The glow plug is only used to pre-heat the combustion chamber on a diesel engine. The glow plugs are electric elements that generate heat as the electrical current passes through the resistance of the glow plug element. Think of it as an incadecent light bulb--as the current flows through the filament the resistance of the filament causes the electrical current to be used and the result is that the filament glows and gives off heat. Also, the glow plug controllers are generally on a timer so that they only work for a short time to get the initial ignition. Once the diesel is running, the glow plugs are no longer needed as the heat in the cylinders from friction and the rise in temperature from combustion are enought to light the fuel off.
Now, meron din diesel than ca start w/o glow plug. One of the biggest differences between diesel engines that can start without glowplugs and those that need glowplugs are pre combustion chamber. May maliit na chamber in the head of the engine, the diesel is injected into this chamber and ignition starts there.
Engines that can start without glowplugs do not have this extra chamber and are called direct injection engines. Some direct injection engines also have glowplugs to assist the starting. Smaller car engines are normally of the sort that do need glowplugs but big truck engines( like yong mga 18 wheeler) and some industrial engines used for waterpumps etc. wala silang glowplugs.
On some engines without normal glowplugs there is one glowplug in the intake manifold together with an injector. While the starter is operated this glowplug and injector is energized. This injector does not work like a normal one but is an electric device. This set up supplies the engine with some preheated diesel in the airsupply and helps the engine to start. You will find this on some farmers tractors sa mga bukid.
[SIZE=6]
Ps.[/SIZE]
Wag kanang magsulat ng parang kulang, I have a hard time to understand. Have nice day