Method and system for preheating at least a piston of an internal combustion engine

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for preheating at least one piston of an internal combustion engine, a system for preheating at least one piston of an internal combustion engine, and use of a system for preheating at least one piston of an internal combustion engine. Such a method and corresponding system for preheating engine parts during starting is for example known from US 2889821A.BACKGROUND ART

[0002] A large part of the emissions associated with an internal combustion engine is caused by an incomplete combustion when starting the internal combustion engine cold. The fuel being injected at the engine start creates a film on the piston top, which is still at least partly present at ignition due to a limited evaporation rate at low temperatures. This results in an incomplete combustion, also known as pool-fire, producing high amounts of pollutants, such as soot and / or only partially burned hydrocarbons. The emission of pollutants, particularly the emission of soot particles and partially burned hydrocarbons, are strongly regulated by legislation. Therefore, systems for reducing the emissions of pollutants, and in particular for reducing the emission of soot particles and partially burned hydrocarbons, are required to comply with the legislation requirements. In this regard, it has been found that a temperature of pistons of the internal combustion engine is an important parameter with respect to the completion of fuel combustion.SUMMARY

[0003] There may, therefore, be a need to provide an improved method and system for preheating at least one piston of an internal combustion engine, particularly a method and / or system for preheating at least one piston of an internal combustion engine allowing an improved combustion, i.e. a combustion generating less pollutants, such as soot particles and / or unburned or partially burned hydrocarbons.

[0004] The object of the present disclosure is solved by the subject-matter of appended independent claims, wherein further embodiments are incorporated in the dependent claims.

[0005] According to a first aspect, there is provided a method for preheating at least one piston of an internal combustion engine. The internal combustion engine at least comprises an oil distributing system including an oil sump and an oil pump for distributing oil to engine parts, an oil storing unit and a piston cooling system. The oil storing unit is selectively connectable to the oil distributing system via a valve and configured to store oil under pressure. The piston cooling system is connectable to the oil distributing system, and includes at least one piston cooling jet being directed towards at least one piston bottom. The method comprises the following steps, not necessarily in this order: starting the oil pump, e.g. by starting the engine, thereby creating an oil pressure in the oil distribution system, opening the valve of the oil storing unit, thereby filling the oil storing unit with a predetermined amount of oil by the oil pressure created by the oil pump, closing the valve of the oil storing unit, thereby storing the predetermined amount of oil under pressure in the oil storing unit, stopping the oil pump, e.g. by turning the engine off, heating the stored oil to a predetermined temperature and / or maintaining the predetermined temperature of the stored oil above a predetermined lower temperature threshold for a predetermined timeframe, i.e. after the engine being turned off, opening the valve of the oil storing unit when an upcoming engine start cranking is detected, thereby releasing the stored oil into the piston cooling system; supplying the stored oil to the piston cooling jets, and ejecting the oil via the piston cooling jets towards the at least one piston bottom, thereby preheating the at least one piston.

[0006] The method may be at least partly computer-implemented, and may be implemented in software or in hardware, or in software and hardware. Further, the method may be carried out by computer program instruction running on means that provide data processing functions. The data processing means may be a suitable computing means, such as an electronic control module etc., which may also be a distributed computer system. The data processing means or the computer, respectively, may comprise one or more of a processor, a memory, a data interface, or the like.

[0007] Preheating the piston shortly before an engine start cranking and / or at engine start cranking and / or even shortly after engine start cranking, allows improving the evaporation of a liquid fuel film on a piston top at ignition. Therefore, the combustion process, particularly in the early cycles of the internal combustion engine, is improved resulting in a reduced pool-fire and therefore in a reduced amount of remaining pollutants, particularly soot and partially burned hydrocarbons. Such method allows decreasing the fuel film mass on the piston of around 40 % to around 90 %, particularly of around 50 % to around 80 %, dependent on the piston temperature shortly before ignition. Consequently, a warm piston around engine starting, i.e. shortly before and / or at and / or shortly after engine starting, may significantly reduce the amount of soot generated during combustion.

