A flame speed look-up table is one method for specifying laminar flame speeds, which are used as input to the flame-propagation model in Ansys Forte.

The look-up table is a file that contains a series of laminar flame-speed data points used to interpolate to an appropriate, local flame speed (unstretched,) during the simulation. A table can be created or edited with the Flame-Speed Table Editor. Access the Flame-Speed Table Editor from the Edit menu or the Flame-Speed Table   button on the toolbar. The pre-installed flame-speed tables provided with Ansys Forte are described in Appendix F: Flame-Speed Tables Installed with Ansys Forte. For details of the flame model, see Flame Model.

The flame-speed table is of the following format (see Example 2.1: Excerpt from flame-speed table file demonstrating .cktbl format ):

Line 1: Dimension of the manifold, which is 4.

Line 2: Names of the dimensions in the manifold. For a flame table, this consists of unburned_temperature(K), pressure(Pa), equivalence_ratio(), and EGR_rate(). The look-up table uses these four manifold dimensions to find the interpolated flame speed.

Line 3: Dimension of the scalar data points; in this case, 5.

Line 4: Names of the scalars; in this case, the names of the manifold plus the flame_speed(m/sec).

Line 5+: Each subsequent line contains a single scalar point of Temperature, Pressure, Equivalence Ratio, Exhaust Gas Recirculation rate, and flame speed. The nature of the interpolation does not require that these points be equidistant in the manifold dimensions.

Equivalence ratio is given as the atomic ratio of 2 carbons plus ½ hydrogens over oxygen. The EGR rate is the fraction of Exhaust Gas Recirculation (EGR) flow rate relative to total intake flow rate, where 0.0 corresponds to no EGR and 1.0 corresponds to 100% EGR. It is defined as

where X _EGR is the total intake mole fraction of the EGR species in the inlet gas mixture, X _fuel is the total mole fraction of the fuel species, and X _air is the total mole fraction of air. The sum of all fractions of EGR species should be 1.0.

In the data directory of the Ansys Forte installation are 5 sample flame-speed look-up table files for the species methane, ethane, propane, heptane, and iso-octane.

4
unburned_temperature(K) pressure(Pa) equivalence_ratio() EGR_rate()
5
unburned_temperature(K) pressure(Pa) equivalence_ratio() EGR_rate() flame_speed(m/sec)
5.00E+02 1.00E+06 4.00E-01 0.00E+00 2.48E-02
6.00E+02 1.00E+06 4.00E-01 0.00E+00 5.54E-02
7.00E+02 1.00E+06 4.00E-01 0.00E+00 1.15E-01
8.00E+02 1.00E+06 4.00E-01 0.00E+00 2.20E-01
9.00E+02 1.00E+06 4.00E-01 0.00E+00 4.10E-01