Aunit injector (UI) is a high-pressure integrated directfuel injection system fordiesel engines, combining theinjectornozzle and theinjection pump in a single component. Theplunger pump used is usually driven by a sharedcamshaft. 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 inGreat Britain for a unit injector resembling those in use today toFrederick Lamplough.[1]
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Commercial usage of unit injectors in theU.S. began in early 1930s onWinton engines powering locomotives, boats, evenUS Navy submarines,[2] and in 1934, Arthur Fielden was granted U.S. patent No.1,981,913[3] on the unit injector design[4] later used for theGeneral Motorstwo-stroke diesel engines. Most mid-sized diesel engines used a single pump and separate injectors, but some makers, such asDetroit Diesel[5] andElectro-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.[6]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 firstelectronic unit injector for commercial vehicles, and other manufacturers soon followed. In 1995, Electromotive Diesel converted its710 diesel engines to electronic fuel injection, using anEUI which replaces the UI.
Today, major manufacturers includeRobert Bosch GmbH,CAT,[7]Cummins, [8]Delphi, [9][10]Detroit Diesel,Electro-Motive Diesel.[11]
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 thecommon rail system .[12]
The unit injector is fitted into the enginecylinder 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 fuelsolenoid 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).[13]
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Technical characteristics:
Advantages:
The basic operation can be described as a sequence of four separate phases: thefilling phase, thespill phase, theinjection phase, and thepressure reduction phase.
A low-pressurefuel delivery pump suppliesfiltereddiesel fuel into thecylinder head fuel ducts, and into each injector fuel port of constant stroke pump plunger injector, which isoverhead camshaft operated.
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).
Unit injector fuel systems are being used on a wide variety of vehicles and engines;commercial vehicles from manufacturers such asVolvo,Cummins,Detroit Diesel,CAT,Navistar International and passenger vehicles from manufacturers such asLand Rover andVolkswagen Group, among others, andlocomotives fromElectromotive Diesel.
The Volkswagen Group mainstreammarques used unit injector systems (branded"Pumpe Düse",[14] commonly abbreviated to"PD") in theirSuction Diesel Injection (SDI) andTurbocharged Direct Injection (TDI)diesel engines,[15] however this fuel injection method has been superseded by a common-rail design, such as the new 1.6 TDI.
InNorth America, theVolkswagen Jetta,Golf, andNew Beetle TDI 2004–2006 arePumpe Düse[16] (available in both the MK4 and MK5 generations, with BEW and BRM engine codes respectively, older models use timing belt-driven injection pump).[citation needed]
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. theDodge Calibre (MY07 BKD, MY08 BMR),Dodge Journey,Jeep Compass,Jeep Patriot.
Volkswagen Group major-interesttruck and diesel engine makerScania AB also uses the unit injector system, which they call "Pumpe-Düse-Einspritzung", or"PDE".
In 1993,CAT andInternational Truck & Engine Corporation[17] introduced "hydraulically actuated electronic unit injection” (HEUI), where the injectors are no longercamshaft-operated and could pressurise fuel independently of engine RPM. First available onNavistar's 7.3L /444 cuin,V8diesel engine. HEUI uses engine oil pressure to power high-pressure fuel injection, where the usual method of unit injector operation is with theengine camshaft.
HEUI applications included the Ford 7.3L and 6.0LPower stroke used between May 1993 and 2007. International also used the HEUI system for multiple engines including theDT 466E, DT 570,T-444E, DT-466–570, MaxxForce 5, 7, 9, 10, MaxxForce DT and VT365 engines.[dubious –discuss]Caterpillar 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 withcommon rail injection solutions, a newer technology, to meet better fuel economy and new emissions standards being introduced.