Internal combustion engine

Abstract

An engine 1 comprises: a cylinder liner 2; a cylinder head 3; a piston 4; a combustion chamber 9 formed therewith; an intake port 5 communicating with the combustion chamber 9; a first injector 12 for injecting methanol into the intake port 5; and a second injector 23 for injecting ignition fuel including biodiesel fuel into the combustion chamber 9.

Description

Internal combustion engine

[0001] The present invention relates to an internal combustion engine.

[0002] Conventionally, inexpensive fuels such as heavy oil have been used in marine diesel engines. However, due to the increasing demand for environmental protection in recent years, instead of fossil fuels such as heavy oil, methanol that does not emit sulfur oxides (SO Ｘ ), soot, etc. during combustion is being considered as a fuel.

[0003] Methanol is environmentally friendly but has poor auto-ignition properties, so it is difficult to ignite even when supplied to the combustion chamber of a diesel engine. Therefore, for example, in Patent Document 1 below, a fuel supply device that injects a mixed fuel of a fuel oil such as heavy oil and a low-ignition fuel such as methanol into the cylinder has been proposed.

[0004] However, since heavy oil and methanol have low compatibility, it is difficult to mix them uniformly. Therefore, Patent Document 2 below shows a fuel for an internal combustion engine that is a mixture of methanol and biodiesel fuel with high compatibility.

[0005] JP-A-2019-132221 JP-A-2024-154598

[0006] Patent Document 2 above shows, as combustion methods for a mixed fuel of methanol and biodiesel fuel (hereinafter also simply referred to as "mixed fuel"), (1) a direct injection method in which the mixed fuel is directly injected into the cylinder (see FIG. 2 of the same document), and (2) a port injection method in which the mixed fuel is injected into the intake port (see FIG. 3 of the same document).

[0007] In the direct injection method described in (1), it is necessary to inject the fuel mixture into the combustion chamber, which has reached high pressure when the cylinder is near top dead center. Therefore, an injector capable of high-pressure injection is required. In order to reduce greenhouse gases, it is required to increase the proportion of methanol in the fuel mixture as much as possible. However, methanol is more difficult to inject at high pressure than heavy oil, etc., so if the proportion of methanol in the fuel mixture is increased, existing injectors cannot be used, and an injector with a special structure is required. In addition, fuel injectors often lubricate themselves with the fuel itself, but methanol has low lubricity, so methanol itself cannot lubricate the injector. Therefore, if the proportion of methanol in the fuel mixture is increased, it becomes necessary to provide a separate lubrication mechanism for the injector. However, in internal combustion engines such as marine diesel engines, it is not practical to use expensive injectors with such special structures. Therefore, when the fuel mixture is injected directly into the combustion chamber, the proportion of methanol in the fuel mixture can only be increased to a level that can be injected into the combustion chamber with existing injectors, and there is a limit to the greenhouse gas reduction effect.

[0008] In contrast, with the port injection method described in (2), the pressure in the intake port is much lower than in the combustion chamber, so even a fuel mixture with a high methanol content can be injected into the intake port using an existing injector. However, because biodiesel fuel has low volatility, when the fuel mixture is injected into the intake port, the biodiesel fuel in the mixture may condense and adhere to the inner wall of the intake port. In this case, the appropriate amount of biodiesel fuel may not be supplied into the cylinder, potentially leading to combustion failure.

[0009] Therefore, the present invention aims to reduce greenhouse gas emissions by increasing the methanol ratio in an internal combustion engine using methanol and biodiesel fuel, without requiring a special injector, and to prevent combustion failure.

[0010] To solve the aforementioned problems, the present invention provides an internal combustion engine comprising a cylinder liner, a cylinder head, a piston, a combustion chamber formed by the cylinder liner, the cylinder head, and the piston, an intake port communicating with the combustion chamber, a first injector for injecting methanol into the intake port, and a second injector for injecting ignition fuel containing biodiesel fuel into the combustion chamber.

[0011] As described above, in the internal combustion engine of the present invention, methanol is injected into the intake port by the first injector, and ignition fuel containing biodiesel fuel is injected into the combustion chamber by the second injector. In this case, by increasing the amount of methanol injected from the first injector, the proportion of methanol in the total fuel supplied to the combustion chamber can be increased, thereby reducing greenhouse gases. Therefore, it is not necessary to blend a large amount of methanol into the ignition fuel injected from the second injector. Accordingly, the second injector does not require a special structure capable of injecting methanol at high pressure, and since it can be lubricated by the biodiesel fuel contained in the ignition fuel, it does not require a separate lubrication mechanism, and existing inexpensive injectors can be used. Furthermore, since the biodiesel fuel is injected directly into the combustion chamber by the second injector and not into the intake port, the biodiesel fuel does not condense in the intake port and adhere to the inner wall of the intake port.

