MACROSCOPIC CHARACTERIZATION OF FLASH-BOILING MULTIHOLE SPRAYS USING PLANAR LASER-INDUCED EXCIPLEX FLUORESCENCE. PART II: CROSS-SECTIONAL SPRAY STRUCTURE

摘要

The cross-sectional fuel distribution of flash-boiling sprays from a multihole direct-injection gasoline injector was investigated by studying spray patterns under various superheated conditions. Planar-laser induced exciplex fluorescence was applied to image the spray liquid and vapor components separately. Fluorobenzene and diethyl-meihyl-amine were added into n-hexane as tracers for the vapor and liquid components, respectively. The effects of the fuel temperature and ambient pressure on macroscopic characteristics of the spray were thoroughly investigated. Results show that with increasing superheat degree, the spray gradually transforms from eight individual plumes into a single body structure. Comparing to liquid phase, the vapor phase is easy to transform and to collapse, which is consistent with the previous axial direction observations. However, the cross-sectional view of the flash-boiling spray reveals the process of the interaction among the individual plumes. As the superheated degree increases, the plumes expand to joint together annually. Then the fuel redistributes to form a new plume in the location between the adjacent plumes, which is the result of the strong plume-to-plume interaction that could finally cause the spray collapse.