Internal combustion engine system and method for increasing the temperature in at least one part of the internal combustion engine system

Abstract

An internal combustion engine system includes a cylinder block with a plurality of cylinders, a gas intake manifold for providing at least air to the cylinder block and an exhaust gas manifold for exiting the exhaust gas from the cylinder block, wherein the exhaust gas manifold includes at least a main exhaust gas outlet and a waste gate exhaust gas outlet, wherein the main exhaust gas outlet is connected to a main exhaust gas pipe for guiding the exhaust gas to a main exhaust gas after treatment system and the waste gate exhaust gas outlet is connected to a waste gate exhaust gas pipe, and wherein the waste gate exhaust gas pipe is reconnected to the main exhaust gas pipe upstream of the main exhaust gas after treatment system and includes at least one waste gate exhaust gas after treatment unit, such as an oxidation catalyst such as a diesel oxidation catalyst, for catalytically treating the exhaust gas streaming through the waste gate exhaust gas pipe, and to a method for increasing the temperature in an internal combustion engine system.

Claims

1. A method for increasing the temperature in an internal combustion engine system during a temperature critical operation situation, the internal combustion, engine system comprising an internal combustion engine, wherein the internal combustion engine comprises a cylinder block with a plurality of cylinders, wherein the plurality of cylinders of the cylinder block are arranged in at least a first cylinder group and a second cylinder group, a gas intake manifold for providing at least air to the first and second cylinder group and an exhaust gas manifold for exiting the exhaust gas from the cylinder block to a main exhaust gas aftertreatment system, the method comprising the steps of: determining that the internal combustion engine system is operated in the temperature critical situation; after determining that the internal combustion engine system is operated in the temperature critical situation, controlling the first cylinder group to be inactive by providing no fuel to the cylinders of the first cylinder group, and controlling the second cylinder group to be active by providing fuel to the cylinders of the second cylinder group; and wherein each cylinder of the internal combustion engine system further comprises at least one intake valve for opening the corresponding cylinder to the intake manifold and at least one exhaust valve for opening the corresponding cylinder to the exhaust gas manifold, the method comprising increasing the temperature in at least one cylinder by controlling the exhaust valve of the at least one cylinder to be at least partially open at the same time as the intake valve is opened, thereby rebreathing a predetermined amount of exhaust gas into the cylinder, wherein the step of rebreathing exhaust gas is performed on the first inactive cylinder group as well as on the second active group of cylinders, wherein a lift of exhaust valves of the second active group of cylinders during exhaust gas rebreathing is smaller than a lift of exhaust valves of the first inactive group of cylinders during exhaust gas rebreathing.

2. The method according to claim 1, wherein at least one cylinder or at least one cylinder group of the internal combustion engine system further comprises an intake throttle for controlling an amount of intake gas into the at least one cylinder or the at least one cylinder group, the method further comprising the step of reducing the amount of intake gas into the inactive cylinder group, wherein the amount of intake gas is zero.

3. The method according to claim 1, wherein each cylinder further comprises a cylinder fuel injector for injecting at least fuel into the cylinder, herein the cylinder fuel injector of at least one cylinder is controlled to inject fuel at least two times per combustion stroke, wherein the second injection is at least 10 crank angle degrees later than the first injection.

4. The method according to claim 1, wherein the first cylinder group comprises at least one first intake throttle, and the second cylinder group comprises at least one second intake throttle, which are adapted to be separably operable, the method further comprising: during the temperature critical situation controlling the first intake throttle of the first cylinder group and the second intake throttle of the second cylinder group to throttle the first cylinders of the first cylinder group to a greater extent than the second cylinders of the second cylinder group.

5. The method according to claim 1, further comprising the step of recirculating at least part of the exhaust gas to the gas intake side of the internal combustion engine, wherein the internal combustion engine system further comprises an exhaust gas recirculation (EGR) pipe for recirculating at least part of the exhaust gas to the gas intake side of the internal combustion engine, wherein the exhaust gas is branched off from at least one of a main exhaust gas pipe, a third exhaust gas pipe downstream of a turbocharger unit and upstream of the main exhaust gas aftertreatment system, and directly from the exhaust gas manifold.

