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Unit injector
A unit injector (UI) is a high-pressure 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 typically lubricated and cooled by the fuel itself.
High-pressure injection delivers power and fuel consumption benefits over earlier lower-pressure fuel injection by injecting fuel as a larger number of smaller droplets, giving a much higher ratio of surface area to volume. This provides improved vaporisation from the surface of the fuel droplets and so more efficient combining of atmospheric oxygen with vaporised fuel, delivering more complete and cleaner combustion.
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 U.S. 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 favouring 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 1994, Robert Bosch GmbH supplied the first electronic unit injector for commercial vehicles, and other manufacturers soon followed. In 1995, Electromotive Diesel converted its 710 diesel engines to electronic fuel injection, using an EUI which replaces the UI.
Today, major manufacturers include Robert Bosch GmbH, CAT, Cummins, Delphi, Detroit Diesel, Electro-Motive Diesel.
The design of the unit injector eliminates the need for high-pressure fuel pipes, and with that, their associated failures, as well as allowing for much higher injection pressure to occur. The unit injector system allows accurate injection timing, and amount of control as in the common rail system .
The unit injector is fitted into the engine cylinder head, where the fuel is supplied via integral ducts machined directly into the cylinder head. Each injector has its own pumping element, and in the case of electronic control, a fuel solenoid valve as well. The fuel system is divided into the low-pressure (<500 kPa) fuel supply system, and the high-pressure injection system (<2000 bar).
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Unit injector
A unit injector (UI) is a high-pressure 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 typically lubricated and cooled by the fuel itself.
High-pressure injection delivers power and fuel consumption benefits over earlier lower-pressure fuel injection by injecting fuel as a larger number of smaller droplets, giving a much higher ratio of surface area to volume. This provides improved vaporisation from the surface of the fuel droplets and so more efficient combining of atmospheric oxygen with vaporised fuel, delivering more complete and cleaner combustion.
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 U.S. 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 favouring 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 1994, Robert Bosch GmbH supplied the first electronic unit injector for commercial vehicles, and other manufacturers soon followed. In 1995, Electromotive Diesel converted its 710 diesel engines to electronic fuel injection, using an EUI which replaces the UI.
Today, major manufacturers include Robert Bosch GmbH, CAT, Cummins, Delphi, Detroit Diesel, Electro-Motive Diesel.
The design of the unit injector eliminates the need for high-pressure fuel pipes, and with that, their associated failures, as well as allowing for much higher injection pressure to occur. The unit injector system allows accurate injection timing, and amount of control as in the common rail system .
The unit injector is fitted into the engine cylinder head, where the fuel is supplied via integral ducts machined directly into the cylinder head. Each injector has its own pumping element, and in the case of electronic control, a fuel solenoid valve as well. The fuel system is divided into the low-pressure (<500 kPa) fuel supply system, and the high-pressure injection system (<2000 bar).