Compression-ignition engine in the context of Liquefied petroleum gas

A diesel locomotive is a type of railway locomotive in which the power source is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving wheels. The most common are diesel–electric locomotives and diesel–hydraulic.

Early internal combustion locomotives and railcars used kerosene and gasoline as their fuel. Rudolf Diesel patented his first compression-ignition engine in 1898, and steady improvements to the design of diesel engines reduced their physical size and improved their power-to-weight ratios to a point where one could be mounted in a locomotive. Internal combustion engines only operate efficiently within a limited power band, and while low-power gasoline engines could be coupled to mechanical transmissions, the more powerful diesel engines required the development of new forms of transmission. This is because clutches would need to be very large at these power levels and would not fit in a standard 2.5 m (8 ft 2 in)-wide locomotive frame, or would wear too quickly to be useful.

A reciprocating engine, more often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert high temperature and high pressure into a rotating motion. This article describes the common features of all types. The main types are: the internal combustion engine, used extensively in motor vehicles; the steam engine, the mainstay of the Industrial Revolution; and the Stirling engine for niche applications. Internal combustion engines are further classified in two ways: either a spark-ignition (SI) engine, where the spark plug initiates the combustion; or a compression-ignition (CI) engine, where the air within the cylinder is compressed, thus heating it, so that the heated air ignites fuel that is injected then or earlier.

A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, typically diesel engines, where the heat generated from compression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.