Editing Indirect injection (section)

==Diesel engines==

===Overview===
The purpose of the divided combustion chamber is to speed the combustion process, and to increase power output by increasing engine speed.<ref>Stone, Richard. "An introduction to ICE", Palgrace Macmillan, 1999, p. 224</ref> The addition of a prechamber increases heat loss to the cooling system and thereby lowers engine efficiency. The engine requires [[Glow plug (diesel engine)|glow plugs]] for starting. In an indirect injection system the air moves fast, mixing the fuel and air. This simplifies engine (piston crown, head, valves, injector, prechamber, etc.) design and allows the use of less tightly toleranced designs which are simpler to manufacture and more reliable. [[fuel injection#Direct injection systems|Direct injection]], by contrast, uses slow-moving air and fast-moving fuel; both the design and manufacture of the injectors is more difficult. The optimisation of the in-cylinder air flow is much more difficult than designing a prechamber. There is much more integration between the design of the injector and the engine.<ref>[[Two-stroke engine]]</ref> It is for this reason that car diesel engines were almost all indirect injection until the ready availability of powerful [[Computational fluid dynamics|CFD]] simulation systems made the adoption of direct injection practical.{{Citation needed|date=October 2008}}

===Classification of indirect combustion chambers===

====Swirl chamber====
[[File:Ricardo comet combustion.gif|thumb|left|Ricardo Comet swirl chamber]]
Swirl chambers are spherical cavities located in the cylinder head and separated from the engine cylinder by a tangential throat. About 50% of the air enters the swirl chamber during the compression stroke of the engine, producing a swirl.<ref>{{cite book|title=Electromechanical Prime Movers: Electric Motors|url=https://books.google.com/books?id=9lNdDwAAQBAJ&pg=PA21|date=18 June 1971|publisher=Macmillan International Higher Education|isbn=978-1-349-01182-7|pages=21–}}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
After combustion, the products return through the same throat to the main cylinder at much higher velocity, so more heat is lost to the walls of the passage. This type of chamber finds application in engines in which fuel control and engine stability are more important than fuel economy. These are also called Ricardo chambers, named after the inventor, [[Harry Ricardo|Sir Harry Ricardo]].<ref name="oldengine">{{cite web|url=http://www.oldengine.org/members/diesel/misc/ricardo.htm |publisher=oldengine.org |title=Sir Harry Ricardo |access-date=8 January 2017 |url-status=dead |archive-url=https://web.archive.org/web/20101017023809/http://www.oldengine.org/members/diesel/misc/ricardo.htm |archive-date=17 October 2010 }}</ref><ref name="google">{{cite book|title=Troubleshooting and Repairing Diesel Engines|author=Dempsey, P.|date=1995|publisher=TAB Books|isbn=9780070163485|url=https://books.google.com/books?id=5nHW-USbN6wC&pg=PA127|page=127|access-date=8 January 2017}}</ref>

====Precombustion chamber====
This chamber is located at the cylinder head and is connected to the engine cylinder by small holes. It occupies 40% of the total cylinder volume. During the compression stroke, air from the main cylinder enters the precombustion chamber. At this moment, fuel is injected into the precombustion chamber and combustion begins. Pressure increases and the fuel droplets are forced through the small holes into the main cylinder, resulting in a very good mix of the fuel and air. The bulk of the combustion actually takes place in the main cylinder. This type of combustion chamber has multi-fuel capability because the temperature of the prechamber vaporizes the fuel before the main combustion event occurs.<ref name=buaa>{{cite book|last=Dempsey |first=Paul |title=Troubleshooting and Repair of Diesel Engines |year=2007 |publisher=McGraw Hill Professional |isbn=9780071595186 |url= https://books.google.com/books?id=xJs7aMuyEygC&q=Troubleshooting+and+Repairing+Diesel+Engines+By+Paul+Dempsey |access-date=2 December 2017}}</ref>

====Air cell chamber====
[[File:Acro-Luftspeicher.jpg|thumb|Acro-type injection system, the predecessor of the Lanova, also designed by Franz Lang]]
The air cell is a small cylindrical chamber with a hole in one end. It is mounted more or less coaxially with the injector, said axis being parallel to the piston crown, with the injector firing across a small cavity which is open to the cylinder into the hole in the end of the air cell. The air cell is mounted so as to minimise thermal contact with the mass of the head. A pintle injector with a narrow spray pattern is used. At its top dead centre (TDC) the majority of the charge mass is contained in the cavity and air cell.{{Citation needed|date=October 2008}}

When the injector fires, the jet of fuel enters the air cell and ignites. This results in a jet of flame shooting back out of the air cell directly into the jet of fuel still issuing from the injector. The heat and turbulence give excellent fuel vaporisation and mixing properties. Also, since the majority of the combustion takes place outside the air cell in the cavity, which communicates directly with the cylinder, there is less heat loss involved in transferring the burning charge into the cylinder.

