Four-stroke engine facts for kids

Four-stroke cycle used in gasoline/petrol engines: intake (1), compression (2), power (3), and exhaust (4). The blue side is the intake port, and the brown side is the exhaust port.

A four-stroke engine is a special type of engine that powers many vehicles we use every day. It's called "four-stroke" because a part inside called a piston moves up and down four times to create power. These four movements, or "strokes," happen in a specific order to make the engine work.

Here are the four steps:

• Intake: Imagine the engine taking a deep breath! The piston moves down, pulling in a mix of air and fuel into the engine's cylinder. A special door, called the intake valve, opens to let this mixture in.
• Compression: Now, the piston moves back up, squeezing the air and fuel mixture into a tiny space. Both valves are closed tightly, trapping the mixture. Squeezing it makes it ready to burn with a lot of energy.
• Combustion (Power): This is where the magic happens! A spark plug creates a tiny spark (or in some engines, the heat from compression does it). This spark ignites the squeezed air-fuel mix, causing a small explosion. This explosion pushes the piston down with great force, creating the power that turns the engine's crankshaft and moves the vehicle.
• Exhaust: After the power stroke, the piston moves up again. This time, another special door, the exhaust valve, opens. The piston pushes out all the burnt gases, like smoke, through the exhaust pipe. Then, the cycle starts all over again!

Four-stroke engines are super common. You'll find them in most automobiles, trucks, motorcycles, and even some trains and small aircraft. They are a very important part of modern transportation.

How Engines Evolved

Engines didn't just appear overnight! Many clever inventors worked hard to make them better and more powerful.

The Otto Engine: A Big Step Forward

An early Otto engine from the 1880s.

A traveling salesman named Nicolaus Otto was very interested in engines. He saw early engines that weren't very efficient. In 1864, Otto and his partner, Eugen Langen, started a company to build engines. Their big breakthrough came in 1876. They created an engine that first squeezed the fuel and air mixture before it was ignited. This made the engine much more powerful and efficient than anything before it. Later, engineers like Gottlieb Daimler and Wilhelm Maybach worked with Otto's ideas. In 1885, they built one of the very first vehicles powered by an Otto engine. The next year, Karl Benz also created a four-stroke car, which many consider the first true automobile.

The Atkinson Cycle: For More Efficiency

This 2004 Toyota Prius hybrid uses an Atkinson-cycle engine.

In 1882, James Atkinson invented a different type of engine cycle. His goal was to make engines even more efficient, meaning they would use less fuel. Modern hybrid cars, like the Toyota Prius, sometimes use ideas from the Atkinson cycle to save fuel.

The Diesel Engine: Power from Pressure

An Audi R15 race car with a powerful diesel engine.

Rudolf Diesel wanted to create an engine that was even more efficient and could use a different, heavier type of fuel. After many years of hard work and even a dangerous accident, he succeeded in 1893. Diesel's engine works by squeezing the air so much that it gets incredibly hot. When fuel is sprayed into this super-hot air, it ignites all by itself, without a spark plug! This powerful engine is now known as the diesel engine. It's often used in large trucks and heavy machinery because it's very strong and efficient.

Fuel and How It Works

The type of fuel an engine uses is very important. It affects how the engine runs and how powerful it can be.

Preventing Early Ignition

In gasoline engines, if the air-fuel mixture gets too hot and ignites before the spark plug fires, it can cause a "knock" or "ping" sound. This is called pre-ignition and can harm the engine. To prevent this, fuels are designed with different qualities. The octane rating tells you how well a fuel resists igniting too early. Higher octane fuels allow engines to squeeze the mixture more, which can make them more powerful and efficient.

Modern Fuel Delivery

Many modern gasoline engines use something called gasoline direct injection (GDI). This means fuel is sprayed directly into the engine's combustion chamber at very high pressure. This helps the engine use fuel more efficiently.

Diesel Fuel

Diesel engines don't use spark plugs. Instead, they rely on the heat created by compressing air to ignite the fuel. The cetane rating for diesel fuel tells you how easily it ignites under compression. Starting a cold diesel engine can be tricky because the air isn't hot enough yet. That's why many diesel engines use glow plugs. These are small heaters that warm up the cylinder to help the fuel ignite when the engine is cold.

How Engines Are Designed

Engineers work hard to design engines that are powerful, efficient, and last a long time.

Making More Power

The amount of power an engine makes depends on how much air it can take in. Engineers try to make air flow smoothly into and out of the engine. They can even smooth out the inside of the engine's air passages, a process called porting, to help air move faster.

Boosting Air Intake

One way to get more air into an engine is to use a special device:

• Superchargers: These are like air pumps driven by the engine itself. They force more air into the cylinders, which means more fuel can burn, creating more power.
• Turbochargers: These are similar to superchargers but are powered by the engine's exhaust gases. The hot gases spin a turbine, which then spins a compressor to push more air into the engine. This makes the engine more efficient because it uses energy that would otherwise be wasted. However, there can be a slight delay, called "turbo lag," before the turbocharger fully kicks in.

Engine Parts and Their Jobs

Engines have many moving parts that must work together perfectly.

Valves and Camshafts

The valves are like doors that open and close to let air and fuel in and burnt gases out. They are controlled by a spinning rod called a camshaft. The camshaft has special bumps, or "cams," that push on the valves at just the right time. Most modern engines have the camshaft located above the cylinders, which allows for higher engine speeds.

Valve Clearance

There's a tiny gap, called valve clearance, between the valve parts. This gap ensures the valves close completely. If the gap is too small, the valves might not close, leading to less power. If it's too big, the engine might make noise. Many modern engines use special parts called hydraulic lifters that automatically adjust this gap.

Engine Efficiency

Engines are amazing, but they don't turn all the fuel's energy into movement. A lot of energy is lost as heat. Modern gasoline engines are about 30% efficient, meaning only about 30% of the fuel's energy actually moves the car. Engineers are always looking for ways to capture this wasted heat. For example, turbochargers recover some energy from exhaust gases. Companies like BMW have even developed systems to turn exhaust heat back into useful energy for the engine. Also, engines are designed to meet rules about emissions, which are gases that come out of the exhaust. Devices like catalytic converters help reduce harmful pollutants, even if it means a slight reduction in efficiency. In the United States, there are rules like the Corporate Average Fuel Economy (CAFE) standards that push car makers to build more fuel-efficient vehicles. This encourages new designs to get more power from less fuel.

See also

In Spanish: Ciclo de cuatro tiempos para niños