Challenge on Combustion

Aim

Perform a combustion simulaion on a combustor model and plot the mass fraction of the different species at different line prob.

Objective:

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. 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.

What is Combustion

Combustion, or burning is a high-temperature exothermic redox chemical reaction between a fuel(the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion doesn't always result in fire, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining.

Combustion of an organic fuel in air is always exothermic because the double bond in O₂ is much weaker than other double bonds or pairs of single bonds, and therefore the formation of the stronger bonds in the combustion products CO2 and H2O results in the release of energy.The bond energies in the fuel play only a minor role, since they are similar to those in the combustion products; e.g., the sum of the bond energies of CH₄ is nearly the same as that of CO2. The heat of combustion is approximately −418 kJ per mole of O₂ used up in the combustion reaction, and can be estimated from the elemental composition of the fuel.

Governing equations

• Continuity equation

The general continuity equation is written as follows:

`frac{partialrho}{partialt}+bar(nabla).(rho barv) =S_m`

Where S_m is a mass source from the discrete phase due to evaporation of droplets.

• Momentum equation

`frac{partial}{partialt}(rhobarv)+bar(nabla).(rho barv barv) =-barnablap+bar nabla.bar tau+barF`

Here p is the static pressure, τ ̅ is the stress tensor and F ⃗ is a body force due to interaction of the discrete phase with the continuous phase and/or a user-defined momentum source. The gravity term in the momentum equation is neglected because of the minimal contribution compared to the high momentum injection event.

• Energy equation

`frac{partial}{partialt}(rhoE)+bar(nabla).(barv(rhoE+p)) =-bar(nabla).[(k+k_t) bar nablaT-sumh_ibarJ_i+(bartau.barv)]+S_e`

Where the term in the square brackets on the right hand side consists of energy transfer due to conduction, species diffusion and viscous dissipation, respectively. S_e is a user-defined energy source. Energy E is defined as follows:

`E=h-frac{p}{rho}+frac{barv.barv}{2}`

Herein h is the enthalpy for ideal gases, and is written as a summation of mass fraction times species enthalpy:

`h=sumY_jh_j`

The enthalpy is calculated by integrating the specific heat from to the instantaneous temperature T, whereby the reference temperature in fluent is 298.15K:

—Species transport equation

In spray simulations there are at least two different species, one species is in the gas phase (oxidizer) and another one is injected (fuel), which after evaporation goes into the gas phase where it can mix with the oxidizer. The Transport equation for the ith species is as follows:

frac{partial}{partialt}(rhoY_i)+frac{partial}{partialx_j}(rho u_jY_i)=frac{partial}{partialx_j}(rho D_i)frac{partialY_i}{partialx_j}+R_i+S_i

S_i is again a source from the liquid droplet phase that is activated when evaporation occurs. Also user-defined sources are included in this term. Species transport due to diffusion is calculated via the diffusion flux `barJ_i`. For turbulent flows this flux is:

Geometry Preparation

• In step one, we first of all import the geometry files into space claim. This is the 3d geometry of the combustor.

• To reduce the computational effort we convert this 3D geometry into 2D. For this first of all creating the plane xy-plane, then we choose the spilt body option and after that we select the desire body and then we cut the desire body.

• we follow the same procedure for the inner two bodies, which are displayed in the below pictures. In the below, i cut the inner cylinder.

• In the below pic i cut the most inner cyliner.

• After that we cut the remaining part of the geometry

Meshing

Case-setup

• Steady state analysis
• we are taking the 2D axis symmetirc geometry
• Solver type:pressure based
• Velocity formulation:absolute
• Viscous model: Standard-K-epsilon model

Near wall treatment : scaleable wall function.

• Mixture Material: Methane-air
• Model: Species transport

The ith species mass fraction transport equation is

`frac{partial}{partialt}(rhoY_i)+frac{partial}{partialx_j}(rho u_jY_i)=frac{partial}{partialx_j}(rho D_i)frac{partialY_i}{partialx_j}+R_i+S_i`

• The mass fraction of the species i is `Y_i`.
• The velocity is u_j.
• D_i is the diffuion coefficient.
• R_i is the reaction source term. Chemicals are modelled as a source term in the species transport equation.
• S_includes all the sources.

