Engine device

Abstract

To provide an engine device that can respond to fuel gas having any fuel composition without providing expensive fuel composition measurement means and can be operated so that emissions of nitrogen oxide satisfy a regulation value.SOLUTION: An engine device 1 that is driven by inputting fuel gas of which fuel composition is changed to an engine 2 includes a control unit 7 that controls air supply pressure and an ignition parameter of the engine 2 so as to suppress nitrogen oxide included in exhaust gas on the basis of the air supply pressure of an air-fuel mixture comprising fuel gas and air to the engine 2 and an exhaust temperature of exhaust gas from the engine 2. The control unit 7 controls the air supply pressure and the ignition parameter so as to suppress nitrogen oxide included in exhaust gas on the basis of the air supply pressure, the exhaust temperature, and engine speed and engine load of the engine 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an engine device that is driven by feeding a fuel gas having a variable fuel composition into the engine. [Background technology]

[0002] Conventionally, some engine devices are driven by feeding fuel gas such as biogas into the combustion chamber in the cylinder of the engine, and the fuel gas is supplied as a mixture with air. In such engine devices, the fuel gas is burned to emit exhaust gas containing nitrogen oxides (NOx). On the other hand, it is necessary to respond to the diversification of fuels and changes in fuel composition against the backdrop of carbon neutrality. Engine devices are required to suppress the emission of nitrogen oxides to satisfy emission regulations and maintain stable operation, regardless of changes in the fuel composition of the fuel gas fed into the engine.

[0003] For example, according to Patent Document 1, a control device for an internal combustion engine to which fuel with a variable composition is supplied includes a fuel composition measuring means disposed in an intake system, a load measuring means for measuring the load of the internal combustion engine, a revolution speed measuring means for measuring the revolution speed of the internal combustion engine, an air-fuel ratio calculating means for calculating the air-fuel ratio, an ignition timing control means for controlling the ignition timing of the internal combustion engine in response to the outputs of the fuel composition measuring means, the load measuring means, the revolution speed measuring means, and the air-fuel ratio calculating means, and an air-fuel ratio control means for controlling the air-fuel ratio. This aims to suppress knocking and generation of NOx when the fuel composition changes.

[0004] According to Patent Document 2, the engine includes a fuel flow rate control valve for controlling the flow rate of the fuel gas, an oxygen sensor for measuring the oxygen concentration of the exhaust gas in an exhaust passage through which exhaust gas from a combustion chamber in which a mixture of fuel gas and combustion air is burned flows, and an air-fuel ratio control means for controlling the air-fuel ratio by adjusting the aperture of the fuel flow rate control valve based on the measurement result of the oxygen sensor. The engine also includes a storage unit for storing a first correspondence relationship between the aperture of the fuel flow rate control valve and the heat value of the fuel gas when the engine is operated in a stoichiometric state by supplying a fuel gas whose heat value is known. The engine also includes a heat value estimation means for estimating the heat value of the fuel gas, which adjusts the aperture of the fuel flow rate control valve by the air-fuel ratio control means based on the output of the oxygen sensor in a state in which the engine is operated by supplying a fuel gas whose heat value is to be estimated, and which estimates the heat value of the fuel gas whose heat value is to be estimated based on the aperture of the fuel flow rate control valve in the stoichiometric state and the first correspondence relationship stored in the storage unit.

[0005] According to Patent Document 3, the engine includes an engine speed control unit that controls the opening of the throttle valve based on the deviation between the engine speed and an engine speed command value, a mixture flow rate control unit that determines a mixture flow rate command value from the load and the engine speed command value, calculates a viscosity-corrected actual mixture flow rate from the mixture temperature, mixture viscosity, mixture pressure, engine speed, charging efficiency, and stroke volume, and controls the opening of the fuel gas control valve based on the deviation between the mixture flow rate command value and the viscosity-corrected actual mixture flow rate, and a discharge timing control unit that determines an exhaust temperature command value from the mixture flow rate command value and controls the timing at which the ignition plug discharges based on the deviation between the exhaust temperature command value and the exhaust temperature. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-148187 A [Patent Document 2] Patent No. 6280711 [Patent Document 3] JP 2011-127544 A Summary of the Invention [Problem to be solved by the invention]

[0007] Conventional engines such as those in Patent Document 1 generally need to be equipped with expensive fuel composition measuring means, but it is usually desirable to construct engines at lower cost. In addition, conventional engines such as those in Patent Document 2 estimate the heating value of fuel gas to control operating conditions, but there are a wide variety of combinations and amounts of the mixed gas composition, and even fuel gases with the same heating value may change in combustion differently depending on the fuel composition. For this reason, it is difficult to estimate the heating value and control the operating conditions in response to various combinations and amounts of mixed gas.

[0008] In Patent Document 3, when the fuel gas composition changes, the fuel gas control valve opening is changed and the mixture flow rate is controlled to a command value, thereby simultaneously correcting the changes in the air-fuel ratio and the calorific value. Furthermore, the change in combustion speed caused by the change in fuel gas composition is corrected by changing the ignition timing to achieve the target exhaust temperature, thereby realizing the same NOx emissions. However, this control does not take into account the combination of the target values ​​of the mixture flow rate and exhaust temperature, and therefore the thermal efficiency and the total amount of hydrocarbons emitted cannot be optimized.

[0009] An object of the present invention is to provide an engine device that can be operated in a manner that satisfies the regulated value for nitrogen oxide emissions in response to fuel gas of any fuel composition without being equipped with an expensive fuel composition measuring means. [Means for solving the problem]

[0010] In order to solve the above problems, the engine device of the present invention is an engine device that is driven by feeding a fuel gas whose fuel composition changes into the engine, and is characterized by having a control unit that controls the supply pressure of a mixture of fuel gas and air to the engine and the exhaust temperature of exhaust gas from the engine, so as to suppress nitrogen oxides contained in the exhaust gas and ignition parameters of the engine. Effect of the Invention

[0011] According to the present invention, there is provided an engine device that can be operated so that the amount of nitrogen oxide emissions satisfies the regulatory value for a fuel gas of any fuel composition without being equipped with an expensive fuel composition measuring means. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram illustrating an example of an engine device according to an embodiment of the present invention. [Diagram 2] 1 is a schematic diagram illustrating an example of an engine device according to an embodiment of the present invention. [Diagram 3] 1 is a graph showing an example of a contour map of an excess air ratio corresponding to a fuel heating value and a mixture flow rate in an engine device. [Figure 4] 4 is a graph showing the relationship between the ignition timing and the intake pressure of an engine in an engine device. [Diagram 5] 3 is a graph showing the relationship between the ignition timing of an engine and the exhaust temperature in an engine device. [Figure 6] 4 is a graph showing the relationship between the intake pressure and the exhaust temperature of the engine in the engine device according to the embodiment of the present invention. [Figure 7] 4 is a graph showing an example in which the intake pressure or the exhaust temperature is exceeded with respect to the relationship between the intake pressure and the exhaust temperature of the engine in the engine device according to the embodiment of the present invention. [Figure 8] 4 is a graph showing an example in which the intake pressure or the exhaust temperature is insufficient in the engine device according to the embodiment of the present invention, with respect to the relationship between the intake pressure and the exhaust temperature of the engine. [Figure 9] 2 is a graph showing the relationship between the ignition timing and the thermal efficiency of an engine in an engine device. [Figure 10] 1 is a graph showing the relationship between engine ignition timing and total hydrocarbons in an engine system. [Figure 11] 2 is a block diagram showing a specific example of a first control and a second control by a control unit in an engine device according to an embodiment of the present invention. FIG. [Figure 12] 2 is a block diagram showing a first specific example of a first control and a second control by a control unit in an engine device according to an embodiment of the present invention. FIG. [Figure 13] 4 is a block diagram showing a second specific example of the first control and the second control by the control unit in the engine device according to the embodiment of the present invention. FIG. [Figure 14] 5 is a table showing a correlation between an ignition timing correction value and an intake pressure correction value used in a second control by a control unit in an engine device according to an embodiment of the present invention. [Figure 15] 4 is a flowchart showing an example of the operation of a first control and a second control by a control unit in the engine device according to the embodiment of the present invention. [Figure 16] 4 is a table showing a correlation between an amount of change in fuel composition and a supply pressure correction value used in a second control by a control unit in an engine device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An engine device 1 according to an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1 and Fig. 2, the engine device 1 includes an engine 2, an intake passage 3, an exhaust passage 4, a turbocharger 5, a recirculation device 6, and a control unit 7.

