The EPA challenge is to further reduce NOx from diesel engine exhaust.  Volvo has chosen to eliminate NOx using the proven and highly efficient process of SCR:  Selective Catalytic Reduction.  Volvo engines with SCR technology have near-zero emissions with less fuel consumption.

Volvo's technique for further reduction of NOx is through the aftertreatment of engine exhaust.  If NOx gases are selectively eliminated in a downstream aftertreatment chamber, the level of NOx produced by the engine can be significantly higher.  This approach allows the engine to be retuned for maximum fuel efficiency.

SCR requires a catalytic converter into which is injected Diesel Exhaust Fluid (DEF).  The primary component of DEF is water; the active organic component is urea.

Urea is a nitrogen compound that turns to ammonia when heated.  When a urea-and-water solution is injected into the exhaust stream and passed over a catalyst, the urea reacts with the NOx to form nitrogen and water vapor -- two clean and harmless components of the air we breathe.

The basic elements of the Volvo SCR system:

• SCR catalyst aftertreatment chamber
• DEF tank
• Pump & lines
• Heating system
• Control & monitoring system