Just about every vehicle on the road is powered by an internal combustion engine. Jean Joseph Etienne Lenoir, a Belgian engineer, is credited with inventing and patenting the first running internal combustion engine in 1860. They’ve come a long way since then and added computers and other bells and whistles along the wat, but in many ways the underlying internal combustion engine isn’t as complicated as you might think. As the name suggests, an internal combustion engine, burns a mixture of fuel and oxygen in an enclosed space called a combustion chamber.

If you’ve ever played with fire you know that gases tend to expand rapidly when they get hot, creating pressure. The pressure from exploding gas is applied to moving parts in the engine which allows us to turn chemical energy stored in fuel into mechanical energy.

There are a multitude of different types of internal combustion engines. Jet engine, rocket engines, rotary, etc… but the most common in road vehicles is the piston engine. Also known as a reciprocating engine, a piston engine, consists of a piston, basically a solid cylinder, with a pivoting rod at the bottom. The piston sits inside a tube called a cylinder.

The piston is driven by the earlier mentioned exploding gas which causes it to travel up and down inside the cylinder. The piston is coupled at its pivot point to connecting rod which attaches the piston to the crankshaft. The reciprocating motion, up and down, of the piston is transmitted by the connecting rod to the crankshaft which spins accordingly. We’ve now turned an explosion, into up and down motion and finally into rotational motion in the crankshaft which can be used to turn the vehicle’s wheels.

The cylinders in an engine are usually part of a larger assembly called the cylinder block. A cylinder head keeps the cylinders sealed and forms the combustion chambers. The cylinder head also tends to contain passageways and parts for the flow of mixture and exhaust gases in and out of the engine.

All of these parts, and many others along with them, have to work in a perfectly coordinated dance together to smoothly generate controlled power through a process called the combustion cycle.

Gasoline Engines vs. Diesel Engine

Gasoline engine ignition systems generally rely on a combination of a lead–acid battery and an induction coil to provide a high-voltage electric spark to ignite the air-fuel mix in the engine’s cylinders. This battery is recharged during operation using an electricity-generating device such as analternator. Gasoline engines take in a mixture of air and gasoline and compress it to not more than 12.8 bar (1.28 MPa), then use a spark plug to ignite the mixture when it is compressed by the piston head in each cylinder.

Diesel engines engines, rely solely on heat and pressure created by the engine in its compression process for ignition. The compression level that occurs is usually twice or more than a gasoline engine. Diesel engines take in air only, and shortly before peak compression, spray a small quantity of diesel fuel into the cylinder via a fuel injector that allows the fuel to instantly ignite. This is also why diesel engines are more susceptible to cold-starting issues. Light duty diesel engines with indirect injection in automobiles and light trucks employ glowplugs that pre-heat the combustion chamber just before starting to reduce no-start conditions in cold weather.

Two-stroke Engines

Engines based on the two-stroke cycle use two strokes (one up, one down) for every power stroke. There are no dedicated intake or exhaust strokes.

The steps involved here are:

  1. Intake and exhaust occur at bottom dead center. Some form of pressure is needed, either crankcase compression or super-charging.
  2. Compression stroke: Fuel-air mix is compressed and ignited. In case of diesel: Air is compressed, fuel is injected and self-ignited.
  3. Power stroke: Piston is pushed downward by the hot exhaust gases.

Two-stroke engines tend to be small and light for their power output and mechanically are very simple; however, they are also generally less efficient and more polluting than their four-stroke counterparts.

Two-stroke engines are widely used in snowmobiles, lawnmowers, string trimmers, chain saws, jet skis, mopeds, outboard motors, and many motorcycles. Two-stroke engines have the advantage of an increased specific power ratio (i.e. power to volume ratio), typically around 1.5 times that of a typical four-stroke engine.

Oddly enough, some of the largest internal combustion engines in the world are two-stroke diesels, used in some locomotives and large ships.

Four-stroke Engines

Engines based on the four-stroke (“Otto cycle”) have one power stroke for every four strokes (up-down-up-down) and employ spark plug ignition. They are used in cars, larger boats, some motorcycles, and many light aircraft. They are generally quieter, more efficient, and larger than their two-stroke counterparts.

The steps involved here are:

  1. Intake stroke: Air and vaporized fuel are drawn in.
  2. Compression stroke: Fuel vapor and air are compressed and ignited.
  3. Combustion stroke: Fuel combusts and piston is pushed downwards.
  4. Exhaust stroke: Exhaust is driven out. During the 1st, 2nd, and 4th stroke the piston is relying on power and the momentum generated by the other pistons. In that case, a four-cylinder engine would be less powerful than a six- or eight-cylinder engine.

Wankel Engines


The Wankel engine (rotary engine) does not have piston strokes. It operates with the same separation of phases as the four-stroke engine, but the phases take place in separate locations in the engine. This engine provides three power ‘strokes’ per revolution per rotor giving it a greater power-to-weight ratio than piston engines. This type of engine was most notably used in the Mazda RX-8 and RX-7.

How an Engine Works Video

Below is a great video that covers the common parts of a car engine and how they function together. The video was created as a Toyota training tool, but if you’ve ever wondered what the terms camshaft, connecting rod, piston, or compression mean, this is for you.

How A Car Engine Works Animated Infographic

Jacob O’Neal put together this animated infographic to explain, in the simplest terms possible, how an engine works.