internal combustion engine

Abstract

Internal combustion engine with at least one main combustion chamber (1) for burning a first fuel mixture (BG1), at least one pre-combustion chamber (2) per main combustion chamber (1) for burning a second fuel mixture (BG2), a first fuel gas mixer (24) for providing the first fuel mixture (BG1), which is connected to a fuel supply line (4) and an air supply line (5), a second fuel gas mixer (25) for providing the second fuel mixture (BG2), which is connected to a fuel supply line (4), an air supply line (5) and a synthesis gas supply line (6), and a first mixture line (10) which is connected to the first fuel gas mixer (24) and the main combustion chamber (1), a second mixture line (10') which is connected to the second fuel gas mixer (25) and the pre-combustion chamber (2), wherein the pre-combustion chamber (2) has at least one through-opening (33) into the main combustion chamber (1), wherein the first fuel gas mixer (24) for the addition of synthesis gas (S) is connected to the synthesis gas supply line (6) and that a control device (31) or a regulating device (31) for controlling or regulating mixing ratios of fuel, air and synthesis gas in the first combustion mixture (BG1) and / or in the second combustion mixture (BG2) is provided, which is connected to the first fuel gas mixer (24) and / or to the second fuel gas mixer (25).

Description

[0001] The present invention relates to an internal combustion engine having the features of the preamble of claim 1 and to a method for operating such an internal combustion engine.

[0002] It is known that in an internal combustion engine with a main combustion chamber and a pre-combustion chamber, synthesis gas from a reformer is supplied to the pre-combustion chamber. Since the synthesis gas contains hydrogen, this improves the ignition behavior of the internal combustion engine.

[0003] In WO 2008 / 150370 A1, an internal combustion engine with exhaust gas recirculation is disclosed, whereby the exhaust gas is reformed together with fuel in a reformer to produce synthesis gas. This serves to reduce undesirable emissions in the exhaust gas of the internal combustion engine.

[0004] Utilizing both of the positive effects described above is difficult because the optimal proportion of synthesis gas in the fuel gas differs depending on the combustion engine's operating point. Furthermore, the use of synthesis gas in gas engines is limited by auto-ignition events, which depend on the gas composition (H2, CO, CH4, hydrocarbons with three or more carbon atoms, and water vapor) and engine operation (power output, turbocharging, etc.), as well as by knocking, which also depends on the gas composition.

[0005] US patent 2004 / 0045514 A1 discloses an internal combustion engine in which processed reaction products from a reformer are fed to both the main combustion chamber and the pre-combustion chamber, with the aim of giving the liquid fuel for the main combustion chamber a high octane rating and improving ignition.

[0006] US 6 739 289 B2 discloses a method and a device for supplying a hydrogen-enriched fuel to a combustion pre-chamber, comprising reforming a quantity of fuel to produce a hydrogen-enriched fuel, supplying the reformed fuel to the combustion pre-chamber, and combining the hydrogen-enriched fuel with a fuel / air mixture to a ratio below stoichiometry.

[0007] US 3 809 039 A discloses an ignition system and a method for its operation, in which a first fuel-air mixture is directed into a pre-chamber of the engine and a second, leaner fuel-air mixture is directed into a main combustion chamber, the first mixture is ignited to ignite the second mixture, and during operation of the engine at more than about 75 percent of the maximum power output, about 5 to about 20 percent of the exhaust gas produced during the combustion of the fuel mixtures is mixed with the second fuel-air mixture in a controlled manner, wherein the amount of exhaust gas mixed with the second fuel-air mixture is directly proportional to the power output of the engine.

[0008] The object of the present invention is to make optimal use of the two positive effects described above and to eliminate the aforementioned limitations completely or partially.

[0009] This problem is solved by an internal combustion engine having the features of claim 1 and a method having the features of claim 8.

[0010] This is achieved, on the one hand, by supplying at least a portion of synthesis gas not only to the pre-combustion chamber but also to the main combustion chamber, and on the other hand, by ensuring that – preferably depending on the operating point of the combustion engine – the fuel gas compositions for the main combustion chamber and the pre-combustion chamber can be adjusted independently of each other by means of two separate fuel gas mixers.

