Numerical Investigation of Flame Structure and Blow Out Limit for Lean Premixed Turbulent Flames Under Gas Turbine Condition

  • Saad Akhtar

Student thesis: Master's Thesis

Abstract

With the forecast of rise in the energy usage globally (Middle-East region in particular), it is imminent that the concentration of toxic emissions such as CO2 and NOx in the ecosystem will increase. One of several industrial techniques to mitigate the emission levels is lean premixed combustion. However, this mode of efficient combustion often leads to the problem of Lean Blow Out (LBO), which is the focus of current study. Considerable extinction studies have been carried out for turbulent non-premixed flames in the literature. On the other hand, numerical investigation of lean blow out in premixed turbulent flames is still scarce. The objective of this study is to predict the behavior of lean flames near extinction in a combustion chamber and estimate the lean blow out limits under high temperature and high pressure conditions. This aims to provide us with the key insights regarding the operational parameters which dictate the flame structure near blow out and lean blow out limits in turbulent premixed flames. A modified Flamelet Generated Manifold (FGM) combustion model is implemented in ANSYS FLUENT to predict the impact of operational parameters, such as pressure, preheat temperature, turbulence intensity at the inlet and inlet bulk velocity on flame position, temperature and emissions for lean premixed methane-air flames. The parametric studies on the lean premixed methane-air combustion show that turbulence intensity at the inlet significantly impact the position of the reaction zone. On the other hand, bulk velocity has a very minor impact on flame position and flame temperature. Increased combustor pressure results in an enhanced flame temperature for the same fuel energy input. NOx levels on the other hand turn out to be weakly dependent on combustor’s pressure. The numerically tuned combustion model was further applied to the extinguishing flames. Using the modified FGM model, the flame stability curve is reproduced within 20% of the experimental limit, which is a very important criteria for an efficient combustor design.
Date of AwardAug 2015
Original languageAmerican English
SupervisorTariq Shamim (Supervisor)

Keywords

  • Extinction
  • Lean Blow Out (LBO)
  • Lean premixed
  • Methane-air
  • Turbulence.

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