WO2021121573A1

WO2021121573A1 - A method for controlling an internal combustion engine arrangement

Info

Publication number: WO2021121573A1
Application number: PCT/EP2019/085848
Authority: WO
Inventors: Martin Petersson
Original assignee: Volvo Truck Corporation
Priority date: 2019-12-18
Filing date: 2019-12-18
Publication date: 2021-06-24

Abstract

The present disclosure relates to a method for controlling an internal combustion engine arrangement (100). In particular, the method of the present disclosure is arranged for controlling the internal combustion engine arrangement (100) to generate pulses of carbon monoxide exhausted towards an oxidation catalyst (106) when a determined deterioration level of the oxidation catalyst (106) is above a predetermined threshold level.

Description

A METHOD FOR CONTROLLING AN INTERNAL COMBUSTION ENGINE ARRANGEMENT

TECHNICAL FIELD

The present disclosure relates to a method for controlling an internal combustion engine arrangement. The method is particularly applicable for internal combustion engines of heavy-duty vehicles. Although the method will mainly be described in relation to a truck, it may also be applicable for other types of vehicles propelled by means of an internal combustion engine. The present disclosure also relates to a corresponding internal combustion engine arrangement, as well as a vehicle comprising such internal combustion engine arrangement.

BACKGROUND

For many years, the demands on internal combustion engines have been steadily increasing and engines are continuously developed to meet the various demands from the market. Furthermore, in the field of trucks, there are applicable law directives that have e.g. determined the maximum amount of certain exhaust gas emissions allowable.

In order to reduce harmful emission gas, and in particular nitrogen oxides (NO_x), the engine exhaust aftertreatment system (EATS) of the vehicles has been equipped with systems to convert NO_x by reduction to gaseous nitrogen. Such systems may comprise a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF) and a selective catalyst reduction device (SCR), where the SCR is positioned downstream the DOC/DPF. The exhaust gas from the internal combustion engine is directed into the DOC/DPF where e.g. NO2 is generated. The SCR thereafter reduces NO and NO2 into e.g. N2 and H2O.

The SCR operates at a substantially optimum when receiving a composition of NO and NO2 with a ratio close to 50:50. Accordingly, it is preferable that the exhaust gas expelled from the DOC/DPF has a substantially 50:50 ratio of NO and NO2.

However, as the DOC/DPF ages, its ability to generate NO2 is reduced. There is thus a desire to be able to enable the DOC/DPF to generate an optimum amount of NO2 also when being aged. SUMMARY

It is an object of the present disclosure to describe a method for controlling an internal combustion engine arrangement which at least partially overcomes the above described deficiencies. This is achieved by a method according to claim 1.

According to a first aspect, there is provided a method for controlling an internal combustion engine arrangement, the internal combustion engine arrangement comprising an internal combustion engine and an exhaust gas aftertreatment system arranged downstream the internal combustion engine for receiving exhaust gas expelled from the internal combustion engine during operation thereof; wherein the exhaust gas aftertreatment system comprises an oxidation catalyst and a catalytic reduction arrangement arranged downstream the oxidation catalyst, the method comprising the steps of receiving a signal indicative of a deterioration level of the oxidation catalyst; comparing the deterioration level with a predetermined threshold level, and controlling the internal combustion engine to generate pulses of carbon monoxide exhausted towards the oxidation catalyst when the deterioration level is above the predetermined threshold level.

The wording “catalytic reduction arrangement” should in the following be understood to mean an arrangement which is configured to reduce NO_x gas contained in the exhaust gas conveyed from the internal combustion engine arrangement during operation thereof. The catalytic reduction arrangement thus reduces NO_x gas which is converted to e.g. nitrogen gas, N2. Further, the oxidation catalyst may preferably be a diesel oxidation catalyst.

Moreover, the deterioration level should be understood as a measure of utilization of the oxidation catalyst. Thus, the deterioration level is used for determining how well the oxidation catalyst can generate nitrogen dioxide (NO2) from the nitrogen monoxide (NO) and oxygen conveyed from the internal combustion engine.

