An internal combustion engine is a remarkable machine that converts chemical energy from fuel into mechanical work. The basic principle involves mixing fuel with air inside a cylinder, igniting this mixture to create a controlled explosion, and using the resulting pressure to push a piston that generates rotational motion.
The four-stroke cycle is the heart of engine operation. First, the intake stroke draws in the air-fuel mixture. Second, compression stroke compresses this mixture to increase its energy density. Third, combustion stroke ignites the compressed mixture, creating the power that drives the piston down. Finally, the exhaust stroke expels the burnt gases, completing the cycle.
The intake and compression strokes prepare the engine for combustion. During intake, the piston moves down while the intake valve opens, creating a vacuum that draws the air-fuel mixture into the cylinder. Then during compression, both valves close and the piston moves up, compressing the mixture to about one-tenth its original volume, dramatically increasing both pressure and temperature for efficient combustion.
The combustion and power stroke is where the engine generates its useful work. The spark plug creates an electric arc that ignites the compressed air-fuel mixture. A flame front rapidly spreads throughout the cylinder, causing a dramatic pressure rise. This explosive force drives the piston downward with tremendous power, converting the chemical energy of fuel into mechanical energy that ultimately turns the wheels.
The exhaust stroke completes the four-stroke cycle by expelling burnt gases from the cylinder. The exhaust valve opens while the piston moves upward, pushing out the waste products. Precise valve timing is crucial for engine efficiency, with carefully coordinated opening and closing of intake and exhaust valves to optimize gas flow and maximize power output throughout the complete cycle.