The management of an automotive Lean NOx Trap (LNT) catalyst requires periodic, brief periods of net rich exhaust to regenerate the catalyst by reducing the stored NOx. During the regeneration event, the fuel rich gas first affects the front of the catalyst then, as reductants are available, reach the downstream sections of the catalyst. In a typical engine test cell, it is not feasible to witness these distributed effects by simultaneously measuring multiple points in a catalyst bed due for a number of practical reasons. This is inconvenient because it is often desired to have a continuous or distributed lump model of the catalyst, which is difficult to calibrate without spatially and temporally resolved measurements. A novel measurement technique is presented which uses internal catalyst temperature measurements to detect the gross chemical reactions occurring in the catalyst during the rich reduction phase. The magnitude of the temperature change is shown to correlate with the mass of NOx and O2 reduced from the catalyst substrate. This information is available at each temperature measurement location, allowing spatial information to be collected non-intrusively. Furthermore, the technique contains temporal information regarding the key reactions. The type of information made available, as well as the convenience of the measurement system, makes the technique useful for a number of applications. The basis of the measurement technique is first presented from a theoretical basis, relating the temperature rise of the substrate to the various gross chemical reactions. Experimental validation of the method is then provided, illustrating the good correlation between the mass of stored NOx and O2 estimated by the method and the mass of stored NOx calculated from traditional gas analyzer measurements during the NOx storage phase. After demonstrating the applicability of the method, several applications are suggested including use of the technique for LNT modeling, LNT regeneration control, and sulfur poisoning detection.
Improved NOx Storage/Release Properties of Ceria-Based Lean NOx Trap Compositions with MnOx Modification