Unit Injector

Unit injector (UI) is an integrated direct fuel injection system for diesel engines, combining the injector nozzle and the injection pump in a single component. The plunger pump used is usually driven by a shared camshaft. In a unit injector, the device is usually lubricated and cooled by the fuel itself.

In 1911, a patent was issued in Great Britain for a unit injector resembling those in use today to Frederick Lamplough.

Commercial usage of unit injectors in the United States began in early 1930s on Winton engines powering locomotives, boats, even US Navy submarines, and in 1934, Arthur Fielden was granted U.S. patent No.1,981,913 on the unit injector design later used for the General Motors two-stroke diesel engines. Most mid-sized diesel engines used a single pump and separate injectors, but some makers, such as Detroit Diesel and Electro-Motive Diesel became well known for favoring unit injectors, in which the high-pressure pump is contained within the injector itself. E.W. Kettering's 1951 ASME presentation goes into detail about the development of the modern Unit injector. Also Cummins PT (pressure-time) is a form of unit injection where the fuel injectors are on a common rail fed by a low pressure pump and the injectors are actuated by a third lobe on the camshaft. The pressure determines how much fuel the injectors get and the time is determined by the cam.

In 1985 the Detroit Diesel division of General Motors Corporation supplied the first electronic unit injector for commercial vehicles in their Series 92 2-stroke diesel engines followed by introduction in the Series 60 4 stroke engines in 1987. Other manufacturers soon followed. In 1995, Electro-Motive Diesel converted its 710 diesel engines to electronic fuel injection, using an EUI which replaces the MUI.

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