Method for operating an internal combustion engine

Abstract

Method for operating an internal combustion engine with the following steps - Providing a fuel (2) - converting a portion of the fuel into a first adapted fuel during operation of the internal combustion engine, wherein the first adapted fuel (7) has a lower ignitability than the unmodified fuel (2) - converting part of the fuel into a second adapted fuel with a higher ignitability (7) than the first adapted fuel during operation of the internal combustion engine, the second adapted fuel (7) having a lower ignitability than the unmodified fuel (2), - Supply of the first adapted fuel (7) with lower ignitability to a cylinder (1) of the internal combustion engine - supplying the second adapted fuel (7) with higher ignitability to the cylinder (1) of the internal combustion engine, in particular for triggering the ignition, wherein the supply of the second adapted fuel (7) to the cylinder takes place during the compression tract of the first adapted fuel in the cylinder, - Driving a piston (9) of the internal combustion engine by the ignition.

Description

[0001] The application relates to a method for operating an internal combustion engine. These are spark-ignited or compression-ignited internal combustion engines with at least one cylinder. The cylinder contains a piston driven by the ignition of a fuel-air mixture. State of the art

[0002] Such internal combustion engines are widespread. Where thermodynamically possible, high levels of efficiency are achieved, particularly with diesel engines. However, this is usually accompanied by increased emissions of soot particles and nitrogen oxides. These must be removed from the exhaust gases using complex exhaust gas purification systems.

[0003] In many cases, fuels – often referred to as fuels in the context of combustion engines – are vaporized and / or converted in order to achieve efficient and low-emission combustion.

[0004] DE 10 2010 012 945 A1 discloses a device for vaporizing liquid fuels. It includes a central air supply that is axially and radially permeable to air. A catalyst system is arranged concentrically around the air supply over at least part of its length. A buffer zone is arranged concentrically around this, around which an absorbent material for fuel distribution is arranged concentrically.

[0005] DE 34 42 628 A1 discloses feeding a lean mixture into a cylinder of an internal combustion engine and introducing a richer mixture or fuel at the end of compression. This then allows ignition.

[0006] WO 2017 / 085301 A1 discloses a method for adjusting the ignition properties of a fuel, using a unit comprising at least one distribution zone, at least one oxidation zone, and at least one conversion zone. Fuel is distributed in the distribution zone, which has a distribution structure. In the oxidation zone, at least a portion of the fuel is oxidized with at least one oxidizing agent on at least one catalyst on a catalyst support. In the conversion zone, at least a portion of the distributed fuel and / or another supplied fuel is thermally and / or catalytically converted.The process is characterized in that the ignition properties of the fuel are adjusted by the molar ratio of oxygen contained in the oxidizing agent to the oxygen required for the complete oxidation of the existing fuel, and / or the pressure in the unit and / or the residence time and / or the temperature.

[0007] From US 2005 / 0 011 486 A1, it is known to convert part of the fuel during operation of an internal combustion engine to produce a more ignitable fuel. The converted fuel is used to ignite the unconverted fuel.

[0008] WO 2004 / 036015 A1 discloses an HCCI engine in which a portion of the fuel is catalytically converted. The combustion timing is adjusted depending on engine parameters, among other things, by selecting the ratio of converted fuel, unconverted fuel, and air.

[0009] From Simon-Florian Haas's 2007 dissertation "Experimental and Theoretical Investigation of Homogeneous and Partially Homogeneous Diesel Combustion Processes" at the University of Stuttgart, it is known, among other things, to operate an internal combustion engine with different fuels, i.e., a first fuel and a second fuel. The first fuel is supplied to a cylinder of the internal combustion engine. The second fuel is supplied to the cylinder during the compression stroke of the first fuel in the cylinder. It is also mentioned that non-ignitable n-butane is provided as the first fuel and ignitable diesel fuel is provided as the second fuel.

