Editing Diesel engine (section)

==Fuel injection==
The fuel is injected at high pressure into either the [[combustion chamber]], "swirl chamber" or "pre-chamber,"<ref name="Pischinger_2016_348" /> unlike petrol engines where the fuel is often added in the [[manifold injection|inlet manifold]] or [[carburetor]]. Engines where the fuel is injected into the main combustion chamber are called [[direct fuel injection|direct injection]] (DI) engines, while those which use a swirl chamber or pre-chamber are called [[indirect fuel injection|indirect injection]] (IDI) engines.<ref name="Reif_2014_28" />

=== Direct injection ===
[[File:Têtes de piston.svg|thumb|Different types of piston bowls]]
{{main|Direct fuel injection}}
Most direct injection diesel engines have a combustion cup in the top of the piston where the fuel is sprayed. Many different methods of injection can be used. Usually, an engine with helix-controlled mechanic direct injection has either an inline or a distributor injection pump.<ref name=buckman/> For each engine cylinder, the corresponding plunger in the fuel pump measures out the correct amount of fuel and determines the timing of each injection. These engines use [[fuel injection|injectors]] that are very precise spring-loaded valves that open and close at a specific fuel pressure. Separate high-pressure fuel lines connect the fuel pump with each cylinder. Fuel volume for each single combustion is controlled by a slanted [[Groove (engineering)|groove]] in the plunger which rotates only a few degrees releasing the pressure and is controlled by a mechanical governor, consisting of weights rotating at engine speed constrained by springs and a lever. The injectors are held open by the fuel pressure. On high-speed engines the plunger pumps are together in one unit.<ref name="Firstdiesel_2009" /> The length of fuel lines from the pump to each injector is normally the same for each cylinder in order to obtain the same pressure delay. Direct injected diesel engines usually use orifice-type fuel injectors.<ref name="Reif_2014_140" />

Electronic control of the fuel injection transformed the direct injection engine by allowing much greater control over the combustion.<ref name="Dieselpower_2007" />

; Common rail
[[Common rail]] (CR) direct injection systems do not have the fuel metering, pressure-raising and delivery functions in a single unit, as in the case of a Bosch distributor-type pump, for example. A high-pressure pump supplies the CR. The requirements of each cylinder injector are supplied from this common high pressure reservoir of fuel. An Electronic Diesel Control (EDC) controls both rail pressure and injections depending on engine operating conditions. The injectors of older CR systems have [[solenoid]]-driven plungers for lifting the injection needle, whilst newer CR injectors use plungers driven by [[piezoelectricity|piezoelectric]] actuators that have less moving mass and therefore allow even more injections in a very short period of time.<ref name="Reif_2014_70" />  Early common rail system were controlled by mechanical means.

The injection pressure of modern CR systems ranges from 140&nbsp;MPa to 270&nbsp;MPa.<ref name="Tschöke_2018_310" />

=== Indirect injection ===
[[File:Ricardo comet combustion.gif|thumb|Ricardo Comet indirect injection chamber]]
{{Main|Indirect injection}}
An indirect diesel injection system (IDI) engine delivers fuel into a small chamber called a swirl chamber, precombustion chamber, pre chamber or ante-chamber, which is connected to the cylinder by a narrow air passage. Generally the goal of the pre chamber is to create increased [[turbulence]] for better air / fuel mixing. This system also allows for a smoother, quieter running engine, and because fuel mixing is assisted by turbulence, [[injector]] pressures can be lower. Most IDI systems use a single orifice injector. The pre-chamber has the disadvantage of lowering efficiency due to increased heat loss to the engine's cooling system, restricting the combustion burn, thus reducing the efficiency by 5–10%. IDI engines are also more difficult to start and usually require the use of glow plugs. IDI engines may be cheaper to build but generally require a higher compression ratio than the DI counterpart. IDI also makes it easier to produce smooth, quieter running engines with a simple mechanical injection system since exact injection timing is not as critical. Most modern automotive engines are DI which have the benefits of greater efficiency and easier starting; however, IDI engines can still be found in the many ATV and small diesel applications.<ref name="Dieselhub" /> Indirect injected diesel engines use pintle-type fuel injectors.<ref name="Reif_2014_140" />

=== Air-blast injection ===
[[File:Stationärdieselmotor 1915.jpg|thumb|right|Typical early 20th century air-blast injected diesel engine, rated at 59&nbsp;kW.]]
{{Main|Air-blast injection}}

Early diesel engines injected fuel with the assistance of compressed air, which atomised the fuel and forced it into the engine through a nozzle (a similar principle to an aerosol spray). The nozzle opening was closed by a [[Needle valve|pin valve]] actuated by the [[camshaft]]. Although the engine was also required to drive an air compressor used for air-blast injection, the efficiency was nonetheless better than other combustion engines of the time.<ref name="Mau_1984_7" /> However the system was heavy and it was slow to react to changing torque demands, making it unsuitable for road vehicles.<ref name="Merker_2014_381" />

=== Unit injectors ===
{{Main|Unit Injector}}
A ''unit injector'' system, also known as "Pumpe-Düse" (''pump-nozzle'' in German) combines the injector and fuel pump into a single component, which is positioned above each cylinder. This eliminates the high-pressure fuel lines and achieves a more consistent injection. Under full load, the injection pressure can reach up to 220&nbsp;MPa.<ref name="Reif Springer Fachmedien Wiesbaden p. 393">{{Cite book |last1=Reif |first1=Konrad |title=Dieselmotor-Management Systeme, Komponenten, Steuerung und Regelung |last2=Springer Fachmedien Wiesbaden |date=2020 |isbn=978-3-658-25072-0 |publication-place=Wiesbaden |page=393 |language=de |oclc=1156847338}}</ref> Unit injectors are operated by a [[Cam (mechanism)|cam]] and the quantity of fuel injected is controlled either mechanically (by a rack or lever) or electronically.

Due to increased performance requirements, unit injectors have been largely replaced by [[common rail]] injection systems.<ref name="Tschöke_2018_295" />