What is the working principle of a four-stroke gasoline engine?
4 Answers
The working principle of a four-stroke gasoline engine is: 1. Intake stroke, the piston descends to draw in the air-fuel mixture; 2. Compression stroke, the piston rises to compress the mixture; 3. Power stroke, ignition burns the fuel, forcing the piston downward to perform work; 4. Exhaust stroke, the piston rises to expel the exhaust gases. Four-stroke engines belong to reciprocating piston internal combustion engines and are classified into three types based on the fuel used: gasoline engines, diesel engines, and gas fuel engines. The working principle of a four-stroke gasoline engine involves four stages: intake, compression, combustion (power), and exhaust, completing one working cycle. During this process, the piston moves up and down between the top and bottom dead centers four times, while the crankshaft rotates twice accordingly.
I've been driving for almost ten years, and the working principle of a four-stroke gasoline engine is quite easy to understand. It operates in four repeating steps: First is the intake stroke, where the piston moves downward, the intake valve opens, and the air-fuel mixture is drawn in. Next is the compression stroke, where both the intake and exhaust valves close, the piston moves upward to compress the mixture, heating it up. Then comes the power stroke, where the spark plug ignites the mixture, causing an explosion that expands and forcefully pushes the piston downward, releasing energy to drive the car. Finally, during the exhaust stroke, the exhaust valve opens, and the piston moves upward to push out the burnt gases for a clean exit. This cycle repeats continuously, keeping the engine running smoothly. If any part malfunctions—like a worn-out spark plug or leaking valves—the car may shake or lose power. During routine checks, I also pay attention to carbon buildup to avoid excessive fuel consumption, especially on long trips.
I often help with engine repairs. The core of a four-stroke gasoline engine lies in the four-step cycle within the cylinder: First, the intake stroke, where the piston moves downward, drawing in a mixture of air and fuel through the open intake valve; Second, the compression stroke, where the piston moves upward with both intake and exhaust valves closed, compressing the mixture to increase temperature and pressure; Third, the power stroke, where the spark plug ignites the mixture, causing rapid combustion and expansion of hot gases that force the piston downward to generate power; Finally, the exhaust stroke, where the piston moves back up to expel burnt gases into the muffler. This system is quite efficiently designed, but it also has many issues, such as uneven fuel injection leading to incomplete combustion and emission pollution. I have to use diagnostic tools to check the oxygen sensor and ignition timing—optimizing these can improve fuel efficiency.
I've been fascinated by automotive history since childhood. The principle of the four-stroke gasoline engine originated from Otto's invention in 1876: it divides the engine operation into four stages - during intake, the piston descends to draw in the air-fuel mixture for combustion; the compression stroke sees the piston rise to compress the gas for enhanced effect; the power stroke occurs when spark ignition releases high-pressure energy; finally, the exhaust stroke pushes out waste gases. This compact and reliable cycle became the heart of modern vehicles, making engines run smoother and quieter, far superior to old-fashioned steam engines.
