WO2013160530A1

WO2013160530A1 - An internal combustion engine and a method of controlling the operation thereof

Info

Publication number: WO2013160530A1
Application number: PCT/FI2013/050219
Authority: WO
Inventors: Arto JÄRVI; Diego Delneri
Original assignee: Wärtsilä Finland Oy
Priority date: 2012-04-27
Filing date: 2013-02-27
Publication date: 2013-10-31
Also published as: FI124805B; FI20125467A

Abstract

The present invention discusses a novel internal combustion engine and a method of controlling the operation of such. The invention is mainly concerned on controlling the temperature of the exhaust gas entering a SCR catalyst (20) arranged between the high-pressure turbine (3) and the low pressure turbine (6) of a two stage turbo charged internal combustion engine.

Description

AN INTERNAL COMBUSTION ENGINE AND A METHOD OF CONTROLLING THE

OPERATION THEREOF

Technical field

[001 ] The present invention relates to an internal combustion engine and a method of controlling the operation of the internal combustion engine. More specifically the present invention discusses a two stage turbocharged internal combustion engine having an SCR catalyst for reducing the engine emissions and means of controlling the temperature of exhaust gas entering the SCR catalyst.

Background art [002] The requirements set for exhaust gas emissions of internal combustion engines become more and more stringent. In order to fulfil such requirements there are various techniques available by means of which the gaseous emissions may be controlled when the engine is running. Naturally, it is clear that the overall performance of the engine should not suffer from actions aiming at reducing the emissions. As examples of the most promising means may be mentioned two-stage turbo charging and the use of an SCR catalyst (SCR stands for Selective Catalytic Reduction).

[003] By two stage turbo charging is understood an arrangement where two turbochargers have been arranged in series in the exhaust and inlet pipings of an internal combustion engine. The turbochargers are called a low-pressure (LP) turbocharger with a low-pressure compressor and a low-pressure turbine, and a high- pressure (HP) turbocharger having a high-pressure compressor and a high-pressure turbine. The exhaust gas discharged from the engine cylinders is first taken to the high pressure turbine, which rotates the high-pressure compressor, and next the exhaust gas is taken to the low-pressure turbine, which rotates the low-pressure compressor. Fresh air is first taken to the low-pressure compressor, and then to the high-pressure compressor, whereafter the charge air is taken to the engine cylinders. The operation of the two turbochargers is controlled by means of by-pass pipes arranged on either one side (compressor or turbine) or both sides of the turbochargers. The basic idea is to control the operation of the turbochargers in all possible loads of the engine such that the best engine efficiency and the lowest emissions are ensured. Thus the turbochargers may be arranged to run without any by-pass whereby both the exhaust gas and the fresh air flow through both turbochargers. Another option is to arrange a partial by-pass such that only a portion of the exhaust gas and/or the fresh air flows through both turbochargers. And yet a further option is that one of the turbochargers is by-passed entirely whereby the exhaust gas and/or the fresh air flows through only one turbocharger. In the following a few documents discussing two stage turbo charging have been referred to.

[004] DE-A1 -102 22 919 discusses an internal combustion engine provided with a two stage turbo charging arrangement and a special valve arrangement controlling the flow of the exhaust gas. The valve arrangement may be used for the recirculation of the exhaust gas to the intake of the engine, for guiding the exhaust gas to the high- pressure turbine, and for guiding the exhaust gas to the low-pressure turbine, i.e. bypassing the high-pressure turbine. Additionally, the valve arrangement may be used as an exhaust brake, too.

[005] EP-A2-1275832 discusses an internal combustion engine with two stage turbo charging. The document teaches how, by means of arranging by-pass pipes with adjustable valves to the side of the high-pressure turbo, both the compressor and the turbine of the high-pressure turbo may be either partially or totally by-passed, whereby the engine may be adapted to varying load conditions.

[006] WO-A1 -20101 12718 discusses an internal combustion engine provided with a two stage turbo charging arrangement with means for bypassing the high-pressure turbine, the low-pressure turbine and the high pressure compressor. Specifically, the document is concerned of controlling the by-pass pipe of a turbine of a turbocharger in view of emission standards and engine performance.

[007] Selective Catalytic Reduction (SCR) is a means of converting nitrogen oxides, also referred to as NO_x with the aid of a catalyst into diatomic nitrogen, N₂, and water, H₂0. A reductant, typically urea, is added to a stream of exhaust gas and is absorbed onto a catalyst. Carbon dioxide, C0₂ is a reaction product when urea is used as the reductant. SCR has proven to be an advantageous method for maintaining the gaseous emissions of internal combustion engines at a low level. SCR has been utilized with success in connection with both 2- stroke and 4- stroke turbocharged internal combustion engines. The positioning of the SCR catalyst in the exhaust piping has been variably either between the engine and the turbocharger, or after the turbocharger. Lately, SCR catalyst has also been suggested to be used in combination with two stage turbo charging. In the following a few documents discussing internal combustion engines with both two stage turbo charging and SCR catalyst have been referred to. [008] WO-A1 -2010052055 discusses in one of its embodiments an internal combustion engine having a two stage turbo charging arrangement with two oxidation catalysts, a denitrification arrangement and a particulate filter. The first oxidation catalyst is located between the engine and the high-pressure turbine, the denitrification arrangement either before or after the high-pressure turbine in the exhaust piping, and the second oxidation catalyst and the particulate filter after the low-pressure turbine. The exhaust piping is additionally provided with an exhaust by-pass pipe bypassing the first oxidation catalyst, the denitrification arrangement and the high-pressure turbine. The by-pass pipe is provided with an adjustable valve, which opens at high load so that the denitrification arrangement is not subject to excessive thermal loads, but the particulate filter after the low-pressure turbine may still be regenerated by means of the hot exhaust gas. In another embodiment the denitrification arrangement is arranged after the high-pressure turbine and the by-pass pipe, whereby the N0₂/NO- ratio of the denitrification arrangement may be controlled by the valve in the by-pass pipe. [009] WO-A1 -2004097195 discusses an internal combustion engine provided with a two stage turbo charging arrangement with a catalyst arranged between the turbines. There are two by-pass pipes arranged in the exhaust pipe system. One bypassing the high-pressure turbine and the catalyst, and the other bypassing the low-pressure turbine. Both by-pass pipes are provided with valves. Additionally, an exhaust gas recirculation from the exhaust manifold to the charge air duct between the compressors is arranged.