6. A method for increasing the temperature in an internal combustion engine system during a temperature critical operation situation, the internal combustion engine system comprising an internal combustion engine, wherein the internal combustion engine comprises a cylinder block with a plurality of cylinders, wherein the plurality of cylinders of the cylinder block are arranged in at least a first cylinder group and a second cylinder group, a first gas intake manifold part which is assigned to the first cylinder group for providing at least air to the first cylinder group, a second gas intake manifold part, which is assigned to the second cylinder group for providing at least air to the second cylinder group, a first exhaust gas manifold part for exiting exhaust gas from the first cylinder group, a second exhaust gas manifold part for exiting exhaust gas from the second cylinder group, and an exhaust gas recirculation duct that connects the first exhaust gas manifold part and the second gas intake manifold part of the internal combustion engine, the method comprising: determining that the internal combustion engine system is operated in the temperature critical situation; and after determining that the internal combustion engine system is operated in the temperature critical situation recirculating exhaust gas from the first cylinder group to the second cylinder group; and wherein each cylinder of the internal combustion engine system further comprises at least one intake valve for opening the corresponding cylinder to the intake manifold and at least one exhaust valve for opening the corresponding cylinder to the exhaust gas manifold, the method comprising increasing the temperature in at least one cylinder by controlling the exhaust valve of the at least one cylinder to be at least partially open at the same time as the intake valve is opened, thereby rebreathing a predetermined amount of exhaust gas into the cylinder, wherein the step of rebreathing exhaust gas is performed on the first inactive cylinder group as well as on the second active group of cylinders, wherein a lift of exhaust valves of the second active group of cylinders during exhaust gas rebreathing is smaller than a lift of exhaust valves of the first inactive group of cylinders during exhaust gas rebreathing.

7. Method according to claim 6, further comprising the step of controlling the first cylinder group to be inactive by providing no fuel to the cylinders of the first cylinder group, and controlling the second cylinder group to be active by providing fuel to the cylinders of the second cylinder group in case the internal combustion engine system is operated in the temperature critical situation.

8. An internal combustion engine system comprising an internal combustion engine, wherein the internal combustion engine comprises a cylinder block with a plurality of cylinders, wherein the plurality of cylinders of the cylinder block are arranged in at least a first cylinder group and a second cylinder group, a first gas intake manifold part which is assigned to the first cylinder group for providing at least air to the first cylinder group, a second gas intake manifold part, which is assigned to the second cylinder group for providing at least air to the second cylinder group, a first exhaust gas manifold part for exiting exhaust gas from the first cylinder group, a second exhaust gas manifold part for exiting exhaust gas from the second cylinder group, and an exhaust gas recirculation duct that connects the first exhaust gas manifold part and the second gas intake manifold part of the internal combustion engine, the internal combustion engine system being arranged to increase the temperature in the internal combustion engine system during a temperature critical operation situation by determining that the internal combustion engine system is operated in the temperature critical situation; and after determining that the internal combustion engine system is operated in the temperature critical situation recirculating exhaust gas from the first cylinder group to the second cylinder group; and wherein each cylinder of the internal combustion engine system further comprises at least one intake valve for opening the corresponding cylinder to the intake manifold and at least one exhaust valve for opening the corresponding cylinder to the exhaust gas manifold, the method comprising increasing the temperature in at least one cylinder by controlling the exhaust valve of the at least one cylinder to be at least partially open at the same time as the intake valve is opened, thereby rebreathing a predetermined amount of exhaust gas into the cylinder, wherein the step of rebreathing exhaust gas is performed on the first inactive cylinder group as well as on the second active group of cylinders, wherein a lift of exhaust valves of the second active group of cylinders during exhaust gas rebreathing is smaller than a lift of exhaust valves of the first active inactive group of cylinders during exhaust gas rebreathing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following preferred embodiments of the system and methods according to the invention will be discussed with the help of the attached Figures. The description of the Figures is considered as simplification of the principles of the invention and is not intended to limit the scope of the claims.

(2) The figures show:

(3) FIG. 1: a schematic illustration of a preferred embodiment of the inventive internal combustion engine system,

(4) FIG. 2a to d: graphical illustrations of preferred embodiments of the valve control mechanism

(5) FIG. 3: a temperature diagram for valve mechanisms of FIG. 2;

(6) FIG. 4a, b: graphical illustrations of preferred embodiments of the valve control mechanism; and

(7) FIG. 5: a temperature diagram for a further preferred valve mechanism.

(8) In the following same or similarly functioning elements are indicated with the same reference numerals.

