Phase doppler measurements: system set-up optimization for characterization of a diesel nozzle

A commercial phase Doppler system was set up, optimized and used to measure the time resolved characteristics of the droplets inside a diesel spray. The purpose of this work was to understand exactly the influence of each system parameter, and to find the best setup enabling measurements in the spray zones that are densest and closest to the injector. Parametric studies were performed to gain an understanding of the particle density limits of the system and their dependence on the system parameters. Then the diesel spray produced by a single-hole injector was measured, with the fuel pressure ranging from 300 to 1300 bar and gas density in the test chamber ranging from ambient conditions to 40 kg/m3. The optic parameters (beam waist size, lenses focal length) were chosen to the best expected values allowed by the optical stand-off of the spray enclosure. The receiver slit width, which was found to have a dramatic effect on the detection of droplets during the injection main period, was tested in the range from 100m to 25m. Tests were carried out with two different slit lengths, namely 1 mm and 50 μm, with results indicating minimal effect on performance. PMT voltage (gain) was held to a moderately low value between 400 and 500 V and the laser power between 400 and 800 mW in the green line. An optimum burst threshold was found to obtain the best quality data regardless of signal background level, which varies greatly in high-density pulsed sprays. In the end, a set of results from the complete nozzle characterization in various conditions is presented in order to show the practical application of the optimization study and to provide some means of appreciating the results accuracy. The results obtained were also used to show that the gas-jet theory can be used to predict if PDPA measurement are possible in a given experimental situation.