What occurs during the compression stroke in a four-stroke engine?

During the compression stroke in a four-stroke engine, the air/fuel mixture is drawn into the cylinder and then compressed as the piston moves upwards. This process occurs between the intake and power strokes, and it is critical for engine performance.

As the piston rises, it decreases the volume of the cylinder, which increases the pressure and temperature of the air/fuel mixture. This compression enhances the efficiency of combustion when the mixture is ignited, leading to a more powerful explosion in the power stroke. Proper compression is essential for smooth engine operation, as it ensures that the mixture ignites at the right moment for maximum efficiency and performance.

Understanding this process is fundamental for diagnosing engine issues related to loss of power, misfires, or poor fuel economy, all of which may stem from improper compression.