Experimental study of flash boiling spray vaporization through quantitative vapor concentration and liquid temperature measurements

• Published in: Experiments in fluids Vol. 55; no. 8
• Main Authors: Zhang, Gaoming, Hung, David L. S., Xu, Min
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2014; Springer
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Engines and turbines; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fluid dynamics; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Instrumentation for fluid dynamics; Multiphase and particle-laden flows; Nonhomogeneous flows; Physics; Research Article; Internal Combustion Engine; Spray Plume; Vapor Concentration; Liquid Temperature; Boiling Condition; Flash evaporation; Two phase flow; Motor fuel injection; Laser induced fluorescence; Calibration; Experimental study; Liquid fuel; Test facility; Liquid vapor interface; Heat mass transfer; Internal combustion engine; Multiple jet; Pulverized fuel
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-014-1804-7

Flash boiling sprays of liquid injection under superheated conditions provide the novel solutions of fast vaporization and better air–fuel mixture formation for internal combustion engines. However, the physical mechanisms of flash boiling spray vaporization are more complicated than the droplet surface vaporization due to the unique bubble generation and boiling process inside a superheated bulk liquid, which are not well understood. In this study, the vaporization of flash boiling sprays was investigated experimentally through the quantitative measurements of vapor concentration and liquid temperature. Specifically, the laser-induced exciplex fluorescence technique was applied to distinguish the liquid and vapor distributions. Quantitative vapor concentration was obtained by correlating the intensity of vapor-phase fluorescence with vapor concentration through systematic corrections and calibrations. The intensities of two wavelengths were captured simultaneously from the liquid-phase fluorescence spectra, and their intensity ratios were correlated with liquid temperature. The results show that both liquid and vapor phase of multi-hole sprays collapse toward the centerline of the spray with different mass distributions under the flash boiling conditions. Large amount of vapor aggregates along the centerline of the spray to form a “gas jet” structure, whereas the liquid distributes more uniformly with large vortexes formed in the vicinity of the spray tip. The vaporization process under the flash boiling condition is greatly enhanced due to the intense bubble generation and burst. The liquid temperature measurements show strong temperature variations inside the flash boiling sprays with hot zones present in the “gas jet” structure and vortex region. In addition, high vapor concentration and closed vortex motion seem to have inhibited the heat and mass transfer in these regions. In summary, the vapor concentration and liquid temperature provide detailed information concerning the heat and mass transfer inside flash boiling sprays, which is important for the understanding of its unique vaporization process.