A high-speed video camera was used to obtain photographs of a transient spray. The spray images were analysed to provide spray characteristics which include the spray tip penetration length, initial spray hesitation, nozzle opening time delay, hole-to-hole spray variation and spray structure. Both single and multi-hole nozzles were used to study these parameters. Fuel droplet characteristics within dense Diesel sprays were studied using Phase Doppler Anemometry (PDA) in an optical rapid compression machine. A comprehensive study of the PDA operating parameters was conducted. Additionally, the effects of injection pressure and in-cylinder pressure and temperature upon spray properties were studied. PDA has proved to be a valuable technique in providing an understanding of the structure and characteristics of sprays. However, the application of PDA to dense sprays is difficult. The results obtained are not always reliable and the accuracy of the results is often questionable. Phase Doppler Anemometers are not immune to errors and by carefully identifying these errors, the accuracy of the technique can be significantly improved. The effects of the PDA system parameters on the measurement accuracy have been studied. It was found that a thorough study of the operating parameters was required to tailor the system to the measurements of dense sprays. The photomultipliers voltages, the laser beam power and the size of the measurement volume all show significant effects on measured droplet diameters. Spray produced from a common-rail injection system proved to be a challenging environment for the PDA. Following the calibration of the PDA, investigations were conducted to study the effects of various parameters on spray characteristics including injection pressure, in-cylinder pressure and temperature. Results are presented for incylinder pressures ranging from 1.6 to 6 MPa and injection pressures from 60 to 160 MPa. The highest injection pressure produced faster droplets and improved the spray atomisation
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