[0012] Methanol is less prone to condensation than biodiesel fuel due to its higher volatility; however, if the temperature inside the intake port is low, methanol may condense inside the intake port and adhere to the inner wall of the intake port. Therefore, it is preferable that the above-mentioned internal combustion engine has a heating unit that heats the methanol injected into the intake port. When the temperature inside the intake port is low, preheating the methanol in the heating unit before injecting it into the intake port suppresses the condensation of methanol inside the intake port, thereby preventing methanol from adhering to the inner wall of the intake port.

[0013] For example, when the load on the internal combustion engine is low, the temperature inside the intake port is low, making methanol more likely to condense inside the intake port. On the other hand, when the load on the internal combustion engine is high, the temperature inside the intake port becomes high, making methanol less likely to condense inside the intake port. Therefore, it is preferable to control the heating unit based on the load conditions of the internal combustion engine.

[0014] The ignition fuel may be a mixture of biodiesel fuel and methanol. By injecting an ignition fuel consisting of a mixture of biodiesel fuel and methanol into the combustion chamber, it is expected that emissions of unburned hydrocarbons and carbon monoxide will be reduced compared to the case where the ratio of methanol to biodiesel fuel in the total fuel is the same and only biodiesel fuel is injected directly into the combustion chamber. In this case, if the ratio of methanol in the ignition fuel is too high, a special injector structure will be required for high-pressure injection, so it is preferable that the ratio of methanol in the ignition fuel be 40% by mass or less.

[0015] The above-described internal combustion engine can be suitably applied to marine diesel engines.

[0016] As described above, according to the present invention, while using an existing inexpensive injector as the second injector, it is possible to reduce greenhouse gases by increasing the proportion of methanol supplied to the combustion chamber, and to prevent combustion failure by supplying an appropriate amount of biodiesel fuel to the combustion chamber.

[0017] This is a cross-sectional view of an internal combustion engine according to one embodiment of the present invention. This is a cross-sectional view of an internal combustion engine according to another embodiment.

[0018] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0019] Figure 1 shows a marine diesel engine 1 (hereinafter simply referred to as "engine 1") as an internal combustion engine according to one embodiment of the present invention. Engine 1 has a cylinder liner 2, a cylinder head 3, and a piston 4. The cylinder head 3 is provided with an intake port 5 and an exhaust port 6, which are opened and closed by an intake valve 7 and an exhaust valve 8. The cylinder liner 2, cylinder head 3, and piston 4 form a combustion chamber 9.

[0020] Engine 1 includes a methanol supply unit 10 that supplies methanol to the intake port 5 and an ignition fuel supply unit 20 that supplies ignition fuel to the combustion chamber 9. In this embodiment, a mixed fuel of biodiesel fuel and methanol is used as the ignition fuel. Biodiesel fuel is produced by reacting methanol with bio-derived oil. In this embodiment, fatty acid methyl ester (FAME), obtained by methyl esterifying vegetable oil, is used as the biodiesel fuel.

[0021] The methanol supply unit 10 includes a methanol storage tank 11, a first injector 12, piping 13 connecting them, and a pump 14 and a flow control valve 15 installed in the middle of the piping 13. Methanol is stored in liquid form in the methanol storage tank 11. The first injector 12 has an injection port that opens into the intake port 5. Methanol is supplied from the methanol storage tank 11 to the first injector 12 by the pump 14, and only methanol is injected into the intake port 5 from the injection port of the first injector 12. At this time, the amount of methanol injected from the first injector 12 into the intake port 5 is adjusted by the flow control valve 15.

[0022] The ignition fuel supply unit 20 includes a biodiesel fuel storage tank 21, a methanol storage tank 22, a second injector 23, and a mixer 24. Biodiesel fuel is stored in liquid form in the biodiesel fuel storage tank 21, and methanol is stored in liquid form in the methanol storage tank 22. The second injector 23 has an injection port that opens into the combustion chamber 9. A pump 26 and a flow control valve 27 are provided in the piping 25 connecting the mixer 24 and the second injector 23. Pumps 30 and 31 and flow control valves 32 and 33 are provided in the piping 28 connecting the mixer 24 and the biodiesel fuel storage tank 21, and in the piping 29 connecting the mixer 24 and the methanol storage tank 22, respectively.

