Diesel and water emulsions have the potential to be used in compression ignition engines to control the emissions of NOx and PM. Very little is known about the influence emulsification will have on the fuel sprays formed during injection. This paper outlines the measurement of the momentum flux of injection sprays of Diesel fuel and Diesel fuel emulsions containing 10% and 20% water, with the goal of hydraulically characterizing the sprays and identifying the influence emulsification may have on them. The momentum flux, mass flow, instantaneous mass flow, discharge coefficient, injection velocity, momentum coefficient and momentum efficiency have been examined. The injections were carried out in a high pressure chamber filled with nitrogen. The measured momentum flux is observed to increase with increasing injection pressure in a linear form. Increasing the ambient density in the chamber resulted in a decrease in the measured momentum flux. The emulsified fuel sprays had a very similar momentum flux as the neat Diesel fuel sprays. The total mass of emulsified fuel injected was less than for neat Diesel at corresponding condition. The instantaneous mass flow rate was determined using a normalized form of the momentum flux measurement and the independently measured total mass injected. The emulsions tended to have a lower discharge coefficient and there is no evidence that the nozzle is cavitating at these conditions. The emulsified fuels have tended to have a higher injection velocity than the neat Diesel fuel sprays. The momentum efficiency is introduced, which uses the instantaneous mass measurement and the theoretical velocity of the spray. The emulsified fuels have a larger momentum efficiency, a result of their high injection velocity compared with the neat Diesel fuel. (C) 2015 Published by Elsevier Ltd.