A Benchtop Engine System (BES) is described to evaluate the NOx emission characteristics of diesel fuels. The BES enables the efficient testing of the combustion and NOx emission features of alternative fuels and additives. The BES comprises a computer controlled single cylinder engine generator, fuel blending and feed system, and NOx analyzer. The engine can be operated at different loads using the programmable load control. NOx concentration are monitored and recorded to evaluate the impact of the diesel fuel and/or additive. Several commercial diesel fuels and one commercial fuel additive were tested in both the 500 HP Heavy Duty Chassis Dynamometer and the BES. The reported results demonstrate the BES capabilities, differences in the NOx emission features of several fuels and additives.