JP2014051968A - Internal combustion engine controlling fuel gas injection pressure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize engine efficiency when operated with fuel having varying energy density.SOLUTION: An engine includes a control unit 17 that controls an amount of a fuel gas to be injected into combustion chambers according to an applied fuel index so as to obtain a desired engine speed at a given engine load. The fuel index defines an amount of the fuel gas to be injected into the cylinders per injection, and the amount of the fuel gas to be injected is controlled by adjusting the duration of a fuel gas injection period. A sensor 40 is provided for measuring the engine load during operation, and an engine control unit controls the injection pressure of the fuel gas into the combustion chambers according to changes in energy density of the fuel gas so that the applied fuel index corresponds to a reference fuel index.

Description

  The present invention relates to a cylinder provided with a fuel gas injector for injecting fuel gas directly into the combustion chamber of the cylinder, and a fuel index applied to obtain a desired engine speed at a given engine load. And at least one engine controller that controls the amount of fuel gas injected into the combustion chamber in response, the fuel index defining the amount of fuel gas injected into the cylinder per injection, The amount of fuel gas relates to an internal combustion engine such as a two-cycle crosshead diesel engine that is controlled by adjusting the duration of the fuel gas injection period.

  There is increasing interest in reducing emissions of carbon dioxide, nitric oxide, and sulfur from the operation of internal combustion engines, and therefore alternative fuels to conventional fuel oils have been studied. For large two-cycle diesel engines such as MAN Diesel 12K80MC-GI-S, operation using fuel gas as the primary fuel is safer, more reliable and environmentally desirable compared to conventional fuel oil. It has been shown that there is a possibility. With regard to large two-cycle diesel engines for the marine market, there is an interest in engines using fuel gas, especially for liquefied natural gas carriers (LNG carriers) that must handle boil-off gas from gas tanks in transit. It is getting higher and higher.

  Therefore, it is desirable to use natural gas and / or boil-off gas from the gas tank of the LNG transport ship for the operation of such an engine. However, the calorific value of the fuel gas from the gas tank of the LNG carrier may change over time, for example, because the boil-off gas reduces the energy density of the fuel gas provided to the cylinder, such as nitrogen It is because it also has. Similarly, a change in the temperature of the fuel gas provided to the cylinder will change the energy density of the fuel gas injected into the combustion chamber of the cylinder.

  If the energy density of the fuel gas injected into the cylinder is different from the energy density of the reference fuel gas, which is the basis for making the engine reference adjustment and for determining the engine reference fuel index, If it is different from the amount of fuel injected into the cylinder to obtain the desired engine speed at a given load, the applied fuel index needs to be adjusted to maintain the engine speed. Conventionally, the change in energy density of the fuel gas has been a change in the applied fuel index from the reference fuel index at the actual engine load.

  For example, if the energy density of the fuel gas is less than the reference fuel gas, the amount of energy injected per unit time is not sufficient to maintain the engine speed and the engine speed will slow down. However, this is so that the fuel index is increased and the amount of energy injected into the cylinder is increased so that the engine speed is at the desired degree, ie the duration of the fuel gas injection period is increased. Thus, it is corrected by the electronic control unit.

  However, this method of correcting for changes in the energy density of the fuel gas and achieving the desired engine speed is less efficient because the maximum combustion pressure in the combustion chamber will be lower than the optimum operating point. Similarly, if the energy density of the fuel gas is greater than the reference fuel gas, the maximum combustion pressure will be higher than the engine designed maximum combustion pressure, increasing engine wear and possible damage. Will increase.

  Accordingly, both the calorific value of the fuel gas and the temperature of the fuel gas affect the density and amount of energy injected into the cylinder per unit time.

  EP 1546532 discloses a system for operating a plurality of fuel engines operating on combustion of fuel oil and fuel gas. The electronic control unit is connected to the engine system, and controls the amount of each of the plurality of fuels delivered to the engine based on the operating characteristics of the engine system such as the fuel gas temperature and the fuel gas pressure.

