Growth of fractal structures in flames with silicon admixture

Abstract

Transmission electron microscopy (TEM) measurements and theoretical analysis are combined to construct the physical picture of formation of SiO2 fractal aggregates in a methane/hexamethyldisiloxane/air atmospheric pressure flame. The formation of SiO2 fractal aggregates is described as a multistage process. The first stage is combustion of fuel in a narrow flame front region with formation of main combustion products including SiO2 molecules. Further downstream SiO2 molecules join in liquid nanoclusters. After cooling combustion products due to heat losses to surroundings, the nanoclusters become solid in a cold flame region and join in fractal aggregates there. Along with growth of fractal aggregates, the restructuring process proceeds in a cold flame region that leads to the decrease of the fractal dimension of fractal aggregates. The measured parameters of fractal aggregates are in accord with those followed from theoretical models.

Angle-Dependent Light Scattering Study of Silica Aggregate Growth in 1-D Methane/Air Flames with Hexamethyldisiloxane Admixture: Effects of Siloxane Concentration, Flame Temperature, and Equivalence Ratio

“…We observe that extractive measurements followed by TEM analysis (Smirnov et al, 2012) for a stoichiometric flame with ∼500 ppm Si at a temperature somewhat higher than here (T ≈ 2090 K) gives similar results to those at 500 ppm Si in Fig. 5, particularly when considering the effect of temperature on described below.…”

“…One-dimensional (1-D) premixed flames yield conditions more amenable to analysis and, as will be discussed below, which can be varied in a straightforward manner. Using ex-situ particle sampling Smirnov et al (Smirnov et al, 2012), for example, analyzed aggregate growth and primary particle size as function of residence time in this type of flame based on transmission electron microscopy (TEM). Other studies in premixed 1-D flames employed in-situ techniques such as dynamic light scattering (Flower and Hurd, 1987;Hurd and Flower, 1988) and angle dependent light scattering (ADLS) (Chang et al, 1998;Ulrich and Riehl, 1982) to characterize silica growth as function of time.…”

Size distribution of silica nanoparticles: its impact on green energy

“…Image pre-processing and analysis were performed using MATLAB software package following closely the procedures described in literature [17,47,48]. Aggregates that touch edges of images were excluded from the analysis, as there were aggregates having too low contrast to the background.…”

“…As mentioned above small amounts of L2 is added to methane, which is oxidized rapidly near the burner surface [17]. We did not investigated in detail the oxidation kinetics of L2 in the flame.…”

“…The thickness and density of deposited silica layers depends on particle morphology and particle size distribution (PSD). Direct use of biogas at production sites may found that the oxidation of L2 proceeds very fast with formation of SiO 2 molecules and compact silica clusters at a height of a few millimeters above the burner deck [17]. When travelling through the flame the silica particles grow due to collisions.…”