FAQ for glow plug sensors
AVL has made a list of frequently asked questions and tricks in order to avoid
typical problems occurring while defining a glow plug adapter.
What is the difference between
an original glow plug and a measurement
Which dimensions are needed
minimum in order to make a proper
The original glow plug is supporting the engine start especially with low ambient
temperatures (cold start). Due to this the tip of the glow plug is designed to
bring as much heat as possible into the fuel / air mixture in the combustion
chamber. One factor that influences the heat contribution is the gap between
the glow plug and the glow plug bore in the cylinder head.
The glow plug adaptors and sensors are used for the pressure measurement
in the combustion chamber without the glow function. It is necessary to have
a minimum gap between the glow plug adaptor / sensor and the bore in
the cylinder head in order to ensure the best possible lifetime of the sensor.
With this design, the heat transfer from combustion to the adaptor and sensor
is reduced to a minimum. Based on this, the diameter and shape of the tip has
to be aligned with the glow plug bore in the cylinder head. The diameter DB,
DK and DC (if applicable) have to be determined with the best possible precision
in order to allow the design department the smallest tolerances.
Beside the lifetime the measurement accuracy is most important. The adapter
construction allows a positioning of the pressure sensor membrane close to
the combustion chamber with a minimum of pipe oscillation.
To ensure a safe and damage-free dismounting a minimum wall thickness
is needed. The pressure sensor GH14P has an outer diameter of 4.3 mm,
therefore the minimum diameter for the usage of a sensor with glow plug
adaptor (modular approach) is a DB of 5 mm. For bore diameters smaller
than 5 mm, AVL can provide a glow plug sensor GH13G. This glow plug
sensor will then be supplication specific and can’t be used in engines with
different bore dimensions.
It is possible to make a design proposal, if:
a) the dimension of the original glow plug is available (but this is a recessed
solution with pipe oszillation)
b) the dimension of the original glow plug and the diameter DB, DK and DC
(if applicable) and the length LA respectively LD are available
c) all dimension / the construction drawing of the glow plug bore and the tip
geometry of the original glow plug (D1 and L2) are available
5.1 PRESSURE SENSORS