## 8.8. Particle Injection Regions

Injection regions can optionally be created to inject particles on sphere or cone locators, or on a custom locator defined by a User Fortran subroutine. The user subroutine should be of type `Particle User Routine` to make it available for selection in the drop-down list.

For each method of injection, apart from the location specification itself, other quantities required are the same as those that would be required at a boundary (for example, temperature would be required if heat transfer was being modeled). For details, see Particle Boundary Options and Behavior. If a User Fortran routine is being used, all physical quantities (apart from mass fractions) can be set either in the Fortran or from the user interface.

The center and the axis (if applicable) of the injector, as well as the injection velocity (for Cartesian or cylindrical velocity components), are interpreted in the local coordinate system. The exception is for user defined injections where 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.

The local coordinate system cannot be specified with a rotating frame motion. When a domain with a rotating frame is included in the injected region, the position from which particles are injected is assumed to rotate along with the domain. For additional information, see Rotating Frames of Reference (RFR) and GGI and MFR Theory in the CFX-Solver Theory Guide.

The following sections outline how to set up the locations using the following options:

- Sphere
- Cone
- Cone with Primary Breakup
- User Defined Injection Regions

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