The glow plug is a device used for assisting the engine in starting by heating it. It is a pencil like structure which has a heating element at the tip. When it is electrified, the heating element, due to its high resistance gets heated up and starts glowing and hence the term glow plug. They resemble a spark plug in size and shape.
Working
When the engine is exposed to very cold temperatures or if the engine has cooled down due to idleness, starting it would take time because the walls of the cylinder and the cylinder heads would easily absorb the heat required for combustion. This is where the glow-plug comes to play.
The working of a diesel engine and the glow plug:
The diesel engine works by following a compression-ignition cycle. Unlike spark-ignition engines, the diesel engine ignites the fuel merely with the heat generated by pressurized air. At first, the suction stroke draws the air in, and then moves up and pressurizes it. While in the case of spark ignition (SI) engines, the compression ratio is about 6-10, the CI engine this ratio is about 16-20. At this point, fuel is injected in and due to high temperature and pressure, it burns further increasing the pressure. This forces the piston down and thus, rotation happens.
The glow-plug is placed in such a way that it can heat the engine and the surrounding areas. If the temperature if the ignition chamber is less than enough for ignition, it gets detected by sensors meant for this. The glow-plugs then switch on automatically and turn red-hot, thus heating up the chamber. When ignition temperature is achieved, the glow-plug switches off.
Types of glow-plugs:
Quick start pencil elements: This type of glow plugs are used in smaller, passenger vehicles where only less heating is needed for ignition. These reach about 1625 degrees Celsius in 30 seconds.
Slow-start pencil elements
These plugs are used in heavier vehicles which require more heating. They reach a temperature of about 2000 degrees in 30 seconds.
Issues faced by a glow plug
The common enemy of a glow plug is wear and tear. It is possible to start the engine with the glow plug on. But when the engine gets ignited, the plug also receives some heat in reverse. This reduces the life of the glow plug
Due to continuous heating, there is a possibility of oxidization. Platinum and iridium are usually used in order to overcome this.
Replacing
The replacement of a glow plug usually follows no schedule. It is usually done according the suggestions given in the manual. Generally, it is good to do it for every six months or for every 60,000 miles. One of the things hat has to be taken care of, while changing the glow-plug is to ensure that the glow plug is cooled down completely.
How to replace a glow plug
First, remove the valve cover and also any cover that covers the plug. Remove the connector, and remove the glow plug using a deep socket wrench. Now screw the new glow plug all the way and put back the connector. Remember, each vehicle has its own specifications about how to replace a glow-plug. It is always best to follow them.
