What happens to the temperature of gases within a four-stroke engine cylinder during the power stroke?

During the power stroke of a four-stroke engine, the temperature of the gases within the cylinder increases. This increase is a result of the combustion process, where the fuel-air mixture ignites and burns, generating high-pressure and high-temperature gases. As the piston moves downwards due to the expansion of these gases, the high thermal energy of the combustion directly contributes to an elevated temperature within the cylinder.

This fundamental principle of thermodynamics highlights that during combustion, energy is added to the system in the form of heat, leading to an increase in kinetic energy of the gas molecules, which, in turn, raises the temperature. The other options represent different scenarios that do not align with the actual behavior of gases during this critical phase of the engine cycle.