Abstract: Apparatus and method for reducing the emissions of a diesel engine. A hydrous alcohol fuel of low proof supplements the diesel fuel, particularly in high acceleration and high r.p.m. conditions. The fuel is fumigated into the airstream of the intake manifold of the engine by a fuel injector that is supplied both the alcohol fuel and air under pressure. Control apparatus begins delivery of the alcohol fuel above a selected engine r.p.m. and the amount delivered generally corresponds to engine r.p.m. Under heavy acceleration, the flow of diesel fuel is reduced and engine power is brought back up by the alcohol fuel. No alcohol fuel is used when the engine is decelerating or reducing its r.p.m.'s.