Roundpixel said:I think you can do it easily with animated masks and blurs.
Check the free tutorial at CMI Studios (duderender has included the link to them) on creating smoke like noise in DF to see what i mean. It´s one of the latest.
By using some of the techniques shown there you could easily create trace fire (several masks travelling in line with scale modifiers, blur, hot spot, the noise could also be useful providing it doesn´t stray off too much from the fire line,....)
And fast to render.