Equation of methane combustion is

`CH_4+2(O_2+3.78N_2)rarr CO_2+2H_2O+7.56N_2`

• Turbulence Chemistry Interactions

• Eddy dissipation
• Reactions: Volumetric
• Enable inlet diffusion and energy Source

• Boundary Conditions:

• At the air inlet, we specify the velocity to be 0.5 m/s and set the mass fraction of O2 species is 0.23.
• In fuel inlet the velocity is taken as 80 m/s so that the high velocity the fuel can be sparyed to a large spread inside. The CH4 species mass fractions is set to 1.
• At the outlets we are taking the 0 gauge pressure
• At the wall, we are taking the 300K temperature.
• Use the Hybrid initialization.
• Run for the 600 iterations.

Results

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.

Residuals

Temperature Contours

In the temperature contours we observe that red colour shows that there is high temperature and combustion takes place here. But blue colour shows that this the non-reaction zone, that's why temp is not high here.

Mass Fractions of CO2

In the above contour of CO2, we observe that red colour shows the intensity of CO2. Aftert a distantance of 0.3 m intensity of CO2 is increased which is easily observed in the above image. Behaviour of CO2 shows the good gareement because the C02 formed after the fuel exit from nozzle.

Mass Fractions of H2O

In the above contour of H2O, we observe that red colour shows the intensity of H2O. Aftert a distantance of 0.3 m intensity of H2O is increased which is easily observed in the above image. Behaviour of H2O shows the good gareement because the H20 formed after the fuel exit from nozzle.

Mass Fractions of CH4

In the above contours we easily observe that near the nozzle intensity of Ch4 is more because at this point fuel is exit.

Mass Fractions of N2

Behaviour of N2 also shows a good agreement because except the fuel inlet everywhere is N2.

Mass Fractions of O2

In the above contours blue colour shows that there is a fuel and red colour shows that there is concentration of O2. Behaviour of the above contours also shows a good agreement.

Mass Fractions of NOx emissions

After the air-fuel burning NOx also formed. Red colour shows the concentration of the pollutant NO.

Mass Fractions of soot formation

In the above image, we easily observed that soot also formed but the concentration of soot formation is too small.

Variation of the Mass fraction of the different species in the simulation using the line probes at different locations of combustors

Line probes

Lines are created at a distance of the following values from the origin(left side)

Line 1 = 0.1

Line 2 = 0.2

Line 3 = 0.3

Line 4 = 0.4

Line 5 = 0.5

Line 6 = 0.6

Line 7 = 0.7

Mass Fractions of CO2

In the above graph we saw the concentration of CO2 at different locations.

• Series1 shows the concentration of CO2 at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CO2 increased and after that 0.01m it is going to decrease and concentration of CO2 goes smooth.
• Series2 shows the concentration of CO2 at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CO2 increased and after 0.019m it is going to decrease and after that concentration of CO2 goes smooth.
• Series3 shows the concentration of CO2 at the 0.3m location at x-axis and observe the trend change along y-direction.. Trend of this curve shows that initially concentration of CO2 increased and after 0.019m it is going to decrease and after that concentration of CO2 goes smooth.
• Series4 shows the concentration of CO2 at the 0.4m location at x-axis at x-axis and observe the trend change along y-direction.. Trend of this curve shows that initially concentration of CO2 increased and after 0.02m it is going to decrease and after that concentration of CO2 goes smooth.
• Series5 shows the concentration of CO2 at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CO2 increased and after 0.01m it is going to decrease and after that concentration of CO2 goes smooth.
• Series6 shows the concentration of CO2 at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CO2 increased and there is no too much decreasing behaviour shows in this curve. Because at this region formation of CO2 are high.
• Series7 shows the concentration of CO2 at the 0.7m location at x-axis at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CO2 increased and there is no too much decreasing behaviour shows in this curve. Because at this region formation of CO2 are high.
• Series8 shows the concentration of CO2 at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CO2 increased and there is no too much decreasing behaviour shows in this curve.

Mass Fractions of H2O

In the above graph we saw the concentration of CO2 at different locations.

