Editing Indirect injection (section)

===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}}