What You Need to Know about Diesel Engine Selective Catalytic Reduction

What You Need to Know about Diesel Engine Selective Catalytic Reduction

Diesel vehicles have received a lot of scrutiny in the past decade or so, especially with the Volkswagen scandal. Even outside of the scandal, many people think of diesel engines as inherently bad for the environment.

However, technology is changing this common misconception and making diesel engines cleaner. One of the technological advancements that has made waves recently was the 2010 federal EPA mandate that diesel engines use selective catalytic reduction (SCR). This mandate caused an uproar because it requires the use of a consumable fluid called diesel exhaust fluid (DEF). Suddenly, diesel owners were required to purchase an another consumable fluid, an additional expense.

Remarkably, sentiment about DEF has changed much in the past few years. DEF actually improves fuel efficiency while reducing emissions—it makes diesel engines more environmentally friendly and saves drivers money. The money-saving aspect has made it worthwhile for diesel motorists to fill up an additional tank every now and then. It seems clear that DEF is here to stay.

What Is SCR and How Does DEF Work?

While SCR has received a lot of attention recently, it is not a new technology. SCR was introduced about half a century ago when it was used by the power industry to reduce nitrogen oxides produced by coal-fired power plants. Nitrogen monoxide and dioxide are the main pollutants produced by diesel combustion, and the regulation of these substances started the Volkswagen diesel scandal.

In an engine with SCR, the exhaust gas from the engine is routed through a filter to remove the soot and ash that are byproducts of burning diesel fuel. This process makes the exhaust less black, one of the problems that historically discouraged people from purchasing diesel vehicles.

Next, the DEF help reduce dangerous oxides. Once the exhaust passes through the filter, it moves by a nozzle that sprays DEF into the gas. DEF consists of both deionized water and a pure form of urea. Then, the exhaust mixed with DEF enters the catalytic converter and the urea helps cause reactions with metallic compounds.

Through this process, nitrogen monoxide and dioxide are converted into nitrogen gas and water. Nitrogen is the primary component in the air we breathe, and it’s completely harmless to humans and the environment. The total process is similar to how a catalytic converter works in a gasoline-powered vehicle, except for the extra step of spraying DEF into the exhaust.

How Have Drivers Reacted to the DEF Mandate?

While many drivers are happy to reduce emissions and achieve better gas mileage with DEF, other people have not taken the regulation in stride. In reality, DEF is inexpensive and the tank only needs to refilled about as often as you change your oil. Since DEF is mostly water, a 2.5-gallon pack sells for less than $20 and this will top off the tanks of most non-commercial vehicles.

The people most impacted by the DEF regulation are those who drive Class 8 semi-trucks. These commercial vehicles will drive millions of miles over their lifespans and the engines consume a lot of fuel and thus a lot of DEF. However, there has been a solution for making the entire process more convenient for these drivers. DEF is now available at the pump at many fuel stations, especially along major highways, which reduces the inconvenience of refilling the tank.

At the same time, DEF does add a complication to driving diesel vehicles—it’s one more fluid you must ensure your vehicle has enough of. Like diesel fuel itself, the vehicle will not run without DEF. Most vehicles give drivers plenty of warnings when they are low on DEF, but this still adds a layer of stress to owning a diesel vehicle and has upset some drivers as much as the added expense.

What Is the Future of SCR and DEF?

SCR is definitely a technology that’s here to stay, and many industries formerly dominated by gasoline-driven vehicles have started to introduce diesel options as a result of the added efficiency and reduction of harmful emissions. For example, more large-engine trucks from Ford, GM, and Dodge are using diesel engines.

In addition, SCR has been introduced to the marine diesel industry. Since ships can have diesel engines the size of a house, SCR is critical for reducing emissions from the marine shipping and cruise industries.

DEF is made easily from chemicals that are already an important part of the agriculture industry, so there is capacity to ramp up production as SCR, and diesel engines in general, become more popular. SCR has already revolutionized industries that depend on diesel engines, like commercial trucking, so it will be exciting to see the impact of this technology on other sectors of the economy.

About the Author

A native of the tri-state area, Patrick James Smith has cultivated a lifelong love for travel during trips for work and leisure alike. In planning for his travels, he has become well-versed in the art of travel hacking and utilizing credit card rewards points to book free vacations around the globe.