Combustion Simulation on the Combustor model using Ansys Fluent
Objective: Perform Combustion Simulation on the Combustor model using Ansys Fluent, plot the variation of the mass fraction of the different species and write a detailed report explaining the results obtained.
Question:
Part I
Perform a combustion simulation on the combustor model and plot the variation of the mass fraction of the different species’ in the simulation using line probes at different locations of the combustor as shown in Fig. You need to plot for CO2, H2O, CH4, N2, O2, NOx emissions & Soot formation.
Part II
As you must have observed from the above simulation, the Nox and soot is getting formed at the outlet of the combustor. Such formation has harmful effects on the environment and humans. The stringent government norms also demand the least formation of Nox and soot and to satisfy those requirements, you need to check the effect of adding the water in the fuel.
In this part, you need to add the water content in the fuel from 5% to 30% by mole and observe the effect of it on the results. It is necessary to provide line plots and contours to prove your claim.
You can use the parametric study approach if required.
Combustion:
Combustion is a process in which the fuel is oxidized and large amount of chemically bound energy is released. This energy heats the products and combustion of fuel such as methane with air leads to a flame temperature of around 1900 °C (2173 K). In the combustion of methane and air, the main products are carbon dioxide and water. However, the formation of these products is very complex and hundreds of different species such as H, O, OH, CH, CH3 etc are intermediated in the combustion process. Besides carbon dioxide and water, a large number of pollutants are formed as, for instance, nitorgen oxides, carbon monoxide and soot particles. The efficiency of the combustion process depends on several parameters, such as oxygen supply, temperature history and mixing properties.
Types of Combustion Simulations:
Based on Mixing:
Non Pre-mixed combustion: This type of combustion occurs when oxidizer and fuel mixture enters the reaction zone in distinct streams or not initially mixed. Example of such a case is diesel engine where the fuel is injected just before the combustion.
Pre-mixed Combustion : The fuel and oxidizer are mixed at molecular level before the combustion similar to a case in carburetor.
Partially Pre-mixed : Its in between non pre-mixed and pre-mixed combustion where the fuel and oxidizer are partially pre-mixed at non-uniform ratios before combustion.
Based on Phase:
Fluid Phase (volumetric): The combustion occurs in a fluid phase.
Wall (Surface Reaction) : Combustion occuring on a surface wall.
Particles (Surface Reaction) : Combustion occurs on surface particles. Example coal combustion.
Porous : Combustion occuring in a porous region.
Case Setup and Execution:
Geometry:
Geometry is imported to Ansys Space Claim.
3-D geometry is converted to 2-D by using sectional view and sketching on the required edges and 3-D components are suppressed for physics.
Named Selections:
Meshing:
Element size: 1mm
Nodes: 68322
Elements: 67418
Capture Curvature and Promixity is switched to yes as shown below.
Setup:
Solver Time:Steady state
Type: Pressure based
2D Space Type: Axisymmetric
Energy equation is enabled
Viscous Model: k-epsilon with standard and with Standard wall functions
Species Model:
Model Name:Species Transport
Reaction Type:Volumetric
Options:Turned on the Inlet Diffusion and Diffusion Energy sources
Turbulence-Chemical Interaction Name: Eddy Disipation
Nox and Soot species to be switched on.
Nox model:
Soot Model:
Boundary Conditions:
Air Inlet:
Inlet velocity: 80 m/sec
Inlet Temperature: 300 k
Species Mass fraction at the air inlet: O2 - 0.23.
Hybrid Initialization is used for initialization.
Simulation is run for 1000 iterations.
Part I:
Boundary Conditions:
Fuel Inlet:
Inlet velocity: 80 m/sec
Inlet Temperature: 300 k
Species Mass fraction at the fuel inlet: CH4 - 1.
Mixture Material: methane-air
Results:
Residuals:
Temparature Contour: Maximum Temparature- 2310K
Temparature Animation:
Mass Fraction Contour of CO2:
Mass Fraction Contour of H2O:
Mass Fraction Contour of CH4:
Mass Fraction Contour of N2:
Mass Fraction Contour of O2:
Mass Fraction Contour of NO:
Mass Fraction Contour of Soot Formation:
Lines are created at different locations in the direction of X-axis at 50mm, 100mm, 150mm, 200mm, 250mm for plotting graphs as shown below.
Mass Fraction chart of CO2:
Mass Fraction Chart of H2O:
Mass Fraction Chart of CH4:
Mass Fraction Chart of N2:
Mass Fraction Chart of O2:
Mass Fraction Chart of NO:
Mass Fraction Chart of Soot Formation:
Part II:
Parametric study is performed to analyse the effect of water addition (5% to 30% of mole fraction) to the fuel inlet.
Mixture Material: methane-air-2-step
Boundary Conditions:
Fuel Inlet:
Inlet velocity: 80 m/sec
Inlet Temperature: 300 k
Parametric study Table:
Results:
DP0:
Residuals:
Temparature Contour: Maximum Temparature- 2310K
Mass Fraction Contour of NO:
Mass Fraction Contour of Soot Formation:
Mass Fraction Chart of NO:
Mass Fraction Chart of Soot Formation:
DP1:
Residuals:
Temparature Contour: Maximum Temparature- 2300K
Mass Fraction Contour of NO:
Mass Fraction Contour of Soot Formation:
Mass Fraction Chart of NO:
Mass Fraction Chart of Soot Formation:
DP2:
Residuals:
Temparature Contour: Maximum Temparature- 2280K
Mass Fraction Contour of NO:
Mass Fraction Contour of Soot Formation:
Mass Fraction Chart of NO:
Mass Fraction Chart of Soot Formation:
DP3:
Residuals:
Temparature Contour: Maximum Temparature- 2250K
Mass Fraction Contour of NO:
Mass Fraction Contour of Soot Formation:
Mass Fraction Chart of NO:
Mass Fraction Chart of Soot Formation:
DP4:
Residuals:
Temparature Contour: Maximum Temparature- 2230K
Mass Fraction Contour of NO:
Mass Fraction Contour of Soot Formation:
Mass Fraction Chart of NO:
Mass Fraction Chart of Soot Formation:
Conclusion:
- With the addition of water, the temperature of the gases at the outlet is decreased with the increase in % of water. The maximum Temparature observed is 2310k at DP0 where water percentage is 0.
- Latent heat absorption of water particle during the combustion will lower the temperature resulting in the reduction of Pollutant NO. So Pollutant NO emissions decrease with an increase in the addition of water.
- Temperature, CO2 and H2O have similar contours, which means that species mass fraction depends on the effective Combustion
- An oscillatory decrease is observed in the formation of soot particles in the order of DP2 > DP3 > DP4 > DP1 > DP0, the lowest valve observed is in DP0 where water percentage is 0.