The internal combustion engine is used to power nearly all land vehicles and many water-based and air-based vehicles as well. In an internal combustion engine, a fuel, such as gasoline, fills a chamber and then is ignited by a spark plug, causing a small explosion which generates work.
The superheated expanding gas created by the explosion pushes a piston, which drives a crankshaft usually connected to an axle. The axle is connected to wheels which turn to drive a vehicle, such as an automobile, forward.
The entire assemblage of a chamber, spark plug, piston, crankshaft, and valves that allow in fuel and air is known as a cylinder. Whereas small appliances such as chainsaws only use one cylinder, autmobiles generally use four to eight. Historic aircraft have had as many as 28 cylinders to provide the power to drive their propellers.
The internal combustion engine is distinct from external combustion engines (such as steam engines), in that the energy generated from the combustion of fuel is efficiently contained within a cylinder. In steam engines, fuel is used to transform water into steam which then moves through a mechanism and provides work. Internal combustion engines took some time to perfect because the cylinder must be able to withstand the wear and tear of many thousands of explosions over the course of its operating lifetime.
Although engineers have been experimenting with automobiles driven by various types of engines since the 18th century, it wasn't until the late 19th century that Germans Daimler and Benz created internal combustion engines suited for mass production and commercialization. This ushered in the modern era of internal combustion engines used for a vast variety of purposes. In common use for more than a century, it could be a while before our engineers devise a new standard of engine for powering our multitude of machines.