## 3 Results
Figure 4: Measured flame heights and widths based on flame images for Series 1 (**top**) and Series 2 (**bottom**). Lines are drawn to guide the eye. Contour plots of the axisymmetric soot temperature field are extracted from images of the flame projection under 650 nm and 900 nm bandpass filters. Assuming a soot dispersion index of unity [16; 24], contour plots of the Series 1 flames are shown in Figure 6. The pyrometry camera is calibrated to detect soot radiative emissions from 1400 K to 2500 K and this results in flame images with smaller dimensions than the full flame images shown in Figures 2 and 3. The temperature contours are an average of 20 flame images taken under each filter. Asymmetry in the temperature contour is detected but the multiple flame images are expected to reduce the impact of asymmetry on the Abel transform to some extent. Flame temperatures exceeding 2000 K are detected in local pockets of the turbulent spray flame as well. In principle, flame asymmetry and hot spots could be minimized by more precise centering of the liquid feed nozzle. Overall, the flame temperatures determined by soot pyrometry at the spray flame centerline agree with the thermocouple  
Figure 5: Measured temperatures at the centerline of the pilot flame without the spray flame using a thermocouple (**a**), centerline measurements of Series 1 spray flames using a thermocouple and soot pyrometry (**b**) and centerline measurements of Series 2 spray flames using a thermocouple (**c**). Lines are drawn to guide the eye. measurements shown in Figure 3.0 The constant dispersion index assumption taken in the pyrometry measurements and differences in turbulent flow field averaging may be the source of discrepancies between the temperature measurement methods. With the flame structure established, the properties of the flame-formed carbon could be examined more effectively. A summary of TEM images for carbon black, formed in both flame series, is shown in Figure 3.1 The aggregate morphology is similar across all flame conditions but trends towards larger aggregates are noticeable for decreased equivalence ratio (Series 1) and increasing coal tar distillate spray feed (Series 2). Decreased oxygen levels in the flame are conducive to carbon particle formation, but the impact of flame temperature on particle formation is not monotonic. The optimum flame temperature is typically understood to lie at approximately 1800 K for soot formation in flames [25; 26] and for yield in a carbon black pyrolysis furnace [2; 4]. Kinetics for the growth of precursors is favored at higher temperatures, but growth reactions eventually reverse at higher temperatures [27]. As such, the size of aggregates in Series 1 flames is a product of competing oxygen and temperature influences. For Series 2, increasing the fraction of coal tar distillates in the spray feed is expected to favor the formation and growth of carbon black due to the introduction of more aromatic particle precursors. Primary particle diameters based on TEM particle projections are shown in Figure 8 for both flame series. The median diameter of the histogram obtained from counting over 200 primary particles for each condition is reported. The median primary particle for the Series 1 flames increases by approximately 1 nm as the pilot flame equivalence ratio increases from 0.43 to 0.50. At lower equivalence ratio, the hotter spray flame temperature may favor carbon black production, but higher oxygen concentration in the spray increases particle oxidation thus hindering growth. Particle formation and growth kinetics are slower at lower flame temperature (p50), but lower oxygen concentrations may allow for a larger primary particle diameter. Figure 3.2 Soot pyrometry results for the Series 1 flames; t65d35 with p40 (**a**), p43 (**b**), p45 (**c**) and p50 (**d**). For flame Series 2, the trend with increasing coal tar distillates is more significant than the effect of oxygen concentration.