Siemens developing automotive SCR catalyst system

1 December 1997

Siemens Automotive is developing an SCR catalytic converter system for passenger car diesel engines that reduces nitrogen oxide (NOx) and hydrocarbon (HC) emissions up to 70%. Known as SINOx, the system uses electronics, sensors and injection technology along with urea as a reducing agent to trigger the chemical reaction that converts NOx and HC into nitrogen and water.

"SINOx is currently the most effective exhaust-gas after-treatment system for reducing NOx and HC emissions on diesel engines—and we're adapting it for diesel passenger car applications," said George Perry, president and CEO of Siemens Automotive Corporation, and senior vice president and general manager of the company's global Powertrain Division.

Diesel engines are attractive to automakers due to their fuel efficiency—especially in Europe where the price of fuel is significantly higher than in North America. In addition, lean-burn diesel engines are being considered around the world for the next generation of fuel-efficient vehicles. However, NOx and HC emissions have remained the diesel engine's greatest drawback, Perry said, and medium-term solutions to such challenges will only be found in the use of exhaust gas aftertreatment systems.

Urea is an odorless, water-soluble, compound of nitrogen. When used as an emissions-reducing agent in diesel exhaust gas management, a quantity of urea equal to approximately 3% of the diesel fuel consumed by the engine can result in significant emissions reductions in NOx (up to 70%) and HC (between 50 and 70%).

The SINOX system's electronic control system processes temperature and emission level information fed from sensors, and then meters and injects appropriate amounts of urea into the system. "The system uses a urea-water solution and injects it into the mixing chamber," Perry explained. "This results in a chemical reaction that releases ammonia, which in turn converts NOx and HC into non-toxic quantities of nitrogen and water."

This process, known as Selective Catalytic Reduction (SCR), is currently the best available for reducing NOx in diesel exhaust emissions, according to Perry. The system's converter module is a sheet-metal jacket housing a ceramic block with a high-titanium and tungsten oxide content, which Perry says makes chemically inert metals and coatings unnecessary.

Source: Siemens Automotive Corporation