Selective Catalytic Reduction (SCR)

SCR is a means to convert nitrogen oxides to diatomic nitrogen and water. 14 Since 2010, most heavy-duty diesel engine manufacturers use SCR. In order to meet Euro VI standards, many diesel vehicles require the addition of AdBlue.

How it works

  • Exhaust gases flow out of the engine into the SCR system where a diesel exhaust fluid (DEF) such as aqueous urea is sprayed onto a special catalyst
  • This sets off a reaction that converts noxious nitrogen oxides into nitrogen, water, and tiny amounts of carbon-dioxide. This then passes through a particulate filter before being expelled via the tailpipe.

Features:

  • SCR systems can help reduce emissions which can help achieve these standards
  • Truck manufacturers in Europe claim that their Euro VI engines designed with SCR are more fuel efficient than their Euro V ones15
  • SCR systems require regular diesel exhaust fluids or AdBlue injection16
  • AdBlue is non-hazardous, non-toxic, and non-inflammable.

Typical use case:

Light-duty vehicles with engine capacity over 2 litres. Heavy-duty vehicles.

Implications for operations:

  • Euro VI trucks with these additional emissions control technologies are heavier and may impact the amount of mass the vehicle can carry.
  • Similarly, there could be an increase in the price of the supply of these trucks to Australia.
  • SCR will require periodic addition of fluids, and there is an operational cost associated with this.
  • Australia is a net importer of Adblue and as such is susceptible to global supply and any issues that may arise during times of instability.
  • Adblue is made by synthesising ammonia with CO2 so while it reduces the direct emissions from diesel engines its production creates greenhouse gas emissions.

14Diesel Technology Forum, Selective Catalytic Reduction, https://dieselforum.org/selective-catalytic-reduction-scr.

15Planet Trucks, Euro 5 and Euro 6 truck comparison Regulation, https://www.planet-trucks.com/truck-news/a43403/euro-5-euro-6-truck-comparison

16Diesel Technology Forum, Selective Catalytic Reduction (SCR), https://dieselforum.org/selective-catalytic-reduction-scr.