Re: why do diesel engines have,,,

Posted by Bob M on November 26, 2002 at 09:37:21 from (165.170.128.68):

In Reply to: why do diesel engines have,,, posted by Bryce Andreasen on November 26, 2002 at 08:10:25:

Bryce - Many early diesels are indirect injected. Here fuel is injected into a small pre-combustion chamber in the head - which in turn connects to the main combustion chamber. Glow plugs are often provided in the precombustion chamber to assist cold starting. The glow plugs get heated to red heat before the motor is cranked. Injected fuel is ignited as it passes the hot plugs so it's already beginning to burn as it enters the main chamber. This promotes a fast, relatively smoke-free start.

Other methods have been used to assist indirect-injected diesels: Intake manifold heater (some Case and Oliver engines). Pony motor - provides faster cranking speeds and pre-heats the diesel block and intake manifold (used by Cat and Deere). And of course the IHC "start on gas" diesel (starts as a low compression gas engine then switches to diesel after it warms a bit)

Most modern diesels however are direct injected i.e. they have no pre-combustion chamber. Direct injection's advantage is it's greater thermodynamic efficiency over an indirect injected diesel. However there is not enough space in a direct injected combustion chamber to fit a glow plug. Offsetting this, a direct injected diesel is inherently somewhat better at cold starting than an indirect diesel. However even a direct injected engine will not start below a certain temperature. Devices such as intake manifold heaters (to heat the incoming combustion air) or ether injection are employed to assist cold starting.

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