[0010] Thus, when aiming at still lower engine emissions the two-stage turbo charging and the selective catalytic reduction has been taken into simultaneous use in internal combustion engines. The SCR catalyst has naturally three possible different positions in the exhaust pipe. In other words, it may be located in the exhaust pipe between the engine and the HP- turbine, between the HP- turbine and the LP- turbine, or after the LP- turbine. An important factor concerning the positioning of the SCR catalyst is the temperature of the exhaust gas entering the catalyst. As the optimal operating temperature of the SCR catalyst is from about 350°C to about 420°C, it is natural to position the SCR catalyst to a location where the exhaust gas temperature is for a considerable, preferably most of the operating time of the engine within that temperature range or very close to that. However, as soon as for instance the engine load is changed from its optimal (in view of the SCR operating temperature) value, the temperature of the exhaust gas is either raised or lowered. Thereby the temperature of the SCR catalyst goes easily beyond the optimal temperature range, and the efficiency of the catalyst is reduced. For the above reason the SCR catalyst has normally been position between the HP- and the LP- turbines, where the temperature control is, for natural reasons, the easiest.

[001 1 ] The above mentioned WO documents discuss internal combustion engines having an SCR catalyst arranged between the HP- and LP- turbines of the two stage turbocharger arrangement.. WO-A1 -2010052055 teaches the presence of a control valve in a by-pass pipe by-passing the HP turbine and introducing the exhaust gases upstream of the SCR catalyst, but the valve and its control are there for controlling the NO₂/NO- ratio not for controlling the operation of the SCR catalyst. [0012] Thus an object of the present invention is to find a proper location for the SCR catalyst in the exhaust piping when the SCR catalyst is arranged in connection with a two-stage turbocharged internal combustion engine.

[0013] It is another object of the present invention to provide a control arrangement for a two-stage turbocharged internal combustion engine with an SCR catalyst for maintaining the gaseous emissions at a low level in all operating conditions of the engine.

[0014] It is also an object of the present invention to provide a method of controlling the temperature of an SCR catalyst used in connection with a two-stage turbocharged internal combustion engine so that the SCR catalyst is able to operate at its optimal temperature.

[0015] It is also a further object of the present invention to introduce a number of ways for controlling the temperature of an SCR catalyst used in connection with a two-stage turbocharged internal combustion engine.

Disclosure of the Invention [0016] At least one of the above and other objects of the invention are met by an internal combustion engine, the engine having an exhaust manifold attached to an exhaust pipe, a charge air receiver attached to a charge air pipe, a high-pressure turbocharger having a high-pressure turbine and a high-pressure compressor, a low- pressure turbocharger having a low-pressure turbine and a low-pressure compressor, an SCR catalyst arranged between the high-pressure turbine and the low-pressure turbine, the high-pressure turbine arranged in flow communication with the exhaust manifold by means of a first exhaust pipe section and with the low-pressure turbine by means of a second exhaust pipe section, the low-pressure turbine being further in flow communication with a third exhaust pipe section, the charge air pipe including a first charge air pipe section between the charge air receiver and the high-pressure compressor and a second charge air pipe section between the high-pressure compressor and the low-pressure compressor, the engine further comprising means for affecting the temperature of the exhaust gas in the second exhaust pipe section, wherein cooling means for lowering the temperature of the exhaust gas entering the SCR catalyst in the second exhaust pipe section, heating means for raising the temperature of the exhaust gas entering the SCR catalyst in the second exhaust pipe section, means (ECU) for controlling the heating means and the cooling means, and a temperature indicator t₆ arranged upstream of the SCR catalyst (20) in the second exhaust pipe section (12) for inputting the temperature value into the ECU.

[0017] At least one of the above and other objects of the invention are met by a method of controlling the operation of an internal combustion engine, the engine having an exhaust manifold attached to an exhaust piping, a charge air receiver attached to a charge air piping, a high-pressure turbocharger having a high-pressure turbine and a high-pressure compressor, a low-pressure turbocharger having a low-pressure turbine and a low-pressure compressor, an SCR catalyst arranged between the high-pressure turbine and the low-pressure turbine, the high-pressure turbine arranged in flow communication with the exhaust manifold by means of a first exhaust pipe section and with the low-pressure turbine with a second exhaust pipe section, the low-pressure turbine being further in flow communication with a third exhaust pipe section, the charge air piping including a first charge air pipe section between the charge air receiver and the high-pressure compressor and a second charge air pipe section between the high-pressure compressor and the low-pressure compressor, the engine further comprising means for affecting the temperature of the exhaust gas in the second exhaust pipe section, the method comprising the steps of providing the engine with means for heating and means for cooling the exhaust gas temperature in the second exhaust pipe section upstream of the SCR catalyst, monitoring the temperature t₆ in the second exhaust pipe section upstream of the SCR catalyst, inputting the monitored temperature value in a control unit (ECU), and controlling the heating means and the cooling means for adjusting the temperature of the exhaust gas upstream of the SCR catalyst for maintaining the temperature t₆ in the second exhaust pipe section upstream of the SCR catalyst within a desired range. [0018] Other characteristic features of the present invention will become apparent from the appended dependent claims.

