Method for reducing the nitrogen oxide concentration in the exhaust of an internal combustion engine or of a firing system

US5540047A · kind A · utility

Assignee

• Siemens Aktiengesellschaft · DE

Inventors

• Christian Dahlheim · Berlin, DE
• Maximilian Fleischer · Ehrenkirchen, DE
• Hans Meixner · Haar, DE

Key dates

• Filing date: Oct 6, 1994
• Grant date: Jul 30, 1996
• Expiry date: Oct 6, 2014

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y02T10/12
• WIPO field: Chemical engineering
• WIPO sector: Chemistry

Abstract

The method reduces the nitrogen oxide concentration in the exhaust of an internal combustion engine. A noticeable reduction in the NO.sub.x emission of a diesel motor can be achieved by applying the Selective Catalytic Reduction (SCR) method. In this method, ammonia is injected into a catalyzer through which the exhaust gas flows, this ammonia reacting with nitrogen monoxide or, respectively, nitrogen dioxide to form nitrogen and water. Since the exhaust gas should contain neither nitrogen monoxide nor excess ammonia, suitable methods are required for regulating the metering of NH.sub.3. For controlling the amount of urea added to the exhaust gas as a reduction agent, the NO and NH.sub.3 concentration is measured using a detector located in the exhaust systems following the SCR catalyzer. The detector contains a vanadate layer manufactured on the basis of a specific sputtering method as a sensitive element. The electrical resistance thereof is highest when the conversion of nitrogen monoxide to form nitrogen and water occurs stoichiometrically.