Combustion Simulation of Methane and Oxygen using ANSYS FLUENT

Types of Combustion Simulations

1. Based On Mixing
2. Based On Phase

Based On Mixing

• Non-premixed Combustion

In non-premixed combustion, fuel and oxidizer enter the reaction zone in distinct streams. This is in contrast to premixed systems, in which reactants are mixed at the molecular level before burning. Examples of non-premixed combustion include pulverized coal furnaces, diesel internal-combustion engines and pool fires.

• 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.Premixed combustion is much more difficult to model than non-premixed combustion. The reason for this is that (subsonic) premixed combustion usually occurs as a thin flame that is stretched and contorted by turbulence.

• Partially Premixed

Partially premixed combustion systems are premixed flames with nonuniform fuel-oxidizer mixtures (equivalence ratios). Such flames include premixed jets discharging into a quiescent atmosphere, lean premixed combustors with diffusion pilot flames and/or cooling air jets, and imperfectly mixed inlets.

Based On Phase

• Fluid Pase

This is the combustion when it takes places in the fluid phases.

• Wall

The combustion which take place near the walls.

• Particle

When the combustion take places in the lagrangian particles.

• Porous Region

The combustion which take places in the pressure drop region

Objective

To perform a combustion simulation on the combustor model.

Chemical Reaction

CH₄[g] + 2 O₂[g] -> CO₂[g] + 2 H₂O[g] + energy

Geometry

Above is the 2D geometry of the combustion model.

Mesh

The mesh has an element size of 1mm which has 34610 elements with Triangle Method.

Residuals

Above the is residual plot for all the spieces in the reactions.

Post Processing

There are 6 Line Probes are placed at a distance of 0.025 m.For the NOx mass fraction plane there are 8 probes with similiar equidistance placing.

Methane Mass Fraction

From the above plot we can see the methane mass fraction. The maximum mass fraction is at the inlet which is equal to 1 and begins to reduce as it moves forward.The chart can clearly show that the mass fraction of methane begins to reduce.

Oxygen Mass Fraction

The above plot shows the oxygen mass fraction.As same as the methane mass fraction the oxygen mass fraction is high concentartion is at the inlets which is 0.25 but as the oxygen begins to mix the mass fraction starts to decrease slowly and it yields to almost zero mass fraction. This can be viewed in the chart below.

Carbondioxide Mass Fraction

Once the reation is complete the one of the by-product is carbondioxide.The mass fraction is about 0.1424 between line 5 and line 6. And its falls to 0.1338 till the outlet.We can see that from the chart.

Water Mass Fraction

Another by-product of the reaction is water. The water mass fraction can be seen heavily after line 5 but it is formed from line 1 but mass fraction is very low about 0.0819 but after line 5 mass fraction is about 0.11696 which can be seen in the chart.

Nitrogen Mass Fraction

We can see the nitrogen mass fraction is high at the inlet of about 0.7706 and it drops to 0.6516. This means that some part of nitrogen has taken part in the reaction.The concentation of nitrogen mass fraction stays 0.6516 till the outlet.This changes can be seen in the charts clearly.

Temperature

We can see the maximum temperature of 2216 K which means the combustion has taken place. But as the temperature decreases gradually from 2216 K to 1760 K. We can see the chart with temperature variation.

Nitric oxide Mass Fraction

We can that NOx mass fraction is almost zero meaning that the formation possible but its concentration very much negligible.Highest concentration was about 0.000394.

Conclusion

• We can see that large amount of carbondioxide amount is released as the product of the reaction between methane and oxygen.
• NOx formation is possible but it is insignificant amount.
• Temperature reached as high of 2216K.