MFL mechanisms provide detailed descriptions of various combustion and emissions processes. They are applicable over a broad range of conditions and include chemistry for many fuel components and their blends. The full MFL mechanisms can be used directly for many reactor models in Ansys Chemkin.
Tip: For flame simulations in Chemkin, a high-temperature version of the full mechanism can be easily extracted in one step using Reaction Workbench.
However, most CFD applications require that the full mechanisms be reduced. Mechanism reduction can be performed using Reaction Workbench, which contains various reduction methods, such as DRG, DRGEP, DFGPFA, sensitivity analysis combined with DRG or DRGEP or DFGPFA, automatic isomer lumping, full sensitivity analysis, and more. Using these methods iteratively with the Mechanism Reduction Sessions facility in Reaction Workbench can effectively reduce a mechanism so that it can be used in many CFD applications, including Ansys Forte and Ansys Fluent.
Mechanism reduction is performed for a specific fuel surrogate of interest and for specific conditions of interest to the CFD application. Therefore, a reduced mechanism is accurate only for the fuels and conditions used for the reduction. We have pre-selected components for different conventional fuels and reduced their mechanisms for typical operating conditions. Table 2.1: Reduced mechanisms provided with the MFL shows the details of these pre-reduced mechanisms.
Table 2.1: Reduced mechanisms provided with the MFL
| Fuel | Surrogate Components | Species name | Low-T auto-ignition | CO, HC, NOx emissions | Num. of species | Soot models that can be used with reduced mechanism |
| Natural gas[a] | methane | ch4 | x | ✓ | 34 | Acetylene-based empirical |
|
93 vol% methane/ 5% ethane/ 2% n-butane | 93 vol% ch4/ 5% c2h6/ 2% c4h10 | ✓ | ✓ | 86 | (a) Acetylene-based empirical | |
| 120 | (b) Pseudo-gas | |||||
| (c) Detailed soot-surface model | ||||||
| Propane | propane | c3h8 | ✓ | ✓ |
65 | (a) Acetylene-based empirical |
| (b) Pseudo-gas | ||||||
| Gasoline | iso-octane | ic8h18 | x | ✓ | 63 | Acetylene-based empirical |
|
22.4 wt% iso-octane/ 30.4% toluene/ 19.1% n-pentane/ 11.2% MCH/ 7.5% 1-hexene/ 7.3% 1,2,4-trimethyl benzene/ 2.1% n-butane | 22.4 wt% ic8h18/ 30.4% c6h5ch3/ 19.1% nc5h12/ 11.2% mch/ 7.5% c6h12-1/ 7.3% tmb124/ 2.1% c4h10 | ✓ | ✓ |
149 | (a) Acetylene-based empirical | |
|
159 | (b) Pseudo-gas | |||||
273 | (c) Detailed soot-surface model | |||||
| Diesel | n-heptane | nc7h16 | ✓ | ✓ | 106 | (a) Acetylene-based empirical |
|
126 | (b) Pseudo-gas | |||||
| 36 wt% n-hexadecane/ 9.7% AMN/ 16.4% HMN/ 38.9% decalin | 36 wt% nc16h34/ 9.7% a2ch3/ 15.4% hmn/ 38.9% decalin | ✓ | ✓ |
174 | (a) Acetylene-based empirical | |
|
265 | (b) Pseudo-gas | |||||
|
326 | (c) Detailed soot-surface model | |||||
| Jet fuel | n-dodecane | nc12h26 | x | ✓ |
74 | Acetylene-based empirical |
| 36.6 wt% n-dodecane/ 32.2% heptamethylnonane/ 10.3% methylcyclohexane/ 20.9% 1,2,4-trimethylbenzene | 36.6 wt% nc12h26/ 32.2% hmn/ 10.3% mch/ 20.9% tmb124 | ✓ | ✓ |
185 | (a) Acetylene-based empirical | |
|
213 | (b) Pseudo-gas | |||||
|
284 | (c) Detailed soot-surface model |
[a] May be used for blends with hydrogen.
Many empirical soot models use only acetylene as the soot precursor. The MFL pseudo-gas soot model is expected to be more accurate than a 2-step empirical model, as it employs acetylene, benzene, and phenyl as soot precursors and has been shown to be predictive over a wide range of fuels and operating conditions. The pseudo-gas soot model can predict soot mass but not particle sizes. The detailed soot-surface chemistry employs more soot precursors and when used with the Method of Moments or Sectional Method can predict soot particle sizes.
The reduced mechanisms for the pre-selected fuels and conditions are applicable for the conditions specified in the table. They should not be used for conditions outside of their range. However, for the multi-component fuels, it should be acceptable to modify the blend as described in the Model Fuel Library Validation Manual.