JP2020070804A - Large 2-stroke uniflow scavenging gas fuel engine and method of reducing preignition or diesel knocking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide gas fuel received from a cylinder liner, a piston, a combustion chamber separated by a cylinder cover, a scavenging air port, an exhaust gas exhaust port, and a supply source of pressurized gas fuel via a gas fuel valve. Multiple gas fuel air supply openings that supply air to the combustion chamber, a combustion gas exhaust port that is connected to the combustion chamber and controlled by the combustion gas valve, and an air supply port of the gas fuel valve from the exhaust port of the combustion gas valve. Or, in a large 2-stroke turbo supercharged uniflow scavenging internal combustion engine equipped with a combustion gas flow path extending to the air supply port of a dedicated combustion gas injection valve, a substance injected into the combustion chamber at the time of fuel injection. Configure to increase the amount of exercise. At the time of fuel injection, gas fuel is injected into a combustion chamber using a gas fuel air supply opening, and at the same time, sequentially, or overlapping, an air supply opening or a dedicated combustion gas is used. Combustion gas is injected into the combustion chamber using the injection valve 36. [Selection diagram] Fig. 3

Description

  TECHNICAL FIELD The present disclosure relates to large two-stroke gas fuel internal combustion engines, and more particularly to large two-stroke uniflow scavenging internal combustion engines with gas fuel injected cross-heads injected from fuel valves located in a cylinder liner.

background

  A large two-stroke turbocharged uniflow scavenging internal combustion engine equipped with a crosshead is used, for example, as a propulsion engine for large ocean going vessels and as a primary mover of a power plant. Not only the size, but the construction of this two-stroke internal combustion engine differs from many other internal combustion engines. Also, the weight of the exhaust valve of this engine is up to 400 kg, the diameter of the piston is up to 100 cm, and the maximum operating pressure of the combustion chamber is usually several hundred bar. The forces associated with such high pressure levels and large piston sizes are enormous.

  Large two-stroke turbocharged internal combustion engine operating on gas fuel injected by a fuel valve arranged inside the length of the cylinder liner, i.e. during the ascending stroke of the piston starting near the closing of the exhaust valve. BACKGROUND ART An engine that injects gas fuel into an engine compresses a gas mixture of gas fuel and scavenging air in a combustion chamber, and a gas mixture compressed at or near top dead center (TDC) by a timed ignition means such as pilot fueling. Ignite

  This type of gas injection with a fuel valve located in the cylinder liner injects the gas fuel when the compression pressure is relatively low so that when the piston approaches top dead center (TDC) (ie combustion The advantage is that significantly lower fuel injection pressures can be used when compared to large two-stroke turbocharged internal combustion engines that inject gaseous fuel (when the compression pressure in the chamber is at or near its maximum). The latter type of engine requires a fuel injection pressure that is significantly higher than the already high maximum combustion pressure. Fuel systems that can withstand this significantly higher gas pressure are expensive and complex due to the volatility of gas fuels and their action at such high pressures (such as diffusion through the steel parts of the fuel system). It becomes a thing.

  Therefore, the combustion supply system of the engine that injects the gas fuel during the compression stroke is significantly less expensive than the engine that injects the gas fuel at or near TDC.

  However, injecting gas fuel during the compression stroke results in pre-ignition and / or diesel knock risk as a result of the piston compressing the mixture of gas fuel and scavenging air.

  Problems with pre-ignition or diesel knock can be reduced by making the fuel fill in the combustion chamber as uniform as possible. However, it is difficult to realize uniform filling of scavenging air and gas fuel. This is because the period of the engine cycle from when the exhaust valve approaches the top dead center is usually in the range of 70 to 90 degrees of the crankshaft angle, which is shorter than the period of the engine cycle that is available in, for example, a 4-stroke engine. Due to this, the period of the engine cycle available to achieve such a uniform filling is only very short (in a four-stroke engine, the gas fuel and the filling air are actually mixed in the intake system). Or at least can be mixed during most of the intake valve opening phase (usually between 40 and 160 degrees of crankshaft angle)).