  In accordance with the present invention, it is desirable to optimize the efficiency of an internal combustion engine when operated with fuel gas of varying energy density.

  For this purpose, the internal combustion engine according to the invention is determined by a reference fuel index determined from the measured engine load and at least one engine controller in order to obtain a desired engine speed at a given engine load. A sensor device is provided for measuring the engine load during operation based on the comparison with the applied fuel index, and the at least one engine control unit is configured to ensure that the applied fuel index corresponds to the reference fuel index. In addition, the fuel gas injection pressure into the combustion chamber is controlled in accordance with a change in the energy density of the fuel gas.

  The electronic control unit can determine the measured engine load and the corresponding reference fuel index based on readings from the sensor device, and the reference fuel index is applied by the engine control unit calculated by the engine control unit. The fuel index can be compared. If there is a difference between the reference fuel index and the applied fuel index, the amount of energy injected per unit time is constant even if the fuel gas calorific value and / or the temperature of the fuel gas changes. The fuel gas injection pressure is adjusted so that

  For example, a rapid engine load disturbance due to output changes such as waves acting on a ship carrying a marine engine according to the present invention or a rapid change in the energy density of the fuel gas causing a speed change from a desired speed Correction is made by quickly adjusting the amount of energy injected into the cylinder in a single injection by adjusting the duration of the injection period. By adjusting the fuel injection pressure, the calorific value of the fuel gas can be corrected to change slowly with time and / or to change the temperature of the fuel gas, and the characteristics of the injected fuel gas Maintains the same heat dissipation and the same efficiency as if. Furthermore, this makes the timing of the combustion process more time efficient than adjusting the duration of the fuel injection period, for example with respect to the timing of injection and the timing of opening and closing the exhaust valve. .

  In addition to the obvious benefits of reduced fuel consumption and exhaust combustion gases, a tuned and balanced engine can greatly reduce maintenance costs and reduce the risk of engine damage.

  In a preferred embodiment in which the engine can be operated more efficiently, the at least one engine control unit controls the injection pressure of the fuel gas into the combustion chamber in accordance with the change in the calorific value and / or temperature of the fuel gas.

  In a simple practical embodiment, the measured engine load is determined from the measurement by the sensor device of shaft torque and shaft rotational speed.

  In another embodiment, the measured engine load is determined from sensor sensor measurements of combustion pressure and shaft rotational speed during the combustion cycle.

  This allows for a particularly advantageous embodiment according to the invention, in which the fuel gas injection pressure depends on the position of the injection timing, depending on the position of the crankshaft, in order to obtain optimum fuel consumption and combustion gas emissions. Adjustment is performed by a combination of adjustment and adjustment of timing for opening and closing the exhaust valve.

  According to a reliable implementation of the invention, the cylinder is provided with a fuel oil injector for injecting fuel oil directly into the combustion chamber of the cylinder and a fuel oil supply system.

  According to a reliable implementation of the invention, the fuel gas supply system is a common rail fuel gas supply system.

  In a practically preferred embodiment, the temperature of the fuel gas provided to the cylinder is in the range of 10-70 ° C. This prevents condensation in the gas supply piping.

  In a preferred embodiment, at 100% engine load, the engine speed is in the range of 45 rpm to 250 rpm. Low speed engines are typically very high power engines, and it is actually a problem to operate the engine efficiently in terms of combustion pressure.

  In a practical and preferred embodiment, the gas supply system for providing fuel gas to the cylinder is connected to the liquefied natural gas tank of the liquefied natural gas transport ship.

  Examples and embodiments of the invention will be described in more detail below with reference to highly schematic drawings.

1 is an overall view of an engine according to the present invention. 1 is a diagram of an example of an engine in a combined fuel oil / fuel gas operation mode according to the present invention. FIG.