[0014] Particularly in this embodiment, the engine device 1 is a gas engine configured to be driven by feeding a fuel gas such as biogas into a combustion chamber 12a of the engine 2. The fuel gas is supplied to the combustion chamber 12a as a mixture with air. For example, the engine device 1 feeds a fuel gas containing a hydrocarbon as a main component and an inert gas such as nitrogen or carbon dioxide, or / and a hydrocarbon fuel different from the main component, or / and a non-hydrocarbon fuel such as hydrogen or ammonia, into the engine 2. The engine device 1 includes a gaseous fuel supply device 8 for supplying a gaseous fuel, which is a fuel gas, to the intake passage 3, an intake pressure adjustment device 9 for adjusting the amount of air or the amount of the mixture supplied from the intake passage 3 to the engine 2, and an ignition device 10 for igniting the fuel gas in the combustion chamber 12a.

[0015] The engine 2 is, for example, a four-stroke engine and is configured with a cylinder block 11 having a plurality of cylinders 12, but only one cylinder 12 is shown in Figures 1 and 2. As shown in Figures 1 and 2, each cylinder 12 is configured with a cylinder 13, a piston 14, and a cylinder head 15, and an ignition device 10 is provided for each cylinder 12.

[0016] The cylinder 13 is formed, for example, in a cylindrical shape within the cylinder block 11, and the piston 14 is slidably housed within the cylinder 13. The cylinder head 15 is attached to the upper side of the cylinder 13, and the cylinder 13 and the cylinder head 15 form a combustion chamber 12a therein.

[0017] Below the cylinder 13, a crankshaft 19 is connected to the piston 14 via a connecting rod 18, and the reciprocating motion of the piston 14 is converted into the rotational motion of the crankshaft 19 via the connecting rod 18.

[0018] The cylinder 13 is provided with a rotation speed sensor 20 such as an encoder that detects the rotation speed of the crankshaft 19, i.e., the rotation speed of the engine 2, and the rotation speed sensor 20 transmits the detection result to the control unit 7. The cylinder 13 is provided with a torque sensor 21 near the crankshaft 19 that detects the engine load (engine torque) of the engine 2, and the torque sensor 21 transmits the detection result to the control unit 7.

[0019] The cylinder head 15 also has an intake port 22 and an exhaust port 23 that communicate with the combustion chamber 12a of the cylinder 13, and is equipped with an intake valve 24 and an exhaust valve 25 that respectively open and close the intake port 22 and the exhaust port 23 to the combustion chamber 12a.

[0020] The intake port 22 is connected to the intake passage 3 and introduces the air-fuel mixture supplied from the intake passage 3 into the combustion chamber 12a, and the exhaust port 23 is connected to the exhaust passage 4 and discharges exhaust gas generated in the combustion chamber 12a into the exhaust passage 4. By opening the intake valve 24, the air-fuel mixture can be taken into the combustion chamber 12a via the intake port 22, while by opening the exhaust valve 25, the exhaust gas generated in the combustion chamber 12a can be exhausted via the exhaust port 23.

[0021] 1 and 2 show an example in which the intake passage 3 and the intake port 22 are directly connected, but in order to connect the intake passage 3 to each of the intake ports 22 of the multiple cylinders 12, an intake manifold having branch passages branching from the intake passage 3 to the multiple cylinders 12 may be provided between the intake passage 3 and the engine 2. Also, while Figures 1 and 2 show an example in which the exhaust passage 4 and the exhaust port 23 are directly connected, in the case of connecting the exhaust passage 4 to each of the exhaust ports 23 of the multiple cylinders 12, an exhaust manifold having branch passages branching from the exhaust passage 4 to the multiple cylinders 12 may be provided between the exhaust passage 4 and the engine 2.

[0022] The intake passage 3 is connected to intake ports 22 of the cylinders 12 of the engine 2, and supplies compressed and cooled air to each cylinder 12 via the intake port 22. A supercharger 5 is provided upstream in the intake direction of the intake passage 3, which compresses air or a mixture of fuel gas and air flowing through the intake passage 3 and sends it downstream in the intake direction. The intake passage 3 may be provided with an air filter (not shown) that purifies fresh air and introduces it into the intake passage 3, and an intercooler (not shown) that cools the air flowing through the intake passage 3.

[0023] The intake passage 3 is provided with a throttle valve 9a as an intake pressure regulator 9 for adjusting the amount of air or mixture delivered to the intake port 22. The throttle valve 9a is controlled by the control unit 7 to adjust its opening, and adjusts the amount of air or mixture delivered to the intake port 22 according to the opening of the throttle valve 9a. This adjusts the flow rate and pressure of the air or mixture flowing through the intake passage 3, thereby adjusting the amount of air or mixture supplied from the intake passage 3 to the engine 2.

[0024] The intake passage 3 is provided with an intake bypass passage 26 that connects the upstream side and downstream side of the turbocharger 5 in the intake direction. A part of the air flowing through the turbocharger 5 is recirculated to the intake passage 3 upstream of the turbocharger 5 via the intake bypass passage 26. The intake bypass passage 26 is provided with an intake bypass valve 9b for adjusting the flow rate of the air or mixture flowing through the intake bypass passage 26. The intake bypass valve 9b is controlled by the control unit 7 to adjust its opening degree, and adjusts the amount of air or mixture recirculated to the intake passage 3 according to the opening degree of the intake bypass valve 9b. Thus, the intake bypass valve 9b acts as an intake pressure regulator 9, and adjusts the flow rate and pressure of the air or mixture flowing through the intake passage 3 to adjust the amount of air or mixture supplied from the intake passage 3 to the engine 2.

[0025] An intake pressure sensor 27 is provided in the intake passage 3 to detect the intake pressure of the mixture supplied from the intake passage 3 to the engine 2 , and the intake pressure sensor 27 transmits the detection result to the control unit 7 .

