Problems by releasing particles

have some problem with the artificial intelligence of the enemies in the game, I do not go well and I have to deliver the science project forum here at school next week. Also I have problems in particular, if any motor vehicle crash with another object or when you walk on wet area, the effect of particles which are not as program. I hope I can help with that, I really do not know what to do. Could you give me any reference or any simple example of this. problems by releasing particles Thanks!