Oily Bits: The Basic Design of an Engine
This month, our mechanic takes us through the basics of an engine.
The vast majority of vehicles are powered by what's known as an internal combustion engine.
It's a concept that's been around for a long time but a Belgian engineer, called Jean Joseph Etienne Lenoir, is credited with inventing and patenting the first viable internal combustion engine in 1860.
The internal combustion engine isn't as complicated as it might sound. As the name suggests, it burns a mixture of fuel and oxygen in an enclosed space called a combustion chamber.
As this mixture burns it becomes hot and expands rapidly, creating pressure. This pressure is applied to moving parts that allow the engine to convert the chemical energy stored in the fuel into mechanical energy.
Consequently an engine, and the mechanical energy it generates, can be utilised for many useful tasks. Besides powering tools, internal combustion engines can be used to propel vehicles.
There are lots of different types of internal combustion engines, including jet engines and rocket engines, but the most common in road vehicles is the piston engine. A piston engine, also known as a reciprocating engine, consists of several key parts. The piston itself is effectively a solid cylinder or disc, typically about 90 mm in diameter, with a pivoting rod at the bottom. It sits inside a tube called a cylinder.
The piston, which travels up and down inside the cylinder, is coupled at its pivot point to connecting rod. This attaches the piston to a part of the engine called the crankshaft. If you've ever ridden a bicycle you'll be familiar how a crankshaft works. The pedals on a bicycle connect to a crank which turns the up and down motion of your feet into rotational motion, driving the chain and pushing the bike forwards.
You'll find the same action in an engine. The reciprocating motion, up and down, of the piston is transmitted by the connecting rod to the crankshaft. The crankshaft then converts it to rotational motion, which can be used to turn the vehicle's wheels.
The cylinders in an engine are usually an integral part of an assembly called the cylinder block, which forms the main bulk of the engine. Keeping the cylinders sealed and forming the combustion chambers is the cylinder head. This also tends to contain passageways and parts which allow for, and control, the flow of mixture and exhaust gases in and out of the engine.
All of these parts, and many others, have to work in time together to smoothly generate controlled power through a process called the combustion cycle. Next, we'll cover what happens in the combustion cycle and also explain how diesel engines differ from petrol ones.
In the meantime, and if you've a moment, why not have a look under the bonnet of a car and see if you can identify the cylinder head and cylinder block?