NOX AFTERTREATMENT TECHNOLOGIES
From today’s point of view, only lean NOx trap (LNT) and SCR technology represent promising solutions to achieve future
NOx reduction targets. The operating principle as well as the specific pros and cons of the two different technologies will
be described in more detail in the following chapters.
LNT technology
The lean NOx trap (LNT) or NOx adsorber catalyst (NAC) is a discontinuously operating aftertreatment technology and is
characterized by the following operating modes (Figure 2):
• NOx storage during lean engine operation
• NOx reduction during rich operation phases
• LNT desulfurization under rich conditions and high temperatures
The most challenging operating modes of a LNT under real transient conditions are the rich operation of the Diesel
engine, the transitions between lean and rich operation, the desulfurization process as well as control of the LNT system
including sensors.
Due to its operating principle the mixture-controlled (quality-controlled) Diesel engine operates with a high amount of
excess oxygen, particularly under part-load, which is most relevant especially for light-duty applications. A thorough
optimization of the Diesel engine air and fuel management is required in order to reduce the high amount of excess
oxygen in the rich operating condition. The removal of oxygen is essential for a successful regeneration of the NOx
adsorber catalyst /7/, /8/. Therefore efficient calibration methodologies based on DoE (Design of Experiments)
approaches, which consider aspects like oil dilution, component limits, CO/HC-ratio, black smoke emissions, combustion
noise, sensor requirements as well as the requirement for smooth maps and map transitions during the calibration
process are necessary.