[0010] DE 10 2015 120 106 A1 discloses a method for adjusting the ignition properties of a fuel, which utilizes a unit comprising at least one distribution zone, at least one oxidation zone, and at least one conversion zone. Fuel is distributed in the distribution zone, which has a distribution structure. In the oxidation zone, at least a portion of the fuel is oxidized with at least one oxidizing agent on at least one catalyst on a catalyst support. In the conversion zone, at least a portion of the distributed fuel and / or another supplied fuel is thermally and / or catalytically converted.The process is characterized in that the ignition properties of the fuel are adjusted by the molar ratio of oxygen contained in the oxidizing agent to the oxygen required for the complete oxidation of the existing fuel, and / or the pressure in the unit and / or the residence time and / or the temperature.

[0011] Furthermore, DE 10 2014 002 905 A1 describes a combustion method for use with a gas engine. The gas engine is configured with a main combustion chamber and a fuel-purged prechamber, which is connected to the main combustion chamber via at least one overflow opening. The gas engine is configured to combust a gaseous fuel-air mixture in the main combustion chamber. To ignite the gaseous fuel-air mixture in the main combustion chamber, a liquid gasoline is injected into the prechamber and ignited therein by an ignition device.

[0012] DE 10 2005 056 479 A1 also relates to a method and a corresponding device for operating an internal combustion engine. The object of this invention is to provide a method and a corresponding device for operating an internal combustion engine, with which fuel can be supplied to a combustion chamber of the internal combustion engine, with which, depending on the operating point, an optimal combustion process is achieved in terms of efficiency, exhaust gas, and noise emissions, and in which the fuel is modified individually or in several parts in such a way that it has a limited boiling point range at low temperatures, wide ignition limits, a high energy density, a self-ignition temperature above the boiling point, high knock resistance during high-load operation, good self-ignition capability in the partial-load range, and a high flame front burn-through speed.According to the invention, this is achieved by changing the properties of a commercially available liquid fuel close to the engine by thermal and / or catalytic molecular conversion and / or separation, depending on the current operating state of the internal combustion engine, whereby optimal combustion with regard to emissions and consumption of the fuel introduced into the combustion chamber of the internal combustion engine with the combustion air introduced into the combustion chamber is achieved.

[0013] US 2005 / 0 011 486 A1 relates to a method for controlling the ignition in an HCCI engine (Homogene Charge Compression Ignition) by injecting a pilot fuel in conjunction with a main fuel.

[0014] The system and method of this invention can be used advantageously in diesel engines and particularly in locomotive engines as well as in any other reciprocating piston engine.

[0015] DE 11 2013 002 524 T5 describes further methods and systems for a vehicle engine. In one example, the method comprises supplying a first fuel to an engine cylinder at least partially during an intake stroke and initiating combustion in the cylinder via an injection of a second fuel into the cylinder. In response to an indication of uncontrolled combustion of premixed first fuel and air, wherein the uncontrolled combustion is initiated by the initiated combustion of the second fuel, the amounts of the first fuel relative to the second fuel in the cylinder are adjusted.

[0016] DE 10 2010 012 945 A1 relates to a device for vaporizing liquid fuels and / or combustibles. The device comprises a catalyst system arranged in a concentrated manner around an air inlet, as well as a porous material arranged concentrically around this catalyst system, which can absorb the fuel and / or combustible material. The porous material is separated from the catalyst system by an intermediate space. Furthermore, the device comprises a gas-tight seal that seals the components arranged concentrically around the air inlet on one side and closes them off from the air supply. Object of the invention and general solution

[0017] The object of the present invention is to provide a method for operating an internal combustion engine in such a way that, on the one hand, high efficiency is achieved and, on the other hand, low pollutant emissions. The invention also relates to a control unit designed to carry out the method and to an internal combustion engine with a conversion unit.

[0018] It was recognized that a method for operating an internal combustion engine with the following steps is useful for this purpose: First, a fuel must be provided. Various fuels are conceivable. The fuel can be selected from the following groups: diesel, gasoline, fuels with additives, electricity-based fuels (so-called power-to-liquid fuels, such as Fischer-Tropsch fuels, oxymethylene ether, methyl formate, dimethyl carbonates), alcohol, especially ethanol, ethers, ketones, biofuels (octanol, biodiesel), propane, butane, methane, etc., as well as blends and mixtures. This list is intended to make it clear that a wide variety of fuels are conceivable.

