On the Dynamic Thermal System Behavior of a Glow Plug

In this paper the thermal system behavior of a glow plug is examined based upon its thermal impedance. The glow plug is a passive and low ohmic device as well as a rather slow sensor this is accounted for by the presented measurement setup and the modality of the system excitation to determine the transfer functions. The impact of the ambient temperature and the surrounding conditions on the thermal impedance is addressed as well. Since the glow plug is directly exposed to the combustion process it can be used as a sensor, e.g. for misfire detection. The combustion causes measurable changes of the temperature dependent resistance. The amplitude of this small signal is influenced by occurring aging processes. They can be compensated by determining the thermal impedance.