Mazda will unveil a diesel-engined CX-7 with a selective catalytic reduction (SCR) system at next month’s Frankfurt Motor Show.

Mazda says that SCR systems substantially reduce nitrogen oxide (NOx) emissions, which helps the 2.2-litre diesel CX-7 to comply with  Euro 5 emissions regulations. The clean-running diesel CX-7 will be launched in Europe in October 2009, with Australian sales following in November.

Mazda’s SCR system purifies vehicle exhaust gases by spraying AdBlue aqueous urea directly into the exhaust flow in front of the catalytic converter. Through a chemical reaction, the urea converts approximately 40% of nitrous oxides into harmless nitrogen. Previously, the large size of SCR systems limited their use to trucks and buses. Mazda has managed to reduce the size and weight of the system components, which include a storage tank fitted under the luggage area. The CX-7 is the first passenger vehicle fitted with such a system.

Even with the added components, the diesel powered CX-7 offers the same 455 litres of luggage space as petrol engine models.

Mazda says that its SCR system will run for 20,000km between refilling the AdBlue tank.