1988-02-01

Structure of a Transient Hollow-Cone Spray 880522

Sprays from an injector with a conical oscillating poppet, as used in some direct-injection stratified-charge engines, have been characterized. Instantaneous injection pressure, poppet lift and the axial component of the drop velocity were measured, and backlit photographs were taken. Hexane and nitrogen were used. Pump speed, amount of injected fuel, gas pressure, and gas temperature were varied. In agreement with the results of others it was found that: the structure of these highly unsteady sprays is generally similar to that of steady hollow-cone sprays; the injection duration, the spray initial axial velocity, the tip penetration and the spray cone angle decrease with increasing gas pressure; injection duration and number of oscillations decrease with increasing pump speed; the maximum of the LDV-measured drop velocity is at the periphery of the spray at atmospheric conditions but shifts toward the axis at higher gas pressures; there is a vortex at the head of the spray but Virtually no recirculation inside the spray cone, and the sprays are in general highly reproducible. In addition it was also found that: the injector can exhibit bimodal operations; the injector tip pressure is different in shape and phase from the line pressure; the spray is not symmetric at high gas pressure; increasing the gas temperature at constant gas density favors the decrease of the tip penetration and of the spray cone angle; and the rms of the fluctuation of the axial drop velocity is in general considerably greater than 20% of the mean, in part due to experimental inaccuracies, but also suggesting both high-frequency turbulence and low-frequency cyclic variations. The extensive set of measurements should also be useful to assess models.

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