Light off temperature based approach to determine diesel oxidation catalyst effectiveness level and the corresponding outlet NO and NO2 characteristics
According to the latest EPA emission regulations, the NOx (Nitrogen oxide compounds) emissions from heavy duty compression ignition engines need to see a dramatic reduction. The current technology used for this purpose is the selective catalytic reduction (SCR) system, which achieves NOx reduction of around 90% . This involves urea injection which is influenced by the NO: NO2 ratio at the inlet to the SCR. Thus, the role of the DOC (Diesel Oxidation Catalyst) where most of the oxidation of the NOx compounds takes place, comes to fore. The focus is also on the effectiveness of the catalyst as it thermally ages. Therefore, the aim of this research project is to correlate the aging in the DOC with the light off temperature of the catalyst and subsequent variation in the NO and NO2 concentration at the outlet of the DOC. This shall be achieved through means of a model developed after extensive experimental procedures. Also, further exhaustive experiments to validate the model over multiple aging cycles of the catalyst shall be undertaken. The DOC was subjected to 2 rigorous kinds of experiments aimed at determining the light off temperature shift as the catalyst aged and to determine the NO and NO2 concentrations at the DOC outlet as it aged. Exhaust stream compounds were measured using exhaust analyzers and DOC temperatures were determined using thermocouples installed inside the DOC and at its inlet and outlet. The data thus obtained was then analyzed and 2 separate models were developed, one for the light off experiments, and the other for the NOx experiments. Aging procedures were carried out at an oven according to prescribed techniques and the DOC was subjected to similar experiments again. Analysis was carried out on the data. From the light off experiments and the model analysis, a clear positive shift in light off temperatures was observed from one aging level to another across the range of set points. It was also observed that even after subjecting the DOC to three thermal aging exercises, its conversion efficiency went up to 90%. Also, as the DOC aged, the NO concentration at the DOC outlet showed a downward trend which was observed across the spectrum of engine set points and aging levels. These experiments were repeated for consistency so that the models could be rendered more useful.
Meckl, Purdue University.
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