What is the working principle of a four-stroke gasoline engine?

[JohnAnn]

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.

[LaBryce]

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.

[Tucker]

I've been driving my own vintage car for half my life, and I'm most familiar with the sound of its engine. The four-stroke process is evident while driving: before starting, the engine emits a light hum—that's the intake valve opening, with the piston drawing in the air-fuel mixture; then, as the throttle is pressed down, the sound becomes muffled and solid, with the piston compressing the mixture upwards, like a tightly wound spring; when you stomp on it, the spark plug flashes to ignite, the explosion drives the piston downward, and the car surges forward with a burst of momentum, delivering the real power; finally, the exhaust pipe gurgles as the piston rises again to release the waste gases. These four steps—intake, compression, power, exhaust—cycle endlessly, with the crankshaft converting the piston's up-and-down motion into wheel rotation, the entire process silently operating within the engine block. It feels like a rhythmic heartbeat, and that explosive thrust while driving is incredibly satisfying, signaling the car's health and vitality, fuel-efficient and smooth.

[CarolineMarie]

Absolutely fascinating! The four-stroke engine is ingeniously simple in design: the first intake stroke, where the valve opens and the piston pulls down to draw in the air-fuel mixture; the second compression stroke, where the valve closes and the piston compresses the mixture upward, preparing for the energy burst; the third power stroke, where the spark plug ignites, the mixture explodes and expands, forcing the piston downward to transfer power to the crankshaft; and the fourth exhaust stroke, where another valve opens and the piston pushes the exhaust gases upward. The entire cycle is highly efficient, with the crankshaft completing two full rotations to deliver one power stroke, converting chemical energy into mechanical energy to propel the vehicle forward. This system is like a micro-engineering masterpiece—optimizing the compression ratio or spark timing can boost horsepower, making modifications even more thrilling!

[LandonLee]

Think about the process of blowing up a balloon, and you'll understand a four-stroke engine: During the intake stroke, it's like taking a deep breath—the piston moves down to suck in the air-fuel mixture. Compression is when the piston rises, squeezing the mixture tightly like a balloon. The power stroke occurs when the spark ignites the mixture, causing an explosion similar to a balloon popping, which pushes the piston down to generate power. Finally, during the exhaust stroke, the piston rises again to expel the waste gases, just like a balloon deflating. This cycle repeats continuously, with the crankshaft converting the piston's motion into wheel rotation. Power is only produced during the ignition stroke, reducing fuel waste and ensuring smooth driving. Everyday driving operates within this continuous cycle.