DETAILED DESCRIPTION

(9) In the schematic representation of FIG. 1 an internal combustion engine system 100 is shown which is used in a vehicle (not shown), for example in a truck or bus, or in any other vehicle comprising an internal combustion engine. The engine system 100 comprises an internal combustion engine 1 with a cylinder block 2 having e.g. six piston cylinders 4. Further, the internal combustion engine 1 has a gas intake side 6 with an intake manifold 8 and an exhaust gas outlet side 10 with an exhaust manifold 12. The exhaust gases are led to a turbocharger 14 comprising a first turbine 16 and a second turbine 18 and onward through a main exhaust gas pipe 20 to an exhaust gas aftertreatment system 22.

(10) The exhaust gas aftertreatment system usually comprises a plurality of exhaust gas aftertreatment units, such as e.g. a diesel oxidation catalyst 24, a particulate filter 26 and a selective catalytic reactor (SCR) 28.

(11) A SCR unit 26 is a means for converting nitrogen oxides by means of a catalyst into nitrogen and water. An optimal temperature range for these reactions is typically between approximately 250° Celsius and approximately 450° Celsius. This optimal operating temperature can be easily kept during normal (driving) operation modes of the engine.

(12) However, during idle or motoring engine operation modes of the internal combustion engine 1, the temperature of the exhaust gas drops. The reason for that is that fresh air at ambient temperature is fed to the intake manifold 6 of the cylinder block 2, even if combustion is reduced considerably (as in the idle engine operation mode) or no combustion takes place at all (as in the motoring engine operation mode). This in turn means that the internal combustion engine 1 is simply pumping fresh and cool air to the exhaust gas side 8 and onward into the exhaust gas aftertreatment system 22. This cool air causes the exhaust gas aftertreatment system 22 to cool down rapidly below its optimal operating, temperature, which in turn results in poor or no exhaust gas purification, so that the required emission levels cannot be achieved.

(13) For increasing the temperature of the exhaust gas streaming through the exhaust gas aftertreatment system 22, a plurality of possibilities will be presented in the following, which may alone or in combination increase the temperature in at least one part of the internal combustion engine system 100.

(14) Even if in the illustration of FIG. 1 a plurality of different approaches are combined it should be one again explicitly mentioned that the combination is only a preferred embodiment and does not limit the scope of protection thereto.

(15) According to the invention a first approach for avoiding a temperature drop in the exhaust gas aftertreatment system is given by adding a waste gate exhaust gas pipe 30. The waste gate exhaust gas pipe 30 is preferably branched off from the exhaust gas manifold 12 and may comprise a valve 32 or opening and closing the waste gate exhaust gas pipe 30 or controlling the amount of exhaust gas streaming through the waste gate exhaust gas pipe 30, a fuel injector 34 for injecting fuel into the exhaust gas, and a diesel oxidation catalyst (DOC) 36 for provoking an exothermic reaction with help of the injected fuel.

(16) Instead of providing a separate waste gate oxidation catalyst 36, it is also possible to use at least a part of the main oxidation device 24. For that, the main oxidation catalyst 24 may have at least two entries, one for the waste gate exhaust gas pipe 30 and another for the main exhaust gas pipe 20. Preferably, the entry for the waste gate exhaust gas pipe 30 is then arranged upstream of the entry for the main exhaust gas pipe 20.

(17) In the depicted embodiment of FIG. 1, the waste gate exhaust gas pipe 30 is connected to the main exhaust gas pipe 20 downstream of the turbocharger 14, thereby establishing a bypass thereto. Bypassing the turbocharger 14 has the advantage that during a temperature critical situation such as running the internal combustion engine 1 with less ignitable fuel, and/or a cold start situation and/or a low load engine operation mode and/or an idle engine operation mode and/or a motoring engine operation mode, the exhaust gas is not cooled down due to warming up the turbocharger 14. Since the turbocharger 14 provides a significant thermal inertia a lot of thermal energy may be lost in this process.

(18) The waste gate exhaust gas pipe 30 works as follows. As soon as a temperature critical situation is detected, the valve 32 is opened and a predeterminable amount of exhaust gas from the exhaust gas manifold 12 is allowed to stream into the waste gate exhaust gas pipe 30. Further, the fuel injector 34 is operated and a predeterminable amount of fuel is injected into the exhaust gas streaming through the waste gate exhaust gas pipe 30. Preferably, the fuel injector and/or the valve are arranged in close vicinity to the exhaust gas manifold. This has the advantage that the exhaust gas still comprises a pulsation (triggered by the cylinder movement), which provides good mixing properties of the exhaust gas and of the injected fuel. The fuel/exhaust gas mixture is then guided to a small DOC unit 36, where oxygen O2 in the exhaust gas stream is used to convert carbon monoxide CO to carbon dioxide CO2 and the hydrocarbons HC provided by the injected fuel are converted to water H2O and CO2. Both reactions are exothermic which consequently increases the temperature of the exhaust gas streaming through the waste gate exhaust gas pipe 30.