[0026] The exhaust passage 4 is connected to an exhaust port 23 of each cylinder 12 of the engine 2, and exhausts exhaust gas generated in each cylinder 12 via the exhaust port 23. A wastegate flow passage 28 that connects the upstream side and downstream side of the turbocharger 5 in the exhaust direction is provided in the exhaust passage 4, and a wastegate valve 9c for adjusting the flow rate of the exhaust gas is provided in the wastegate flow passage 28.

[0027] The wastegate valve 9c has its opening adjusted under the control of the control unit 7, and the flow rate of exhaust gas flowing into the turbocharger 5 is adjusted according to the opening of the wastegate valve 9c, thereby adjusting the amount of compression of the air or mixture by the turbocharger 5. That is, the wastegate valve 9c acts as an intake pressure regulator 9, and by adjusting the opening of the wastegate valve 9c, the flow rate and pressure of the air or mixture flowing through the intake passage 3 are adjusted, thereby adjusting the intake pressure of the mixture supplied from the intake passage 3 to the engine 2.

[0028] An exhaust temperature sensor 29 is provided in the exhaust passage 4 to detect the exhaust temperature of the exhaust gas discharged from the engine 2 into the exhaust passage 4 , and the exhaust temperature sensor 29 transmits the detection result to the control unit 7 .

[0029] The turbocharger 5 compresses the air or air-fuel mixture flowing through the intake passage 3 and sends it downstream in the intake direction. The turbocharger 5 has a turbine 5a and a compressor 5b. The turbine 5a is disposed in the exhaust passage 4, and the compressor 5b is disposed in the intake passage 3. The turbine 5a is rotated by the exhaust gas flowing through the exhaust passage 4, and the compressor 5b is driven by the rotational force of the turbine 5a, thereby compressing the air or air-fuel mixture flowing through the intake passage 3.

[0030] The recirculation device 6 recirculates exhaust gas flowing through the exhaust passage 4 and supplies it to the intake passage 3. The recirculation device 6 is connected to the exhaust passage 4 downstream of the turbocharger 5 (turbine 5a) in the exhaust direction, and is connected to the intake passage 3 upstream of the turbocharger 5 (compressor 5b) in the intake direction.

[0031] The recirculation device 6 is configured to have, for example, a recirculation flow path 6a, a recirculation cooler 6b, and a recirculation valve 6c. The recirculation device 6 introduces exhaust gas flowing in the exhaust passage 4 downstream of the turbocharger 5 in the exhaust direction to the recirculation cooler 6b via the recirculation flow path 6a, and the exhaust gas is cooled and recirculated by the recirculation cooler 6b, and is supplied to the intake passage 3 upstream of the turbocharger 5 in the intake direction. The recirculation valve 6c functions as a recirculation flow rate adjustment device, and its opening is controlled by the control unit 7 to adjust the flow rate of the recirculated exhaust gas flowing into the intake passage 3 via the recirculation flow path 6a according to the opening of the recirculation valve 6c, thereby allowing the exhaust gas to be introduced into the intake side.

[0032] The gaseous fuel supply device 8 is provided upstream of the intake passage 3 or the turbocharger 5, and is controlled by the control unit 7 to supply gaseous fuel, which is fuel gas supplied from a gaseous fuel tank (not shown), to the intake passage 3 or the upstream side of the turbocharger 5. A mixture of air supplied from the intake passage 3 or the upstream side of the turbocharger 5 and fuel gas supplied from the gaseous fuel tank (not shown) is supplied from the intake port 22 to the combustion chamber 12a. The gaseous fuel supply device 8 is controlled by the control unit 7 in terms of the supply amount (supply pressure), supply timing, etc. of the fuel gas.

[0033] 1, the gaseous fuel supply device 8 includes a fuel flow rate regulating valve 8a that regulates the flow rate of the gaseous fuel, and a venturi mixer 8b that mixes the gaseous fuel with the air flowing upstream of the turbocharger 5. Alternatively, the gaseous fuel supply device 8 may include an admission valve 8c that is configured by an injection method and injects the gaseous fuel toward the intake passage 3, or may include an injector or the like instead of the admission valve 8c, as shown in FIG. 2. The fuel flow rate regulating valve 8a can function as an intake pressure regulating device 9.

[0034] The ignition device 10 is provided in a cylinder head 15 of each cylinder 12. The ignition device 10 is, for example, a spark ignition type device using an ignition plug. In the spark ignition type ignition device 10, the timing and duration of energization of the spark plug are controlled by the control unit 7, and ignition parameters such as ignition timing according to the energization timing and ignition energy according to the energization duration are controlled.

[0035] Alternatively, the ignition device 10 may be a micro-pilot type device that injects a small amount of liquid fuel, and is composed of an injector or the like that injects liquid fuel supplied from a liquid fuel tank (not shown) into the combustion chamber 12a (auxiliary chamber) below the cylinder head 15. In the micro-pilot type ignition device 10, the timing and duration of energization of the injector are controlled by the control unit 7, and the injection timing according to the energization timing and the fuel injection amount according to the energization duration, i.e., ignition energy and other ignition parameters are controlled.

[0036] The control unit 7 is a computer such as an ECU (Engine Control Unit) that controls the operation of the engine 2, and includes a CPU, ROM, RAM, etc., and is configured to control each part of the engine 2. The control unit 7 may store various programs for controlling the engine 2, and control the engine 2 by reading and executing the programs.

[0037] As a base control, the control unit 7 of this embodiment simultaneously corrects changes in the air-fuel ratio of the mixture (ratio of fuel to components other than fuel) and the heat generation amount by controlling the opening of the fuel flow control valve 8a or the throttle valve 9a so that the mixture flow rate (air intake pressure) becomes determined by the engine load and engine speed when the fuel gas composition changes or when exhaust gas is introduced into the air intake side.

[0038] FIG. 3 shows an example of a contour map of the excess air ratio corresponding to the fuel heating value and the mixture flow rate. According to this example, when the fuel heating value changes, the fuel flow rate is controlled so as to keep the mixture flow rate (boost pressure) constant, thereby achieving approximately the same excess air ratio (air-fuel ratio) and input heat amount. For example, in the case of a gaseous fuel supply device 8 having a Venturi mixer 8b on the upstream side of a turbocharger 5 as shown in FIG. 1, the fuel flow rate can be changed by the opening degree of a fuel flow rate control valve 8a, and the boost pressure can be controlled to a target value. Also, in the case of a gaseous fuel supply device 8 having an admission valve 8c as shown in FIG. 2, since the fuel flow rate changes due to the output control, the opening degree of a throttle valve 9a can be changed to control the boost pressure to a target value.

[0039] Furthermore, as a first control, the control unit 7 performs control so as to suppress nitrogen oxides contained in the exhaust gas based on the intake pressure of the mixture supplied from the intake passage 3 to the engine 2 and the exhaust temperature of the exhaust gas discharged from the engine 2. Moreover, as a second control, the control unit 7 performs control so as to optimize the thermal efficiency of the engine 2 and the total hydrocarbons contained in the exhaust gas based on the intake pressure and the exhaust temperature.

[0040] First, the first control will be described. In the engine device 1 that uses biogas as fuel gas as in the present invention, the fuel composition of the fuel gas supplied changes. The nitrogen oxides contained in the exhaust gas of the engine device 1 differ depending on the fuel composition of the fuel gas input to the engine 2 and the ignition timing of the engine 2.

