I'm looking for a "polluting" engine

[Graineater]

Coalition engines tend to appear as a plume of fire from a welding torch more than a coal engine. But if there are stinkier plumes I'd be glad to know.
Small freighter with advanced coalition engine:


Border world train with coalition engine appears more like.. a ship on fire.


Unfortunately there is no long trail of smoke.

Random fun fact: Playing coalition destroyer, every battle it gets hit by at least a dozen cruise disruptors for the plume of flames out of that afterburner seems to appear as if the destroyer just gone into cruise mode.

Extra edit note: having bought an engine just to try it out, and post screenshot to let OP know.
I returned to mention:
Coalition transport engine is like
STARING INTO THE SURFACE OF THE SUN