  The internal combustion engine 1 according to a preferred embodiment of the present invention may be a two-cycle crosshead diesel engine as shown in FIG. Such an engine 1 can be, for example, a model MC or ME manufactured by MAN Diesel, a model Sulzer RT-flex or Sulzer RTA manufactured by Wartsila, or manufactured by Mitsubishi Heavy Industries. This type of engine is a large engine typically used as the main engine of a ship or as a stationary engine in a power plant. The cylinder can have, for example, a bore ranging from 25 cm to 120 cm, and the engine can have an output ranging from, for example, 3000 kW to 120,000 kW. Engine speed is typically in the range of 40 rpm to 250 rpm. The compression ignition internal combustion engine according to the present invention can typically use heavy oil fuel as the primary fuel.

  The engine 1 of FIG. 1 has a plurality of cylinders provided with a cylinder liner 2 attached to a cylinder portion 3 of an engine frame 4. The exhaust valve housing 5 is attached to a cylinder cover 6 and an exhaust pipe 7 extends from an individual cylinder to an exhaust sump 8 common to a plurality or all of the cylinders. In the exhaust reservoir, the pressure fluctuation caused by the exhaust pulse discharged from the exhaust pipe is equalized to a more uniform pressure, and the one or more turbochargers 9 receive the exhaust from the exhaust reservoir 8 and receive the exhaust reservoir. Similarly, compressed air is sent to a scavenging system including a scavenging receiver 10 which is a long pressure vessel.

  In each cylinder, a piston is attached to a piston rod, which is connected to a crankpin on the crankshaft via a crosshead and a connecting rod (not shown). The fuel injector injects fuel into the combustion chamber. When the injected fuel is fuel oil, the fuel oil automatically ignites because the air above the piston is hot. The piston is hot because it compressed the inlet air during the upward compression stroke.

  The present invention is preferably implemented in a marine diesel engine equipped with a dual fuel supply system, and in the following, the present invention will be described using such an example, but it should be understood that the present invention is a single fuel system. May be implemented. The engine of this example is an electronically controlled engine that electronically controls the injection of oil and gas, and reliably optimizes fuel injection and combustion. Furthermore, this is done on the basis of the high-pressure gas injection principle with pilot fuel oil injection for igniting the combustion of the fuel gas. With this principle, the diesel combustion process can be fully utilized, thereby obtaining the same high thermal efficiency as in the case of fuel oil combustion. In FIG. 2, the cylinder portion 3 is shown as a single cylinder 11, but the engine has a plurality of cylinders, such as 4 to 16 cylinders. As schematically shown in FIG. 2, the internal combustion engine 1 provides fuel oil and fuel gas to be provided to the combustion chamber of the cylinder 11 to the fuel oil injection system 20 and the fuel gas injection system 30, respectively. A fuel oil supply system 23 and a fuel gas supply system 19 are provided. In this example, the fuel oil injection system 20 and the fuel gas injection system 30 respectively control the injection of fuel oil and fuel gas into the combustion chamber of the cylinder 11. The general principle of the fuel injection systems 20, 30 is that each cylinder 11 has one or more fuel injection devices 15, 16, such as fuel pumps and valves, connected to the fuel injectors 13, 14 of the cylinder cover 6. This is associated with the cylinder controller 12 to be controlled. The number of injectors 13, 14 per cylinder depends on the output of the cylinder 11. In a preferred embodiment, each cylinder comprises at least a fuel oil injector 13 and a fuel gas injector 14. For smaller engines, one injector per fuel type may be sufficient to inject the amount of fuel required for a single combustion process, but for larger, higher power engines Two or three injectors may be required for each fuel type. When several injectors are provided for each cylinder 11, there may be one fuel injection device 15 per injector 13 and one fuel injection device 16 per injector 14. The cylinder control unit 12 of the fuel injection systems 20 and 30 is controlled by an engine control unit 17 that communicates with a ship bridge.

