Four-Stroke Engine: Operation and Principles A four-stroke engine is a type of internal combustion engine that completes four distinct phases—intake, compression, power, and exhaust—in two full revolutions of the crankshaft (720 degrees). This design is widely used in automobiles, motorcycles, and other machinery due to its efficiency, reliability, and balanced power delivery. 1. Intake Stroke The cycle begins with the intake stroke. The piston moves downward, creating a vacuum in the cylinder. The intake valve opens, allowing a mixture of air and fuel (in gasoline engines) or just air (in diesel engines) to enter the combustion chamber. The exhaust valve remains closed during this phase. 2. Compression Stroke As the piston moves upward, both valves close, compressing the air-fuel mixture (or air in diesel engines) into a smaller volume. This compression increases the mixture’s pressure and temperature, preparing it for combustion. In diesel engines, the high compression ignites the fuel without a spark plug, while gasoline engines rely on a spark for ignition. 3. Power Stroke (Combustion Stroke) At the top of the compression stroke, ignition occurs. In gasoline engines, the spark plug fires, igniting the compressed mixture. In diesel engines, fuel is injected and ignites due to high pressure and temperature. The rapid combustion forces the piston downward, converting chemical energy into mechanical energy. This is the only stroke that produces power, driving the crankshaft. 4. Exhaust Stroke The piston moves upward again, pushing the burned gases out through the open exhaust valve. The intake valve remains closed during this phase. Once the exhaust gases are expelled, the cycle repeats. Advantages and Applications Four-stroke engines are more fuel-efficient and produce fewer emissions compared to two-stroke engines. They also have better lubrication and durability since oil is not mixed with fuel. These engines are commonly used in cars, trucks, generators, and industrial equipment. Conclusion The four-stroke engine’s design ensures smooth operation, efficient fuel use, and reduced pollution. By completing four distinct phases, it optimizes energy conversion, making it a cornerstone of modern transportation and machinery.