Reciprocal engine system and operating method for reciprocal engine

Abstract

To further enhance an effect of reduction of emissions of carbon dioxide in a reciprocal engine that uses ammonia as fuel.SOLUTION: A reciprocal engine system includes: a reciprocal engine having a cylinder that forms a combustion chamber, a piston reciprocating in the cylinder, an ammonia fuel supply device for supplying gaseous ammonia to the cylinder for premixing with air and a liquid auxiliary fuel supply device that supplies liquid auxiliary fuel for igniting the ammonia into the cylinder; and a control device that performs a mixed combustion operation using the ammonia and the liquid auxiliary fuel while a compression end temperature in the cylinder is equal to or higher than a predetermined temperature that prevents combustion delay of the ammonia.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a reciprocating engine system and a method for operating a reciprocating engine. This application claims priority based on Japanese Patent Application No. 2021-186474, filed on November 16, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] In recent years, there has been a demand to reduce emissions of carbon dioxide (CO2), a greenhouse gas, as a measure against global warming. Ammonia (NH3) has been attracting attention as a new fuel that does not emit carbon dioxide when burned. The following patent applications have been filed regarding reciprocating engines that use ammonia as fuel: [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6702475 [Patent Document 2] Patent No. 4919922 Summary of the Invention [Problem to be solved by the invention]

[0004] When ammonia is used as a fuel, a problem arises in that it is more difficult to burn than conventional fuels such as heavy oil, light oil, gasoline, and natural gas.

[0005] Patent Document 1 describes a reciprocating engine in which gaseous ammonia is premixed with air and compressed in a cylinder, and fuel oil such as heavy oil is injected from a fuel injection valve into the combustion chamber to ignite, thereby mixing and burning the ammonia and fuel oil as an ignition source. Here, an example is described in which the ratio of ammonia to heavy oil is 80% and the ratio of ammonia is 20% in terms of heat value. The reason why the ratio of ammonia to the total fuel is only 20% is that the ratio of ammonia must be reduced because ammonia is difficult to burn. In this case, the effect of reducing carbon dioxide emissions is limited.

[0006] Patent Document 2 describes a reciprocating engine in which ammonia and a combustion supporting fuel are injected into an intake pipe, and the mixture of ammonia, the combustion supporting fuel, and air is ignited by spark discharge from an ignition plug. Patent Document 2 also describes increasing the proportion of ammonia used as the rotation speed of the internal combustion engine decreases, or increasing the proportion of ammonia used as the load on the internal combustion engine increases. Patent Document 2 does not specify what percentage of ammonia is relative to the total fuel, but it can be understood that it is not easy to increase the proportion of ammonia.

[0007] The present invention has been made in consideration of the above problems, and has an object to increase the effect of reducing carbon dioxide emissions in a reciprocating engine that uses ammonia as fuel. [Means for solving the problem]

[0008] A reciprocating engine system according to one embodiment of the present invention includes a reciprocating engine having a cylinder that forms a combustion chamber, a piston that reciprocates within the cylinder, an ammonia fuel supply device that supplies gaseous ammonia to the cylinder and premixes it with air, and a liquid auxiliary fuel supply device that supplies liquid auxiliary fuel into the cylinder to ignite the ammonia, and a control device that performs a mixed-fuel operation using the ammonia and the liquid auxiliary fuel when the compression end temperature in the cylinder is equal to or higher than a predetermined temperature at which no combustion delay of the ammonia occurs.

[0009] When using ammonia as fuel in a reciprocating engine system, the problem is that it is more difficult to burn than conventionally used fuels. In the past, attempts were made to mix ammonia with auxiliary fuels because it was difficult to start combustion with ammonia alone. In addition, in previous research and patent applications, attempts were made to ensure the combustion of ammonia by selecting the type of auxiliary fuel or increasing the mixing ratio of the auxiliary fuel. As a result of intensive research, the inventors of the present application have come to the conclusion that it is optimal to perform a mixed combustion operation in a reciprocating engine by premixing ammonia in a gaseous state with air, compressing the mixture in the cylinder, injecting liquid auxiliary fuel into the cylinder and igniting the mixture of gaseous ammonia and air. The inventors of the present application have also found that, when the mixture is compressed in the cylinder, the work from the piston is converted into heat, thereby increasing the temperature of the mixture in the cylinder, but good combustion of ammonia is possible by setting the compression end temperature, which is the temperature of the mixture when the piston reaches the top dead center, to a predetermined temperature or higher at which ammonia combustion delay does not occur. This allows the ratio of ammonia to the liquid auxiliary fuel to be increased compared to the conventional ratio, and the effect of reducing carbon dioxide emissions can be further increased in a reciprocating engine that uses ammonia as fuel. Here, as the liquid auxiliary fuel, any liquid fuel that self-ignites at a predetermined compression end temperature can be used, and fuels generally used in diesel engines, specifically heavy oil, light oil, vegetable oil, etc., can be suitably used.

[0010] In the above reciprocating engine system, the predetermined temperature may be 750K.

[0011] The ignition temperature of ammonia is about 652°C (925K), which is more than 100°C higher than that of diesel, which is about 247°C (520K), and that of methane, the main component of natural gas, which is 537°C (810K). In the examples of conventional research and patent applications, the compression end temperature of the mixture is not sufficiently high. Therefore, when liquid auxiliary fuel is injected into a cylinder and ignited, the ammonia mixture that is close to the flame caused by the combustion of the liquid auxiliary fuel is exposed to the high temperature of the flame and burns, but the mixture that is far from the flame does not burn sufficiently. On the other hand, based on the findings of the inventors of the present application, if the compression end temperature is set to a predetermined temperature or higher at which ammonia combustion delay does not occur, specifically 750K or higher, the mixture of gaseous ammonia and air is compressed and held in the combustion chamber at a temperature close to the ignition temperature of ammonia. Therefore, when the ammonia mixture is ignited by the ignition of an appropriate amount of liquid auxiliary fuel, the flame caused by the combustion of ammonia propagates through the combustion chamber, and the mixture burns throughout the entire combustion chamber. The predetermined compression end temperature at which no ammonia combustion delay occurs is specifically 750K or higher, but can be changed depending on conditions such as the size of the cylinder, the engine speed, the operating state, etc. In addition, in the embodiment of the invention described below, a four-stroke engine is used as an example of a reciprocating engine, but the same principle can be applied to a two-stroke engine.

[0012] In the above reciprocating engine system, the stroke volume of each of the cylinders may be 5000 cc or more, and the rated rotation speed of the reciprocating engine may be 1200 rpm or less.

[0013] If the compression of the mixture in the cylinder by the piston is ideal adiabatic compression, the compression end temperature of the mixture rises according to the compression ratio. However, in reality, the compression end temperature is lower than in the case of ideal adiabatic compression because heat escapes to the inner surface of the combustion chamber. The cylinder, cylinder head, and piston that form the inner surface of the combustion chamber each have heat capacity and are cooled by cooling water and lubricating oil, which causes the compression end temperature to drop. The amount of heat that escapes from the combustion chamber correlates with the area of ​​the inner surface of the combustion chamber, and the amount of heat generated in the combustion chamber correlates with the volume of the combustion chamber, so the relationship is according to the square cube law. In order to raise the compression end temperature to a predetermined temperature or higher at which ammonia combustion delay does not occur, it is effective to make the combustion chamber larger. Specifically, the stroke volume per cylinder is set to 5000cc or more. In addition, in order to secure the time required for ammonia combustion in the combustion stroke, the rated rotation speed of the reciprocating engine is set to 1200rpm or less. Generally, in reciprocating engines that burn a natural gas mixture, the compression ratio is often set to about 13 to 14. However, in the case of a reciprocating engine that burns an ammonia mixture, it is more desirable to set the compression ratio higher, to 15 or more, in terms of increasing the compression end temperature.

[0014] In the reciprocating engine system, the control device may increase a co-combustion ratio of the ammonia to the total fuel in accordance with an increase in output of the reciprocating engine during the co-combustion operation, and the maximum co-combustion ratio of the ammonia may be 80% or more in terms of a heat ratio.

[0015] In the actual operation of a reciprocating engine, it is necessary to increase or decrease the output. When the output of a reciprocating engine is small, the temperature rise caused by the combustion of fuel in the cylinder is small, the temperature of the inner surface of the combustion chamber is decreased, and the compression end temperature also tends to decrease. In addition, when the output of a reciprocating engine is large, the tendency is the opposite to that when the output is small. Therefore, in order to ensure the combustion of the ammonia mixture, when the output is small, the ammonia co-firing ratio with respect to the entire fuel is reduced, and the ammonia co-firing ratio is increased as the output increases. In addition, by setting the maximum ammonia co-firing ratio near the maximum output to 80% or more in terms of heat ratio, a sufficient effect of reducing carbon dioxide emissions can be obtained. In addition, the processing of the above-mentioned control device can be expressed as follows: In the co-firing operation, the ammonia co-firing ratio with respect to the entire fuel is increased as the compression end temperature increases, and the maximum ammonia co-firing ratio is set to 80% or more in terms of heat ratio.

[0016] In the above reciprocating engine system, the control device may set an equivalence ratio of the total fuel to the air to be not less than 0.5 and not more than 1.0 during the multi-fuel operation.

[0017] When ammonia is used as fuel, the generation of nitrous oxide (N2O) is considered a problem. Nitrous oxide is one of the greenhouse gases, and if a large amount of nitrous oxide is generated, it will offset the effect of reducing carbon dioxide by using ammonia as fuel. As a result of research, the inventors of the present application have found that the generation of nitrous oxide is related to the equivalence ratio of the total fuel to air (the sum of the equivalence ratio of ammonia and the equivalence ratio of the liquid auxiliary fuel). More specifically, they found that when the equivalence ratio of the total fuel to air is less than 0.5, the generation of nitrous oxide increases rapidly as the equivalence ratio decreases. Therefore, in dual-fuel operation, it is desirable to set the equivalence ratio of the total fuel to air to 0.5 or more. Also, when the equivalence ratio of the total fuel to air is 1.0 or more, there is not enough air to burn the fuel, and the fuel is discharged as an unburned component. In this case, ammonia is more difficult to burn than liquid auxiliary fuel, so ammonia is the main component discharged as an unburned component. Therefore, in multi-fuel operation, it is desirable to keep the equivalence ratio of the total fuel to air at 1.0 or less.

[0018] In the above reciprocating engine system, the control device may set the ammonia co-fuel ratio to zero in an operating region where an equivalence ratio of the total fuel to the air is less than a predetermined value, and operate the reciprocating engine system using only the liquid auxiliary fuel.

