Diesel aftertreatment systems

Abstract

A method for improving NOx conversion efficiency of a NOx-reducing catalyst by determining an accurate amount of reductant required is presented. The method includes calculating an initial reductant injection amount based on a steady state amount of NOx in the engine feedgas and adjusting the initial amount to compensate for transient NOx emissions. The compensation is initiated in response to an engine transient, such as impending acceleration or deceleration. This method further results in improved vehicle fuel economy.

Description

BACKGROUND OF INVENTION[0001] 1. Field of Invention[0002] The present invention relates to a system and a method for improving performance of a lean exhaust gas aftertreatment device and, more particularly, to controlling an amount of reductant injection to achieve optimum NOx conversion efficiency while minimizing the fuel economy penalty.[0003] 2. Background of the Invention[0004] Current emission control regulations necessitate the use of catalysts in the exhaust systems of automotive vehicles in order to convert carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) produced during engine operation into harmless exhaust gasses. Vehicles equipped with diesel or lean gasoline engines offer the benefits of increased fuel economy. Such vehicles have to be equipped with lean exhaust aftertreatment devices, such as, for example, an Active Lean NOx Catalysts (ALNC) or Selective Catalytic Reduction (SCR) catalysts, which continuously reduce NOx emissions, even in an oxygen r...

AI Technical Summary

Benefits of technology

0010] In another aspect of the present invention, a method for improving efficiency of a NOx-reducing catalyst coupled downstream of an internal combustion engine includes: providing an indication of an impending engine transient; and adjusting an amount of reductant injection into the NOx-reducing catalyst to compensate for variations in engine feedgas NOx caused by said impending engine transient.

0011] The present invention provides a number of advantages. In particular, NOx conversion efficiency of the NOx-reducing catalyst is improved by adjusting the injected reductant amounts to compensate for transient increases or decreases in the engine feedgas NOx amounts. Further, monitoring the rate of change of pedal position provides a quick and accurate indication of an impending engine transient and the associated change in engine feedgas NOx. Thus, reductant injection amount can be timely adjusted to compensate for NOx variations. Another advantage of the present invention is improved fuel economy due to optimized reductant usage. For example, reductant injection amount can be reduced in anticipation of engine deceleration to compensate for a reduction in engine feedgas NOx.

Problems solved by technology

Since the amount of reductant injection is typically calculated based on steady state engine operating conditions, these transient NOx variations result in over or under-injection of reductant and negatively impact fuel economy and emission standards.

Images