Selective reduction

Mazda claims that its CX-7 SUV will be the first passenger vehicle produced by a Japanese automaker to be equipped with a urea-selective catalytic reduction (SCR) system.

Mazda's SCR will be combined with the company's newly developed MZR-CD 2.2L turbo diesel engine in the vehicle.

Planned for introduction in 2009, the SCR system will spray aqueous urea directly into the exhaust gas flow where it will convert nitrogen oxides into nitrogen and water.

Unlike technologies that use extra fuel to burn off nitrogen oxides, the method minimally affects fuel economy and power output.

Because an aqueous urea storage tank and other specialist equipment are required for the SCR system, space limitations in passenger vehicles have previously restricted the use of such systems to trucks and buses.

Mazda's MZR-CD 2.2L turbo diesel engine actually produces low volumes of nitrogen oxides, which means that the SCR system needs to remove less in post-processing, resulting in a reduced amount of urea that needs to be used; hence a smaller tank can be installed in the Mazda CX-7.