(19) The exhaust gas streaming through the waste gate exhaust gas pipe 30 is reunited with the cool exhaust gas streaming through the main exhaust gas pipe 20 downstream of the turbocharger 14. The hot exhaust gas from the waste gate exhaust gas pipe 30 provides enough thermal energy to increase the temperature of the complete exhaust gas to such an extent that at least one of the exhaust gas aftertreatment units 24, 26 and/or 28 is in its operation temperature range. Preferably, the exhaust gas temperature now comprises a temperature above the working temperature of the main diesel oxidation catalyst 24. The thermal energy provided by the DOC 24 in turn provides enough heat for the reactions taking place in the selective catalytically reactor 28.

(20) Alternative or additionally, the temperature of the exhaust gas may also be increased by operating only a part of the cylinders 4 during temperature critical situations. Since temperature critical situations often occur at low load or at idle engine operation modes, where no fuel or not enough fuel is injected into the cylinders, it has been suggested by the inventors to “split” the cylinders of cylinder block 2 into a first cylinder group 2a and a second cylinder group 2b. In the embodiment shown in FIG. 1, the cylinders are evenly divided into three+three cylinders. However, any other total number of cylinders or cylinder partition even an uneven partition is possible.

(21) The cylinders 4a of the first cylinder group 2a are controlled to be inactive that means no fuel is injected into the cylinders 4a. The cylinders 4b of the second cylinder group 2b in contrast are controlled to be active. That means the load required for operating the engine in the low load mode is only provided by the second cylinder group 2b. That in turn means that the exhaust gas from the second cylinder group 2b has a significantly higher temperature than the exhaust gas from the first cylinder group 2a, which in turn increases the overall temperature of the whole exhaust gas.

(22) Preferably, also the intake manifold 8 is split into a first part 8a and a second part 8b, whereby both parts comprise a separate intake throttle 101a and 101b, respectively, for controlling the amount of air flowing into the cylinders. For enhancing the temperature increasing effect, the first intake throttle may reduce the air intake to the first inactive cylinder group 2a to almost zero or zero. Since only a small amount of cold air is allowed to pass the cylinders, the exhaust has temperature is increased.

(23) Additionally, for further enhancing the temperature increasing effect, it is also advantageous to split the exhaust gas manifold 12 into a first part 12a which is assigned to the first cylinder group 2a of inactive cylinders and into a second part 12b which is assigned to the second cylinder group 2b of active cylinders 4b. Preferably, the waste gate exhaust gas pipe 30 is arranged to branch of at the second part of the exhaust gas manifold 12b. Thereby, hot exhaust gas is provided to the DOC 36 which further heats up the exhaust gas streaming through the waste gate exhaust gas pipe 30. Thereby, the exhaust gas in the waste gate exhaust gas pipe 30 is heated to such an extent that also the exhaust gas streaming through the first exhaust gas pipe 20 is heatable to the desired temperature, even if the main part of the exhaust gas streaming through the first exhaust gas pipe 20 is provided by the inactive cylinders.

(24) Preferably, the second part of the exhaust gas manifold 12b comprises an exhaust gas outlet which is adapted also to connect the second exhaust gas manifold part 12b to the turbocharger 14. Preferably, the turbine 16 of the turbocharger is a dual entry turbine which allows supplying exhaust gas from the first cylinder group 2a and the second cylinder group 2b to the same turbocharger 14. Of course it is also possible to use for each cylinder group a separate turbocharger, but this increases the overall weight of the vehicle and the overall number of vehicle parts which ordinarily should be avoided.

(25) Besides the above described possibilities for increasing the temperature, it is also possible to reduce the air intake into the cylinders by recirculating exhaust was to the gas intake side 6 of the internal combustion engine 1. This may be done with an exhaust gas recirculation (EGR) pipe 40 which may be branched off at the exhaust gas manifold 12 and preferably at the exhaust gas manifold part 2a assigned to the inactive cylinder group 2a. The exhaust recirculation pipe is 40 is further connected at its other side with the intake manifold 8 and preferably with the intake manifold part 8b which is assigned to the active cylinder group 2b.