[0041] In order for the nitrogen oxides in the exhaust gas to meet the emission regulation limits when the amount of nitrogen oxides exhausted under each operating condition is kept the same, as shown in Fig. 4, the more advanced the ignition timing is, the higher the boost pressure tends to be, but when the flow rate of the exhaust gas recirculated by the recirculation device 6 is changed, the boost pressure according to the ignition timing differs according to the recirculation flow rate (EGR). In other words, when the fuel composition of the fuel gas input to the engine 2 changes, the boost pressure according to the ignition timing differs according to the fuel composition of the fuel gas.

[0042] This is because, although the air-fuel ratio is adjusted by base control, the combustion speed changes depending on the fuel composition of the fuel gas. For example, if the combustion speed slows down by increasing the EGR rate and increasing the CO2 in the air-fuel mixture, it is necessary to enrich the air-fuel ratio by reducing the intake pressure in order to maintain the same combustion state and NOx emissions. The above example shows a case where the amount of exhaust gas recirculation is changed, but the same applies when the amount of CO2 in the fuel gas (biogas) is changed.

[0043] Furthermore, in order for the nitrogen oxides in the exhaust gas to meet the emission regulation values ​​when the engine device 1 is operated, assuming that the amount of nitrogen oxide emissions under each operating condition is the same, the more advanced the ignition timing is, the lower the exhaust temperature tends to be, as shown in Figure 5, but when the flow rate of the exhaust gas recirculated by the recirculation device 6 is changed, the exhaust temperature according to the ignition timing differs depending on the recirculation flow rate (EGR). In other words, when the fuel composition of the fuel gas input to the engine 2 changes, the exhaust temperature according to the ignition timing differs depending on the fuel composition of the fuel gas.

[0044] This is also because the combustion speed changes depending on the fuel composition of the fuel gas, even though the air-fuel ratio is adjusted by base control. For example, if the combustion speed slows down by increasing the EGR rate and increasing the CO2 in the mixture, in order to maintain the same combustion state and NOx emissions, it is necessary to enrich the air-fuel ratio by reducing the intake pressure, and this enrichment increases the exhaust temperature. The above example shows a case where the amount of exhaust gas recirculation is changed, but the same applies when the amount of CO2 in the fuel gas (biogas) is changed.

[0045] As described above, in the engine system 1, in a situation where the nitrogen oxides in the exhaust gas meet the emission regulation value, the boost pressure and exhaust temperature change depending on the ignition timing and the recirculation flow rate, and the relationship between the boost pressure and the exhaust temperature at each ignition timing and each recirculation flow rate shows that, assuming the nitrogen oxide emissions under each operating condition are the same, the exhaust temperature tends to decrease as the boost pressure increases, as shown in Fig. 6. Here, it can be seen that the boost pressure and the exhaust temperature have a correlation that changes substantially constantly, for example, a linear correlation, regardless of the ignition timing and the recirculation flow rate (EGR). In other words, the correlation between the boost pressure and the exhaust temperature is a linear correlation such that a constant exhaust temperature (or a constant boost pressure) is obtained for a predetermined boost pressure (or a predetermined exhaust temperature).

[0046] Therefore, if the boost pressure and exhaust temperature detected during operation of the engine device 1 are on a line indicating the correlation between boost pressure and exhaust temperature as shown in Fig. 6, the nitrogen oxides in the exhaust gas will satisfy the emission regulation value, and such a line becomes the target line L during operation of the engine device 1. Note that the correlation between boost pressure and exhaust temperature may be a linear correlation having a certain width that allows a certain range (width) of exhaust temperature (or a certain boost pressure) for a certain boost pressure (or a certain exhaust temperature), that is, the target line L during operation of the engine device 1 may have a certain width.

[0047] Furthermore, in the engine system 1, the correlation between the intake air pressure and the exhaust temperature may differ depending on the operating conditions of the engine 2, such as the engine speed and the engine load, and therefore the target line L during operation of the engine system 1 differs depending on the operating conditions of the engine system 1.

[0048] If the intake pressure and exhaust temperature detected during operation of the engine device 1 deviate from the correlation between the intake pressure and exhaust temperature as described above, the nitrogen oxides in the exhaust gas of the engine device 1 will no longer satisfy the emission regulation limits.

[0049] For example, when the exhaust temperature increases at a given intake pressure detected during operation of the engine device 1 with respect to a target line L showing the correlation between intake pressure and exhaust temperature as shown in FIG. 7, it can be determined that the exhaust temperature is increasing and nitrogen oxides are decreasing due to a delay in combustion caused by a change in the fuel gas components.

[0050] Furthermore, when the exhaust temperature is decreasing at a given intake pressure detected during operation of the engine device 1 with respect to target line L showing the correlation between intake pressure and exhaust temperature as shown in FIG. 8, it can be determined that the exhaust temperature is decreasing and nitrogen oxides are increasing due to promotion of combustion caused by a change in the fuel gas components.

[0051] Therefore, in the engine device 1 of this embodiment, as a first control, the control unit 7 controls each part so that the supply pressure to the engine 2 and the exhaust temperature of the exhaust gas discharged from the engine 2, which are detected during operation, as well as the engine speed and engine load of the engine 2, so as to maintain a constant relationship between the supply pressure and the exhaust temperature.

[0052] Specifically, the control unit 7 controls the intake pressure of the engine 2 and ignition parameters (ignition timing, ignition energy, etc.) when igniting the engine 2 to suppress nitrogen oxides contained in the exhaust gas and satisfy the emission regulation values. At this time, the control unit 7 feedback-controls the intake pressure and ignition parameters of the engine 2 so that the intake pressure and exhaust temperature detected during operation satisfy the correlation between the intake pressure and exhaust temperature as described above.

[0053] First, in the engine system 1 of this embodiment, correlation information such as a relational expression or a map showing the correlation between the intake pressure and the exhaust temperature is stored in the control unit 7. For example, the correlation between the intake pressure and the exhaust temperature may be obtained from data detected when the engine system 1 is operated experimentally, and the correlation information may be constructed in advance. Alternatively, the correlation information may be obtained from data detected when the engine system 1 is operated practically, and the correlation information may be constructed in real time. Furthermore, in the engine system 1, correlation information showing the correlation between the intake pressure and the exhaust temperature is stored in the control unit 7 for each operating condition such as the engine speed and engine load of the engine 2 (for example, for each combination of engine speed and engine load).

[0054] During operation of the engine device 1, the control unit 7 detects the engine speed of the engine 2 by the speed sensor 20, and detects the engine load of the engine 2 by the torque sensor 21. Then, the control unit 7 reads out correlation information between the intake pressure and the exhaust temperature that corresponds to the detected engine speed and engine load of the engine 2 from the stored correlation information between the intake pressure and the exhaust temperature.

[0055] During operation of the engine system 1, the control unit 7 detects the intake pressure supplied to the engine 2 from the intake passage 3 by the intake pressure sensor 27, and detects the exhaust temperature of the exhaust gas discharged from the engine 2 to the exhaust passage 4 by the exhaust temperature sensor 29. Then, the control unit 7 compares the detected intake pressure and exhaust temperature (current intake pressure and current exhaust temperature) with the read correlation information between the intake pressure and the exhaust temperature, and judges whether the detected intake pressure and exhaust temperature match the correlation information. For example, the control unit 7 judges whether the detected intake pressure and exhaust temperature are on a target line L between the intake pressure and the exhaust temperature, which is the correlation information as shown in FIG. 6. If the detected intake pressure and exhaust temperature are not on the target line L, the control unit 7 corrects the intake pressure and ignition parameters so that the intake pressure and exhaust temperature are on the target line L.

