Challenges and Solutions in Diesel Emission Control

Andy Walker

HDD Global Technology Director, Johnson Matthey, Wayne, PA

Abstract

The role and requirements of Diesel emission control systems have changed substantially since the introduction of the early Diesel Oxidation Catalysts (DOC) to control carbon monoxide (CO) and hydrocarbon (HC) emissions from light duty Diesel vehicles. Since then, emissions legislation has tightened significantly around the world, driving the development and implementation of complex systems to control emissions of Particulate Matter (PM) and nitrogen oxides (NOx), as well as CO and HC. This presentation provides an overview of the systems currently being used to meet today∍s Diesel legislation, and looks ahead to the catalyst systems that will be used to meet future, incoming regulations.

An overview will be given of the requirements and capabilities of the current DOC plus Diesel Particulate Filter (DPF) systems being used to control CO, HC and PM emissions with very high efficiency. The challenges that these systems face, and the ways in which these challenges have been overcome will be outlined. The future direction of this technology will be discussed.

Some of the main challenges currently facing the catalyst/engine community relate to the control of NOx emissions from Diesel engines. Reducing NOx (to nitrogen) under the highly oxidizing conditions prevalent in the Diesel exhaust is extremely challenging, but two approaches have already been successfully introduced into large scale series production.

NOx Adsorber Catalysts (NAC) operate by storing NOx under oxidizing conditions, and then reducing this NOx during the periodic, short-term reducing events created by running the engine under fuel-rich conditions. An overview of the operating principles, capabilities and future challenges in the NAC area will be given.

Selective Catalytic Reduction (SCR) systems operate by using ammonia to react selectively with the NOx under oxidizing conditions. SCR systems are already in use on heavy duty Diesel vehicles in Europe, and are starting to be introduced into the North American market. The performance capabilities and future challenges facing SCR catalyst technology will be discussed. Some alternative NOx control approaches are also being considered, and a brief overview of the most promising will be given.

The increasingly stringent legislation requires simultaneous very high conversions of all four regulated pollutants. This can be achieved by combining DPF and NOx control systems. The configurations being used to provide the necessary emissions control are presented, and the future direction of Diesel emission control will be discussed.

Speaker’s Bio - Dr. Walker is Heavy Duty diesel Global Technology Director at Johnson Matthey, Emission Control Technologies. He is leading the development of JM products for the global on-road and non-road HDD markets.