CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application of PCT/EP2018/082534, filed Nov. 26, 2018, and published on Jun. 4, 2020, as WO 2020/108725 A1, all of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to an aftertreatment system. The disclosure also relates to a method for controlling a corresponding aftertreatment system. The aftertreatment system and method is applicable for vehicles, in particularly low, medium and heavy duty vehicles commonly referred to as trucks. Although the disclosure will mainly be described in relation to a truck, it may also be applicable for other type of vehicles.

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. Reduction of exhaust gases, increasing engine efficiency, i.e. reduced fuel consumption, and lower noise level from the engines are some of the criteria that becomes an important aspect when choosing vehicle engine. Furthermore, in the field of trucks, there are applicable law directives that have e.g. determined the maximum amount of exhaust gas pollution allowable.

In order to reduce harmful emissions, and in particular nitrogen oxide (NOx), the engine exhaust aftertreatment system (EATS) of the vehicles are continuously developed. The EATS often comprises a selective catalytic reduction (SCR) downstream the combustion cylinder, by which NOx can be converted into diatomic nitrogen (N2) and water (H2O). However, the exhaust temperature should preferably exceed a predetermined temperature threshold for proper functioning of the SCR.

There is thus a desire to improve the engine aftertreatment system, in particular to improve the system such as to reduce NOx gases both during low load operation where the temperature of the exhaust gas is relatively low, as well as during normal operation of the internal combustion engine when the temperature of the exhaust gas has reached a normal working temperature.

SUMMARY

The present disclosure describes an aftertreatment system which functions in a desirable manner during substantially the entire load spectrum of an internal combustion engine. This is at least partly achieved by an aftertreatment system according to claim1.

According to a first aspect, there is provided an aftertreatment system connected downstream an internal combustion engine arrangement for receiving combustion gas exhausted from the internal combustion engine arrangement during operation thereof, the aftertreatment system comprising a primary aftertreatment system comprising a primary reduction system, the primary reduction system comprising a first catalytic reduction arrangement; a secondary reduction system comprising a second catalytic reduction arrangement, the secondary reduction system being positioned in a first conduit and arranged in fluid communication between the internal combustion engine arrangement and the primary aftertreatment system; a bypass conduit connected between the internal combustion engine arrangement and the primary aftertreatment system, wherein the bypass conduit and the first conduit are connected in parallel with each other; a first valve arrangement connected to the bypass conduit, the first valve arrangement being operable in a first state in which combustion gas exhausted from the internal combustion engine arrangement is directed through the first conduit to the primary aftertreatment system via the secondary reduction system, and second state in which combustion gas exhausted from the internal combustion engine arrangement is directed through the bypass conduit to the primary aftertreatment system bypassing the secondary reduction system; and a second valve arrangement arranged in the first conduit in fluid communication between the second catalytic reduction arrangement and the primary aftertreatment system.

The wording “primary aftertreatment system” and “secondary reduction system” should be interpreted as two separate systems of the aftertreatment system, whereby combustion gas from the internal combustion engine can be selectively directed to either directly to the primary aftertreatment system, or to the primary aftertreatment system via the secondary reduction system, depending on the current operating mode of the internal combustion engine arrangement.

A reduction system should be construed as a system which is arranged to convert environmentally harmful combustion gas to less harmful gas. An example, as will be described further below, is a selective catalytic reduction arrangement (SCR) which converts/reduces NOx gas to N2. Moreover, the first and second catalytic reduction arrangements are preferably operable in substantially similar temperature ranges, although the material configuration of the two catalytic reduction arrangements may differ to some extent. Preferably, the first and second catalytic reduction arrangements are operational in a temperature range between 200-500° C.

The present disclosure is based on the insight that by providing the aftertreatment system with a secondary reduction system, it is possible to selectively direct the combustion gas either directly to the primary aftertreatment system or to the primary aftertreatment system via the secondary reduction system based on the load situation of the internal combustion engine. Thus, the first valve arrangement is advantageously used for directing the combustion gas to the respective systems. Hereby, the combustion gas can be delivered to the aftertreatment system most capable of providing a proper reduction process.

Furthermore, the secondary reduction system can preferably be used as a close coupled reduction system, which is arranged closer to an outlet of the internal combustion arrangement in comparison to the primary aftertreatment system and which does not include other exhaust treatment devices, such as an oxidation catalyst or particulate filter, which would absorb heat. Hereby, the secondary reduction system can be heated relatively quickly such that reduction of combustion gas can be initiated thereto during e.g. cold start. Thereafter, when the primary aftertreatment system has reached a suitable operating temperature, the secondary reduction system can be bypassed. This will reduce the overall fuel consumption of the internal combustion engine. Also, the secondary reduction system can be designed to be highly chemically efficient in the available space close to the engine.

