With a tighter regulatory environment, reduction of hydrocarbon
(HC) and NOx 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 NOx
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
NOx 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 NOx aftertreatment system for diesel
engines.