Whenever you travel by car, plane, ship, or even spaceship, you are powered by fire - roaring flames or carefully controlled explosions happening inside the engine.
Fossil fuels such as oil, coal, and gas still provide about 80 percent of the power we use every day. Gasoline (made from oil) packs huge amounts of energy into a tiny volume of liquid, so it is particularly good for use in vehicles.
Engines are the machines that release this energy, using a chemical reaction called combustion. When fuels burn with oxygen from the air, their molecules smash apart and release their energy as heat. Engines capture this heat and convert it into a force that powers us down roads, over waves, or through the sky.
In car engines, fuel (gasoline or diesel) explodes inside sturdy metal cylinders, pushing pistons up and down to generate the power that drives the wheels. Piston engines go through four simple steps, called a four-stroke cycle, which repeat over and over again, moving the car along.
1. Suck: The cycle begins when the intake valve opens at the top of the cylinder. The piston moves down, and fuel and air are sucked in through the open valve. They swirl together to make a highly explosive mixture.
2. Squeeze: The valve closes and the piston rises, squashing the mixture into about a tenth of the space and heating it up. The more the mixture is compressed, the more energy it will release when it burns and expands.
3. Bang: A carefully timed burst of electricity makes the sparkplug fire, igniting the mixture and causing it to explode. The explosion pushes the piston down and turns the crankshaft, which powers the engine.
4 Blow: When the fuel burns with oxygen, it turns into carbon dioxide gas, steam, and pollution that must be removed. The exhaust valve opens and the piston pushes up, driving the waste gases out, ready for the cycle to start again.