For a reliable cold start, particularly at low ambient temperatures, diesel engines depend on the support of glow plugs.
This is because when starting, the cylinders and engine have cooled down significantly. They extract energy in addition to the already cold environmental air. The temperature required for self-ignition is no longer reached through compression of the air alone.
This is where the glow plug comes into play. It is screwed into the cylinder head. Its glow tube projects into the combustion chamber and heats it up as soon as it is supplied with current. Depending on the glow plug, it can reach over 1000°C, and in this manner it heats up the combustion chamber. This process before the actual starting of the engine is also called "pre-glowing".
After-glowing - What does it mean?
Glowing after the start, while the engine is running, reduces white/blue-smoke and eliminates cold start knocking. The glow system itself consists of the glow plugs made of metal, or ceramic, and an electronic glow-time control unit.