A diesel engine (also known as a compression ignition engine
and sometimes capitalized as Diesel engine) is an
internal combustion engine that uses the heat of
compression to initiate ignition to burn the fuel,
which is injected into the combustion chamber
 during the final stage of compression.
Rudolf Diesel, of German nationality, was born in 1858 in Paris where his parents were Bavarian immigrants. He was educated at Munich Polytechnic. After graduation he was employed as a refrigerator engineer but his true love lay in engine design. Diesel designed many heat engines, including a solar-powered air engine. In 1893, he published a paper describing an engine with combustion within a cylinder, the internal combustion engine.

In 1894, he filed for a patent for his new invention, dubbed the Diesel engine. His engine was the first to prove that fuel could be ignited without a spark. He operated his first successful engine in 1897.

In 1898, Diesel was granted U.S. Patent 608,845 for an "internal combustion engine".

Diesel engines have several advantages over other internal combustion engines:

  • They burn less fuel than a petrol engine performing the same work, due to the engine's higher temperature of combustion and greater expansion ratio. Gasoline engines are typically 25 percent efficient while diesel engines can convert over 30 percent of the fuel energy into mechanical energy.
The life of a diesel engine is generally about twice as long as that of a petrol engine due to the increased strength of parts used. Diesel fuel has better lubrication properties than petrol as well.
In common rail systems, the separate pulsing high pressure fuel line to each cylinder's injector is also eliminated. Instead, a high-pressure pump pressurizes fuel at up to 2,500 bar (250 MPa; 36,000 psi), in a "common rail". The common rail is a tube that supplies each computer-controlled injector containing a precision-machined nozzle and a plunger driven by a solenoid or piezoelectric actuator.