What is the working principle of a four-stroke gasoline engine?
2 Answers
The working principle of a four-stroke gasoline engine is that air and gasoline are mixed in a certain proportion to form a good mixture, which is drawn into the cylinder during the intake stroke. The mixture is compressed and ignited to generate thermal energy. The high-temperature gas acts on the top of the piston, driving the piston to move linearly in a reciprocating motion, and mechanical energy is output externally through the connecting rod and crankshaft flywheel mechanism. The four-stroke gasoline engine completes a working cycle in the intake stroke, compression stroke, power stroke, and exhaust stroke. Driven by the crankshaft, the piston moves from the top dead center to the bottom dead center. At this time, the intake valve opens, the exhaust valve closes, and the crankshaft rotates 180°. During the piston movement, the cylinder volume gradually increases, the gas pressure in the cylinder gradually decreases from pr to pa, and a certain degree of vacuum is formed in the cylinder.
I've been repairing cars for over twenty years and have witnessed firsthand how a four-stroke gasoline engine operates. It's like a diligent little engine, tirelessly cycling through four steps: First, intake—the piston moves downward, the intake valve opens, drawing in a mixture of air and gasoline into the cylinder, much like a person breathing; then compression—the piston pushes upward, the valves close, tightly compressing the mixture, storing energy, waiting to explode; when it's time for power, the spark plug flashes a spark, igniting the mixture, resulting in a loud explosion, the expanding gases forcefully push the piston downward, turning the machine and propelling the wheels forward; finally, exhaust—the piston rises again, the exhaust valve opens, expelling the burnt gases, concluding the performance. The entire process completes in two rotations of the crankshaft, with each ignition producing power to make the car speed ahead. It's highly efficient because the tasks are separated, reducing fuel waste. During maintenance, checking the spark plugs and valve wear is crucial to prevent the engine from coughing and stalling.
