performing a Combustion Simulation on a combustor model using ANSYS FLUENT

• 600 iterations were made to run the calculation.

OBJECTIVE:

To perform a combustion simulation on the combustor model and plot the variation of the mass fraction of different species.

Possible types of combustion simulation in FLUENT:

Based on Mixing:

1.Non-Premixed combustion:

A non-premixed combustion occurs when the fuel and oxidizer are not mixed prior to reacting. An example of this is the diffusion flame is Lighter. Lighter fuel is typically compressed butane which is liquid inside the lighter canister, but rapidly expands to gas once released from the lighter nozzle. The concentration of the butane near the nozzle is too high for combustion, and the flame cannot form until it mixes with the surrounding air. Diffusion flames are typically much cooler than premixed flames as the mixing step limits the overall combustion.

2.Premixed combustion:

In premixed combustion, fuel and oxidizer are mixed at the molecular
level prior to ignition. Combustion occurs as a flame front propagating into the unburnt reactants. Examples of premixed combustion include aspirated internal combustion engines, lean-premixed gas turbine combustors, and gas-leak explosions.

3.Partially-premixed combustion:

Partially premixed combustion (PPC), also known as PPCI (partially-premixed compression ignition) or GDCI (gasoline direct-injection compression-ignition) .It is a modern combustion process used in IC Engines of automobiles and other motorized vehicles in the future. Its high specific power, high fuel efficiency and low exhaust pollution. A PPC engine injects and premixes a charge during compression stroke. Thus premixed charge is too lean to ignite during the compression stroke, the charge will ignite after the last fuel injection ends near Top dead centre. The fuel efficiency and working principle of a PPC engine resemble those of diesel engine.

Based on phase:

4.Fluid phase:

If the combustion takes place in the fluid phase,then this is said to be Volumetric reaction.

5.Wall:

If the combustion takes place at wall surface,then this is said to be surface reaction.

6.Particles (surface reaction):

Langragian particles in which reaction takes place. for example: coal combustion-Combustion of the coal is at the heart of the boiler. The mass release and the heat release due to coal combustion must be known in both space and time in order to calculate the heat transfer to the walls.

7.Porous region:

Reaction which takes place at porous region.

For this project we are going to simulate a non-premixed combustion model

METHODOLOGY:

1.GEOMETRY-SPACECLAIM:

fig.3D model geometry

fig,2D model for calculation

• 3D model will lead to high computational cost and time.Therefore,we converted into 2D geometry for easier simulation.

2.MESH:

fig.Named Selections

fig.Mesh

• Mesh element size-2 mm
• Triangle method.
• capture proximity turned on.

3.SETUP:

• Solver:pressure based,steady,axisymmetric(2D space).
• Model: viscous:K-epsilon,standard wall function.
• Energy equation turned on
• Species:
• Boundaries: Air_inlet- velocity :0.5 m/s , Temperature:300k , species: `ounderset2()`=0.23. Fuel_inlet-velocity :80 m/s,Temperature:300k,species:`CHunderset4()`=1.pressure outlet-zero gauge pressure.
• Hybrid initialization
• 600 iterations were made to run the calculation.

4.SOLUTION:

1.Residual plot:

• solution is converged at 105 iteration.

2.Temperature contour:

3.Temperature contour with line probe to estimate the mass fraction at different location along x axis.

• Yellow colour line indicates line probe which is marked at x=0.1m,0.3m,0.5m,0.7m from the origin.

4.Mass fraction plot for CH4:

5.Mass fraction plot for O2:

6.Mass fraction plot for CO2:

7.Mass fraction plot for H2O:

8.Mass fraction plot for N2:

9.Mass fraction plot for NO:

SOLUTION ANIMATION:

RESULT AND INFERENCE:

From the solution we see that,

• Maximum temperature reaches upto 2309K.
• mass fraction of O2 at near inlet it goes upto 0.23 and it reduces as we go along x axis.This is because O2 molecule is burnt over there.
• In CH4 mass fraction plot , it decreases from 1 to 0 along Y axis.
• H2O and CO2 shows wavy plots,This is because mass fraction is high at centre of the flame.
• Near the inlet region the NO plot shows lower value value(apprx 0.0005) but as we move along x axis,mass fraction further reduces and it becomes nearly zero after x=0.7m.
• N2 mass fraction values ranges between 0.68-0.78 for all the line probes.
• mass fraction of the pollutant produce lesser value than rest of the species.

CONCLUSION:

Performed the combustion simulation of a combustor model and plotted the results.