Glowplug

A glow plug is an electrical heating element in the combustion chamber of internal combustion engines and heaters. The glow plug is electrically heated only briefly at startup.

Glow plugs are used as:

  • Cold starting device for diesel engines
  • Igniter in the operation of Nitro engines
  • Ignition when starting operated with oil or kerosene gas turbines and oil heaters

Glow plug cold start aid for diesel engines

The injected into the combustion chamber during the cold start of a diesel engine diesel fuel usually does not ignite as easily by yourself as it describes the theory of the diesel process.

Reasons for this are:

  • The walls of the combustion chamber ( cylinder walls, piston bottom ) are still cold and have a high specific heat capacity ( iron material ) on. In contrast, at the start of the electric starter motor, the piston speed is low, so that the heat of compression generated low, the compressed air also has a low heat capacity as well as small thermal conductivity. Thus, the compression heat is quickly transferred to the cylinder walls and piston crown.
  • Especially chamber motors have a large, effective for the heat flux surface. Starting a cold engine is possible without direct Glühkerzenunterstützung at about -10 ° C air temperature at the vortex chamber injection above 30 ° C and 60 ° C for about indirect injection.
  • The cold engine has higher blow -by losses, ie the compressed air can escape past the piston rings from the combustion chamber so that the final compression pressure and thus the compression temperature is less. Due to the lower piston speed, the blow -by losses increase further during tempering.
  • Different grades of fuel, especially when the engine is much more fuel efficient and will burn zündunwillige fuels.

For these reasons, an electrically heated glow plug ( glow plug, glow plug ) is inserted into the combustion chamber which is preheated in the starting phase ( pre-heating ). The current is about 20-40 amps per cylinder, which represents a significant additional load on the starter battery next to the starter. After starting, the glow plug to reduce pollutants in the exhaust gas by unburnt hydrocarbons heated on for some time.

Technological development has the duration of this process from a few minutes (which became jokingly known as " Rudolf-Diesel- minute of silence " in car magazines ) reduced to a few seconds.

The temperature of the glow plug reaches Glühschaftes metal case to about 1,000 ° C, the ceramic glow plugs up to 1,300 ° C.

With direct injection is due to the compact combustion chamber, a preliminary annealing at most with chilly outside temperatures necessary. Here, the glow plug is switched occasionally to achieve a low-noise and low-emission combustion in this phase during cold operation.

A metallic glow plug is comprised of a coil which is pressed with an insulating powder (e.g., magnesia) in a steel pipe. The coil consists of two parts - the spiral-wound filament at the tip and the control coil in the rear part. The filament is made of a high alloy steel with a temperature-independent resistance, whereas the control coil has an increasing resistance with temperature. This results in cold candle rapid heating especially at the tip and an electronic current limiting when also the area of the control coil is heated.

Metal glow plugs are available in two versions: Bordspannungsglühkerzen with an operating voltage of 11 volts and so-called low-voltage glow plugs with an operating voltage less than 11 volts. With on-board voltage glow plugs 2006 Heating times of about 6 seconds at 850 ° C were possible.

An even shorter warm-up time is possible with low voltage glow plugs. On heating these glow plugs can be driven with a voltage above its operating voltage. This voltage is generated with an electronic glow control by pulse width modulation of the on-board voltage. So that heating-up time of 3 seconds at 1000 ° C are reached.

Ceramic glow plugs

Modern car engines with low compression ratio require glow plugs, make the maximum temperatures of up to 1,300 ° C and long annealing times without aging at about 1,150 ° C is possible. The demand for gasoline engine like Immediately start even at very low temperatures makes heating rates of up to 600 K / s necessary. This is possible with ceramic glow plugs.

For the combination of high thermal shock and hot gas corrosion exposure glow plugs with silicon nitride -based ceramic heaters have been developed. The ceramic heater is composed of electrically insulating silicon nitride, in the highly electrically conductive leads and a internal heating conductors are embedded. In contrast to metallic glow plugs here the heating and control function is combined in the heat conductor. The heater is fixed in a metal pipe and a gas-tight press-fit into a housing. The electrical contact of the positive pole is realized via a port pin. The ground connection to the engine block is made through the metal tube and the housing. By adjusting the heating resistor to create 11 -volt and low-voltage variants. The control of ceramic glow plugs on the glow time is analogous to metallic glow plugs.

The main advantage of ceramic glow plugs is that the case of metallic glow plugs often observed decrease of the annealing temperature is unlikely to occur due to aging and the gradual deterioration caused by the cold start and cold running behavior. Even with constant very high annealing temperatures of 1200 ° C, the annealing temperature decreased after 3000 hours typically by less than 50 K.

In Figure 1 is shown with optimized injection jet and Glühkerzenlage for a modern direct-injection diesel engine glow plugs, the relationship between annealing temperature and the so-called smoke opacity ( visible smoke ). It turns out that only at very high annealing temperatures above 1150 ° C, a maximum reduction of smoke opacity during cold start and cold idle can be achieved.

Glow plug Entflammungsvorrichtung of Glühzündermotors

Nitro engines are internal combustion engines without controlled high voltage ignition through flashover.

Instead this is a glow plug mounted with a permanent red-hot wire coil, which is (usually a platinum -iridium alloy ) coated by vapor deposition of ultra- thin with a catalyst material. Characterized the ignition of the fuel -air mixture is ensured. To start the engine the wire coil is supplied with electricity and heated to incandescence. After a short period of the power supply can be switched off, as the glow plug glows now continue through the heat of combustion.

The ignition timing ( time of ignition of the mixture ) is determined by the heat range of the glow plug, the compression of the engine and through the fuel mixture. Also important is the octane number of the fuel.

Typical thread sizes in the range of commercial static and automotive engines: 1/4 "× 32 imperial thread, max 6 mm long.

Glow in gas turbines and oil heating

Entflammungsvorrichtungen to oil-fired gas turbines and oil or kerosene heaters require no catalytic coating, since the ignition temperature without these is low enough.

Manufacturer

Ampere
269541
de