Electrically Heated Catalysts for Cold-Start Emissions in Diesel Aftertreatment

With a tighter regulatory environment, reduction of hydrocarbon (HC) and NO_x emissions during cold-start has emerged as a major challenge for diesel engines. In the complex diesel aftertreatment system, more than 90% of engine-out NO_x is removed in the underfloor SCR. However, the combination of low temperature exhaust and heat sink over DOC delays the SCR light-off during the cold start. In fact, the first 350 seconds during the cold light-duty FTP75 cycle contribute more than 50% of the total NO_x tailpipe emission due to the low SCR temperature. For a fast SCR light-off, electrically heated catalyst (EHC) technology has been suggested to be an effective solution as a rapid warm-up strategy.

In this work, the EHC, placed in front of DOC, utilizes both electrical power and hydrocarbon fuel. The smart energy management during the cold-start was crucial to optimize the EHC integrated aftertreatment system. With the EHC warm-up strategy, the underfloor SCR reached the operation temperature within 100 seconds and achieved more than 90% conversion between 150 and 350 seconds during the cold FTP75. Furthermore, the integrated system provides an opportunity to improve fuel economy. In summary, the EHC has been demonstrated as an enabling technology for a clean and energy efficient NO_x aftertreatment system for diesel engines.