Ammonia storage control

Abstract

Various methods for controlling ammonia levels stored in a catalyst by controlling exhaust gas temperatures are provided. In one embodiment, a temperature of a catalyst in an internal combustion engine is determined. If the temperature of the catalyst exceeds a first threshold at which an ammonia capacity of the catalyst for the temperature is below a current stored ammonia level in the catalyst, a load of the engine is reduced including adjusting a torque output of a motor operatively coupled to the engine.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present application claims priority to German Patent Application No. 102012212051.3, filed on Jul. 11, 2012, the entire contents of which are hereby incorporated by reference for all purposes.FIELD[0002]The disclosure relates to a method for controlling ammonia levels stored in a catalyst of an internal combustion engine.BACKGROUND AND SUMMARY[0003]Internal combustion engines may include one or more catalysts configured to reduce the level of emissions produced during fuel combustion. For example, a selective catalytic reduction (SCR) catalyst may be used to reduce levels of nitrogen oxides (NOx) emitted following fuel combustion. The SCR catalyst may use one or more reductants to enhance NOx conversion, such as ammonia. For a given temperature, the SCR catalyst has a storage capacity which determines the level of reductant which may be stored in the catalyst. Exhaust gas temperatures, and the temperature of the SCR catalyst, may be c...

AI Technical Summary

Benefits of technology

The patent text describes a method for controlling ammonia levels in a catalyst of an internal combustion engine. The method involves measuring the temperature of the catalyst and adjusting the engine load and torque output to ensure that the catalyst has sufficient ammonia stored in it for NOx conversion. The technical effect of this method is to accurately control ammonia levels in the catalyst and prevent ammonia slip, which can lead to increased NOx emissions.

Problems solved by technology

For example, ammonia stored in the SCR catalyst may be released to the ambient environment abruptly and unintentionally if the torque demanded by a vehicle operator is suddenly increased.

Ammonia slip in this example may be caused by a sharp rise in exhaust gas temperatures due to the increased driver-demanded torque, as these temperatures have exceeded those at which ammonia storage in the catalyst is ensured.

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