Two-dimensional light extinction, flame luminosity, and OH* chemiluminescence images were captured at a constant ambient temperature of 823K and two gas densities (20 and 26kg/m(3)), with injection pressures of 800-2500 bar using nozzle orifices with diameters of 0.19 and 0.10mm. Soot volume fraction and OH distribution images were obtained using the Abel inversion method, and the local equivalence ratio in the lift-off length region was predicted. The results show that the equivalence ratio along the jet's center at the lift-off length was found to play a critical role in soot formation. Reductions in thickened the OH zone in the upstream region of the jet, reducing the volume corresponding to the maximum soot volume fraction. The expansion of the OH zone also helped reduce the sooting zone's width. Under high sooting conditions (e.g.,, the sooting zone width in the downstream jet was independent of phi(CL).