[0019] In reciprocating engines, a method of adjusting the amount of fuel supplied is generally used to adjust the output. Here, in so-called lean burn engines, the equivalence ratio of fuel to air is not fixed to around 1, but is operated at a lower equivalence ratio. In this lean burn engine, when the amount of fuel supplied is reduced to reduce the output, the reduction rate of the fuel supply is greater than the reduction rate of the air supply, and the equivalence ratio tends to decrease. In an engine that operates by co-firing ammonia and liquid auxiliary fuel, if the total fuel supply is reduced to reduce the output, the amount of heat generated is reduced, making ammonia less flammable. In addition, in a region where the equivalence ratio falls below a predetermined value, specifically below 0.5, the problem of the increase in nitrous oxide described above occurs. Therefore, in an operating region where the equivalence ratio of the total fuel to air is less than a predetermined value, the co-firing rate of ammonia is set to zero, and operation is performed using only liquid auxiliary fuel. This prevents the generation of unburned ammonia and nitrous oxide. The operating region in which the equivalence ratio is less than the predetermined value varies depending on the specific conditions of the engine, but examples include idling and operation at low output close to idling.

[0020] In the above reciprocating engine system, the control device may perform control to increase the compression end temperature in an operating region where the compression end temperature is lower than the predetermined temperature.

[0021] For a while after the start of the reciprocating engine, the temperature of the inner surface of the combustion chamber is low, so that the compression end temperature does not easily rise. In addition, when the output of the reciprocating engine is low and the amount of fuel supplied is small after the start of the reciprocating engine, the generation of heat is small, so that the compression end temperature does not easily rise. In such an operating region, if the supply of ammonia is started and mixed combustion with the liquid auxiliary fuel is performed, there is a possibility that the generation of unburned ammonia increases. Therefore, in an operating region where the compression end temperature is low, control is performed to increase the compression end temperature. Examples of the control to increase the compression end temperature include control to increase the target value of the cooling temperature in the air cooler provided downstream of the compressor of the turbocharger, control to heat the air downstream or upstream of the compressor of the turbocharger, and control to increase the effective compression ratio of the reciprocating engine. In particular, when the output of the reciprocating engine is increased after the start of the reciprocating engine or from a state where the output of the reciprocating engine is low, it is effective to perform control to increase the compression end temperature before starting the supply of gaseous ammonia. In addition, the above-mentioned control can be performed to enable mixed combustion of ammonia even in a region where the output of the reciprocating engine is low.

[0022] The control for increasing the compression end temperature may be control for heating intake air of the reciprocating engine.

[0023] As a control for increasing the compression end temperature, it is effective to provide a device for heating the intake air (hereinafter also referred to as "supply air") downstream or upstream of the compressor of the turbocharger in the intake passage of the reciprocating engine, thereby controlling the heating of the intake air.

[0024] The above-mentioned reciprocating engine system may further include a turbocharger having a compressor and a turbine for supercharging the reciprocating engine, and the control device may perform control to heat the intake air in an operating region where the temperature of the intake air downstream of the compressor is lower than a predetermined temperature.

[0025] The factors governing the compression end temperature include the temperature of the outside air taken into the reciprocating engine, the temperature rise due to the compression work of the compressor of the supercharger, and the temperature rise due to the compression work of the cylinder of the reciprocating engine. Here, the compression ratio of the cylinder of the reciprocating engine is a design value that is determined in advance to a desired value, and can be understood as a volume ratio even when a variable mechanism such as a variable valve timing is used. On the other hand, the compression ratio of the compressor of the supercharger depends on the operating conditions of the reciprocating engine. In addition, the temperature of the outside air depends on the environmental conditions. Here, the temperature of the intake air downstream of the compressor is a combination of the influence of the temperature of the outside air and the compression ratio of the compressor, so it is effective to control the heating of the intake air using this as a judgment criterion. For example, in an operating condition where the output of the reciprocating engine is low, the temperature rise of the intake air due to the compression work of the compressor is small, and therefore an operating region occurs in which the temperature of the intake air downstream of the compressor does not reach a temperature (e.g., 50°C) required to obtain an appropriate compression end temperature. This is more noticeable when the temperature of the outside air is low. Therefore, in an operating region where the temperature of the intake air downstream of the compressor is lower than a predetermined temperature, the control device performs control to heat the intake air in order to obtain an appropriate compression end temperature.

[0026] In the above reciprocating engine system, the control device may keep the supply amount of the liquid auxiliary fuel constant and regulate the supply amount of the ammonia during the multi-fuel operation.

[0027] In multi-fuel operation, a control method that keeps the supply amount of liquid auxiliary fuel constant and controls the supply amount of gaseous ammonia is simple and effective. As described above, in multi-fuel operation, it is effective to increase the ratio of ammonia to the total fuel as the output increases. In addition, in the operation of a reciprocating engine, speed control is required to increase or decrease the supply amount of fuel so that the reciprocating engine reaches a target rotation speed. These two requirements can be met simultaneously by keeping the supply amount of liquid auxiliary fuel constant at the supply amount required to maintain the output of the reciprocating engine at a low level and controlling the supply amount of gaseous ammonia in response to the demand for increased output.

[0028] In the above reciprocating engine system, the control device may map-control the supply amount of the liquid auxiliary fuel and regulate the supply amount of the ammonia during the multi-fuel operation.

[0029] As a more advanced control method, it is more effective to map-control the supply amount of the liquid auxiliary fuel according to the operating conditions and regulate the supply amount of the gaseous ammonia. For a while after the start of the reciprocating engine, or when the output of the reciprocating engine is low and the supply amount of fuel is small, the temperature of the inner surface of the combustion chamber is low, so ammonia is not easily burned. Therefore, in such a state, it is desirable to increase the supply amount of the liquid auxiliary fuel. On the other hand, when the reciprocating engine continues to operate, especially when the output of the reciprocating engine is high and the supply amount of fuel is large, the temperature of the inner surface of the combustion chamber is high and ammonia is easily burned. Therefore, in such a state, it is desirable to reduce the supply amount of the liquid auxiliary fuel and increase the supply amount of the ammonia instead. Therefore, if the supply amount of the liquid auxiliary fuel is map-controlled according to operating conditions such as the output, operating time, and measured values ​​of the temperatures of each part of the reciprocating engine, and the supply amount of the gaseous ammonia is regulated based on the map, control that is more responsive to the operating state of the reciprocating engine is possible.

[0030] The above-mentioned reciprocating engine system may further include a turbocharger having a compressor and a turbine for supercharging the reciprocating engine, an intake passage connecting the compressor and the reciprocating engine, an exhaust passage connecting the reciprocating engine and the turbine, and at least one of a first short-circuit path of an open / close type connecting the intake passage and the exhaust passage and a second short-circuit path of an open / close type connecting the intake passage and the downstream of the turbine, and the control device may perform opening and closing control of at least one of the first short-circuit path and the second short-circuit path depending on the exhaust temperature of the reciprocating engine.

[0031] When the engine is operated by co-firing gaseous ammonia with liquid auxiliary fuel, the equivalence ratio of the entire fuel is higher than that of conventional diesel engines and gas engines using fuels such as natural gas. Therefore, at medium to high loads, the exhaust temperature at the turbine inlet may exceed the allowable temperature of the turbine. Therefore, at medium to high loads, the air at the compressor outlet is bypassed to the turbine inlet to lower the temperature of the exhaust flowing into the turbine, and the exhaust temperature at the catalyst inlet, which will be described later, is also made appropriate. On the other hand, at low loads, the turbocharger is not working sufficiently, so the pressure at the turbine inlet is higher than the pressure at the compressor outlet, and there is a risk of exhaust gas flowing back from the turbine inlet to the compressor outlet. Therefore, at low loads, the air at the compressor outlet is bypassed downstream of the turbine (catalyst inlet) to make the temperature of the exhaust gas flowing to the catalyst appropriate. Here, as a specific example of the opening and closing control of either the first short-circuit path or the second short-circuit path, for example, a temperature sensor may be provided at the turbine inlet or the catalyst inlet, and either the first short-circuit path or the second short-circuit path may be opened or closed based on the measured value.

[0032] The above reciprocating engine system may further include a throttle valve that limits an amount of air on an intake side of the reciprocating engine, and the control device may control an opening degree of the throttle valve so that an equivalence ratio of the ammonia to the air falls within a range that enables the multi-fuel operation.

[0033] When an engine is operated by co-firing gaseous ammonia with liquid auxiliary fuel, it is necessary to maintain the equivalence ratio of gaseous ammonia to air within a certain range. The maintenance of this equivalence ratio is related to the generation of exhaust gas components such as nitrous oxide, unburned ammonia and other nitrogen oxides, as described above, and combustion stability. However, during low-load operation, the absolute amount of ammonia required is small, and even in a naturally aspirated state where the turbocharger does not work sufficiently, the amount of air is large, so the equivalence ratio of gaseous ammonia falls below the target range. Therefore, the equivalence ratio of ammonia is maintained within a target range that allows co-firing operation by providing a throttle valve at the intake inlet to throttle the intake amount. The target range of ammonia equivalence ratio is preferably 0.4 to 0.8. When the co-firing rate of ammonia is 80%, this is converted to an equivalence ratio of the entire fuel including the liquid auxiliary fuel of 0.5 to 1.0, which is consistent with the above-mentioned equivalence ratio of the entire fuel to air being 0.5 or more and 1.0 or less.

[0034] In the above-mentioned reciprocating engine system, the control device may start the reciprocating engine using only the liquid auxiliary fuel, operate the reciprocating engine using only the liquid auxiliary fuel until the compression end temperature reaches the predetermined temperature, and perform the multi-fuel operation after the compression end temperature reaches the predetermined temperature.

[0035] Since ammonia is difficult to burn, it is difficult to burn ammonia as fuel when the reciprocating engine is stopped and cooled. Therefore, the engine is started using only the liquid auxiliary fuel, and is operated using only the liquid auxiliary fuel until the compression end temperature reaches a predetermined value. After the compression end temperature reaches the predetermined value, the mixed combustion operation using the liquid auxiliary fuel and gaseous ammonia is performed. The compression end temperature may be measured by providing a sensor in the combustion chamber. The compression end temperature may be calculated as an estimated value from the design value of the reciprocating engine, the measured values ​​of the temperatures of each part, and the operating conditions. Alternatively, the compression end temperature may not be controlled by calculating an actual measured value or an estimated value, but a condition may be set in advance under which the compression end temperature reaches a predetermined value with a certain margin. After the condition is reached, the mixed combustion operation using the liquid auxiliary fuel and gaseous ammonia may be started. To express the above-mentioned processing of the control device in another way, in the operating region where the compression end temperature does not become equal to or higher than a predetermined temperature where ammonia combustion delay does not occur, the supply of gaseous ammonia is reduced to zero and operation is performed using only liquid auxiliary fuel.

[0036] In the above-mentioned reciprocating engine system, the control device may start the reciprocating engine using only the liquid auxiliary fuel, operate the reciprocating engine using only the liquid auxiliary fuel until the reciprocating engine reaches a predetermined output, and perform the multi-fuel operation after the reciprocating engine reaches the predetermined output.

[0037] As an example of a condition under which the compression end temperature reaches the predetermined value with a certain margin, the control device may first start up using only the liquid auxiliary fuel, operate using only the liquid auxiliary fuel until a predetermined output is reached, and then perform a mixed combustion operation using the liquid auxiliary fuel and gaseous ammonia after the predetermined output is reached. Since the output and the compression end temperature are correlated, it is simple and practical to use the output as a reference for the control parameter.