[0019] In practice, fuel preparation means that the fuel is fed from a tank, usually provided, to the combustion engine. More specifically, the portion of the fuel to be converted must first be fed to a conversion unit where its ignition properties can be adjusted or modified. The modified or adjusted fuel has different ignition properties than the original fuel. The modified fuel is mixed with the combustion air. The ignition properties are modified in such a way that premature ignition does not occur during compression. The fuel-air mixture is then ignited via diesel direct injection or a spark plug.

[0020] Furthermore, a conversion of part of the fuel into an adapted fuel is planned during operation of the internal combustion engine, whereby the adapted fuel has a lower ignitability than the unmodified fuel. The statement that this takes place during operation of the internal combustion engine is not intended to rule out the possibility that the conversion may begin before the internal combustion engine starts operating, or that the conversion may continue during short breaks in operation - for example, when a vehicle is stopped at a traffic light - or for a short period of time after the internal combustion engine has been switched off. However, a distinction should be made between this and dual-fuel technology, in which an adapted fuel is produced from one fuel in a refinery, for example, and two tanks are provided for the internal combustion engine, i.e., one tank for the adapted fuel and one tank for the unmodified fuel.Dual-fuel technology is well known, and numerous publications confirm that it can reduce emissions. Typically, two fuels with different fuel properties are carried separately. According to the invention, only a single fuel is carried to achieve this goal. In addition to the logistical considerations that make refueling and carrying two fuels difficult, especially in a motor vehicle, there is another key technical consideration. During conversion, the fuel is generally not only converted but also vaporized. Therefore, due to the high volume of the gaseous fuel, it is not possible to store any significant amount of the converted fuel in a motor vehicle if one wants to avoid complex and energy-consuming compression. Therefore, the conversion must take place while the internal combustion engine is running.

[0021] In this case, the focus is on a conversion, particularly a catalytic conversion, of the fuel. This differs from, for example, DE 34 42 628 A1 mentioned above. The success in pollutant reduction appears to be primarily attributable to the conversion.

[0022] It should also be noted that in this case, conversion to a fuel with lower ignitability is envisaged. The approach described above in US 2005 / 0 011 486 A1 may be advantageous in many cases. However, it has been shown that the goal of "low pollutant emissions and high efficiency" can be successfully achieved with the approach pursued here.

[0023] Furthermore, the adjusted fuel must be supplied to a cylinder of the internal combustion engine. For the sake of clarity, we will always refer to one cylinder. Of course, the method is generally used in internal combustion engines with multiple cylinders. Since the same thing happens in all cylinders—at least with regard to the present invention—we will not illustrate any additional cylinders here.

[0024] Likewise, unaltered fuel must be supplied to the cylinder of the internal combustion engine, especially to trigger the ignition. It is therefore possible to operate the internal combustion engine in such a way that, without the supply of unaltered fuel, no ignition or an unsatisfactory ignition would occur. This is precisely what enables efficient and low-emission ignition. However, ignition can also be achieved by an ignition electrode (spark ignition).

[0025] The supply of unmodified fuel to the cylinder occurs during the compression phase in the cylinder. The injection timing of the unmodified fuel is selected to ensure optimized operation in terms of emissions and consumption. Particularly when there is no ignition device and ignition is to be triggered solely by the supply of unmodified fuel, this results from the normal operation of the internal combustion engine, in which ignition occurs when the piston is in the "upper" region. In common illustrations and the usual installation position, this is actually at the top; although this is often technically advantageous, it is not mandatory. Nevertheless, the upper region should be referred to. Accordingly, the point at which the piston changes its direction of movement is technically referred to as top dead center.

[0026] As usual, the piston of the internal combustion engine is driven by the ignition.

[0027] In a further embodiment, the unmodified fuel is converted into at least two batches of the modified fuel, which differ in their ignitability, but the ignitability of the two batches is always lower than the ignitability of the unmodified fuel. Thus, a first modified fuel with lower ignitability and a second modified fuel with higher ignitability are provided.

