Staff

Motivation

Regarding an actual combustion system with fuel consisting of C- and H-atoms only, one always has to deal with products of imperfect combustion. By law, most of these substances are classified as pollutants due to their hazardousness to humans and the environment. The corresponding EU Regulation for vehicles (Nr. 715/2007/EG) therefore includes emission standards for carbon monoxide, unburned hydrocarbons, particles and nitrogen monoxide (NO) as well as nitrogen dioxode (NO2). Since their introduction these standards have been tightened continuously. From Euro 5 to the currently valid Euro 6 standard, particularly nitrogen oxide (NOX) emissions were notably adjusted downwards, from 180 to 80 mg/km. To follow these standards either raw engine emissions must be decreased or NOX has to be removed from the exhaust gas in an after-treatment process. However, during the phase of development both approaches rely on a method for measuring the NOX concentrations in the exhaust gas. Tunable Diode Laser Absorption Spectroscopy (TDLAS) offers a suitable, non-invasive laseroptical method of measurement. TDLAS can achieve high temporal resolution and sensitivity without disturbing the process under consideration, in contrast to methods based on the extraction of gas samples.

Method

With TDLAS the emission wavelength of a diode laser is tuned over a single absorption line of the species to examine, thus making it possible to determine the concentration along the light path. Because NO and NO2 convert into each other, both molecules must be considered seperately. Concentrations as small as in this particular application should be detected using mid-wavelength infrared light, since NOX absorption lines are sufficiently strong in that spectral range only. To achieve sensitivities of 100 ppm and less, the absorption path length is increased by using a multiple-reflection cell. In summary, the challenge of this project is the development of a fiber-coupled infrared-spectrometer for harsh exhaust environments. In addition to high temperatures, there can be plenty of parasitic absorption, for instance via water vapor or particles.

This project is funded by Fritz und Margot Faudi-Stiftung.