US 2009/0151339 A1Published application

Method and Arrangement for Improving the Hydrolysis of a Reduction Agent in an Exhaust Gas Post Treatment System

AssigneeMan Truck & Bus AG

InventorAndreas Doring

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Abstract

A method and arrangement for improving hydrolysis of a reduction agent in an exhaust gas post treatment system for selective catalytic reduction of NOx in the exhaust gas of an internal combustion engine operated with excess air. A partial exhaust gas stream is branched off from an exhaust gas stream upstream of an SCR catalytic converter. A hydrolysis catalytic converter, is disposed in the partial exhaust gas stream downstream of a metering arrangement for supplying reduction agent thereto. The partial stream is conveyed back to the main stream downstream of the hydrolysis catalytic converter and upstream of the SCR catalytic converter. The temperature at the hydrolysis catalytic converter is maintained within prescribed limits by actively controlling exhaust gas quantity conveyed in the partial stream by entirely or partially blocking the partial stream, via a flow control device, if temperature values at the hydrolysis catalytic converter and the main or partial stream exceed or do not reach specified or threshold values, and/or if certain operating conditions or condition changes of the engine occur.

Claims19

Dependent claims

A method of improving the hydrolysis of a reduction agent in an exhaust gas post treatment system for the selective catalytic reduction of NOx in the exhaust gas of an internal combustion engine (1) that is operated with excess air, including the steps of:

providing an SCR catalytic converter (9);
upstream of said SCR catalytic converter (9), branching off from an exhaust gas stream (2) a partial exhaust gas stream (3) that is quantitatively smaller than said exhaust gas stream (2);
disposing in said partial exhaust gas stream (3) a metering arrangement (17) for supplying a reduction agent to said partial exhaust gas stream (3);
disposing a hydrolysis catalytic converter (16) in said partial exhaust gas stream (3) downstream of said metering arrangement (17);
conveying said partial exhaust gas stream (3) back to said exhaust gas stream (2) downstream of said hydrolysis catalytic converter (16) and upstream of said SCR catalytic converter (9);
disposing a flow control device (12) in said partial exhaust gas stream (3) upstream or downstream of said hydrolysis catalytic converter (16), wherein a degree of opening of said flow control device (12) is adapted to be controlled or regulated;
and
maintaining the temperature at said hydrolysis catalytic converter (16) within prescribed limits by actively controlling or regulating the quantity of exhaust gas conveyed via said partial exhaust gas stream (3) by entirely or partially blocking or opening said partial exhaust gas stream (3), via said flow control device (12), if measured or indirectly determined temperature values at said hydrolysis catalytic converter (16) and in said exhaust gas stream (2) and/or in said partial exhaust gas stream exceed or do not reach specified threshold values, and/or if certain operating conditions and/or operating condition changes of the internal combustion engine (1) occur.

5 more elements

An arrangement for effecting improvement of the hydrolysis of a reduction agent in an exhaust gas post treatment system for the selective catalytic reduction NOx in the exhaust gas of an internal combustion engine (1) that is operated with excess air, comprising;

an SCR catalytic converter (9) disposed in an exhaust gas stream (2) of the internal combustion engine (1), wherein a partial exhaust gas stream (3), which is quantitatively smaller than said exhaust gas stream (2) is branched off from said exhaust gas stream upstream of said SCR catalytic converter (9);
a metering arrangement (17), for supplying a reduction agent to said partial exhaust gas stream (3), disposed in said partial exhaust gas stream;
a hydrolysis catalytic converter (16) disposed in said partial exhaust gas stream (3) downstream of said metering arrangement (17), wherein said partial exhaust gas stream (3) is returned to said exhaust gas stream (2) downstream of said hydrolysis catalytic converter (16) and upstream of said SCR catalytic converter (9);
a flow control device (12) disposed in said partial exhaust gas stream (3):
a control unit (4);
and
a drive mechanism (13) for operating said flow control device (12), wherein said drive mechanism (13) is activated by said control unit (4) via a control signal formed by said control unit as a function of at least one first signal value, which corresponds to at least one prescribed temperature value at said hydrolysis catalytic converter (16), and/or of at least one second signal value, which corresponds to at least one prescribed temperature value in said exhaust gas stream (2) or said partial exhaust gas stream (3), and/or of at least one third signal value, which corresponds to at least one prescribed value of at least one operating parameter of the internal combustion engine (1) and/or a periodic change thereof.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 12/335,790Filed 16 Dec 2008
Priority: DE 10 2007 061 005.118 Dec 2007
Published: 18 Jun 2009
Term ends: Not estimatedThe source records don’t support an estimate.

Classification26 codes

B01D 53/9431
Nitrogen oxides: processes characterised by a specific device
B01D 53/9495
By catalytic processes: controlling the catalytic process
F01N 3/103
By thermal or catalytic conversion of noxious components of exhaust: oxidation catalysts for HC and CO only
F01N 3/2053
Specially adapted for catalytic conversion: by-passing catalytic reactors, e.g. to prevent overheating