In the last two decades engine technology has been progressing at breakneck speed. Each year the automobile industry refines engine technology with new fuel systems and computer modules that improve power and gas mileage. However, the fundamentals of the internal combustion engine have not changed in nearly a century, and the heart of every automobile is still a four-stroke gasoline engine.
To understand how a four-stroke engine operates we must first understand how an engine generates power. It may come as a surprise, but a gasoline engine is essentially a contained explosion! The explosion is contained within the engine’s cylinders, where gasoline is compressed by a piston and burned. This process takes four steps or strokes to produce power: the intake stroke, compression stroke, power stroke, and the exhaust stroke. Next we will look at each.
Intake Stroke
Before gasoline can be burned it must first enter the engine. Each stage of an engine’s cycle is determined by the position of the piston within the cylinder. During the intake stroke the piston moves downward in the cylinder, and just like drawing back the plunger of a syringe this action draws air and gasoline into the cylinder. This step is crucial because it takes more than just gasoline to powers an engine: gasoline cannot burn without being mixed with the oxygen in the air. The intake strokes also acts to aerosolize the gasoline into tiny droplets, creating a volatile mixture that is ripe for combustion.
Compression Stroke
During the next step in the engine’s cycle the piston begins moving upward in the cylinder, compressing the air and fuel mixture. It is this step which primes the engine for an explosion—just like the exploding gunpowder which pushes a bullet down a gun barrel, the exploding gasoline must be compressed to produce energy. The final step in the compression stroke happens when the spark plug fires, causing the air and gasoline to explode violently.
Power Stroke
As the gasoline burns it creates a shock wave of hot gases which push the piston back down the cylinder. This energy is transferred from the piston through the connecting rod to the drive wheel of the engine—the spinning drive wheel is what turns the wheels of the car. Although it is dizzying to imagine, this process takes places thousands of times inside the engine each minute. A typical automobile engine can have four, six or eight cylinders, and inside each cylinder small explosions are continually propelling the vehicle.
Exhaust Stroke
Although the engine has now produced useful energy there are still hot gases left over from the burning gasoline. The majority of this gas is carbon dioxide which must be cleared from the cylinder before another explosion can take place. During the exhaust stroke the piston again moves upward, pushing the exhaust gases out of the engine and through the exhaust pipe. Once the cylinder is empty the engine is ready to begin the process all over again and the intake stroke begins drawing new air and fuel into the engine.
- How Does a Car Engine Work?
- What is a 4 Stroke Engine?
- What is a 2 Stroke Engine?
- What is a Two Stroke Engine?
- What is Engine Pinging?
