Loading...

Study of the Effects of Mass Fraction and Flow Velocity Fluctuations on Diffusion Flame

Khosousi, Ali | 2009

1161 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40069 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Farshchi, Mohammad
  7. Abstract:
  8. In this work, the unsteady response of a laminar diffusion flame to harmonic mass fraction oscillations and also to flow velocity fluctuations is investigated. Flame-sheet assumption is utilized to model the laminar unsteady two-dimensional co-flow diffusion flame mathematically. The initial combustion of most combustion chambers is through diffusion mechanism. Therefore, developing analytical model of diffusion combustion is of great importance. The flow is assumed subsonic (incompressible), inviscid, and uniform. The convection-diffusion equation for conserved scalar variable with appropriate boundary conditions is solved. Considering stoichiometric mass fraction surface to be the flame surface, it is possible to obtain the flame zone. In addition, different types of flame structures and transition from overventilated flame to underventilated flame are studied. Assuming that unburnt species have not passed across the flame surface and that the diffusion coefficient is constant, heat release rate can be considered proportionate to flame area. This method, for the first time in this work, is applied to diffusion flames to calculate heat release rate. Heat release rate oscillations, in the form of flame response function to fuel mass fraction fluctuations, flow velocity perturbations, and the simultaneous fluctuations of mass fraction and flow velocity, for the first and the second modes are acquired. At each Peclet number, frequency domain is divided into three regions, diffusion-dominant region, convection-diffusion region, and convection-dominant region. The obtained results indicate that the magnitude of response function decreases as excitation frequency increases. While phase difference approaches a constant value. As Peclet number increases, the amplitude of heat release rate oscillations, in diffusion-dominant region and convection-diffusion region, increases, but it does not vary significantly in convection-dominant region
  9. Keywords:
  10. Excitation Frequency ; Diffusion Flame ; Mass Fraction ; Flame Structure ; Heat Release Rate

 Digital Object List

  • محتواي پايان نامه
  •   view

 Bookmark