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((use dmy dates |date=January 2024))

[[File:Unit injector early.jpg|thumb|upright|Early [[Lucas Industries plc|Lucas]] electronic [[diesel engine|diesel]] unit injector]]

A '''unit injector''' ('''UI''') is a high pressure integrated direct [[fuel injection]] system for [[diesel engine]]s, 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.

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 vaporization from the surface of the fuel droplets and so more efficient combining of atmospheric oxygen with vaporized fuel, delivering more complete and cleaner combustion.

== History ==
In 1911, a patent was issued in [[Great Britain]] for a unit injector resembling those in use today to [[Frederick Lamplough]].<ref>((cite web
  |title=History of fuel injection
  |last=DeLuca
  |first=Frank
  |url=http://www.disa.it/pdf/01HystoryOfDieselFuelInj.pdf
  |work=www.disa.it
  |access-date=28 November 2009
  |archive-date=16 May 2011
  |archive-url=https://web.archive.org/web/20110516052152/http://www.disa.it/pdf/01HystoryOfDieselFuelInj.pdf
  |url-status=dead
  ))</ref>

[[File:Napier Deltic Diesel Engine National Railway Museum (4).jpg|thumb|[[Napier Deltic]] opposed-piston two-stroke, sectioned. The unit injectors are low down, below the yellow fuel passages, driven by a camshaft to their left and injecting into the centre of the [[cylinder liner]] (pale blue).]]

Commercial usage of unit injectors in the [[U.S.]] began in early 1930s on [[Winton Motor Carriage Company|Winton]] engines powering locomotives, boats, even [[US Navy]] submarines,<ref>((cite web
 |title       = The Winton 201A Diesel Engine
 |url         = http://www.rypn.org/RyPN/articles/viewarticles.asp?filename=061130231209.txt
 |access-date  = 28 November 2009
 |archive-url  = https://web.archive.org/web/20090626084920/http://www.rypn.org/RyPN/articles/viewarticles.asp?filename=061130231209.txt
 |archive-date = 26 June 2009
))</ref> and in 1934, Arthur Fielden was granted U.S. patent No.1,981,913<ref>((cite web
  |title=United States Patent 1981913
  |url=http://www.freepatentsonline.com/1981913.html
  |access-date=28 November 2009
))</ref> on the unit injector design<ref>((cite web
  |title=A. Fielden Fuel Pump
  |url=http://www.freepatentsonline.com/1981913.pdf
  |access-date=28 November 2009
))</ref> later used for the [[General Motors]] [[two-stroke diesel engine]]s. Most mid-sized diesel engines used a single pump and separate injectors, but some makers, such as [[Detroit Diesel]]<ref>((cite book
  |first1=A. |last1=Asmus
  |first2=B. |last2=Wellington
  |title=Diesel Engines and Fuel System
  |year=1994
 |publisher=Robert Bosch GmbH
 |isbn=1-56091-542-0
))</ref> 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.<ref>((cite conference |url=https://books.google.com/books?id=QuUiAQAAMAAJ|title=History and Development of the 567 Series General Motors Locomotive Engine |last=Kettering |first=E.W. |date=29 November 1951 |publisher=Electro-Motive Division, General Motors Corporation |conference=ASME 1951 Annual Meeting |location=Atlantic City, New Jersey))</ref>
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 [[Electronically controlled unit injector|electronic unit injector]] for commercial vehicles, and other manufacturers soon followed. In 1995, Electro-Motive Diesel converted its [[EMD 710|710]] diesel engines to electronic fuel injection, using an [[Electronically controlled unit injector|EUI]] which replaces the UI.