[0028] Furthermore, the first adapted fuel must be supplied to a cylinder of the internal combustion engine. Likewise, the second adapted fuel must be supplied to the cylinder of the internal combustion engine, in particular to trigger the ignition.

[0029] It is therefore possible to operate the combustion engine in such a way that, without the addition of the second, adapted fuel with higher ignitability, no ignition or only unsatisfactory ignition would occur. This is precisely what enables efficient and low-emission ignition. However, ignition can also be achieved using an ignition electrode (spark ignition).

[0030] The second, adapted fuel is supplied to the cylinder during the compression phase. The injection timing of the second, adapted fuel is selected to ensure optimized operation in terms of emissions and consumption. Particularly when no ignition device is present and ignition is to be triggered solely by the supply of the second, adapted fuel, this results from the normal operation of the internal combustion engine, in which ignition occurs when the piston is in the "upper" range.

[0031] As usual, the piston of the internal combustion engine is driven by the ignition.

[0032] In most embodiments, no modification to the internal combustion engine is required to implement the method, apart from the fuel conversion unit. For example, in a conventional diesel engine, the combustion air is compressed, and diesel is injected at the end of compression. If, in this case, adapted fuel, which is normally in gaseous form, is mixed with the combustion air and fed into the cylinder, and diesel is also injected at the end of compression—albeit in a smaller quantity, since adapted fuel has already been introduced into the cylinder—then the same internal combustion engine can be used. Only the control system needs to be adapted, which can be achieved, for example, by updating the engine control software.This means that the method according to the invention can be carried out by means of a manageable retrofitting, namely the installation of a unit for converting the fuel into an adapted fuel and an update of the engine control software.

[0033] This is a crucial aspect, since many existing diesel-powered vehicles produce unacceptable, or at least undesirable, pollutant emissions. The present invention allows a solution to this problem with reasonable effort.

[0034] In one embodiment, the ratio between unmodified fuel and modified fuel is selected depending on the operating state of the combustion engine. This allows combustion to be optimized. For example, at low power, it may be advisable to convert relatively less fuel in order to still inject enough unmodified fuel to trigger ignition.

[0035] While it is known from WO 2004 / 036015 A1, mentioned above, that the ignition timing can be influenced by selecting the ratio of converted to unconverted fuel, there is no teaching that this can be achieved by supplying the unaltered fuel. In the present case, the ignition timing is also significantly determined by the time of supply of the unaltered fuel, unless the ignition is provided by an additional ignition device.

[0036] In an important embodiment, the process is operated in such a way that pollutant emissions, in particular the emission of particulate matter and / or nitrogen oxides, and / or fuel consumption are minimized. There are often conflicting objectives between the goals of reducing fuel consumption and reducing pollutant emissions.

[0037] High combustion temperatures are advantageous for high efficiency. High combustion temperatures are also beneficial for reducing the formation of soot particles. However, high combustion temperatures also promote the formation of nitrogen oxides. This example is intended to demonstrate that minimizing pollutant emissions and fuel consumption cannot usually be achieved effectively by aiming to minimize one pollutant without considering other pollutants and fuel consumption. Rather, optimization must be carried out taking all relevant parameters into account. The reduction of carbon dioxide emissions is not mentioned as a goal here, as this is achieved anyway by reducing fuel consumption. It should be noted that the reduction of fuel consumption is not the focus here, as efficiency is often largely optimized.A currently pressing problem is pollutant emissions, which, according to current knowledge, lead to non-negligible health problems.

[0038] In one embodiment, the adapted fuel is mixed with the air intended for combustion to form a charge gas. The adapted fuel is supplied by feeding the charge gas into the cylinder of the internal combustion engine. After conversion, the fuel is usually in gaseous form. This makes it possible to introduce the adapted fuel together with the combustion air. This often leads to improved mixing of the adapted fuel and combustion air. This improved mixture formation can reduce harmful soot and NOx emissions within the engine. This also allows an unchanged cylinder structure. The combustion air must be supplied in any case. Therefore, no changes to the cylinder structure are necessary.

