"The Single Fuel Forward Policy" legislation enacted in the United States mandates that deployed U.S. military ground vehicles must be operable with aviation fuel (JP-8). This substitution of JP-8 for diesel raises concerns about the compatibility of this fuel with existing reciprocating piston engine systems. This study investigates the combustion, emissions, and performance characteristics of blends of JP-8 and Ultra Low Sulfur Diesel (ULSD) fuels with similar cetane numbers (CN), 48 (JP-8) and 47(ULSD), respectively, in a direct injection (DI) compression ignition engine over the load range of 3-8 bar imep at 1400 rpm. The results showed that JP-8 blends and ULSD had ignition delays ranging from approximately 1.0-1.4 ms and an average combustion duration time in the range of 47-65 CAD. Cylinder maximum heat flux values were found to be between 2.0 and 4.4 MW/m₂, with radiation flux increasing much faster than convection flux while increasing the imep. Combustion maximum bulk temperature was in the range of 1700 K to 2500K, and also increased with load. Both mechanical and overall efficiencies increased with imep at constant speed but were minimally influenced by the fuel blend. Soot showed an increase at higher loads ranging between 0.01-0.18 g/kWh while NOx increased with higher loads and higher cycle temperatures. Carbon dioxide (CO₂) emissions showed an increase in value by increasing imep at constant speed while the UHC (unburned hydrocarbons) emissions decreased with load and maintained similar for all blends at constant imep. The results suggest that JP-8 and ULSD with similar CN have highly comparable combustion characteristics in a DI compression ignition engine despite differences in fuel properties and that CN is the paramount characteristic in comparing ULSD and JP-8.