Method for minimizing ammonia slip from SCR catalysts

Abstract

The invention discloses a method for minimizing ammonia slip from SCR catalysts. Embodiments for reducing ammonia slip are provided. In one example, a method for reduction of ammonia emissions from an engine exhaust gas aftertreatment device with an SCR catalyst comprises determining a concentration of NOx and / or ammonia in the exhaust gas aftertreatment device, comparing a determined value of NOx and / or ammonia concentration with a nominal value for ammonia and NOx, respectively, and if an actual or shortly forecasted ammonia concentration is above the respective nominal value, triggering engine conditions with higher exhaust NOx concentration. In this way, ammonia slip may be reduced without degrading fuel economy.

Description

[0001] related application [0002] This application claims priority from European Patent Application No. 11172069.4 filed 30 June 2011, the entire content of which is hereby incorporated by reference for all purposes. technical field [0003] The present invention relates to methods and systems for reducing ammonia emissions from exhaust aftertreatment devices of internal combustion engines having SCR catalysts. Background technique [0004] Recently, internal combustion engine aftertreatment devices have been equipped with catalytic systems to reduce NOx based on the recombination reaction of NOx with ammonia over SCR (Selective Catalytic Reduction) catalysts to nitrogen and water. The ammonia required is usually obtained from an external source - like a water-based urea solution --supply. Alternatively, ammonia can be synthesized in situ from NOx in the exhaust by specific catalysts. Regardless of which of the aforementioned methods is used to provide ammonia in a par...

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Problems solved by technology

This additional catalyst therefore makes the aftertreatment device even more expensive and should therefore be avoided

[0010] In short, although many approaches address the control of reductant injection and avoid leakage of reductant into the environment, there remains the problem of controlling ammonia slip, especially under transient conditions when rapid increases in exhaust flow rate and temperature occur

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