As mentioned in Section 15.6.2, you can define the composition of a fuel stream (i.e., the standard fuel or a secondary fuel) empirically. For an empirically-defined stream, you will need to enter the atomic mass fractions in addition to the inputs for lower caloric (heating) value of the fuel and the mean specific heat of the fuel that were described previously.
The heat of formation and molecular weight of an empirical fuel stream is calculated from the heating value and the atomic composition. The fuel inlet temperature and fuel specific heat are used to calculate the sensible enthalpy.
When an empirically-defined fuel or secondary stream is specified in the Chemistry tab (equilibrium chemistry model only) of the Species Model panel, you must specify the atom fractions of C, H, O, N, and S in that stream instead of the species mass or mole fractions. To avoid confusion, the species fraction inputs for an empirically-defined stream will be grayed out in the table within the Boundary tab, leaving only the fields for atom fractions (i.e., c, h, o, n, and s).