How to make a Particle expanding ring

Hi,
Here is my problem: In my game I want to make a ring of fire, witch spawns around the player and then expands till the end of the screen.

(Blue: Player, Black dots: Fire Particles, Arrows: Initial speed) Now how do I do this? If I make a Min of -200 and a Max of 200 in initial location, The fire expands in all directions, but there are still particles with the speed 0, because 0 is between -200 and 200. So it should only be -200 and 200, and nothing in between. I could make multiple emitters with different initial location (for each arrow one emitter), but I think there should be a much simpler solution. Any ideas?