Nutzung der keramischen Glühkerze als Sensorelement

The high cycle rate of technological advancement in the automotive sector ena-
bles information extraction from the engine compartment with using of existing
hardware in the vehicle, without additional space, material and cost. Above all,
the shortage of space in the engine block makes it difficult to use additional sen-
sors in the combustion chamber. In this context, ceramic glow plugs, which are
used in diesel vehicles to support and optimize the combustion process, are in-
vestigated. They usually remain active for three minutes. The ceramic glow plug
differs from metal glow plugs primarily in terms of start time and heat provided.
It has a higher resistance at the cap, which extends into the combustion chamber.
The question is what these could be useful for after three minutes. On the one
hand, ceramic glow plugs could remain active as an actuator to reduce emissions.
On the other hand, these can be used as a sensor. This work is shown that glow
plugs are able to reliably provide useful information from the combustion cham-
ber of a diesel vehicle. The first step is a simulative analysis of the glow plug,
using an FDM model. ... mehrStarting from the conversion of electrical energy into he-
at, the quality of heat absorption determines the basis of this analysis. It turned
out that temperature changes in the immediate vicinity of the glow plug modify
its resistance. The results of the simulation can be confirmed with measurement
data.
The resistance of the ceramic glow plug, which has a dependence with the
environmental influences such as temperature, is used as a sensor signal. This
signal is filtered with a bandpass filter so that the high-frequency noise and the
changes of the low-frequency temperature are suppressed as much as possible.
A total of four variables are determined using these sensor signals: the speed,
the moment and duration of injection, the combustion chamber temperature and
the pressure. The exact determination of the speed (5 % standard deviation of the
speed), the moment of injection as well as its duration can be determined using
the sensor signal. Using existing measurement data, the moment of injection
could only be suf f iciently verified in the lower speed range up to 1500 min−1
and satisfactory results were obtained.
The temperature and pressure are determined using a Hammerstein model.
The measurement data recorded during this work does not include all engine ope-
rating points. In particular, the dynamic combustion temperature signal could not
be recorded on the engine test bench to verify the estimate for various reasons.
This work shows that the initialization of the glow plug must be improved.
This would make the estimation methods of the temperature and pressure less
dependent on the scattering of the glow plug parameters, which has a direct ne-
gative effect on the error of the specific pressure/temperature. Another interes-
ting topic would be a combustion chamber design for measuring the temperature
with a higher sampling rate by a camera, or using a CFD combustion chamber
model to verify the temperature estimation results. The models must then be
optimized and verified using new measurement data.