Liquid/Vapour Visualization of Common Rail Diesel Sprays in Different Ambient Conditions with Visible and UV Laser Light Scattering and PLIF

In this paper UV-visible elastic light scattering and Planar Laser Induced Fluorescence (PLIF) have been applied for measuring the vaporization process of a diesel fuel in an optically accessible vessel at engine ambient conditions. The spray has been generated by an electronically controlled Common Rail injection system and emerged from an axial single-hole electroinjector, 0.18 mm in diameter (L/d = 5.55). The injected fluid has been a commercial Diesel fuel and a single strategy (1.0 ms in duration) has been implemented at the injection pressure of 60.0 MPa. The measurements have been carried out in a quiescent bomb filled with SF6 gas at pressures of 0.39 MPa and temperature ranging between 293 to 533 K. The ambient gas densities has varied from 12.64 kg/m3 to 23.0 kg/m3, equivalent to the diesel engine conditions between the Start of Injection (SOI) and the Start of Combustion (SOC). A Nd-YAG pulsed laser sheet has been used for excitation of the spray along its axis at two wavelengths: 532 and 355 nm; the sheet thickness and light pulse duration have been 0.10 mm and 12 ns, respectively. The scattered light has been collected and synchronized at different instant from the SOI. The comparison of the images of the fuel at different instant from the SOI has permitted the analysis of the spray characteristics in terms of tip penetration, cone angle and spray fragmentation. Elastic visible and UV scattering radiation have allowed investigations on the size of the droplets along a plane centered on the spray axis. Planar Laser Induced Fluorescence (PLIF) measurements on the same plane have been carried out exciting the droplets at 355 nm and collecting the light through an interference filter centered at 430 nm. PLIF has allowed a correlation between the liquid and the vapor structures of the jets in all the examined ambient conditions.