A pulsed Malvern drop-size analyzer, based on Fraunhofer diffraction, was utilized to determmine droplet size size ranges of diesel fuels under different conditions of injection. the effects of fuel properties, design and operating parameters on the formation of diesal spray are discussed. In these studies, the spray is formed by injecting a calibrated amount of fuel into air with the frequency of the intermittent behavior controlled by the speed of the fuel pump. In this study, an injection cycle was tailored so that it was divided into several increments which were injected sequentially. A two mm diammeter collimated beam illuminated a cylindrical volume perpendicular to the axis of the fuel spray, and its attenuation was recorded and stored on the oscilloscope. With the optical measurement being synchronized to the needle lift of the injector, the output of the needle lift transducer and the optical signal was recorded simultaneously. Thus, the arrival and the duration of the spray at various positions along its axis were measured.

The droplet size distributions were obtained directly as penetration measurements were made. However, by applying a delay time through the synchronization feature of the sizer, information about droplet size evolution within the same spray was possible. Distribution widths are plotted as a function of time for different chamber pressures, injection pressures, different positions, and different fuels. Coagulation seems to be a dominant phenomenon in these studies.

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