The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, or flat (also known as horizontally opposed or boxer), as shown in the following figures.
Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.
Let's look at some key engine parts in more detail.
The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.
The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.
A piston is a cylindrical piece of metal that moves up and down inside the cylinder.
Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:
- They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.
Most cars that "burn oil" and have to have a quart added every 1, 000 miles are burning it because the engine is old and the rings no longer seal things properly.
The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.
The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.
The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).