[0038] In the above reciprocating engine system, the control device may start the reciprocating engine using only the liquid auxiliary fuel, increase an injection amount of the liquid auxiliary fuel, and perform a mixed combustion operation using the liquid auxiliary fuel and the ammonia after an equivalence ratio of the total fuel to the air reaches a predetermined value.

[0039] As described above, from the viewpoint of suppressing the generation of nitrous oxide, it is desirable to set the equivalence ratio of the total fuel to air to 0.5 or more. Therefore, it is desirable to start only with liquid auxiliary fuel, increase the injection amount of liquid auxiliary fuel to increase output, and after the equivalence ratio reaches a predetermined value, start the supply of gaseous ammonia to perform multi-fuel operation. In addition, when increasing the injection amount of liquid auxiliary fuel, the supply air pressure may be controlled to control the supply air amount, so that the equivalence ratio can be controlled more accurately.

[0040] In the above-mentioned reciprocating engine system, the control device may start the reciprocating engine using only the liquid auxiliary fuel, operate the reciprocating engine using only the liquid auxiliary fuel until a temperature of an exhaust gas from the reciprocating engine reaches a predetermined temperature, and perform a mixed combustion operation using the liquid auxiliary fuel and the ammonia after the temperature of the exhaust gas reaches the predetermined temperature.

[0041] As a condition for starting the multi-fuel operation, the temperature of the exhaust gas from the reciprocating engine is measured by a sensor. Then, the multi-fuel operation is started on the condition that the measured value of the sensor has risen to a predetermined temperature determined in advance by experiments or the like. This is expected to result in good combustion of ammonia. Furthermore, when a catalytic treatment device for treating exhaust gas is used as described below, the nitrogen oxides (NOx), nitrous oxide, and unburned ammonia generated by the multi-fuel operation can be treated by starting the multi-fuel operation after the temperature of the exhaust gas has reached a treatment temperature at which the catalyst functions.

[0042] In the above-mentioned reciprocating engine system, a catalytic treatment device is provided downstream of the exhaust passage of the cylinder and treats the exhaust gas exhausted from the cylinder using a catalyst, and the control device may start the reciprocating engine using only the liquid auxiliary fuel, operate the engine using only the liquid auxiliary fuel until the temperature of the catalytic treatment device reaches a treatment temperature at which the catalyst functions, and perform the mixed combustion operation after the temperature of the catalytic treatment device has reached the treatment temperature.

[0043] When a catalytic converter is used to treat exhaust gas, the temperature of the catalytic converter is measured by a sensor. Then, when the sensor measurement value reaches the treatment temperature at which the catalyst functions, the mixed combustion operation is started. This allows the nitrogen oxides (NOx), nitrous oxide, and unburned ammonia generated by the mixed combustion operation to be effectively treated.

[0044] The above reciprocating engine system may further include a heating device that heats the catalytic treatment device, and the control device may heat the catalytic treatment device using the heating device so that the temperature of the catalytic treatment device reaches the treatment temperature.

[0045] If a reciprocating engine is started using only liquid auxiliary fuel, the catalytic treatment device is heated by the exhaust gas generated by the combustion of the liquid auxiliary fuel. However, in order to raise the temperature of the catalytic treatment device to a treatment temperature at which the catalyst functions, it is necessary to increase the supply of liquid auxiliary fuel and maintain the increased output state for a while, and heat the catalytic treatment device with high-temperature exhaust gas. If the catalytic treatment device is heated by a heating device, it will reach the treatment temperature at which the catalyst functions in a shorter time, and mixed combustion operation can be started. As a heating device, an electric heater or a device that heats by burning fuel can be used.

[0046] In the above-mentioned reciprocating engine system, the reciprocating engine may be a marine engine that directly or indirectly drives a propeller, and the control device may increase an output by increasing the amount of the liquid auxiliary fuel supplied, and then increase the amount of the ammonia supplied while decreasing the amount of the liquid auxiliary fuel supplied.

[0047] In the case where the reciprocating engine is a marine engine that directly or indirectly drives a propeller, the amount of liquid auxiliary fuel supplied may be increased to increase the output, and then the amount of gaseous ammonia supplied may be increased while decreasing the amount of liquid auxiliary fuel supplied. As described above, when the output of the reciprocating engine is small, the amount of heat generated is small, so ammonia is difficult to burn. Therefore, the amount of liquid auxiliary fuel supplied is increased to increase the output, the amount of heat generated is increased, and the temperature of the reciprocating engine body and the cooling water is raised. In this state, if the amount of gaseous ammonia supplied is increased while decreasing the amount of liquid auxiliary fuel supplied, it is possible to perform a multi-fuel operation while suppressing an increase in the emission of unburned ammonia. The increase in output by increasing the amount of liquid auxiliary fuel supplied may be performed until the rotation speed or output reaches the rated value, or may be performed until an appropriate intermediate output is reached below the rated value. Here, the term "the reciprocating engine directly drives the propeller" includes the case where the output shaft of the reciprocating engine mechanically drives the propeller via a reduction gear etc. if necessary. The term "the reciprocating engine indirectly drives the propeller" includes the case where the reciprocating engine drives a generator and the resulting electricity is used to drive the propeller with a motor.

[0048] In the above reciprocating engine system, the reciprocating engine may be a power generation engine that drives a generator, and the control device may increase the amount of the liquid auxiliary fuel supplied when a load is applied, thereby increasing an output, and then increase the amount of the ammonia supplied while decreasing the amount of the liquid auxiliary fuel supplied.

[0049] In the case where the reciprocating engine is a power generation engine that drives a generator, when a load is applied, the amount of liquid auxiliary fuel supplied may be increased to increase the output, and then the amount of gaseous ammonia supplied may be increased while decreasing the amount of liquid auxiliary fuel supplied. In particular, in the case of a power generation engine used for power generation, a load application operation is required in which the load on the power system is divided into several parts and connected to the generator in stages. When a load is applied, it is necessary to increase the output in a short time, but if the amount of ammonia supplied is increased in a short time, there is a concern that the amount of unburned ammonia will increase. When a load is applied, the amount of liquid auxiliary fuel supplied is increased to increase the output, and then the amount of gaseous ammonia supplied is increased while decreasing the amount of liquid auxiliary fuel supplied, so that a large load can be applied while suppressing the increase in unburned ammonia.

[0050] In the above reciprocating engine system, the reciprocating engine may have a multi-combustion operation mode in which the multi-combustion operation is performed, and a diesel operation mode in which the reciprocating engine is operated using only the liquid auxiliary fuel without supplying the ammonia.

[0051] In addition to a mixed combustion operation mode in which mixed combustion is performed, a reciprocating engine can have a diesel operation mode in which the required output is continuously output only with liquid auxiliary fuel without supplying gaseous ammonia. In marine engines, in order to ensure operational redundancy, there is a demand for operation only with liquid auxiliary fuel in addition to operation using gaseous ammonia. In addition, in power generation engines, there is a demand for operation only with liquid auxiliary fuel from the viewpoint of continuity of operation in an emergency. If a common rail type fuel injection device is used as a fuel injection device for injecting liquid auxiliary fuel during mixed combustion operation, it is advantageous in terms of control of injection timing and number of injections. By providing a mechanical fuel injection valve device in addition to this common rail type fuel injection device, operation only with liquid auxiliary fuel is also possible. In addition, by making the common rail type fuel injection device compatible with a range of larger injection amounts, one fuel injection device may be used to operate both the mixed combustion operation mode and the diesel operation mode.

[0052] The above-mentioned reciprocating engine system may further include an air supply device that supplies additional air to an intake side of the reciprocating engine, and the control device may temporarily supply air from the air supply device when switching from the multi-fuel operation mode to the diesel operation mode.

[0053] In a reciprocating engine system capable of operating in both a mixed-fuel operation mode and a diesel operation mode, if any problem occurs in maintaining operation in the mixed-fuel operation mode, it is necessary to switch to the diesel operation mode in a short time. Examples of such problems include a large load fluctuation that exceeds expectations or a symptom of an abnormality in the reciprocating engine system. When the engine is operated by mixing gaseous ammonia and liquid auxiliary fuel, the operating point of the turbocharger is significantly different from when the engine is operated with only liquid auxiliary fuel at the same load. The operating point of the turbocharger is significantly higher when the engine is operated with only liquid auxiliary fuel, in terms of the air volume and the boost pressure. On the other hand, when a reciprocating engine is operated by mixing gaseous ammonia, a valve provided in the exhaust bypass is opened to lower the operating point of the turbocharger, and a valve provided in the intake bypass is used to release a certain amount of air. Therefore, if the fuel is instantly switched from gaseous ammonia fuel to liquid fuel, there is a concern that smoke will be emitted due to a lack of air, and that the engine output and engine speed will decrease. Therefore, in order to compensate for the shortage of air, additional air is supplied from the air supply device until the rotation speed of the turbocharger increases after the valves provided in the intake bypass passage and the exhaust bypass passage are closed, thereby ensuring the amount of air required for combustion of the liquid auxiliary fuel. As the air supply device, for example, an air tank filled with air is simply used, or an electric blower may also be used.

[0054] The reciprocating engine system may include a variable capacity turbocharger having a variable mechanism in a compressor or a turbine, and the control device may control a capacity of the turbocharger in the multi-fuel operation mode to maintain a rotation speed of the turbocharger higher than a speed required for supercharging, and may supply more air by controlling the capacity of the turbocharger when switching from the multi-fuel operation mode to the diesel operation mode.

[0055] As mentioned above, when the fuel is instantly switched from gaseous ammonia fuel to liquid fuel, a shortage of air occurs. Therefore, a variable displacement turbocharger equipped with a variable mechanism in the compressor or turbine is used. As a variable displacement turbocharger, there is one in which a wedge-shaped movable vane is provided at the intake port on the compressor side, and the amount of air sucked into the impeller is adjusted by changing the angle of the movable vane (inlet guide vane, IGV). As another variable displacement turbocharger, there is one in which a movable vane is provided at the nozzle part where the exhaust gas is blown in on the turbine side. For example, in the case of an IGV, the movable vane is controlled to a state in which it is narrowed down more than the optimal value for the operating state at that time during multi-combustion operation, so that the rotation speed of the turbocharger is maintained higher than necessary. Then, when switching from the multi-combustion operation mode to the diesel operation mode, the movable vane is temporarily opened to convert the rotational energy of the turbocharger into the amount of air, and a large amount of air is temporarily secured.

[0056] The reciprocating engine system may further include a catalytic treatment device provided downstream of an exhaust passage of the cylinder for treating exhaust gas exhausted from the cylinder using a catalyst, and the ammonia fuel supply device may supply a portion of the ammonia as a reducing agent to the catalytic treatment device during the multi-fuel operation.

