Aftertreatment

Aftertreatment refers to processes and devices that remove pollutants from exhaust gases or other effluents after the primary source has produced them. In automotive and industrial contexts, aftertreatment systems are installed downstream of the emission source to reduce the release of harmful substances and help meet environmental regulations and performance targets. In vehicles, aftertreatment aims to lower emissions of nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM).

Common aftertreatment technologies include catalytic converters, diesel oxidation catalysts, diesel particulate filters, and selective catalytic reduction systems. Catalytic converters, used mainly on gasoline engines, employ a three-way catalyst to convert CO and HC to CO2 and H2O, and NOx to nitrogen and water under near-stoichiometric conditions. Diesel oxidation catalysts oxidize CO and HC in diesel exhaust. Diesel particulate filters trap soot and require periodic regeneration to burn off accumulated particulates. Selective catalytic reduction systems inject urea or ammonia into the exhaust, enabling NOx to be reduced to nitrogen and water, a solution widely used on modern diesel engines. Lean NOx traps and other NOx control schemes store and subsequently reduce NOx during varying engine operation. Aftertreatment performance depends on operating temperature, catalyst health, and proper integration with engine management and exhaust flow, with regeneration and potential sulfur poisoning posing ongoing maintenance considerations.

Regulatory frameworks, such as Euro 6 and EPA standards, drive the adoption and evolution of aftertreatment technologies. Developments focus on greater efficiency, lower backpressure, longer life, and compatibility with alternative fuels, while retrofit and adaptation for older engines remain important in reducing overall emissions.