[0056] For example, when fuel gas with a slow combustion speed is burned in the engine 2, the plot of the exhaust temperature will be located above the target line L, as shown in Fig. 7. In this case, the control unit 7 determines that the combustion speed of the fuel gas is slow. Therefore, the control unit 7 controls the intake pressure regulator 9, such as the fuel flow rate control valve 8a, the throttle valve 9a, the intake bypass valve 9b, and the wastegate valve 9c, and the ignition device 10, so that the intake pressure and exhaust temperature are on the target line L by advancing the ignition timing and reducing the intake pressure.

[0057] Furthermore, when fuel gas with a high combustion speed is burned in the engine 2, the plot of the exhaust temperature will be located below the target line L, as shown in Fig. 8. In this case, the control unit 7 determines that the combustion speed of the fuel gas is high. Therefore, the control unit 7 controls the intake pressure regulator 9, such as the fuel flow rate control valve 8a, the throttle valve 9a, the intake bypass valve 9b, and the wastegate valve 9c, and the ignition device 10, by retarding the ignition timing and increasing the intake pressure so that the intake pressure and exhaust temperature are on the target line L.

[0058] Next, the second control will be described. In the engine system 1, when the amount of nitrogen oxide emissions is the same under each operating condition, as shown in Fig. 9, the more the ignition timing of the engine 2 is advanced, the higher the thermal efficiency of the engine 2 tends to be, and in order to optimize the thermal efficiency, it is necessary to correct the ignition timing. When the flow rate of the exhaust gas recirculated by the recirculation device 6 is changed, the thermal efficiency according to the ignition timing differs depending on the recirculation flow rate (EGR). In other words, when the fuel composition of the fuel gas input to the engine 2 changes, the thermal efficiency according to the ignition timing differs depending on the fuel composition of the fuel gas.

[0059] Furthermore, in the engine system 1, as shown in Fig. 10, the more the ignition timing is advanced, the more total hydrocarbons tend to be contained in the exhaust gas, and in order to suppress total hydrocarbons, it is necessary to correct the ignition timing, for example, to retard it. If the flow rate of the exhaust gas recirculated by the recirculation device 6 is changed, the total hydrocarbons according to the ignition timing will differ depending on the recirculation flow rate (EGR). In other words, if the fuel composition of the fuel gas input to the engine 2 changes, the total hydrocarbons according to the ignition timing will differ depending on the fuel composition of the fuel gas.

[0060] When the thermal efficiency of engine 2 and total hydrocarbons in the exhaust gas are compared with the correlation between the intake air pressure and the exhaust temperature, as shown in FIG. 6, on the target line L for the intake air pressure and the exhaust temperature, there exists an operating point P1 where the thermal efficiency is optimal and an operating point P2 where the total hydrocarbons are minimal.

[0061] Therefore, as a second control, the control unit 7 sets a target operating point on the target line L depending on the situation, regardless of whether the detected boost pressure or exhaust temperature (current boost pressure and current exhaust temperature) is on the target line L or not, and corrects the boost pressure and ignition parameters so that the boost pressure or exhaust temperature moves to the target operating point or its vicinity.

[0062] Next, a specific example of the first control and the second control by the control unit 7 will be described with reference to the block diagram of FIG.

[0063] When the control unit 7 detects the engine speed and engine load of the engine 2 (B1), it reads out correlation information between the boost pressure and exhaust temperature corresponding to the engine speed and the engine load (B2). When the control unit 7 detects the boost pressure and exhaust temperature (B3), it compares the read out correlation information with the detected boost pressure and exhaust temperature (current boost pressure and current exhaust temperature), and sets a target boost pressure and target exhaust temperature on the target line of the correlation information (B4).

[0064] Control unit 7 calculates an intake pressure difference, which is the difference between the detected intake pressure and a target intake pressure, and an exhaust temperature difference, which is the difference between the detected exhaust temperature and a target exhaust temperature (B5). Then, control unit 7 controls intake pressure regulator 9 and ignition device 10 so that the intake pressure difference and the exhaust temperature difference approach zero. Note that control unit 7 may input the detected intake pressure and exhaust temperature and output the intake pressure difference and the exhaust temperature difference, or may input the detected intake pressure and output the target exhaust temperature, or may input the detected exhaust temperature and output the target intake pressure.

[0065] Next, as a first specific example of the first control and the second control, an example in which the ignition timing is corrected in the first control will be described with reference to the block diagram of FIG.

[0066] As in the specific example described above, when the control unit 7 detects the engine speed and engine load of the engine 2 (B11), it reads out correlation information between the intake air pressure and the exhaust temperature corresponding to the engine speed and the engine load (B12).

[0067] The control unit 7 sets the boost pressure uniformly based on the detected engine speed and engine load of the engine 2 so as to achieve the engine speed and engine load (B13), and controls each part to control the boost pressure to a constant level. At this time, the control unit 7 controls the fuel flow rate control valve 8a or the throttle valve 9a so as to achieve the set boost pressure (current boost pressure) (B13).

[0068] As the first control, the control unit 7 compares the read correlation information with the set supply pressure (current supply pressure) and sets the exhaust temperature corresponding to the set supply pressure on the target line of the correlation information as the target exhaust temperature (B14). When the control unit 7 detects the exhaust temperature of the exhaust gas (B15), it calculates the difference between the detected exhaust temperature (current exhaust temperature) and the target exhaust temperature as the exhaust temperature difference (B16).

[0069] The control unit 7 calculates an ignition timing correction value for correcting the set ignition timing (current ignition timing) based on the calculated exhaust temperature difference (B17). The control unit 7 corrects the set ignition timing (current ignition timing) by the calculated ignition timing correction value (B18), and at this time, if it is desired to increase the exhaust temperature, the ignition timing is retarded, whereas if it is desired to decrease the exhaust temperature, the ignition timing is advanced.

[0070] As the second control, the control unit 7 calculates an intake pressure correction value for correcting the set intake pressure (current intake pressure) based on the calculated ignition timing correction value so as to optimize the thermal efficiency of the engine 2 and total hydrocarbons in the exhaust gas (B19). For example, the control unit 7 sets and stores in advance a map as shown in FIG. 14 showing the correlation between the ignition timing correction value and the intake pressure correction value, and calculates the intake pressure correction value based on the map. The control unit 7 corrects the set intake pressure (current intake pressure) with the calculated intake pressure correction value (B20). After performing the second control, the control unit 7 repeats the first control.

[0071] Next, as a second specific example of the first control and the second control, an example in which the boost pressure is corrected in the first control will be described with reference to the block diagram of FIG.

[0072] As in the first specific example described above, when the control unit 7 detects the engine speed and engine load of the engine 2 (B21), it reads out correlation information between the intake air pressure and the exhaust temperature corresponding to the engine speed and the engine load (B22).