• Series1 shows the concentration of H2O at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of H2O increased and after that 0.01m it is going to decrease and concentration of H2O goes smooth.
• Series2 shows the concentration of H2O at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of H2O increased and after 0.019m it is going to decrease and after that concentration of H2O goes smooth.
• Series3 shows the concentration of H2O at the 0.3m location at x-axis and observe the trend change along y-direction.. Trend of this curve shows that initially concentration of H2O increased and after 0.019m it is going to decrease and after that concentration of H2O goes smooth.
• Series4 shows the concentration of H2O at the 0.4m location at x-axis at x-axis and observe the trend change along y-direction.. Trend of this curve shows that initially concentration of H2O increased and after 0.02m it is going to decrease and after that concentration of H2O goes smooth.
• Series5 shows the concentration of H2O at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of H2O increased and after 0.01m it is going to decrease and after that concentration of H2O goes smooth.
• Series6 shows the concentration of H2O at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of H2O increased and there is no too much decreasing behaviour shows in this curve. Because at this region formation of H2O are high.
• Series7 shows the concentration of H2O at the 0.7m location at x-axis at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of H2O increased and there is no too much decreasing behaviour shows in this curve. Because at this region formation of H2O are high.
• Series8 shows the concentration of H2O at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of H2O increased and there is no too much decreasing behaviour shows in this curve.

Mass Fractions of CH4

In the above graph we saw the concentration of CH4 at different locations.

• Series1 shows the concentration of CH4 at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 decreased and after that concentration of CH4 goes smooth.
• Series2 shows the concentration of CH4 at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 decreased and after that concentration of CH4 goes smooth.
• Series3 shows the concentration of CH4 at the 0.3m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 decreased and after that concentration of CH4 goes smooth.
• Series4 shows the concentration of CH4 at the 0.4m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 decreased and after that concentration of CH4 goes smooth.
• Series5 shows the concentration of CH4 at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 almost zero because all the mass of fuel are evaporated.
• Series6 shows the concentration of CH4 at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 almost zero because all the mass of fuel are evaporated.
• Series7 shows the concentration of CH4 at the 0.7m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 almost zero because all the mass of fuel are evaporated.
• Series8 shows the concentration of CH4 at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of CH4 almost zero because all the mass of fuel are evaporated.

Note

Spontaneously decrease of CH4 shows that all the mass are going to decreased.

Mass Fractions of N2

In the above graph we saw the concentration of N2 at different locations.

• Series1 shows the concentration of N2 at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of N2 increased and after that 0.02m concentration of N2 goes smooth.
• Series2 shows the concentration of N2 at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of N2 increased and after that concentration of N2 goes smooth.
• Series3 shows the concentration of N2 at the 0.3m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of N2 increased and after that concentration of N2 goes smooth.
• Series4 shows the concentration of N2 at the 0.4m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of N2 increased and after that concentration of N2 goes smooth.
• Series5 shows the concentration of N2 at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of N2 increased and after that concentration of N2 goes smooth.
• Series6 shows the concentration of N2 at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no more change in the concentration of N2. Because at this region every where is N2.
• Series7 shows the concentration of N2 at the 0.7m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no more change in the concentration of N2. Because at this region every where is N2.
• Series8 shows the concentration of N2 at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no more change in the concentration of N2. Because at this region every where is N2.

Mass Fractions of O2

In the above graph we saw the concentration of O2 at different locations.

• Series1 shows the concentration of O2 at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of O2 increased and after that 0.02m concentration of O2 goes smooth.
• Series2 shows the concentration of O2 at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of O2 increased and after that concentration of O2 goes smooth.
• Series3 shows the concentration of O2 at the 0.3m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of O2 increased and after that concentration of O2 goes smooth.
• Series4 shows the concentration of O2 at the 0.4m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of O2 increased and after that concentration of O2 goes smooth.
• Series5 shows the concentration of O2 at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of O2 increased and after that concentration of O2 goes smooth.
• Series6 shows the concentration of O2 at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no more change in the concentration of O2. Because at this region every where is O2.
• Series7 shows the concentration of O2 at the 0.7m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no more change in the concentration of O2. Because at this region every where is O2.
• Series8 shows the concentration of O2 at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no more change in the concentration of O2. Because at this region every where is O2.

Mass Fractions of NOx emission

In the above graph we saw the concentration of NO at different locations.