A deteriorated oxidation catalyst has a decreased ability to generate a desirable amount of NO2. The inventor of the present disclosure has unexpectedly realized that by generating pulses of carbon monoxide (CO), a deteriorated oxidation catalyst can be “re-boosted” to improve generation of NO2. When generating CO pulses to the oxidation catalyst, a chemical reaction in the coating material of the oxidation catalyst will occur. Preferably, the coating material of the oxidation catalyst increases its chemical metallic properties, i.e. the ability to lose its outer valence electrons, which will improve the generation of NO₂. The coating material may, for example, be formed by a noble metal, in one or several layers. Such noble metal may, for example, be platinum, rhodium, iridium, palladium, ruthenium, osmium or rhenium, although other alternatives are conceivable, such as e.g. aluminum, etc. The result of this chemical reaction has thus been proven to modify the intrinsic properties of the material of the oxidation catalyst to better generate NO₂. An advantage is thus that a relatively simple modification of e.g. engine operation can improve the functionalities of the oxidation catalyst, which will reduce harmful emission gas pollution such as e.g. pollution by NO_x. Also, the oxidation catalyst can be used a longer period of time, thus presenting an economical advantage. A further advantage is that improved passive soot regeneration can be achieved as the soot combustion increases with an increased amount of NO₂.

According to an example embodiment, pulses of carbon monoxide may be generated by reducing an air-fuel ratio (AFR) supplied into a combustion chamber of the internal combustion engine.

Hereby, the amount of air relative the amount of fuel supplied to the combustion chamber is reduced. This will thus generate pulses of carbon monoxide in a relatively simple manner. This can, for example, be controlled by a throttle reducing the intake of air into the combustion chamber.

According to an example embodiment, the step of controlling the internal combustion engine to generate pulses of carbon monoxide may be performed when the internal combustion engine is operating in a transient mode of operation.

The wording “transient mode of operation” should be construed as a mode in which operating points of the engine changes. Examples of such changes may, for example, be changes in engine speed and/or engine torque. Hence, at the transient mode of operation, the output of the engine is not constant over a certain period of time. As a non-limiting example, the transient mode may relate to a situation where the vehicle is accelerating or decelerating, while an opposite mode, i.e. a steady state mode, corresponds to the situation where the vehicle is driving at cruise control on a substantially flat highway.

According to an example embodiment, the method may further comprise the steps of receiving a signal indicative of an increase in gas throttle level of the internal combustion engine; and controlling the internal combustion engine to generate pulses of carbon monoxide when the increase in the gas throttle level exceeds a predetermined increase rate.

An increase in gas throttle level is thus when the vehicle is accelerating. At this point in time it can be advantageous to generate pulses of carbon monoxide by, for example, increasing the supply of fuel to the internal combustion engine. Hence, the AFR is reduced as more fuel is suppled in relation to the amount of supplied air.

According to an example embodiment, the method may further comprise the steps of receiving a signal indicative of an increase in torque level of an output shaft of the internal combustion engine connected to a vehicle transmission; and controlling the internal combustion engine to generate pulses of carbon monoxide when the increase in the torque level exceeds a predetermined torque increase.

According to an example embodiment, the method may further comprise the steps of receiving a signal indicative of the ability of the oxidation catalyst to generate nitrogen dioxide (NO₂); and determining the deterioration level based on the ability to generate NO2.

The ability to generate NO₂ can be determined by, for example, an engine map controlled by a control unit of the vehicle. The engine map describes the level of NO₂ at different operating conditions. Another example is to predict the ability to generate NO₂ by receiving information of the temperature exposure of the oxidation catalyst over time. As a still further and non-limiting example, the ability to generate NO₂ can be determined by a sensor positioned to measure the amount of NO₂ generated by the oxidation catalyst. According to an example embodiment, the signal indicative of the deterioration level may be based on a signal indicative of a time period during which the oxidation catalyst has been positioned in the exhaust gas aftertreatment system.

Hereby, the time period at which the oxidation catalyst has been connected to the internal combustion engine arrangement can be used as a measure of the deterioration level. Statistics may be used for determining how long time period an oxidation catalyst can be used until it is determined to be deteriorated. A control unit may thus contain information of when the oxidation catalyst was replaced and how many hours the internal combustion engine has been operated by being connected to the specific oxidation catalyst.

According to an example embodiment, the method may further comprise the steps of receiving a signal indicative of a temperature level of the exhaust gas conveyed to the oxidation catalyst; and determining the deterioration level of the oxidation catalyst based on the exhaust gas temperature level the oxidation catalyst being exposed to.

The temperature level may, for example, be determined by receiving a temperature signal from a temperature sensor or the like. When exposed to high temperature levels, the oxidation catalyst tends to deteriorate more rapidly.

