EP1554478A1

EP1554478A1 - Nox trap regeneration system for a diesel engine

Info

Publication number: EP1554478A1
Application number: EP03778426A
Authority: EP
Inventors: Mickael Gascoin; Piet Ameloot; Ali Chaouche; Djamal Medioun; Yvon Beauge
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2002-10-23
Filing date: 2003-10-21
Publication date: 2005-07-20
Also published as: AU2003285425A1; WO2004038202A1; FR2846370B1; FR2846370A1

Abstract

The invention relates to a system for aiding the regeneration of a NOx trap with NOx storage/release, which is built into an exhaust line (5) of a diesel engine (4) of a motor vehicle. The inventive system is characterised in that it comprises: gas inlet means for delivering gas to the engine, fuel injection means (11) for injecting fuel into the cylinders of the engine in the form of at least main and pilot injections; and control means (12) for controlling the aforementioned gas inlet means and/or fuel injection means (11) in order periodically to switch the engine (4) from a lean-mixture standard operating mode with storage of NOx in the trap (6) to a rich-mixture regeneration operating mode with a pilot injection and at least two main injections and release of NOx from the trap (6) and regeneration of same.

Description

REGENERATION SYSTEM FOR A NOX TRAP FOR A DIESEL ENGINE

The present invention relates to a system for reducing polluting emissions linked to the operation of a diesel engine of a motor vehicle and relates more particularly to a system for assisting the regeneration of a storage / destocking Nox trap, integrated in a exhaust line of such an engine.

It is known that on direct injection diesel engines for motor vehicles, the reduction of NOx emissions by DeNOx catalysis with storage / destocking is a technical solution envisaged to meet the standards relating to this type of discharge and in particular to the EURO IV standards. To this end, it is envisaged to use a NOx trap composed for example of barium sulphate intended to absorb NOx during standard engine operation.

When this trap is saturated, it is proposed to trigger a transient destocking phase by momentarily switching the engine from this standard lean mixture operating mode to a rich mixture regeneration operating mode to produce reducers, such as for example HC and CO , which reduces the NOx which is then desorbed from the trap, as in a traditional catalyst.

However, this poses problems in controlling the operation of the engine under rich mixture, in a stable manner over the whole of its operating field, without impact on the driving pleasure of the vehicle and the combustion noise, etc. ...

The object of the invention is therefore to solve these problems. To this end, the subject of the invention is a system for assisting the regeneration of a NOx trap for storage / release, integrated in an exhaust line of a diesel engine of a motor vehicle, characterized in that it comprises means for admitting gas into the engine and means for injecting fuel into the cylinders thereof in the form of at least pilot and main injections and means for controlling these means for admitting gas and / or fuel injection to periodically switch the engine from a standard lean mixture operating mode, NOx storage in the trap, to a rich mixture regeneration operating mode, to pilot injection and at least two main injections, destocking the NOx of the trap and regenerating it.

According to other characteristics:

- The control means are adapted to control the gas intake means in order to reduce the quantity of gas admitted into the engine when the latter is in its regeneration operating mode;

the control means are adapted to control the gas intake and / or fuel injection means according to these standard operating and regeneration modes for engine loads greater than a predetermined threshold value;

- the predetermined load threshold value is defined by an effective average pressure of approximately 3 bars;

- the pilot injection is triggered in a range between about 50 ° crankshaft and 5 ° crankshaft, before the top dead center of the cylinder concerned and in that the main injections are triggered in a range between about 20 ° crankshaft before the top point and 120 ° crankshaft after top dead center;

the control means are adapted to control the gas intake and / or fuel injection means in order to run the engine in lean mixture for approximately 60 seconds and in rich mixture for approximately 2 seconds;

- The engine being associated with means for recirculating the exhaust gases at the inlet thereof, the control means are adapted to regulate the operation of these recirculation means during operation of the rich mixture engine. The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

- Figs.1 and 2 illustrate the phases of storage and release of NOx in a trap used in the constitution of a system according to the invention; - Fig.3 illustrates the operation of fuel injection means implemented in an assistance system according to the invention; and

- Fig.4 shows a block diagram illustrating the structure of a system according to the invention. As indicated above, the invention relates to a system for assisting the regeneration of a NOx trap for storage / retrieval integrated into an exhaust line of a diesel engine of a motor vehicle.

These storage and retrieval phases are illustrated in Figures 1 and 2.

As has also been indicated, the NOx trap absorbs NOx during standard operation of the lean mixture engine, while in a rich mixture regeneration operating mode, these NOx are destocked and treated by the production of reducers such as HC and CO, which reduces the NOx which is then desorbed from the trap as in a traditional catalyst.

However, and as has been indicated previously, the problem arises of operating a diesel engine at such richness, in a stable manner over the entire engine field, without impact on the driving pleasure and the combustion noise between other.

The operation of switching to a stoichiometric or rich mixture is necessary to purge the NOx trap but also to desulfate it, since the sulfur contained in the fuel causes poisoning of the trap.

This operation is longer than the purge, which lasts only a few seconds, and is therefore even more difficult to manage.

