Visualization of the evaporation of a Diesel spray using combined Mie and Rayleigh scattering techniques

Abstract- Evaporating Diesel sprays are studied by laser Rayleigh scattering measurements in an optically accessible high-pressure/high-tempera-ture cell that reproduces the thermodynamic con-ditions which exist in the combustion chamber of a Diesel engine during injection. n-Decane is injected into the vessel using a state-of-the-art near-production three-hole nozzle. Global images of the distributions of the liquid and vapor phases of the injected fuel are obtained using a combined schlieren and Mie scattering setup. More details about the evaporation are revealed when the spray is illuminated by a laser light sheet: laser light can be scattered by molecules in the gas phase (Rayleigh scattering) or comparably large fuel droplets (Mie scattering). The former is seen in regions where the fuel has completely evaporated, and the latter is dominant in regions with high droplet concentrations. Studying the polarization of the signal light allows the distinction of three different regions in the spray that are character-ized by a moderate, low or negligible concentra-tion of liquid fuel droplets. The characteristics of fuel evaporation are investigated for different ob-servation times after the start of injection, cham-ber conditions and injection pressures. For quantitative measurements of fuel concentra-tions, a calibration method that uses propane as a reference gas is presented and tested. At high am-bient temperatures, the accuracy of the concentra-tion measurements is limited by pyrolysis of the fuel molecules