[0011] By regulating or controlling the proportion of synthesis gas, the optimal operating point for the combustion engine can be achieved. This results, on the one hand, from the increase in combustion efficiency of the engine with increasing synthesis gas proportion, i.e., increasing hydrogen content in the fuel gas. On the other hand, the energy efficiency of the plant decreases with a higher synthesis gas proportion, since greater losses occur in the reformer. This relationship is described in Fig. 2 clarifies.

[0012] Further advantageous embodiments of the invention are defined in the dependent claims.

[0013] To provide the control unit or regulating device with as much information as possible regarding the engine's condition, flow meters can be installed in the fuel supply line, air supply line, exhaust line, steam supply line, and / or synthesis gas supply line, and connected to the regulating device or regulating device. The flow meters can also be designed as flow control valves, which, in addition to flow measurement, feature a control valve and a feedback loop.

[0014] Preferably, the control unit or regulating device allows for the calculation of target mixture ratios, and the mixture ratios of fuel, air, and / or synthesis gas in the first and second fuel mixture units of the internal combustion engine can be regulated or controlled according to these target mixture ratios. The target mixture ratios differ depending on the operating point and application, as well as, of course, between the main combustion chamber and the pre-combustion chamber of the engine.

[0015] By adjusting the fuel gas composition to a specific application (high engine power, high engine efficiency, low emissions), optimal engine operation should be achieved depending on the fuel used and the emission requirements. It is advantageous if the proportions of hydrogen, carbon monoxide, methane, and higher hydrocarbons are adjusted within certain concentration limits.

[0016] For example, to optimize a gas engine for the lowest possible pollutant emissions, the initial fuel mixture for the main combustion chamber (target fuel gas composition) can contain 20% to 30% hydrogen and 5% to 10% carbon monoxide. (All percentages refer to volume fractions.)

[0017] A second example is a gas engine designed to run on fuel containing not only methane but also higher hydrocarbons, where the goal is to achieve the highest possible engine power. In this case, the target fuel gas composition of the first combustion mixture can contain 35% to 45% hydrogen, 5% to 10% carbon monoxide, and a maximum of 5% higher hydrocarbons.

[0018] For improved ignition performance and emission reduction of a gas engine, the target fuel gas composition of the second combustion mixture for the pre-combustion chamber can contain 25% to 40% hydrogen, 5% to 10% carbon monoxide and 20% to 30% methane.

[0019] To make the composition of the synthesis gas accurately predictable for the control unit or regulating device, a reformer transfer function can be used to calculate the target mixing ratios.

[0020] This avoids the need for complex measurements of the various concentrations of the synthesis gas components, as the concentrations of the different components of the produced synthesis gas are calculated as values ​​of the reformer transfer function, depending on the volumetric flow rates of the material streams entering the reformer and the inlet and outlet temperatures. The reformer transfer function can be generated through measurements or thermodynamic simulations.

[0021] To further improve the ignition behavior in the pre-combustion chamber, a compressor can be arranged in the second mixture line, thereby achieving a higher injection pressure in the pre-combustion chamber.

[0022] The combustion engine may be equipped with a reformer for synthesis gas production, connected to a fuel supply line and an air supply line. It can be advantageous if the reformer is also connected to a water supply line and / or an exhaust gas line. Recirculating the exhaust gas back into the reformer increases the system efficiency.

[0023] Further advantages and details of the invention will become apparent from the figures and the accompanying figure description. These show: Fig. 1 a schematic representation of an internal combustion engine according to the invention and Fig. 2 a diagram to illustrate the optimal operating point of an internal combustion engine according to the invention.

[0024] Fig. Figure 1 shows the circuit diagram of an internal combustion engine-reformer system. The main combustion chamber 1, the pre-combustion chamber 2, and the reformer 3 are shown. Air L is supplied to the internal combustion engine 30 via the air supply lines 5, fuel from a fuel reservoir T is supplied via the fuel supply lines 4, and synthesis gas S is supplied via the synthesis gas supply line 6. The first fuel gas mixer 24 and the second fuel gas mixer 25 mix these into the first combustion mixture BG1 and the second combustion mixture BG2, respectively. The first combustion mixture BG1 is supplied to the main combustion chamber 1 via the first mixture line 10, and the second combustion mixture BG2 is supplied to the pre-combustion chamber 2 via the second mixture line 10'. When the second fuel mixture BG2 is ignited in the pre-chamber 2, an ignition flare passes through the through-opening 33, which ignites the first fuel mixture BG1 in the main combustion chamber 1.Furthermore, the internal combustion engine 30 can have a compressor 26 in the second mixture line 10' and a turbocharger 27. The exhaust gas A of the internal combustion engine 30 is discharged via the exhaust line 9.

