Mazda Becomes First Japanese Automaker to Develop a Urea SCR System for Cars

16 March 2009

Urea SCR system diagram. Click to enlarge.

The refreshed version of Mazda Motor Corporation’s crossover, the Mazda CX-7, will be the first passenger vehicle produced by a Japanese automaker to be equipped with a urea selective catalytic reduction (SCR) system.

Mazda’s urea SCR system, which is smaller than previous systems, will be combined with Mazda’s newly developed MZR-CD 2.2-liter turbodiesel engine. Mazda’s MZR-CD 2.2L turbodiesel engine produces low volumes of engine-out NO_x, which means that the SCR system needs to remove less NO_x in post processing, resulting in a reduced amount of urea required for NO_x reduction.

This means a smaller urea tank is required, allowing it to be comfortably installed in the Mazda CX-7.

The new MZR-CD 2.2 diesel. Click to enlarge.

The MZR-CD 2.2L engine’s diesel particulate filter (DPF) features a Mazda-developed catalyst activation mechanism that enhances the removal of particulate matter (soot), a characteristic of diesel engine exhaust gases. (Earlier post.) The new catalytic combustion treatment process enables the DPF to burn off particulate matter approximately 60% faster than current systems.

The engine, which is also applied to the Mazda6, achieves torque of 400 Nm (295 lb-ft) and improved fuel efficiency through its updated fuel injectors, lower compression ratio and other enhancements.

The fuel pressure inside the common rail is increased to 200 MPa (2,000 bar), the injector nozzles are almost 20% smaller than before, and the minimum injection interval is 30% shorter. As a result of these improvements, the fuel spray pattern is more accurate, and the fuel injection frequency, timing, volume and particle size can all be optimally controlled. The net effect is that fuel consumption and the amount of soot generated in the exhaust are reduced.

A low compression ratio, precision fuel injection technology, a larger exhaust gas recirculation (EGR) system and a highly rigid lower block structure have enabled reductions in noise and vibration energy.

Mazda plans to introduce the urea SCR system in 2009, together with the new facelifted Mazda CX-7. The Mazda CX-7 with urea SCR will conform to Euro 5 regulations.