[0008] Furthermore, even fuel disposed in a crevasse formed between a piston skirt, the piston top and liner has an increased evaporation rate, which In turn reduces the amount of unburned hydrocarbons. In particular, preheating the piston before ignition, i.e. before engine start cranking allows achieving a significantly reduced amount of pollutants at engine starting. Preheating the piston during the first engine revolutions without ignition and / or during early combustion cycles allows achieving a reduced amount of pollutants, which may be less reduced than the amount of pollutants, when preheating the piston before engine start cranking. In other words, preheating the piston at and / or shortly after engine starting reduces the amount of generated pollutants, but less than preheating the piston before engine start cranking.

[0009] Preheating the piston at and / or shortly after engine start cranking may allow ensuring the preheating of the piston in cases, in which the engine is actually about to be started, and thereby preventing the preheating of the piston in cases, in which the driver opens a door and / or turns the key without the intention of starting the engine, but, e.g., for starting the dashboard, entertainment systems etc.

[0010] In contrast to currently known systems, such as exhaust after treatment systems, this method allows reducing pollutants in emissions of the internal combustion engine proactively. This means, that the method according to the first aspect allows reducing the amount of pollutants generated during ignition instead of reducing pollutants after they have been generated.

[0011] Furthermore, the method may be performed by already existing systems, the function of which is changed to allow preheating the at least one piston before engine start cranking. For example, in modern internal combustion engines, a piston cooling system may be provided, because the pistons may require cooling during high loads. Usually, the piston cooling jets may be activated when necessary using a high pressure mode on the oil pump.

[0012] The oil pump may be a variable pump capable of generating low pressure as well as high pressure. For example, the oil pump may be able to deliver oil at low pressure of around 2 bar during a normal load mode of the internal combustion engine, which is sufficient for lubricating the working parts of the internal combustion engine. Further, the oil pump may be able to deliver oil at high pressure of around 4-5 bar during a high load mode of the internal combustion engine, in which a cooling of the pistons may be needed.

[0013] According to an example, the method may further comprise an oil exchanging process being performed at least once before stopping the pump; the oil exchanging process comprising the following steps, not necessarily in this order: opening the valve of the oil storing unit thereby releasing the stored oil into the oil distribution system; filling the oil storing unit with the predetermined amount of oil by the oil pressure created by the oil pump; and closing the valve of the oil storing unit, thereby storing the predetermined amount of oil under pressure in the oil storing unit.

[0014] Such oil exchanging process may allow storing low temperature oil as soon as the internal combustion engine starts, thereby reducing the total thermal inertia of the internal combustion engine. Then, when the internal combustion engine is warm, the low temperature oil may be released, and warm oil will then be stored. This may correspond to a very efficient way with regard to energy consumption. Further, the oil exchanging process may be performed twice of more times while the internal combustion engine is running.

[0015] According to an example, the step of heating the stored oil to a predetermined temperature and / or the step of maintaining a temperature of the stored oil above a predetermined lower temperature threshold for a predetermined timeframe may be performed by providing external, particularly electrical, heating to the oil storing unit.

[0016] Electrical heating may be performed using electric resistance. Further, the oil storing unit may have insulating characteristics which passively help to maintain the temperature of the stored oil. Additionally, electrical heating may be performed using modern battery technology provided in vehicles, such as the traction battery of a hybrid vehicle or the vehicle battery.

[0017] According to an example, the lower temperature threshold may correspond to a temperature around 90°C to 130°C and / or the predetermined timeframe may correspond to a timespan of at least 36 hours, and particularly around 56 hours. The predetermined timeframe of at least 36 hours results from European emission legislation, and therefore the predetermined timeframe may vary dependent on the respective national and / or regional emission legislation. When impinging the piston bottom with oil at 130°C for about 10 sec, a piston top average temperature may be increased to about 70°C.

[0018] According to an example, the oil storing unit may comprise an opening for introducing and discharging the oil into and out of the oil storing unit, the opening being arranged at a bottom of the oil storing unit.