[0025] The mixing ratios for the first fuel gas mixer 24 and the second fuel gas mixer 25 are determined in the control unit 31, which is connected to both fuel gas mixers. The connections of the control unit 31 to all flow control valves 32 are not shown, as this would be difficult to illustrate and would not contribute to understanding. At least one flow control valve 32 is located in each of the fuel supply line 4, the air supply line 5, the synthesis gas supply line 6, the steam supply line 8, and the exhaust gas line 9. Using the flow rates controlled in the flow control valves 32 and, if necessary, a reformer transfer function, the control unit 31 is able to adjust the mixing ratios so that the desired concentrations of hydrogen, carbon monoxide, methane, etc., are present in the fuel mixtures.

[0026] In this embodiment, air and exhaust gas from the combustion engine 30 are supplied to the further mixing device 18 via an air supply line 5 and an exhaust gas line 9. A first material stream is mixed in the further mixing device 18 and conveyed via the supply line 11.

[0027] Water is supplied from a water reservoir W to an evaporator 20 via a water supply line 7 using pump 36. This evaporator 20 can be designed in various ways. A preferred embodiment is one in which the evaporator 20 is designed as a heat exchanger in thermal coupling with the exhaust gas line 9 or as a heat exchanger in thermal coupling with the synthesis gas line 6.

[0028] A heating element 23 is arranged in the water supply line 7. This element can also be designed as a heat exchanger. The heating element 23 can then be in thermal coupling with the synthesis gas line 6 between the first cooling element 16 and the second cooling element 17, or in thermal coupling with the first cooling element 16.

[0029] The steam generated in the evaporator 20 is fed to the further mixing unit 19 via a steam supply line 8. Fuel is also supplied to the further mixing unit 19 via a fuel line 4. In the further mixing unit 19, a second stream of substances is mixed from the steam and fuel and conveyed via the second supply line 12.

[0030] Furthermore, a preheating element 21, which can be designed as a heat exchanger, is connected upstream of the mixing device 19 in the fuel line 4. The preheating element can be thermally coupled to the first cooling element 16, to a cooling circuit of the combustion engine, and / or to the synthesis gas line 6. The cooling circuit is not shown, as it is well known in the prior art.

[0031] Air and exhaust gas from the combustion engine 30 are supplied to the further mixing unit 18 via an air supply line 5 and an exhaust gas line 9. The first material stream is mixed in the further mixing unit 18 and then conveyed via the supply line 11.

[0032] The first supply line 11 and the second supply line 12, after passing through the first heat exchanger 13 and the second heat exchanger 14 respectively, open into the mixing unit 28. A mixture is produced there, which is then fed to the reformer 3 via the mixture line 29. The synthesis gas supply line 6 leading from the reformer 3 passes through the first heat exchanger 13 and the second heat exchanger 14, with a bypass line 22 providing an alternative route around the second heat exchanger 14. The synthesis gas cooling system 15, consisting of the first cooling element 16 and the second cooling element 17, is also arranged in the synthesis gas supply line 6.

[0033] The synthesis gas can be reheated using the heating element 34 in the synthesis gas supply line 6 after the synthesis gas cooling process. Through this sequence of cooling, water separation, and heating, the relative humidity of the synthesis gas can be maintained at a level suitable for the engine.

[0034] A heat exchanger 21 is arranged in the exhaust pipe 9.

[0035] In this embodiment, a compressor 35 is arranged in the air supply line 5.

[0036] In Fig. Figure 2 illustrates the qualitative behavior of both the overall plant efficiency and the combustion efficiency. Combustion efficiency increases with the addition of synthesis gas, while the overall plant efficiency decreases with an increased proportion of synthesis gas in the fuel gas. The optimal operating point is found in the area between the vertical lines, which corresponds to the point where the two graphs intersect.

