Challenge on Combustion

Theory:

A large percent of worldwide energy conversion processes are based on combustion.

Because chemical kinetics are highly nonlinear, turbulence–chemistry interactions should be taken into account to accurately predict
turbulent reacting flows. Fluid dynamics software from ANSYS offers a wide range of turbulence–chemistry interaction models of
various complexities suitable for almost every turbulent reacting flow application.

Types of combustion simulations used:

Fast Chemistry
The eddy dissipation model (EDM), in combination with the finite rate chemistry model, allows accurate simulation of the heat
release and the distribution of the main chemical species for many industrial applications, such as gas turbines, internal combustion
engines, furnaces and thrusters.

Non-Premixed Combustion
With the non-premixed (or diffusion flame) model, the turbulence– chemistry interaction is described using an assumed shape of
probability density function (PDF). The thermodynamic state of the fluid, related to the mixture fraction and the chemistry is
calculated either from equilibrium or by using a tabulated steady flamelet approach. The non-premixed model offers a robust and fast
solution for any turbulent reacting flow that is at or near chemical equilibrium. This model is often used for gas turbine, process furnace
and IC engine applications.

Premixed and Partial Premixed Combustion
For a premixed flame, an additional transport equation is solved for the reaction progress variable, flame surface density or distance to
the flame front. The solution of this variable predicts the position of the flame front. For closure of the source term, ANSYS offers different
proven correlations related to the turbulent burning velocity. These correlations provide the best practical method to predict turbulent
premixed flames. In combination with the equilibrium or flamelet model, this approach is applicable to partially premixed and fully
premixed combustion.

Laminar Combustion

This model approximates the turbulent flame as a series of laminar flamelet regions concentrated just around the stoichiometric surfaces of

the reacting mixture.This model exploits the use of experimental data for determining relations between the variables considered like mass fraction,

temperature etc. The nature and type of dependence of the variables is predicted through experimental data obtained during laminar diffusion flame

experiment and laminar flamelet relationship is deduced based on the same.

Pollutant Formation Model
Pollutant species, such as NOx, SOx or soot, typically can be calculated by post-processing a combusting flow solution. ANSYS offers several
pathways to predict NOx formation in gas, oil and coal flames using thermal, fuel and prompt NOx mechanisms and to predict NOx
reduction via re-burning or selective non-catalytic reduction (SNCR). One- and two-step soot models are available; soot radiation can be
included in the simulation.

Depending on phase

In many applications, fuel is fed into the combustion chamber as a fluid or a solid. Examples are gasoline or diesel for internal combustion
engines or pulverized coal for power plants.

Fluid phase: When combustion takes place in fluid,For liquid spray fuels, the common assumption is that the liquid can be described with a Euler–Lagrange or Euler–Euler model, and that vaporization is complete before the actual combustion process starts.

solid phase:Combusting solid fuels generally undergo moisture evaporation and devolatilization followed by combustion of volatiles in the gaseous phase and heterogeneous gas–solid reaction of the char.

Depednding on region:

Wall: Combustion taking place at the walls

Particles: Combustion on surface of particle

porous region:Combustion taking place inside the region

Geometry:

2d geometry was made in spaceclaim:

Mesh:

Base mesh of 2mm

Inflation of 2 layers and a scale of 2

Boundary condition:

Air inlet :0.5m/s

Fuel inlet:80m/s

species : ch4-air

Air mass fraction:0.23

CH4 mass fraction:1

Eddy dissiption model was used with pressure based solver

Results:

Temperature contour:

max temperature reached was 2313k

Eddy viscosity:

Mass fraction of o2:

Mass fraction of N2

Mass fraction of CH4:

Mass fraction of Co2

Variation of mass fraction:

Charts:

Locations :X axis :0.2,0.4,0.6,0.8 m away

1. CH4 Mass fraction:

2.O2 Massfraction:

3. N2 Massfraction:

4. H2o Massfraction:

Combustion below 1300 C forms less concentration of NOX emission so it can be ignored .

Less NOX means more efficient combustion ,to get the NOX data we need to turn onn the NOX Model from species

Mass fraction of NOX

NOX formation in the combustion simulation is of the order 1.4 e-3

Conclusion:

• Mass fraction of all the species at diffrent location was obtained
• Mass fraction of NOX was obtained and was observed to be 1.4e-3
• Max temperature achieved was 2313k