According to an example embodiment, the method may further comprise the steps of receiving a signal indicative of contamination in the exhaust gas conveyed to the oxidation catalyst; and determining the deterioration level of the oxidation catalyst based on the contamination level the oxidation catalyst being exposed to.

The contamination may relate to the amount of contamination in the exhaust gas and/or the specific type of contaminant in the exhaust gas. According to the latter, different types of contaminants may affect the oxidation catalyst to different degree.

According to an example embodiment, the internal combustion engine arrangement may comprise a nitrogen dioxide detecting sensor positioned downstream the oxidation catalyst, wherein the method may further comprise the steps of receiving a signal indicative of the amount of NO₂ from the nitrogen dioxide detecting sensor; determining a ratio between the amount of NO₂ and the amount of nitrogen monoxide (NO) present in the exhaust gas expelled from the oxidation catalyst; and controlling the internal combustion engine to generate pulses of carbon monoxide when the NO2/NO ratio is below a predetermined limit.

It is preferable that the ratio between NO2 and NO is as close as possible to 1. Thus, a 50:50 ratio is desirable. It is preferable to provide a continuous control of the ratio whereby pulses of carbon monoxide is generated for maintaining the NO2/NO ratio as close to 50:50 as possible.

The amount of NO can be determined by, for example, using the above described engine model for calculating the amount of NO being produced for the specific operating condition. Another example is to use a NO_x sensor.

According to an example embodiment, a frequency of generated carbon monoxide pulses may be proportional to the deterioration level of the oxidation catalyst.

Accordingly, pulses of carbon monoxide may be generated more frequently when the deterioration level is high compared to when the deterioration level is low.

According to an example embodiment, the internal combustion engine arrangement may comprise a lambda sensor for measuring an air-fuel ratio (AFR) of the exhaust gas conveyed from the internal combustion engine, wherein the method may comprise the steps of receiving a signal indicative of the AFR level of the exhaust gas; and controlling the internal combustion engine to generate pulses of carbon monoxide thus maintaining the AFR level of the exhaust gas below a predetermined level.

According to a second aspect, there is provided an internal combustion engine arrangement comprising an internal combustion engine and an exhaust gas aftertreatment system arranged downstream the internal combustion engine for receiving exhaust gas expelled from the internal combustion engine during operation thereof; the exhaust gas aftertreatment system comprising an oxidation catalyst and a catalytic reduction arrangement arranged downstream the oxidation catalyst, wherein the internal combustion engine arrangement further comprises a control unit configured to receive a signal indicative of a deterioration level of the oxidation catalyst; compare the deterioration level with a predetermined threshold level;; and control the internal combustion engine to generate pulses of carbon monoxide exhausted towards the oxidation catalyst when the deterioration level is above the predetermined threshold level.

According to an example embodiment, the oxidation catalyst may be a diesel oxidation catalyst.

According to an example embodiment, the internal combustion engine arrangement may further comprise a diesel particulate filter arranged in fluid communication with and upstream from the catalytic reduction arrangement. Hereby, the exhaust gas conveyed from the internal combustion engine can be filtered before being provided into the catalytic reduction arrangement.

Further effects and features of the second aspect are largely analogous to those described above in relation to the first aspect.

According to a third aspect, there is provided a computer program comprising program code means for performing the steps of any one of the embodiments described above in relation to the first aspect when the program is run on a computer.

According to a fourth aspect, there is provided a computer readable medium carrying a computer program comprising program means for performing the steps of any one of the embodiments described above in relation to the first aspect when the program means is run on a computer.

According to a fifth aspect, there is provided a vehicle comprising an internal combustion engine arrangement according to any one of the embodiments described above in relation to the second aspect.

Effects and features of the third, fourth and fifth aspects are largely analogous to those described above in relation to the first and second aspects.

Further features and advantages of the present invention will become apparent when studying the appended claims and the following description. The skilled person will realize that different features may be combined to create embodiments other than those described in the following, without departing from the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages, will be better understood through the following illustrative and non-limiting detailed description of an exemplary embodiment, wherein:

Fig. 1 is a lateral side view illustrating an example embodiment of a vehicle in the form of a truck;

Fig. 2 is a schematic illustration of an internal combustion engine arrangement according to an example embodiment; and

Fig. 3 is a flow chart of a method for controlling an internal combustion engine arrangement according to an example embodiment.

