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The particulate matter (PM) emitted by a diesel engine is collected and then combusted in a diesel particulate filter (DPF). A sudden decrease of the engine load of DPF undergoing regeneration, referred to as a drop to idle (DTI), may create a transient temperature peak much higher than under stationary feed conditions. This transient temperature rise may cause local melting or cracking of the filter. We report here the dependence of the maximum temperature following a DTI on the DPF properties and its dependence on the operating conditions.

The mechanism for the purging of a lean NOx trap has been investigated. For realistic purge times (e.g., 2 to 5 seconds), the stored NOx species do not decompose simply from equilibrium considerations (i.e., from the drop in O2 and NO concentrations during the rich purge). Instead, the decomposition of stored NOx is promoted by the reductants in the exhaust by a process referred to as reductive elimination. H2 is far more effective than CO or C3H6 for promoting this reductive elimination, particularly at low temperatures (e.g., 250°C). As long as H2 is available in the feedgas, H2O does not participate in the reductive elimination. However, if CO is the only reductant, H2O is needed to convert some of the CO to H2 through the water-gas-shift reaction. H2O is also important for the efficient storage of NOx during lean operation, possibly by enhancing the spillover of NO2 from a precious metal site to a NOx storage site.

A one-dimensional two-phase model of an adsorptive catalytic monolith reactor is used to analyze the Lean NOx Trap (LNT). The model simulates the features of NOx storage and reduction (NSR), a periodic process involving the sequential trapping on a storage component and conversion of NOx to nitrogen on a precious metal catalyst under lean conditions found in the exhaust of lean burn and diesel vehicles. A detailed storage kinetic model is used for the simulations. The NOx storage phase on Pt/BaO/Alumina catalyst has been studied in detail with particular attention to the effect of fluid velocity, storage time and storage component loading. The reductive phase is also analyzed. The simulated results are compared with our lab experimental data. The model predictions are in good agreement with the experimental observations and trends reported in the literature.

Packed bed reactors are well known for their vast and diverse applications in the chemical industry; from gas absorption, to stripping, to catalytic conversion. Use of this type of reactor in terrestrial applications has been rather extensive because of their simplicity and relative ease of operation. Developing similar reactors for use in microgravity is critical to many space-based advanced life support systems. However, the hydrodynamics of two-phase flow packed bed reactors in this new environment and the effects of one physicochemical process on another has not been adequately assessed. Surface tension or capillary forces play a much greater role which results in a shifting in flow regime transitions and pressure drop. Results from low gravity experiments related to flow regimes and two-phase pressure drop models are presented in this paper along with a description of plans for a flight experiment on the International Space Station (ISS).

A one-dimensional two-phase model of an adsorptive catalytic monolith reactor (used as Lean NOx Trap, LNT) is developed and analyzed. The model simulates the features of NOx storage and reduction (NSR), a periodic process involving the sequential trapping on a storage component and conversion of NOx to nitrogen under lean conditions found in the exhaust of lean burn and diesel vehicles. The effect of design and operating parameters, such as the lean and rich times and feed temperature, on NO2 conversion is examined. Using a relatively simple kinetic model and without any attempt to fit data, the LNT model predicts the dependencies of NO2 conversion on several feed parameters that are in good agreement with experimental observations.