[duanwuCHEN]

I am modeling a C2H4/O2 laminar diffusion flame in ANSYS fluent and want to evaluate the soot formation process of the field. In comparison with the experiment data, the magnitude of the soot peak volume fraction is correct, but the contours show a significant difference between the simulation and experiment.

Here is my case setup:
Mesh and boundary conditions: 2D axisymmetric, velocity: 0.04 m/s, radius: 5.25 mm for the fuel inlet and velocity: 0.642 m/s, radius: 48.85 mm for the air inlet (O2 23%), which follows the following reference:

Zhiwei Sun, Bassam Dally, Graham Nathan, and Zeyad Alwahabi, ‘Effects of hydrogen and nitrogen on soot volume fraction, primary particle diameter and temperature in laminar ethylene/air diffusion flames’, (2016) Combustion and Flame, Submitted

For the model part,
- Energy: Energy Equation
- Viscous Model: Laminar
- Radiation Model: DO, DO/Energy Coupling, 10 energy iterations per radiation iteration, theta and phi divisions 3, theta and phi pixels, number of bands 0.
- Species: species transport, volumetric reaction, stiff chemistry solver, diffusion energy source, full multicomponent diffusion, thermal diffusion.
- Chemical mechanism: the following mechanism refers to "On the relative contributions of soot to radiative heat transfer at different oxygen indices in ethylene – O2/CO2 laminar diffusion flames" and "Global Reaction Mechanism for Ethylene Flames with Preferential Diffusion"

ELEMENTS
O H C N
END

SPECIES
O2 C2H4 CO H2 O
CO2 OH H H2O C2H2 N2
END

REACTIONS
O2 + C2H4 = 2CO + 2H2 7.8E+23 0.000 35500.00
O + CO +M = CO2 + M 5.3E+13 0.000 -4540.00
! O + CO(+M) = CO2(+M) 5.3E+13 0.000 -4540.00
OH + CO = H + CO2 4.4E+6 1.500 -740.00
O2 + H2 = OH + OH 1.7E+20 0.000 48000.00
O2 + H = OH + O 2.6E+14 0.000 16800.00
OH + H2 = H + H2O 2.2E+17 0.000 5150.00
O + H2 + M = H2O + M 1.1E+20 -2.000 0.00
2H + M = H2 + M 2.4E+19 -1.000 0.00
C2H4 = C2H2 + H2 2.5E+12 0.000 71530.00
C2H2 + 2OH = 2H2 + 2CO 5.38E+22 0.000 14000.00
END

In the mixture properties:
- Mixture Species: names
- Reaction: finite-rate
- Mechanism: reaction-mechs
- Density: incompressible-ideal-gas
- Cp: mixing-law
- Thermal Conductivity: ideal-gas-mixing-law
- Viscosity: ideal-gas-mixing-law
- Mass Diffusivity: kinetic-theory
- Thermal Diffusion Coefficient: kinetic-theory
- Absorption Coefficient: wsggm-domain-based
- Scattering Coefficient: constant, 0
- Scattering Phase Function: isotropic
- Refractive Index: constant, 1

For the soot model,
- Model: Moss-Brookes
- Soot precursor: C2H2, C2H4
- Surface growth: C2H2, C2H4
- Soot Oxidation Model: Fenimore-Jones
- OH Model: instantaneous
- Soot-Radiation Interaction

I also use two UDF to modify the value of C_alpha to 1800 and C_oxid to 0.015.

Here is my simulation result and experiment result.
Forgive the ugly layout XD.

https://i.postimg.cc/T2SXtGy7/compare.png

It is pretty obvious, that the peak of the soot volume fraction should locate at the boundary (or the "wing"?) of the flame, not the center. But no matter how I change my model, the soot shape doesn't change.

Thank you for your help in advance.