What happens during the second piston stroke in an engine?

During the second piston stroke in an engine, the correct process involves the piston compressing the fuel and air mixture. This compression stroke is crucial because it increases the temperature and pressure of the air-fuel mixture inside the cylinder, making it more conducive for combustion.

As the piston moves upward, it reduces the volume in the cylinder, and this compression prepares the mixture for ignition. Proper compression ensures that when the spark plug fires, the fuel-air mixture ignites efficiently and produces power. This is a fundamental aspect of the thermodynamic cycle in internal combustion engines, specifically the four-stroke cycle.

The other options describe different stages that happen either before or after this compression stroke. For instance, fuel injection typically occurs prior to the compression stroke, while ignition and exhaust release happen subsequently. Understanding this sequence is essential for grasping how an internal combustion engine operates.