precursor nanoparticles concentration is reduced, and the structural transformation is delayed.

KEYWORDS:

• Laminar flames
• precursor nanoparticles
• laser-induced fluorescence
• laser-induced incandescence
• scattering

Acknowledgments

This research was funded by the Australian Research Council.