Twin-LNT System for Advanced Diesel Exhaust Gas Aftertreatment

The most significant challenge in emission control for compression ignited internal combustion engines is the suppression of NO_x. In the US, NO_x-levels have faced a progressive reduction for several years, but recently the introduction of the Real Driving Emissions legislation (RDE) in Europe has not only significantly increased the severity of the required emission reduction but now is in the advent of stretching technology to its limits. Emission control is based on engine-internal optimization to reduce the engine-out emissions in conjunction with aftertreatment technologies, that are either Selective Catalytic Reduction (SCR) or Lean NO_x Trap (LNT) based systems. Due to its ability to control high amounts of NO_x, SCR is widely used in heavy-duty applications and is becoming more popular in light-duty and passenger car applications as well. This work in contrast shows that the LNT concept can be enhanced significantly to also offer robust emission control, providing good cold-start capabilities, package advantages and the lack of customer-interaction for refill of the diesel exhaust fluid. As an advanced engineering solution to the problem described, a twin LNT technology package has been designed to provide a wide emission control window, ideal for high and low load dynamic driving. The interactions when cleaning both LNTs from stored NO_x are investigated, the requirements of purges to clean the LNTs from stored NOx and their performance are analyzed; coupled with an intensive investigation of sulfur storage and release.