[0019] By arranging the opening of the oil storing unit at a bottom of the oil storing unit, and particularly at the lowest position possible at the oil storing unit, air being present in the empty oil storing unit may not be able to exit the oil storing unit while oil is introduced or pumped into the oil storing unit. Therefore, the air inside the oil storing unit may be compressed and therefore acting like a biasing member or a pressure element on the oil stored in the oil storing unit. This may result in maintaining the oil pressure, even when the valve may be closed and the oil storing unit may be separated or isolated from the oil distribution system cycling the oil through the internal combustion engine.

[0020] According to an example, the valve may be an electrically operated valve. The electronically operated valve may be simple to control and further, may be controllable by a software performing the method. The valve may be configured to separate or isolate the oil storing unit from the oil distributing system, thereby keeping the oil storing unit pressurized. In other words, one can say that the valve my retain the thermal energy associated with the oil thermal inertia as well as the potential energy associated with the oil pressure.

[0021] According to an example, the oil pressure inside the oil storing unit may be between around 2 bar to around 6 bar, particularly between around 3 bar to around 5 bar.

[0022] Such pressure may be sufficiently high to supply the stored oil to the piston cooling system and to eject the oil by the at least one piston cooling jet towards the at least one piston button without needing a pump. In other words, the pressure inside the oil storing unit may be sufficiently high such that no further element, machines and the like may be needed for supplying the stored oil from the oil storing unit to the at least one piston bottom, when the valve may be opened.

[0023] According to an example, the step of ejecting the oil via the piston cooling jets towards the at least one piston bottom may be performed for around 1 to 15 sec, particularly for around 5 to 10 sec. Such timespan may be sufficient to increase the temperature of the at least one piston top in a manner that the combustion at engine start cranking is improved.

[0024] According to a second aspect, there is provided a system for preheating at least one piston of an internal combustion engine. The system comprises an oil distributing system including an oil sump and an oil pump for distributing oil to engine parts, an oil storing unit and a piston cooling system. The oil storing unit is selectively, and particularly fluidly, connectable to the oil distributing system via a valve, and configured to store oil under pressure. The piston cooling system is connectable to the oil distributing system, and includes at least one piston cooling jet being directed towards at least one piston bottom. The oil storing unit is further configured to heat the stored oil to a predetermined temperature and / or to maintain the predetermined temperature of the stored oil above a lower temperature threshold for a predetermined timeframe. The valve is configured to be open for filling the oil storing unit with oil from the oil distribution system while the oil pump is running, and to be closed when a predetermined amount of oil being stored in the oil storing unit is achieved. Further, the valve is configured to be open at least when an upcoming engine start cranking is detected, for supplying at least a part of the stored oil to the piston cooling jets, and the at least one piston jet is configured to eject the oil towards the at least one piston bottom, thereby preheating the at least one piston before the engine start cranking.

[0025] The system allows preheating the piston shortly before engine start cranking, the evaporation of a liquid fuel film on a piston top at ignition is improved. Therefore, the combustion process is improved resulting in a reduced pool-fire and therefore in a reduced amount of remaining pollutants, particularly soot and partially burned hydrocarbons. Such method allows decreasing the fuel film mass on the piston of around 40 % to around 90 %, particularly of around 50 % to around 80 %, dependent on the piston temperature shortly before ignition. Consequently, a warm piston at engine starting may significantly reduce the amount of soot generated during combustion. Furthermore, even fuel disposed in a crevasse formed between a piston skirt, the piston top and liner has an increased evaporation rate, which In turn reduces the amount of unburned hydrocarbons.

[0026] In contrast to currently known systems, such as exhaust after treatment systems, this system allows reducing pollutants in emissions of the internal combustion engine proactively. This means, that the system according to the second aspect allows reducing the amount of pollutants generated during ignition instead of reducing pollutants after they have been generated.

[0027] Furthermore, the system may use already existing components of the internal combustion engine but at least partly with a different functionality. The expression "before engine start cranking" or "shortly before engine start cranking" corresponds to a timespan of several seconds, e.g. about 5 to 20 sec, before the engine start cranking. An upcoming engine start cranking may be detected by an event usually happening before engine start cranking, such as opening the vehicle, seating of a driver in a driver's seat, inserting a car key into the ignition lock, and the like.