(26) During temperature critical situations, this arrangement enables guiding fresh air through the first inactive cylinder group 2a and then as fresh air to the second active cylinder group 2b. Consequently, the intake of fresh ambient air for the second cylinder group is controlled to be almost zero. Thereby, the overall air intake may be significantly reduced and the temperature in the cylinders 4b of the second active cylinder group and later on the temperature of the exhaust gas may further be increased.

(27) Additionally or alternatively, the EGR pipe 40 or a further EGR pipe may be branched off from the first exhaust gas pipe 20 downstream of the turbocharger 14 or even further downstream e.g. between or downstream of the elements of the exhaust gas aftertreatment system 22. In case the EGR pipe is branched off between the elements of the exhaust gas aftertreatment system 22, it is preferred to branch off the EGR pipe downstream of the particulate filter 26 for recirculating cleaned exhaust gas but upstream of the selective catalytic reduction unit 28 for avoiding unwanted components, such as ammonia in the internal combustion engine 1.

(28) For increasing the exhaust gas temperature even further, the internal combustion engine 1 may be controlled to be operated by a so called post-injection. That means the injection to the preferably active cylinders 4b is split from a single injection to at least two injections, whereby the overall amount of fuel injected into the cylinders remains constant. For instance, instead of injecting ca. 30 mg fuel at once, first ca. 20 mg fuel may be injected and significantly later the remaining ca. 10 mg fuel are injected. In terms of crank angle degrees (CAD) significantly later means at least 10 CAD, preferably at least 20 CAD later than the first injection, which is usually close to TDC. If advanced injection timing strategies are used with very early injections, than the here mentioned late post injection should be positioned at least 10 CAD after TDC (top dead center) and preferably more than 20 CAD after TDC.

(29) Additionally, a so called very late post injection may be used which provides unburned fuel to the exhaust gas (rich engine operation condition) This engine operation condition further generates an increase amount of CO, which in turn may decrease the ignition temperature of the oxidation catalyst 36, respectively 24. A preferred method for operating the inventive internal combustion engine may comprise the following steps: 1. Operating the second cylinder group with late post injection. 2. When the temperature of the exhaust gas in the waste gate exhaust gas pipe or at the waste gate exhaust gas aftertreatment unit has been reached roughly 150° C., operating the second cylinder group with a very late post injection for producing CO and H2, preferably using a suitable air to fuel ratio for maximizing the CO and H2 content in the exhaust gas. 3. initializing operation (igniting) of the waste gate exhaust gas aftertreatment unit at roughly 150° C. due to the presence of CO and H2 in the exhaust gas of the waste gate exhaust gas pipe. 4. Terminating very late post injection and initializing operation of the waste gate fuel injector. 5. Maintaining thereby conditions in the waste gate exhaust gas pipe close to a stoichiometric mixture of fuel and air for initializing operation of the main exhaust gas aftertreatment system at roughly 150° C. due to the presence of CO and H2. 6. After ignition of the main exhaust as aftertreatment system, increasing the fuel amount at the waste gate fuel injector for providing at least slightly rich, preferably rich conditions in the waste gate exhaust gas pipe for providing unburned fuel to the main oxidation catalyst, which in turn result in rapid heating of the main exhaust gas aftertreatment system. 7. Optionally, operating the first cylinder group for providing sufficient power if required

(30) In the following the increase in the exhaust temperature using the above described methods will be shortly discussed.

(31) 1. Waste Gate Exhaust Gas Pipe (Waste Gate Combustion):

(32) As mentioned above a waste gate exhaust gas pipe 30 for controlling the exhaust gas flow is added to the exhaust gas manifold 12. In the regarded embodiment it is connected to the active cylinders 4b to lead the exhaust gases past the turbines 16, 18 to preserve the energy. In addition to this, to fuel injector 34 together with a small DOC 36 is placed in the waste gate exhaust gas pipe 30 to add the extra energy for igniting the main DOC 24. The fuel injector 34 and the DOC 36 should be placed close to the exhaust gas manifold 12 to maintain the exhaust pulse by capturing the pulse energy. This pulse will be of help when mixing the fuel injected by the fuel injector 34.

(33) As soon as the engine starts (cold start situation) the waste gate exhaust gas pipe 30 is controlled to be opened by valve 32 so that roughly 10% of the overall exhaust gas flow goes through the waste gate exhaust gas pipe 30. These 10% are intended to have a temperature such high that the small DOC 36 is enabled to ignite the fuel injected by the fuel injector 34. The temperature required for this is roughly 250° C. For providing such a temperature fuel should be injected into the active cylinders 4b. After the small DOC 36 has ignited the extra fuel, the exhaust gas coming out from the waste gate exhaust gas pipe 30 is warm enough to give the resulting mixed gas a temperature close too 300° C. which is the temperature needed to keep the main DOC 24 running.