[0019] The present invention, when solving at least one of the above-mentioned problems, improves the emission control of internal combustion engines. Brief Description of Drawing

[0020] In the following, the of the present invention is explained in more detail with reference to the accompanying Figures, of which

Figure 1 illustrates schematically a prior art internal combustion engine provided with two-stage turbo charging,

Figure 2 illustrates schematically the internal combustion engine in accordance with a first preferred embodiment of the present invention,

Figure 3 illustrates schematically the internal combustion engine in accordance with a second preferred embodiment of the present invention,

Figure 4 illustrates schematically the internal combustion engine in accordance with a third preferred embodiment of the present invention,

Figure 5 illustrates schematically the internal combustion engine in accordance with a fourth preferred embodiment of the present invention,

Figure 6 illustrates schematically the internal combustion engine in accordance with a fifth preferred embodiment of the present invention,

Figure 7 illustrates schematically the internal combustion engine in accordance with a sixth preferred embodiment of the present invention, and

Figure 8 illustrates schematically a few alternatives for controlling the operation of the embodiments of the present invention discussed in connection with Figures 2 - 7.

Detailed Description of Drawings

[0021 ] Figure 1 illustrates schematically a prior art internal combustion engine provided with two-stage turbo charging. The engine unit, i.e. the cylinders, cylinder block and the cylinder head/s are shown by reference numeral 1 . The internal combustion engine is also provided with two turbochargers, i.e. a high-pressure (HP) turbocharger 2 having an HP- turbine 3 and an HP- compressor 4 and a low-pressure (LP) turbocharger 5 having an LP- turbine 6 and an LP- compressor 7. An exhaust manifold 8 is attached at its one end to the engine unit 1 in flow communication with its exhaust ports (not shown), and at its opposite end to an exhaust piping formed of three exhaust pipe sections. The exhaust manifold 8 is arranged in flow communication with the HP- turbine 3 by means of a first exhaust pipe section 9 for taking the exhaust gas from the engine cylinders to the HP- turbocharger 2. The HP- turbine 3 is arranged in flow communication with the LP- turbine 6 by means of a second exhaust pipe section 12. The LP- turbine 6 discharges the exhaust gas to a third exhaust pipe section 13, which may, if desired, be provided with a particulate filter. A charge air receiver 10, which could also be called as the inlet manifold, is also attached to the engine unit 1 for introducing charge air into the inlet ports (not shown) of the engine unit 1 . The charge air receiver 10 connects the engine unit to the charge air piping, and is arranged in flow communication with the HP- compressor 4 by means of a first charge air pipe section 1 1 . The combustion air enters the engine and the LP- compressor 7 via an intake air silencer 14. From the LP- compressor 7 a second charge air pipe section 15 takes the charged air to the HP- compressor 4.

[0022] Figure 1 also shows how the charge air path from the intake silencer 14 to the charge air receiver 10 is provided with a charge air inter cooler 16 arranged in the second charge air pipe section 15 between the LP- and the HP- compressors, and with a charge air after cooler 17 arranged in the first charge air pipe section 1 1 between the HP- compressor 4 and the charge air receiver 10. Naturally, it has to be understood, already at this stage, that the presence of both the inter cooler 16 and the after cooler 17 or the presence of one of them is not necessary for the working of the invention. However, the use of the charge air coolers 16 and 17 is advantageous as it increases greatly the efficiency of the internal combustion engine.

[0023] When an SCR catalyst 20 is installed in the exhaust gas path or exhaust piping of an internal combustion engine provided with two-stage turbo charging the best location for the SCR catalyst 20 is in the second exhaust pipe section 12 between the HP- and LP- turbines as shown in Figure 2. The temperature range for the SCR catalyst is, in general, too low after the LP-turbine 6 and too high before the HP-turbine 3. However, when the SCR catalyst 20 is located between the turbines in a two stage turbocharged engine, the temperature of the SCR catalyst is easily in the upper end of the desired temperature range of the SCR catalyst 20, though sometimes the temperature of the SCR catalyst may tend to decrease below the desired lower borderline value. As mentioned already earlier the proper operating temperature of an SCR catalyst is from about 350°C to about 420°C. Thus the temperature of the exhaust gas entering the catalyst has to be monitored and adjusted whenever needed. Figures 2 through 4 illustrate a few preferred embodiments for lowering the temperature of the exhaust gas entering the SCR catalyst, and Figures 5 through 7 a few preferred embodiments for raising the temperature of the exhaust gas entering the SCR catalyst.

