Calculations for steady, laminar non-premixed, partially premixed and premixed flames established with n-dodecane, iso-octane and a blend of n-dodecane and iso-octane are performed for understanding the fuel effects on flame characteristics. Gas phase chemistry is described with the SERDP-2014 mechanism that consists of 522 species and 6398 reactions. Calculations have predicted the flame shapes and heights reasonably well. Calculations have also a predicted decrease in soot when the fuel was diluted with nitrogen and/or premixed with air. However, when iso-octane was added to n-dodecane in a non-premixed, partially premixed or premixed flame, calculations predicted only small changes to the flame structure. Detailed comparisons of flame structures along the centerline for pure fuels and a blended fuel are made. Consumption of fuel components and formation of intermediate fuel fragments and polycyclic aromatic hydrocarbon (PAH) species are investigated for understanding the growth of soot in these flames. Detailed comparisons of the flame structures revealed that non-premixed flames are most sensitive to the type of fuel (iso-octane or n-dodecane). However, when these two fuels are blended, flame characteristics seemed to be dominated by those of n-dodecane. Differences in flame characteristics diminished with premixing of fuel with air. A premixed flame showed very little sensitivity to the fuel type, whether it is iso-octane or n-dodecane.