The modern Diesel engine is one of the most versatile power sources available for mobile applications. The high fuel economy and torque of the Diesel engine has long resulted in global application for heavy-duty applications. Moreover, the high power and excellent driveability of today's turbo-charged small high-speed Diesel engines, coupled with their low CO2 emissions, has resulted in an increasing demand for Diesel powered light-duty vehicles.
However, the demand for Diesel vehicles can only be realised if their exhaust emissions meet the increasingly stringent emissions legislation being introduced around the world. In the USA, light-duty Diesel (LDD) vehicles will have to meet the same emissions legislation as gasoline vehicles from 2004 onwards, while in Europe a similar target is expected when European Stage 5 legislation is introduced. In practice, such targets mean very high reductions (up to 90%) of nitrogen oxides (NOx) and particulate matter (PM) emissions may be required from today's levels. Drastically reduced NOx and PM emissions from heavy-duty Diesel (HDD) engines are also required in Europe and the USA in a similar time frame.
This paper reviews the developments in Diesel exhaust emissions control devices. The application of Diesel oxidation catalysts, particulate filters, and NOx control catalysts (NOx adsorber catalysts and Selective Catalytic Reduction systems) to help meet both light- and heavy-duty legislation is discussed. An overview of likely catalyst system designs to achieve high levels of PM and NOx conversion is given.