[0073] As in the first specific example described above, the control unit 7 uniformly sets the boost pressure based on the detected engine speed and engine load of the engine 2 so as to achieve the engine speed and engine load (B23), and controls each section to control the boost pressure to a constant level. At this time, the control unit 7 controls the fuel flow rate control valve 8a or the throttle valve 9a so as to achieve the set boost pressure (current boost pressure) (B23).

[0074] As a first control, when the control unit 7 detects the exhaust temperature of the exhaust gas (B24), it calculates an air boost pressure correction value for correcting the set air boost pressure based on the read correlation information, the set air boost pressure (current air boost pressure), and the detected exhaust temperature (current exhaust temperature) (B25). For example, the control unit 7 sets the air boost pressure corresponding to the detected exhaust temperature on the target line of the correlation information as a target air boost pressure, calculates the difference between the set air boost pressure and the target air boost pressure as an air boost pressure difference, and calculates an air boost pressure correction value based on the calculated air boost pressure difference. The control unit 7 corrects the set air boost pressure (current air boost pressure) with the calculated air boost pressure correction value (B26).

[0075] As the second control, the control unit 7 calculates an ignition timing correction value for correcting the set ignition timing (current ignition timing) so as to optimize the thermal efficiency of the engine 2 and total hydrocarbons in the exhaust gas based on the calculated intake pressure correction value (B27). For example, like the first specific example, the control unit 7 pre-sets and stores a map as shown in FIG. 14 showing the correlation between the ignition timing correction value and the intake pressure correction value, and calculates the ignition timing correction value based on the map. The control unit 7 corrects the set ignition timing (current ignition timing) with the calculated ignition timing correction value (B28). After performing the second control, the control unit 7 repeats the first control.

[0076] When the intake pressure is changed, the air-fuel ratio changes, and the exhaust temperature also changes. Therefore, the control unit 7 repeats the first and second feedback controls until the fluctuations in the exhaust temperature settle down.

[0077] Next, an example of the operation of the above-mentioned first control and second control will be described with reference to the flowchart of FIG.

[0078] First, when the operating conditions of the engine 2, such as the engine speed and engine load, are set, the control unit 7 sets the boost pressure that achieves the engine speed and engine load as a target boost pressure (step S1). The control unit 7 also reads correlation information between the boost pressure and exhaust temperature that corresponds to the engine speed and engine load, and sets the exhaust temperature that corresponds to the target boost pressure on the target line of the correlation information as the target exhaust temperature (step S1).

[0079] The control unit 7 controls the boost pressure regulator 9 to operate the engine 2 so as to achieve the target boost pressure that has been set (step S2).

[0080] The control unit 7 detects the exhaust temperature (current exhaust temperature) by the exhaust temperature sensor 29 while the engine 2 is operating, and determines whether the detected exhaust temperature deviates from the target exhaust temperature (step S3). If the detected exhaust temperature does not deviate from the target exhaust temperature (step S3: No), the control unit 7 continues the operation of the engine 2 without performing the first control and the second control.

[0081] On the other hand, if the detected exhaust temperature (current exhaust temperature) deviates from the target exhaust temperature (step S3: Yes), the control unit 7 calculates the difference between the detected exhaust temperature and the target exhaust temperature as the exhaust temperature difference, calculates an ignition timing correction value for correcting the ignition timing (current ignition timing) based on the calculated exhaust temperature difference, and corrects the ignition timing using the calculated ignition timing correction value (step S4).

[0082] Furthermore, the control unit 7 calculates an intake pressure correction value for correcting the intake pressure (current intake pressure) based on the calculated ignition timing correction value, and resets the target intake pressure by correcting the intake pressure with the intake pressure correction value (step S5). The control unit 7 also resets the exhaust temperature corresponding to the reset target intake pressure as the target exhaust temperature on the target line of the correlation information between the intake pressure and the exhaust temperature (step S5). Then, the control unit 7 proceeds to step S2 and repeats the control.

[0083] As described above, according to this embodiment, the engine device 1 is an engine device 1 that is driven by supplying fuel gas whose fuel composition changes to the engine 2, and includes a control unit 7 that controls the supply pressure and ignition parameters of the engine 2 based on the supply pressure of a mixture of the fuel gas and air to the engine 2 and the exhaust temperature of exhaust gas from the engine 2, so as to suppress nitrogen oxides contained in the exhaust gas.

[0084] As a result, on the premise that the boost pressure regulator 9 controls the boost pressure to be the boost pressure determined by the engine speed and engine load, the engine unit 1 can determine the control amounts of the boost pressure and ignition parameters for suppressing the emission of nitrogen oxides contained in the exhaust gas to a constant level based only on the relationship between the boost pressure and the exhaust temperature, regardless of the fuel composition of the fuel gas. Therefore, the engine unit 1 can operate in response to fuel gas of any fuel composition so that the emission of nitrogen oxides satisfies the regulated value, without being equipped with an expensive fuel composition measuring means.

[0085] Furthermore, according to this embodiment, the control unit 7 controls the boost pressure and ignition parameters based on the boost pressure and exhaust temperature, as well as the engine speed and engine load, so as to suppress nitrogen oxides contained in the exhaust gas.

[0086] As a result, the engine system 1 can utilize the relationship between intake pressure and exhaust temperature that suppresses nitrogen oxide emissions, according to various operating conditions, even if the relationship between intake pressure and exhaust temperature differs depending on the operating conditions of engine speed and engine load.

[0087] Furthermore, according to this embodiment, the engine device 1 is provided with a recirculation flow path 6a that recirculates the exhaust gas and circulates it to the intake side of the engine 2, and a recirculation valve 6c (recirculation flow rate control device) that adjusts the recirculation flow rate of the exhaust gas through the recirculation flow path 6a.

[0088] As a result, in a configuration in which a mixture containing recirculated exhaust gas is input to the engine 2, the engine system 1 can suppress the emission of nitrogen oxides contained in the exhaust gas based on the relationship between the intake air pressure and the exhaust temperature, even if the recirculation flow rate of the exhaust gas changes.

[0089] Furthermore, according to this embodiment, the control unit 7 pre-stores correlation information between the boost pressure and the exhaust temperature at which the nitrogen oxides become constant, based on operating conditions corresponding to the engine speed and the engine load, and controls the boost pressure and ignition parameters based on the correlation information.

[0090] This allows the engine system 1 to more specifically define the relationship between the intake pressure and the exhaust temperature for suppressing the amount of nitrogen oxide emissions contained in the exhaust gas regardless of the fuel composition of the fuel gas, and to more effectively control the intake pressure and ignition parameters. Therefore, the engine system 1 can operate in a manner that satisfies the regulated value for nitrogen oxide emissions in response to fuel gas of any fuel composition without being equipped with an expensive fuel composition measuring means.

[0091] Also, according to this embodiment, in the engine device 1, the engine 2 is a four-stroke engine and includes an ignition device 10 that ignites the engine 2 by a micro-pilot system or a spark ignition system, a gaseous fuel supply device 8 that supplies gaseous fuel, which is a fuel gas, to the intake side of the engine 2 by an injection system or a mixer system, and an intake pressure regulating device 9 that adjusts the intake pressure and includes at least one of a fuel flow control valve 8a, a throttle valve 9a, a bypass valve, and a wastegate valve 9c.