  The relatively short duration of the engine cycle available to achieve this uniform fill increases the difficulty of avoiding pre-ignition or diesel knock in large two-stroke diesel engines.

  Non-uniform filling of the combustion chamber with gaseous fuel and scavenging air increases the risk of pre-ignition or diesel knock, which can result in significant engine damage.

  The prior art attempts to solve the problem of pre-ignition or diesel knock in the engine by the following method.

  One known large uniflow scavenging two-stroke engine includes a piston moving in a cylinder liner, a cylinder head with an exhaust valve, and a scavenging air port circumferentially arranged in the cylinder liner. Several fuel injectors are circumferentially located in place on the cylinder liner above the scavenging air port. Fuel is injected at a crank angle of at least 90 degrees before TDC.

  Further, in a known large uniflow scavenging two-stroke engine, gas fuel is injected into the air flowing into the combustion chamber from the scavenging port. Further, a water jet nozzle is provided on the cylinder head. To lower the temperature of the mixture of fuel and air, water is injected into the combustion chamber during compression to prevent pre-ignition or diesel knock.

  However, it has been found that the above solutions do not effectively prevent pre-ignition or diesel knock in large two-stroke compression ignition internal combustion engines.

  The two-stroke engine disclosed in JP 2012-154188 A is provided as a cylinder, a piston that slides in the cylinder, and one end portion in the stroke direction of the cylinder, and exhausts exhaust gas generated in the cylinder. The exhaust port that is opened and closed for this purpose, the scavenging port that is provided on the inner peripheral surface on the other end side of the cylinder in the stroke direction and that sucks active gas into the cylinder according to the sliding movement of the piston, and the inner peripheral surface of the cylinder A fuel injection valve for injecting fuel gas on the surface and an inert material injection valve for injecting an inert material so as to collide with the injected fuel gas are provided. Injecting a small amount of inert material at low pressure during engine operation thus reduces nitrogen dioxide emissions. In the region where the concentration of the fuel gas is locally high in the combustion chamber, a large amount of the inert substance is supplied, and in the region where the concentration of the fuel gas is low, the supply of the unnecessary inert substance is suppressed. This reduces nitrogen oxides with a small amount of inert material, and reduces pre-ignition or diesel knock caused by the deviation of the ignition timing of the fuel gas when the inside of the cylinder liner becomes hot. However, injecting a small amount of inert material to impinge on the fuel gas does not adequately solve the problem of preignition or diesel knock. Also, the engine proposed in JP 2012-154188 requires the supply of pressurized inert gas, but no feasible solution for an inert gas source is shown.

  Therefore, there is a need to improve fuel injection in such large two-stroke turbocharged internal combustion engines in order to solve or at least mitigate the problems associated with pre-ignition or diesel knock.

Summary

  Therefore, a large uniflow scavenging two-stroke turbocharged engine that runs on gas fuel injected from a cylinder liner fuel valve, injects gas fuel during the compression stroke to prevent pre-ignition or diesel knock. It is an object to provide an engine that can be reduced at least.

  The above and other objects are achieved by the features of the independent claims. Further embodiments are set forth in the dependent claims, the description of the invention and the drawings.

According to the first aspect, a large two-stroke turbocharged uniflow scavenging internal combustion engine is provided. This engine
A combustion chamber separated by a cylinder liner, a piston, and a cylinder cover;
A scavenging air port located on the cylinder liner,
An exhaust gas exhaust port arranged on the cylinder cover and controlled by an exhaust valve;
One or more gas fuel supply openings arranged in the cylinder liner for supplying gas fuel received from a source of pressurized gas fuel into the combustion chamber via a gas fuel valve;
A combustion gas exhaust port connected to the combustion chamber and controlled by a combustion gas valve;
A combustion gas passage extending from the exhaust port of the combustion gas valve to the air supply port of the gas fuel valve or the air supply port of the dedicated combustion gas injection valve;
The engine is
The gas fuel is supplied, and at the same time, sequentially, or overlapping, the combustion gas is injected into the combustion chamber at the time of fuel injection and injected into the combustion chamber at the time of fuel injection. It is configured to enhance the momentum of matter.

