Fuel efficiency facts for kids

Fuel efficiency (also called fuel economy) is a measure of how well a machine turns fuel into useful energy. It is most often used to talk about cars and trucks. If a vehicle is fuel-efficient, it can travel a long distance using only a small amount of fuel.

This concept is important for saving money on gas and for protecting the environment. When we use less fuel, we create less pollution. Factories and power plants also try to be fuel-efficient to work better and cleaner.

Measuring fuel use

Different countries measure fuel efficiency in different ways:

• Miles per gallon (mpg): This is used in the United States and the United Kingdom. It tells you how many miles a car can drive on one gallon of fuel. A higher number is better.
• Liters per 100 kilometers (L/100 km): This is used in many countries that use the metric system, like in Europe. It tells you how many liters of fuel are needed to drive 100 kilometers. In this case, a lower number is better because it means the car uses less fuel.

Designing efficient vehicles

Engineers work hard to design cars that use less fuel. There are several ways to do this:

• Aerodynamics: Cars are shaped to cut through the air easily. This reduces "drag" or air resistance.
• Weight: Lighter cars need less energy to move. Engineers use special lightweight materials to build them.
• Engines: Modern engines are built to waste less heat and energy.
• Tires: Special tires can roll more smoothly on the road, which saves gas.

Hybrid cars

Hybrid vehicles are cars that use two sources of power. Usually, they have a regular gasoline engine and an electric motor.

When a driver uses the brakes, energy is normally lost as heat. In a hybrid car, this energy is captured and turned into electricity. The car stores this electricity in a battery and uses it to help the engine later. This makes hybrid cars very efficient, especially in city traffic.

Different types of fuel

Not all fuels contain the same amount of energy. The energy inside a fuel is called its energy content. For example, diesel fuel packs more energy into every liter than gasoline does. This is one reason why diesel engines can often drive further on the same amount of fuel.

The table below shows the energy content of common fuels.

Transportation methods

This chart shows the types of vehicles produced in the US. Over time, more people started buying trucks and SUVs (the red and blue areas), which often use more fuel than smaller cars.

The way we travel affects how much energy we use.

• Trains: Trains are very efficient because they carry hundreds of people at once. Many trains run on electricity. If that electricity comes from clean sources like wind or solar power, the train creates very little pollution.
• Cars: Personal cars are convenient but use a lot of energy per person. Driving carefully—without speeding up or slowing down too fast—can help save fuel.
• Planes: Airplanes use a lot of fuel to take off. However, because they travel very fast and carry many people, they can sometimes be as efficient per passenger as a car with only one person in it.

Hydrogen power

Some modern vehicles run on hydrogen. These cars use a device called a fuel cell. The fuel cell mixes hydrogen with oxygen from the air to create electricity. This electricity powers the car's motor.

The amazing thing about hydrogen cars is that their exhaust is just pure water! They do not release harmful smoke. However, we still need to make sure the hydrogen itself is made using clean energy.

Science in space

Did you know that fire burns differently in space? NASA has done experiments to see how fuel burns in microgravity (the condition of floating in space).

On Earth, hot air rises. This is why a candle flame is tall and pointy. In space, hot air does not rise because there is no gravity to pull cold air down. As a result, a flame in space forms a perfect blue sphere.

NASA found that fire burns more completely and efficiently in space. Understanding this helps scientists design better engines for use on Earth.

See also