Spray tip penetration and dispersion in high pressure diesel engines have been simulated experimentally with a special emphasis on the effect of swirl. A constant volume chamber was designed to be rotatable in order to generate a continuous swirl and to have the flow field closely resembling a solid body rotation. Emulsified fuel was injected into the chamber and the developing process of fuel sprays was visualized. The effect of swirl on the spray tip penetration was quantified through modeling.Results show that the spray tip penetration is qualitatively different between low and high pressure injections. For high pressure injection, good agreement is achieved between the experimental results and the modeling accounting the effect of swirl on spray penetration. For low pressure injection, reasonable agreement is obtained. The modeling result can be used as basic design data in diesel injector development.