How diesel emissions are controlled
Diesel emissions are controlled from the source through engine design and modifications or through after treatment technologies of the exhaust gas. The two types of after treatment devices for diesel exhaust are diesel traps and diesel catalysts. Diesel traps are filters that control particulate matter emissions by physically trapping them. However, the major challenge with diesel particulate filters is how to regenerate the filter from the accumulated particulate matter in an efficient and cost effective manner. In order to regenerate the filter, the vehicle must be driven in the highway at a specific speed otherwise; the filter will need to be cleaned by a mechanic. If the filter becomes blocked, it can compromise the performance of the vehicle.
How to control diesel emissions through the diesel oxidation catalyst
Diesel oxidation catalyst is an after treatment pollution control that can be installed on a new or existing vehicle or off-road equipment to reduce hazardous emissions that include particulate matter, hydrocarbons, nitrogen oxides, carbon monoxide and other toxic pollutants. The catalyst is placed within the engine muffler as a flow-through honeycomb structure coated with a precious metal catalyst and surrounded by stainless steel housing. When the hot diesel flows through the honeycomb structure, the precious metal coating causes a catalytic reaction that will break down the pollutants. The catalyst works best when fuel sulfur is 15 ppm or less but it can be formulated to operate at fuel sulfur levels of 500 ppm or less. The catalyst can be used on diesel engines with closed crankcase ventilation, selective catalytic reduction or lean NOx catalyst technologies to enhance the reduction of emissions.
The evolution of diesel oxidation catalyst
The main objective of the catalyst research in the late 1980’s and early 1990’s in both the United States and Europe was to optimize the performance of the catalyst. With the introduction of the low sulfur content fuels, moderate reduction in particulate matter emissions became possible. In highway engine applications of the diesel catalysts, the particulate matter reductions became the most important function of the technology. Today, diesel catalysts have been commercialized on heavy duty diesel engines in the US and on most light duty engines in Europe. It was also anticipated that diesel catalysts will function towards the reduction of nitrogen oxide emissions because it still exhibits some limited activity towards the conversions of nitrogen oxides. Only about 10 to 20% NOx conversions have been observed in diesel exhaust.