Development of a Methodology to Generate On-Board Diagnostic
Threshold Selective Catalytic
for Heavy-Duty Diesel
Inclusive Dates: 03/15/13 – 03/15/14
Background — The on-board diagnostics (OBD) system monitors engine and aftertreatment components that affect the emissions performance of a vehicle. When the malfunction illumination light (MIL) is illuminated, at least one emission-related problem has been detected, and the driver is notified that vehicle service is needed. The OBD system stores malfunction codes in the engine control unit (ECU) and assists the service technician in diagnosing and repairing the problem. For heavy-duty diesel engine applications, the California Air Resources Board (CARB) mandates that heavy-duty OBD systems be implemented for all on-highway engines offered for sale in California beginning with model year (MY) 2013. Even though urea-based selective catalyst reduction (SCR) technology has been used as a primary means to meet the US 2010 diesel NOx emissions requirements in North America, technical challenges still exist across the industry. Among them, there was no proven method to consistently create an OBD threshold SCR catalyst in the laboratory environment.
Approach — A novel methodology has been developed through this project to consistently age zeolite SCR catalysts to the OBD threshold level. The approach was to use SwRI's FOCAS® HGTR® burner technology to thermally age the SCR catalysts to the levels to meet OBD threshold calibration requirements. A US 2010 certified MY 2011 Ford PowerStroke 6.7L diesel engine was used for the project. The heavy-duty federal test procedure (FTP) cycle was measured on the engine and replicated using the FOCAS HGTR system for SCR performance evaluation. An SCR thermal aging cycle was developed for aging SCR catalyst to threshold NOx levels, while the steady-state NOx efficiencies were monitored and compared to the simulated FTP tests. At the conclusion of the aging set, the FOCAS HGTR aged SCR catalysts were then emissions tested using the Ford PowerStroke 6.7L diesel engine. These final FTP tests were used to confirm the burner FTP test results.
Accomplishments — The key conclusions from this work included that the OBD aging cycle embedded steady-state SCR efficiency monitoring can be used to accurately guide the aging to a desired level of degradation. OBD threshold level was achieved for the state-of-the-art CuZ SCR as used on the Ford PowerStroke diesel engine. The procedures developed provided a solution to the technical challenges currently imposed by the lack of a consistent method to create OBD threshold SCR catalysts. This method is unique to the burner system and cannot be replicated with currently available industry approaches. A paper has been published at the SAE Emissions Conference 2014. An invention disclosure has been filed.