[0057] In the case of ammonia and liquid auxiliary fuel co-firing operation, in addition to the generation of nitrogen oxides (NOx), which was also a problem in conventional diesel engines, there is a concern about the generation of nitrous oxides and unburned ammonia. It is difficult to deal with these issues with the engine alone. Therefore, it is advisable to provide a selective reduction catalyst that processes nitrogen oxides and nitrous oxides and an oxidation catalyst that processes unburned ammonia, or an oxidation-reduction catalyst that performs both the functions of a reduction catalyst and an oxidation-reduction catalyst. Here, since unburned ammonia acts as a reducing agent that takes oxygen away from nitrogen oxides and nitrous oxides in the selective reduction catalyst or the oxidation-reduction catalyst, it is necessary to consider the generation ratio of these in the exhaust gas. When the ratio of the amount of unburned ammonia generated is greater than the amount of nitrogen oxides and nitrous oxide generated, most of the nitrogen oxides and nitrous oxides are reduced by the unburned ammonia and become harmless. In addition, the remaining unburned ammonia that has not been reduced to nitrogen oxides and nitrous oxides is oxidized by oxygen in the exhaust gas in the oxidation catalyst or the oxidation-reduction catalyst and becomes harmless. On the other hand, when the ratio of the amount of unburned ammonia generated is smaller than the amount of nitrogen oxides and nitrous oxide generated, the nitrogen oxides and nitrous oxides that cannot be reduced are discharged. Therefore, gaseous ammonia is supplied upstream of the selective reduction catalyst or the oxidation reduction catalyst. This makes it possible to make up for the shortage of ammonia even when the ratio of the amount of ammonia generated is small. In addition, as the gaseous ammonia to be supplied, a branch is provided in the system of the gaseous ammonia supplied from the ammonia supply device to the reciprocating engine as fuel, and a part of the ammonia as fuel is diverted and supplied to the catalyst. This allows the ammonia storage equipment and replenishment work to be shared. Here, it is desirable to provide sensors such as a NOx sensor and an ammonia sensor in the exhaust passage and adjust the amount of gaseous ammonia supplied depending on the components of the exhaust gas to be measured.

[0058] In the above reciprocating engine system, the ammonia fuel supply device may further supply a portion of the ammonia as a reducing agent to the catalytic treatment device even when the reciprocating engine system is operated using only the liquid auxiliary fuel.

[0059] As described above, in the mixed combustion operation of ammonia and liquid auxiliary fuel, a state occurs in which the amount of ammonia supplied is set to zero and the engine operates only with the liquid auxiliary fuel. There is also a demand for a diesel operation mode in which the required output is continuously output only with the liquid auxiliary fuel without supplying gaseous ammonia. On the other hand, since it is necessary to increase the compression end temperature in a reciprocating engine that uses ammonia as fuel, when the engine operates only with the liquid auxiliary fuel, there is a possibility that the generation of NOx will increase more than in a conventional diesel engine. Therefore, in an operating state in which only liquid auxiliary fuel is supplied to the reciprocating engine, NOx is treated by supplying gaseous ammonia upstream of the selective reduction catalyst or the oxidation reduction catalyst. Here, when only liquid auxiliary fuel is supplied, it is desirable to increase the amount of gaseous ammonia supplied compared to when mixed combustion operation of ammonia and liquid auxiliary fuel is performed. This is because, when only liquid auxiliary fuel is supplied, there is no generation of unburned ammonia, and it is necessary to compensate for this by increasing the amount of gaseous ammonia supplied.

[0060] A method for operating a reciprocating engine according to one embodiment of the present invention is a method for operating a reciprocating engine having a cylinder that forms a combustion chamber, a piston that reciprocates within the cylinder, an ammonia fuel supply device that supplies gaseous ammonia to the cylinder and premixes it with air, and a liquid auxiliary fuel supply device that supplies liquid auxiliary fuel to the cylinder to ignite the ammonia, wherein a multi-fuel operation is performed using the ammonia and the liquid auxiliary fuel when the compression end temperature within the cylinder is equal to or higher than a predetermined temperature at which no combustion delay of the ammonia occurs.

[0061] As a result of intensive research, the inventors of the present application have concluded that it is optimal to perform a mixed combustion operation in a reciprocating engine by premixing ammonia in a gaseous state with air, compressing the mixture in the cylinder, injecting liquid auxiliary fuel into the cylinder and igniting the mixture of gaseous ammonia and air. Furthermore, the inventors of the present application have found that, although the temperature of the mixture in the cylinder rises when the mixture is compressed in the cylinder as the work from the piston is converted into heat, good combustion of ammonia can be achieved by setting the compression end temperature, which is the temperature of the mixture when the piston reaches the top dead center, to a predetermined temperature or higher at which ammonia combustion delay does not occur. As a result, it is possible to set the ratio of ammonia to liquid auxiliary fuel to, for example, 80% or more in terms of heat ratio, and the effect of reducing carbon dioxide emissions can be further increased in a reciprocating engine that uses ammonia as fuel. Effect of the Invention

[0062] According to the above aspect of the present invention, in a reciprocating engine that uses ammonia as fuel, the effect of reducing carbon dioxide emissions can be increased. [Brief description of the drawings]

[0063] [Figure 1] 1 is a configuration diagram of a reciprocating engine system according to an embodiment. FIG. [Diagram 2] FIG. 2 is an explanatory diagram illustrating the operation of a diesel operation mode of the reciprocating engine according to one embodiment. [Diagram 3] FIG. 4 is an explanatory diagram illustrating the operation of a multi-fuel operation mode of the reciprocating engine according to one embodiment. [Figure 4] 1 is a configuration diagram of an intake and exhaust system of a reciprocating engine system according to an embodiment of the present invention; [Diagram 5] FIG. 4 is a configuration diagram showing a modified example of an intake and exhaust system of the reciprocating engine system according to the embodiment. [Figure 6] 1 is a configuration diagram of a catalyst treatment device according to an embodiment; [Figure 7]1 is a graph showing a relationship between the compression end temperature in the cylinder according to an embodiment and the combustion delay of a mixture of gaseous ammonia and air, based on the injection timing of liquid auxiliary fuel. [Figure 8] 1 is a graph showing the relationship between the equivalence ratio of the entire fuel and N2O and unburned NH3 in the exhaust gas in a multi-combustion operation of gaseous ammonia and liquid auxiliary fuel according to an embodiment. [Figure 9] FIG. 4 is an explanatory diagram illustrating the operation of a reciprocating engine according to one embodiment when the engine is a marine engine. [Figure 10] 1 is a diagram illustrating the operation of a power generation engine in which a reciprocating engine drives a generator according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0065] FIG. 1 is a configuration diagram of a reciprocating engine system 1 according to one embodiment. As shown in Fig. 1, the reciprocating engine system 1 includes a reciprocating engine 2 and a control device 3 for the reciprocating engine 2. The reciprocating engine 2 shown in Fig. 1 is a marine engine that directly or indirectly drives a propeller. Note that the reciprocating engine 2 may also be a power generation engine that drives a generator, as described below.

[0066] The reciprocating engine 2 includes a cylinder 11 that forms a combustion chamber 10, a piston 12 that reciprocates within the cylinder 11, a crankshaft 13 connected to the piston 12, a rotation detection sensor 14 that detects the rotation of the crankshaft 13, and a torque detection sensor 15 that detects the torque of the crankshaft 13. The crankshaft 13 is connected to, for example, the rotating shaft of a propeller of a ship.

[0067] An intake passage 20 and an exhaust passage 30 are connected to the cylinder head of the cylinder 11. In addition, an intake valve 21 for opening and closing the intake passage 20 and an exhaust valve 31 for opening and closing the exhaust passage 30 are provided in the cylinder head. In addition, a liquid fuel injection valve 53 for injecting liquid auxiliary fuel into the combustion chamber 10 and an ignition device 55 are provided in the cylinder head. The ignition device 55 is, for example, a micro pilot oil injection valve, and is used in a mixed combustion operation mode described later.

[0068] The intake passage 20 includes a compressor 22 that compresses air for combustion, an air cooler 23 installed downstream of the compressor 22, and a fuel gas injector 43 installed downstream of the air cooler 23. The fuel gas injector 43 injects gaseous ammonia, which serves as fuel, into the intake passage 20. The gaseous ammonia is premixed with compressed air in the intake passage 20 to form an air-fuel mixture, which is then supplied into the cylinder.

[0069] The air cooler 23 may be an air cooler / heater having not only the function of cooling air with cold water but also the function of heating air with hot water, a heater, or the like. If necessary, an air heater 24 may be provided upstream of the compressor 22 in the intake passage 20. The air heater 24 may have, for example, a cooling / heating system 25 that uses a refrigerant that has exchanged heat with the reciprocating engine 2 as a heat source.

[0070] The exhaust passage 30 includes a turbine 33 that is rotated by the exhaust gas discharged from the combustion chamber 10, and a catalytic treatment device 60 that is installed downstream of the turbine 33 and treats substances contained in the exhaust gas. As shown in Fig. 4, which will be described later, the rotating shaft of the turbine 33 is connected to the compressor 22, and the exhaust gas serves as a rotation source to rotate the compressor 22. In other words, the turbine 33 and the compressor 22 constitute a turbocharger 4.

[0071] 1, the catalytic treatment device 60 uses a catalyst to treat specific substances such as nitrogen oxides (NOx), nitrous oxide, and unburned ammonia that are generated by the combustion of ammonia and liquid auxiliary fuel. The catalytic treatment device 60 is equipped with a detection sensor 61 that detects the specific substances.

[0072] The reciprocating engine 2 includes an ammonia fuel supply device 40 that supplies ammonia into the cylinder 11, and a liquid auxiliary fuel supply device 50 that supplies liquid auxiliary fuel that ignites the ammonia into the cylinder 11. The ammonia fuel supply device 40 includes an ammonia tank 41, a vaporizer 42, and a fuel gas injector 43.

[0073] The ammonia tank 41 contains liquid ammonia. The vaporizer 42 vaporizes the liquid ammonia discharged from the ammonia tank 41 to generate gaseous ammonia. Here, the vaporizer 42 may include a pressure pump that pressurizes the gaseous ammonia. The vaporizer 42 is connected to the fuel gas injection valve 43 via an ammonia supply path 44. The ammonia supply path 44 includes a regulator 44a and a pressure sensor 44b installed downstream of the regulator 44a.

[0074] The ammonia supply path 44 further includes a second ammonia supply path 45 branched off upstream of the regulator 44a. The second ammonia supply path 45 is connected to the above-mentioned catalytic treatment device 60. The second ammonia supply path 45 includes a regulator 45a and a pressure sensor 45b disposed downstream of the regulator 45a.

[0075] The liquid auxiliary fuel supply device 50 includes a liquid auxiliary fuel tank 51, a first liquid fuel supply pump 52, a liquid fuel injection valve 53, a second liquid fuel supply pump 54, and an ignition device 55. The liquid auxiliary fuel tank 51 stores liquid auxiliary fuel. The first liquid fuel supply pump 52 supplies the liquid auxiliary fuel stored in the liquid auxiliary fuel tank 51 to the liquid fuel injection valve 53.

[0076] The liquid fuel injection valve 53 is, for example, a mechanical fuel injection device used in a diesel operation mode described later. The second liquid fuel supply pump 54 supplies the liquid auxiliary fuel stored in the liquid auxiliary fuel tank 51 to the ignition device 55. The ignition device 55 is, for example, a common rail type fuel injection device used in a multi-fuel operation mode described later.

[0077] The reciprocating engine 2 having the above-described configuration has a multi-fuel operation mode in which ammonia and liquid auxiliary fuel are used for multi-fuel operation, and a diesel operation mode in which operation is performed using only the liquid auxiliary fuel without supplying ammonia.