[0024] In accordance with Figure 2 a first preferred embodiment of the present invention discusses a couple ways of lowering the temperature of the exhaust gas entering the SCR catalyst 20. The cooling of the exhaust gases comes into question not only in exceptionally high loads of the engine, but also ambient air has an effect on the exhaust gas temperature. In other words, the hotter are the suction air temperature and coolant (charge air cooler) temperature, the higher is the exhaust temperature. The cooling of the exhaust gases is performed, in this embodiment of the present invention, by introducing air, preferably charge air, to the exhaust gas upstream of the SCR catalyst 20 into the second exhaust pipe section 12. In order to be able to introduce the air among the exhaust gas the air to be introduced has to be at a higher pressure. At high loads the charge air is in overpressure compared to exhaust gases. At engine loads of roughly 30% - 100% the pressure is higher in the charge air receiver 10. At engine loads below -30% the pressure is higher in the exhaust piping, whereby air bypass cannot be used. However, such is not needed as the temperature of the exhaust gases entering the SCR may, at such a low engine load, be even too low. Thus, a first option to find air at a sufficient pressure is to arrange an air by-pass (ABP) pipe 22 to introduce air from the charge air receiver 10 or slightly upstream thereof, i.e. after the HP- compressor 4 from the first charge air pipe section 1 1 , to the second exhaust pipe section 12 upstream of the SCR catalyst 20. The air flow is controlled by an adjustable valve 24 and the air is introduced to pipe section 12 by means of a distributor 26, which mixes the air evenly to the exhaust gas such that the temperature of the exhaust gas is lowered evenly before the combination of gases enter the SCR catalyst 20.

[0025] A second option to find air at a sufficient pressure, though at a lower pressure than in the above discussed first option, is to arrange an air by-pass pipe 28 with an adjustable valve 30 from the second charge air pipe section 15 after the inter cooler 16 (if such exists), i.e. downstream thereof to take charge air to the second exhaust pipe section 12 upstream of the SCR catalyst 20. And naturally, a third option is to have both pipes 22 and 28 collect the cooling air and to control the cooling air introduction by means of adjustable valves 24 and 30 arranged in both by-pass pipes 22 and 28. The by-pass pipes 22 and 28 may have a common inlet conduit to the distributor 26 as shown in Figure 2, but the by-pass pipes 22 and 28 may also extend as separate pipes all the way from their origin in the charge air piping to the distributor 26. Even a separate distributor for each charge air by-pass pipe may be considered. The air for cooling the exhaust gas may also be taken before one or both of the charge air coolers 16 and 17, if such exist/s, but, as long as cooling is the main purpose of the air introduction to the exhaust gas upstream of the SCR catalyst 20, it is, naturally, preferable to take the air after one or both of the coolers, as the cooler the charge air is the less charge air is needed to cool the exhaust gas upstream of the SCR catalyst, and the less the charge air by-pass interferes in the operation of the HP-compressor 4. Figure 2 also shows an electronic control unit (ECU) that is used for controlling the valves 24 and 30, for instance by means of the pressure (p₆) and temperature (t₆) data collected from the second exhaust pipe section 12 upstream of the SCR catalyst 20.

[0026] Figure 3 illustrates schematically as a second preferred embodiment of the present invention the cooling air introduction directly to the exhaust manifold 8 or to the first exhaust pipe section 9. The cooling air is again taken from the charge air receiver 10 or slightly upstream thereof from the first charge air pipe section 1 1 to an air bypass pipe 32 and introduced, in a first option, to the first exhaust pipe section 9 upstream of the HP- turbine 3. The introduction of air is controlled by an adjustable valve 34 arranged in the charge air air by-pass pipe 32. A second option is to connect the air by-pass pipe 36 to the exhaust manifold 8. In view of these two options it is clear that the air admission in the exhaust piping may be done in any position upstream of the HP- turbine 3. In this embodiment no distributor of cooling air is needed when introducing air among the exhaust gas, as the HP- turbine 3 mixes air evenly with exhaust gas. Figure 3 illustrates an electronic control unit (ECU) that is used for controlling the valves 34, for instance by means of the pressure (p₆) and temperature (t₆) data collected from the second exhaust pipe section 12 upstream of the SCR catalyst 20.

[0027] Figure 4 illustrates as a third embodiment of the present invention means for injecting water to the exhaust gas upstream of the SCR catalyst 20. One option is to arrange water injection 40 to the exhaust manifold 8 or to the first exhaust pipe section 9 thereafter, in any case upstream of the HP turbine 3, and another option is to arrange the water injection 42 to the second exhaust pipe section 12 directly upstream of the SCR catalyst 20. Water is efficiently cooling down the excessive exhaust gas temperature. Naturally, also the water injection is controlled by means of valves 44 and 46 or some other appropriate means. Figure 4 Illustrates an electronic control unit (ECU) that is used for controlling the valves 44 and 46, for instance by means of the pressure (p₆) and temperature (t₆) data collected from the second exhaust pipe section 12 upstream of the SCR catalyst 20. [0028] Sometimes the temperature of the exhaust gas entering the SCR catalyst 20 is not sufficient. Such may happen, for instance, when performing a cold start of the engine, at low loads and/or when Variable Inlet valve Closure (VIC) is in full use. 2- stage turbocharged engines operate with early Miller timing and at part load variable inlet valve closing (VIC) is utilised. VIC means that the inlet valve may be closed later, meaning reduced Miller effect and, as a result, increased amount of air into the cylinder/s. The increased amount of air again lowers the exhaust gas temperature. Figures 5 - 7 discuss a few alternatives for heating the exhaust gas before introducing such to the SCR catalyst.

[0029] Figure 5 discusses as a fourth preferred embodiment of the present invention a novel alternative to reduce boost and thus to increase the exhaust gas temperature in the second exhaust pipe section 12 upstream of the SCR catalyst 20. In this embodiment a waste gate or exhaust by-pass pipe 60 is arranged to by-pass the LP- turbine 6, whereby the exhaust or part of it is taken to the outlet of the LP- turbine 6 or to the third exhaust pipe section 13. The control of the by-pass flow is performed by means of an adjustable valve 62 in the by-pass pipe 60. The by-pass pipe 60 may branch from the second exhaust pipe section 12 either as shown in Figure 6, i.e. between the SCR catalyst 20 and the LP- turbine 6, or upstream of the SCR catalyst 20. In this embodiment the exhaust gas temperature increase in the entrance of the SCR catalyst 20 is due to lower boost only. Figure 5 illustrates, again, the electronic control unit (ECU) that is used for controlling the valve 62, for instance by means of the pressure (p6) and temperature (t6) data collected from the second exhaust pipe section 12 upstream of the SCR catalyst 20.

