Characterization of Droplets and Vapor Concentration Distributions in Split-Injection Diesel Sprays by Processing UV and Visible Images(<Special Issue>Recent Combustion Technology in Internal Combustion Engines)

Recent experimental studies have shown that with split injection strategy, the soot and NO_x emissions from a diesel engine can be reduced significantly in comparison with a conventional non-split injection. To understand the mechanism of emissions reduction, it is essential to clarify the process of mixture formation in the diesel spray. For characterizing the droplets and vapor concentration distributions inside a fuel spray, a dual-wavelength laser absorption-scattering technique (LAS) was developed by using the 2nd harmonic (532 nm) and the 4th harmonic (266 nm) of an Nd : YAG laser and using dimethylnaphthalene as a test fuel. By applying the ultraviolet-visible LAS imaging technique, the distributions of droplets and vapor concentrations in the spray, which was injected into a high-temperature and high-pressure nitrogen ambient in a constant volume vessel by a common-rail diesel injection system, were measured and quantitatively analyzed. The effect of injection mass ratio of double-pulse injections on distributions of equivalence ratios of vapor and droplets in the sprays was examined.