The objective of the work reported in this paper was to develop and demonstrate an injection nozzle which can be used to inject both diesel fuel and methanol in to a direct injection diesel engine. The constraints on the nozzle were that it must provide acceptable fuel metering and atomization for the diesel fuel so that the engine can be operated at rated load on diesel fuel alone, or operate at full load with the diesel fuel as a pilot for the methanol. An additional constraint was that the nozzle design was to be easily adaptable to the existing injection nozzle so that engine head modifications are not required.The initial design was evaluated in a constant volume test chamber in which the pressure was varied from atmospheric to engine compression pressures. The design variables were optimized in the injection chamber to provide two separate injections with acceptable injection characteristics as determined from records of the injection pressures and high-speed movies of the two sprays.The results of the optimization experiments are discussed in terms of the important design parameters. In addition, the design optimized in the injection chamber was installed in a single-cylinder research test engine and further optimization was performed. The engine performance and the steady-state gas phase emissions are presented on a comparative basis with the equivalent baseline data obtained during operation in the standard configuration with diesel fuel. The results are discussed in terms of the design criteria for best performance based on the results of the engine experiments.