Ken Yves Haffner

Investigation of mechanistic aspects of the catalytic CO2 reforming of methane in a dielectric-barrier discharge using optical emission spectroscopy and kinetic modeling

The CO2 reforming of methane by the combination of catalysts with a dielectric-barrier discharge is investigated as an alternative approach to the conventional pure catalytic process. It is shown that the use of nickel or calcium-promoted nickel catalysts in combination with the discharge leads to an increase in the CO yield of 20 to 40%. The identified products are CO, H2, water, ethane and ethylene, propane, n-butane and methanol. In addition to the experimental investigation, extensive kinetic modeling was performed. Besides a good description of the plasma reactions by a set of 308 reactions and 57 species, the programs used offered the possibility of identifying the main reaction routes towards the different products. To get an insight into the mechanistic aspects of the catalyst–plasma interaction, the gas phase was investigated with optical emission spectroscopy (OES) during the experiment. Special emphasis was placed on the interpretation of differences in the emission spectra from experiments with and without a catalyst in the discharge. A significant difference was observed for the CH A 2Δ–X 2Π band. Therein, the intensity of the signal was proportional to the activity of the catalysts used, in the sense that the CH signal was higher for a more active catalyst. Based on these results, a tentative reaction scheme is proposed that explains the enhancing effects of the catalysts in the CO2 reforming reaction. It starts with the adsorption of methane and methane fragments from the gas phase, followed by their gasification by oxygen and oxygen-containing species supplied by the discharge plasma.

Low-coherence interferometric tip-clearance probe

We propose an all-fiber, self-calibrating, economical probe that is capable of near-real-time, single-port, simultaneous blade-to-blade tip-clearance measurements with submillimeter accuracy (typically < 100 microm, absolute) in the first stages of a gas turbine. Our probe relies on the interference between backreflected light from the blade tips during the 1-micros blade passage time and a frequency-shifted reference with variable time delay, making use of a low-coherence light source. A single optical fiber of arbitrary length connects the self-contained optics and electronics to the turbine.

Gas temperature measurement in CH4/CO2 dielectric-barrier discharges by optical emission spectroscopy

The gas temperatures were determined by optical emission in a dielectric-barrier discharge at atmospheric pressure. The feed gases were either pure CH4 to yield higher hydrocarbons or CH4/CO2 mixtures to yield synthesis gas (H2/CO). The monitored emission was from the CH radical A 2Δ–X 2Π electronic system and the gas temperature range characterized was from 300 to 600 K. The technique described in this article enables the measurement of the neutral gas temperature in the discharge that is not accessible via conventional methodology using thermocouples. A bimodal rotational population distribution in the CH A 2Δ v′=0 state was determined in the investigated gas mixtures of CO2/CH4 and in pure methane. Most of the rotational population was at temperatures from 300 to 600 K depending on experimental conditions, which are only slightly higher than the set temperature of the reactor. A small fraction of the emitting species was found to have a much higher rotational temperature of ∼4000 K for the pure methane...