Combustion using Eddy Dissipation in Ansys Fluent

COMBUSTION:-

• Combustion is a high temperature exothermic chemical reaction, between fuel and oxygen that produce oxidized, often gaseous product in a mixture termed as smoke.
• Combustion doesn\'t always result in fire, but when it does, a flame is a characteristics in the indicator of reaction.

`C_xH_y + zO_2 + 3.77zN_2 rightarrow xO_2+frac{y}{2}H_2O+3.77zN_2`

• Although, in presence of fuel and oxygen fire is not created. It also require spark to ignite as I.C. Engine to take place for combustion as shown in above diagram.

POSSIBLE TYPES OF COMBUSTION SIMULATION:-

• Based on mixing

1. Non - Premixed combustion
2. Premixed combustion
3. Partially Premixed combustion

• Based on phase

1. Fluid phase
2. Wall
3. Particle Surface
4. Porous region

BASED ON MIXING:-

1. Non-Premixed Combustion:-(Diffusion)

• In non-premixed combustion, fuel and oxidized enter the reaction zone in distinct stream.
• This is in contrast to premixed system, in which reactant are mixed at the molecular level before burning.
• Example:- Non-Premixed combustion include methane combustion, pulverised coal furance and diseal internal combustion engine.

2. Premixed Combustion:-

• In premixed combustion, fuel and oxidized are mixed at the molecular level prior to ignition combustion occur as a flame frone propogating into the ubrunt reactant.
• Example:- Premixed combustion include aspired internal combustion engine, lean premixed gas turbine combustor and gas leak explosion. Carburetor is used to mix the fuel and air before combustion separately.

3. Partially Premixed Combustion:-

• Partially Premixed combustion system are premixed flame with non uniform fuel oxidizer mixture.
• Such flame include premixed jet discharge into a quiescent atmosphere, lean premixed combustor with diffusion pilot flame and cooling jet and imperfectly mixed inlet.

BASED ON PHASE:-

1. Fluid:-

• Theoretical information about species transport and finite rate chemistry as related to volumetric reaction are presented in the fluid phase.
• The rate of transport of the species or particle is dervied from the single fluid flow field.
• The local concentration of species or particle may affect the flow field itself.
• The species transport equation is given by the concentration of the chemical spieces is c.

2. Wall:-

• For gas phase reaction, the reaction rate is defined on a volumetric basis and the rate of creation and destruction of chemical species becomes a source term in the species conservation equation.
• Heterogenous surface reaction create source of chemical species in the gas phase as well.
• But also alter surface converge for surface site reaction and may deposit for bulk reaction.

3. Particle:-

• Defining multiple particle surface reaction to model the surface combustion of combusting discrete phase particle.
• This section provide a theortical background of particle surface reaction
• Reaction on surface are reaction in which at least one of the step of the reaction mechanism is the adsorption of one or more reactant.
• The mechanism of these reaction and the rate equation are of extreme importance for heterogenous catalyst.

4. Porous Region:-

• The porous region model can be used for a wide variety of single phase and multiphase problem, including flow through packed beds, filter paper peforated plate, flow distributor and tube banks.
• When you use this model, you define a cell zone in which the porous media is applied and the pressure loss in the flow is determined with the help of input.

GEOMETRY:-

Given 3D Geometry

• Although we cannot see the combustion phenomenon in 3 D geometry, thus we have to convert this 3 D geometry into the 2 D geometry
• Firstly, the body is present in three different component we need to combine them and then by split body we need to split it in face as shown in below figure.

Above figure we can perform simulation for combustion

MESH:-

Mesh Method:- All Triangular Method

Mesh Size:- 0.7 mm

Number of Element:- 289684

Zoom View for Mesh in which proximatority is Yes and number of Nodes is 3

NAMED SELECTION:-

SETUP:-

Geometry:-

1. Solver- Pressure Based
2. Time- Steady State
3. 2 D space - Axisymmetry
4. Gravity - Off

Model:-

1. Energy - On
2. Viscous - K Epsilion - Standard
3. Species

• Model - Species Transport
• Reaction - Volumetric Reaction
• Chemistry Solver - Explicit Source
• Option - Inlet Diffuser , Diffuser Energy Source
• Mixture Material - Methane air
• Turbulance - Chemistry Interaction - Eddy Dissipation

Boundary Condition:-

1. Air Inlet- Velocity Inlet (0.5 m/s), Thermal (300 K), Species (`O_2`=0.23 remaining all remain zero)
2. Fuel Inlet - Velocity Inlet (80 m/s), Thermal (300 K), Species(`CH_4`=1 remaining all remain zero)

Method:-

1. Scheme - Coupled
2. Initialization - Hybrid
3. Number of Iteration - 1000

RESIDUAL:-

From the above residual plot we can say that the solution is covergence after 300 iteration. Hence, we have convergence solution at 300 iteration.

TEMPERATURE CONTOUR:-

2 D view for temperature contour

TEMPERATURE ANIMATION:-

VOLUME RENDERING:-

Isometric view for Temperature contour in Volume Rendering

VELOCITY:-

2 D view of velocity

EDDY VISOCITY:-

2 D view of Eddy Viscosity

TURBULANCE KINECTIC ENERGY:-

2 D view of Turbulance Kinectic Energy

TURBULANCE EDDY DISSIPATION:-

2 D view of Turbulance Eddy Dissipation

LINE METHOD:-

Lines has been set at location 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7

Line Method view

Mass fraction of `CO_2`:-

2 D view for Mass fraction of `CO_2`

Plot for Mass Fraction `CO_2`

Mass fraction of `CH_4`:-

2 D view for Mass Fraction of `CH_4`

Plot for Mass Fraction of `CH_4`

Mass Fraction of `H_2O`

2 D view for Mass Fraction of `H_2O`

Plot for Mass Fraction of `H_2O`

Mass Fraction of `O_2`:-

2 D view for Mass Fraction of `O_2`

Plot for Mass Fraction of `O_2`

Mass Fraction of `N_2`:-

2 D view for Mass Fraction of `N_2`

Plot for Mass Fraction of `N_2`

Mass Fraction for `NO_x`:-

• In this simulation, the mass fraction of `NO_x` was not generated.
• Nitrogen is high ionization enthalpy, which means that it does not react with other species.
• The mass formed form the Nitrogen is in very small and negligble quantity.
• If `NO_x` compound less, the combustion process is more efficient.
• To obtain mass fraction of `NO_x`from the simulation, we need to \'on\' the `NO_x`model as shown in below figure.

Model view of `NO_x` model

Mass Fraction of Pollutant NO:-

2 D view for Mass Fraction of Pollutant NO

Plot for Mass Fraction of Pollutant NO

Mass Fraction of Pollutant `N_2O`:-

2 D view for Mass Fraction of Pollutant `N_2O`

Plot for Mass Fraction of Pollutant `N_2O`

CONCLUSION:-

• This combustion simulation is done by Eddy Dissipation model.
• The maximum temperature attained by the system is 2309.97 K and maximum velocity is 88.88 m/s.
• The mass species depend upon how effectively the combustion takes place. This can observed by comparing mass fraction of `CO_2 and H_2O`.
• Any we can see the emission of `NO_x`is low for methan air mixture. From this we can conclude that Methane is an Eco-Friendly Gas.