Evaluation of NOx Emission Control Technologies for SIDI Engines

Spark-Ignited Direct-Injection (SIDI) engines, such as the Mitsubishi GDI family of engines, are being used by automobile manufacturers to improve fuel economy and reduce CO₂ emissions. They are effective because they routinely operate in a lean combustion mode at light loads. However, three-way catalysts used in more conventional stoichiometric gasoline engine exhausts, have low NO_x conversion efficiency in lean SIDI exhaust. To overcome this drawback, catalyst manufacturers have developed the NO_x storage-reduction catalyst, sometimes referred to as the NO_x storage catalyst, the lean NO_x trap catalyst, or NO_x adsorber catalyst.

The Department of Emissions Research at Southwest Research Institute (SwRI™) performed a test program for the Coordinating Research Council (CRC) of Alpharetta, Georgia, to assess “state-of-the-art” and “next generation” NO_x reduction catalyst technologies with respect to their sensitivity to poisoning associated with sulfur in the fuel. This assessment focused on the sulfur tolerance of NO_x reduction technologies that reportedly had the demonstrated potential to achieve the very high levels of NO_x reduction that will be required to meet the Tier 2 emissions regulations.