Today, major manufacturers include [[Robert Bosch GmbH]], [[Caterpillar Inc.|CAT]],<ref>((cite web
  |title=HEUI Fuel Systems
  |url=http://www.cat.com/cda/files/87775/7/pehp9526.pdf
  |publisher=Caterpillar Inc.
  |work=Cat.com
  |year=1999
  |access-date=4 November 2009
))</ref> [[Cummins]],<ref>((cite web
  |title=Fuel Systems - High Pressure Injection (HPI) Systems
  |url=http://www.cummins.com/fuelsystems
  |publisher=Cummins Inc.
  |work=Cummins.com
  |access-date=29 April 2015
))</ref> [[Delphi Automotive|Delphi]],<ref>((cite web
 |title       = Injection Systems and Components - Delphi E1 Diesel Electronic Unit Injector
 |url         = http://delphi.com/manufacturers/cv/powertrain/injection-systems-and-components/e1-diesel-electronic-unit-injector/
 |publisher   = Delphi Automotive LLP. - Manufacturer Products : Commercial Vehicle Industry
 |work        = Delphi.com
 |access-date  = 4 November 2009
 |archive-url  = https://web.archive.org/web/20091230112216/http://delphi.com/manufacturers/cv/powertrain/injection-systems-and-components/e1-diesel-electronic-unit-injector/
 |archive-date = 30 December 2009
))</ref><ref>((cite web
  |title=Injection Systems and Components - Delphi E3 Diesel Electronic Unit Injector
  |url=http://delphi.com/manufacturers/cv/powertrain/injection-systems-and-components/e3-diesel-electronic-unit-injector/
  |publisher=Delphi Automotive LLP. - Manufacturer Products : Commercial Vehicle Industry
  |work=Delphi.com
  |access-date=4 November 2009
))</ref> [[Detroit Diesel]], [[Electro-Motive Diesel]].<ref name="autonews">((cite web|url=http://europe.autonews.com/article/20051017/ANE/510170842/denso-targets-french-us-automakers |title=Denso targets French, US automakers |publisher=Europe.autonews.com |date=2005-10-17 |access-date=2018-07-08))</ref>

==Design and technology==
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 control as in the [[common rail]] system .<ref>((cite web
  |url=http://www.kfztech.de/kfztechnik/motor/diesel/pumpeduese.htm
  |title=Pumpe Düse Einspritzung (PDE - UIS)
  |work=kfztech.de|language=de
  |access-date=15 September 2009
))</ref>

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&nbsp;[[kPa]]) fuel supply system, and the high-pressure injection system (<2000&nbsp;[[bar (unit)|bar]]).<ref>((cite web
 |title       = The efficient pump injector unit
 |url         = http://www.boschautoparts.co.uk/pcDies6.asp?c=2&d=1
 |publisher   = Robert Bosch GmbH - Automotive
 |work        = BoschAutoParts.co.uk
 |access-date  = 2008-09-30
 |archive-url  = https://web.archive.org/web/20090331184810/http://www.boschautoparts.co.uk/pcDies6.asp?c=2&d=1
 |archive-date = 2009-03-31
))</ref>

((more references|list|date=November 2020))

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==
[[File:Injector3.gif|thumb|right|350px|Animated cut through diagram of a typical fuel injector (click to see animation)]]
[[File:Unit injector.jpg|thumb|Delphi E1 UI on the [[Volvo D13A]] engine]]
[[File:Delphi E 1 Unit Injector.JPG|thumb|Delphi E1 unit injector parts]]

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 pump|fuel delivery pump]] supplies [[wiktionary:Filter|filter]]ed [[diesel fuel]] into the [[cylinder head]] fuel ducts, and into each injector fuel port of constant stroke pump plunger injector, which is [[overhead camshaft]] 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 [[solenoid valve]] 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 energized and the fuel line is now closed. The fuel can not 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]].
;Pressure reduction phase: The plunger is still on its way down, the [[engine control unit|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 wide variety of vehicles and engines; [[commercial vehicle]] from manufacturers such as [[Volvo trucks|Volvo]], [[Cummins]], [[Detroit Diesel]], [[Caterpillar Inc.|CAT]], [[Navistar International]] and passenger vehicles from manufacturers such as [[Land Rover]] and [[Volkswagen Group]], among others, and [[locomotive]]s from [[Electro-Motive Diesel]].