[0030] Figure 6 discusses as a fifth embodiment of the present invention exhaust by- passing of both turbines 3 and 6. In other words, a waste gate or exhaust by-pass pipe 70 is arranged to run from the exhaust manifold 8 or the first exhaust pipe section 9 upstream of the HP- turbine 3 to the outlet of the LP- turbine 6 or to the third exhaust pipe section 13. Thus a part of the hot exhaust gas, controlled by adjustable valve 72, is taken in practice directly from the exhaust manifold 8 to the exhaust gas discharge. The heating of the SCR catalyst 20 is, thus, based on the lower overall boost level. Figure 6 illustrates once again the electronic control unit (ECU) that is used for controlling the valve 72, for instance by means of the pressure (p₆) and temperature (t₆) data collected from the second exhaust pipe section 12 upstream of the SCR catalyst 20. [0031 ] The arrangement of Figure 6, i.e. the by-passing of the both turbines has proved to be especially advantageous for the following reasons. When using exhaust waste gate for controlling the temperature of the SCR between the HP- and LP- turbines, there are in practice three options, either to arrange the exhaust waste gate over either one of the turbines or to arrange the exhaust waste gate over both turbines.

[0032] Performed experiments have shown that when the exhaust waste gate is arranged over the HP- turbine and the ambient temperature decreases, the operating point of the LP- compressor, in the compressor map, moves up towards the surge line. If the engine load is increased, while the exhaust waste gate is arranged over the HP- turbine, the operating point moves straight up towards, and finally over, the surge line. Such cannot be accepted as the engine has to be able to tolerate overload.

[0033] In a similar manner the experiments have shown that when the exhaust waste gate is arranged over the LP- turbine and the ambient temperature is decreased the operating point of the LP- compressor moves down substantially parallel with the surge line, i.e. the compressor speed decreases. If the engine load is increased, while the exhaust waste gate is arranged over the LP- turbine, the operating point moves straight down. In both cases the speed of the HP- compressor increases and its operating point moves up. For compensating the operation of the LP- compressor the HP- turbine should have speed margin in both cold and overload conditions, but, as the speed of the HP- turbine has already increased, there is no speed margin available.

[0034] The experiments have, however, shown that when arranging the exhaust waste gate over both turbines the operating point remains in place irrespective of the load. Thus, for overload conditions the EWG over both turbines is the optimal choice.

[0035] In cold operating conditions, when using EWG over both turbines, the operating point of the LP- compressor, however, moves towards the surge line, while the compressor speed remains substantially the same. This feature is not acceptable, and brings in the need for compensating the transfer tendency of the operating point. The performed experiments have shown that opening the air by- pass (ABP) (shown by reference numerals 22 and 32 in Figures 2, 3 and 8) is a suitable remedy for maintaining the position of the operating point substantially optimal on the compressor map. Simultaneously, the ABP affects in lowering the SCR temperature.

[0036] Figure 7 discloses a sixth embodiment of the present invention where charge air may be discharged either via an adjustable (or on/off) valve 80 (so called Air Waste Gate, AWG) from the second inlet section 15 after the intercooler 16 or via an adjustable (or on/off) valve 82 from the charge air receiver 10 or from between the charge air receiver and the charge air cooler 17. Naturally, the Air Waste Gates (AWG) 80 and 82 could be arranged just downstream of the LP- and/or HP- compressors 7 and/or 4, too, i.e. upstream of the charge air coolers 16 and 17. However, if the AWG is arranged upstream of the charge air coolers, the temperature of the charge air may be so high that the air from the AWG cannot be discharged to the engine room but is, for instance, discharged to the exhaust pipe after the LP turbine 6. By reducing the amount of charge air (by opening the AWG valve/s), and the boost, the temperature of the exhaust gases is raised. Figure 7 also shows an electronic control unit (ECU) that is used for controlling the valves 80 and 82, for instance by means of the pressure (p₆) and temperature (t₆) data collected from the second exhaust pipe section 12 upstream of the SCR catalyst 20.

[0037] Yet a further way (not shown) of affecting the temperature of the exhaust gas entering the SCR catalyst 20 is to control the inlet valve closing (VIC= Variable Inlet valve Closing). In practise VIC is used at part load and it may also be used to control SCR temperature. If the temperature is too low (at part load) the valve closing may be advanced, whereby the SCR temperature increases. At part load it may be the only way to increase SCR temperature.

[0038] At this stage it has to be understood that all the above discussed ways of affecting the exhaust gas temperature upstream of the SCR catalyst may be in use in connection with a single internal combustion engine. Thus the division of the ways of affecting the exhaust gas temperature in separate embodiments is done for the sake of clarity only. In other words, it is clear that two or more above discussed ways of affecting the exhaust gas temperature upstream of the SCR catalyst may be used together depending only on the emission requirements of the engine or the desires of the user.

