General Information
OPERATION OF PREGLOW SYSTEMA. General information
On a diesel engine, combustion is effected by self- ignition of the fuel sprayed into the highly compressed and thereby highly heated combustion air.
In the cold engine, the self-ignition temperature is not attained by compression alone. A preglow system is therefore required, which serves the purpose of increasing the temperature of the compressed air to facilitate the firing of the cold engine by the ignition of fuel particles on filament of glow plug.
The duration of preglowing depends on temperature of engine and on ambient temperature.
Design of pencil element glow plugs
Pencil element glow plugs consist essentially of a housing with M 12 x 1.25 screw-in threads and a pencil element pressed into housing.
The single-pole connecting pin is glued to housing by means of a non-releasable round aluminum nut.
The pencil element glow plugs are designed for a current of 11 volts and are operated in parallel.
The pencil element is heated indirectly by means of a heater element. This heater element, a coil made of a resistance wire, is embedded and insulated in a ceramic compound.
When the glow system is switched on, each glow plug is subject to a current of approx. 20 amps (peak impulse of approx. 40 amps).
Under the influence of increasing heat, the inherent resistance of the glow plug increases and will limit the current to approx. 8 amps.
After a glow period of approx. 20 seconds a heater pencil element temperature of 900°C / 1652°F will be attained, after approx. 50 seconds the max. temperature will be 1080°C / 1976°F.
Design of quick-start pencil element glow plugs
Except for heater element, the design of a quick-start pencil element glow plug is the same as that of a pencil element glow plug.
As an external identification, the connecting pin is screwed to the housing by means of a non-releasable round brass nut.
The heater element consists of a heater and control coil connected in series.
When the glow system is switched on, each glow plug will be subject to a current of approx. 30 amps.
The glow plug is heated very quickly by heater coil. With increasing temperature, the control coil increases its resistance and limits the current to approx. 815 amps. This will protect the glow plug against overloads.
After a glow period of 9 seconds a pencil element temperature of approx. 900°C / 1652°F is attained, after 30 seconds the max. temperature amounts to 1180°C / 1976°F.