[0092] In such an engine device 1, the control unit 7 adjusts the intake pressure by controlling at least one of the opening degree of the fuel flow control valve 8a, the opening degree of the throttle valve 9a, the opening degree of the bypass valve, and the opening degree of the wastegate valve 9c.

[0093] This allows the engine unit 1 to more accurately control the intake pressure so as to satisfy the relationship between the intake pressure and the exhaust temperature.

[0094] In addition, in such an engine system 1, the control unit 7 controls the ignition parameters by controlling the energization timing or energization time of the spark ignition type ignition plug or the micro-pilot type injector.

[0095] This enables the engine system 1 to more accurately control the ignition parameters to satisfy the relationship between the intake air pressure and the exhaust temperature.

[0096] According to this embodiment, the engine unit 1 inputs biogas into the engine 2 as fuel gas.

[0097] Furthermore, according to this embodiment, the engine device 1 supplies fuel gas, which is mainly composed of hydrocarbons and contains an inert gas and / or a hydrocarbon fuel different from the main component and / or a non-hydrocarbon fuel, to the engine 2.

[0098] This allows the engine unit 1 to operate in a manner that satisfies the regulated value for the amount of nitrogen oxide emissions while adapting to various fuel gases having different fuel compositions.

[0099] Furthermore, according to this embodiment, when a change in the fuel composition of the fuel gas retards the combustion speed in the engine 2, the control unit 7 executes at least one of an advancement of the ignition timing, which is an ignition parameter, an increase in the ignition energy, and a reduction in the intake pressure, which are ignition parameters, based on information on the correlation between the intake pressure and the exhaust temperature.

[0100] Alternatively, when the control unit 7 determines, based on the correlation information between the intake air pressure and the exhaust gas temperature, that a change in the fuel composition of the fuel gas retards the combustion speed in the engine 2, it executes at least one of the following ignition parameters: advancement of the ignition timing, an increase in the ignition energy, a reduction in the intake air pressure, and a decrease in the recirculation flow rate.

[0101] Alternatively, according to this embodiment, when a change in the fuel composition of the fuel gas increases the combustion speed in the engine 2 based on the correlation information between the intake air pressure and the exhaust gas temperature, the control unit 7 executes at least one of retarding the ignition timing, which is an ignition parameter, decreasing the ignition energy, and increasing the intake air pressure, which are ignition parameters.

[0102] Alternatively, when the control unit 7 determines based on the correlation information between the intake air pressure and the exhaust gas temperature that a change in the fuel composition of the fuel gas increases the combustion speed in the engine 2, it executes at least one of the following ignition parameters: retarding the ignition timing, decreasing the ignition energy, increasing the intake air pressure, and increasing the recirculation flow rate.

[0103] As a result, the engine system 1 can predict changes in the fuel composition of the fuel gas based on correlation information between the intake pressure and the exhaust temperature, thereby more effectively controlling the intake pressure and ignition parameters, and effectively suppressing nitrogen oxides contained in the exhaust gas.

[0104] In the above embodiment, an example has been described in which the control unit 7 in the engine system 1 corrects the ignition timing or the boost pressure based on a map that is set in advance as a correlation between the ignition timing correction value and the boost pressure correction value in the second control for optimizing the thermal efficiency or the total hydrocarbons. However, the present invention is not limited to this example.

[0105] As another example Therefore, in the first control, the control unit 7 may use the exhaust gas recirculation flow rate (EGR rate) as a control variable instead of the ignition timing or the intake pressure. That is, when the fuel composition changes, the EGR flow rate is changed so as to satisfy the target exhaust temperature. If the EGR flow rate is decreased, the mixture composition changes so as to increase the combustion speed, and the exhaust temperature decreases. If the EGR flow rate is increased, the mixture composition changes so as to decrease the combustion speed, and the exhaust temperature increases.

[0106] When the EGR flow rate is changed in the first control, the control unit 7 may correct the ignition timing or the boost pressure in the second control, or may correct both. In the second control, the control unit 7 may estimate the amount of change in the fuel composition of the fuel gas based on the relationship between the exhaust temperature or the boost pressure and the ignition timing, and calculate the boost pressure correction value for correcting the boost pressure based on the estimated amount of change. In this case, the control unit 7 preliminarily sets and stores a map as shown in FIG. 16 showing the correlation between the amount of change in the fuel composition of the fuel gas (e.g., the ratio of exhaust gas to be recirculated relative to the fuel gas, i.e., the EGR rate) and the boost pressure correction value or the ignition timing correction value, and calculates the boost pressure correction value or the ignition timing correction value based on the map. The EGR rate may be replaced with a measurement item that can indirectly estimate the EGR rate (e.g., the EGR flow rate, the opening of the recirculation valve 6c, the exhaust gas pressure, etc.). Then, the control unit 7 corrects the intake pressure or the ignition timing based on the calculated intake pressure correction value or the ignition timing correction value.

[0107] In addition, the engine device 1 may be a gas engine that can be driven by feeding biogas fuel gas containing gaseous fuel into the engine 2, or it may be a dual-fuel engine that can be driven by feeding at least one of biogas fuel gas and liquid fuel such as light oil or heavy oil into the engine 2.

[0108] In addition, the present invention can be modified as appropriate within the scope that does not contradict the gist or concept of the invention that can be read from the claims and the entire specification, and engine devices involving such modifications are also included in the technical concept of the present invention.

[0109] [Appendix to the invention] The following will provide an overview of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0110] <Appendix 1> An engine device that is driven by feeding a fuel gas having a variable fuel composition into the engine, An engine device comprising: a control unit that controls the intake pressure of the fuel gas, which is a mixture of gaseous fuel and air, to an engine and the exhaust temperature of the exhaust gas discharged from the engine, so as to suppress nitrogen oxides contained in the exhaust gas.

[0111] <Appendix 2> The engine apparatus according to claim 1, wherein the control unit controls the intake pressure and the ignition parameters so as to suppress nitrogen oxides contained in the exhaust gas based on the intake pressure and the exhaust temperature, as well as an engine speed and an engine load of the engine.

[0112] <Appendix 3> a recirculation flow path for recirculating the exhaust gas and distributing it to an intake side of the engine; and a recirculation flow rate control device that controls a recirculation flow rate of the exhaust gas passing through the recirculation flow passage.

[0113] <Appendix 4> 4. The engine apparatus according to claim 2, wherein the control unit pre-stores correlation information between the boost pressure and the exhaust temperature at which the nitrogen oxides are constant for each operating condition according to the engine speed and the engine load, and controls the boost pressure and the ignition parameters based on the correlation information.

[0114] <Appendix 5> The engine is a four-stroke engine, An ignition device that ignites the engine using a micro-pilot system or a spark ignition system; A gaseous fuel supply device that supplies the gaseous fuel to an intake side of the engine by an injection method or a mixer method; 5. The engine device according to claim 1, further comprising: an intake pressure regulator that includes at least one of a throttle valve, a bypass valve, and a wastegate valve and that adjusts the intake pressure.

[0115] <Appendix 6> 6. The engine device according to claim 5, wherein the control unit adjusts the intake pressure by controlling at least one of an opening degree of the throttle valve, an opening degree of the bypass valve, and an opening degree of the wastegate valve.

