What is the Purpose of an Engine? Why is an Engine Necessary?

An engine provides the power to move a vehicle such as a car or truck.  Without the engine, the vehicle would not have a source of power to accelerate or keep moving. 

Engine fuel types

Typical engines are powered by gasoline, diesel, or in some cases other fuels such as compressed natural gas (CNG) or LPG (liquified petroleum gas).  This type of engine is the internal combustion engine (ICE).  The internal combustion burns the fuel to produce power.  These generally operate on the Otto cycle, though there are other types of engines. 

Engine power output

The engine is generally mated to a transmission.  (The output shaft of the engine going to the input of the transmission).

Interference vs non-interference

Depending on engine design, it may be interference (possibility for contact between the pistons and valves), or non-interference (no possibility of contact between the pistons or valves).