Flame Simulation

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Flame Simulation

• By Chi Chau Chi Chau -_-!!

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Flame Simulation

• Bunsen Burner Model

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Bunsen Burner Model

• The Bunsen burner is a simple experimental
  configuration that avoids many complications of
  modern gas turbine combustors such as complex
  fluid mechanics and high levels of turbulence.
• The flame is stabilized by a delicate balance
  between heat-loss and fluid mechanical strain.
• The flame is surrounded by a shroud of dilution
  air that affects the burning.

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Purpose of the Bunsen Burner Model

• The purpose is to shows that global
  chemiluminescence measurements can be modeled and
  understood using simple physical principles
  without detail information about the exact
  burning process.

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Modeling Approach

• Left illustration of Bunsen burner flame
• Right actual photograph of Bunsen flame

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Model

• Bunsen burner flame model

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Model Cont

• Some elements of the real flame are carried over
  to the model.
• Some simply ignore.
• The Bunsen flame curvature is the most
  significant aspect neglected in the model.

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Model Cont

• The cone is divided into differential segments.
• The flame element is defined by its location
  relative to the burner rim both in terms of
  height and radius.
• The location of the flame element defines the
  heat-loss from the flame as well as the
  equivalence ratio of the incoming mixture for the
  element.

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Model Cont

• The local heat-lost together with the local
  equivalence ratio determine the burning rate for
  the element via calculations using the 1-D
  premixed flame program PREMIX.
• The local burn-rate is integrated over the entire
  cone to obtain an overall burn-rate.

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General Equation

• This is the general form for the integration for
  some quantity F distributed over the surface
• F takes the place of the mass flow-rate per unit
  area which is either heat-release rate per unit
  area or chemiluminescence power per unit area)

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Equation

• In our model calculations the flame base is kept
  constant.
• The height of the flame is determined by
  iteration.
• The experimental flame has a specific fuel
  flow-rate

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Model Components

• Relationship between different element and all
  other flame relevant quantities must be obtain to
  provide closure for the model.
• The model will translate position into both
  heat-loss and local equivalence ratio using a low
  order approximation of the heat-transfer and
  mixing observed in the flame.
• Some flame-related quantities like burn-rate will
  performed using PREMIX.

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Mixing Model (Components)Semi-empirical

• Here is the equation for mixing between co-flow
  of air, main premixed fuel and air stream exists.
• ?1 represents the leanest equivalence ratio at
  the edge of the flame, b is a parameter governing
  how evenly the equivalence ratio increase from ?1
  to the main stream equivalence ratio ?0, which is
  always constant 30. hch is the height at which
  the main stream equivalence ratio is reached.

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Heat-loss Model (Components)Semi-empirical

• Heat-loss from the Bunsen burner flame is by
  radiation and conduction.
• Here is the equation for heat-loss by radiation
  and conduction.
• Tflame stands for flame temperature
• Trim stands for temperature of the burner rim,
  which is the major heat sink
• ? conductivity is always 0.04 W/(m-K)
• dst is the stand-off distance of the edge of the
  flame
• Tsink radiation sink constant 298K

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PREMIX 1-D flame

• We use PREMIX to calculate the flame result
• Remember hest-loss and local equivalence ratio
  determine all other flame variables such as local
  burn-rate, flame temperature and such before it
  goes to PREMIX.
• Moreover, burner flow-rate is related directly to
  heat-loss.

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Result from PREMIX

• Flame temperature as a function of heat-loss
• Note Flame temperature is most sensitive to
  heat-loss at lower equivalence ratios

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Result from PREMIX

• Flame speed as a function of heat-loss
• Flame speed directly related to burn-rate per
  unit area

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Last step before RESULT

• Now we have obtained parameters from mixing
  model, heat-loss model, experimental flow-rate
  60cc/sec of air, equivalence ratio of .90 from
  PREMIX and some constants value

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Modeling Result

• Compare modeling result and experimental data
• This model predict the general trend with
  equivalence ratio.

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Reference

• http//scholar.lib.vt.edu/theses/available/etd-031
  42001-144036/unrestricted/11Chapter_7.pdf