Week 10 - Simulating Combustion of Natural Gas.
AIM:
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.
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.
APPROACH TO SOLVE THE PROBLEM:
to perform the simulation and get the results we have to process through the five steps. these five steps are very important and if we do any mistake it will affect the solution.
THE FIVE STEPS ARE :
- GEOMETRY PREPARATION USING THE SPACE CLAIM.
- MESHING USING THE ANSYS MESHER.
- PROBLEM SETUP USING ANSYS FLUENT.
- SOLVING USING THE ANSYS FLUENT.
- OBTAINING THE RESULTS USING THE CFD POST.
1.GEOMETRY PREPARATION USING THE SPACE CLAIM
- first we have to import the given geometry of the combustion chamber.
- to minimize the computational time and the complications we simplify the geometry of 3D into 2D.
- we choose the plane option and we click on the origin that creates the three perpendicular section planes.
- than we use the split tool to cut off the geometry.
- after than we have to obtain the we have to use combine tool to combine and make ita s the one plane geometry.
- this is the 2D geometry in which we have to perform the simulation.
- this is the simplest geometry that we can do sumulation on that and we can find similar results.
2.MESHING USING THE ANSYS MESHER.
3.PROBLEM SETUP USING ANSYS FLUENT. AND SOLVER REQUIREMENT
Setup :
- Perform mesh check.
- Enable Axisymmetric option in 2D space of general settings.
- Enable the energy model.
- Enable viscous model(we have used k-epsilon standard model).
- Enable the species transport model.
- Enable NOx model, also thermal and prompt NOx pathways.
- Set the boundaries, air inlet and fuel inlet.
- Set the solution method, initialize with hybrid initialization.
- Set the contours and simulate the problem.
Result :
- Create a plane and color it with various variables like species mass fraction, temperature.
- Create the line contour and analyze the changes in graph.
Post-processing details:
Part 1: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.
Conventional case
Convergence of iteration
NOX emission plot
Soot emission plot
Temperature distribution in volumetric domain
Line plot distribution at different section
Mass fraction of CH4 reacting species
Graphical variation of CH4 at different location of combustion chamber
Mass fraction of CO2 reacting species
Graphical variation of CO2at different location of combustion chamber
Mass fraction of H2O reacting species
Graphical variation of H2O at different location of combustion chamber
Mass fraction of N2 reacting species
Graphical variation of N2 at different location of combustion chamber
Mass fraction of O2 reacting species
Graphical variation of O2at different location of combustion chamber
Mass fraction of NOX pollutant
Graphical variation of NOX at different location of combustion chamber
Mass fraction of soot
Graphical variation of soot at different location of combustion chamber
Part 2:
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.
Percentage of water addition to fuel- 5%
Convergence of iteration
NOX emission plot
Soot emission plot
Temperature distribution in volumetric domain
Mass fraction of CH4 reacting species
Graphical variation of CH4 at different location of combustion chamber
Mass fraction of CO2 reacting species
Graphical variation of CO2at different location of combustion chamber
Mass fraction of H2O reacting species
Graphical variation of H2O at different location of combustion chamber
Mass fraction of N2 reacting species
Graphical variation of N2 at different location of combustion chamber
Mass fraction of O2 reacting species
Graphical variation of O2 at different location of combustion chamber
Mass fraction of NOX pollutant
Graphical variation of NOX at different location of combustion chamber
Mass fraction of soot
Graphical variation of soot at different location of combustion chamber
Case 2:
Percentage of water addition to fuel- 15%
Convergence of iteration
NOX emission plot
Soot emission plot
Temperature distribution in volumetric domain
Mass fraction of CH4 reacting species
Graphical variation of CH4 at different location of combustion chamber
Mass fraction of CO2 reacting species
Graphical variation of CO2at different location of combustion chamber
Mass fraction of H2O reacting species
Graphical variation of H2O at different location of combustion chamber
Mass fraction of N2 reacting species
Graphical variation of N2 at different location of combustion chamber
Mass fraction of O2 reacting species
Graphical variation of O2at different location of combustion chamber
Mass fraction of NOX pollutant
Graphical variation of NOX at different location of combustion chamber
Mass fraction of soot
Graphical variation of soot at different location of combustion chamber
Case 3:
Percentage of water addition to fuel- 30%
Convergence of iteration
NOX emission plot
Soot emission plot
Temperature distribution in volumetric domain
Mass fraction of CH4 reacting species
Graphical variation of CH4 at different location of combustion chamber
Mass fraction of CO2 reacting species
Graphical variation of CO2at different location of combustion chamber
Mass fraction of H2O reacting species
Graphical variation of H2O at different location of combustion chamber
Mass fraction of N2 reacting species
Graphical variation of N2 at different location of combustion chamber
Mass fraction of O2 reacting species
Graphical variation of O2 at different location of combustion chamber
Mass fraction of NOX pollutant
Graphical variation of NOX at different location of combustion chamber
Mass fraction of soot
Graphical variation of soot at different location of combustion chamber
Comparison between conventional case and water added fuel case:
The table shows the comparison between various combustion products after analysis
|
Combustion product |
Conventional case |
Fuel+water-5% |
Fuel+water-15% |
Fuel+water-30% |
|
Temperature |
2.312e3 |
2.301e3 |
2.27e3 |
2.229e3 |
|
Mass fraction of CH4 |
1 |
0.95 |
0.85 |
0.7 |
|
Mass fraction of CO2 |
0.1428 |
0.1423 |
0.1411 |
0.1386 |
|
Mass fraction of H2O |
0.1204 |
0.123 |
0.1507 |
0.3 |
|
Mass fraction of N2 |
0.77 |
0.77 |
0.77 |
0.77 |
|
Mass fraction of O2 |
0.23 |
0.23 |
0.243 |
0.241 |
|
Mass fraction of NOX |
4.212e-4 |
3.394e-4 |
2.083e-4 |
8.167e-5 |
|
Mass fraction of soot |
6.482e-2 |
5.419e-2 |
3.75e-2 |
1.989e-2 |
From the above comparison table, we can find that small addition of water in fuel plays an important role in pollution control and less production of nox and soot material. Emission of nox and soot are potentially harmful to environment and human health. The general observation from the combustion analysis tells that the level of nox and soot decreases with increase in water content inside fuel. The temperature also decreases at the outlet section due to this factor. Among all the cases 30% addition of water content inside fuel is found to be best and also supports the claim to reduce the pollutants effectively and increase the life span of engine.
Conclusions:
- A two step methane air mixture is followed by nox and soot modelling which predicts the amount of pollutants at the outlet.
- With appropriate addition of water, the reduction of pollutants at the outlet is obtained.
- The CFD predicted analysis supports the claim to reduce the pollutant at the outlet with certain of fuel water mixture.