Electrically heated doc using hcscr cold start NOX controls

Abstract

An exhaust gas treatment system for an internal combustion engine is provided. The system includes an exhaust gas conduit extending from the engine configured to receive an exhaust gas stream from the engine, a first injector in fluid communication with the exhaust gas conduit configured to selectively inject fuel containing unburned hydrocarbon (HC) into the exhaust gas conduit and an oxidation catalyst disposed in the exhaust gas conduit downstream from the first injector. The system further includes a hydrocarbon selective catalyst reduction (HCSCR) catalyst applied on the oxidation catalyst, a heating device positioned at an upstream side of the oxidation catalyst configured to heat the oxidation catalyst and HCSCR catalyst, a selective catalyst reduction (SCR) device disposed within the exhaust gas conduit downstream from the oxidation catalyst, and a particulate filter positioned downstream from the selective catalyst reduction device.

Description

FIELD OF THE INVENTION[0001]The subject invention relates to an exhaust gas treatment system, and in particular, an exhaust gas treatment system with improved operating characteristics at low temperatures.BACKGROUND[0002]Exhaust gas emitted from an internal combustion engine is a heterogeneous mixture that may contain gaseous emissions such as a carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions typically disposed on catalyst supports or substrates are provided in an engine exhaust system to convert certain, or all of the exhaust constituents into non-regulated exhaust gas components.[0003]In an exhaust treatment technology, there are several known catalyst and filter structures used that have displayed effectiveness in reducing or removing regulated constituents from exhaust gas. For example, an oxidation catalyst may be used to...

AI Technical Summary

Benefits of technology

The invention provides an exhaust gas treatment system for an internal combustion engine that reduces NOx in the exhaust gas stream during a cold start. The system includes an exhaust gas conduit, first injector, oxidation catalyst, hydrocarbon selective catalyst reduction (HCSCR) catalyst, second injector, selective catalyst reduction (SCR) device, and particulate filter. The system also includes a heating device and a temperature sensor to monitor the temperature of the oxidation catalyst and SCR device, and deactivates the heating device and ends operation of the first injector when the temperature of the SCR device exceeds a certain threshold. The technical effect of this invention is to effectively reduce NOx in the exhaust gas stream during a cold start of an internal combustion engine.

Problems solved by technology

In addition, NOx reduction or removal may occur at the SCR device once the SCR device reaches an adequate operating temperature, typically around 200° C. However, an oxidation catalyst and SCR device do not efficiently oxidize HC and CO, and remove or reduce NOx, respectively, at low temperatures, for example during cold start of an internal combustion engine.

Thus, from a time period between the start of the engine until a sufficient operating temperature is reached in an exhaust gas conduit, and in turn, at the oxidation catalyst and SCR device, regulated constituents such as HC, CO and NOx may not be satisfactorily reduced.

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