Study On Interactions Between Gas Liquid Two Phases And Jet Spray In Effervescent Sprays

Fuel injection and atomization have an important impact on engine performance.Effervescent spray has the characteristics of being able to achieve good atomization at low pressure and low gas consumption, and is insensitive to liquid viscosity and structure geometric parameters. Therefore, the effervescent spray has a good application prospects in internal combustion engine, steam turbine, incinerator, and other fields.The effervescent atomizer was set as the research object in this dissertation, and the gas-liquid two-phase mixing patterns, the gas-liquid flow behavior in the exit orifice region, the influence of the gas-liquid flow regimes on the spray, and the effect of gas expansion disturbance on the jet breakup, the time-frequency characteristics of spray acoustic, and the spray unsteadiness were researched. The fundamental research could be contributed to deepen the atomization mechanism of effervescent spray, and providing important theoretical and experimental basis for the study of effervescent spray technique.The structure design together with the structural geometric parameters of the visual effervescent atomizer was carried out on the basis of existing structures and geometric parameters from the relevant research at home and abroad. The designed effervescent atomizer was of good exchanging and adjusting capabilities, and could achieve a satisfied visual observation function. The gas-liquid flow patterns, the spray shape and parameters, and the processing methods of the spray acoustics were presented in the effervescent spray experiments.The gas-liquid two-phase flow pattern together with its, influencing factors, and the gas-liquid mixing shape features under churn and bubbly flow in the mixing chamber were experimentally studied by the visual effervescent spray system. The bubble generation simulation model and the gas-liquid two-phase flow simulation model were established. On this basis, the bubble generation, detachment and their influencing factors, the temporal and spatial distribution characteristics of the gas void fraction, and the flow structural features were studied. The influence laws of different conditions on the gas-liquid flow regimes, the gas-liquid mixing shape features under specified flow regimes, the bubble evolution law, the bubble detachment mechanism,and the temporal and spatial distribution of flow parameters under different flow regimes in the mixing chamber were determined clearly.The simulation model of gas-liquid two-phase flow in the exit orifice of effervescent atomizer was established. Based on this, the development of gas-liquid flow shape under different flow regimes and single bubble shape in the exit orifice region, and the pulsating characteristics of the flow parameters at the exit orifice section were studied. The bubble expansion potential energy release of single bubble through exit orifice was analyzed by the energy statistical method. The gas-liquid fow features of different flow regimes in the exit orifice, the bubble shape evolution mechanism during its expansion, elongation and rupture in the exit orifice, and the flow parameters' pulsating characteristics under different flow regimes at the exit section of the orifice were clarified.The spray shapes of different gas-liquid flow regimes in the atomizer were experimental studied by the visual effervescent spray system. The droplet distribution characteristics in the spray field of different flow regimes were studied by simulation method. Then, a novel simulation method based on the gas-liquid flow regimes of effervescent spray and atomization was proposed. The variation law of spray shape together with its pulsation characteristic, and the droplet distribution features in the spray field of different flow regimes were determined clearly.The experimental study on the effect of gas expansion disturbance on jet shape was carried out by the visual effervescent spray system. The simulation model of the jet and gas contained liquid filament breakup considering gas expansion disturbance were established. Through the study, the jet breakup law and the shape evolution feature of gas contained liquid filament breakup under the effect of gas expansion disturbance were clarified.A novel method was put forward to study the effervescent spray by the time-frequency analysis on spray acoustic signal. The spray acoustical characteristics under specified flow regimes, the amplitude fluctuation characteristic of acoustic signal, the acoustic energy influences, and the spray unsteadiness influences were carried out by the AOK time-frequency spectrum and HHT spectrum method. Based on the research, a quantitative evaluation method of effervescent spray unsteadiness based on the HHT spectrum energy of the spray acoustic was proposed. The relationship between the gas-liquid flow pattern and the time-frequency spectrum of the effervescent spray acoustic signal was clarified, the influencing factors together with influence laws on spray unsteadiness were determined clearly.