Controlling Particulate Emission from Diesel Engines with Catalytic Aftertreatment

Compared with gasoline powered engines, the diesel engine naturally emits dramatically lower levels of gaseous hydrocarbons, carbon monoxide, and oxides of nitrogen. The primary form of health affecting airborne pollution from diesel engines is in the form of particulate emissions. While the full potential health impact of diesel particulates remains to be understood, the combination of poor urban visibility due to “noxious smoke” emissions, inhalation related irritations, and the odor associated with diesel emissions provides ample potential for quality of life improvement through abatement of these emissions. Modern catalytic aftertreatment of diesel exhaust can have substantial impact on the particulate portion of the emission spectrum, primarily through the oxidation of the heavy hydrocarbons comprising the “soluble organic fraction” (SOF) of the particulate distribution. New catalyst composition strategies will be described with a particular emphasis on particulate emissions reduction. By analyzing the operating characteristics of a targeted vehicle, the appropriate type and volume of catalyst can be selected to maximize the return on this technology investment. In contrast to gasoline engines, the diesel powered vehicle fleet can benefit relatively immediately from catalytic aftertreatment in both OEM and potentially retrofit applications. The highly oxidizing exhaust stream which is a natural consequence of the diesel powerplant's operating characteristics provides the chemical environment necessary for effective catalyst application. No need for elaborate electronic controls or sensors, such as are called for on gasoline engines, are necessary for effective catalyst implementation on diesel vehicles.