Make a superscope, set it to lines/dots depending on your preference. And set it to "Waveform".
in the Init field. And
in the Per Point field.
That gives you an oscilloscope at the bottom of the screen. Make a movement with
and "rect coords" checked, and that's a simple style of fire. Obviously, change the colours however you want.
I suggest making the superscope yellow and then adding a colour fade.
For the colour fade, put all three sliders in the middle. Then move the third one to the left 5 or 6 pixels.
Hope that helps!
 Here's a screen cap: