### 9.11.4. Laminar Burning Velocity

The laminar burning velocity is an input parameter for the burning velocity combustion model (partially premixed model).

#### 9.11.4.1. Value

Specify the laminar burning velocity. It is recommended that you use an expression that accounts for dependency of the burning velocity on equivalence ratio or mixture fraction. Properties of the unburnt mixture, such as temperature, density, specific heat capacity, and thermal conductivity may be used in order to account for preheating and mixture dependency.

#### 9.11.4.2. Metghalchi and Keck

Built-in correlation fitted for the laminar burning velocities of simple hydrocarbon fuels. The type of fuel is indicated by its carbon index, that is, the number of carbon elements in the fuel molecule:

Molecule | Carbon Index
--- | ---
Methane CH4 | 1
Propane C3H8 | 3
Iso-octane C8H18 (gasoline) | 8

The correlation accounts for preheat temperature and pressure. However, the flammability limits are assumed to be the same as at (25 [C], 1 [atm]) for all temperatures and pressure. Therefore, the correlation is expected to show its best accuracy at near-standard conditions.

#### 9.11.4.3. Equivalence Ratio Correlation

Laminar burning velocity specified as the product of the burning velocity at reference conditions multiplied by corrections for preheat and pressure dependency. For details, see Equivalence Ratio Correlation in the CFX-Solver Theory Guide.

##### 9.11.4.3.1. Reference Burning Velocity

Define the correlation for the laminar burning velocity at reference conditions as a function of the local equivalence ratio of the mixture.

- Beta Function in the CFX-Solver Theory Guide

- Quadratic Decay in the CFX-Solver Theory Guide

- Fifth Order Polynomial in the CFX-Solver Theory Guide

For the quadratic decay and fifth order polynomial options, the fit range defines the range of equivalence ratio for which the polynomials are valid. For equivalence ratios outside the fit range, the reference burning velocity is assumed to decay linearly until it becomes zero at the flammability limit.

##### 9.11.4.3.2. Flammability Limits

Specify the range for equivalence ratio in which the mixture is flammable. The laminar burning velocity becomes zero if the local equivalence ratio is less than the lean flammability limit or larger than the rich flammability limit.

##### 9.11.4.3.3. Preheat Temperature Dependency

Specify the reference temperature and the coefficients for the temperature exponent. When all coefficients are set to zero, there will be no dependency on preheat temperature.

##### 9.11.4.3.4. Pressure Dependency

Specify the reference pressure and the coefficients for the pressure exponent. When all coefficients are set to zero, there will be no dependency on pressure.

##### 9.11.4.3.5. Residual Material Dependency

Specify the coefficients for the residual material dependency of the laminar burning velocity. The residual material dependency is optional. If unspecified or when all coefficients are set to zero, there will be no dependency on the residual material concentration.

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