Combustion simulation of Methane
Introduction:
Combustion is a high-temperature exothermic chemical reaction between fuel and air. it produces a flame, heat and unburnt gases. Any combustion at high temperature in atmospheric air which contains 78% Nitrogen will create `NO_x`. In this challenge, The combustion is going to take place in the combustion chamber. The fuel mixture for the combustion is a methane-air mixture.
Possible types of Combustion simulation:
1) Based on Mixing:
i) Non-premixed combustion - In this type of combustion simulation, the mixing of fuel with air takes place at the combustion chamber. It can be called as Direct injection or late injection. This type of simulation is suitable for diesel engine combustion.
ii) Premixed combustion - In this type of combustion simulation, the mixing of fuel with air takes place before the combustion chamber. This type of simulation is suitable for the petrol engine where the air and fuel mixed at the carburetor.
iii) Partially premixed - In this type of combustion simulation, the fuel and air are mixed partially before entering into the combustion chamber.
2) Based on phase:
i) Fluid phase - The volumetric reaction takes place in the fluid region. The example is direct injection combustion.
ii) Wall - These are surface reactions. The example of this reaction is evaporation.
iii) Particles - These are also surface reactions. The example of this combustion is coal combustion.
iv) Porous region - These reactions take place above the high-pressure drop region.
Fig. Combustion Chamber
Fig. 2D Axi-symmetry view of Combustion chamber
Reaction equation for combustion Methane-Air mixture:
`CH_4+a_r*(O_2+3.76*N_2)->a*CO_2+b*H_2O+c*N_2`
The above reaction shows the reactants and products of the combustion of the Methane-Air mixture.
Mesh details:
Element size = 2.5 mm
Number of elements = 10960
Capture Proximity is enabled. The number of cells across the gap is 3.
Material properties:
Methane-air mixture:
Thermal conductivity = 0.0454 `W/(m*K)`
Viscosity = 1.72e-5 `(Kg)/(m*s)`
Mass diffusivity = 2.88e-5 `(m^2)/s`
Boundary conditions:
Air-inlet:
Velocity = 0.5 m/s
Temperature = 300 K
Mass fraction of `O_2` = 0.23
Fuel-inlet:
Velocity = 80 m/s
Temperature = 300 K
Mass fraction of `CH_4` = 1
Outlet:
Pressure-outlet
Pressure = 0 Pa (Relative)
Models:
1) Viscous model - k-epsilon (Turbulence model)
2) Species model - Species model with Volumetric reactions
Eddy dissipation model ( Turbulence - chemistry interaction)
Solution method: Pressure-Velocity coupling
The above details are used to simulate the combustion of methane-air mixture in the combustion chamber.
Results:
1) Residual graph:
The solution has been converged after the 500th iteration.
2) Temperature contour:
The maximum temperature reached by this methane-air mixture combustion is 2310.03 K.
3) `CH_4` Mass fraction contour:
4)
From the above chart, the mass fraction of methane gets reduced at different lengths of the combustor.
5) `CO_2` Mass fraction contour:
6)
From the above chart, The mass fraction of `CO_2` gets increased at different lengths of the combustor.
7) `H_2O` Mass fraction contour:
8)
From the above chart, the mass fraction `H_2O`of gets increased at different lengths of the combustor.
9) `N_2` Mass fraction contour:
10)
From the above chart, the mass fraction `N_2`of gets increased at different lengths of the combustor.
11) `O_2` Mass fraction contour:
12)
From the above chart, the mass fraction `O_2`of gets reduced at different lengths of the combustor.
13) NO mass fraction contour:
14)
`NO_x` emission can be obtained by enabling the Thermal `NO_x` model. From the above chart, the mass fraction of NO gets increased at different lengths of the combustor. But the amount of emission of NO was very less comparatively other combustion products.
Combustion Animation video:
Conclusions:
1) The mass fraction of combustion reactants and products have been calculated at different lengths of the combustor.
2) The emission of NO was comparatively very lower than other combustion products.