本研究以水及空氣為工作流體，針對剪切式同軸噴注器(shear coaxial injectors)之幾何結構(面積比)及噴注速度(速度比)對霧化效果的影響作為研究目標。主要觀察霧化角(spray angle)、SMD粒徑分布(droplet size distribution)、二維質量機率分布(2D Mass probability distribution)及均勻度(Patternation Index, P.I.)隨參數之變化；實驗採用(1)正面噴霧流場影像、(2) Malvern粒徑分析及(3) PLIF光學觀測等三種不同方式觀測霧化現象：從實驗結果顯示，霧化角受氣體動力作用力之影響，會隨著氣體流速增加而擴張，而氣層厚度的增加則使得霧化液滴受氣層包覆作用而縮減霧化角。SMD粒徑分布則隨氣/液體速度比增加而粒徑減小，且因液滴持續之空氣動力不穩性，下游區域粒徑較上游端為小；而氣層厚度增加，則因氣層對液滴提供更具持續性之剪切力，其霧化液滴粒徑亦明顯減小。而PLIF觀察之液滴二維質量機率分布顯示隨著速度比增加及氣層厚度增加，其霧化液滴分布均勻度亦隨之增加。

This research focused on the characterization of the sprays from water/air coaxial injectors. The spray angle, droplet size, and the mass distribution pattern were analyzed by images from digital camera, Malvern droplet size analyzers and PLIF techniques, respectively. Experiments at various velocity ratios (540) and different thickness of the annular air flows were conducted. The results showed that the spray angles increased with increasing air velocities as well as velocity ratios. With thicker annular air flows, the spray angles were smaller because of the increasing constrain from the air flow to the droplets. For droplet size observation, the SMD of water droplets decreased with increasing velocity ratio and down stream distance for the effect of aerodynamic instability. With thicker annular air flows, the SMD of water droplets were smaller because of the increase of the continuous interaction between high speed air flow and water droplets. The uniformities or patternation index (P.I.) of droplet mass distributions analyzed by PLIF were shown to increase with air/water velocity ratio as well as the thickness of the annular air flow of the coaxial injector.

參考文獻
[1]Lefebvre, A. H, “Atomization and Spray”, Hemisphere Publishing Corporation, pp3-60, 1989

[2]Weber, C., “On the Disruption of Liquid Jets”, Math. Mech., Vol. 11, pp. 136, 1931

[3]Vigor Yang, Mohammed Habiballah, Michael Popp ,”Liquid Rocket Thrust Chambers: Aspects of Modeling, Analysis, And Design” , AIAA, pp.201-260, 2004

[4]Mayer, W. O. H., “Coaxial atomization of a round liquid jet in a high speed gas stream: A phenomenological study”, Experiments in Fluids, Vol.16, pp 401-410, 1994

[5]Mayer, W. O. H., Branam, R., “Atomization characteristics on the surface of a round liquid jet”, Experiments in Fluids, Vol.36, pp. 528-539, 2004

[6]Matthew P. Juniper and Sebastien M. Candel, “The stability of ducted compound flows and consequences for the geometry of coaxial injectors”, Journal of Fluid Mechanics, Vol. 482, pp. 257-269, 2003

[7]Lasheras, J. C., Hopfinger, E. J., “LIQUID JET INSTABILITY AND ATOMIZATION INA COAXIAL GAS STREAM”, Annu. Rev. Fluid Mech. Vol. 32, pp. 275–308, 2000

[8]Lasheras, J. C., Villermaux E. and Hopfinger, E. J., “Break-up and Atomization of a Round Water Jet by a High-Speed Annular Air Jet”, Journal of Fluid Mechanics, Vol. 357, pp. 351-379, 1998

[9]Baoe Yang and Micale Oschwald, “Atomization and Flames in LOX/H2 and LOX/CH4 Spray Combustion”, Journal of Propulsion and Power, Vol. 23, No. 4, 2007

[10]Gautam, V., Gupta, A. K., ”Cryogenic Flow and Atomization from a Coaxial Injector”, Journal of Propulsion and power, Vol. 25, No. 1, 2009
[11]Gorokhovski, M., Jouanguy J. and Chtab-Desportes, A., “Stochastic model of the near-to-injector spray formation assisted by a high-speed coaxial gas jet”, Fluid Dynamics Research, Vol.41, 2009
[12]Ji-Hyuk Im, Insang Moon, “Comparative Study of Spray Characteristics of Gas-centered and Liquid-Centered Swirl Coaxial Injectors”, Journal of Propulsion and Power, Vol. 26, No.6, 2010

[13]Ferraro, M., Kujala, R. J., Thomas, J.-L., Glogowski, M. J. and Micci, M. M., “Effects of GH2/LOX Velocity and Momentum Ratios on Shear Coaxial Injector Atomization”, Journal of Propulsion and Power, Vol. 18, No. 1: Technical notes, 2001

[14]Soltani, M.R., Ghorbanian, K., Ashjaee, M., Morada, M.R., “Spray characteristics of a liquid–liquid coaxial swirl atomizer at different mass flow rates”, Aerospace Science and Technology, Vol.9, pp.592–604, 2005

[15]Engelbert, C., Hardalupas, Y. and WhiteLaw, J. H., “Breakup Phenomena in Coaxial Airblast Atomizers”, Proc. R. Soc. Lond. A., Vol.451, pp 189-229, 1995

[16]Dombrowski, N. and Johns, W. R. , “The Aerodynamics Instability and Disintegration of Viscous Liquid Sheets”, Chemical Engineering Science, Vol. 18, pp. 203-214, 1963.