EMPI - Reactive Fluids

The reaction rate coefficient of fast chemical reactions at high temperatures is investigated in shock tubes equipped with ultra-fast detection methods. A shock wave caused by gas expansion heats the reactive gas mixture to temperatures of up to several thousand Kelvin within microseconds, and the subsequent reactions are observed mostly via optical in situ methods. By using highly sensitive spectroscopic methods, it is possible to measure time-resolved concentration profiles of the reacting or forming atomic and molecular species. By selecting the gas mixture, individual elementary reactions in highly diluted homogeneous reaction systems can be specifically investigated and their reaction rate coefficients determined.
For this purpose, four different shock-tubes are used in our laboratory. They all have an inner diameter of about 8 cm, a driver length of about 3 m and a test section of about 6 m in length. The shock speed of the incident shock wave is determined with fast piezo-pressure sensors and used for the calculation of reflected-shock pressure and temperature. The gas mixtures are prepared in separate mixing tanks.

The four shock tubes are equipped with different measurements techniques. Two of them are ultra-clean shock tubes pumped in between experiments with turbomolecular pumps to pressures below 10^–6 mbar. They are equipped with time-resolved ultra-sensitive concentration measurement techniques (ARAS, RDLAS, ICAS). These techniques enable time-resolved detection of atomic and molecular species with sub-ppm sensitivity, so that uni- and bimolecular rate coefficients of organic substances (fuels) and nanoparticle precursors (metal-organic) can be determined. Measurements are performed at pressures of about 1 bar.

The third shock-tube is equipped with different measurement techniques such as a kinetics spectrometer for fast broad-band absorption spectroscopy, reaction time-resolved LIF and LII, IR diode lasers and laser extinction. These measurement techniques enable a wide range of investigations with time-resolved measurements:
Ignition processes (CO, temperature) and CO production of fuel-rich mixtures with TDLAS
Soot formation in oxidation and pyrolysis systems (soot extinction, temperature and CO concentration)
Examination of young soot formation (LIF, LII, time-resolved UV absorption, laser extinction)
Kinetics of LIF tracers (reaction-time resolved LIF, time-resolved UV absorption, effect on the ignition of tracers LIF on hydrocarbon fuels)

The fourth shock-tube is used to determine the rate coefficients of the decomposition of organic substances (fuels) and nanoparticle precursors. Two corresponding measurement techniques can be used:
Use of the shock-tube in the single-pulse mode. Using a dump tank prevents reheating of the mixture and the mixture stays within specific pressure and temperature conditions for a known time, and thus the reaction progress can be investigated by analyzing gas samples by GC/MS. The product analysis has the advantage that also reaction with very low conversions can be investigated, and unimolecular decomposition can be studied in a very wide temperature range. To extend the measurements to lower temperatures, a flow reactor is used, to extend the measurements to higher temperatures the HRR-TOF-MS technique enables time-resolved detection of educts and products.