Abstract: A secondary fueling system for a diesel internal combustion engine includes an injector which injects an oxygen-containing secondary fuel into the engine's air intake system, a pump which pumps the secondary fuel to the injector, a sensor which senses pressure in the air intake system, and a secondary fuel controller which receives output signals from the sensor and pump, operator inputs for the engine, and data signals pertaining to operation of the engine from the main engine controller, determines an injection amount of the secondary fuel based thereon, and controls the pump based on the determined injection amount. A position of the injector in the engine's air intake system is distant from the engine's intake valves and is based on the engine's displacement, e.g., it relates to approximately equal to one quarter of the engine's displacement.