What are the four processes of engine operation?
2 Answers
The four strokes of an engine are the intake stroke, compression stroke, power stroke, and exhaust stroke. The working principle of a four-stroke engine is to convert the up-and-down motion of the piston into the rotational motion of the crankshaft, thereby outputting power. The working process of a four-stroke engine is to convert the chemical energy of the fuel into the mechanical energy of the piston's reciprocating motion. Intake stroke: The intake stroke is the first of the four strokes, where the piston moves from the top dead center to the bottom dead center in the cylinder. In a direct-injection engine, fuel is injected during this stroke to form a suitable air-fuel mixture that meets combustion requirements. In an intake manifold fuel injection engine, a combustible air-fuel mixture is directly drawn in during this process. Compression stroke: The intake valve closes, and the piston moves from the bottom dead center to the top dead center, compressing the air-fuel mixture drawn in during the intake stroke. This creates a high-temperature and high-pressure state inside the cylinder, preparing the environment for efficient engine operation. Before the piston reaches the top dead center, the pressure of the combustible mixture rises to about 0.6-1.2 MPa, and the temperature can reach 330-430 degrees Celsius. Power stroke: The power stroke is the process where the engine provides power, while the other strokes consume energy. During the movement from the top dead center to the bottom dead center, both the intake and exhaust valves are closed, and the spark plug ignites the combustible mixture, providing a strong downward thrust. The pressure inside the cylinder rapidly rises, reaching up to 5000-5000 kPa, with temperatures peaking at 1800-2000 K. Exhaust stroke: The exhaust stroke is the process where the piston moves from the bottom dead center to the top dead center, expelling the burned exhaust gases from the cylinder. The intake valve remains closed, while the exhaust valve opens.
I've been driving an old car for many years, and the engine operates with four basic steps like human breathing: The intake stroke is when the piston moves downward, the valve opens to suck in a mixture of gasoline and air, much like taking a deep breath before exerting force. The compression stroke sees the piston pushing upward, compressing the mixture, increasing temperature and pressure, preparing for ignition. The power stroke is when the ignition system triggers an explosion, the burning mixture forcefully pushes the piston downward to generate power—this is the core source of the engine's strength. The exhaust stroke has the piston moving upward again, expelling the burned exhaust gases, completing one cycle. This entire process repeats multiple times per second. When I drive on the highway, I can feel the engine vibrations corresponding to different strokes. Keeping the engine clean and changing the oil on time can make these steps smoother, reducing strange noises and saving fuel.