[0028] According to an example, the oil storing unit may be a pressure vessel configured to store the oil under pressure and may comprise an opening for introducing and discharging the oil into and out of the oil storing unit, the opening being arranged at a bottom, and in particular at the lowest point, of the oil storing unit.

[0029] By arranging the opening of the oil storing unit at a bottom of the oil storing unit, and particularly at the lowest position possible at the oil storing unit, air being present in the empty oil storing unit may not be able to exit the oil storing unit while oil is introduced or pumped into the oil storing unit. Therefore, the air inside the oil storing unit may be compressed and therefore acting like a biasing member or a pressure element on the oil stored in the oil storing unit. This may result in pushing the oil out of the oil storing unit when the valve is open and supplying the oil through the oil distributing system, the piston cooling system and the at least one piston cooling jet to the at least one piston bottom. In other words, there is no need for a separate pump configured to actively pump the oil stored in the oil storing unit through the oil distributing system, the piston cooling system and the at least one piston cooling jet to the at least one piston bottom.

[0030] Thus, according to an example, the system may not include an additional pump configured to pump the stored oil, when the oil pump is turned off. The term "additional pump" means a pump which is an separate element independent of the oil pump, wherein pump describes a device configured to move fluids by mechanical action, typically converted from electrical energy into hydraulic energy.

[0031] According to an example, the oil storing unit may be at least partially arranged, and particularly integrated, in the oil sump.

[0032] By at least partially arranging the oil storing unit in the oil sump, a required space for the system may be reduced. In other words, the system packaging may be improved. As an oil volume actively used in the engine is reduced by the amount of oil stored in the oil storing unit, the oil sump may provide sufficient space to accommodate the oil storing unit at least partially.

[0033] According to an example, the oil storing unit may comprise a pressure element configured to keep the oil stored in the oil storing unit pressurized. Further the pressure element may be configured to push the oil stored in the oil storing unit under pressure out of the oil storing unit and to the at least one piston bottom, when the valve is open.

[0034] According to an example, the pressure element may be formed as an air pocket being formed by air inside the empty oil storing unit being compressed by the oil being pumped into the oil storing unit under the oil pressure. Alternatively, the pressure element may be resilient member capable of storing potential energy and configured to release such energy, when the valve is opened, e.g. a spring, an elastic membrane and the like.

[0035] According to an example, the system may be configured to perform a method according to the first aspect.

[0036] According to a third aspect, there is provided a use of a system according to the second aspect to perform a method according to the first aspect.

[0037] It should be noted that the above examples may be combined with each other irrespective of the aspect involved. Accordingly, the method may be combined with structural features and, likewise, the system may be combined with features described above with regard to the method.

[0038] These and other aspects of the present disclosure will become apparent from and elucidated with reference to the embodiments described hereinafter.BRIEF DESCRIPTION OF DRAWINGS

[0039] Exemplary embodiments of the invention will be described in the following with reference to the following drawings. Fig. 1shows a schematic view of an exemplary internal combustion engine comprising a system for preheating at least one piston of the internal combustion engine. Fig. 2shows four schematic views of a fuel film evolution on a piston top at different temperatures. Fig. 3shows a diagram displaying a temperature of a piston top dependent on a time of ejecting warm oil onto a piston bottom. Fig. 4shows a flowchart, schematically illustrating an exemplary method for preheating at least one piston of an internal combustion engine.

[0040] The figures are merely schematic representations and serve only to illustrate embodiments of the invention. Identical or equivalent elements are in principle provided with the same reference signs.DESCRIPTION OF EXAMPLES

[0041] Figure 1 shows an example of an internal combustion engine 100 for a vehicle (not illustrated). The internal combustion engine 100 comprises an oil distributing system 102, an oil storing unit 104 and a piston cooling system 106. The oil distributing system 102 includes an oil sump 108 and an oil pump 110 for distributing oil to parts of the internal combustion engine 100, particularly when the internal combustion engine 100 is running. The oil storing unit 104 is a pressure vessel being selectively connectable to the oil distributing system 102 by a valve 112. The oil storing unit 104 is configured to store oil under pressure, and the valve 112 is configured to be open for filling the oil storing unit 104 with oil (not illustrated) from the oil distributing system 102, while the oil pump 110 is running. Further, the valve 112 is configured to be closed when a predetermined amount of oil being stored in the oil storing unit 104 is achieved, and is configured to be open at least when an upcoming engine start cranking is detected, thereby supplying at least part of the stored oil to the piston cooling system 106.

