Question

During starting of the engine, the journal bearings operate in ____________ friction.

(a) rolling

(b) hydrodynamic friction

(c) partial-film

(d) none of the mentioned

The question was asked in class test.

Origin of the question is Mechanical Friction topic in chapter Engine Friction and Lubrication of IC Engine

Answer 1

The correct answer is:

(c) partial-film

During engine startup, the journal bearings typically operate under partial-film friction. At this stage, the oil film may not yet fully form, leading to some metal-to-metal contact and higher friction compared to when the engine reaches normal operating conditions and the full hydrodynamic oil film is established.