The aim of this study is to investigate the detailed soot formation characteristics of crude Jatropha oil (CJO) and heavy fuel oil (HFO) blends (lower heating value (LHV) basis: 50%/50%) in a 550 kW-class combustion test furnace equipped with an industry-scale steam atomizing burner using optical measurement systems. In the present study, time-resolved flame images through the high-speed photography, flame radiation intensity through Hottel & Broughton (H&B) two-color method, instantaneous soot volume fraction and the velocity field around the fuel nozzle through laser induced incandescence (LII) and particle image velocimetry (PIV), and the soot absorbance through the dust analyzer were obtained. The results of this study show that soot volume fraction around the fuel nozzle became lower with blending CJO in HFO, thereby the flame radiation intensity decreasing. This seems to be caused by fewer polycyclic aromatic hydrocarbons (PAHs) in the CJO. By the exhaust gas recirculation (EGR), a larger soot volume fraction around the fuel nozzle and a lower soot volume fraction in the downstream region were obtained, which are probably due to a decrease in oxygen concentration slowing the soot oxidation rate around the fuel nozzle and the increase in oxygen concentration behind overtire air holes, respectively. (C) 2019 Elsevier Ltd. All rights reserved.