[0078] FIG. 2 is an explanatory diagram for explaining the operation of the reciprocating engine 2 in the diesel operation mode according to one embodiment. 2, in the diesel operation mode, liquid auxiliary fuel such as heavy oil is injected from the liquid fuel injector 53 into the combustion chamber 10 and is ignited and burned in the compressed air compressed by the piston 12. At this time, the fuel gas injector 43 is stopped.

[0079] FIG. 3 is an explanatory diagram for explaining the operation of the reciprocating engine 2 in the multi-fuel operation mode according to one embodiment. As shown in Fig. 3, in the multi-fuel operation mode, gaseous ammonia is injected from the fuel gas injector 43 into the intake passage 20 and premixed with air just before the combustion chamber 10. Next, liquid auxiliary fuel for ignition is injected from the ignition device 55 into the combustion chamber 10, and the mixture compressed by the piston 12 is ignited and burned. At this time, the liquid fuel injector 53 is stopped.

[0080] FIG. 4 is a configuration diagram of an intake and exhaust system of the reciprocating engine system 1 according to one embodiment. As shown in FIG. 4, the intake and exhaust system of the reciprocating engine system 1 includes a load L, a reciprocating engine 2, a turbocharger 4, an air cooler 23, a pressure sensor 26, a rotation detection sensor 14, a torque detection sensor 15, a first drive unit 70, a first flow control valve 71, a second drive unit 80, a second flow control valve 81, an intake passage 20, an intake bypass passage 20a, an exhaust passage 30, an exhaust bypass passage 30a, and a control device 3.

[0081] The load L is a load that impedes the rotation of the engine. For example, when the reciprocating engine system 1 is installed in a ship, the load L includes a mechanical load when driving a propeller, etc. When the reciprocating engine system 1 is installed in a vehicle, the load L includes a mechanical load when driving a clutch, gears, a throttle valve, wheels, etc. When the reciprocating engine system 1 is used for power generation, the load L includes an electrical and mechanical load when driving a generator, etc.

[0082] The reciprocating engine 2 includes, for example, a plurality of cylinders (combustion chambers) 11. Air compressed and supplied by the turbocharger 4 is sent to an air cooler 23 via an intake passage 20, and then sent to the reciprocating engine 2.

[0083] The reciprocating engine 2 burns air compressed and supplied by the turbocharger 4 in each cylinder 11, causing the internal pistons 12 to reciprocate. The reciprocating engine 2 converts the reciprocating motion of the pistons 12 in the cylinders 11 into rotational motion by connecting rods and crankshafts 13 (not shown). As a result, the reciprocating engine 2 provides energy based on this rotational motion to a load L, thereby driving the load L.

[0084] As described above, the turbocharger 4 includes the compressor 22 and the turbine 33. The compressor 22 takes in air from the outside in response to the rotation of the turbine 33, and compresses the pressure of the taken-in air to atmospheric pressure or higher. The compressor 22 then supplies the compressed air to the reciprocating engine 2 via the intake passage 20. The turbine 33 takes in exhaust gas combusted in the reciprocating engine 2, and rotates in accordance with the amount of the taken-in exhaust gas. The turbine 33 then exhausts the exhaust gas used as a driving source for rotation to the outside.

[0085] The air cooler 23 is provided in a part of the intake passage 20 for supplying air from the turbocharger 4 to the reciprocating engine 2. The air cooler 23 cools the air passing through the inside of the intake passage 20 with cooling water supplied at a predetermined pressure from the outside via a supply passage (not shown). The cooling water is, for example, industrial water, seawater, or circulating cooling water.

[0086] The pressure sensor is provided, for example, in the intake passage 20 downstream of the air cooler , and measures the pressure of the air cooled by the air cooler (for example, in units of [Pa]).

[0087] The rotation detection sensor 14 detects, for example, the rotation speed of the rotating shaft of the crankshaft 13. Note that the rotation detection sensor 14 may detect the number of rotations or the rotation angular velocity of the rotating shaft.

[0088] The torque detection sensor 15 detects, for example, the amount of torsion (e.g., the amount of displacement) of the rotating shaft of the crankshaft 13, and derives the torque based on the amount of torsion and the radius of the rotating shaft. Note that one or both of the rotation detection sensor 14 and the torque detection sensor 15 may be a torsion detection sensor such as a shaft horsepower meter, or may be an eddy current type electric dynamometer.

[0089] The first drive unit 70 and the second drive unit 80 are, for example, electromagnetic, hydraulic, or pneumatic actuators. Each of the first drive unit 70 and the second drive unit 80 is driven under the control of the control device 3. The first drive unit 70 drives the first flow rate adjustment valve 71 and adjusts the valve opening degree of the first flow rate adjustment valve 71. The second drive unit 80 drives the second flow rate adjustment valve 81 and adjusts the valve opening degree of the second flow rate adjustment valve 81.

[0090] The intake bypass passage 20a is provided in a part of the intake passage 20, and supplies a part of the air passing through the inside of the intake passage 20 to the compressor 22 of the turbocharger 4 for circulation. As shown in Fig. 4, for example, the intake bypass passage 20a is provided in the intake passage 20 on the upstream side of the air cooler 23. Note that the intake bypass passage 20a may be provided in the intake passage 20 on the downstream side of the air cooler 23. In this case, the intake bypass passage 20a supplies a part of the air cooled by the air cooler 23 to the compressor 22 of the turbocharger 4 for circulation.

[0091] The exhaust bypass passage 30 a is provided in a part of the exhaust passage 30 , and discharges a part of the exhaust gas passing through the inside of the exhaust passage 30 to the outside without passing through the turbine 33 of the turbocharger 4 .

[0092] The first flow rate control valve 71 is provided in the intake bypass passage 20a and adjusts the flow rate of air circulating to the compressor 22 via the intake bypass passage 20a. The first flow rate control valve 71 divides the air supplied from the compressor 22, for example, into the intake passage 20 toward the air cooler 23 and the intake bypass passage 20a in an amount corresponding to the valve opening. When the first flow rate control valve 71 is fully open (when the valve opening is "1"), the air supplied from the compressor 22 is divided into the intake passage 20 toward the air cooler 23 and the intake bypass passage 20a. When the first flow rate control valve 71 is closed (when the valve opening is "0"), the entire amount of air supplied from the compressor 22 flows only into the intake passage 20 toward the air cooler 23.

[0093] The second flow rate control valve 81 is provided in the exhaust bypass passage 30a and controls the flow rate of exhaust gas discharged to the outside through the exhaust bypass passage 30a. The second flow rate control valve 81 divides the exhaust gas discharged from the reciprocating engine 2, for example, into the exhaust passage 30 toward the turbocharger 4 and the exhaust bypass passage 30a in an amount corresponding to the valve opening. For example, when the valve is fully open (when the valve opening is "1"), the exhaust gas discharged from the reciprocating engine 2 is divided into the exhaust passage 30 toward the turbocharger 4 and the exhaust bypass passage 30a. When the valve is closed (when the valve opening is "0"), the exhaust gas discharged from the reciprocating engine 2 flows entirely into only the exhaust passage 30 toward the turbocharger 4.

[0094] The control device 3 includes, for example, a first control unit 110, a second control unit 120, a common unit thereof, and a storage unit (not shown). The common unit is a third control unit different from the first control unit 110 and the second control unit 120, and a part or all of the processing performed by the control device 3 itself may be performed by the first control unit 110 or the second control unit 120.

[0095] Any or all of the above-mentioned first control unit 110, second control unit 120, and common unit (third control unit) are realized by, for example, a processor such as a CPU (Central Processing Unit) executing a program stored in a storage unit. In addition, one or both of the first control unit 110 and the second control unit 120 may be realized by hardware such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array).

[0096] The storage unit is realized by, for example, a hard disk drive (HDD), a flash memory, an electrically erasable programmable read only memory (EEPROM), a read only memory (ROM), a random access memory (RAM), etc. The storage unit stores firmware, programs executed by the processor, etc.

[0097] In the common section of the control device 3, for example, the output (work load [kW]) for the current load is derived based on the rotation speed detected by the rotation detection sensor 14 and the torque detected by the torque detection sensor 15, and the load factor is derived based on this current output and the rated output previously stored in the storage section. The load factor is derived, for example, by dividing the current output by the rated output. The process of deriving the load factor may be performed by the first control section 110 or the second control section 120.

[0098] The first control unit 110 controls the first drive unit 70, which adjusts the valve opening degree of the first flow control valve 71, based on the boost pressure target value based on the load factor of the reciprocating engine 2 calculated by the common unit and the boost pressure measured by the pressure sensor 26.

[0099] First control unit 110 derives the pressure in intake passage 20 to be targeted during feedback control (hereinafter referred to as boost pressure target value) using the derived load factor and boost pressure target value derivation information previously stored in a storage unit. The boost pressure target value derivation information is information indicating a relationship between a predetermined load factor and boost pressure target value. This information is previously stored in the storage unit as, for example, a map or a function.

[0100] The second control unit 120 controls the second drive unit 80, which adjusts the valve opening degree of the second flow rate control valve 81, based on the valve opening degree information stored in advance in the storage unit and the load factor derived by the first control unit 110. In this way, the second control unit 120 controls the rotation speed of the turbocharger 4 based on the load factor of the internal combustion engine in operation.

[0101] The valve opening information is information indicating the relationship between a predetermined load rate and the valve opening of the second flow rate control valve 81 that is set so that the pressure in the exhaust passage 30 is an ideal value. The ideal value of the pressure in the exhaust passage 30 is, for example, the pressure in the exhaust passage 30 that is adjusted so that the pressure in the intake passage 20 can be kept at the boost pressure target value in a state in which the valve opening of the first flow rate control valve 71 at each load rate is maintained at a predetermined value or does not exceed a predetermined value. This valve opening information is stored in advance in a storage unit as, for example, a map or a function.

[0102] Fig. 5 is a configuration diagram showing a modified example of the intake and exhaust system of the reciprocating engine system 1 according to one embodiment. The intake and exhaust system shown in Fig. 5 shows a configuration that can be implemented additionally or alternatively in the intake and exhaust system shown in Fig. 4 described above. In Fig. 5, the same components as those described in Fig. 4 are given the same numbers. In the following, the description of the components given the same numbers will be omitted.

[0103] The reciprocating engine system 1 includes a turbocharger 4 having a compressor 22 and a turbine 33 for supercharging the reciprocating engine 2, an intake passage 20 connecting the compressor 22 and the reciprocating engine 2, and an exhaust passage 30 connecting the reciprocating engine 2 and the turbine 33.

