Procedure to determine the sulfur removal of NOx storage catalytic converter

Abstract

The invention concerns a procedure to determine the sulfur removal of a NOx storage catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine, whereby conditions, in which a surplus of the reducing agent is generated in the internal combustion engine, are adjusted in the internal combustion engine for the sulfur removal, whereby a SOx removal amount is determined in a SOx removal calculation using a model from the reducing agent flow and from additional operating parameters of the internal combustion engine. In so doing, dynamic effects during the desulferization of the NOx storage catalytic converter can be better taken into account for the SOx removal calculation; and in so doing, the subsequent effect of the NOx storage catalytic converter on the reduction of the nitrogen oxides in the exhaust gas can be more accurately predicted, which makes the process management more streamlined and consequently more fuel efficient.

Description

The invention is explained in detail using the examples of embodiment depicted in the figures. The following items are shown:

FIG. 1 a schematic depiction of an internal combustion engine with an exhaust gas aftertreatment system as the application example of the procedure,

FIG. 2 a schematic depiction of the SO_x removal calculation.

FIG. 1 shows as an example a technical layout, in which the procedure according to the invention is operating. In the Figure an internal combustion engine 1 consisting of an engine block 40 and an incoming air duct 10, which supplies the engine block 40 with combustible air, is depicted, whereby the amount of air in the incoming air duct 10 can be determined using an incoming air measurement mechanism 20. The exhaust gas of the internal combustion engine 1 is thereby carried by way of an emission control system, which has in the example shown an exhaust gas duct 50 as its main component. A particle filter 70 (DPF) and subsequently a NO_x storage catalytic converter 90 are disposed in the exhaust gas duct 50 in the direction of flow. Provision is additionally made for a fuel metering mechanism 30 in the form of a diesel injection system, which is controlled, respectively actuated, in a closed-loop by way of an engine control unit 110.

The closed-loop control of a work mode of the internal combustion engine 1 can result on the basis of selected operating parameters. It is, for example, therefore conceivable by means of Lambda probes 60 and/or NO_x sensors 100 disposed in the exhaust gas duct 50 to determine the composition of the exhaust gas. Additionally an exhaust gas temperature can, for example, in the area of the emission control system, for example between the particle filter 70 and the NO_x storage catalytic converter 90, be determined using one or several temperature probes 80. From the signals of the various probes 60, 80, 100, which are connected to the engine control unit 110, as well as from the data acquired by the incoming air measurement mechanism 20, the mixture can be calculated and the fuel metering mechanism 30 can be accordingly actuated to meter the fuel. Provision is thereby made according to the invention for a SO_x removal calculation 120 to be implemented as software in the engine control unit 110.

The discharge of sulfur during a desulfurization process (DeSO_x process), which is necessary for the regeneration of the NO_x storage catalytic converter 90, is essentially dependent on

• • the composition of the reducing agent in the rich fuel mixture,
  • the temperature of the NO_x storage catalytic converter 90,
  • the exhaust gas mass flow,
  • the entire amount of sulfur embedded and
  • the progress of the process,

whereby during the desulfurization process all of these parameters are constantly changing.

A suitable removal model deals with the sulfur discharge as a function of the conditions, as it is schematically depicted in a flow diagram in FIG. 2.

Provision is made in the procedure according to the invention for conditions, in which a reducing agent flow 122 in the exhaust gas is generated, to be adjusted in the exhaust gas for the sulfur removal. In so doing, a SO_x removal amount 126 can be determined from a reducing agent flow 122 and from additional operating parameters of the internal combustion engine 1 derived from a model, whereby the reducing agent flow 122 in the exhaust gas during the sulfur removal is determined from a reducing agent characteristic diagram 121. This characteristic diagram 121 is constructed from the operating state, from a rotational speed and from a torque of the internal combustion engine 1.

Provision is made in a correction step for the reducing agent flow 122 to be corrected with a Lambda correction 123, which is calculated from a deviation from a set point Lambda value, which is calculated for the desulfurization from an actual Lambda value. In this desulfurization phase, a significant discharge of the sulfur out of the NO_x storage catalytic converter 90 as a result of the short richening of the exhaust gas (λ<1) can be observed. For that reason, the Lambda correction 123 takes into account a Lambda deviation from the set point Lambda value, which occurs, if especially during the dynamic operation, the desired Lambda value is not achieved; and the reducing agent flow 122 consequently deviates from the ideal exhaust gas composition.

Provision is made in a procedural variation for the reducing agent flow 122 corrected by the Lambda correction 123 to be integrated; and when a specifiable reducing agent threshold value 127 is achieved, for the operating conditions generating the reducing agent flow in the exhaust gas to be terminated after a specifiable time, i.e. the rich operation is terminated before a release of hydrogen sulfide (H₂S).

Provision is made in an additional step for the reducing agent flow 122 to be corrected with a temperature correction 124, which is calculated from the temperature of the NO_x storage catalytic converter 90. In addition it is advantageous if the temperature probe 80 is thermally connected to the NO_x storage catalytic converter 90. This temperature correction 124 can be determined, in that the desulfurization is implemented repeatedly at different temperatures and the effect is compared.

Provision is made in the procedure according to the invention in a third step for the reducing agent flow 122 to be corrected with a DeSO_x progression correction 125 concerning the desulfurization process. The DeSO_x progression correction 125 is calculated proportionally from the time duration of the desulfurization, whereby the penetrating properties of the reducing agent flow 122 into the NO_x storage catalytic converter are depicted. These properties constantly change with the passage of time.

With the procedure described for the SO_x removal calculation 120, dynamic effects during a desulfurization of the NO_x storage catalytic converter can be better taken into account; and in so doing, the subsequent effect of the NO_x storage catalytic converter 90 on the reduction of the nitrogen oxides in the exhaust gas can be better predicted, which makes the process management more streamlined and thereby more fuel efficient.

Claims

1. A method of determining sulfur removal of a NOx catalytic converter in an exhaust gas aftertreatment system of an internal combustion engine, the method comprising: adjusting conditions in which a reducing agent surplus is generated for the sulfur removal; anddetermining an SOx removal amount in an SOx removal calculation using a model from a reducing agent flow and from additional operational parameters of the internal combustion engine.

2. A method according to claim 1, wherein the reducing agent flow in an exhaust gas is determined during sulfur removal from a reducing agent characteristic diagram, which is constructed from an operating state, a rotational speed, and a torque of the internal combustion engine.

3. A method according to claim 1, further comprising correcting the reducing agent flow with a Lambda correction, which is calculated from a deviation from a set point Lambda value and an actual Lambda value.

4. A method according to claim 1, wherein the reducing agent flow, which is corrected with the Lambda correction, is integrated; and when a specifiable reducing agent threshold value is achieved, the operating conditions for the generation of the reducing agent flow in the exhaust gas are terminated according to a specifiable time.

5. A method according to claim 1, wherein the reducing agent flow is corrected with a temperature correction, which is calculated from the temperature of the NOx storage catalytic converter.

6. A method according to claim 5, wherein the temperature correction is determined, in that the desulferization is implemented repeatedly at different temperatures, and the effect is compared.

7. A method according to claim 1, wherein the reducing agent flow is corrected with a DeSOx progression correction, which is proportionally calculated from a time duration of the desulferization.

8. A method according to claim 1, wherein the SOx removal calculation is implemented as software in an engine control unit.