A low emission, direct injection, compression ignition, internal combustion engine operates with reduced charge-air oxygen concentration levels to control localized peak combustion temperatures and reduce NOx formation. Low cetane fuel, below 43 cetane, and most preferably with a cetane rating below 30, is utilized with the combustion system to reduce smoke and PM formation simultaneously with the reduced NOx formation. In a preferred embodiment, FCC Naptha fuel, with a cetane rating below 30 and an end boiling point below 120 degrees Celsius, is used with the combustion system together with the reduced charge-air oxygen concentration levels to produce engine-out NOx emissions of 0.2 g/bhp-hr or lower, and PM emissions at 0.01 g/bhp-hr or lower, without the need for NOx (and potentially PM) aftertreatment. Potential commercial applications of the fuel and combustion system are discussed, including application to vehicle fleets, with novel methods of operating a vehicle fleet (and of providing fuel to such fleets) to meet motor vehicle emissions regulations at a reduced cost also being disclosed.