Sometimes flames come out from the exhaust due to bearing distress or turbine blade fracture.
Can such flames/fire be considered an engine fire?
Aviation Stack Exchange is a question and answer site for aircraft pilots, mechanics, and enthusiasts. It only takes a minute to sign up.Sign up to join this community
If the fire is momentarily and stops by itself: No, this is not an engine fire. Flames can come out of the engine at both ends in a compressor stall (also called surge - watch the movie which is linked in the question!), but that is no engine fire. See this question for another example where spectacular flames develop, yet the engine is not on fire.
If the fire can only be stopped by shutting off the fuel supply or the engine itself: Yes, that is an engine fire. I guess you refer in your question to this bulletin on PW4000s, where the No. 4 bearing overheated due to insufficient lubrication. In that case the oil itself overheated and burned, but this still makes it an engine fire.
Engine surge or stall occurs when there is a breakdown in smooth flow of air through the jet engine compressor.
It can be caused by incorrect airflow control within the engine itself by faulty scheduling of Inlet Guide Vanes (IGVs) within the compressor or overfueling during acceleration due to faults within airfuel control. Ice ingestion or heavy bird ingestion may damage the compressor by disrupting airflow and creating a surge in extreme cases. Surges may be recognised as burbling or popping in mild cases with airflow disruption within one or a couple of compressor stages only, or large explosive bang in extreme cases of compressor or turbine damage.
Surges in flight may occur at altitudes depending on throttle handling and type / generation / condition / cleanliness of the compressor or airplane involved. Fire breakout is not the normal consequence of an engine surge unless there is severe damage by failure of a rotating part at high power. Perfection of design, materials and computerized engine control has reduced surge events dramatically over last 15 years or so.