Blender Rocket Exhaust test 

got bored.
This uses only polygons; no volumetric materials. The exhaust mesh is made of spheres and smooth cones. They're not that accurate, as I went by memory with no references.
Faces that point away from the camera are faded to appear as fake volumes. The technique is intended to be adapted into a GPU shader to use for a certain project that I might start talking about on this channel soon.