[0104] The upstream side of the air cooler 23 in the intake passage 20 and the upstream side of the turbine 33 in the exhaust passage 30 are short-circuited via short-circuit paths 96, 97, and 98 (first short-circuit path). A first short-circuit valve 91 is provided between the short-circuit paths 96 and 97, and a second short-circuit valve 92 is provided between the short-circuit paths 97 and 98. A branch is provided in the short-circuit path 97, and one end of a short-circuit path 99 is connected to the branch via a third short-circuit valve 93, and the other end of the short-circuit path 99 is connected to the exhaust passage 30 downstream of the turbine 33. The intake passage 20 and the downstream of the turbine are short-circuited via the short-circuit paths 96, 97, and 99 (second short-circuit path). A catalytic treatment device 60, which will be described later, is provided further downstream in the exhaust passage 30. Temperature sensors 66, 67, and 68 are provided at the inlet of the turbine 33 in the exhaust passage 30, the inlet of the catalytic treatment device 60, and the catalytic treatment device 60, respectively. The catalyst treatment device 60 is also provided with a heater 69 for heating the catalyst treatment device 60 as required.

[0105] When the engine is operated by co-firing gaseous ammonia with liquid auxiliary fuel, the equivalence ratio of the entire fuel is higher than that of conventional diesel engines or gas engines using fuels such as natural gas, and therefore, at medium to high loads, the exhaust temperature at the inlet of the turbine 33 may exceed the allowable temperature of the turbine 33. Therefore, at medium to high loads, the air at the outlet of the compressor 22 is bypassed to the inlet of the turbine 33 by the first short-circuit path, thereby lowering the temperature of the exhaust gas flowing into the turbine 33 and making the exhaust temperature at the inlet of the catalytic treatment device 60 appropriate. When bypassing by the first short-circuit path, the third short-circuit valve 93 is closed, and the first short-circuit valve 91 and the second short-circuit valve 92 are opened, and the opening degree is adjusted by the control device 3.

[0106] On the other hand, when the load is low, the turbocharger 4 is not working sufficiently, so that the inlet pressure of the turbine 33 is higher than the outlet pressure of the compressor 22, and there is a risk of exhaust gas flowing back from the inlet of the turbine 33 to the outlet of the compressor 22. Therefore, when the load is low, the air at the outlet of the compressor 22 is bypassed downstream of the turbine 33 (catalyst inlet) through the second short-circuit path, so that the temperature of the exhaust gas flowing to the catalyst treatment device 60 is made appropriate. When bypassing through the second short-circuit path, the second short-circuit valve 92 is closed, and the first short-circuit valve 91 and the third short-circuit valve 93 are opened, and the opening degree is adjusted by the control device 3. If necessary, the first short-circuit valve 91 is closed, the second short-circuit valve 92 and the third short-circuit valve 93 are opened, and the opening degree is adjusted by the control device 3, resulting in a configuration similar to that of the second flow rate adjustment valve 81 described above, and the amount of exhaust gas supplied to the turbine 33 as the exhaust bypass path 30a can also be controlled.

[0107] The reciprocating engine system 1 is provided with a throttle valve 94 that limits the amount of air on the intake side of the reciprocating engine 2. In this embodiment, a throttle valve 94 is provided at the inlet of each of six cylinders 11, #1 to #6. The control device 3 controls the opening of the throttle valve 94 so that the equivalence ratio of ammonia to air falls within a range that enables multi-fuel operation using ammonia and liquid auxiliary fuel.

[0108] When the engine is operated by co-firing gaseous ammonia with liquid auxiliary fuel, the equivalence ratio of gaseous ammonia to air must be maintained within a certain range in relation to exhaust gas components such as nitrous oxide, unburned ammonia and other nitrogen oxides and combustion stability. However, since the absolute amount of ammonia required during low-load operation is small, the equivalence ratio of gaseous ammonia falls below the target range even in a naturally aspirated state in which the turbocharger 4 is not working. Therefore, a throttle valve 94 is provided at the intake inlet to throttle the intake amount, thereby maintaining the equivalence ratio of ammonia within a target range that allows co-firing operation. Here, the target range of the equivalence ratio of ammonia is 0.4 to 0.8. In this embodiment, a throttle valve 94 is provided at the inlet of each of the six cylinders 11, #1 to #6. However, a single throttle valve 94 may be provided in the intake passage 20 near the outlet or inlet of the air cooler 23, before the intake passage 20 branches off toward each cylinder.

[0109] The reciprocating engine system 1 includes an air tank device 95, which is an air supply device that supplies additional air, connected to the intake side of the reciprocating engine 2, specifically, near the outlet of the compressor 22 of the intake passage 20. The control device 3 temporarily supplies air from the air tank device 95 when switching from the multi-fuel operation mode to the diesel operation mode.

[0110] In the reciprocating engine system 1 capable of operating in both the multi-fuel operation mode and the diesel operation mode, it may be necessary to switch to the diesel operation mode in a short time if some problem occurs in maintaining operation in the multi-fuel operation mode. In this case, there is a concern that smoke will be emitted, and that the engine output and engine speed will decrease due to a shortage of air. Therefore, additional air is supplied from the air tank device 95 to make up for the shortage of air until the speed of the turbocharger 4 increases by closing the valves provided in the intake bypass passage 20a and the exhaust bypass passage 30a, thereby ensuring the amount of air required for combustion of the liquid auxiliary fuel.

[0111] As another example that does not use the air tank device 95, a variable displacement type (IGV) may be used in which a wedge-shaped movable vane (wing) is provided at the intake port of the compressor 22 of the turbocharger 4, and the amount of air sucked into the impeller is adjusted by changing the angle of the movable vane. In the multi-fuel operation mode, the control device 3 controls the movable vane to a state in which the angle is narrowed more than the optimal angle in the operating state of the multi-fuel operation at that time, thereby maintaining the rotation speed of the turbocharger higher than necessary. Then, when switching from the multi-fuel operation mode to the diesel operation mode, the control device 3 controls the movable vane to be temporarily opened. This converts the rotational energy of the turbocharger into the amount of air, and temporarily ensures a large amount of air. After the switch to the diesel operation mode is completed, the control device 3 controls the movable vane to be at an angle suitable for diesel operation.

[0112] FIG. 6 is a configuration diagram of a catalyst treatment device 60 according to one embodiment. 6(a) includes a selective reduction catalyst tank 62 for treating exhaust gas discharged from the reciprocating engine 2, and an oxidation catalyst tank 63 for further treating exhaust gas discharged from the selective reduction catalyst tank 62. A portion of the gaseous ammonia supplied as fuel to the reciprocating engine 2 is branched and guided to the upstream side of the selective reduction catalyst tank 62 via the second ammonia supply passage 45, and is injected into the exhaust gas from an injection nozzle (not shown). At least one of the downstream side of the selective reduction catalyst tank 62 and the downstream side of the oxidation catalyst tank 63 is provided with a detection sensor 61 such as a NOx sensor or an ammonia sensor, and the supply amount of gaseous ammonia is adjusted according to the components in the exhaust gas to be measured.

[0113] In the mixed combustion operation of ammonia and liquid auxiliary fuel, in addition to nitrogen oxides (NOx), nitrous oxide and unburned ammonia are generated in the exhaust gas of the engine. This unburned ammonia acts as a reducing agent that removes oxygen from the nitrogen oxides and nitrous oxide in the selective reduction catalyst tank 62. When the generation rate of unburned ammonia is insufficient compared to the generation rate of nitrogen oxides and nitrous oxide, the shortage of gaseous ammonia is injected into the exhaust gas from the injection nozzle of the second ammonia supply passage 45.

[0114] Most of the nitrogen oxides and nitrous oxides are reduced and rendered harmless in the selective reduction catalyst tank 62. In addition, in the operation of co-firing gaseous ammonia and liquid auxiliary fuel, it is desirable that the equivalence ratio of the total fuel to air is between 0.5 and 1.0, and most actual operation is performed in the lean burn region where the equivalence ratio is less than 1.0. Therefore, a certain proportion of oxygen is contained in the exhaust gas. In cases where the generation rate of unburned ammonia is high compared to the generation rates of nitrogen oxides and nitrous oxide, for example, and excess ammonia remains in the exhaust gas, the ammonia is oxidized by the oxygen in the exhaust gas in the downstream oxidation catalyst tank 63 and rendered harmless.

[0115] In the example shown in Fig. 6(b), an oxidation catalyst tank 64 is further provided between the reciprocating engine 2 and the selective reduction catalyst tank 62 in the example shown in Fig. 6(a). In this way, the oxidation catalyst tank 64 immediately after the reciprocating engine 2 can more effectively treat unburned hydrocarbons and carbon monoxide in the exhaust gas.

[0116] In the example shown in Fig. 6(c), an oxidation-reduction catalyst tank 65 is provided downstream of the reciprocating engine 2. The oxidation-reduction catalyst tank 65 promotes both the reduction reaction of nitrogen oxides and nitrous oxide by ammonia and the oxidation reaction of ammonia by oxygen in the exhaust gas. In this example as well, the effects of the reduction of nitrogen oxides and nitrous oxide by ammonia and the oxidation of ammonia by oxygen in the exhaust gas can be obtained.

[0117] The reciprocating engine system 1 having the above-mentioned configuration is characterized in that it performs a mixed combustion operation using ammonia and liquid auxiliary fuel when the compression end temperature in the cylinder 11 is equal to or higher than a predetermined temperature at which ammonia combustion delay does not occur. The following Figures 7 and 8 show the results of a mixed combustion test of gaseous ammonia and liquid auxiliary fuel, which was conducted using a rapid compression and expansion device that reproduced only the cylinder 11 portion of the above-mentioned reciprocating engine 2.

[0118] FIG. 7 is a graph showing the relationship between the compression end temperature in the cylinder 11 according to one embodiment and the combustion delay of the mixture of gaseous ammonia and air, based on the injection timing of the liquid auxiliary fuel. In the figure, the dashed line shows the measured values ​​of the combustion delay (ignition delay) versus the compression end temperature when the intake pressure is 0.1 MPa and the compression end pressure is 2.6 MPa, while the dashed line shows the measured values ​​when the intake pressure is 0.2 MPa and the compression end pressure is 5.3 MPa. In either case, the combustion delay increases when the compression end temperature is below 750 K, and the combustion delay is particularly significant under the former condition of low intake pressure. Thus, it can be seen that the compression end temperature has a dominant effect on the combustion of ammonia mixture.

[0119] 8 is a graph showing the relationship between the equivalence ratio of the entire fuel and the amount of N2O (solid line) and unburned NH3 (dashed line) in the exhaust gas in a mixed combustion operation of gaseous ammonia and liquid auxiliary fuel according to one embodiment. When the equivalence ratio of the entire fuel to air is less than 0.5, the generation of nitrous oxide increases rapidly as the equivalence ratio decreases. Also, when the equivalence ratio of the entire fuel to air is set to 1.0 or more, there is a shortage of air required for fuel combustion, and the fuel is discharged as an unburned component. In this case, it can be seen that ammonia is mainly discharged as an unburned component because ammonia is more difficult to burn than the liquid auxiliary fuel.

[0120] The specifications of the reciprocating engine 2 (actual in-line engine) shown in FIG. 1 and the preliminary test single-cylinder engine used in the preliminary experiment are as follows:

[0121] (1) Single-cylinder engine for preliminary testing Number of cylinders: 1 Bore x stroke 180 x 200 mm Stroke volume per cylinder 5089 cc Rated speed: 1000~1200 rpm

[0122] (2) In-line engine for actual aircraft Number of cylinders: 6 Bore x stroke 280 x 390 mm Stroke volume per cylinder 24014 cc Rated speed: 750 ~800 rpm

[0123] Next, an operation of the reciprocating engine system 1 having the above configuration (a method of operating the reciprocating engine 2) will be described. Note that the following operation is mainly controlled by the control device 3.