Air cell injection can be considered as a compromise between indirect and direct injection, gaining some of the efficiency advantages of direct injection while retaining the simplicity and ease of development of indirect injection.{{Citation needed|date=October 2008}}

Air cell chambers are commonly named Lanova air chambers.<ref name="google2">{{cite book|title=Troubleshooting and Repairing Diesel Engines|author=Dempsey, P.|date=1995|publisher=TAB Books|isbn=9780070163485|url=https://books.google.com/books?id=5nHW-USbN6wC&pg=PA128|page=128|access-date=8 January 2017}}</ref> The Lanova combustion system was developed by the Lanova company, which was founded in 1929 by Franz Lang, Gotthard Wielich and Albert Wielich.<ref>{{cite journal|title=The Lanova Combustion System|journal=The Commercial Motor|date=6 January 1933|url=http://archive.commercialmotor.com/article/6th-january-1933/38/the-lanova-combustion-system|access-date=11 November 2017}}</ref>

In the US, the Lanova system was used by [[Mack Trucks]]. An example is the Mack-Lanova ED diesel engine fitted to the [[Mack NR]] truck.

===Advantages of indirect injection combustion chambers===
* Smaller diesels can be produced.
* The injection pressure required is low, so the injector is cheaper to produce.
* The injection direction is of less importance.
* Indirect injection is much simpler to design and manufacture, especially for gasoline engines. Less injector development is required and the injection pressures are low (1500&nbsp;psi/100 bar versus 5000&nbsp;psi/345 bar and higher for direct injection)
* The lower stresses that indirect injection imposes on internal components mean that it is possible to produce [[petrol]] and indirect injection diesel versions of the same basic engine. At best such types differed only in the cylinder head and the need to fit a [[distributor]] and [[spark plug]]s in the petrol version whilst fitting an [[injection pump]] and [[fuel injector|injectors]] to the diesel. Examples include the BMC [[BMC A-Series engine|A-Series]] and [[BMC B-Series engine|B-Series]] engines and the [[Land Rover]] 2.25/2.5-[[litre]] 4-cylinder types. Such designs allow petrol and diesel versions of the same vehicle to be built with minimal design changes between them.
* Higher engine speeds can be reached, since burning continues in the prechamber.
* Alternative fuels like [[bio-diesel]] and [[waste vegetable oil]] are less likely to damage the fuel system in an indirect-injection diesel engine, as high injection pressures are not needed. In direct-injection engines (especially modern engines using high-pressure [[common rail]] fuel systems), keeping fuel filters in good condition is more critical as debris can damage the pumps and injectors when waste vegetable oil or waste engine oil are used.

===Disadvantages===
* [[Fuel efficiency]] with diesel engines is lower than with direct injection as the larger exposed areas tend to dissipate more heat and the air moving through the ports tending to increase pressure drops. However, using higher compression ratios will somewhat negate this inefficiency.
* [[Glow plug (diesel engine)|Glow plugs]] are needed for a cold engine start on diesel engines; many indirect injection diesel engines cannot start at all in cold weather without glow plugs.
* Because the heat and pressure of combustion is applied to a very small area on the [[piston]] as it exits the precombustion chamber or swirl chamber, such engines are less suited to high [[Power-to-weight ratio|specific power]] outputs (such as [[turbocharger|turbocharging]], [[supercharger|supercharging]], or tuning) than direct injection diesels. The increased temperature and pressure on one part of the [[piston]] crown causes uneven expansion which can lead to cracking, distortion, or other damage, although advancements in manufacturing techniques have allowed manufacturers to largely mitigate the effects of uneven expansion, allowing for indirect injection diesels to use turbocharging.
* Indirect engines are often much noisier than direct injection common-rail engines.
* Starting fluid ("ether") often cannot be used in an indirect injection diesel engine as the glow plugs greatly increase the risk of preignition compared to direct injection diesels.