STIMULATED RAMAN-SCATTERING OF FUEL DROPLETS - CHEMICAL CONCENTRATION AND SIZE DETERMINATION

The strong stimulated Raman scattering (SRS) from diesel fuel droplets has the potential of providing the relative concentration of multicomponent fuel and the absolute size of individual droplets. The morphology-dependent resonances (MDRs) of a sphere cause the droplet to act as an optical resonator which greatly lowers the SRS threshold. The number density, quality factor, and frequency shift of several MDRs are calculated as a function of the ratio of the index of refraction of the liquid and the surrounding gas, which approaches unity at the thermodynamic critical condition for the fuel spray. The SRS spectra of monodispersed droplets of toluene, pentane, Exxon-Aromatic-150, and Mobil D-2 are presented. The exponential growth region of the SRS intensity I1S as a function of the input laser intensity Iinput is investigated for the toluene carbon ring breathing mode v2 and the pentane C-H stretching region. The I1S ratio of toluene and pentane is measured as a function of the ratio of the toluene and pentane concentration for monodispersed droplets. The reduced fluctuation in I1S when Iinput is changed from multimode to single-mode is displayed as a histogram of the I1S of the v2 mode of toluene droplets. © 1990 Springer-Verlag.