Locally resolved investigation of the vaporization of GDI sprays applying different laser techniques

As an example for a highly developed technical spray system, the vaporization of isooctane fuel sprays of a gasoline direct-injection (GDI) multihole injector has been investigated in a heated injection chamber for different injection pressures and fuel temperatures ranging from 4 to 10 MPa and from 323 to 383 K, respectively. In this investigation, to the best of our knowledge for the first time, pure rotational coherent anti-Stokes Raman spectroscopy (RCARS) has been applied to the study of vaporizing sprays in combination with other laser techniques. Gas-phase temperatures inside the sprays have been determined with high spatial and temporal resolution by RCARS. Droplet sizes and number densities have been measured using phase-Doppler anemometry, and the correlation of these results with two-dimensional laser sheet Mie scattering images allows an improved interpretation of the spray vaporization process. In particular, it was found that a vaporization barrier exists in the spray front of the GDI sprays due to the large amount of droplets available at these locations, which leads to nearly the same vaporization-dependent temperature drop of about 30 K for all pressures and fuel temperatures studied.