A unit injector (UI) is a high-pressure integrated direct

fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All c ...

system for

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

s, combining the

injector An injector is a system of ducting and nozzles used to direct the flow of a high-pressure fluid in such a way that a lower pressure fluid is Entrainment (hydrodynamics), entrained in the jet and carried through a duct to a region of higher pres ...

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe (material), pipe. A nozzle is often a pipe or tube of varying cross ...

and the injection pump in a single component. The

plunger pump A plunger pump is a type of positive displacement pump where the high-pressure seal is stationary and a smooth cylindrical plunger slides through the seal. This makes them different from piston pumps and allows them to be used at higher pressure ...

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.

History

In 1911, a patent was issued in

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for a unit injector resembling those in use today to Frederick Lamplough. Commercial usage of unit injectors in the

U.S. The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguous ...

began in early 1930s on Winton engines powering locomotives, boats, even

US Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

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 General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. The company is most known for owning and manufacturing f ...

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 Electro-Motive Diesel (abbreviated EMD) is a brand of diesel-electric locomotives, locomotive products and diesel engines for the rail industry. Formerly a division of General Motors, EMD has been owned by Progress Rail since 2010. Electro-Motive ...

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 Cummins Inc. is an American multinational corporation, multinational corporation that designs, manufactures, and distributes engines, electric vehicle components, and power generation products. Cummins also services engines and related equipmen ...

, ⁣

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, ⁣ Detroit Diesel,

Design and technology

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 A solenoid valve is an electromechanically operated valve. Solenoid valves differ in the characteristics of the electric current they use, the strength of the magnetic field they generate, the mechanism they use to regulate the fluid, and the ...

as well. The fuel system is divided into the low-pressure (<500 kPa) fuel supply system, and the high-pressure injection system (<2000 bar). Technical characteristics: *The special feature of the unit injector system is that an individual pump is assigned to each cylinder *The pump and nozzle are therefore combined in a compact assembly which is installed directly in the cylinder head *The unit injector system enables high injection pressures up to 2,200 bar. Advantages: *High performance for clean and powerful engine *High engine power balanced against low consumption and low engine emissions *High degree of efficiency due to compact design *Low noise level due to direct assembly in the engine block *Injection pressures up to 2,200 bar for the ideal combination of air-fuel mixture.

Operation principle

The basic operation can be described as a sequence of four separate phases: the ''filling phase'', the ''spill phase'', the ''injection phase'', and the ''pressure reduction phase''. A low-pressure fuel delivery pump supplies filtered

diesel fuel Diesel fuel, also called diesel oil, heavy oil (historically) or simply diesel, is any liquid fuel specifically designed for use in a diesel engine, a type of internal combustion engine in which fuel ignition takes place without a spark as a re ...

into the cylinder head fuel ducts, and into each injector fuel port of constant stroke pump plunger injector, which is

overhead camshaft An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustio ...

operated. ;Fill phase: The constant stroke pump element on the way up draws fuel from the supply duct in to the chamber, and as long as the electric

remains de-energized the fuel line is open. ;Spill phase: The pump element is on the way down, and as long as the solenoid valve remains de-energized the fuel line is open and fuel flows in into the return duct. ;Injection phase: The pump element is still on the way down, the solenoid is now energised and the fuel line is immediately closed. The fuel cannot pass back into the return duct, and is now compressed by the plunger until pressure exceeds specific “opening” pressure, and the injector nozzle needle lifts, allowing fuel to be injected into the

combustion chamber A combustion chamber is part of an internal combustion engine in which the air–fuel ratio, fuel/air mix is burned. For steam engines, the term has also been used for an extension of the Firebox (steam engine), firebox which is used to allow a mo ...

. ;Pressure reduction phase: The plunger is still on its way down, the engine ECU de-energizes the solenoid when the required quantity of fuel is delivered. The fuel valve opens, fuel can flow back into the return duct, causing the pressure to drop. Which in turn causes the injector nozzle needle to shut; hence no more fuel is injected. ;Summary: The start of an injection is controlled by the solenoid closing point, and the injected fuel quantity is determined by the closing time, which is the length of time the solenoid remains closed. The solenoid operation is fully controlled by the engine ECU.