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which an exemplary embodiment is shown. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, this embodiment is provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

With particular reference to Fig. 1, there is provided a vehicle 10 in the form of a truck. The vehicle 10 comprises a prime mover 100 in the form of an internal combustion engine arrangement 100. The internal combustion engine arrangement 100 may preferably be propelled by e.g. a conventional fuel such as diesel, although other alternatives are conceivable. The internal combustion engine arrangement 100 is preferably operated in a four-stroke fashion, i.e. operated by an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. As further depicted in Fig. 1, the internal combustion engine arrangement 100 also comprises a control unit 112 for controlling operation of the internal combustion engine arrangement 100. Turning to Fig. 2, which is a schematic illustration of the internal combustion engine arrangement 100 in Fig. 1 according to an example embodiment, it can be seen that the internal combustion engine arrangement 100 comprises a plurality of combustion cylinders 101, each having an inlet valve 103 for receiving air, and an outlet valve 105 for exhausting combusted exhaust gas. Although each cylinder 101 is depicted as having only one inlet valve 103 and one outlet valve 105, the cylinder may also comprise two or more inlet valves and two or more outlet valves.

The internal combustion engine arrangement 100 also comprises an inlet manifold 107 and an exhaust manifold 109. The air is thus provided into each of the combustion cylinders 101 via the inlet manifold 107 and the inlet valves 103, while exhaust gas is directed out from the combustion cylinders 101 via the outlet valves 105 and further through the exhaust manifold 109.

Moreover, the internal combustion engine arrangement 100 further comprises an air throttle 111 arranged in communication with the inlet manifold 107. Hereby, the amount of air provided into the inlet manifold 107, and further into the combustion cylinders 101 can be controlled by means of controlling the opening degree of the air throttle 111. The air throttle 111 is preferably electrically connected and operated by the control unit 112.

As is further depicted in Fig. 2, the internal combustion engine arrangement 100 comprises an exhaust gas aftertreatment system 104. The exhaust gas aftertreatment system 104 is particularly useful for reducing harmful emissions exhausted from the combustion cylinders 101. The exhaust gas aftertreatment system 104 comprises an oxidation catalyst 106, a particulate filter 114 and a catalytic reduction arrangement 108. As described above, the internal combustion engine arrangement may preferably be propelled by diesel fuel, whereby the oxidation catalyst 106 is preferably a diesel oxidation catalyst, and the particulate filter 114 is a diesel particulate filter. The exhaust gas conveyed from the combustion cylinders 101 is first directed into the oxidation catalyst 106, thereafter provided into the particulate filter 114 and finally directed through the catalytic reduction arrangement 108.

As also depicted in Fig. 2, a nitrogen dioxide detecting sensor 110 positioned downstream the oxidation catalyst 106. The nitrogen dioxide detecting sensor 110 can thus detect the amount of nitrogen dioxide (NO2) present in the exhaust gas downstream the oxidation catalyst 106.

One main function of the oxidation catalyst 106 is to oxidize nitrogen monoxide (NO) into NO2. The oxidation catalyst 106 preferably comprises a catalyst carrier having the ability to absorb oxygen. One purpose of generating NO2 in the oxidation catalyst is to support the performance of the particulate filter 114 and the catalytic reduction arrangement 108 for NO_x reduction. Preferably, the ratio between the amount of NO2 and the amount of NO present in the exhaust gas expelled from the oxidation catalyst should be as close as possible to 50:50 for optimum performance of the particulate filter 114 and the catalytic reduction arrangement 108 to reduce NO_x. In a situation where the exhaust gas expelled from the oxidation catalyst 106 contains too much NO2, the reduction of NO_x in the catalytic reduction arrangement 108 will be slower, which may result in e.g. emissions of NO2 to the ambient environment.

As the oxidation catalyst deteriorates, due to e.g. age, high temperature exposure, contamination exposure, etc., the ability for the oxidation catalyst to generate NO2 may be reduced. Reference is made to Fig. 3 which illustrates a flow chart of a method for controlling the internal combustion engine arrangement 100 according to an example embodiment. In particular, the method described below is particularly useful for boosting the oxidation catalyst 106 for being able to sufficiently generate NO2 when being deteriorated to various degrees.

