You need to tell Niagara which way to go in world space.
- Set up a vector parameter in your Niagara system called something like user.velocity
- use it to drive the velocity of your particle (with an addvelocity module)
- Using blueprints get the forward vector of your character and multiply it by the speed you want
- Use the result in your user.velocity parameter
- Activate your Niagara system and it should move forward from your character.
Good luck!