BASIC COMBUSTION SIMULATION USING ANSYS FLUENT

Objectives:

1. Briefly explaining about the possible types of combustion simulations in FLUENT
2. Performing a combustion simulation on the combustor model and ploting the variation of the mass fraction of the different species’ in the simulation using line probes at different locations of the combustor and ploting CO2, H2O, CH4, N2, O2 and NOx emissions.

1. Possible types of combustion simulations in FLUENT

Based on mixing

Non-premixed combustion(Direct Injection,Late Injection)

Premixed combustion(Carburator)

Partially premixed combustion

Based on phase

Fluid phase(Volumetric reactions)

Wall(surface reactions)

Particles(surface reaction)

Porous region(After Treatment system)

Turbulent combustion:

chemical kinetics are highly nonlinear, turbulence-chemistry interactions should be taken into account to accurately predict turbulence 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.

Fast chemistry:

The eddy dissipation model(EDM), in combination with 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, furnances and thrusters, The EDM can be used for all types of combustion as well as in combination with advanced scale-resolving turbulence and multiphase models.

Non-Premixed combustion:

With the non-premixed model, the turbulence-chemistry interaction is describes using assumed shape of probability function(PDF). The thermodynamic state of fluid is related to the mixture fraction and the chemistry is calculated either from equillibrium or by using tabulated steady flamelet approach. The non-premixed model offers a robust and fast solution for any tgurbulent reacting flow that is at or near chemical equilibrium. This model is often used for gas turbine, process furnance 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. 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 equillibrium or flamelet model, this approach is applicable to partially premixed and fully premixed combustion.

Geometry:

L = 2m

H = 0.23m

Meshing:

Element size = 0.01

No of elements = 9796

Setup:

Axisymmetry

Steady-state - Pressure-based - k-epsilon

Mixture properties- methane-air

Eddy Dissipation

Species - Transport- Volumetric

air inlet - 0.5m/s

fuel inlet - 80m/s

Temperature = 300k

species o2 = 0.23 ch4 = 1

iterations - 1200

Scalar Residuals:

Results:

Ch4 plane:

Co2 plane:

H2o plane:

N2 plane:

O2 plane:

Pressure plane:

Temperature:

Velocity:

Eddy Viscosity:

Line:(The line probes can be plotted equidistant from each other)

Ch4:

Co2:

H20:

N2:

O2:

The above mentioned charts are the massfractions except mass of pollutions because of emissions, the fraction of NOx concentration is very low. by turning on the Nox equation in setup species model, the following plane and chart can be achevied for Nox.

NOX:

NOX:

Conclusion:

The solution is converged at 186 iterations.

Maximum temperature attained is 2248k.

As that there is no heat source to ignite mixture when proper mixing of the particle happens due to turbulence model and eddy dissipation igniton occurs.