What happens to the pistons during the exhaust and compression strokes?

During the exhaust and compression strokes in a diesel engine, the pistons are indeed pushed back past top dead center by momentum. This phenomenon occurs due to the design of the engine and the movement of other components connected to the crankshaft.

During the exhaust stroke, after the combustion process has expelled the exhaust gases, the piston moves upward in the cylinder, pushing the remaining gases out through the exhaust valves. When the piston reaches the top dead center (TDC), it momentarily stops before starting its downward movement during the power stroke, driven by the force of combustion.

Then, in the compression stroke, as the piston moves downward, it creates a vacuum that draws in air before compressing it. However, due to the kinetic energy and momentum that the crankshaft and connected components have, the pistons can often continue their movement slightly past the TDC position. This momentum is essential for the smooth operation of the engine and aids in transitioning between strokes.

This understanding of piston movement is crucial for diagnosing performance issues and ensuring the mechanical integrity of a diesel engine. The other options do not accurately describe the mechanics involved during these strokes in a diesel engine.