  The fuel gas supply system 19 is preferably connected to a liquefied natural gas (LNG) tank 18 of an LNG transport ship operating at sea. The LNG tank of the LNG transport ship is kept at a low temperature, but is inevitably heated because external heat from seawater and the atmosphere is transmitted through the heat insulating material of the tank. When external heat enters, a part of LNG is vaporized, that is, boiled off, and the pressure of the tank gradually increases. In order to keep the tank pressure at an acceptable level, a reliquefaction system (not shown) may be used to reliquefy the boil-off gas. Alternatively, or in combination with a reliquefaction system, the boil-off gas compressor may provide a high pressure boil-off gas when so commanded by the fuel gas injection system 30. In the cylinder, the fuel injection device 16 controlled by the cylinder controller 12 provides the timing and opening of the fuel gas injector 14. The fuel gas is preferably provided to the fuel gas injection system by a double rail gas supply line 26 of a common rail design. In the common rail design, the fuel gas injector 14 valve is controlled by an auxiliary control oil system. This auxiliary control oil system consists in principle of a hydraulic control oil system and an electronic gas injection valve, supplying high pressure controlled oil to the gas injector 14, thereby opening and closing the gas valve of the gas injector 14. And control. Efficient gas injection is when the gas delivery pressure is between 150 and 400 bar, depending on the engine load, and the fuel gas is between 30 ° C and 60 ° C, preferably about 45 ° C. can get. The buffer tank 22 is used to store boil-off gas before being provided to the fuel gas injection system 30 by the fuel gas supply system 19. The amount of unavoidable boil-off gas in the LNG tank of the LNG carrier is usually insufficient as the only fuel for the operation of the internal combustion engine of the LNG carrier, but according to the present invention this amount of boil-off gas Can be advantageously used in combination with fuel oil of an internal combustion engine. The operation of the fuel gas injection system 30 is insensitive to gas composition and changes in gas composition. Therefore, liquefied petroleum gas (LPG), usually made of higher hydrocarbons such as propane and butane, maintains the same rating as fuel oil without changing engine performance in terms of speed, thermal efficiency, and power output. It can be applied as a fuel gas like LNG.

  In the fuel oil injection system 20, the fuel oil input device 15 may be a fuel pump, in which case the fuel oil supply system 23 is fueled at a relatively low supply pressure in the supply pipe 24, such as in the range from 2 bar to 15 bar. It is only necessary to deliver fuel oil from the oil tank 21 to the fuel injection device. Alternatively, the fuel oil injection device 15 may be a valve, i.e. a valve connected to a metering device, in which case the fuel supply pipe is connected to the fuel at a pressure greater than the injection pressure, such as a supply pressure ranging from 500 bar to 1500 bar This is a high pressure pipe with high pressure. Such a fuel oil supply system 23 is called a common rail system. In any case, the fuel oil injection device 15 is connected to the fuel supply pipe 24 by a branch pipe with a valve that is maintained in the open position during normal engine operation. The fuel oil injection device 15 is connected to the fuel oil injector 13 via a high pressure fuel oil pipe. The recursion pipe leads from the fuel oil injector to a fuel oil return pipe (not shown). The fuel oil provided to the cylinder is typically heavy oil or marine diesel oil.

  The internal combustion engine 1 according to the present invention may be provided by installing the fuel gas supply system 19 and the fuel gas injection system 30 in an existing engine having the fuel oil supply system as described above. The injection control may be either one cylinder control unit or independent cylinder control units 12a and 12b that control the amounts of fuel oil and fuel gas provided to the combustion chamber of the cylinder 11, respectively. Similarly, the fuel oil injection system 20 and the fuel gas injection system 30 can be controlled either by one engine controller 17 or separately in independent engine controllers 17a, 17b. When operating an internal combustion engine according to the present invention, engine adjustment of fuel injection is performed by either the fuel oil injection system 20 or the fuel gas injection system 30. In general, the engine controller 17 receives engine speed signals and other engine operating parameters from the sensor device 40 and controls the amount and speed of fuel to be provided to the combustion chamber of the cylinder 11, which Also known as engine governor control. The internal combustion engine according to the present invention can be operated in a fuel oil operation mode, a fuel gas operation mode, and a fuel oil / fuel gas combined operation mode. The mode of operation may be commanded from the ship's bridge except for safety reasons such as when the engine is automatically and quickly switched to the fuel oil mode of operation, for example, gas leaks.