[0039] Thus for instance, a preferred alternative is to use in connection with the exhaust by-pass 70 of Figure 6, air by-pass 32 or 36 of Figure 3 and the air waste gate 80 or 82 of Figure 7. The main functions are, as already discussed above, as follows: exhaust by-pass for heating the SCR catalyst, air by-pass for cooling the exhaust, and air waste gate for protecting the engine against too high firing pressures and surging due to cold suction air. When the engine is provided with a set of controls like the ones discussed above, the operator is able to run the engine in all imaginable conditions, including starting and running the engine in low and high temperatures and changing the engine load rapidly. [0040] Without saying it is clear that the various adjustable valves discussed in connection with the above embodiments need a control system. Figures 2 through 7 have shown an electronic control unit (ECU) and discussed such briefly, but now the control system will be discussed in more detail. Figure 8 discusses a few different alternatives for the control system. One way of controlling the operation of the valves is to measure or monitor directly the temperature t₆ at the entrance of the SCR catalyst 20 in the second exhaust pipe section 12. Thus, depending on the temperature indication the ECU instructs the control valves of the charge air by-pass pipes, and/or the water injection and/or the exhaust waste gates and/or the charge air waste gates to open or close.

[0041 ] For instance, if t₆ indicates a temperature below the desired SCR catalyst temperature window, the ECU instructs at least one of the exhaust gas waste gate or by-pass pipe valves 62 and 72, or charge air waste gate valves 80 and 82 (shown in Figures 5 - 7) to open. Or, if only the charge air by-pass is available for controling the temperature of the exhaust gas, i.e. to cool down the exhaust gas entering the SCR catalyst 20, the ECU instructs one or more of the valves 24, 28 and 34 (shown in Figures 2 and 3) to be throttled, i.e. to reduce cooling air flow, or to close such entirely.

[0042] In a similar manner, if water injection is used to control the temperature, the ECU instructs the feed of water to be reduced by means of valve/s 44 and/or 46 (shown in Figure 4) for increasing the temperature of the exhaust gas. Also if the charge air by-pass and/or the exhaust by-pass and/or the water injection are utilized in combination, it is possible to decrease the cooling effect by throttling, or closing, one or more charge air by-pass valves 24, 28, and 34 (shown in Figures 2 and 3) or one or more water injection valves 44 and 46 (shown in Figure 4), and/or to increase the heating effect by opening one or more exhaust by-pass valves 62 and 72 (shown in Figures 5 and 6), or charge air waste gate valves 80 and 82 (shown in Figure 7). Naturally, if the goal is to cool down the SCR catalyst temperature, the actions to be performed are opposite.

[0043] The following table shows, referring to Figures 2 - 7, the options there are available for controlling the temperature of the SCR catalyst. The table should be read such that for both heating and cooling there are eight variables, valves or the like, with which the SCR catalyst temperature may be changed. The leftmost column shows the variable, i.e. the valve in question, which naturally refers to the use of the entire bypass pipe or water injection. The two columns to the right show the desired action concerning the SCR catalyst temperature. The '-' sign indicates that the valve should be either closed or at least throttled for decreasing the flow in the pipe in question. The '+' sign indicates that the valve should be entirely open or at least opened for increasing the flow in the pipe in question.

[0044] As mentioned already above the number of SCR temperature control means may change depending on, for instance, the application in question, the accuracy of the desired control, the desires of the user, etc. Thus the above table should be understood such that if heating is the only action needed, i.e. if the exhaust gas temperature is either appropriate for the SCR catalyst operation or too low, the internal combustion engine needs to be provided with only means for heating the exhaust gas upstream of the SCR catalyst. Such means have been shown in the 'Heating' column by '+' sign, i.e. the engine has to be provided with one or more such means. In a corresponding manner, if the gas need only be cooled upstream of the SCR catalyst, the engine has to be provided with one or more means shown by '+' sign in the 'Cooling' column. And, in the most probable option, when the gas entering the SCR catalyst need to be either cooled or heated depending, for instance, on the load of the engine, the engine has to be provided with at least one means having a '+' sign in the 'Cooling' column, and with at least one means having a '+' sign in the 'Heating' column. [0045] Another applicable control mechanism also shown schematically in Figure 8 is based on monitoring the boost pressure p₃ in the charge air receiver 10, the charge air pressure pi after the intercooler 16 in the second inlet section 15 and the exhaust gas pressure p₆ after the HP turbine 3 in the second exhaust pipe section 12. In addition to those temperature and/or pressure measurements the engine load and the VIC position are monitored, too. When these parameters are inputted in the control unit (ECU), the control unit may, by using maps pre-programmed in the memory of the control unit, control the positions (i.e. opening angles) of one or more of the air by-pass valves 24, 28 and 34, the exhaust gas waste gate or by-pass valves 62 and 72, feed water injection valves 44 and 46, and air waste gate valves 80 and 82 to ensure appropriate temperature for the SCR catalyst 20. The benefit of these pre-programmed or predefined maps is the fast response they give. Compared to that measuring directly the exhaust gas temperature t₆ results in a slow response as then the reaction to load changes etc. is very slow.

[0046] The above mentioned maps may be created by running actual tests covering all possible variations of the following variables: boost pressure p₃ in the charge air receiver 10, the boost pressure in the first charge air pipe section 1 1 , the charge air pressure pi after the charge air intercooler 16 in the second charge air pipe section 15, the exhaust gas pressure p₆ after the HP turbine 3 in the second exhaust pipe section 12, the engine load, the VIC position, the opening positions of each one of the air bypass valves 24, 28 and 34, the opening positions of each one of the exhaust gas waste gate or by-pass valves 62 and 72, the opening positions (i.e. opening angles) of each one of the air waste gate valves 80 and 82, and the opening positions (i.e. opening angles) of each one of the feed water injection valves 44 and 46 and the temperature t₆ in the second exhaust pipe section 12 upstream of the SCR catalyst 20. Naturally also other variables may be included in the maps like engine emissions, efficiency, fuel consumption etc. This procedure results in a huge number of maps of which only those having the temperature t₆ within the desired range are chosen to be stored in the memory of the control unit.

