This is a 2.5m diameter engine I've made for use in the game Kerbal Space Program. I thought of something very sci-fi using electro-magnetism or more advanced energy with blue/white lightnings between the sparks which may slowly increased as thrust get higher.

There is also an associated fuel tank available separately (included in the max scene).

Part is ready to import in Unity, with only one material use.
Template included (in GIMP format only).