[0124] The reciprocating engine system 1 of this embodiment uses ammonia as fuel. As shown in Fig. 1, the ammonia used as fuel is pressurized and stored in an ammonia tank 41 in a liquid state, and is vaporized by a vaporizer 42 to become gaseous ammonia. The pressure of the gaseous ammonia is controlled by a regulator 44a, and the gaseous ammonia is supplied to the intake passage 20 via a fuel gas injection valve 43 (electromagnetic valve). In addition, a part of the gaseous ammonia is branched off, and the pressure is controlled by a regulator 45a, and the gaseous ammonia is supplied to a catalyst treatment device 60.

[0125] The liquid auxiliary fuel is injected into the combustion chamber 10 by the liquid fuel injection valve 53 and the ignition device 55. The liquid fuel injection valve 53 is, for example, a mechanical fuel injection device, and the ignition device 55 is, for example, a common rail fuel injection device. In the mixed combustion operation mode of gaseous ammonia and liquid auxiliary fuel, a common rail fuel injection device (ignition device 55) that allows easy adjustment of fuel injection timing is mainly used, but a mechanical fuel injection device (liquid fuel injection valve 53) may also be used as an auxiliary. In addition, by performing multi-stage injection using the common rail fuel injection device (ignition device 55), there is an effect of improving the combustibility of ammonia.

[0126] In the diesel operation mode using only liquid auxiliary fuel, a mechanical fuel injection device (liquid fuel injection valve 53) is mainly used. Heavy oil and light oil can generally be used as the liquid auxiliary fuel. The liquid auxiliary fuel used here may be a CO2-free alternative fuel such as biofuel, which prevents the generation of carbon dioxide over its life cycle. In this case, combined with the effect of using ammonia, it is possible to reduce carbon dioxide emissions by almost 100%.

[0127] A valve train having a variable valve timing mechanism may be used as the valve train of the intake valve 21. This allows the effective compression ratio to be varied by making the timing of closing the intake valve 21 earlier than the timing of the bottom dead center of the piston 12 in the intake stroke (early closing) or later than the timing of the bottom dead center (late closing). For example, when the reciprocating engine 2 is started or in an operating state with low output, the compression end temperature can be increased by increasing the effective compression ratio, and the engine can be shifted from an operation using only liquid auxiliary fuel to an operation using gaseous ammonia and liquid auxiliary fuel at an earlier timing. In addition, by lowering the effective compression ratio in an operating state with high output, the pressure inside the cylinder 11 can be prevented from becoming excessively high, and the Miller cycle can be used to improve efficiency.

[0128] In the intake passage 20, an air cooler 23 is provided downstream of the compressor 22 of the turbocharger 4. The air cooler 23 may be an air cooler and heater having not only a function of cooling the intake air with cold water but also a function of heating the intake air with hot water, a heater, or the like. If necessary, an air heater 24 for heating the intake air may be provided upstream of the compressor. The air heater 24 has a cooling and heating system 25 that uses the cooling water that has exchanged heat with the reciprocating engine 2 as a heat source. When the reciprocating engine 2 is started or in an operating state with low output, the intake air can be heated by the air cooler 23 or the air heater 24 to increase the compression end temperature, and the operation can be shifted from an operation using only liquid auxiliary fuel to a mixed combustion operation using gaseous ammonia and liquid auxiliary fuel at an earlier timing. In addition, a temperature sensor (not shown) may be provided at a position downstream of the compressor 22 in the intake passage 20, more specifically, near the outlet of the air cooler 23. In an operating range where the temperature of the intake air measured by this temperature sensor is lower than a predetermined temperature, the air cooler 23 or the air heating device 24 may heat the intake air.

[0129] FIG. 9 is an explanatory diagram for explaining the operation of the reciprocating engine 2 according to one embodiment when it is a marine engine. Here, a case where the reciprocating engine 2 directly drives a fixed pitch propeller will be described as a representative example. Even when the reciprocating engine 2 drives a variable pitch propeller, the same as FIG. 9 will be described except that the lines indicating the output and fuel supply amount shift up and down depending on the propeller pitch. Also, when the reciprocating engine 2 drives a generator and the motor drives a propeller with the obtained electric power, the amount of power generation may be increased or decreased while the rotation speed of the reciprocating engine 2 is constant. In this case, the operation conforms to the example of a generator engine that drives a generator described later, but when the amount of power generation is increased or decreased while the engine rotation speed is increased or decreased, the operation conforms to this embodiment.

[0130] The horizontal axis of FIG. 9 shows an example of time passage, the vertical axis (a) shows the rotation speed of the reciprocating engine 2, (b) shows the output of the reciprocating engine 2, and (c) and (d) show the amount of fuel supply. In the example shown in FIG. 9, the reciprocating engine 2 is started at T0, and the reciprocating engine 2 is operated at a constant rotation speed in an idling state until T1. The output of the reciprocating engine 2 during this time is zero, but a constant amount of fuel is supplied to maintain idling. The reciprocating engine 2 is speed-governed, and the amount of fuel supply is speed-governed so that the rotation speed of the reciprocating engine 2 becomes a target rotation speed. When the propulsion of the ship starts at T1, and the target rotation speed of the reciprocating engine 2 is gradually increased until it reaches the rated rotation speed at T2, the amount of fuel supply is gradually increased by the action of the speed-governing control, and the output of the reciprocating engine 2 gradually increases, and the rated output is reached at T2. When the propeller pitch is constant, the relationship between power output and rotational speed follows the so-called marine cubic curve, in which power output is proportional to approximately the cube of the rotational speed.

[0131] FIG. 9(c) shows an example of fuel supply control suitable for a case where the speed increase is relatively slow or where the stroke volume per cylinder 11 of the reciprocating engine 2 is relatively large. In an idling state after starting the reciprocating engine 2, a substantially constant amount of liquid auxiliary fuel is supplied. After idling for an appropriate period of time, the temperature of the reciprocating engine 2 rises and reaches a hot state, and when the compression end temperature reaches a predetermined temperature or higher, the operation mode is switched from the diesel operation mode to the mixed combustion operation mode, and the supply of gaseous ammonia by speed control is started. When the supply amount of liquid auxiliary fuel is kept constant and the target rotation speed is gradually increased, the supply amount of gaseous ammonia is gradually increased by the action of the speed control. When the rotation speed and output reach the rated value, the mixed combustion rate of ammonia is 80% or more in terms of heat ratio.

[0132] FIG. 9(d) is an example of fuel supply control suitable for a case where the speed increase is relatively fast or where the stroke volume per cylinder 11 of the reciprocating engine 2 is relatively small. After idling, when the compression end temperature does not reach a predetermined temperature or higher, the supply amount of the liquid auxiliary fuel is controlled by speed regulation, and when the target rotation speed is gradually increased, the supply amount of the liquid auxiliary fuel is gradually increased by the speed regulation. In this example, operation is performed only with the liquid auxiliary fuel until the rotation speed and output reach the rated value. When the output increases and the temperature of the reciprocating engine 2 rises, and the compression end temperature reaches a predetermined temperature or higher, the diesel operation mode is switched to the mixed combustion operation mode, and the supply of gaseous ammonia is started by speed regulation. After the supply of gaseous ammonia starts, the supply amount of the liquid auxiliary fuel is gradually decreased, and the supply amount of gaseous ammonia is increased by the speed regulation. The mixed combustion rate of ammonia is finally 80% or more in terms of heat ratio.

[0133] In this example, the reciprocating engine 2 is operated only with the liquid auxiliary fuel until the rotation speed and output reach the rated value. However, as shown by the dashed line in FIG. 9(d), the engine may be operated only with the liquid auxiliary fuel until the output reaches a suitable level at which the compression end temperature can be equal to or higher than a predetermined temperature, for example, 50% output, and the supply of gaseous ammonia may be started at that stage. In that case, the hatched area above the dashed line in FIG. 9(d) is also the ammonia supply area. In this case, too, after the supply of gaseous ammonia is started, the supply amount of the liquid auxiliary fuel is gradually reduced, and the supply amount of gaseous ammonia is increased by the action of the speed control. By controlling the supply amount of the liquid auxiliary fuel according to the operating conditions using a map, and controlling the supply amount of the gaseous ammonia using a speed control, appropriate control in various patterns is possible.

[0134] 10 is an explanatory diagram illustrating the operation of a power generation engine in which the reciprocating engine 2 according to one embodiment drives a generator. Here, as a typical example, a case where a generator is driven by a power generation engine on land to supply power to a power grid will be described as a representative example, but even when generating power on a ship, if the amount of power generation increases or decreases while the rotation speed of the reciprocating engine 2 is constant, the same applies to this example.

[0135] In the example shown in FIG. 10, the reciprocating engine 2 is started at T0, and the reciprocating engine 2 is operated at a constant rotation speed in an idling state until T1. The reciprocating engine 2 is speed-governed, and the amount of fuel supplied is speed-governed so that the rotation speed of the reciprocating engine 2 becomes the target rotation speed. Next, the target value of the rotation speed of the reciprocating engine 2 is increased, and at T2, the rotation speed of the reciprocating engine 2 reaches the rated rotation speed according to the power generation frequency. During this time, the output of the reciprocating engine 2 is zero, but a certain amount of fuel is supplied to maintain the rotation. At T3, the first load is applied to the generator. When the load is applied, the amount of fuel supplied is increased in a short time to maintain the rotation speed. Furthermore, a second load is applied at T4, the amount of fuel supplied is increased again, and the reciprocating engine 2 reaches the rated output. Note that the number of times of load application is not limited to two, and may be divided into more times or may be only once.

[0136] Here, when applying a load, it is necessary to increase the amount of fuel supplied in a short period of time. However, particularly when the temperature of the reciprocating engine 2 has not risen sufficiently and the compression end temperature has not risen sufficiently, if the amount of gaseous ammonia supplied is increased in a short period of time, the gaseous ammonia may not be burned sufficiently, resulting in an increase in unburned ammonia.

[0137] In the example of Figure 10(c), the engine is operated using only liquid auxiliary fuel until the first load application, which is often performed immediately after the reciprocating engine 2 has started and before the temperature has risen sufficiently, and then the supply amount of liquid auxiliary fuel is gradually reduced to a constant value, and the supply amount of gaseous ammonia is gradually increased by the speed control. After the first load application, some time passes and the temperature of the reciprocating engine 2 rises, and the second load application is performed, but at this time the compression end temperature has risen sufficiently, so the load application is handled by increasing the supply amount of gaseous ammonia. Eventually, the ammonia co-firing ratio reaches 80% or more in terms of heat value.

[0138] The example of Fig. 10(d) is an example of fuel supply control in the case where load application is completed in a shorter time or where the stroke volume per cylinder 11 of the reciprocating engine 2 is relatively small. In this example, operation is performed using only liquid auxiliary fuel until multiple load applications are completed, and then the supply amount of liquid auxiliary fuel is gradually reduced to a constant value, and the supply amount of gaseous ammonia is gradually increased by the action of speed control. Finally, the ammonia co-firing ratio reaches 80% or more in terms of heat ratio.

