Simultaneous reduction of nitric oxide and particulate matter emissions from a light-duty diesel engine using combustion development and diesel oxidation catalyst

The following document highlights the successful development of a scientifically-based approach for creating diesel engine combustion that yields lower levels of nitric oxide (NOx) and particulate matter (PM) emissions while minimizing the associated fuel consumption penalty and raised levels of hydrocarbon (HC) and carbon monoxide (CO) emissions. The 93% reduction in NOx, coupled with the simultaneous 79% reduction in PM places the newly developed engine calibration within the emission targets established for this research development. The primary distinguishable features of this strategy are premixed and low-temperature combustion. Both characteristics shift combustion to a region where simultaneous reductions in NOx and PM occur, thus defeating the perennial PM-NOx tradeoff associated with conventional diesel combustion. The increase in fuel consumption, 5% over the studied conventional combustion strategy, could possibly be recovered in part through optimal development of the engine system from the turbocharger to the combustion chamber design.; The new combustion development approach opens an opportunity to run the diesel engine rich of stoichiometric air-fuel ratios, while maintaining near-zero EI-PM emissions. Exhaust concentrations of CO as high as 5% emitted from the rich diesel condition create enough of the reducing agent necessary for an aggressive regeneration of a NOx storage aftertreatment device. The rise in fuel consumption, greater than that associated with the newly developed lean combustion strategy, prevents this condition from usefully serving as a standard operating mode; its intention is to operate only as necessary to maintain high NOx removal efficiency. Related to this, the 99% reduction in NOx and 98% reduction in PM---relative to the studied conventional diesel combustion strategy---assist in preventing PM and NOx interference during the regeneration of a NOx storage device.; Increased levels of HC and CO species result as diesel combustion burns in the new premixed, low-temperature fashion. A diesel oxidation catalyst (DOC) was studied to determine its ability to remove the higher levels of HC and CO species associated with the newly developed combustion strategies. The catalyst-out concentrations of emissions produced from the newly developed lean strategy lessen such that all emissions, i.e. NOx, PM, CO, and HC, satisfactorily meet the most stringent of upcoming federal emission regulations, at the studied engine speed and load. However, this study postulates that dramatic reductions in combustion temperature at the newly developed rich strategy alter HC species, which thereby completely quench the oxidation activity of the DOC. An increase of 100°C in exhaust temperature or an increase of exhaust oxygen concentration to 2% of total exhaust volume at the rich strategy does not improve the DOC's ability to remove HC or CO.