Spatially and Temporally Resolved Measurements of NO Adsorption/Desorption over NOx-Storage Catalyst.

The two-dimensional (2D) temporal evolution of the NO-concentration over a NOx-storage catalyst is investigated in situ with planar laser-induced fluorescence (PLIF) in an optically accessible parallel wall channel reactor. Signal accumulated phase-correlated 2D-recordings of repetitive adsorption/desorption cycles are obtained by synchronizing the switching of the NO gas flow (on/off) with the laser and detection system, thereby significantly increasing the signal-to-noise ratio. The gas compositions at the reactor outlet are additionally monitored by ex-situ analytics. The impacts of varying feed concentration, temperature and flow velocities are investigated in an unsteady state. Transient kinetics and the mass transfer limitations can be interpreted in terms of the NO concentration gradient changes. The technique presented here is a very useful tool to investigate the interaction between surface kinetics and the surrounding gas flow, especially for transient catalytic processes.

Two-dimensional spatial resolution of concentration profiles in catalytic reactors by planar laser-induced fluorescence: NO reduction over diesel oxidation catalysts.

Planar laser-induced fluorescence (PLIF) enables noninvasive in situ investigations of catalytic flow reactors. The method is based on the selective detection of two-dimensional absolute concentration maps of conversion-relevant species in the surrounding gas phase inside a catalytic channel. Exemplarily, the catalytic reduction of NO with hydrogen (2 NO+5 H2 →2 H2 O+2 NH3 ) is investigated over a Pt/Al2 O3 coated diesel oxidation catalyst by NO PLIF inside an optically accessible channel reactor. Quenching-corrected 2D concentration maps of the NO fluorescence above the catalytic surface are obtained under both, nonreactive and reactive conditions. The impact of varying feed concentration, temperature, and flow velocities on NO concentration profiles are investigated in steady state. The technique presented has a high potential for a better understanding of interactions of mass transfer and surface kinetics in heterogeneously catalyzed gas-phase reactions.

Soot formation and oxidation in oscillating methane-air diffusion flames at elevated pressure.

Comparisons with respect to the sooting tendency are made between stationary diffusion flames and diffusion flames with pulsations induced by oscillating fuel flow. Time-resolved measurements of the soot particle properties in the flames are obtained by combining Rayleigh-scattering, laser-induced incandescence, and extinction measurements into the RAYLIX method. Furthermore, flame luminosity at 590 nm and OH*-chemoluminescence signals at 310 nm are monitored to obtain data regarding the flame structure. Mean soot volume fractions of oscillating flames are significantly different from those of stationary flames with the same mean fuel flow rate; oscillations of the total amount of soot are phase shifted and asymmetric compared with fuel flow oscillations.

Size distributions of nanoscaled particles and gas temperatures from time-resolved laser-induced-incandescence measurements.

Laser-induced-incandescence (LII) signal decays are measured in sooting premixed atmospheric and low-pressure flames. Soot particle temperatures are obtained from LII signals measured at two wavelengths. Soot particle size distributions P(r) and flame temperatures T are measured spatially resolved by independent techniques. Heat and mass transfer kinetics of the LII process are determined from measured soot particle temperatures, flame temperatures, and particle sizes. Uncertainties of current LII models are attributed to processes during the absorption of the laser pulse. Implications for LII experiments are made in order to obtain primary soot particle sizes. Soot particle size distributions and flame temperatures are assessed from measured particle temperature decays by use of multi-D nonlinear regression.