### 8.8.4. User Defined Injection Regions

User defined injection regions enable you to use Fortran to specify a custom injection region. The routine may optionally return a range of values (such as temperature, particle mass flow rate, and so on) or they can be specified by enabling the appropriate toggles in CFX-Pre. Information on setting up a particle routine is available in Particle User Routines in the CFX-Pre User's Guide.

Note: In the case of user defined injection, the particle position and the injection velocity – if returned from the user routine – refer to the global coordinate frame `Coord 0` rather than to the one specified under Coordinate Frame.

An example of a Fortran routine is given below. This routine returns the following variables:

- Particle Position (X, Y, Z)

- Particle Mass Flow Rate

- Mean Particle Diameter

- Velocity (u, v, w)

- Temperature

As a result, the respective options under Define Particle Behavior are not entered. Similar to other routines, after the Fortran routine is written, a shared library should be created. For details, see Creating the Shared Libraries. The routine should then be defined as a User Particle Routine in CFX-Pre. For details, see Particle User Routines in the CFX-Pre User's Guide.

In the `<install_dir>\examples\UserFortran` directory, you can find an injection routine, pt_injection.F, and corresponding CCL template, pt_injection.ccl.

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