Study on Low NOX Emission Control Using Newly Developed Lean NOX Catalyst for Diesel Engines 2007-01-0239
In recent years, emission regulations have become more stringent as a result of increased environmental awareness in each region of the world. For lean-burn diesel engines, since it is not possible to use three-way catalytic converters, reducing NOX emissions is a difficult technical challenge.
To respond to these strict regulations, an exhaust gas aftertreatment system was developed, featuring a lean NOX catalyst (LNC) that uses a new chemical reaction mechanism to reduce NOX.
The feature of the new LNC is the way it reduces NOX through an NH3-selective catalytic reduction (SCR), in which NOX adsorbed in the lean mixture condition is converted to NH3 in the rich mixture condition and reduced in the following lean mixture condition. Thus, the new system allows more efficient reduction of NOX than its conventional counterparts. However, an appropriate switching control between lean and rich mixture conditions along with compensation for catalyst deterioration was necessary.
As a result, this study established a method of regulating the supply of reductant to the catalyst by monitoring the air-fuel ratio of exhaust gases and the amount of intake air, and simultaneously realized a lower fuel penalty and emission cleanliness.