## 4 Discussion  
The carbon black synthesis method reported here occurs under oxidizing conditions in contrast to the conventional pyrolysis process. The liquid coal tar distillate precursor is sprayed directly into the pilot flame to form a new turbulent spray flame from entrained oxygen. A significant portion of precursor and particles are lost to the gas-phase under high-temperature oxidizing conditions. Particles collected downstream are survivors of this hostile environment. Nonetheless, the compact configuration of the flame and control of synthesis parameters may justify the lower yield of carbon black particles. This is especially promising for high-surface-area grades in which the yield in the pyrolysis processes is also known to decrease [2; 3; 4].  
Carbon black produced in the current study is high surface area, with primary particle diameters approaching ASTM N110. An optimal condition is found, such that enough  
Figure 9: Raman spectra for carbon black formed in the Series 1 flames along with an example 3-peak curve fitting (**top**) and the ratio of the fitted D-band to G-band intensity extracted from the fitted spectra (**bottom**). Solid lines are measured; black dotted line is the fitted spectrum; the 3 fitted peaks are shown in grey dotted lines.  
oxygen is supplied to the spray for the full vaporization of the heavy precursor to form dry carbon particles, which survive the oxidation zone. Preliminary conditions for producing substantially more (and presumably larger) particles than reported above were achieved by lowering the pilot oxygen flow and by decreasing the atomizing nitrogen flow rate. Both of these parameters have the effect of reducing the entrainment of oxygen into the spray, thus favoring particle production and growth. The current conditions are chosen for ease of operation to minimize particle build up on the chamber window and carbon coating during thermocouple measurements. Operating under heavier production conditions would increase the difficulty of systematic flame imaging and thermocouple measurements and thus are left for future work.  
The current work reports carbon black formation from a precursor that is relevant to industrial production. Global models for conversion of a generic hydrocarbon precursor in furnace black reactors have been presented [2; 34; 35]. More recently, detailed chemical kinetic models have been presented based on methane [36; 37], acetylene [38], benzene [39], methylnaphthalene [40], and waste tire oil [41] feedstocks. Any experiments accompanying these modeling studies do not directly explain furnace black processes using petroleum or tar distillate precursors. The current work uses a real heavy aromatic feedstock, but the synthesis does not occur in a pyrolysis reactor. Nonetheless, the relatively simple turbulent spray flame configuration is a suitable approach to investigate physics-based combustion kinetics and particle growth from an industrially relevant feedstock.  
Conceptualization, H.R.-F. and J.C.; methodology, H.R.-F., K.D.S., S.D. and J.C.; software, S.D.; investigation, H.R.-F., K.D.S., S.D. and J.C.; resources/funding.J.C.; writing--original draft preparation, H.R.-F., K.D.S., S.D. and J.C.; writing--review and editing, H.R.-F., K.D.S., S.D. and J.C. All authors have read and agreed to the published version of the manuscript.  
The work was supported by NSF Combustion and Fire Systems program under Award 1841357.  
Not applicable.  
The authors declare no conflict of interest.