The FLACS species database contains the material properties of a range of hydrocarbons and other common gases. If your fuel composition contains species not already defined in the FLACS database, you can add a user-defined species to the database.

In this article

Add new species in CASD

In a situation where you need to use a species that is not defined in the FLACS database, you need to add it as a user-defined species and define all the related parameters.

You can add the user-defined species directly in CASD. In the scenario settings sidebar, go to Species. If the Species section is not visible, right-click in the scenario sidebar area and select Species from the list.

Add the Species section to the CASD scenario settings sidebar

Once checked, the Species section will appear in the scenario sidebar. Add a new species by clicking on Add and define the relevant parameters under Properties. Scroll down to see the entire list of parameters for the species' properties section.

Properties for a user-defined species

Populate the properties of new species

Obtaining the properties of the new species is the main challenge in creating a user-defined species. The most practical way to do this is to extract the properties of a similar species from the FLACS database. Use the listspecie utility and then modify those parameters that are relevant to your simulation.

To extract properties of an existing species in FLACS, do the following:

  • Click on the Command window icon in RunManager to open a command window (see picture below)
Open the command window from FLACS RunManager to list the species in the FLACS database
  • In the command window, type listspecie and you will get a list of species that exist in the FLACS database
  • Choose the species which you want to extract its properties from, and type listspecie followed by the species' name, for example: listspecie CO2 to get the properties of carbon dioxide

The same can be done in Linux by typing run listspecie in the terminal command line istead of listspecie.

Not all the properties are needed for all kinds of simulations. A comprehensive table listing the properties needed for the different types of simulations is available in the Species section in the FLACS User’s Manual. Make sure that at least the relevant properties for your scenario types are updated with the correct values.

Edit the gasdata file

For a user-defined species, the gasdata file read by Flacs should be modified.

  1. For a dispersion simulation (no combustion involved) where the variable of interest is the integrated volume of the fuel-air concentration within the flammable range, you should follow the steps in Example using a modified gasdata file for dispersion in the FLACS User’s manual.
  2. For an explosion simulation you should determine (from the literature, experimental results, etc.) the laminar burning velocity at standard thermodynamic condition SLAM for different values of ER. This is described in the FLACS User’s manual in Modifying laminar burning velocities in the gasdata file for explosion simulations.
  3. For both dispersion and explosion simulations, go to the FLACS folder on your disk, and navigate to the standard gasdata library (on Windows: C:\Program Files\GexCon\FLACS_v10.5\bin\files\gasdata2.5.4)
  4. Copy the gasdata file for one of the predefined species in FLACS from the standard gasdata library to your current working directory, naming the copied file USERSPEC_1 (corresponding to the name in the Gas composition and volume section in CASD).
  5. Modify (using a text editor) the file USERSPEC_1.

To determine SLAM at intermediate ER values, Flacs uses an interpolation routine. The interpolation can lead to unexpected oscillations in the resulting laminar burning velocities if the given ER/SLAM points do not result in a sufficiently smooth curve. As a basic test, the laminar burning velocity for the initial equivalence ratio should be checked in the simulation log file (rt<jobno>.dat3 or tt<jobno>). In general, replacing the FLACS default values of the gas properties means that the validation lapses and should therefore only be done when reliable experimental data is available.

Use the new species in simulations

Once the new species is defined in the Species scenario section, you can use the species like any other material from the FLACS database.

The use of user-defined species and its fraction in the fuel composition is defined in the volume fractions in the Gas composition and volume section in the scenario sidebar. Userspec 1 in the volume fractions list corresponds to the new species (USERSPEC_1) you defined in the Species section. Userspec 2 and Userpec 3 corresponds to USERSPEC_2 and USERSPEC_3, respectively.

Adding the user-defined species to the gas composition in CASD

Add all other relevant input for your scenario (gas monitor region, monitor points, panels etc.), in addition to a setup file with the following content:

The setup file for including a modified gasdata file