Date of Award
Open Access Master's Thesis
Master of Science in Mechanical Engineering (MS)
Administrative Home Department
Department of Mechanical Engineering-Engineering Mechanics
Jeffrey D. Naber
John H. Johnson
Committee Member 1
Boopathi S. Mahadevan
Medium and heavy-duty diesel engines contribute nearly a third of all NOx emissions nationwide. Further reduction of NOx emissions from medium and heavy-duty diesel engines is needed in order to meet National Ambient Air Quality Standards (NAAQS) for ambient particulate matter and ozone. Current diesel engine aftertreatment systems are very efficient at reducing NOx emissions at exhaust temperatures above 200 °C, however at exhaust temperatures below 200 °C there are significant NOx emissions at the tailpipe. Therefore, a reduction of diesel engine cold start and low speed/load operation emissions, where exhaust temperatures are below 200 °C, is needed. Utilizing a passive NOx adsorber (PNA) to adsorb NOx emissions at temperatures below 200 °C and reduce tailpipe NOx emissions is part of the solution. In this research, over 200 hours of experimental testing was carried out on a Johnson Matthey Diesel Cold Start Concept Catalyst (dCSC™), a passive NOx adsorber with hydrocarbon trapping ability on an oxidation catalyst.
Storing NOx emissions while the aftertreatment system downstream of the PNA is at temperatures below 200 °C needs to be supplemented by externally heating the aftertreatment system downstream of the PNA. This would reduce the time the aftertreatment system is at temperatures below 200 °C. The faster the aftertreatment system reaches operating temperature the less risk of substantial NOx emissions at the tailpipe, because the storage capacity of the dCSC™ is finite. Methods such as electric heaters, fuel burners, engine calibration, engine hardware changes, and others to quickly reach desired aftertreatment temperatures are being researched. The EPA and CARB are preparing to monitor the emissions regulation compliance of medium and heavy-duty diesel engines by using on-board diagnostics, throughout the useful life of the engine. They are also investigating thermal and chemical catalyst poisoning in order to accurately age and predict the life of the aftertreatment system. Improving processes and reducing contaminants in fuels can reduce the risk of chemical catalyst poisoning.
A 2013 6.7L Cummins ISB (280 hp) diesel engine was used for a series of experiments to quantify the NO, NO2, and NOx storage and release performance of the dCSC™. NOx storage experiments were performed at a range of temperatures from 80 to 250 °C and NOx release experiments were performed at temperatures from 200 to 450 °C. The portion of NO, NO2, and NOx that is converted and the portion that remains stored on the dCSC™ and the oxidation characteristics of the dCSC™ at these temperatures were also quantified.
Peak NOx storage capacity of the dCSC™ was found to be at temperatures from 125 to 150 °C. Throughout the testing, a decrease in the total NOx storage capacity was observed. However, the 200-second dCSC™ NOx storage capacity remained constant throughout testing. The percentage of stored NOx released was observed to be over 70% if the dCSC™ temperature ramped through 200 to 265 °C and/or reached 350 °C. These temperatures coincide with the desired operating temperatures of current aftertreatment systems. The dCSC™ also shows over 50% NO to NO2 oxidation at temperatures from 200 to 400 °C and a peak oxidation performance of 90% at 300 °C. At temperatures of 150 °C and above, the dCSC™ oxides 90 to 100% of CO to CO2. At 80 to 125 °C, the dCSC™ oxidizes 50 to 70% of the CO entering the substrate to CO2.
Berndt, Conor, "AN EXPERIMENTAL STUDY OF A PASSIVE NOx ADSORBER (PNA) FOR THE REDUCTION OF COLD START DIESEL EMISSIONS", Open Access Master's Thesis, Michigan Technological University, 2019.