Deepening the knowledge of carbon particulate matter features in the BSS flame configuration

Abstract

The paper reports a detailed study on carbon particulate matter (PM) sampled in ethylene flames stabilized on a burner-stabilized stagnation (BSS) system, aiming to give more insights on the characteristics of particles produced in this peculiar flame configuration. The study employs various diagnostic tools to analyze PM collected on the stagnation plate of flames at a constant equivalence ratio (Φ =2.07) and different flame temperatures obtained by varying the cold gas flow velocity. The carbon network of PM was analyzed by Raman and UV–Visible spectroscopy verifying the strong temperature effect on the nanostructure. The FTIR analysis allowed to quantitatively follow the temperature effect on the aromatic and aliphatic CH bonds, also evaluating the H/C atomic ratio that was found to be rather high (ranging from 0.3 to 0.5) initially decreasing and finally re-increasing as the flame temperature rises. The initial hydrogen loss with the rise of temperature was due to the loss of aromatic hydrogen, followed at higher temperature by the relevant enrichment of hydrogen bonded to aliphatic carbon. This observation is in contradiction with the expectation that higher flame temperatures would lead to an enhanced dehydrogenation of carbon particles, thereby reducing also aliphatic hydrogen. It was suggested that the enrichment in aliphatic hydrogen could be due to the small size of particles having higher radical character and surface area. Indeed, the peculiar features of such carbon particles deserve further work for understanding soot formation and growth and the relevance of BSS carbon material for optical and electronic applications.