During operation of the internal combustion engine arrangement 100, a signal is received S1 from the control unit 112, which signal is indicative of the deterioration level of the oxidation catalyst 106. The deterioration level of the oxidation catalyst 106 is thus preferably an indication of the performance of the oxidation catalyst 106 and is provided to receive an indication of how well the oxidation catalyst can generate NO2. The deterioration level can also be determined by receiving a signal from the control unit 112 with information on duration of the time period during which the oxidation catalyst has been positioned in the exhaust gas aftertreatment system 104. The control unit 112 can thus keep track of when the oxidation catalyst was installed to the exhaust gas aftertreatment system 104 as well as the number of operating hours in use. As the oxidation catalyst ages, its ability to generate NO2 will likely be reduced. According to another example, the deterioration level can be determined by means of the temperature and/or contamination it is, or has been, exposed to. The control unit 112 can thus continuously receive signals with information of the temperature level of the oxidation catalyst. The temperature level can be measured by e.g. a temperature sensor of the oxidation catalyst 106, or a temperature sensor positioned upstream the oxidation catalyst 106 to measure the temperature level of the exhaust gas directed into the oxidation catalyst 106. The control unit 112 can also continuously receive signals with information on the amount of contaminant supplied by the exhaust gas into the oxidation catalyst 106.

In order to determine if the oxidation level is too deteriorated, the deterioration level of the oxidation catalyst is compared S2 to a predetermined threshold level. Hereby, a level for determining if the oxidation catalyst 106 is able to sufficiently generate NO2 is provided. If the deterioration level is above the predetermined threshold level, the oxidation catalyst 106 is determined to be unable to sufficiently generate NO2, while if the deterioration level is below the predetermined threshold level, the oxidation catalyst 106 is determined to function properly. The following will describe the actions taken when the deterioration level is above the predetermined threshold level.

When the deterioration level is above the predetermined threshold level, the internal combustion engine arrangement 100 is controlled S3 to generate pulses of carbon monoxide (CO) towards the oxidation catalyst. Providing pulses of CO will boost the oxidation catalyst 106 for improving the generation of NO2. Hereby, the coating material of the oxidation catalyst will preferably increase its chemical metallic properties, i.e. the ability to lose its outer valence electrons, which will improve the generation of NO2. In other words, the generation of CO pulses will preferably increase the activity of the coating material of the oxidation catalyst. The pulses of CO can be generated by, for example, reducing the air-fuel ratio (AFR) supplied into the combustion chambers of the internal combustion engine 102. Hereby, the amount of supplied air relative to the amount of supplied fuel is reduced. The AFR can be controlled by controlling the air throttle 111 to reduce the flow of air into the inlet manifold 107.

Furthermore, in order to reduce the risk of soot generation when generating pulses of CO towards the oxidation catalyst 106, it can be advantageous to supply the pulses of CO during specific operating conditions of the vehicle 10. According to a first example, the internal combustion engine arrangement 100 can be controlled to generate pulses of CO when the vehicle is increasing the throttle level. In this case, the amount of fuel supplied to the combustion cylinders is increased when e.g. the driver is pushing the accelerator pedal. Thus, pulses of CO are generated when an increase in gas throttle level exceeds a predetermined increase rate. According to another example, the internal combustion engine arrangement 100 can be controlled to generate pulses of CO when the torque level of an output shaft (not shown) of the internal combustion engine 102 exceeds a predetermined increase in torque.

Moreover, the oxidation catalyst 106 may be deteriorated to different degrees. Thus, the oxidation catalyst 106 may be able to generate NO2 at different degrees depending on how deteriorated the oxidation catalyst 106 is. The control unit 112 may hereby control the internal combustion engine arrangement 100 to increase the frequency of CO pulses based on the deterioration level of the oxidation catalyst 106. Accordingly, pulses of CO are generated on a more frequent basis for a severely deteriorated oxidation catalyst 106 compared to a less deteriorated oxidation catalyst 106.

It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

1. A method for controlling an internal combustion engine arrangement (100), the internal combustion engine arrangement (100) comprising an internal combustion engine (102) and an exhaust gas aftertreatment system (104) arranged downstream the internal combustion engine (102) for receiving exhaust gas expelled from the internal combustion engine during operation thereof; wherein the exhaust gas aftertreatment system (104) comprises an oxidation catalyst (106) and a catalytic reduction arrangement (108) arranged downstream the oxidation catalyst (106), the method comprising the steps of:

- receiving (S1) a signal indicative of a deterioration level of the oxidation catalyst (106);

- comparing (S2) the deterioration level with a predetermined threshold level, and

- controlling (S3) the internal combustion engine to generate pulses of carbon monoxide exhausted towards the oxidation catalyst (106) when the deterioration level is above the predetermined threshold level.