  The combined fuel oil / fuel gas operation mode may be implemented by automatically switching between the fuel oil operation mode and the fuel gas operation mode. Switching between the fuel oil operation mode and the fuel gas operation mode may be commanded by an engine mode selection function unit 25 connected to the fuel oil injection system 20 and the fuel gas injection system 30, and preferably the engine The switching function part is a part of the fuel gas supply system 19. Therefore, the switching is controlled by the engine control unit 17 b dedicated to the fuel gas injection system 30. In the combined fuel oil / fuel gas operation mode, the engine mode selection function unit 25 determines whether combustion in the internal combustion engine is started by the fuel oil injection system 20 or the fuel gas injection system 30, that is, the engine mode selection function unit 25. Determines whether to switch the governor control function of the engine control unit 17 using the fuel oil injection system 20 or the fuel gas injection system 30.

  In the fuel gas operation mode, the fuel gas injection and timing of the combustion process are controlled by the fuel gas injection system 30. This is done according to a predetermined reference fuel index that defines the fuel gas injection time and fuel gas injection pressure required to optimally operate the engine at a given engine load, i.e. the fuel gas index. Before operation is performed, the engine is tested at various loads along the propeller curve to determine the optimal reference fuel gas injection time and fuel gas injection pressure at various loads. Thus, when the engine control unit 17, 17b searches the engine map to find the exact timing of fuel gas injection, the exact timing of opening and closing the exhaust valve, and the hydraulic pressure, for example, It also finds both the commanded fuel gas injection time and the commanded fuel gas injection pressure required to operate at engine load.

  When the engine is operated in the fuel gas mode, the governor control of the engine controller 17, 17b is the fuel injected by calculating the fuel index to obtain the desired engine speed at a given engine load. Control the amount of gas. Thus, because the change in engine load causes a difference between the engine speed and the desired engine speed, the applied fuel index is adjusted to achieve the desired engine speed. For example, when the calorific value of the fuel gas is smaller than the calorific value of the reference gas, less energy is injected into the cylinder during the fuel gas injection period. As a result, the engine speed decreases, and the engine speed is measured by the sensor device 40 that communicates with the engine control units 17 and 17b. In order to obtain the desired engine speed, the engine controller 17, 17b increases the applied fuel index so that the fuel gas injection period is lengthened, thereby increasing the amount of fuel gas injected. The same principle for maintaining the desired engine speed is used by the engine controller 17a of the fuel oil injection system to control the sudden changes in engine load very efficiently and quickly. However, in the fuel gas mode of operation, the desired engine speed is achieved at a lower maximum pressure in the combustion chamber, which is less efficient than using the reference gas for which the engine is designed. If the calorific value of the fuel gas is greater than the reference gas, the maximum combustion pressure in the combustion chamber will be higher than the maximum combustion pressure for which the engine is designed, increasing engine component wear and possibly damaging the engine .

  If the cylinder is provided with constant pressure fuel gas, the lower fuel gas temperature compared to the reference fuel gas temperature will cause the fuel gas energy density to be greater than the reference fuel gas energy density, so the maximum combustion pressure will be Will be higher than the designed maximum combustion pressure. Therefore, changes in the calorific value and temperature of the fuel gas provided to the cylinder have the same effect in the combustion process, and such changes are considered as changes in the engine load by the engine controller, and therefore The index is adjusted by the engine control units 17 and 17b.

  Therefore, when the fuel index is adjusted with quick control by adjusting the fuel injection period according to the change of the energy density of the fuel gas, the applied fuel index used by the engine control unit 17, 17b is actually The reference fuel index corresponding to the engine load of the engine will vary with time. The actual engine load, and thus the reference fuel index, is determined by the engine controller 17, 17b based on, for example, the engine speed received from the sensor device 40 and a measurement of average cylinder combustion pressure or crankshaft torque. May be.