(34) Preferably the waste gate exhaust gas pipe 30 may have a diameter of 30 mm. The flow through the waste gate exhaust gas pipe 30 is controlled by a throttle or valve 32 on the exhaust gas manifold 12. The amount of fuel injected in the fuel injector 36 may be 30 mg/cycle. As soon as the main DOC 24 is warm enough the waste gate exhaust gas pipe 30 is closed and all the exhaust gases pass through the turbocharger 14. This method can be used both when cold starting an engine and when the vehicle is running on low load e.g. going down a long slope.

(35) Simulations have been performed with a fuel injection of 35 mg fuel on the active cylinders 4b and the fuel injector 34 injected additional 40 mg fuel/cycle. This resulted in the required temperature of 250° C. in the waste gate exhaust gas pipe 30 so that the small DOC 36 is enabled to ignite the fuel injected by the fuel injector 34. The total temperature in the exhaust gas pipe 20 then reached 270° C. In case this temperature is not high enough a larger amount of the hot exhaust gas may pass through the waste gate exhaust gas pipe 30. Changing from 11% of the total flow to 20% through the waste gate exhaust gas pipe 30 increased the temperature in the main exhaust gas pipe 20 to 290° C.

(36) This shows that it is possible to reach the right temperature if only the right amount of fuel is injected from the fuel injector 34 and enough of the gases pass through the waste gate. Work is lost in the process of injecting fuel into the exhaust gases but it gives the gases enough temperature to heat up the main DOC 24 to its working temperature rapidly.

(37) Table 1 shows data based on the following conditions: 600 rpm, 35 mg fuel/active cylinder, 20% through waste gate exhaust gas pipe, 40 mg fuel/cycle from fuel injector 36:

(38) TABLE-US-00001 TABLE 1 Temp@exhaust [K] 560 Bmep [g/kW-h] 0.71171 Shaft Power [kW] 4.54686 Cyltemp@ignition/max [K]  920/1207 Temp@group1/group2 [K] 530/350 Massflow in [g/s] 54.3 Inlet Temp@WG-pipe [K] 520
2. Exhaust Rebreathing and Inlet Throttle:

(39) As mentioned above, a second strategy is to use an exhaust rebreathing mechanism called bump to pump some exhaust gas hack into the cylinders 4 by lifting the exhaust valve 105 while the intake valve 103 is open. This will lower the engines mass flow and thus letting the temperature build up in the system. As discussed above, this method may also be run on part of the cylinders to minimize the fuel consumption. When only injecting fuel on a part of the cylinders 4b a throttle on the inactive cylinders 4a without injection could be used to increase the exhaust temperature even further since the throttle is preventing the inactive cylinders 4b to pump cold air through the internal combustion engine 1. Different bumps may be used. The valve lift profile called “bumpO” opens the exhaust valve as the inlet valve at maximum lift. The valve lift profiles called “bump1”, “bump2” and “bump3” reopens the exhaust valve closer to the end of the inlet valve lift.

(40) FIG. 2 shows different graphs of valve lift on the x axis and crank angel at the y-axis for “bumpO” (FIG. 2a), “bump1” (FIG. 2b), “bump2” (FIG. 2c) and “bump3” (FIG. 2d). As can be seen in FIG. 2a “bump” has the exhaust valve reopening in the middle of the inlet valve opening and for “bump1” (FIG. 2b) it takes one step to the right and so on until “ibump3” (FIG. 2d). The graph 42 represents the exhaust valve lilt and the graph 44 the inlet valve lift.

(41) The results for the exhaust gas rebreathing concerning, the exhaust gas temperatures are summarized in the following, table 3 and are graphically illustrated in FIG. 3:

(42) TABLE-US-00002 TABLE 2 Original valve lift Bump Bump1 Bump2 Bump3 Temp@exhaust 430.0 393.0 407.0 427.0 466.0 [K] Shaft Power 3.23 −1.96 −0.75 0.5 1.86 [kW] Temp@igni-  913/1142 938/936  970/1011 1045/1306 1077/1287 tion/max [K] Temp@group1/ 515/358 370/440 391/435 464/380 592/364 group2 [K] Massflow in 50.7 2.5 3.5 8.1 13.0 [g/s]

(43) FIG. 3 shows a diagram with the crank angel degree on the x axis and the temperature on the y-axis.

