Alumina-based lean NOx trap system and method of use in dual-mode HCCI engines

Abstract

An alumina-based lean NOx trap system for use in a HCCI engine exhaust is provided which includes at least one alumina-based lean NOx trap comprising a catalyst, an alumina NOx absorbent material, and optionally, from 0 to about 4 wt % of an alkaline earth metal oxide; and a conventional three-way catalyst. The lean NOx trap system substantially oxidizes HC and CO and converts at least a portion of NOx contained in the exhaust gas to N2 at a temperature between about 150° C. to about 250° C. in HCCI mode. The system also effectively removes HC, CO and NOx at high temperature when the engine is in SI mode (stoichiometric conditions). The alumina-based lean NOx trap in the system also undergoes efficient desulphurization and maintains its activity with extended use.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application No. 60 / 649,331, entitled SYSTEM FOR TREATING EMISSIONS FROM DIESEL EXHAUST GAS, filed Feb. 2, 2005. The entire contents of said application are hereby incorporated by reference.BACKGROUND OF THE INVENTION [0002] The present invention relates to a lean NOx trap system for treating emissions from dual-mode HCCI engines, and more particularly, to a system including at least one lean NOx trap which utilizes alumina as a NOx storage material. The alumina-based lean NOx trap achieves high NOx, HC and CO conversion efficiencies at the low temperatures encountered in the lean exhaust gas of HCCI engines. In addition, the alumina-based lean NOx trap maintains its activity with extended use and undergoes efficient desulphurization. [0003] Government regulations, created in response to environmental and health concerns, have necessitated the treatment of exhaust gas from vehicle e...

AI Technical Summary

Benefits of technology

[0010] The present invention meets those needs by providing a lean NOx trap (LNT) system for use in a dual-mode HCCI engine which includes at least one lean NOx trap which utilizes alumina as a NOx storage (absorbent) material. The alumina-based LNT, when incorporated in a HCCI engine exhaust system along with a conventional three-way catalyst, effectively converts HC, CO and NOx at the low temperatures (about 150° C.) encountered during the HCCI operational mode of such engines. In addition, the alumina-based LNT system functions as an oxidation catalyst in the HCCI engine exhaust and provides effective oxidation of HC and CO (above 90%) at low exhaust temperature. Further, the alumina-based LNT maintains its activity with extended use and undergoes efficient desulphurization.

[0011] When the engine operates in SI mode, the engine exhaust gas is at stoichiometric conditions with high temperatures (500 to 600° C.), and the gas includes all three pollutants (HC, CO and NOx). For such conditions, the three-way catalyst in the lean NOx trap system of the present invention effectively converts these pollutants.

[0020] It should be noted that when the lean NOx trap system is exposed to SI engine exhaust gas (stoichiometric) containing HC, CO and NOx, the HC, CO and NOx are converted to H2O, CO2 and N2 at a temperature above about 450° C. During the transition of HCCI mode to SI mode, this system can oxidize HC and CO at low temperature (<350° C.) and raise the temperature of the exhaust gas to shorten the light-off time of the downstream three-way catalyst.

Problems solved by technology

However, at high loads, operation of the engine in HCCI mode is difficult.

), and the exhaust gas is very lean.

A three-way catalyst cannot effectively reduce the level of NOx, CO and HC under these conditions.

However, conventional lean NOx traps currently in use are most effective at an operating temperature range of about 200° C. to about 500° C., while the exhaust gas temperature (catalyst inlet) during HCCI mode is typically less than 200° C. Thus, a conventional LNT cannot remove NOx in HCCI exhaust gas.

Another disadvantage of conventional LNTs is that they become poisoned over time by the accumulation of sulfur (SOx) on the LNT due to combustion of the sulfur contained in the fuel.

However, desulphurization of a conventional LNT requires high temperatures (650° C. to 800° C.) for relatively long times (5 to 10 minutes).

This thermally damages the conventional LNT with each de-SOx cycle, which reduces the activity of the LNT.

In addition, the de-SOx process results in a considerable fuel consumption penalty (up to 5%).

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