The performance of a pressure atomizer with a flow obstruction upstream of the nozzle

The internal flow and the spray formed by a pressure atomizer with an orifice diameter of 1mm and a length to diameter ratio of 10 were studied at injection pressures between 70 and 5000 kPa. Obstructions to flow were also introduced inside the injector to examine their effect on the injector's performance. Visualization of the flow inside the injector indicated that the obstructions caused the flow to cavitate. However, even without any obstruction, cavitation occurred at injection pressures as low as 170 kPa. These results also showed that cavitation can occur in four different modes, depending on the mass flow rate of fuel through the nozzle and the type of obstruction. Images of the resulting spray indicated that the cavitation enhances atomization significantly. Single-component phase Doppler particle analysis and laser diffraction particle sizing were conducted 50 mm, 100mm and 150 mm downstream of the nozzle face to examine the size and velocity distributions of the droplets in the spray. These measurements indicated that for a given liquid flow rate the droplet size was not affected by the structure of the cavitation. Velocity measurements in the spray indicated that the cavitation produces a wider spray cone angle at lower mass flow rates.