The Diesel locomotive is a type of railroad locomotive in which the prime mover is a Diesel engine. Several types have been developed, the major distinction being in the means by which the prime mover's mechanical power is conveyed to the driving wheels or drivers.
Early internal combustions engine powered locomotives used gasoline as their fuel. Soon after Dr. Rudolf Diesel patented his first compression ignition engine in 1892, its application for railway propulsion was considered.
Diesel engine progress was slow, however, because of the poor power-to-weight ratio of the early engines, as well as the difficulty inherent in mechanically applying power to multiple driving wheels on swiveling trucks.
Steady improvements in the Diesel engine's design gradually reduced its physical size and improved its power-to-weight ratio to a point where one could be mounted in a locomotive.
Once the concept of Diesel-electric drive was accepted the pace of development quickened.
By the mid 20th century, the Diesel engine locomotive had become the dominant type of locomotive in much of the world, offering greater flexibility and performance than the steam locomotive, as well as substantially lower operating and maintenance costs. Currently, almost all Diesel engine locomotives are Diesel-electric.
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