Temperature measurements within combustion engines

An important physical parameter for technical combustion is the temperature. Actually it has an essential denotation concerning the development of new combustion concepts for future engine generations.

With the aid of laser induced fluorescence (LIF) temperature information can be obtained contactless and with high temporally and spatial resolution. In the working group Photonic Sensor Technology, such a LIF-technique is used. In this connection a tracer molecule is excited and we utilizethe fact that in the excited state an energy distribution to several energy levels is taking place. The population of these states can be described with the Boltzmann distribution. If the thermalization is finished, the molecule is in thermal equilibrium with the environmental temperature. Thus the population density is temperature dependent. The population density is represented in the respective fluorescence intensity. In this technique the thermalization has to be finished within the fluorescence lifetime. For this technique developed in the working group Photonic Sensor Technology, formaldehyde is used as a tracer molecule and it is excited with a frequency trebled Nd:YAG-laser.

In the spectrocopic monitoring, the population densities of two excited states are detected with the aid of a spectrometer and an image intensified camera. With the ratio from these two fluorescence intensities a temperature information can be calculated via the Arrhenius equation.

This technique was examined with a temperature-controlled pressure chamber. Thereby experiments were done with both formaldehyde/air-mixtures and fuel/air-mixtures, which are enriched with formaldehyde. Figure 1 and 2 show the temperature dependency of the ratio from the transitions 2⁰₂4¹₀ (403mn) and 2⁰₁4¹₂ (413nm).

This technique will be implemented in a sensor system, which makes it possible to execute one dimensional measurements in a non-fired engine mode. Furthermore, a two dimensional measurement technique with intensified camera systems is developed

Co-operation partner:

• Volkswagen AG

Further information:

Müller, R. Beushausen, V., 2005: „Grundlegende Untersuchungen zur Bestimmung der Ladungstemperatur in Verbrennungskraftmaschinen“, 13. Fachtagung Lasermethoden in der Strömungsmesstechnik (GALA), Cottbus

Müller, R., Beushausen, V., 2007: „Messverfahren zur Bestimmung der Ladungstemperatur in Verbrennungskraftmaschinen mit Hilfe laserinduzierter Fluoreszenz“, Tagung Motorische Verbrennung 2007, München