The air entrainment characteristics of a transient high-pressure diesel spray were investigated with respect to time and location for injection pressures ( Pinj = 76 or 137 MPa) and ambient density (ρa = 15.6 kg/m3) under the non-evaporating condition (303 K). A particle image velocimetry analysis was introduced and some parameters were defined to express air entrainment characteristics. The air entrainment rate increased greatly as the flow moved downstream owing to a larger contact surface area and a recirculating flow. Higher pressure led to a greater entrainment rate with higher effectiveness. The speed (spray tip and front ambient gas) and volume (spray and laterally entrained gas) relations suggested the possibility for the renewal against the lateral-dominant entrainment mechanism.
