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Analytical and Experimental Investigation of Spray Flame Front in Bidirectional Vortex Flow

Dehghani, Saeed Reza | 2009

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 39818 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saidi, Mohammad Hassan; Mozafari, Ali Asghar; Ghafourian, Akbar
  7. Abstract:
  8. Vortex engine has shown to be a credible substitute in thermal power and aerospace industries mainly due to their advantages such as better mixing, improved combustion, and considerable cooled walls of combustion chamber. The engine geometry and tangential inlet oxidizer create inner and outer vortices rotating in the same angular direction. The inner vortex moves from head to the end of engine in the axial direction and outer vortex moves in the opposite direction. In the vortex engine, vortices affect spray droplets and force them to have a spiral path and apply a centrifugal force on the droplets to push them towards sidewall. Also axial relative velocity of droplets and flow filed act as a counter-direction force against spray axial penetration. Axial and radial forces influence directly axial penetration and radial dispersion of spray. Droplet resident time and vaporization rate as well as spray characteristics may be varied by changing swirl intensity and axial velocity in bidirectional vortex flow field. In this work governing equations of droplets motion and vaporization relations in the form of nonlinear, coupled, and second order ODE are solved by a numerical scheme. Numerical results predict azimuthal and radial velocity of droplets Also vaporization rate and life time of droplets and the longitudinal droplets movement before complete vaporization will be found. An optimum value of radial dispersion and complete vaporization of the droplets provides to the favorite case. In addition, effective length of one-dimensional combustion chamber in a dilute monopropellant spray located in a constant area chamber is analytically predicted. This method can be used in the design of combustion chambers with optimum length. Spray equation and distribution function in one-dimensional coordinate, and in direction of coordinate axis provide a new analytical solution to predict the effective length of chamber. In this approach, non-zero initial velocity of oxidizer is defined as a new variable affecting the chamber length. The present research shows importance of some influential parameters. According to the results, increasing initial velocity of oxidizer increases the effective chamber length. An adjustable chamber length equipped with inlet oxidizer line, pressurized fuel vessel, gas analyzer, and exhaust ventilation system which is run in both axial and vortex mode, is used in the experimental rig. Results show that extra dispersion of spray can not improve the combustion quality. Also spray dispersion should be limited to inner vortex, which is a hot and high velocity zone, to reduce unburned hydrocarbon in the combustion products. Experimental results of the effect of increasing inlet velocity on effective chamber length are compared with corresponding theoretical values. The comparison shows acceptable compatibility between trend of theoretical prediction and experimental results.

  9. Keywords:
  10. Swirling Flow ; Two Phase Flow ; Vortex Combustion Chamber ; Axial Combustion Chamber ; Spray Combustion

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