Starting a diesel engine: differences from gasoline engines
A diesel engine starts completely differently than a gasoline engine. Volatile gasoline, even at a temperature of -40° C, is ready to ignite from one spark, which is created in the cylinders by spark plugs. Due to its low volatility, diesel fuel - even winter fuel - needs the same 40 degrees for ignition, but with a plus sign (and summer fuel - +62° C). It’s not for nothing that diesel fuel is called heavy fuel.
The high temperature required for diesel combustion in the cylinder is created by air compression by the piston. Like any gas, air is compressed reluctantly, but its pressure and temperature increase. When an injector injects a portion of diesel fuel, it ignites on its own from contact with hot compressed air - because of this, it is often said that a diesel engine is started by pressure or explosion. Old diesel engines, not equipped with electronic injection and sensors, can easily operate without a battery, since the ignition of the fuel in the cylinders occurs mechanically, without any sparks or spark plugs.
But the diesel idyll is destroyed by Mother Nature: when the temperature drops to sub-zero temperatures, the air compression in the cylinders is no longer enough to heat the fuel until it ignites spontaneously. Therefore, it is impossible to completely abandon spark plugs in a diesel engine. It’s just that spark plugs are needed here not to ignite the fuel-air mixture, but to heat it.
Glow plug design
Anyone who has held a boiler or heating element from a water heater in their hands will immediately understand the principle of operation of a diesel glow plug. By the way, the first glow candles had an open spiral and actually looked like a mini-boiler. The heating coil of modern candles is covered with a durable rod body (usually steel, sometimes ceramic) filled with magnesium oxide - magnesia. When an electric current passes, the spiral heats up, giving off heat to the rod, which transfers heat to the air in the combustion chamber and the fuel-air mixture, helping it ignite. The tip of the rod is located exactly in the place of the combustion chamber where turbulence of the mixture is formed when fuel is injected by the nozzle.
Plug with open heating element and modern rod glow plug
The warm-up time for the first glow plugs in the 1920s was an endless 180 seconds - a full 3 minutes for the driver to wait for the plugs to reach operating temperature to start the engine! Modern candles with a steel rod heat up completely in less than 10 seconds (record holders - in 4 seconds), and the temperature of the rod reaches 800–1000 °C.
Candles with ceramic rods are even more effective: warm-up in 2 seconds and a maximum temperature of 1350 °C. Such spark plugs are used in highly accelerated diesel engines that meet the most stringent environmental requirements. But the cost of ceramic candles in comparison with classic steel ones is noticeably higher.
Glow plug relay on Volkswagen
The device on Volkswagen cars is located behind the fuse box, which, in turn, is located in the vehicle interior under the dashboard on the driver’s side. In order to dismantle the glow relay, this mechanism must be removed. These actions are carried out in the following sequence:
- The safety block is removed from the mountings.
- Rotates counterclockwise.
- In the depths of the structure there are fuses and filament relays.
The above actions apply not only to Volkswagen cars. When replacing a glow relay, it is necessary to take into account the country and company that produced the replacement part. Chinese fakes will not last long, and their use can lead to more serious damage.
Why check the performance of glow plugs and relays?
Glow plugs are located directly in the combustion chamber. They provide heating of the fuel so that ignition is as smooth and clear as possible. We can say that they are a pre-starting device for the engine. Their performance is especially important in winter. Due to a malfunction in the glow parts control unit, the driver simply will not be able to start the engine.
They are made from different materials. They may have a closed or open heating element. Their control circuit takes into account fuel temperature, air heating, and resistance changes. When the engine does not start, many drivers initially check this particular system.
There are many reasons why spark plugs can fail. This is the expiration date of the element, the weather conditions of the region in which the car is used. The cause of the problem may lie in electrical wires or other system components.
What shortens the life of spark plugs?
As already mentioned, the working life of the CV depends on the operating conditions of the vehicle. Although these elements are quite durable, they can still fail prematurely.