Additional functions

The use of electronic control allows for special functions; such as temperature controlled injection timing, cylinder balancing (smooth idle), switching off individual cylinders under part load for further reduction in emissions and fuel consumption, and multi-pulse injection (more than one injection occurrence during one engine cycle).

Usage & Applications

Unit injector fuel systems are being used on a wide variety of vehicles and engines; commercial vehicles from manufacturers such as

Volvo The Volvo Group (; legally Aktiebolaget Volvo, shortened to AB Volvo, stylized as VOLVO) is a Swedish multinational manufacturing corporation headquartered in Gothenburg. While its core activity is the production, distribution and sale of truck ...

, Detroit Diesel, CAT,

Navistar International International Motors, LLC (formerly Navistar International Corporation) is an American manufacturer of commercial vehicles and engines, established in 1986 as a successor to the International Harvester company. International Motors produces ...

and passenger vehicles from manufacturers such as Land Rover and

Volkswagen Group Volkswagen AG (), known internationally as the Volkswagen Group, is a German public multinational conglomerate manufacturer of passenger and commercial vehicles, motorcycles, engines and turbomachinery. Headquartered in Wolfsburg, Lower Saxon ...

, among others, and

locomotive A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pull train, push–pull operation has become common, and in the pursuit for ...

s from Electromotive Diesel. Bosch Unit Injector

The Volkswagen Group mainstream marques used unit injector systems (branded "Pumpe Düse", commonly abbreviated to "PD") in their Suction Diesel Injection (SDI) and Turbocharged Direct Injection (TDI)

s, however this fuel injection method has been superseded by a common-rail design, such as the new 1.6 TDI. In

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, the Volkswagen Jetta,

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, and New Beetle TDI 2004–2006 are ''Pumpe Düse'' (available in both the MK4 and MK5 generations, with BEW and BRM engine codes respectively, older models use timing belt-driven injection pump). TDI engines incorporating PD unit injector systems manufactured by the Volkswagen Group were also installed on some cars sold in Europe and other markets where the diesel fuel was conveniently priced, amongst those there were some Chrysler/Dodge cars of the DaimlerChrysler era, e.g. the Dodge Calibre (MY07 BKD, MY08 BMR), Dodge Journey, Jeep Compass, Jeep Patriot. Volkswagen Group major-interest

truck A truck or lorry is a motor vehicle designed to transport freight, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construct ...

and diesel engine maker Scania AB also uses the unit injector system, which they call "''Pumpe-Düse-Einspritzung''", or "PDE".

Hydraulically actuated electronic (HEUI) development and applications

In 1993, CAT and International Truck & Engine Corporation introduced "hydraulically actuated electronic unit injection” (HEUI), where the injectors are no longer camshaft-operated and could pressurise fuel independently of engine RPM. First available on Navistar's 7.3L /444 cuin, V8

. HEUI uses engine oil pressure to power high-pressure fuel injection, where the usual method of unit injector operation is with the

engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...

camshaft. HEUI applications included the Ford 7.3L and 6.0L Power stroke used between May 1993 and 2007. International also used the HEUI system for multiple engines including the DT 466E, DT 570, T-444E, DT-466–570, MaxxForce 5, 7, 9, 10, MaxxForce DT and VT365 engines.

Caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...

incorporated HEUI systems in the 3116, 3126, C7, C9 among others and the Daimler-Detroit Diesel Series 40 engine supplied by International also incorporated a HEUI fuel system. Isuzu fitted a HEUI system to their 3.0 LTR 4JX1 engine fitted to the Trooper and its variants. The HEUI system has been replaced by many manufacturers with common rail injection solutions, a newer technology, to meet better fuel economy and new emissions standards being introduced.

Notes

References

*Diesel Fuel Injection published by Robert Bosch GmbH, 1994 *Diesel Engines and Fuel Systems by A. Asmus & B. Wellington, 1988 {{Automotive engine, collapsed Diesel engine components Diesel engine technology Engine fuel system technology