[0042] The piston cooling system 106 is connectable to the oil distributing system 102, e.g. by one or more valves, and includes at least one, in figure 1 four piston cooling jets 114. The piston cooling jets 114 are configured to eject oil towards at least one piston bottom. The piston cooling system 114 is usually used to eject oil towards the at least one piston bottom for cooling the at least one piston, e.g. in a high load mode of the internal combustion engine. However, the piston cooling system 114 can also be used to eject warm oil towards the at least one piston bottom for warming or preheating the at least one piston, when the piston is cold, e.g., before an upcoming cold start of the internal combustion engine 100. Additionally, the oil distribution system 102 as shown in figure 1 is configured to lubricate bearings 115 inside the internal combustion engine 100.

[0043] Furthermore, the oil storing unit 104 is configured to heat the stored oil to a predetermined temperature and / or to maintain the predetermined temperature of the stored oil above a lower temperature threshold for a predefined timeframe. Therefore, the oil storing unit 104 may have insulating characteristics and / or includes external heating (not illustrated). The oil distributing system 102, the oil storing unit 104, the piston cooling system 106 and the valve 112 form a system 116 for preheating at least one piston (not illustrated).

[0044] Figure 2 shows schematic views of a fuel film evolution on a piston top 118 at different temperatures and a diagram showing the fuel film mass evolution on the piston top for different temperatures graphically. Figures 2(a) and 2(c) illustrate an example of an evolution of the fuel film mass 120 on the piston top 118 having a temperature of around 27°C before an ignition. Figures 2(b) and 2(d) illustrate an example of the evolution of the fuel film mass 120 on the piston top 118 having a temperature of around 77°C before the ignition. The fuel film 120 is formed by deposition on the piston top 118, when fuel being injected during an induction stroke, particularly before ignition, reaches the surfaces of a combustion chamber, and particularly the piston top 118. The injected amount of fuel is the same for all temperatures shown in Figure 2.

[0045] From Figures 2(a) and 2(b), it can be seen that the fuel film mass 120 on the piston top 118 is higher for the piston top 118 having the temperature of around 27°C (Figure 2(a)) than for the piston top 118 having the temperature of around 77°C (Figure 2(b)). This results from limited evaporation rates at low temperatures, i.e., the lower the temperature in the combustion chamber, and particularly of the piston top, the lower the evaporation rate of the fuel being injected into the combustion chamber, and consequently, the larger the fuel film mass 120 formed by deposition on the piston top 118.

[0046] From Figure 2(b), it can be seen that, for the piston top 118 having the temperature of 27°C, part of the fuel film mass 120 is still present on the piston top 118 at ignition. That means that the liquid fuel forming the fuel film mass 120 does not completely evaporate before ignition, resulting in an incomplete combustion process, also known as pool-fire. When the combustion is incomplete, high amounts of pollutants, such as soot and partially burned hydrocarbons, are produced. Since the amount of pollutant emission is strictly regulated by emission legislation, exhaust comprising high amounts of pollutants needs to be cleaned before being discharged into the environment.

[0047] From Figure 2(d), it can be seen that, for the piston top 118 having the temperature of 77°C, low fuel film mass is left on the piston top 118. This means that the liquid fuel forming the fuel film mass 120 almost completely evaporates before ignition resulting in a substantially complete combustion process, resulting in only small amounts of pollutants, such as soot and partially burned hydrocarbons, are produced. Thus, in this case, the exhaust only needs a reduced amount of cleaning afterwards to reduce the amount of soot and partially burned hydrocarbons to an allowable amount.

