Synchrotron Radiation Studies of Additives in Combustion, III: Ferrocene

Abstract

Small-angle X-ray scattering (SAXS) has been used to examine the growth of soot primary particles (∼15–20 nm) and aggregates of primaries (>30 nm) formed in an ethylene flame doped with ferrocene. It is found that, early in the flame, the size of the primary particles formed when ferrocene is added tracks that for an undoped flame. Higher up (at height z above the burner greater than 18 mm), both primary and aggregate sizes are significantly smaller with ferrocene doping compared to the undoped flame. Within experimental error, the number densities of primary (N1) particles in the ferrocene flame are about the same as for the pure ethylene flame at low heights and higher (factor of 10) at larger heights (above 18 mm). On the other hand, the number concentration of aggregate particles (N2) in the doped flame is always greater than in the pure ethylene flame regardless of the height but with drops and increases in the ferrocene-doped flame case that can be correlated with corresponding increases and decreases in aggregate size. SAXS data at sufficiently long residence times in the flame show, through the value of the Porod exponent, that the particle surfaces of primaries and aggregates are much rougher in the doped versus undoped flame, which we interpret as being the effect of iron oxide inclusion that produces enhanced oxidation inside the soot material.