Stricter emission limitations for NOx and
particulates in mobile applications will require the use of active
aftertreatment methods like Diesel Particulate Filters (DPF),
Selective Catalytic Reduction (SCR) with urea and Lean
NOx Trap (LNT) as combinations in the 2010's. Due to
the significant total space and required investments, a lot of
efforts have been focused recently on the optimization of the
combinatory aftertreatment systems (ATS).
In this study the possibilities to intensify the catalytic ATS
were analyzed and reviewed by the examples and studies with
engines, laboratory reactors and simulations. The focus was on
diesel applications, where the number of needed ATS units is the
widest. The diesel engine modifications on SCR or EGR engines have
to be also designed together with ATS. The intensification includes
the principles of down-sizing and the integration of ATS units with
control systems. The reaction engineering of catalytic reaction and
regenerations (DPF, LNT) was also analyzed. The intensification
covered the examples about the integration of DOC, LNT and SCR on
DPF, high cell density substrates (metallic) and the integration of
hydrolysis and ammonia slip catalysis on the SCR unit. The
intensification cases were analyzed by the observed catalytic
activities, pressure drop, the volume of systems and costs. The LNT
coating on DPF gave a promising possibility to integrate PM,
nitrate and sulfate regeneration methods and OBD. The integration
of control units and their functions is also a modern way to keep
emissions, complexity and costs low.
The use of natural gas as fuel results in low PM emissions and
no DPF is needed in Euro 6. However, the intensification of ATS may
result in a stoichiometric engine with a three-way catalyst instead
of a lean combustion engine with oxidation and SCR catalysts in
heavy-duty natural gas applications.