16.4.1 Setting Boundary Stream Species

In combustion, a large number of intermediate and product species may be produced from a small number of initial boundary species. In ANSYS FLUENT you need to input only the species composition of your boundary species in the fuel, oxidizer, and (if appropriate) secondary streams. ANSYS FLUENT will calculate all intermediate and product species automatically. The following suggestions may be helpful in the definition of the system chemistry:

• For coal combustion, char in the coal should be represented by C(s).

  Care should be taken to distinguish atomic carbon, C, from solid carbon, C(s). Atomic carbon should be selected only if you are using the empirically-defined input method.

• If your fuel composition is known empirically (e.g., C $_{0.9}$H $_{3}$O $_{0.2}$), use the option for an empirically-defined stream (see below).

• If you wish to include the sulfur that may be present in a hydrocarbon fuel, note that this may hinder the convergence of the equilibrium solver, especially if the concentration of sulfur is small. It is therefore recommended that you include sulfur in the calculation only if it is present in considerable quantities.

Including Condensed Species

In addition to gaseous species, liquid and solid species can be included in the chemistry calculations. They are often indicated by an "l'' or an "s'' in parentheses after the species name. If you add a condensed species to the equilibrium chemical system, its density will be retrieved from ANSYS FLUENT's chemical property database file propdb.scm if you are using the thermodynamic database file thermo.db that is also supplied with ANSYS FLUENT. If you are using a custom thermodynamic database file and want to include a condensed species in the equilibrium system that does not exist in propdb.scm, a density of 1000 kg/m $3$ will be assumed. The condensed species density can be changed in the Create/Edit Materials dialog box after the PDF table has been calculated. If you modify the condensed species density in this manner, you will then need to recalculate the PDF table.