The diesel unsteady laminar flamelet model can only be enabled when conditions for compression-ignition are met:
A detailed chemical mechanism is required which should contain kinetic reactions appropriate for compression ignition. The mechanism can include pollutant formation reactions as well if you are interested in modeling emissions.
To access the model inputs, enable the Create Table or Set Table Parameters under PDF Options. In the Chemistry tab, select Diesel Unsteady Flamelet.
With the Diesel Unsteady Flamelet model enabled, you can define the stream compositions (Section 15.9) and the flamelet controls (Section 15.10.2). Note that while you can enter the Number of Grid Points in Flamelets in the Flamelet tab (Section 15.11.2), you will not be able to calculate the flamelets. This is also true when calculating a PDF table (Section 15.12). In the Table tab, you can set the table parameters, but you will not be able to run the calculation. The reason for this behavior is because the table creation and the flamelet calculation are performed at every time step of the FLUENT simulation, and not just in a pre-processing step as in other non-premixed combustion models.