Optical and Spectroscopic Characterization of a Coflow Ethylene/Air Flame

The need to control the emission of combustion by-products of environmental concern requires a better physical and chemical understanding of the mechanisms leading to pollutant formation. A significant research effort on polycyclic aromatic hydrocarbons (PAH) and soot has been undertaken during recent years but many important details remain poorly understood. Particularly, the process whereby the molecular species are transformed to nanoparticles and their coagulation and carbonization to soot particles is still a subject of debate. The existence of soot precursor nanoparticles has mainly been inferred by spectroscopic and optical characterization in laminar premixed flames and a detailed reaction mechanism has been developed to simulate their formation and growth [1]. Modeling results indicate that the formation and growth of nanoparticles is triggered by the presence in the combustion system of both PAHs and small radicals [2]. This environment is typical of oxidative pyrolytic regimes such as those encountered in the post-oxidation zone of rich premixed flames whereas it is restricted to specific locations of non-premixed combustion systems where the pyrolysis of the fuel is almost decoupled from the oxidation chemistry. Consequently, it is not clear if the formation of carbonaceous nanoparticles similar to those measured in premixed flames is allowed also in diffusion flames. Thus, the purpose of this communication is to use advanced optical and spectroscopic diagnostics, already tested in premixed flames, for the identification of PAHs, nanoparticles and soot in a coflow ethylene/air flame at atmospheric pressure.