[0039] In one embodiment, the timing of the supply of unaltered fuel relative to the position of the piston in the cylinder is selected depending on the operating state of the internal combustion engine. As already mentioned, it is clear that ignition must occur when the piston is in the "upper" range, i.e., the mixture to be ignited—whatever it is—is compressed.

[0040] The optimal ignition timing also depends on the operating condition of the combustion engine. Therefore, it is advisable to consider not only the position of the piston in the cylinder but also the operating condition of the combustion engine.

[0041] In one embodiment, an ignition device, in particular a spark plug, is provided for ignition. Although ignition can usually be triggered satisfactorily by injecting unaltered fuel, it may sometimes be helpful to provide an ignition device. Although many types of ignition devices, such as ignition lasers and the like, are conceivable, a spark plug is generally suitable.

[0042] In one embodiment, the fuel is converted into the adapted fuel in such a way that the adapted fuel exhibits desired properties depending on the operating state of the internal combustion engine. For example, at high power levels of the internal combustion engine, where more fuel is to be burned in a single ignition to provide the corresponding energy, the fuel can be converted in such a way that even with a fuel-rich charge gas, self-ignition does not occur due to compression.

[0043] At this point, however, it should be noted that the converted fuel can exhibit the same properties in all operating conditions. Therefore, it is always advisable to operate the combustion engine in such a way that the mixture of adapted fuel and combustion air does not ignite spontaneously due to compression. However, fulfilling this condition is sufficient, so the exact ignition quality of the fuel is often irrelevant. This is not to say, however, that converting the fuel into adapted fuel, dependent on the operating condition of the combustion engine, would be completely unnecessary.

[0044] The invention also relates to a control unit designed to control an internal combustion engine using the method described above. As already explained above, the unmodified internal combustion engine can often be used. Accordingly, only minor modifications to the control unit are usually required. Reprogramming is usually sufficient. Of course, a device for controlling the unit to convert the fuel into an adapted fuel is also required.

[0045] In one embodiment, the control unit has a first module and a second module, the first module being a known control unit for a known internal combustion engine, and the second module serving to configure the control unit for carrying out the method described above. This modular design is particularly useful for retrofitting, such as the above-described retrofitting of a motor vehicle with a diesel engine. The first module can be the existing control unit for the diesel engine, which simply needs to be reprogrammed. The second module has the task of controlling the unit for converting part of the fuel into adapted fuel. For this purpose, certain parameters, such as the power and speed of the internal combustion engine, are logically transferred from the first module to the second module. Since this data is already available in the first module, this does not pose a problem.

[0046] The invention also relates to an internal combustion engine, in particular a diesel engine, with a device for supplying fuel to a cylinder, - a conversion unit to convert part of the fuel into fuel with lower ignitability, - a device for supplying adapted fuel, - a device for supplying combustion air to the cylinder, wherein the device for supplying adapted fuel and for supplying combustion air can be combined; designed to carry out the method described above.

[0047] The combustion engine will not be described in detail here, as this has already been done by describing the process and the control unit.

[0048] In a particular embodiment, the converted fuel undergoes reliquefaction after conversion, i.e., the gaseous components are mixed with the combustion air as described above. The reliquefied fuel residue can either be mixed with the unaltered fuel or collected separately. In both cases, the reliquefied fuel residue is injected into the cylinder. In both cases, both the gaseous portion of the modified fuel and the reliquefied fuel residue have lower ignitability than the unaltered fuel. Reliquefaction is performed using a customized cooling unit. Character description

[0049] Further details will be explained using figures. Fig. 1 a representation of a cylinder during intake of charge air with a supply of unchanged and adjusted fuel, combustion air and a conversion unit for fuel Fig. 2 the cylinder during compression of the charge gas in the cylinder Fig. 3 the cylinder after ignition Fig. 4 the cylinder during the removal of exhaust gas

[0050] Fig. 1 shows a cylinder 1. The fuel used is diesel, which is supplied through a fuel line 2 from a tank (not shown). The majority of the fuel is fed through line 3 to a conversion unit 4. Air from the intake line 5 is also fed to the conversion unit 4 through an air branch line 6. In the conversion unit 4, the diesel is oxidized and converted using the air supplied through the air branch line 6. This produces a modified fuel 7 with lower ignitability than diesel, which is mixed with the air to produce charge gas 8.