  The engine control units 17 and 17b compare the applied fuel index with the reference fuel index, and adjust the fuel gas injection pressure so that the applied fuel index corresponds to the reference fuel index. Therefore, the engine control units 17 and 17b have the same amount of energy injected into the cylinder per unit time as stored in the map of the engine control units 17 and 17b, for example, under the adjustment of the engine manufacturing standards. The fuel gas injection pressure is controlled by commanding the adjusted fuel gas pressure from the fuel gas supply system 19 so as to be kept constant at some degree. Since the adjusted adjustment of the fuel gas injection pressure and the amount of energy injected per unit time results in a change in engine output, the governor control of the engine controls 17, 17b was applied. The fuel index is adjusted to maintain engine power, so that a constant engine speed results in an applied fuel index that corresponds to the reference fuel index.

  Thus, a reduced calorific value of the fuel gas results in an increase in fuel gas injection pressure, while an increased calorific value of the fuel gas results in a decrease in fuel gas injection pressure. Similarly, when the temperature of the fuel gas becomes lower than the reference gas, the energy density of the fuel gas is increased, and the fuel gas injection pressure commanded from the fuel gas supply system 19 is decreased by the engine control unit 17b. Thus, when the temperature of the fuel gas becomes higher than the reference gas, the energy density of the fuel gas is lowered, and the fuel gas injection pressure commanded from the fuel gas supply system 19 is raised by the engine control unit 17b.

Claims (10)

A fuel gas supply system;
A cylinder provided with a fuel gas injector for injecting fuel gas directly into the combustion chamber of the cylinder;
At least one engine controller that controls the amount of fuel gas injected into the combustion chamber in response to an applied fuel index to obtain a desired engine speed at a given engine load;
With
The fuel index defines the amount of fuel gas injected into the cylinder per injection, and the amount of fuel gas injected is controlled by adjusting the duration of the fuel gas injection period An internal combustion engine such as a two-cycle crosshead diesel engine,
Based on a comparison of a reference fuel index determined from the measured engine load and an applied fuel index determined by the at least one engine controller to obtain a desired engine speed at a given engine load A sensor device for measuring the engine load during operation, wherein the at least one engine control unit is configured to provide energy of the fuel gas so that the applied fuel index corresponds to the reference fuel index. An internal combustion engine characterized by controlling an injection pressure of fuel gas into the combustion chamber according to a change in density.   The said at least 1 engine control part controls the injection pressure of the said fuel gas to the said combustion chamber according to the calorie | heat amount value and / or temperature change of the said fuel gas, The said fuel gas is characterized by the above-mentioned. Internal combustion engine.   3. Internal combustion engine according to claim 1 or 2, characterized in that the measured engine load is determined from the measurement by means of a sensor device of the combustion pressure and the rotational speed of the shaft during the combustion cycle.   The internal combustion engine according to claim 1 or 2, characterized in that the measured engine load is determined from measurement by a sensor device of shaft torque and shaft rotational speed.   The fuel gas injection pressure is adjusted in combination with adjustment of injection timing and timing of opening and closing the exhaust valve according to the position of the crankshaft in order to obtain optimal fuel consumption and combustion gas emission The internal combustion engine according to claim 1, wherein:   The fuel oil injector for injecting fuel oil directly into the combustion chamber of the cylinder and a fuel oil supply system are provided in the cylinder, The fuel oil supply system according to any one of claims 1 to 5 characterized by things. The internal combustion engine described.   The internal combustion engine according to any one of claims 1 to 6, wherein the fuel gas supply system is a common rail fuel gas supply system.   The internal combustion engine according to any one of claims 1 to 7, wherein the temperature of the fuel gas provided to the cylinder is in a range of 10 to 70 ° C.   9. Internal combustion engine according to any one of the preceding claims, characterized in that the engine speed is in the range from 45 rpm to 250 rpm at 100% engine load.   The internal combustion engine according to any one of claims 1 to 9, wherein a gas supply system for supplying fuel gas to the cylinder is connected to a liquefied natural gas tank of a liquefied natural gas transport ship.

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