Tier 2 Test Fuel Impact to Tier 3 Aftertreatment Systems and Calibration Countermeasures 2018-01-0941
During the course of emissions and fuel economy (FE) testing, vehicles that are calibrated to meet Tier 3 emissions requirements currently must demonstrate compliance on Tier 3 E10 fuel while maintaining emissions capability with Tier 2 E0 fuel used for FE label determination. Tier 3 emissions regulations prescribe lower sulfur E10 gasoline blends for the U.S. market. Tier 3 emissions test fuels specified by EPA are required to contain 9.54 volume % ethanol and 8-11 ppm sulfur content. EPA Tier 2 E0 test fuel has no ethanol and has nominal 30 ppm sulfur content. Under Tier 3 rules, Tier 2 E0 test fuel is still used to determine FE. Tier 3 calibrations can have difficulty meeting low Tier 3 emissions targets while testing with Tier 2 E0 fuel. Research has revealed that the primary cause of the high emissions is deactivation of the aftertreatment system due to sulfur accumulation on the catalysts. The emissions drive cycles used in the test sequence play a significant role in catalyst deactivation. It is possible to desulfur the catalyst by employing an aggressive drive cycle to sustain catalyst temperatures above 650°C (1202°F). Drive cycles that produce the higher sustained catalyst temperatures are not found in the miles per gallon (MPG) method FE test sequence. Therefore, the aftertreatment system and calibration must be robust to sulfur accumulation during less aggressive drive cycles. A number of control tuning strategies were tested, and their robustness to sulfur accumulation on the catalysts was determined.