[0047] The maps are used for controlling the SCR catalyst temperature as follows. When running the engine at a certain load only such maps may be used that have the same load. Now that the temperature of the SCR catalyst, or actually the gas entering the catalyst, approaches a borderline value of the desired temperature range or exceeds such, the control unit chooses from the maps the one giving the best overall performance. This may mean, for instance, minimum number of changes in the variables, smallest emissions, best efficiency etc. After the map is chosen the control unit makes the required changes in the variables, for instance changes the opening angle of one or more control valves. As an example, if a certain amount of water is being injected upstream of the SCR catalyst, and now the temperature t₆ approaches the lower borderline value of the temperature range, the control unit decreases the opening angle of the water injection control valve, whereby less water is injected, and the temperature t₆ is made to remain within the desired range.

[0048] Like the above example shows, the maps do not necessarily need the combination of all variables. In other words, also such combinations of variables are possible that a change in a variable has an effect on only one or more variable in the combination, but not on a single variable outside the combination.

[0049] Another way of creating the maps is a computerized model of the operation of an internal combustion engine. Naturally the functionability of the model may be checked by running experiments in different operating conditions of an engine.

[0050] As to the exact positions where the temperature and the pressures are measured, the temperature t₆ may be measured upstream of the distributor 26, especially if it is a question of using a control unit utilizing a predefined map, whereby the temperature t₆ gives the control unit sufficient information for controlling the positions (i.e. opening angles) of one or more of the air by-pass valves 24, 30 and 34, the exhaust gas waste gate or by-pass valves 62 and 72, the air waste gate valves 80 and 82, and feed water injection valves 44 and 46. However, if it is a question of direct control of one or more of the air by-pass valves 24, 30 and 34, the exhaust gas waste gate or by-pass valves 52, 62 and 72, the air waste gate valves 80 and 82, and feed water injection valves 44 and 46 by the temperature t₆, it is necessary to position the temperature measurement t₆ after the distributor 26.

[0051 ] It should be understood that the above is only an exemplary description of the novel and inventive internal combustion engine, and a method of controlling the temperature of SCR catalyst therein. It should be understood that the above description discusses only a few preferred embodiments of the present invention without any purpose to limit the invention to the discussed embodiments and their details only. In other words, it is clear that the number of turbochargers is not limited to just those two discussed in the exemplary embodiments, but it is possible that the engine may have one LP- turbocharger and two HP turbochargers in parallel, or the engine may have one HP- turbocharger and two LP turbochargers in parallel, or the engine may have two parallel LP- turbochargers and two parallel HP turbochargers. In very large internal combustion engines the number of turbochargers may even exceed the above examples. Thus the above specification should not be understood as limiting the invention by any means but the entire scope of the invention is defined by the appended claims only. From the above description it should be understood that separately discussed embodiments or features of the invention may be used in connection with other separately discussed features even if such a combination has not been specifically shown in the description or in the drawings.

Claims

An internal combustion engine, the engine having

• an exhaust manifold (8) attached to an exhaust pipe,

• a charge air receiver (10) attached to a charge air pipe,

• a high-pressure turbo charger (2) having a high-pressure turbine (3) and a high-pressure compressor (4),

• a low-pressure turbo charger (5) having a low-pressure turbine (6) and a low-pressure compressor (7),

• an SCR catalyst (20) arranged between the high-pressure turbine (3) and the low-pressure turbine (6),

- the high-pressure turbine (3) arranged in flow communication with the exhaust manifold (8) by means of a first exhaust pipe section (9) and with the low-pressure turbine (6) by means of a second exhaust pipe section (12),

- the low-pressure turbine (6) being further in flow communication with a third exhaust pipe section (13),

- the charge air pipe including a first charge air pipe section (1 1 ) between the charge air receiver (10) and the high-pressure compressor (4) and a second charge air pipe section (15) between the high-pressure compressor (4) and the low-pressure compressor (7),

- the engine further comprising means for affecting the temperature of the exhaust gas in the second exhaust pipe section (12),

characterized in

• cooling means (24, 30, 34, 44, 46) for lowering the temperature of the exhaust gas entering the SCR catalyst (20) in the second exhaust pipe section (12), • heating means (62, 72, 80, 82) for raising the temperature of the exhaust gas entering the SCR catalyst (20) in the second exhaust pipe section (12),

• means (ECU) for controlling the heating means and the cooling means, and

• a temperature indicator t₆ arranged upstream of the SCR catalyst (20) in the second exhaust pipe section (12) for inputting the temperature value into the ECU.

2. The internal combustion engine as recited in claim 1 , characterized in that the controlling means is a control unit arranged to selectively control at least one of the cooling means (24, 30, 34, 44, 46) and/or at least one of heating means (62, 72, 80, 82) to adjust the temperature of the gas entering the SCR catalyst (20).

3. The internal combustion engine as recited in claim 1 , characterized in that said cooling means is a charge air by-pass pipe (22, 28, 32, 36) between the charge air piping (1 1 , 15) and the exhaust piping (8, 9, 12) for taking charge air to the exhaust piping (8, 9, 12) to cool the exhaust gas upstream of the SCR catalyst (20).

