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The influence of spray-wall interaction on air entrainment in an unsteady non-evaporating diesel spray was studied using laser Doppler anemometry. The spray was injected into confined quiescent air at ambient pressure and temperature and made to impact on a flat wall. The air velocity component normal to a cylindrical surface surrounding the spray was measured during the entire injection period, allowing to evaluate the time history of the entrained air mass flow rate. The influence of wall distance and spray impingement angle on air entrainment characteristics has been investigated and the results indicate that the presence of a wall increases the entrained mass flow rate in the region close to the surface, during the main injection period. Normal impingement appears to produce stronger effects than oblique incidence at 30 and 45 deg. A qualitative explanation of the results is also proposed, based on the drop-gas momentum exchange mechanism.

The air entrainment in a transient non-evaporating diesel spray was studied using laser Doppler velocimetry, to provide information on the mixing properties in the near-field region extending to 160 nozzle diameters (40 mm). The spray was injected into confined quiescent air at ambient pressure and temperature. The air velocity component normal to a cylindrical surface surrounding the spray was measured during the entire injection period, allowing the instantaneous air mass flow rate and the entrainment rates to be evaluated as a function of time. Two injection conditions were examined and their influence on the entrainment quantified. In the near field zone investigated, the air entrainment in transient liquid jets appears to be lower than that in steady gaseous jets, but larger than that in steady liquid jets.