2. The method according to claim 1 , wherein pulses of carbon monoxide are generated by reducing an air-fuel ratio (AFR) supplied into a combustion chamber of the internal combustion engine.

3. The method according to any one of claims 1 or 2, wherein the step of controlling the internal combustion engine to generate pulses of carbon monoxide is performed when the internal combustion engine is operating in a transient mode of operation.

4. The method according to any one of the preceding claims, further comprising the steps of:

- receiving a signal indicative of an increase in gas throttle level of the internal combustion engine; and

- controlling the internal combustion engine to generate pulses of carbon monoxide when said increase in the gas throttle level exceeds a predetermined increase rate.

5. The method according to any one of the preceding claims, further comprising the steps of:

- receiving a signal indicative of an increase in torque level of an output shaft of the internal combustion engine connected to a vehicle transmission; and - controlling the internal combustion engine to generate pulses of carbon monoxide when said increase in the torque level exceeds a predetermined torque increase.

6. The method according to any one of the preceding claims, further comprising the steps of:

- receiving a signal indicative of the ability of said oxidation catalyst to generate nitrogen dioxide (NO2); and

- determining the deterioration level based on said ability to generate NO2.

7. The method according to any one of the preceding claims, wherein the signal indicative of the deterioration level is based on a signal indicative of a time period during which the oxidation catalyst has been positioned in the exhaust gas aftertreatment system.

8. The method according to any one of the preceding claims, further comprising the steps of:

- receiving a signal indicative of a temperature level of the exhaust gas conveyed to the oxidation catalyst; and

- determining the deterioration level of the oxidation catalyst based on the exhaust gas temperature level the oxidation catalyst being exposed to.

9. The method according to any one of the preceding claims, further comprising the steps of:

- receiving a signal indicative of contamination in the exhaust gas conveyed to oxidation catalyst,

- determining the deterioration level of the oxidation catalyst based on the contamination level the oxidation catalyst being exposed to.

10. The method according to any one of the preceding claims, wherein the internal combustion engine arrangement comprises a nitrogen dioxide detecting sensor (110) positioned downstream the oxidation catalyst (106), the method further comprising the steps of:

- receiving a signal indicative of the amount of NO2 from said nitrogen dioxide detecting sensor; - determining a ratio between the amount of NO2 and the amount of nitrogen monoxide (NO) present in the exhaust gas expelled from the oxidation catalyst; and

- controlling the internal combustion engine to generate pulses of carbon monoxide when said ratio is below a predetermined limit.

11. The method according to any one of the preceding claims, wherein a frequency of generated carbon monoxide pulses is proportional to the deterioration level of the oxidation catalyst.

12. The method according to any one of the preceding claims, wherein the internal combustion engine arrangement comprises a lambda sensor for measuring an air-fuel ratio (AFR) level of the exhaust gas conveyed from the internal combustion engine, the method comprising the steps of:

- receiving a signal indicative of the AFR level of the exhaust gas; and

- controlling the internal combustion engine to generate pulses of carbon monoxide maintaining the AFR level of the exhaust gas below a predetermined level.

13. An internal combustion engine arrangement (100) comprising an internal combustion engine (102) and an exhaust gas aftertreatment system (104) arranged downstream the internal combustion engine (102) for receiving exhaust gas expelled from the internal combustion engine during operation thereof; the exhaust gas aftertreatment system (104) comprising an oxidation catalyst (106) and a catalytic reduction arrangement (108) arranged downstream the oxidation catalyst (106), wherein the internal combustion engine arrangement (100) further comprises a control unit (112) configured to:

- receive a signal indicative of a deterioration level of the oxidation catalyst (106);

- compare the deterioration level with a predetermined threshold level,

- control the internal combustion engine (102) to generate pulses of carbon monoxide exhausted towards the oxidation catalyst (106) when the deterioration level is above the predetermined threshold level.

14. The internal combustion engine arrangement according to claim 13, wherein the oxidation catalyst (106) is a diesel oxidation catalyst.

15. The internal combustion engine arrangement according to any one of claims 13 or 14, further comprising a diesel particulate filter (114) arranged in fluid communication with and upstream from the catalytic reduction arrangement (108).

16. A computer program comprising program code means for performing the steps of any one of claims 1 - 12 when the program is run on a computer.

17. A computer readable medium carrying a computer program comprising program means for performing the steps of any one of claims 1 - 12 when the program means is run on a computer.

18. A vehicle comprising an internal combustion engine arrangement (100) according to any one of claims 13 - 15.