[0048] Actually, exhaust after treatment systems substantially comprise catalysts and / or filters, which have a high cleaning efficiency at operating temperatures of about 400°C to 600°C. However, at engine start, particularly, at engine cold start, the catalysts and / or filters of the exhaust after treatment systems are cold, and therefore, have a significantly reduced cleaning efficiency, which, in combination with an high amount of generated pollutants, results in that the early driving cycles of the engine generates the largest part of the total emission of a vehicle. Thus, reducing the generated amount of pollutants at cold start of an engine may allow a significant reduction on the loads of the, particularly cold and therefore less efficient, exhaust after treatment systems. Further, reducing the generated amount of pollutants at cold start of the engine may allow significantly reducing the total emission of the vehicle.

[0049] Figure 3 shows an exemplary diagram displaying a temperature of a piston top 118 (see Figure 2) dependent on a timespan of ejecting warm oil onto a piston bottom. The exemplary diagram shows the temperature evolution of the piston top 118 having a temperature of around 20°C at the beginning (0 sec), when being sprayed with oil having a temperature of around 130°C in the piston jet, over time, wherein a first graph displays the evolution of maximum temperatures Tmax achieved in this example and a second graph display the evolution of average temperatures Tavg achieved in this example. From Figure 3, it can be seen that spraying oil having the temperature of around 130°C at the piston bottom for around 10 sec can raise the temperature of the piston top 118 from around 20°C to around 70°C on average.

[0050] Figure 4 shows a flowchart of an exemplary method 200 for preheating at least one piston of an internal combustion engine 100, wherein the internal combustion engine 100 at least comprises an oil distributing system 102 including an oil sump 108 and an oil pump 110 for distributing oil to engine parts, an oil storing unit 104 and a piston cooling system 106 (see Figure 1). The method 200 comprises the following steps, not necessarily in this order: In a step S1, the oil pump 110 is started, e.g. by starting the engine, thereby creating an oil pressure in the oil distribution system 102. In a step S2, the valve 112 of the oil storing unit 104 is opened, thereby filling the oil storing unit 104 with a predetermined amount of oil by the oil pressure created by the oil pump 110. In a step S3, the valve 112 of the oil storing unit is closed, thereby storing the predetermined amount of oil under pressure in the oil storing unit 104. In a step S4, the oil pump 110 is stopped, e.g. by turning the internal combustion engine 100 off. In a step S5, the stored oil is heated to a predetermined temperature and / or in a step S6 the predetermined temperature of the stored oil is maintained above a predetermined lower temperature threshold for a predetermined timeframe, i.e. after the engine being turned off. In a step S7, the valve 112 of the oil storing unit 104 is opened, when an upcoming engine start cranking is detected, thereby releasing the stored oil into the piston cooling system 106. In a step S8, the stored oil is supplied to the piston cooling jets, particularly only by the pressure present in the oil storing unit 104, and in a step S9, the oil is ejected via the at least one piston cooling jet towards the at least one piston bottom, thereby preheating the at least one piston before the engine start cranking.LIST OF REFERENCE SIGNS

[0051] 100internal combustion engine 102oil distributing system 104oil storing unit 106piston cooling system 108oil sump 110oil pump 112valve 114piston cooling jet 115bearing 116system 118piston top 120fuel film mass 200method Tmaxmaximum temperature Tavgaverage temperature

Claims

1. A method (200) for preheating at least one piston of an internal combustion engine (100), the internal combustion engine (100) at least comprising: an oil distributing system (102) including an oil sump (108) and an oil pump (110) for distributing oil to engine parts, an oil storing unit (104) being selectively connectable to the oil distributing system (102) via a valve (112) and configured to store oil under pressure, and a piston cooling system (106) being connectable to the oil distributing system (102), and including at least one piston cooling jet (114) being directed towards at least one piston bottom, the method (200) comprising the following steps: starting the oil pump (110), thereby creating an oil pressure in the oil distribution system (102), opening the valve (112) of the oil storing unit (104), thereby filling the oil storing unit (104) with a predetermined amount of oil by the oil pressure created by the oil pump (110), closing the valve (112) of the oil storing unit (104), thereby storing the predetermined amount of oil under pressure in the oil storing unit (104), stopping the oil pump (110); heating the stored oil to a predetermined temperature and / or maintaining the predetermined temperature of the stored oil above a predetermined lower temperature threshold for a predetermined timeframe, opening the valve (112) of the oil storing unit (104), when a an upcoming engine start cranking is detected, thereby releasing the stored oil into the piston cooling system (106); supplying the stored oil to the at least one piston cooling jet (114), and ejecting the oil via the at least one piston cooling jet (114) towards the at least one piston bottom, thereby preheating the at least one piston before the engine start cranking.