An advantage of using a second valve arrangement after the second catalytic reduction arrangement is that the gas pressure level over the second catalytic reduction arrangement increases. This will in turn increase the temperature level in the second catalytic reduction arrangement, thereby providing improved operation of the second catalytic reduction arrangement. Also, the use of a second valve arrangement will imply that the flow velocity in the second catalytic reduction arrangement is reduced. Hereby, the molecules in the combustion gas can be kept in the second catalytic reduction arrangement for a longer duration of time which will increase the chances of successful NOx reduction. Moreover, using a second valve arrangement can enable the use of a first valve arrangement which is relatively simple in design. Also, the second valve arrangement can prevent undesirable diffusion of exhaust gas into the primary aftertreatment system.

A further advantage is that the durability of the secondary reduction system will be improved as it will be less exposed to e.g. exhaust gas when only operated during e.g. cold start.

According to an example embodiment, the first valve arrangement may comprise a three-way valve for selectively directing combustion gas to the first conduit and the bypass conduit. Hereby, the three-way valve can be relatively easily controlled to direct combustion gas solely to the primary aftertreatment system, or to the secondary reduction system. Other type of valves are also conceivable, such as e.g. a butterfly valve in combination with the below described second valve arrangement.

According to an example embodiment, the second valve arrangement may be operable from a closed position to an open position when a gas pressure level in the first conduit exceeds a predetermined gas pressure threshold limit. Hereby, the secondary reduction system can be allowed to operate at relatively high pressures, which will result in higher reduction performance over the secondary reduction system and higher combustion gas temperature which will result in a faster heating of the aftertreatment system. Also, combustion gas in the first conduit is allowed to enter the primary aftertreatment system only when the gas pressure level exceeds the predetermined gas pressure threshold limit.

According to an example embodiment, the second valve arrangement may preferably be one of a pneumatically controlled check valve or an electronically controlled valve connected to a control unit for control of operation thereof. A pneumatically controlled check valve may preferably use a spring or the like which will position the check valve in the open position when the pressure level exceeds the predetermined limit. If using an electronically controlled valve, a pressure sensor or the like is preferably used for detecting a pressure level in the first conduit. The second valve arrangement is then opened in response to a signal from the pressure sensor being indicative of a pressure level above the predetermined limit. An electronically controlled valve may preferably be connected to the below described control unit for controlling operation thereof.

According to an example embodiment, the first and second catalytic reduction arrangements may be respective selective catalytic reduction devices arranged to convert nitrogen oxides (NOx) into diatomic nitrogen (N2).

According to an example embodiment, the secondary reduction system may comprise a reducing agent injector arranged in the first conduit upstream the second catalytic reduction arrangement for supplying reducing agent to the combustion gas before the combustion gas enters the second catalytic reduction arrangement.

According to an example embodiment, the secondary reduction system may comprise a reducing agent injector arranged in the exhaust conduit, preferably near the turbine. Thus the reductant can be well mixed with the turbulent flow created by the turbo and/or exhausts port, and thereby enabling a very short distance between the engine and the second catalytic device.

According to an example embodiment, the aftertreatment system may further comprise a control unit connected to the first valve arrangement for controlling operation thereof.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

According to an example embodiment, the control unit may be configured to receive a signal indicative of a temperature level of the first catalytic reduction arrangement; compare the temperature level with a predetermined temperature threshold limit; control the first valve arrangement to direct combustion gas from the internal combustion engine arrangement to the primary aftertreatment system via the first conduit if the temperature level of the first catalytic reduction arrangement is below to the predetermined temperature threshold limit; and control the first valve arrangement to direct combustion gas from the internal combustion engine arrangement to the primary aftertreatment system via the bypass conduit if the temperature level of the first catalytic reduction arrangement is above or equal to the predetermined temperature threshold limit.

According to an example embodiment, the control unit may be configured to receive a signal indicative of a temperature level of the internal combustion engine arrangement; compare the temperature level of the internal combustion engine arrangement with a predetermined engine temperature threshold limit; control the first valve arrangement to direct combustion gas from the internal combustion engine arrangement to the primary aftertreatment system via the first conduit if the temperature level of the internal combustion engine arrangement is below the predetermined engine temperature threshold limit; and control the first valve arrangement to direct combustion gas from the internal combustion engine arrangement to the primary aftertreatment system via the bypass conduit if the temperature level of the internal combustion engine arrangement is above or equal to the predetermined engine temperature threshold limit.

The predetermined temperature threshold limit may preferably be a temperature limit when the primary aftertreatment system operates as desired, i.e. a temperature limit where the primary aftertreatment system is able to provide a desirable reduction process.

Hereby, during e.g. cold start and operation when the internal combustion engine arrangement is relatively cold, combustion gas is guided to the secondary reduction system before the combustion gas is provided to the primary aftertreatment system. The combustion gas will thus have an increased temperature level when reaching the primary aftertreatment system in comparison to a situation when the secondary reduction system is bypassed.

The temperature level may additionally, or in combination, be determined by measuring the temperature level of the engine coolant. Also, the control unit may be arranged to receive a signal indicative of an amount of ammonia present in the primary aftertreatment system, and control the first valve arrangement to direct combustion gas to the secondary reduction system or to bypass the secondary reduction system.

