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

[DiFrancisco]

The working principle of a four-stroke gasoline engine is relatively simple. This type of engine operates through four strokes: intake stroke, compression stroke, power stroke, and exhaust stroke. During the intake stroke, the intake valve opens, and the piston moves downward to draw in air or a combustible air-fuel mixture. In the compression stroke, both the intake and exhaust valves close, and the piston moves upward to compress the combustible mixture. During the power stroke, the spark plug ignites the compressed mixture, causing it to burn and push the piston downward. In the exhaust stroke, the exhaust valve opens, and the piston moves upward to expel the combustion gases. Intake methods of four-stroke gasoline engines: Four-stroke gasoline engines can be naturally aspirated, turbocharged, or supercharged. While these three types differ in their intake methods, their fundamental four-stroke working principles remain the same. Working principle of four-stroke gasoline engines: In actual usage, conditions are more complex, so most engines are also equipped with variable valve lift systems and variable valve timing systems to adjust engine performance under different operating conditions.

[TessaDella]

For someone like me who has long been involved in car maintenance, the working principle of a four-stroke gasoline engine is actually quite intuitive. The piston moves up and down in the cylinder, completing a cycle in four steps: The first is the intake stroke, where the intake valve opens as the piston descends, drawing in a mixture of gasoline and air; the second is the compression stroke, where the piston rises to compress the mixture with the valves closed; the third is the expansion stroke, also known as the power stroke, where the spark plug ignites the compressed mixture, causing an explosion that rapidly drives the piston downward, generating thrust; finally, the exhaust stroke occurs as the piston rises again with the exhaust valve open to expel the waste gases. These four actions connect and repeat in a cycle, converting the motion through the crankshaft into wheel power. The entire process is quiet, efficient, and more environmentally friendly and fuel-efficient than older two-stroke engines. When driving, avoid frequent sudden acceleration, as it can easily lead to carbon buildup clogging the spark plugs and causing unstable ignition. Regular oil changes and maintenance can extend the engine's lifespan, keeping the car running smoothly for many years.

[GideonAnn]

As someone who enjoys explaining automotive knowledge in simple terms, I liken a four-stroke gasoline engine to a continuous little machine dance. The first beat is the piston pulling down to suck in air and fuel; the second beat is the piston pushing up to compress this mixture. The third beat is the spark plug flashing to ignite the explosion, pushing the piston downward—this step generates power. The fourth beat is the piston moving up again to expel the burned exhaust. These four movements complete neatly, causing the crankshaft to rotate and drive the car forward. The key point is that ignition occurs instantly after compression, ensuring thorough combustion and minimal pollution emissions. In daily driving, this system is reliable, quiet, and fuel-efficient, but it's important to avoid overloading—for example, controlling RPM when climbing mountain roads to prevent overheating, component damage, and poor fuel efficiency.

[PrestonRose]

I always find the four-stroke engine design clever and practical. During the intake stroke, the piston moves down to open the valve and draw in the air-fuel mixture; the compression stroke sees the piston moving up to compress the mixture; then ignition occurs, pushing the piston down to generate power; finally, the piston moves up again to expel exhaust gases. This four-step cycle efficiently turns the wheels. It offers numerous advantages, such as high fuel efficiency, reduced oil consumption, smooth operation, and quieter performance compared to motorcycle engines. During routine maintenance, checking the spark plug connections and preventing carbon buildup can significantly improve the car's responsiveness and longevity.

[StJune]

As a common driver, the operation of a four-stroke gasoline engine is as regular as a heartbeat. First, the piston descends to draw in the air-fuel mixture; then the valves close and the piston rises to compress it; next, ignition occurs, causing an explosion that pushes the piston down to generate power; finally, the exhaust piston rises to complete one cycle. Repeating this process provides smooth, fuel-efficient driving. The precise ignition timing at the end of compression ensures full combustion, minimizing waste. The benefits include smooth operation and low pollution, making it ideal for family cars and long-distance driving. However, regular cleaning of the air filter is essential to prevent impurities from obstructing airflow and affecting performance.

[DelEleanor]

From my practical experience, the ingenuity of a four-stroke engine lies in the seamless integration of its four phases. The piston moves downward with the intake valve open, drawing in the fuel-air mixture; then moves upward with the valves closed to compress the mixture into high pressure; the power stroke ignites the mixture via the spark plug, pushing the piston down to deliver power; finally, the exhaust valve opens as the piston moves up to expel the residual gases. This entire process operates in an efficient cycle, with the crankshaft continuously rotating to drive the vehicle. The key is complete combustion, which reduces exhaust issues and improves fuel economy. For long-term use, ensuring an effective cooling system prevents overheating, and maintaining good spark plug condition avoids misfires, thereby extending the engine's overall durability.