[0116] <Appendix 7> The engine device according to claim 5 or 6, wherein the control unit controls the ignition parameters by controlling a current supply timing or a current supply time for an ignition plug constituting the spark ignition type ignition device or an injector constituting the micro-pilot type ignition device.

[0117] <Appendix 8> 8. The engine device according to any one of claims 1 to 7, wherein biogas is fed into the engine as the fuel gas.

[0118] <Appendix 9> The engine device according to any one of claims 1 to 8, characterized in that the fuel gas is a fuel mainly composed of a hydrocarbon and containing an inert gas, a hydrocarbon fuel different from the main component, and a non-hydrocarbon fuel, which is fed into the engine.

[0119] <Appendix 10> The engine device according to any one of appendices 1 to 9, wherein the control unit determines whether or not a change in fuel composition of the fuel gas slows down combustion in the engine based on correlation information between the intake air pressure and the exhaust temperature, and if the control unit determines that the change in fuel composition of the fuel gas slows down combustion in the engine, executes at least one of the ignition parameters of advancing the ignition timing, increasing the ignition energy, and reducing the intake air pressure.

[0120] <Appendix 11> The engine device according to any one of appendixes 3 to 9, wherein the control unit determines whether or not a change in fuel composition of the fuel gas slows down combustion in the engine based on correlation information between the intake air pressure and the exhaust temperature, and if the control unit determines that the change in fuel composition of the fuel gas slows down combustion in the engine, executes at least one of the following: advancing the ignition timing, which is the ignition parameter; increasing the ignition energy, which is the ignition parameter; reducing the intake air pressure; and decreasing the recirculation flow rate.

[0121] <Appendix 12> The engine device according to any one of appendices 1 to 9, wherein the control unit determines whether or not a change in the fuel composition of the fuel gas causes abrupt combustion in the engine based on correlation information between the intake air pressure and the exhaust temperature, and if the control unit determines that a change in the fuel composition of the fuel gas causes abrupt combustion in the engine, executes at least one of retarding the ignition timing, which is the ignition parameter, decreasing the ignition energy, and increasing the intake air pressure, which are the ignition parameters.

[0122] <Appendix 13> The engine device according to any one of appendixes 3 to 9, wherein the control unit determines whether or not a change in the fuel composition of the fuel gas causes abrupt combustion in the engine based on correlation information between the intake air pressure and the exhaust temperature, and if the control unit determines that a change in the fuel composition of the fuel gas causes abrupt combustion in the engine, executes at least one of retarding the ignition timing, which is the ignition parameter, decreasing the ignition energy, increasing the intake air pressure, and increasing the recirculation flow rate. [Explanation of symbols]

[0123] 1 Engine unit 2 Engine 3 Intake passage 4 Exhaust passage 5. Turbocharger 5a Turbine 5b Compressor 6 Recirculation device 6a Recirculation flow path 6b Recirculation Cooler 6c Recirculation valve 7. Control Unit 8 Gaseous fuel supply device 8a Fuel flow control valve 8b Venturi Mixer 9 Air supply pressure regulator 9a Throttle valve 9b Air supply bypass valve 9c Wastegate valve 10 Ignition system 11 Cylinder block 12 cylinders 12a Combustion chamber 13 Cylinder 14 Piston 15 Cylinder head 18 Connecting rod 19 Crankshaft 20 Rotational speed sensor 21 Torque sensor 22 Intake port 23 Exhaust port 24 Intake valve 25 Exhaust valve 26 Air supply bypass passage 27 Air supply pressure sensor 28 Wastegate passage 29 Exhaust temperature sensor

Claims

1. An engine device driven by a fuel gas having a variable fuel composition, and a control unit that controls the intake pressure and ignition parameters of the engine based on the intake pressure of the mixture of fuel gas and air to the engine and the exhaust temperature of exhaust gas from the engine so as to suppress nitrogen oxides contained in the exhaust gas.

2. 2. The engine apparatus according to claim 1, wherein the control unit controls the intake pressure and the ignition parameters so as to suppress nitrogen oxides contained in the exhaust gas based on the intake pressure and the exhaust temperature, as well as engine speed and engine load.

3. a recirculation flow path for recirculating the exhaust gas and distributing it to an intake side of the engine; 2. The engine apparatus according to claim 1, further comprising: a recirculation flow rate adjustment device that adjusts a recirculation flow rate of the exhaust gas passing through the recirculation flow passage.

4. 3. The engine apparatus according to claim 2, wherein the control unit pre-stores correlation information between the boost pressure and the exhaust temperature at which the nitrogen oxides become constant, based on operating conditions corresponding to the engine speed and the engine load, and controls the boost pressure and the ignition parameters based on the correlation information.

5. The engine is a four-stroke engine, An ignition device that ignites the engine using a micro-pilot system or a spark ignition system; a gaseous fuel supply device that supplies the gaseous fuel, which is the fuel gas, to an intake side of the engine by an injection method or a mixer method; 2. The engine system according to claim 1, further comprising an intake pressure regulator, the intake pressure regulator comprising at least one of a fuel flow rate regulator, a throttle valve, a bypass valve, and a wastegate valve, for regulating the intake pressure.

6. 6. The engine apparatus according to claim 5, wherein the control unit adjusts the intake pressure by controlling at least one of an opening degree of the fuel flow control valve, an opening degree of the throttle valve, an opening degree of the bypass valve, and an opening degree of the wastegate valve.

7. 6. The engine apparatus according to claim 5, wherein the control unit controls the ignition parameters by controlling a current supply timing or a current supply time for the spark ignition plug or the micro-pilot injector.

8. 2. The engine device according to claim 1, wherein biogas is fed into the engine as the fuel gas.

9. 2. The engine device according to claim 1, characterized in that the fuel gas fed to the engine is a fuel that is mainly composed of a hydrocarbon and contains an inert gas, and / or a hydrocarbon fuel different from the main component, and / or a non-hydrocarbon fuel.

10. 2. The engine apparatus according to claim 1, wherein the control unit executes at least one of the following ignition parameters: an advancement of ignition timing, which is the ignition parameter; an increase in ignition energy, which is the ignition parameter; and a reduction in the intake pressure, when a change in the fuel composition of the fuel gas retards a combustion speed in the engine, based on correlation information between the intake pressure and the exhaust temperature.

11. 4. The engine device according to claim 3, wherein the control unit executes at least one of the following when a change in the fuel composition of the fuel gas retards a combustion speed in the engine based on correlation information between the intake air pressure and the exhaust temperature: advancing an ignition timing, which is the ignition parameter; increasing an ignition energy, which is the ignition parameter; reducing the intake air pressure; and decreasing the recirculation flow rate.

12. 2. The engine apparatus according to claim 1, wherein the control unit executes at least one of retarding the ignition timing, which is the ignition parameter, decreasing the ignition energy, and increasing the intake pressure, which is the ignition parameter, when a change in the fuel composition of the fuel gas increases a combustion speed in the engine, based on correlation information between the intake pressure and the exhaust temperature.

13. 4. The engine apparatus according to claim 3, wherein the control unit executes at least one of retarding the ignition timing, which is the ignition parameter, decreasing the ignition energy, increasing the intake pressure, and increasing the recirculation flow rate, when a change in the fuel composition of the fuel gas increases a combustion speed in the engine, based on correlation information between the intake pressure and the exhaust temperature.

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