Combustion on methane-air mixture analyze by ANSYS Fluent

Combustion process:

      Combustion is a chemical process or a reaction between a fuel (Hydrocarbon) and oxygen. When fuel and oxygen react it releases the heat and light energy. Heat and light energy then result in the flame. The combustion process takes place inside the cylinder.

Example: Hydrobcarbon + Oxygen = Heat energy

In this challenge, we are using the methane+air mixture.

Possible types of combustion simulation in Fluent:

• Based on mixing

  Non-premixed combustion (Direct injection, Late injection)

In this type of simulation, the mixing of fuel with air takes place at the combustion chamber. This type of combustion is suitable for diesel engine combustion.  

  Premixed combustion (Carburetor)

In this type of simulation, the mixing of fuel with air takes place before the combustion chamber. This type of combustion is suitable for petrol engine combustion. 

  Partially premixed

In this type of simulation, the mixing of fuel and air is partially mixed before entering into the combustion chamber.

• Based on phase 

  Fluid phase (Volumetric reactions)

In this case, the volumetric reaction takes place. The example of this reaction is direct injection combustion.

  Wall (Surface reactions)

In this case, the surface reaction takes place. The example of this reaction is evaporation.

  Particles(surface reaction)

In this case, the surface reaction takes place. The example of this reaction is coal combustion.

  Porous region 

This type of reaction takes place above the high-pressure drop region.

Geometry: 

cut section:

   The above figure shows the cut section of the combustion chamber. The left side fuel and air enter, the right side is the pressure outlet. 

Mesh details:

Element size = 2.5 mm

Element order is Quadratic 

Capture proximity enabled and the gap between no of cells is 3

No. of elements = 10930

No. of nodes = 33989 

Solving:

Reaction equation for combustion metahane- air mixture:

Materials:

Methane-air mixture 

Thermal conductivity = 0.0454 w/m.k

Viscosity = 1.72 e-5 Kg/ m.s

Mass diffuity = 2.88 e-5 m^2/s

Solving method:

Time = Steady

Type = Pressure based

Mixture material = methane-air

Initialization method = Hybrid

Turbulence model = k-epsilon (2eq)

Species model = Eddy dissipation model

Boundary conditions:

Air inlet 

Velosity =0.5 m/s

Temperature = 300 k

Mass fraction of O2 =0.23

Fuel inlet:

Velocity = 80 m/s

Temperature = 300 k

Mass fraction of CH4 =1

Results:

Residuals:

     The solution is converged after 7600th iterations.

Temperature plot:

     The maximum temperature reaches the methane-air mixture is 2300K.

Co2 mass fraction factor:

H2O mass fraction factor:

CH4 mass fraction factor:

N2 mass fraction factor:

O2 mass fraction factor:

NOx mass fraction factor:

Temperature animation of methane-air mixture:

Conclusion:

1. Comparing the above results of all the mass factor NO emission is less 0.03.