2. The method (200) according to claim 1, further comprising an oil exchanging process being performed at least once before stopping the oil pump (110); the oil exchanging process comprising: opening the valve (112) of the oil storing unit (104) thereby releasing the stored oil into the oil distribution system (102); filling the oil storing unit (104) with the predetermined amount of oil by the oil pressure created by the oil pump (110); and closing the valve (112) of the oil storing unit (104), thereby storing the predetermined amount of oil under pressure in the oil storing unit (104).

3. The method (200) according to claim 1 or 2, the step of heating the stored oil to a predetermined temperature and / or the step of maintaining a temperature of the stored oil above a predetermined lower temperature threshold for a predetermined timeframe being performed by providing external, particularly electrical, heating to the oil storing unit (104).

4. The method (200) according to any of claims 1 to 3, the lower temperature threshold corresponding to a temperature around 90°C to 130°C and / or the predetermined timeframe corresponding to a timespan of at least 36 hours.

5. The method (200) according to any of claims 1 to 4, the oil storing unit (104) comprising an opening for introducing and discharging the oil into and out of the oil storing unit (104), the opening being arranged at a bottom of the oil storing unit (104).

6. The method (200) according to any of claims 1 to 5, the valve (112) being an electrically operated valve.

7. The method (200) according to any of claims 1 to 6, the oil pressure inside the oil storing unit (104) being between around 2 bar to around 6 bar, particularly between around 3 bar to around 5 bar.

8. The method (200) according to any of claims 1 to 7, the step of ejecting the oil via the at least one piston cooling jet (114) towards the at least one piston bottom being performed for around 1 to 15 sec, particularly for around 5 to 10 sec.

9. A system (116) for preheating at least one piston of an internal combustion engine (100), comprising: an oil distributing system (102) including an oil sump (108) and an oil pump (110) for distributing oil to engine parts, an oil storing unit (104) being selectively connectable to the oil distributing system (102) via a valve (112), and configured to store oil under pressure, and a piston cooling system (106) being connectable to the oil distributing system (102), and including at least one piston cooling jet (114) being directed towards at least one piston bottom, the oil storing unit (104) being further configured to heat the stored oil to a predetermined temperature and / or to maintain the predetermined temperature of the stored oil above a lower temperature threshold for a predetermined timeframe, the valve (112) being configured to be open for filling the oil storing unit (104) with oil from the oil distribution system (102) while the oil pump (110) is running, the valve (112) being configured to be closed when a predetermined amount of oil being stored in the oil storing unit (104) is achieved, the valve (112) being configured to be open at least when a upcoming engine start cranking is detected, for supplying at least a part of the stored oil to the at least one piston cooling jet (114), and the at least one piston jet (114) being configured to eject the oil towards the at least one piston bottom, thereby preheating the at least one piston before the engine start cranking.

10. The system (116) according to claim 9, the oil storing unit (104) being a pressure vessel configured to store the oil under pressure and comprising an opening for introducing and discharging the oil into and out of the oil storing unit (104), the opening being arranged at a bottom of the oil storing unit (104).

11. The system (116) according to any of claims 9 to 10, the oil storing unit (104) being at least partially arranged in the oil sump (108).

12. The system (116) according to any of claims 9 to 11, the oil storing unit (104) comprising a pressure element configured to keep the oil stored in the oil storing unit (104) pressurized.

13. The system (116) according to claim 12, the pressure element comprising an air pocket being formed by the air inside the empty oil storing unit (104) being compressed by the oil being pumped into the oil storing unit (104).

14. The system (116) according to any of claims 9 to 13, the system (116) being configured to perform a method (200) according to any of claims 1 to 8.

15. A use of a system (116) according to any of claims 9 to 13 to perform a method (200) according to any of claims 1 to 8.