(44) The results could be further improved by using a smaller lift on the three active cylinders 4b. The lift profile on the three passive cylinders was the same as above described and is illustrated in FIG. 4, where FIG. 4a, the diagram on the left, illustrates the smaller bump and FIG. 4b the diagram on the right the bump used before. The results for the waste gate exhaust gas pipe are listed in the table 3 below:

(45) TABLE-US-00003 TABLE 3 Temp@exhaust [K] 460 Bmep [g/kW-h] 0.465939 Shaft Power [kW] 2.97673 Cyltemp@ignition/max [K] 1034/1300 Temp@group1/group2 [K] 570/400 Massflow in [g/s] 12.4 Massflow group1/2 [g/s] 11.3/1.5 lambda 2.79942

(46) Using a smaller bump further increased the exhaust gas temperature compared to a larger bump since the large bump slowed down the flow through the system too much.

(47) Exhaust rebreathing is not the only method for minimizing the flow of cold air through the passive cylinders. In addition a throttle on the inlet pipes to the passive cylinders 4a may be used. The throttle may have a high impact on the mass flow, presumably, it could change from 5 g/s to 1 g/s with a low pressure drop of only 1 kPa. With idle load on the engine the size of the bump was also of importance. Changing the valve lift with only 1 mm on the active cylinders 4b had a big impact on the results as seen in the tables above.

(48) 3. Combining Waste Gate Exhaust Gas Pipe and Exhaust Rebreathing:

(49) When combing the above described methods care should be taken since the waste gate exhaust gas pipe 30 allows the bump to pump the exhaust gases backwards through the system 100. This may be avoided by using exhaust rebreathing on the inactive cylinders 4a without injection and ordinary valve lift on the active cylinders 4b with injection. This minimizes the flow of cold air through the cylinders 4a in the passive cylinder group 2a but let the active cylinders 4b pump the flow in the right direction.

(50) Provided the waste gate exhaust was pipe 30 had a mass flow of 13% and the active cylinders 4b got an injection of 30 mg/cycle, this resulted in an inlet temperature in the waste gate exhaust gas pipe of 240° C. which could be enough for the small DOC 36 to ignite the fuel injected by the fuel injector 34. If not, a higher temperature can easily be achieved by injecting more fuel into the active cylinders 4b. Together with an injection of 20 mg/cycle from the fuel injector 34 a temperature of 300° C. in the main exhaust gas pipe 20 were obtained. This is due to the exhaust rebreathing mechanism stopping the flow of cold air through the passive cylinders 4b. The results are summarized in the following table 4:

(51) TABLE-US-00004 TABLE 4 Temp@exhaust [K] 570 Inlet Temp@WG-pipe [K] 510 Shaft Power [kW] 3.7666 Temp@ignition/max [K]  906/1146 Temp@group1/group2 [K] 518/400 Massflow in [g/s] 39.3 Massflow group1/2 [g/s] 23.6/2.18

(52) As can be seen in the table 4 the exhaust rebreathing mechanism lowers the mass flow through a cylinder significantly. In the regarded case the mass flow through the passive cylinders 4a is ten time lower than the mass flow through the active cylinders 4b.

(53) Exhaust rebreathing was only performed on the three inactive cylinders 4a without injection. This lowered the flow through inactive cylinder group 2a and thereby prevented the warm exhaust gas from the active cylinder group 2b from cooling down. The resulting temperature in the main exhaust pipe 20 may be further adjusted by adjusting the amount of fuel injected by the fuel injector 34.

(54) When closing the waste gate exhaust gas pipe 30 in order to study the impact of the exhaust rebreathing mechanism alone the following results were obtained:

(55) TABLE-US-00005 TABLE 5 Temp@exhaust [K] 450.0 Shaft Power [kW] 3.73241 Temp@ignition/max [K]  908/1145 Temp@group1/group2 [K] 517/391 Massflow in [g/s] 30.9 Massflow group1/2 [g/s] 27.7/3..67

(56) In this case there is a higher mass flow through the active and the inactive cylinder group 4a, 4b although the total mass flow is lower. This is due to the closed waste gate exhaust gas pipe 30. As can be seen even the rebreathing mechanism alone increased the exhaust temperature significantly.