4. The internal combustion engine as recited in claim 1 , characterized in that said heating means is an exhaust by-pass pipe (70) by-passing the HP- turbine (3), the LP- turbine (6), and the SCR catalyst (20) for reducing boost in the charge air piping in order to produce hotter exhaust gas upstream of the SCR catalyst (20).

5. The internal combustion engine as recited in claim 1 , characterized in that said cooling means is water injection (40, 42) arranged in the exhaust piping upstream of the SCR catalyst (20).

6. The internal combustion engine as recited in claim 1 , characterized in that said heating means is a charge air waste gate (80, 82) arranged to the first charge air pipe section (1 1 ), to the second charge air pipe section (15) and/or to the charge air distributor (10).

7. The internal combustion engine as recited in claim 3 or 4, characterized in a distributor (26) upstream of the SCR catalyst (20) for mixing the by-passed charge air evenly to the exhaust gas in the second exhaust pipe section (12).

8. The internal combustion engine as recited in claim 3, characterized in valves (24, 30, 34) in the charge air by-pass pipes (22, 28, 32, 36) for controlling the charge air by-pass flow.

9. The internal combustion engine as recited in claim 5, characterized in valves (44, 46) for controlling the amount of water to be injected into the exhaust piping.

10. The internal combustion engine as recited in claim 3 or 4, characterized in valves (72) in the exhaust gas by-pass pipe (70) for controlling the exhaust gas by- pass flow.

1 1 . The internal combustion engine as recited in any one of the preceding claims, characterized in a pressure indicator p-ι arranged upstream of the HP- compressor (4) in the second charge air pipe section (15) for inputting the pressure value into the ECU.

12. The internal combustion engine as recited in any one of the preceding claims, characterized in a pressure indicator p₃ arranged in the first charge air pipe section

(1 1 ) or in the charge air receiver (10) for inputting the pressure value into the ECU.

13. The internal combustion engine as recited in any one of the preceding claims, characterized in a pressure indicator p₆ arranged upstream of the SCR catalyst (20) in the second exhaust pipe section (12) for inputting the pressure value into the ECU.

14. The internal combustion engine as recited in any one of the preceding claims, characterized in that the control unit after having collected the various indicator values is used for preprogramming maps for controlling the operation of the heating means and/or the cooling means.

15. A method of controlling the operation of an internal combustion engine, the engine having an exhaust manifold (8) attached to an exhaust piping, a charge air receiver (10) attached to a charge air piping, a high-pressure turbo charger (2) having a high-pressure turbine (3) and a high-pressure compressor (4), a low-pressure turbo charger (5) having a low-pressure turbine (6) and a low-pressure compressor (7), an SCR catalyst (20) arranged between the high-pressure turbine (3) and the low- pressure turbine (6), the high-pressure turbine (3) arranged in flow communication with the exhaust manifold (8) by means of a first exhaust pipe section (9) and with the low- pressure turbine (6) with a second exhaust pipe section (12), the low-pressure turbine (6) being further in flow communication with a third exhaust pipe section (13), the charge air piping including a first charge air pipe section (1 1 ) between the charge air receiver (10) and the high-pressure compressor (4) and a second charge air pipe section (15) between the high-pressure compressor (4) and the low-pressure compressor (7), the engine further comprising means for affecting the temperature of the exhaust gas in the second exhaust pipe section (12), characterized by • providing the engine with means for heating and means for cooling the exhaust gas temperature in the second exhaust pipe section (12) upstream of the SCR catalyst (20),

• monitoring the temperature t₆ in the second exhaust pipe section (12) upstream of the SCR catalyst (20), ,

• inputting the monitored temperature value in a control unit (ECU), and

• controlling the heating means and the cooling means for adjusting the temperature of the exhaust gas upstream of the SCR catalyst (20) (by means of the control unit) for maintaining the temperature t₆ in the second exhaust pipe section (12) upstream of the SCR catalyst (20) within a desired range.

The method as recited in claim 15, characterized by

• monitoring the ambient temperature, the charge air pressure pi after the charge air intercooler (16) in the second charge air pipe section (15), the boost pressure p₃ in the charge air receiver (10) or in the first charge air pipe section (9), the exhaust gas pressure p₆ after the HP turbine (3) in the second exhaust pipe section (12), and the engine load, and

• inputting the monitored temperature, pressure and load values in the control unit.

The method as recited in claim 15 or 16, characterized by

• monitoring the VIC position,

• inputting the monitored position values in the control unit.

The method as recited in claim 16 or 17, characterized by

• monitoring the positions of the charge air by-pass valve (24, 28, 34), the exhaust gas by-pass valve (52, 62, 72), charge air waste gate valve (80, 82) and the injection water valve (44, 46)

• inputting the monitored position values in the control unit.

The method as recited in any one of claims 16 - 18, characterized by

• creating preprogrammed maps from the values collected from various sources, and • using the preprogrammed maps for controlling at least one of the charge air by-pass valve (24, 28, 34), the exhaust gas by-pass valve (72), charge air waste gate valve (80, 82) and the injection water valve (44, 46).

20. The method as recited in claim 15, characterized by controlling at least one of the charge air by-pass valve (24, 28, 34), the exhaust gas by-pass valve (72), charge air waste gate valve (80, 82) and the injection water valve (44, 46) for maintaining the temperature t₆ in the second exhaust pipe section (12) upstream of the SCR catalyst (20) within a desired range.

21 . The method as recited in any one of the preceding claims 15 - 20, characterized in that the desired range for the temperature t₆ in the second exhaust pipe section (12) upstream of the SCR catalyst (20) is from about 350°C to about 420°C.