What is the function of the glow plugs in a diesel engine?

The function of glow plugs in a diesel engine is to preheat the combustion chamber to facilitate cold starting. Diesel engines rely on compression ignition, where air is compressed to a high degree, raising its temperature to a point where injected fuel will spontaneously ignite. However, during cold weather, the engine block absorbs heat from the compressed air, reducing the temperature and making it difficult for the fuel to ignite. Glow plugs are electric heating elements located inside the combustion chamber, typically one per cylinder. When the engine is cold, the glow plugs are activated by the engine control unit (ECU), heating the air inside the combustion chamber. This preheating ensures that the air temperature is high enough for the fuel to ignite reliably, even in cold weather. The glow plugs are typically activated for a short period of time before the engine is started, and they may remain activated for a short period after starting to improve combustion and reduce emissions. The amount of time the glow plugs are activated depends on the engine temperature. In warmer weather, they may not be needed at all. A malfunctioning glow plug can make it difficult or impossible to start the engine in cold weather. Common symptoms of a bad glow plug include hard starting, excessive white smoke from the exhaust during startup, and a rough-running engine. Glow plugs are an essential component of a diesel engine's cold-starting system, ensuring reliable starting and reducing emissions in cold weather conditions.