[0037] The invention is not limited to the present embodiment. In particular, the composition of the fuel gas can also be determined by direct measurement or by a running simulation of the reformer. These measurement or simulation values ​​can then be transmitted to the control or regulating device for controlling or regulating the mixing ratios.

Claims

[1] Internal combustion engine with - at least one main combustion chamber (1) for burning a first fuel mixture (BG1), - at least one pre-combustion chamber (2) per main combustion chamber (1) for burning a second fuel mixture (BG2), - a first fuel gas mixer (24) for providing the first fuel mixture (BG1), which is connected to a fuel supply line (4) and an air supply line (5), - a second fuel gas mixer (25) for providing the second fuel mixture (BG2), which is connected to a fuel supply line (4), an air supply line (5) and a synthesis gas supply line (6), and - a first mixture line (10) which is connected to the first fuel gas mixer (24) and the main combustion chamber (1), - a second mixture line (10') which is connected to the second fuel gas mixer (25) and the pre-combustion chamber (2), wherein the pre-combustion chamber (2) has at least one through-opening (33) into the main combustion chamber (1), characterized by , that the first fuel gas mixer (24) for the addition of synthesis gas (S) is connected to the synthesis gas supply line (6) and that a control device (31) or a regulating device (31) for controlling or regulating mixing ratios of fuel, air and synthesis gas in the first combustion mixture (BG1) and / or in the second combustion mixture (BG2) is provided, which is connected to the first fuel gas mixer (24) and / or to the second fuel gas mixer (25). [2] Internal combustion engine according to claim 1, characterized by, that at least one volume flow meter (32) is provided in the fuel supply line (4) and / or in the air supply line (5) and / or in an exhaust gas line (9) and / or in a steam supply line (8) and / or in the synthesis gas supply line (6), which is connected to the control device (31) or regulating device (31). [3] Internal combustion engine according to claim 2, characterized by , that in the control device (31) or regulating device (31) target mixing ratios can be calculated based on volume flows, wherein the volume flows can be measured by the at least one volume flow meter (32), and the mixing ratios of fuel, air and synthesis gas in the first fuel gas mixer (24) and in the second fuel gas mixer (25) can be regulated or controlled according to the target mixing ratios. [4] Internal combustion engine according to claim 3, characterized by, that the target mixture ratios for achieving the target fuel gas composition in the control device (31) or the control device (31) can be calculated using a reformer transfer function. [5] Internal combustion engine according to at least one of claims 1 to 4, characterized by , that a compressor (26) is arranged in the second mixture line (10'). [6] Internal combustion engine according to at least one of claims 1 to 5, characterized by , that a reformer (3) is provided for synthesis gas production, which is connected to a fuel supply line (4) and an air supply line (5). [7] Internal combustion engine according to claim 6, characterized by , that the reformer (3) is connected to a steam supply line (8) and / or an exhaust gas line (9). [8] Method for operating an internal combustion engine (30) wherein - a first fuel mixture (BG1) and a second fuel mixture (BG2) are mixed from a fuel, air and a synthesis gas (S) and - the first fuel mixture (BG1) is supplied to a main combustion chamber (1) and the second fuel mixture (BG2) is supplied to a pre-combustion chamber (2). [9] Method according to claim 8, wherein at least one volume flow is measured in a fuel supply line (4) and / or in an air supply line (5) and / or in an exhaust gas line (9) and / or in a steam supply line (8) and / or in a synthesis gas supply line (6). [10] Method according to claim 9, wherein target mixture ratios of fuel, air and synthesis gas (S) are calculated based on the at least one measured volume flow rate for mixture ratios of the first fuel mixture (BG1) and / or the second fuel mixture (BG2). [11] Method according to claim 10, wherein the target mixture ratios to achieve the target fuel gas composition are calculated using a reformer transfer function. [12] Method according to at least one of claims 8 to 11, wherein the second fuel mixture (BG2) is compressed before being fed to the pre-combustion chamber. [13] Method according to at least one of claims 8 to 12, wherein the synthesis gas (S) is produced in a reformer (3).

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