(57) 4. Late Post Injection:

(58) The above described late post injection resulted in roughly additional 25° C. in the exhaust gases compared to the exhaust rebreathing mechanism without late post injection. FIG. 5 shows the corresponding temperature curve for an active cylinder 4b, with the crank angle degree on the x-axis and the temperature on the y-axis. The results are summarized in the following table 6:

(59) TABLE-US-00006 TABLE 6 Temp@exhaust [K] 465.0 Shaft Power [kW] 2.11612 Temp@ignition/max [K] 1052/1195 Temp@group1/group2 [K] 620/415 Massflow in [g/s] 11.9 Massflow group1/2 [g/s] 11.2/1.12 lambda 2.8038

(60) As can be seen, 0.8 kW is lost in shaft power so once again some power is lost for increasing the temperature in the exhaust. The 485 K in the table above is the total temperature in the main exhaust gas pipe while the temperature out of the active cylinders is 620 K. Combining this with the waste gate exhaust gas pipe method a temperature above 530 K, which is the temperature needed to ignite the fuel from the fuel injector 34, may be achieved.

(61) As mentioned above, the above described methods may also be used for engines with partial premixed combustion (PPC). PPC combustion has been shown to work well at medium to high loads. Since PPC can simplified be described as running a diesel engine on bad gasoline, it is not surprising that there is at cold start, idle and low load a problem with excessive HC and CO engine out emissions.

(62) The above discussed exhaust rebreathing mechanism has been shown to improve this situation. This will increase in cylinder temperature and reduce CO and HC emissions. It is further known that HC and CO emission are not a problem if the exhaust gas aftertreatment system is active. But the conversion efficiency drops to unacceptable levels when the catalyst temperature drops below 250° C. Consequently, the exhaust gas aftertreatment system should be maintained at its temperatures above 250° C. also during low load engine operation situations.

(63) Inventively at low load the cylinders of the PPC engine are controlled to be split into a first inactive cylinder group 2a and a second active cylinder group 2. Additionally or alternatively, also the intake manifold 8 is split in two parts 8a and 8b in order to be able to have a separate throttle for each cylinder group 2a, 2b. For reducing the air flow through the inactive cylinders 4a as much as possible without overheating the nozzles or overthrottling, the PPC engine is then operated comprising at least one of the following steps: Activate exhaust rebreathing on all cylinders; Throttle the active cylinders 4b slightly in order to increase combustion temperature; Throttle the inactive cylinders 4a more than the active cylinders 4b for reducing the pumping of cold air through the inactive cylinders.

(64) This strategy results in a sufficiently increased load (on the active cylinder group) for moving out of the PPC problem zone and in an increased temperature on the active cylinder group which helps with the PPC low load problem. This strategy also helps to increase exhaust gas temperature in order to make the catalyst active for CO and HC oxidation due to the increased exhaust gas temperature from the active cylinder group 4b and/or air heating in the inactive cylinder group 4a.

(65) As earlier mentioned, the exhaust pulse diminishes rapidly with lower loads. By increasing the load on one cylinder group it is possible to gain better pulses in the flow stream through the turbine. This increases the turbocharger heat recovery in the to load range of roughly 10-25%. Above roughly 25% load it is not likely that a divided cylinder group approach is applicable since that corresponds to 50% load on the active cylinders.

(66) In summary, the different aspects of the inventive method and/or the inventive internal combustion engine system allow for a higher exhaust gas temperature during temperature critical engine operation situations such as PPC, cold start, low load, idle and/or motoring engine operation modes. Since either the temperature in the cylinders themselves or the temperature of the exhaust gas or both is significantly increased during the temperature critical engine operation situations, the exhaust gas aftertreatment system may be brought to its working temperature rapidly and may be maintained at its working temperature for a long period of time.

REFERENCE NUMERALS

(67) 100 internal combustion engine system 1 internal combustion engine 2 cylinder block 2a inactive cylinder group 2b active cylinder group 4 cylinder 4a inactive cylinder 4b active cylinder 6 gas intake side 8 intake manifold 8a inactive intake manifold part 8b active intake manifold part 10 exhaust gas side 12 exhaust gas manifold 12a inactive exhaust gas manifold part 12b active exhaust gas manifold part 14 turbocharger 16 first turbine 18 second turbine 20 first/main exhaust gas pipe 22 exhaust gas aftertreatment system 24 main diesel oxidation catalyst 26 main particle filter 28 selective reduction reactor 30 waste gate exhaust gas pipe 32 valve 34 fuel injector 36 small diesel oxidation catalyst 40 EGR pipe 42 exhaust valve lift 44 intake valve lift