Diesel-hydraulic

A diesel locomotive is a type of railway locomotive in which the prime mover is a diesel engine. Several types of diesel locomotive have been developed, differing mainly in the means by which mechanical power is conveyed to the driving wheels (drivers).

Early internal combustion engine-powered locomotives and railmotors used gasoline as their fuel. Soon after Dr. Rudolf Diesel patented his first compression ignition engine in 1892, it was considered for railway propulsion. Progress was slow, however, as several problems had to be overcome.

Power transmission was a primary concern. As opposed to steam and electric engines, internal combustion engines work efficiently only within a limited range of turning frequencies. In light vehicles, this could be overcome by a clutch. In heavy railway vehicles, mechanical transmission never worked well or wore out too soon. Experience with early gasoline powered locomotives and railcars was valuable for the development of diesel traction. One step towards diesel-electric transmission was the petrol-electric vehicle, such as the Acsev Weitzer railmotor, which could operate from batteries and electric overhead wires too. (1903 ff.)

Steady improvements in diesel design (many developed by Sulzer Ltd. of Switzerland, with whom Dr. Diesel was associated for a time) 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, and by 1925 a small number of diesel locomotives of 600 horsepower were in service in the United States. In 1930, Armstrong Whitworth of the United Kingdom delivered two 1,200 hp locomotives using engines of Sulzer design to Buenos Aires Great Southern Railway of Argentina.

By the mid-1950s, with economic recovery from the Second World War, production of diesel locomotives had begun in many countries and the diesel locomotive was on its way to becoming the dominant type of locomotive. It offered greater flexibility and performance than the steam locomotive, as well as substantially lower operating and maintenance costs, other than where electric traction was in use due to policy decisions. Currently, almost all diesel locomotives are diesel-electric, although the diesel-hydraulic type was widely used between the 1950s and 1970s.

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