Exhaust Gas Re-Circulation (EGR)
Large volumes of air and extreme heat are required for efficient diesel combustion. Unfortunately, these two factors also encourage the formation of nitrogen oxides (NOx) a family of pollutants strictly regulated by the EPA. Nitrogen oxide contaminants contribute to smog, acid rain and ailments such as asthma, bronchitis and emphysema.
Many clean diesel engines incorporate EGR systems that recirculate into the engine gases from the exhaust to reduce nitrogen oxide emissions. With the introduction of these gases, the overall air volume is reduced and the engine temperature cools to discourage nitrogen oxide formation. This method can be quite effective, but its effectiveness can vary based on driving and load conditions, and it can increase by as much as 30 percent the production of particulates, hydrocarbons and carbon monoxide (CO).
Selective Catalytic Reduction (SCR)
Selective catalytic reduction represents an alternate approach to the reduction of nitrogen oxide. As the exhaust stream goes through the SCR system, it passes through a catalytic chamber and is sprayed with a urea-based diesel exhaust fluid (DEF). The ammonia in the fluid reacts with the nitrogen oxide which prompts a chemical reaction that converts the harmful pollutant into its base components, nitrogen and water, which can safely be released.
The selective catalytic reduction system is an effective way to decrease a range of emissions. SCR decreases nitrogen oxide by 90 percent, hydrocarbons and monoxide by 50 percent to 90 percent, and particulates by 30 percent to 50 percent. While the process itself is automatic and requires no driver intervention, to ensure a continuous supply of diesel exhaust fluid, vehicles are designed with an on-board tank to hold the fluid which needs to be replenished regularly. Some vehicles are designed to lock the starting system the next time the car is started if the DEF levels have fallen below an established level to prevent drivers from circumventing the SCR system.
Diesel Particulate Filter (DPF)
In an effort to further reduce emissions, vehicles designers also install a diesel particulate filter in the exhaust pipe to trap soot and particles before the exhaust is released. Many DPFs are classified as self-regenerating, but a dirty one can cause engine issues, so the filter should be removed and cleaned every 80,000 to 120,000 miles.
The majority of clean diesel vehicles depend on some sort of combination of these technologies. Most incorporate EGR or SCR systems which are supplemented with diesel particulate filters in an effort to further reduce emissions by straining any remaining soot particles from the exhaust stream. For more information about clean diesel, contact us here at Asher Automotive with the link below!