3 Key Systems Make Clean Diesel Possible
There are more than 7 million diesel cars, SUVs, trucks and vans on American roads. Whether you’re in the market for a clean diesel vehicle or you’re simply interested in learning more, it helps to have a basic grasp of three key technologies used to reduce diesel emissions and help new-gen vehicles earn the clean diesel moniker.
Exhaust Gas Recirculation (EGR)
Efficient diesel combustion requires large volumes of air and extreme heat. Unfortunately, these two factors also encourage the formation of nitrogen oxides (NOx), a family of pollutants the EPA now strictly regulates. NOx contaminants contribute to smog, acid rain and ailments such as asthma, bronchitis and emphysema.
To reduce NOx emissions, some clean diesel engines incorporate EGR systems that recirculate into the engine gases from the exhaust. Introducing these gases reduces overall air volume and cools engine temperatures to discourage NOx formation. While this method can be quite effective, its effectiveness can vary based on driving and load conditions, and it can increase by as much as 30% the production of particulates, hydrocarbons and carbon monoxide (CO).
Selective Catalytic Reduction (SCR)
Selective catalytic reduction represents an alternate approach to NOx reduction. As the exhaust stream travels 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 NOx prompting a chemical reaction that converts the harmful pollutant into its base components, nitrogen and water, which can safely be released.
SCR is an effective way to decrease a range of emissions. It reduces NOx by 90%, hydrocarbons and carbon monoxide by 50% to 90%, and particulates by 30% to 50%. The process itself is automatic and requires no driver intervention, but to ensure a continuous supply of diesel exhaust fluid, vehicles are designed with an onboard tank to hold the fluid which must be replenished on a regular basis. To prevent drivers from circumventing the SCR system, some are designed to lock the starting system the next time the car is started if the DEF levels have fallen below an established level.
Diesel Particulate Filter (DPF)
To further reduce emissions, vehicle makers also install a diesel particulate filter in the exhaust pipe to trap soot and particles before the exhaust is released. While many DPFs are classified as self-regenerating, a dirty one can cause engine issues, so the filter should be removed and cleaned every 80,000 to 120,000 miles.
Many clean diesel vehicles rely on some combination of these technologies. Most incorporate EGR or SCR systems, supplemented with diesel particulate filters to further reduce emissions by straining any remaining soot and particles from the exhaust stream.