[0023] Pumps 30 and 31 supply methanol and biodiesel fuel from the biodiesel fuel storage tank 21 and methanol storage tank 22 to the mixer 24. At this time, flow control valves 32 and 33 adjust the ratio of methanol to biodiesel fuel supplied to the mixer 24. For example, the flow rates of each fuel are adjusted by flow control valves 32 and 33 so that the proportion of methanol in the total fuel supplied to the mixer 24, that is, the proportion of methanol in the ignition fuel produced in the mixer 24, is 40% or less.

[0024] Then, methanol and biodiesel fuel are mixed in the mixer 24 to produce ignition fuel. Because biodiesel fuel has high compatibility with methanol, mixing them in the mixer 24 allows for uniform compatibility between methanol and biodiesel fuel. The ignition fuel produced in the mixer 24 is then supplied to the second injector 23 by the pump 26 and injected into the combustion chamber 9 from the nozzle of the first injector 23. At this time, the amount of ignition fuel injected from the first injector 23 into the combustion chamber 9 is adjusted by the flow control valve 27.

[0025] When engine 1 is running, methanol is injected into the intake port 5 from the first injector 12, and at the same time, the intake valve 7 opens and the piston 4 descends, supplying methanol from the intake port 5 into the cylinder (combustion chamber 9). Subsequently, as the intake valve 7 closes and the piston 4 rises, the methanol in the combustion chamber 9 is compressed, and when the piston 4 reaches near top dead center, ignition fuel is injected into the combustion chamber 9 from the second injector 23. As a result, the biodiesel fuel contained in the ignition fuel self-ignites, and this pilot ignition ignites the methanol in the ignition fuel and the methanol supplied from the intake port 5, causing an explosion.

[0026] To reduce greenhouse gas emissions, it is necessary to maximize the proportion of methanol in the fuel mixture burned in the combustion chamber 9. In this embodiment, since methanol is injected from the first injector 12 to the intake port 5, the proportion of methanol in the fuel mixture can be increased by increasing the amount of methanol injected from the first injector 12. In this case, the amount of methanol in the ignition fuel injected into the combustion chamber 9 from the second injector 23 can be reduced, so the second injector 23 does not need to have a special structure capable of injecting methanol at high pressure. Furthermore, since the second injector 23 can be lubricated by the biodiesel fuel contained in the ignition fuel, there is no need to provide a separate lubrication mechanism for the second injector 23. Therefore, an existing inexpensive injector capable of injecting heavy oil or the like at high pressure can be used as the second injector 23.

[0027] Furthermore, as described above, by directly injecting the ignition fuel containing biodiesel fuel into the combustion chamber 9, the less volatile biodiesel fuel is not supplied to the intake port 5, thus preventing the biodiesel fuel from condensing and adhering to the inner wall of the intake port 5. In this way, by directly injecting the ignition fuel containing biodiesel fuel into the combustion chamber 9, an appropriate amount of biodiesel fuel is always supplied to the combustion chamber 9, thereby preventing combustion failure.

[0028] Furthermore, as described above, by directly injecting an ignition fuel consisting of a mixture of biodiesel fuel and methanol into the combustion chamber 9, it is expected that emissions of unburned hydrocarbons and carbon monoxide will be reduced compared to the case where the ratio of methanol to biodiesel fuel in the total fuel is the same and only biodiesel fuel is directly injected into the combustion chamber 9.

[0029] Methanol is less prone to condensation than biodiesel fuel, but it is not completely condensation-free, and condensation can occur if the temperature inside the intake port 5 is low. Therefore, in this embodiment, a heating unit is provided to heat the methanol supplied to the intake port 5. In the illustrated example, a heater 40 is provided on the outer circumference of the piping 13 of the methanol supply unit 10. The heater 40 is located downstream of the pump 14, and in the illustrated example, it is located directly in front of the first injector 12. By injecting methanol heated by this heater 40 into the intake port 5 from the first injector 12, condensation of methanol inside the intake port 5 is suppressed, and methanol adhesion to the inner wall of the intake port 5 can be reliably prevented.

