16.2.4 Choosing to Define the Fuel Stream(s) Empirically

The empirical fuel option provides an alternative method for defining the composition of the fuel or secondary stream when the individual species components of the fuel are unknown. When you do not select this option, you will define which chemical species are present in each stream and the mass or mole fraction of each species, as described in Section  16.4. The option for defining an empirical fuel stream is particularly useful for coal combustion simulations (see Section  16.4.5) or for simulations involving other complex hydrocarbon mixtures.

To define a fuel or secondary stream empirically

1.   Turn on the Empirical Fuel Stream option under Stream Options in the Chemistry tab of the Species Model dialog box. If you have a secondary stream, enable the Empirical Secondary Stream option, or both as appropriate.

2.   Specify the appropriate lower heating value (e.g. Empirical Fuel Lower Caloric Value, Empirical Secondary Lower Caloric Value), specific heat ( Empirical Fuel Specific Heat, Empirical Secondary Specific Heat), and molecular weight ( Empirical Fuel Molecular Weight, Empirical Secondary Molecular Weight) for each empirically defined stream.

The empirical definition option is available only with the full equilibrium chemistry model. It cannot be used with the rich flamability limit (RFL) option or the steady and unsteady laminar flamelet models, since equilibrium calculations are required for the determination of the fuel composition.

The empirical fuel and secondary molecular weights are only required if your empirical streams are entering the domain via an inlet boundary, or if you are using the partially premixed model. If you are using the non-premixed model and the empirically defined streams originate from the dispersed phase (for example, if you are modeling coal or liquid fuel combustion) the molecular weights are not required for the computation.

The empirical definition option is available only with the full equilibrium chemistry model. It cannot be used with the rich flammability limit (RFL) option or the steady and unsteady laminar flamelet models, since equilibrium calculations are required for the determination of the fuel composition.