• Series1 shows the concentration of NO at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of NO are less and almost thers is no formation of NO.
• Series2 shows the concentration of NO at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that formation of NO are started here.
• Series3 shows the concentration of NO at the 0.3m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that concentration of NO are increased as compared to the series-2.
• Series4 shows the concentration of NO at the 0.4m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that concentration of NO are also increased more as compared to the series-3.
• Series5 shows the concentration of NO at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that formation of NOx are too much high here as compared to the others curves.
• Series6 shows the concentration of NO at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that formation of NOx are now going to decrease as compared to the series-5.
• Series7 shows the concentration of NO at the 0.7m location at x-axis at x-axis and observe the trend change along y-direction. Trend of this curve shows that formation of NOx are now going to decrease as compared to the series-6.
• Series8 shows the concentration of NO at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that formation of NOx are now going to decrease as compared to the series-7.

Mass Fractions of soot

In the above graph we saw the concentration of soot at different locations.

• Series1 shows the concentration of soot at the 0.1m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of soot increased and after 0.057m it is going to decrease.
• Series2 shows the concentration of soot at the 0.2m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of soot increased and after 0.057m it is going to decrease.
• Series3 shows the concentration of soot at the 0.3m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that initially concentration of soot increased and after 0.078 it is going to decreased.
• Series4 shows the concentration of soot at the 0.4m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that there is no increase of soot formation.
• Series5 shows the concentration of soot at the 0.5m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that the formation of soot is almost zero.
• Series6 shows the concentration of soot at the 0.6m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that the formation of soot is almost zero.
• Series7 shows the concentration of soot at the 0.7m location at x-axis at x-axis and observe the trend change along y-direction. Trend of this curve shows that the formation of soot is almost zero.
• Series8 shows the concentration of soot at the 0.8m location at x-axis and observe the trend change along y-direction. Trend of this curve shows that the formation of soot is almost zero.

Results

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.

Why NOx and soots should be reduced

Nitrogen oxides (NOx) are poisonous gases derived from nitrogen and oxygen combustion under high pressure and temperatures. NOx is composed of nitric oxide (NO), and a smaller percentage of more poisonous nitrogen dioxide (NO2).

NOx has direct and indirect effects on human health. It can cause breathing problems, headaches, chronically reduced lung function, eye irritation, loss of appetite and corroded teeth. Indirectly, it can affect humans by damaging the ecosystems they rely on in water and on land—harming animals and plants. In Britain alone, known NO2 emissions have been estimated to kill 23,500 people every year, according to aerosol science professor Ian Colbeck of the University of Essex, southeastern England.

Note

• All the geometry and mesh settings are same. Only change occur is that we have to increase the percentage water with fuel, the boundary condition for fuel changes.
• To simplify the process, we can set input parameter for the percentage of water and CH4.
• To view the change in the NOx and soot emission, we can set the output parameters of the mass fraction.

Parametric table

Results Discussion

In this parametric study, we observe that the adding the water in CH4, formation of NOx are decresed but the formation of soots are increasd. Formation of NOx are decreased because water has the more capacity to carry the heat.

NOx contours results for different percentage of water

0% addition of water

Mass fraction of NOx emission

5% addition of water

10% addition of water

15% addition of water

20% addition of water

25% addition of water

30% addition of water

NOx graphs for different percentage of water

0% addition of water

5% addition of water

10% addition of water

15% addition of water

20% addition of water

25% addition of water

30% addition of water

soots contours results for different percentage of water

0% addition of water

5% addition of water

10% addition of water

15% addition of water

20% addition of water

25% addition of water

30% addition of water

Soots graphs for different percentage of water

0% addition of water

5% addition of water

10% addition of water

15% addition of water

20% addition of water

25% addition of water

30% addition of water

Conclusion

• In this challenge we analyze the combustion process and also oberved the concentarion of different species which participate in this combustion process and also species formation after the combustion process and during the process.
• Near the inlets mass fraction of O2 is vary from 0 to 0.23 as gone higher along the y-axis. But after X=0.3 it goes decreases. This shows that O2 molecules are burnt over there.
• For CH4, the fuel inlet is from origin. The mass fraction of CH4 decreases from 1 to 0 along the y-axis. Far from the inlets it burnt very low but not completely burnt.
• Both CO2 and H2O have the simillar trend.
• We are observing that as we add the water content in the fuel. we can see that formation of NOx gets reduced.
• All the contours and graphs are shown a good agreement of results behaviour.