When does cylinder pressure start to decline during the combustion process?

The correct response indicates that cylinder pressure begins to decline in the middle of the steady combustion phase. This phase is characterized by sustained combustion, during which fuel continues to burn and produce energy. As the combustion process continues, the cylinder pressure initially rises sharply as the air-fuel mixture ignites and starts expanding rapidly due to the heat produced.

However, as the combustion phase progresses toward the middle, the rate of combustion stabilizes, and the available quantity of combustible gases decreases as they get consumed. Consequently, the pressure in the combustion chamber begins to decrease as energy is converted to work and the gases expand against the volume of the cylinder.

This understanding highlights the intricate relationship between pressure, temperature, and volume in the thermodynamic cycles of an engine. Recognizing the behavior of cylinder pressure during each phase of combustion is crucial for effective engine operation and diagnostics.