[[File:Bosch Unit Injector.JPG|thumb|left|[[Robert Bosch GmbH|Bosch]] UI on a Scania R164 V8 engine]]

The Volkswagen Group mainstream [[Brand|marques]] used unit injector systems (branded '''"Pumpe Düse"''',<ref name=VWoA >((Cite web
 |title=1.9 litre TDI engine with Pump Düse
 |url=http://www.myarchive.us/richc/VW_TDI_with_PumpeDuse.pdf
 |publisher=[[Volkswagen Group of America|Volkswagen of America, Inc]]
 |id=Self-Study Program - Course Number 841303|date=October 2003
 |access-date=4 November 2009
 |location=Auburn Hills, MI 48326, USA
))</ref> commonly abbreviated to '''"PD"''') in their [[Suction Diesel Injection]] (SDI) and [[Turbocharged Direct Injection]] (TDI) [[diesel engine]]s,<ref>((cite web
 |title       = Passenger-car systems - Unit Injector System (UIS)
 |url         = http://rb-k.bosch.de//en/powerconsumptionemissions/dieselsysteme/dieselsystem/passenger-car/injection_systems/uis/index.html
 |publisher   = Robert Bosch GmbH - Automotive Technology - Diesel systems
 |work        = Bosch.de
 |access-date  = 4 November 2009
 |archive-url  = https://web.archive.org/web/20091029064042/http://rb-k.bosch.de/en/powerconsumptionemissions/dieselsysteme/dieselsystem/passenger-car/injection_systems/uis/index.html
 |archive-date = 29 October 2009
))</ref> however this fuel injection method has been superseded by a common-rail design, such as the new 1.6 TDI.

In [[North America]], the [[Volkswagen Jetta]], [[Volkswagen Golf|Golf]], and [[Volkswagen New Beetle|New Beetle]] TDI 2004–2006 are ''Pumpe Düse''<ref>((cite web|url=http://myturbodiesel.com/forum/showthread.php?t=331|title=Volkswagen Mk4 turbodiesel "how to" index, for 2004–2005 Jettas and 2004–2006 New Beetles and Golfs))</ref> (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|date=June 2008))

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 Caliber]] (MY07 BKD, MY08 BMR), [[Dodge Journey]], [[Jeep Compass]], [[Jeep Patriot]].

Volkswagen Group major-interest [[truck]] and diesel engine maker [[Scania (company)|Scania AB]] also use the unit injector system, which they call "''Pumpe-Düse-Einspritzung''", or '''"PDE"'''.

==Hydraulically actuated electronic (HEUI) development and applications==
In 1993, [[Caterpillar Inc.|CAT]] and [[Navistar International|International Truck & Engine Corporation]]<ref name="hotshotsecret">((cite web |url=https://www.hotshotsecret.com/history-of-the-heui/ |title=History of the HEUI - Hot Shot's Secret |access-date=2018-04-18 |archive-url=https://web.archive.org/web/20171211062751/http://www.hotshotsecret.com/history-of-the-heui/ |archive-date=2017-12-11 ))</ref> introduced "hydraulically actuated electronic unit injection" (HEUI), where the injectors are no longer [[camshaft]]-operated and could pressurize fuel independently from engine RPM.  First available on [[Navistar T444E engine|Navistar's 7.3L /444 cuin]], [[V8 engine|V8]] [[diesel engine]].  HEUI uses engine oil pressure to power high-pressure fuel injection, where the usual method of unit injector operation is with the [[internal combustion engine|engine]] camshaft.

HEUI applications included the Ford 7.3L and 6.0L [[Powerstroke]] used between May 1993 and 2007. International also used the HEUI system for multiple engines including the [[Navistar DT engine|DT 466E]], DT 570, [[Navistar T444E engine|T-444E]], DT-466–570, MaxxForce 5, 7, 9, 10, MaxxForce DT and VT365 engines.((Dubious|date=August 2020)) [[Caterpillar Inc.|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 with [[common rail]] injection solutions, a newer technology, to meet better fuel economy and new emissions standards being introduced.

==See also==
*[[Anti-dribble valve]]
*[[unit pump]]

== Notes ==
((reflist))

== References ==
((refbegin))
*Diesel Fuel Injection published  by Robert Bosch GmbH, 1994 ((ISBN|1-56091-542-0))
*Diesel Engines and Fuel Systems by A. Asmus & B. Wellington, 1988 ((ISBN|0-7299-0013-4))
((refend))

((Automotive engine|collapsed))

[[Category:Diesel engine components]]
[[Category:Diesel engine technology]]
[[Category:Engine fuel system technology]]

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