If you are modeling premixed combustion (see Modeling Premixed Combustion), the fluid material in your domain should be assigned the properties of the unburnt mixture, including the thermal diffusivity ( in Equation 8–77 in the Theory Guide). is defined as , and values at standard conditions can be found in combustion handbooks (for example, [83]). To determine values at non-standard conditions, you must use a third-party 1D combustion program with detailed chemistry. You can set the Unburnt Thermal Diffusivity in the Create/Edit Materials Dialog Box.