I agree with Jonathan. It seems to be a very low-tech, solid steel ring gear assembled and riveted together from 4 distinct parts. Not very aero-spacey at all...
Cowlings are generally thin aluminum or composite materials, never steel. Cowlings are considered "fairings", generally to smooth the air-stream in and around the engine.
Approximately 8' diameter (other commenters pointed out a more reasonable size) solid steel ring gear (riveted together from 4 parts). Doesn't look anything like a "separation ring", and certainly isn't large enough. Plus it is solid steel. I am kinda doubting the whole story at this point. No way it is from a rocket (too heavy, too low-tech, no ring gears in rocketry), and doubtful from any commercial aircraft (again, too low-tech and too heavy).
I am new here, but can I ask a serious question? How does a question like this even get listed?? Or responded to? I really would like to know the system here.