[0139] As conditions for starting the mixed combustion operation of the liquid auxiliary fuel and ammonia after starting the reciprocating engine 2 only with the liquid auxiliary fuel, other conditions may be used as necessary in addition to the above-mentioned compression end temperature, the output of the reciprocating engine 2, and the equivalence ratio of the total fuel to air. As shown in FIG. 5, a temperature sensor 67 is provided at the inlet of the catalytic treatment device 60 of the exhaust passage 30. The control device 3 starts the reciprocating engine 2 only with the liquid auxiliary fuel, and continues the operation with the liquid auxiliary fuel until the temperature of the exhaust gas measured by the temperature sensor 67 reaches a predetermined temperature. This predetermined temperature is obtained in advance by experiment as the temperature of the exhaust gas at which the catalyst functions. When the temperature of the exhaust gas reaches the predetermined temperature, the control device 3 starts the mixed combustion operation of the liquid auxiliary fuel and ammonia.

[0140] 5, the catalytic treatment device 60 is provided with a temperature sensor 68 for measuring the temperature of the catalytic treatment device 60. The control device 3 starts the reciprocating engine 2 using only the liquid auxiliary fuel, and continues operation using the liquid auxiliary fuel until the temperature of the catalytic treatment device 60 measured by the temperature sensor 68 reaches a predetermined temperature. This predetermined temperature is determined in advance by experiment as the treatment temperature at which the catalyst functions. When the temperature of the catalytic treatment device 60 reaches the above-mentioned treatment temperature, the control device 3 starts a mixed combustion operation using the liquid auxiliary fuel and ammonia.

[0141] 5, the catalytic treatment device 60 includes a heater 69 for heating the catalytic treatment device 60. The control device 3 heats the catalytic treatment device 60 with the heater 69 until the temperature of the catalytic treatment device 60 reaches the above-mentioned treatment temperature. When the temperature of the catalytic treatment device 60 reaches the above-mentioned treatment temperature, the control device 3 starts a mixed combustion operation using the liquid auxiliary fuel and ammonia. When the mixed combustion operation starts and the temperature of the catalytic treatment device 60 reaches a state where it can maintain a predetermined temperature, the control device 3 stops heating with the heater 69. Furthermore, the control device 3 continues to measure the temperature of the catalytic treatment device 60 with the temperature sensor 68, and resumes heating with the heater 69 when the temperature of the catalytic treatment device 60 falls below the predetermined temperature.

[0142] Although preferred embodiments of the present invention have been described and illustrated above, it should be understood that these are illustrative of the present invention and should not be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the present invention. Although a four-stroke engine has been described as a preferred embodiment, the same principles apply to a two-stroke engine. Also, actual measurement of the compression end temperature in the cylinder is not necessarily required, but can be reasonably estimated from the design values ​​and operating conditions of the reciprocating engine. Therefore, the present invention should not be considered as limited by the foregoing description, but is limited by the scope of the appended claims. [Explanation of symbols]

[0143] 1 … Reciprocating engine system 2 … Reciprocating engine 3 … Control device 4 … Turbocharger 10... Combustion chamber 11 ... Cylinder 12 ... Piston 20 ... Intake passage 30 … Exhaust duct 40 … Ammonia fuel supply device 50…Liquid auxiliary fuel supply device 60 ... Catalyst treatment device 94 ... Throttle valve 95 ... Air tank device (air supply device) 96, 97, 98 ... Short circuit (first short circuit) 96, 97, 99 ... Short circuit (second short circuit)

Claims

1. a cylinder forming a combustion chamber; a piston that reciprocates within the cylinder; an ammonia fuel supply device for supplying ammonia to the cylinder; a liquid auxiliary fuel supply device that supplies a liquid auxiliary fuel that ignites the ammonia into the cylinder; a control device that performs a multi-fuel combustion operation using the ammonia and the liquid auxiliary fuel in a state where the compression end temperature in the cylinder is equal to or higher than a predetermined temperature at which a combustion delay of the ammonia does not occur, The control device, during the dual combustion operation, sets an equivalence ratio of the total fuel to air to be 0.5 or more and 1.0 or less. Reciprocating engine system.

2. The predetermined temperature is 750K.

2. The reciprocating engine system according to claim 1.

3. The stroke volume per cylinder is 5000 cc or more, and the rated rotation speed of the reciprocating engine is 1200 rpm or less.

2. The reciprocating engine system according to claim 1.

4. the control device increases a mixed-fuel ratio of the ammonia to the total fuel in accordance with an increase in output of the reciprocating engine during the mixed-fuel operation, The maximum ammonia co-firing ratio is 80% or more in terms of heat ratio.

2. The reciprocating engine system according to claim 1.

5. The ammonia fuel supply device supplies the gaseous ammonia to the cylinder and premixes it with air.

2. The reciprocating engine system according to claim 1.

6. the control device sets the ammonia co-firing ratio to zero in an operating region where the equivalence ratio of the total fuel to the air is less than a predetermined value, and operates using only the liquid auxiliary fuel.

2. The reciprocating engine system according to claim 1.

7. The control device performs control to increase the compression end temperature in an operating region where the compression end temperature is lower than the predetermined temperature. The reciprocating engine system according to any one of claims 1 to 6.

8. The reciprocating engine system according to claim 7, wherein the control for increasing the compression end temperature is control for heating intake air of the reciprocating engine.

9. Further, a supercharger having a compressor and a turbine for supercharging the reciprocating engine is provided, the control device performs control to heat the intake air in an operating region where the temperature of the intake air downstream of the compressor is lower than a predetermined temperature. The reciprocating engine system according to any one of claims 1 to 6.

10. The control device, in the multi-fuel operation, performs map control of the supply amount of the liquid auxiliary fuel and speed control of the supply amount of the ammonia. The reciprocating engine system according to any one of claims 1 to 6.

11. the reciprocating engine further includes a throttle valve that limits the amount of air on an intake side thereof, and the control device controls the opening of the throttle valve so that the equivalence ratio of the ammonia to the air falls within a range that enables the multi-fuel operation. The reciprocating engine system according to any one of claims 1 to 6.

12. the control device starts the reciprocating engine using only the liquid auxiliary fuel, operates the reciprocating engine using only the liquid auxiliary fuel until the compression end temperature reaches the predetermined temperature, and performs the multi-fuel operation after the compression end temperature reaches the predetermined temperature. The reciprocating engine system according to any one of claims 1 to 6.

13. the control device starts the reciprocating engine using only the liquid auxiliary fuel, operates the reciprocating engine using only the liquid auxiliary fuel until the reciprocating engine reaches a predetermined output, and performs the multi-fuel operation after the reciprocating engine reaches the predetermined output. The reciprocating engine system according to any one of claims 1 to 6.

14. the control device starts the reciprocating engine using only the liquid auxiliary fuel, operates the reciprocating engine using only the liquid auxiliary fuel until a temperature of the exhaust gas from the reciprocating engine reaches a predetermined temperature, and performs the multi-fuel operation after the temperature of the exhaust gas reaches the predetermined temperature. The reciprocating engine system according to any one of claims 1 to 6.

15. a catalytic treatment device provided downstream of the exhaust passage of the cylinder for treating exhaust gas discharged from the cylinder using a catalyst; the control device starts the reciprocating engine using only the liquid auxiliary fuel, operates the engine using only the liquid auxiliary fuel until the temperature of the catalytic treatment device reaches a treatment temperature at which the catalyst functions, and performs the mixed combustion operation after the temperature of the catalytic treatment device reaches the treatment temperature. The reciprocating engine system according to any one of claims 1 to 6.

16. a heating device for heating the catalyst treatment device; the control device heats the catalytic treatment device using the heating device so that the temperature of the catalytic treatment device reaches the treatment temperature; 16. The reciprocating engine system of claim 15.

17. the reciprocating engine is a marine engine that directly or indirectly drives a propeller, the control device increases the output by increasing the supply amount of the liquid auxiliary fuel, and then increases the supply amount of the ammonia while decreasing the supply amount of the liquid auxiliary fuel. The reciprocating engine system according to any one of claims 1 to 6.

18. the reciprocating engine is a power generation engine that drives a generator, the control device increases the amount of the liquid auxiliary fuel supplied when a load is input, thereby increasing the output, and then increases the amount of the ammonia supplied while decreasing the amount of the liquid auxiliary fuel supplied. The reciprocating engine system according to any one of claims 1 to 6.

19. The reciprocating engine system according to any one of claims 1 to 6, wherein the reciprocating engine has a multi-fuel operation mode in which the multi-fuel operation is performed, and a diesel operation mode in which the reciprocating engine is operated using only the liquid auxiliary fuel without supplying the ammonia.

20. a catalytic treatment device provided downstream of the exhaust passage of the cylinder for treating exhaust gas discharged from the cylinder using a catalyst; the ammonia fuel supply device supplies a portion of the ammonia as a reducing agent to the catalytic treatment device during the mixed-fuel combustion operation. The reciprocating engine system according to any one of claims 1 to 6.

21. The ammonia fuel supply device further supplies a portion of the ammonia as a reducing agent to the catalytic treatment device even when the ammonia fuel supply device is operated using only the liquid auxiliary fuel.

21. The reciprocating engine system of claim 20.

22. A cylinder forming a combustion chamber; a piston that reciprocates within the cylinder; an ammonia fuel supply device that supplies gaseous ammonia to the cylinder and premixes it with air; a liquid auxiliary fuel supply device that supplies a liquid auxiliary fuel that ignites the ammonia into the cylinder; a control device for performing a multi-fuel operation using the ammonia and the liquid auxiliary fuel in the reciprocating engine, The control device, during the dual combustion operation, sets an equivalence ratio of the total fuel to air to be 0.5 or more and 1.0 or less. Reciprocating engine system.

23. a cylinder forming a combustion chamber; a piston that reciprocates within the cylinder; an ammonia fuel supply device for supplying ammonia to the cylinder; a liquid auxiliary fuel supply device that supplies a liquid auxiliary fuel that ignites the ammonia into the cylinder, performing a multi-fuel combustion operation using the ammonia and the liquid auxiliary fuel in a state where the compression end temperature in the cylinder is equal to or higher than a predetermined temperature at which a combustion delay of the ammonia does not occur, In the multi-fuel combustion operation, the equivalence ratio of the total fuel to air is set to 0.5 or more and 1.0 or less. How to operate a reciprocating engine.

24. A cylinder forming a combustion chamber; a piston that reciprocates within the cylinder; an ammonia fuel supply device that supplies gaseous ammonia to the cylinder and premixes it with air; a liquid auxiliary fuel supply device that supplies a liquid auxiliary fuel that ignites the ammonia into the cylinder, A method for operating a reciprocating engine that performs a mixed combustion operation using the ammonia and the liquid auxiliary fuel, comprising: In the multi-fuel combustion operation, the equivalence ratio of the total fuel to air is set to 0.5 or more and 1.0 or less. How to operate a reciprocating engine.

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