[0051] In the Fig. In the operating phase of cylinder 1 shown in Figure 1, a piston 9 moves downward. An exhaust valve 10 located at the top right is closed, while an intake valve 11 located at the top left is open. This draws charge gas 8, a homogeneous combustible mixture of adapted fuel 7 and combustion air 5, into cylinder 1.

[0052] At the Fig. The conversion unit described in paragraph 4 may be a device for the catalytic conversion of fuel, as described in WO 2017 / 085301 A1 mentioned at the beginning.

[0053] The following described Fig. 2, Fig. 3 and Fig. 4 are for Fig. 1 are largely identical, so only the respective differences are described.

[0054] Fig. 2 shows the Fig. 1 subsequent operating phase, in which piston 9 moves upward. Exhaust valve 10 and intake valve 11 are closed during this time. This compresses the charge gas 8. Due to the low ignitability achieved by the conversion in the conversion unit 4, no auto-ignition occurs due to the compression.

[0055] When the piston 9 has reached the top, diesel is fed through the fuel line 2 to an injector 12 and injected into the cylinder 1. This triggers the ignition.

[0056] As in Fig. As can be seen in Figure 3, the ignition and the resulting expansion push piston 9 downward, thereby transferring power to a crankshaft (not shown). It is understood that exhaust valve 10 and intake valve 11 remain closed during this process.

[0057] Fig. Finally, Figure 4 shows piston 9 moving upwards again after the downward movement caused by ignition, with the exhaust valve 10 open and the intake valve 11 closed. This discharges the exhaust gas produced during ignition via the exhaust line 13. When operated properly, this exhaust gas contains significantly fewer pollutants than the exhaust gas of a conventional diesel engine.

[0058] The one in the Fig. 1 to Fig. The section shown within the dashed area in Figure 4 is constructed like a conventional diesel engine. This clearly demonstrates that a conventional diesel engine can be retrofitted with manageable effort. List of reference symbols 1 cylinder 2 Fuel supply 3 Fuel supply to the conversion unit 4 Conversion unit 5 Air supply 6 Air supply to the conversion unit 7 adapted fuel 8 Charging gas 9 pistons 10 Exhaust valve 11 Inlet valve 12 Injector nozzle 13 Exhaust pipe

Claims

[1] Method for operating an internal combustion engine with the following steps - Providing a fuel (2) - converting a portion of the fuel into a first adapted fuel during operation of the internal combustion engine, wherein the first adapted fuel (7) has a lower ignitability than the unmodified fuel (2) - converting part of the fuel into a second adapted fuel with a higher ignitability (7) than the first adapted fuel during operation of the internal combustion engine, the second adapted fuel (7) having a lower ignitability than the unmodified fuel (2), - Supply of the first adapted fuel (7) with lower ignitability to a cylinder (1) of the internal combustion engine - supplying the second adapted fuel (7) with higher ignitability to the cylinder (1) of the internal combustion engine, in particular for triggering the ignition, wherein the supply of the second adapted fuel (7) to the cylinder takes place during the compression tract of the first adapted fuel in the cylinder, - Driving a piston (9) of the internal combustion engine by the ignition. [2] Method according to claim 1, characterized by that the process is operated in such a way that pollutant emissions, in particular the emission of particulate matter and / or nitrogen oxides, and / or fuel consumption are minimised. [3] Method according to one of the preceding claims, characterized by that the time of supply of the second adapted fuel (7) relative to the position of the piston (9) in the cylinder (1) is selected depending on the operating state of the internal combustion engine. [4] Method according to one of the preceding claims, characterized bythat an ignition device, in particular a spark plug, is provided for ignition. [5] Method according to one of the preceding claims, characterized by that the conversion of fuel (2) into the first and / or second adapted fuel (7) takes place in such a way that the first and / or second adapted fuel has desired properties depending on the operating state of the internal combustion engine. [6] Control unit designed to control an internal combustion engine using a method according to one of the preceding claims.

Images