Under these conditions, aid for the regeneration of such a NOx trap for storage / destocking requires the development of a specific multiple injection strategy over the entire engine field, on the basis of several engine adjustment parameters. In fact, this injection strategy must make it possible to:

- operate at wealth close to 1;

- produce a sufficient quantity of CO, which is the preferred reducing agent;

- limit the level of O2;

- limit the level of HC; - respect the smoke level;

- respect the exhaust gas temperature for reasons of mechanical strength; and finally

- respect the services provided to customers, namely driving pleasure and engine operating noise. To this end, the present invention proposes to improve the characteristics of combustion in stability and in noise, at points with predetermined engine loads, by applying an injection strategy to a pilot injection and at least two main injections, such as this is illustrated in FIG. 3. The application of these two main injections also makes it possible to maintain the temperature of the exhaust gases within limits admissible by the architecture of the engine (cylinder head, valves, manifold, etc.).

Furthermore, a recirculation of the burnt gases (EGR) may then be necessary or not to comply with the criteria for regenerating the NOx trap. On points with predetermined loads, such as for example for an effective average pressure (PME) also known in the state of the art under the English name "Brake mean effective pressure", greater than about 3 bars, the two injection strategy main therefore makes it possible to meet the criteria for regenerating the NOx trap, because it makes it possible to significantly reduce the combustion instabilities thanks to the phasing of the two main injections, to reduce the noise also thanks to this phasing of the two injections, to maintain the exhaust gas temperature to allowable values and finally generate an engine map for the regeneration of the NOx trap based on a unique strategy. As indicated above, this strategy can be applied to points with predetermined engine operating loads, the EGR level then being appropriately controlled.

This is illustrated in FIG. 3, where we recognize the pilot injection designated by the reference 1 and the two main injections designated by the general references 2 and 3.

This pilot injection can be triggered in a range between about 50 ° crankshaft and 5 ° crankshaft before the top dead center of the cylinder concerned, and the main injections can be triggered in a range between about 20 ° crankshaft before top dead center and 120 ° after top dead center. It is recognized in FIG. 4, a diesel engine of a motor vehicle designated by the general reference 4, the outlet of which is connected to an exhaust line 5 in which a NOx trap 6 is integrated. This engine is also associated with air intake means designated by the general reference 7 comprising means 8 for adjusting the quantity of air admitted.

This engine can also be associated with means for recirculating exhaust gas at the inlet thereof, designated by the general reference 9, associated with means for controlling the circulation of gases designated by the general reference 10.

These recirculation means are therefore connected between the outlet and the inlet of the engine to ensure the recirculation of the exhaust gases (EGR). The adjustment means 8 and control means 10 can conventionally comprise controllable valves.

Furthermore, the engine is also associated with means 11 for injecting fuel into the cylinders thereof, in the form of pilot and main injections, as has been indicated, having any suitable structure. .

These various means, that is to say the gas recirculation means, the air intake means and the injection means are controlled by control means designated by the general reference 12, comprising any appropriate computer. , receiving for example as input, engine rotation speed and pressure information from the injection means, respectively from corresponding data acquisition means 13 and 14.

The standard operating modes with lean mixture for storing NOx in the trap, and for operating with regeneration with rich mixture, destocking of NOx from the trap and therefore for regenerating the latter, can be switched periodically, by the means control 12, the motor 4 operating for example in lean mixture for about 60 seconds, and in rich mixture for about 2 seconds. The control means 12 then act on the air intake means 7 in the engine 4 and the fuel injection means 11 in the cylinders thereof, for periodically switching the engine from the standard operating mode lean mix in the rich mix regeneration mode of operation.

These control means 12 can indeed be adapted to control the gas intake means in order to reduce the quantity of gas admitted into the engine when the latter is in its regeneration operating mode and for controlling the injection means in the manner indicated above.

These control means can also be adapted to regulate the operation of the exhaust gas recirculation means 9 during the operation of the rich mixture engine.

Of course, other embodiments can be envisaged.

Claims

1. System for assisting the regeneration of a NOx trap for storage / destocking, integrated in an exhaust line (5) of a diesel engine (4) of a motor vehicle, characterized in that it comprises means for admitting gas into the engine and means for injecting fuel (11) into the cylinders thereof in the form of at least pilot and main injections and control means (12) for these means gas inlet and / or fuel injection (11) to periodically switch the engine (4) from a standard operating mode with lean mixture, NOx storage in the trap, to a regeneration operating mode at rich mixture, with a pilot injection (1) and at least two main injections (2,3), destocking of the NOx of the trap (6) and regeneration of the latter.

2. System according to claim 1, characterized in that the control means (12) are adapted to control the gas intake means in order to reduce the quantity of gas admitted into the engine (4) when the latter is in its mode of regeneration operation.

3. System according to claim 1 or 2, characterized in that the control means (12) are adapted to control the gas intake and / or fuel injection means (11) according to these standard operating modes. sting and regeneration for engine loads greater than a predetermined threshold value.

4. System according to claim 3, characterized in that the predetermined load threshold value is defined by an effective average pressure (PME) of approximately 3 bars.

5. System according to any one of the preceding claims, characterized in that the pilot injection is triggered in a range between approximately 50 ° crankshaft and 5 ° crankshaft, before the top dead center of the cylinder concerned and in that the main injections are triggered in a range between approximately 20 ° crankshaft before top dead center and 120 ° crankshaft after top dead center.

6. System according to any one of the preceding claims, characterized in that the control means (12) are adapted to control the gas intake and / or fuel injection means (11) in order to make run the engine (4) in lean mixture for approximately 60 seconds and in rich mixture for approximately 2 seconds.

7. System according to any one of claims 3 to 6, characterized in that the engine (4) being associated with means for recirculating the exhaust gases (9) at the inlet thereof, the control means ( 12) are suitable for controlling the operation of these recirculation means (9) during operation of the rich mixture engine.