Explain the working of diesel engine glow plugs with neat sketch

Explain the working of diesel engine glow plugs with neat sketch
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Answer :

Glow plug is an aid for cold starting of a C.I. engine. The self-ignition temperature of diesel is 250°C. For compression ignition, the charge (air + diesel) should reach a temperature of about 550°C. Cold weather conditions make it difficult to happen. So, a glow plug is used in Compression Ignition Engines. The glow plug heats to starting temperature (approx. 850°C) as rapidly as possible.

Operation of Glow Plug Circuit: On modern vehicles, engine's central ECU controls- high electrical glow-plug current, indicator lamp, Safety over ride and automatic switching off the Glow- plugs. An ignition starter lock controls the current supply for the glow system. As the switch is actuated a relay connects the glow plug to the battery circuit, and the Indicator lamp comes on. When the lamp goes out turning the switch further to the starting position brings the engine to life. As long as the starter switch is held in the glow position, a holding circuit assures that the glow- plugs remain on. Then after starting, when the ignition switch is released, they are automatically switched off. A safety circuit prevents running the battery down if the engine fails to start immediately. After a maximum of 90 seconds glow time, current to the glow plugs is automatically interrupted. But starting may be attempted again as soon as the driver wishes. 

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