According to an example embodiment, the aftertreatment system may further comprise a burner arrangement positioned in fluid communication between the internal combustion engine arrangement and the first valve arrangement. Hereby, the combustion gas can be heated which is beneficial for operation of the reduction systems.

According to an example embodiment, the primary aftertreatment system may further comprise a primary reducing agent injector arranged upstream the first catalytic reduction arrangement for supplying reducing agent to the combustion gas before the combustion gas enters to the first catalytic reduction arrangement. Hereby, it can be assured that reductant is available for the reduction process.

According to an example embodiment, the primary aftertreatment system may further comprise an oxidation catalyst and a particulate filter upstream the first catalytic reduction arrangement.

The oxidation catalyst may be a diesel oxidation catalyst and the particulate filter may be a diesel particulate filter in case the internal combustion engine arrangement is a diesel engine. By providing an oxidation catalyst and particulate filter, a further reduction of environmentally harmful combustion gases is achieved. The oxidation catalyst has the primary function to oxidize hydrocarbons and carbon monoxide with oxygen to carbon dioxide. The oxidation catalyst may also oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO2). The functioning of the particulate filter is to catch soot and oxidize the soot with NO2 and O2 to carbon dioxide. To enable the soot oxidation by NO2, the particulate filter preferably comprises an oxidation catalytic layer which oxidizes NO to NO2.

According to an alternative, the primary aftertreatment system may comprise a particulate filter with SCR coating, a so-called SCR on DPF, also trademarked as SCRF and SDPF.

According to an example embodiment, the oxidation catalyst may comprise a plurality of catalyst layers for oxidizing components in the combustion gas. The layers may advantageously be arranged for oxidizing components like hydrocarbons, nitrogen monoxide, carbon monoxide, soot, UREA and ammonia.

According to an example embodiment, the plurality of catalyst layers may comprise a material composition of metal oxides and/or zeolites. The plurality of catalyst layers may be arranged at the inlet of the oxidation catalyst. The metal oxides and/or zeolites may be arranged form a selective ammonia oxidation catalyst. The metal oxides may e.g. be Al2O3, TiO3. The zeolites may e.g. be CHA, BEA, and/or LTA. The metal oxides may include the noble metals Palladium and Platinum and the zeolite can be ion exchanged with either copper or iron. This type of selective ammonia oxidation catalyst placed in the primary aftertreatment system is especially beneficial when the reductant injector is placed in the exhaust conduit. After the cold start, urea deposit and liquid film may be left on the exhaust pipe wall and slowly evaporate. When the secondary reduction system is bypassed, the vapors from the deposit and liquid films are selectively oxidized to N2 and H2O. It also enables purging of the injector without engaging the secondary reduction system.

According to an example embodiment, the oxidation catalyst may further comprise a substrate layer comprising cordierite. The substrate layer may alternatively comprise metal sheets.

According to a second aspect, there is provided a method for controlling an aftertreatment system connected downstream an internal combustion engine arrangement, the aftertreatment system comprises a primary aftertreatment system comprising a primary reduction system, the primary reduction system comprising a first catalytic reduction arrangement; a secondary reduction system comprising a second catalytic reduction arrangement, the secondary reduction system being arranged in fluid communication between the internal combustion engine arrangement and the primary aftertreatment system via a first conduit; and a bypass conduit connected between the internal combustion engine arrangement and the primary aftertreatment system, wherein the bypass conduit and the first conduit are connected in parallel with each other, the method comprising the steps of determining if the internal combustion engine arrangement is operating in a first operating mode or in a second operating mode; directing combustion gas from the internal combustion engine arrangement to the primary aftertreatment system via the secondary reduction system if the internal combustion engine arrangement is operating in the first operating mode; directing combustion gas from the internal combustion engine arrangement to the primary aftertreatment system via the bypass conduit for bypassing the secondary reduction system if the internal combustion engine arrangement is operating in the second operating mode.

According to an example embodiment, the internal combustion engine arrangement may be operating in the first operating mode if the temperature level of the first catalytic reduction arrangement is below a predetermined temperature threshold limit.

The gas pressure level in the secondary catalytic reduction arrangement, when the internal combustion engine arrangement is operated in the first operating mode, is preferably controlled by a second valve arrangement in the first conduit.

According to an example embodiment, the method may further comprise the steps of determining an amount of ammonia absorbed in the first catalytic reduction arrangement; and determining that the internal combustion engine arrangement is operating in the first operating mode if the amount of absorbed ammonia is below a predetermined threshold limit.

According to an example embodiment, the internal combustion engine arrangement may be operating in the first operating mode if the temperature level of the internal combustion engine arrangement is below a predetermined engine temperature threshold limit.

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 vehicle comprising an internal combustion engine arrangement and an aftertreatment system according to any one of the embodiments described above in relation to the first aspect.

According to a fourth 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 second aspect when the program is run on a computer.

According to a fifth 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 second aspect when the program means is run on a computer.

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

