Metal rod glow plugs

Metal rod glow plugs from NGK for the pre-glowing in diesel engines, even at the lowest outside temperatures.
Metal rod glow plugs from NGK

Metal rod glow plugs are equipped with a heating coil in a glow rod made of heat-resistant metal. A ceramic material - magnesium oxide - in the interior of this glow rod protects the heating coil from vibrations and shocks. Because magnesium oxide is also an outstanding thermal conductor, the heat that is produced can quickly be dissipated outward.

Metal rod glow plugs can be allocated into three main groups: Standard Glow Plugs, Self Regulating Glow Plugs, and Controlled Glow Plugs.

Standard Glow Plugs 
They operate with a voltage from 11 to 12 V and reach a maximum temperature of approximately 800 C in 13 – 17 seconds.

Self Regulating Glow Plugs (SRM)
This type comes with operating voltages between 11 and 12 V and offers a maximum temperature of about 900 °C within approximately 4 seconds. To do so, they are equipped with a heating coil and a regulating coil. The heating coil heats very quickly, and the regulating coil increases its resistance as the temperature increases to control the current flow. Control of such glow plugs takes place via a glow plug relay or a simple glow plug control unit.

The task of the heating coil

Heating and control coils are enclosed in a glow rod made of heat-resistant light-metal alloy. They form a common resistor element, whereby the heating coil combined with the front part of the glow rod forms the heat zone and the control coil is fastened to the current-carrying connecting bolt. The insulating powder (magnesium oxide) is packed between the coil and rod.

The heating coil is not exposed directly to the combustion and the shockwaves which arise through the rapid expansion of the mixture. The glow rod provides the heating coil a certain amount of protection against the carbon arising from the combustion. It does not deposit there, so no short circuit occurs.

360 ° view of a metal rod glow plug

Related topics

Standard rod glow plugs: Standard rod glow plugs have a heating coil whose resistances does not change with increasing temperature.

Rapid-start glow plugs: Rapid-start glow plugs are distinguished by a short pre-glowing time, because their temperature increases very quickly.

Self-regulating rod glow plugs: These so-called SRM glow plugs have a heating coil and a control coil. The heating coil heats up very quickly. The control coil increases the resistance as the temperature increases.

European standards: The European emission standards, or Euro standards, define the emission classes for new automobiles.