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

During the compression stroke of a four-stroke engine, the piston moves upward within the cylinder, effectively compressing the air/fuel mixture that has been drawn in during the intake stroke. This compression increases the pressure and temperature of the mixture, preparing it for ignition. The efficiency of combustion is significantly influenced by this compression, as a higher compression ratio typically results in a more powerful explosion when the mixture is ignited.

As the piston approaches the top of the cylinder, the exhaust valves are closed, which prevents any combustion byproducts from escaping. This sealed environment ensures that the ignition of the compressed mixture will produce maximum power when the spark plug fires. This process is crucial for the engine's performance, as effective compression contributes to an increase in power output and engine efficiency.