In which of the four strokes of the cycle is the cylinder pressure at its highest in a running diesel engine?

In a running diesel engine, the cylinder pressure reaches its highest point during the power stroke. This is primarily due to the combustion of the air-fuel mixture that occurs after compression. During the compression stroke, the piston moves upward, compressing the air inside the cylinder, which leads to an increase in pressure but not as high as during the power stroke.

When the fuel is injected into the highly compressed air, combustion occurs almost instantaneously, resulting in a rapid expansion of gases. This expansion generates a significant force on the piston, causing it to move downward and creating the power that drives the engine. The pressures generated during this phase can reach several thousand psi, reflecting the energetic reaction between the fuel and compressed air.

The intake stroke involves drawing the air into the cylinder, and the exhaust stroke involves expelling combustion gases, both resulting in lower pressures compared to the explosive force generated during the power stroke. Thus, the power stroke is where the cylinder pressure peaks as a result of the thermodynamic processes at play in a diesel engine.