Week 10 - Simulating Combustion of Natural Gas.
Aim:
- Perform a combustion simulation on the combustor model.
Case 1:
- Plot the variation of the mass fraction of the different species in the simulation using line probes at different locations of the combustor and to plot for CO2, H2O, CH4, N2, O2, NOx emissions & Soot formation.
Case 2:
- Add the water content in the fuel from 5% to 30% by mole and observe the effect of it on the results.
Description:
1. COMBUSTION
- Combustion is defined as achemical reaction in which a hydrocarbon reacts with an oxident to form products, accompanied by the release of energy in the form of heat.
- Combustion manifests as awode domain during the design, analysis, and performance characteristics stage by being an integral part of various engineering applications like internal combustion engines,furnaces and power station conbustors.
2. Conbustion model for CFD Analysis
- Comptational fluid dynamics modeling of combustion calls upon the proper selection and implementation of model suitable to faithfully represent the complex physical and chemical phenomenon associated with any combustion process.
- The model should be competent enough to deliver information related to the species concentration, theri volumetric generation or destruction rate and changes in the parameters of the system like enthalpy, temperature and mixture density.
- The model should be capable of solving the general transport equations for fluid flow and heat transfer as well as additional equations of combustion chemistry and chemical kinetics incorporated into that as per the simulating environment desired.
3. Possible types of Combustion Simulation possible in Ansys Fluent
The simulation of combustion can be divided into two types-
Combustion based on Mixing
- Non-Premixed Combustion
- In non-premixed combustion, fuel and oxidizer enter the reaction zone in distinct streams.
- It occours during direct injection or late injection of fuel in IC engines.
- Examples of non-premixedcombustion includes pulvarized 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 flames front propagating into the unburnt reactants.
- Examples of premixed combustion include aspirated internal combustion engines, lean- premixed gas turbine combustors, and gas-leak explosions.
- Partially Premixed Combustion
- Partially premixed combustion systems are premixed flames with non-uniform fuel-oxidizer mixtures(equivalence ratios).
- Such falmes include premixed jets discharging into an inert atmosphere, lean premixed combustors with difussion pilot fames and cooling air jets, and imperfectly mixed inlets.
Combustion based on Phase
- Fluid Phase (Volumetric Reactions)
- Combustion takes place in the fluid region.
- Wall (Surface Reactions)
- Combustion takes place on the wall or a solid surface.
- Particles ( Surface Reactions)
- Combustion takes place on the Lagrangian particles.
- Combustion of coal is an example of particle combustion.
- Porous Region
- Combustion takes place in a porous region.
- The reactions in an after-treatment system is am example of combustion in the porous regions.
Simulation procedure:
- Open Ansys Drag ansys fluent to the main window of thw software.
- Go to geometry to import/create the geometry. Change the 3d axismetry geometry to 2d surface for further analys.
- Then go to the mesh select and name the edges such as " Air inlet, fuel inlet, wall, axis, outlet" respectively.
- Then select the required body to be mesh enter the appropriate mesh size then generate the mesh.
- After the meshing go to the setup to setting up the solver and change the boundary condition and select the species model,NoX model and soot model as required.
Solver:
Species model:
NoX model:
Soot model:
BOundary conditions;
Air inlet:
Fuel inlet:
- Then initialize the simulation with hybrid type and enter the iteration number then run the simulation.
- After that create required contours and go to the post processing to get appropriate plots.
- Repeat the same process with different water content in fuel for case 2.
Results:
Case 1:
Residual:
Temperature distribution:
CH4 mass fraction:
Co mass fraction:
Co2 mass fraction:
H2o mass fraction:
N2 mass fraction:
O2 mass fraction:
NoX mass fraction:
Soot mass fraction:
Animation:
https://drive.google.com/file/d/110z1yxbJN6jjd0TG4HuH-f3g8q_dvDYs/view?usp=sharing
Charts:
The charts shows that the variation of the mass fraction of the different species in the simulation at different locations of the combustor.
CH4 mass fraction chart:
Co mass fraction chart:
Co2 mass fraction chart:
H2o mass fraction chart:
N2 mass fraction chart:
O2 mass fraction chart:
NoX mass fraction chart:
Soot mass fraction chart:
Case 2:
i) CH4 - 95 %
H2o - 5%
Residual:
Temperature distribution:
CH4 mass fraction:
Co mass fraction:
Co2 mass fraction:
H2o mass fraction:
N2 mass fraction:
O2 mass fraction:
NoX mass fraction:
Soot mass fraction:
CH4 mass fraction chart:
Co mass fraction chart:
Co2 mass fraction chart:
H2o mass fraction chart:
N2 mass fraction chart:
O2 mass fraction chart:
NoX mass fraction chart:
Soot mass fraction chart:
ii) CH4 - 90%
H2o - 10%
Residual:
Temperature distribution:
CH4 mass fraction:
Co mass fraction:
Co2 mass fraction:
H2o mass fraction:
N2 mass fraction:
O2 mass fraction:
NoX mass fraction:
Soot mass fraction:
CH4 mass fraction chart:
Co mass fraction chart:
Co2 mass fraction chart:
H2o mass fraction chart:
N2 mass fraction chart:
O2 mass fraction chart:
NoX mass fraction chart:
Soot mass fraction chart:
iii) CH4 - 80 %
H2o - 20%
Residual:
Temperature distribution:
CH4 mass fraction:
Co mass fraction:
Co2 mass fraction:
H2o mass fraction:
N2 mass fraction:
O2 mass fraction:
NoX mass fraction:
Soot mass fraction:
CH4 mass fraction chart:
Co mass fraction chart:
Co2 mass fraction chart:
H2o mass fraction chart:
N2 mass fraction chart:
O2 mass fraction chart:
NoX mass fraction chart:
Soot mass fraction chart:
iv) CH4 - 70 %
H2o - 30%
Residual:
Temperature distribution:
CH4 mass fraction:
Co mass fraction:
Co2 mass fraction:
H2o mass fraction:
N2 mass fraction:
O2 mass fraction:
NoX mass fraction:
Soot mass fraction:
CH4 mass fraction chart:
Co mass fraction chart:
Co2 mass fraction chart:
H2o mass fraction chart:
N2 mass fraction chart:
O2 mass fraction chart:
NoX mass fraction chart:
Soot mass fraction chart:
