System and method for treating diesel exhaust gases

Abstract

A system for treating diesel exhaust gases includes an engine for producing a diesel exhaust stream, a diesel particulate filter downstream of the engine and adapted to remove particulates from the exhaust stream, a heater upstream of the filter adapted to deliver energy in sufficient amounts to the exhaust stream to cause active regeneration of the filter, and a diesel oxidation catalyst upstream of the heater adapted to cause passive regeneration of the filter when the exhaust stream is above a light-off temperature of the diesel oxidation catalyst. A NOx reduction catalyst can be provided downstream of the heater. Methods for treating diesel exhaust gases are also disclosed.

Description

BACKGROUND AND SUMMARY[0001]The present invention relates, generally, to systems and methods for treating diesel exhaust gases and, more particularly, to systems and methods for treating non-stationary diesel exhaust gases.[0002]Diesel engines tend to have low emissions of gas phase hydrocarbons and carbon monoxide, however, they tend to have relatively high emissions of nitrogen oxides (NOx) and particulates. As standards for NOx and particulate emissions become more stringent, it is increasingly important to devise strategies for reducing these emissions.[0003]In diesel engines, a DPF can be used downstream of the engine to filter particulates from the engine exhaust. If too much soot collects in the DPF, the soot can burn in an uncontrolled manner and may crack or melt the DPF. This phenomenon is sometimes referred to as a “runaway” or uncontrolled regeneration. Other problems can result from excessive soot accumulation in the DPF as well, such as an increase in engine backpressu...

AI Technical Summary

Benefits of technology

"The present invention relates to systems and methods for treating diesel exhaust gases. The technical effects of the invention include reducing NOx emissions and preventing damage to the diesel particulate filter (DPF) from uncontrolled regeneration (also known as runaway regeneration). The invention achieves this by providing a heater upstream of the DPF to raise the exhaust stream temperature to a level suitable for active regeneration, while also delivering energy to a diesel oxidation catalyst (DOC) upstream of the heater to cause passive regeneration of the DPF. Additionally, a NOx reduction catalyst can be used downstream of the heater to further reduce NOx emissions. The invention also includes a method for periodically delivering energy to the exhaust stream to cause active regeneration of the DPF and a method for periodically heating the NOx reduction catalyst to a light-off temperature to cause passive regeneration of the DPF."

Problems solved by technology

Diesel engines tend to have low emissions of gas phase hydrocarbons and carbon monoxide, however, they tend to have relatively high emissions of nitrogen oxides (NOx) and particulates.

If too much soot collects in the DPF, the soot can burn in an uncontrolled manner and may crack or melt the DPF.

Other problems can result from excessive soot accumulation in the DPF as well, such as an increase in engine backpressure, which can have an adverse effect on engine operation and affect fuel consumption.

Active regeneration results in some efficiency losses and thermal stress on the filter, and it is desirable to limit its use.

However, at ordinary exhaust temperatures, passive regeneration generally occurs too slowly to remove accumulated particles.

Images