[0030] When the temperature inside the intake port 5 is high, methanol is less likely to condense inside the intake port 5. Therefore, if methanol is heated by the heater 40 only when the temperature inside the intake port 5 is low, the methanol can be heated only when necessary, thus reducing energy consumption. For example, if a temperature sensor is installed to measure the temperature inside the intake port 5, the heater 40 can be controlled based on the temperature detected by this sensor. However, this would incur costs for the temperature sensor itself, and would require a redesign of the cylinder head 3 to install the temperature sensor in the intake port 5.

[0031] Therefore, in this embodiment, the heater 40 is controlled based on the load status of the engine 1. Specifically, when the load on the engine 1 is low, for example when the engine 1 is idling, the temperature of the entire engine 1, including the intake port 5, is low, so the heater 40 is operated to heat the methanol and suppress the aggregation of methanol in the intake port 5. On the other hand, when the load on the engine 1 is high, for example when the ship is accelerating rapidly, the entire engine 1, including the intake port 5, is hot, so the heater 40 is stopped to reduce energy consumption.

[0032] When controlling the heater 40 based on the load conditions of the engine 1 as described above, it is preferable to create a mapping in advance that shows the relationship between the load applied to the engine 1 and the temperature of the intake port 5. During operation of the engine 1, the load applied to the engine 1 can be measured, and the heater 40 can be controlled based on this load and the mapping described above. At this time, based on the load conditions of the engine 1, only the ON / OFF state of the heater 40 may be controlled, or the magnitude of the output of the heater 40 (for example, the current value supplied to the heater 40) may be controlled.

[0033] The present invention is not limited to the embodiments described above. Other embodiments of the present invention will be described below, but redundant explanations of points similar to those in the embodiments described above will be omitted.

[0034] In the above embodiment, the ignition fuel is shown to be a mixture of biodiesel fuel and methanol, but the ignition fuel may also be composed of biodiesel fuel alone. In this case, as shown in Figure 2, the ignition fuel supply unit 20 can have a simple configuration without a methanol storage tank 22, a mixer 24, etc. Specifically, the ignition fuel supply unit 20 has an ignition fuel storage tank 34, a second injector 23, and a pump 26 and a flow control valve 27 provided in the piping 25 connecting them. The pump 26 and flow control valve 27 supply a predetermined amount of biodiesel fuel from the ignition fuel storage tank 34 to the second injector 23, and it is injected into the combustion chamber 9 from the nozzle of the second injector 23.

[0035] Alternatively, a pre-mixed fuel of biodiesel fuel and methanol may be used as the ignition fuel. In this case, the ignition fuel, in which biodiesel fuel and methanol are uniformly mixed, is stored in the ignition fuel storage tank 34 shown in Figure 2. A predetermined amount of ignition fuel (mixed fuel) is supplied from the ignition fuel storage tank 34 to the second injector 23 by the pump 26 and the flow control valve 27, and injected into the combustion chamber 9 from the nozzle of the second injector 23.

[0036] In the above embodiment, the methanol supply unit 10 is provided with a heating unit (heater 40) for heating methanol, but if it is not particularly necessary, the heating unit (heater 40) may be omitted as shown in Figure 2.

[0037] The present invention is not limited to diesel engines, but can also be applied to other internal combustion engines, such as engines that ignite fuel supplied to the fuel chamber with a spark plug.

[0038] 1. Marine diesel engine (internal combustion engine) 2. Cylinder liner 3. Cylinder head 4. Piston 5. Intake port 6. Exhaust port 7. Intake valve 8. Exhaust valve 9. Combustion chamber 10. Methanol supply unit 11. Methanol storage tank 12. First injector 20. Ignition fuel supply unit 21. Biodiesel fuel storage tank 22. Methanol storage tank 23. Second injector 40. Heater (heating unit)

Claims

1. An internal combustion engine comprising: a cylinder liner; a cylinder head; a piston; a combustion chamber formed by the cylinder liner, the cylinder head, and the piston; an intake port communicating with the combustion chamber; a first injector for injecting methanol into the intake port; and a second injector for injecting ignition fuel containing biodiesel fuel into the combustion chamber.

2. The internal combustion engine according to claim 1, having a heating section for heating methanol.

3. The internal combustion engine according to claim 2, wherein the heating unit is controlled based on the load conditions of the internal combustion engine.

4. The internal combustion engine according to claim 1, wherein the ignition fuel comprises methanol.

5. The internal combustion engine according to claim 4, wherein the ratio of methanol in the ignition fuel is 40% by mass or less.

6. A marine diesel engine comprising an internal combustion engine according to any one of claims 1 to 5.

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