  The purpose of injecting the combustion gas is to increase the momentum of the injected substance by injecting a reactive substance that does not change the heat generation amount of the injected substance into the combustion chamber. The increased momentum promotes mixing of the gas fuel and scavenging air, which increases the uniformity of the charge and reduces the risk of pre-ignition or diesel knock.

  Although the combustion gas is a reactive substance, it does not change the calorific value of the substance injected into the combustion chamber. However, the momentum is added by the injection of the combustion gas to increase the total momentum of the injected substance, thereby reducing the risk of knock or early combustion.

  The momentum (p) is represented by the product of the mass m (kg) of the object and the velocity v (m / s) (p = mv (kg · m / s)).

  Therefore, the total momentum of the substance injected into the combustion chamber during the fuel injection is the sum of the product of the mass of the injected fuel and the velocity and the product of the mass of the injected combustion gas and the velocity. Become.

  The velocity of the injected gas fuel is limited by the speed of sound. Therefore, the speed of the injected gas fuel cannot be increased infinitely. The mass of gaseous fuel injected during a single injection or per engine cycle is determined by the engine load. Therefore, it is impossible to change the injection mass of gas fuel without changing the engine load, and under most operating conditions the engine load determines the injection quantity of gas fuel and not the other way around. Therefore, after the gas fuel reaches the sonic velocity, it is usually impossible to further increase the momentum of the injected gas fuel.

  However, the inventor of the present invention increases the injection mass by injecting the combustion gas in addition to the injection of the gas fuel to increase the momentum of the substance injected during one injection, thereby increasing the momentum of the injected gas fuel. We obtained the knowledge that That is, the momentum is increased by high-speed injection of additional gas (in particular, combustion gas).

  The inventor has also found that the additional combustion gas lowers the fuel filling temperature in the combustion chamber during compression, which further reduces the risk of pre-ignition or diesel knock.

  The combustion gas injected with the gas fuel in order to increase the momentum of the injected substance is the combustion gas obtained from the combustion chamber. This combustion gas is obtained from the high pressure combustion chamber, which reduces the pumping force required to inject the combustion gas back into the combustion chamber.

  Further, the injection of the combustion gas into the combustion chamber during the fuel injection is performed in the form of recirculation of the exhaust gas and the combustion gas, so that the oxygen concentration of the air-fuel mixture in the combustion chamber is lowered. This lowers the combustion temperature and reduces the amount of nitrogen oxides (NOx) produced.

  Furthermore, the reduced oxygen concentration in the combustion chamber itself also reduces pre-ignition or diesel knock.

  In this way, three effects reduce pre-ignition or diesel knock. The first is a decrease in oxygen concentration, and the second is a decrease in temperature. Thirdly, the momentum of the substance injected during the fuel injection is increased, which promotes the mixing of the scavenging air and the gas fuel, and makes the air-fuel mixture in the combustion chamber more uniform. This also reduces pre-ignition or diesel knock. This is because if the air-fuel mixture is not uniform, pre-ignition or diesel knock is likely to occur.

  By making premature ignition or diesel knock less likely to occur, the compression pressure can be increased, which is advantageous in terms of energy output and fuel efficiency.

  Furthermore, the reduction of the risk of pre-ignition or diesel knock can be facilitated by lowering the injection pressure of the gas fuel, which reduces the costs of making and operating the gas fuel supply system.

  According to a possible first embodiment of the first aspect, the combustion gas flow path comprises a combustion gas receiver and a combustion gas supply conduit connecting the combustion gas valve and an inlet of the combustion gas receiver. Including.

  According to a possible second embodiment of the first aspect, the combustion gas flow path comprises a combustion gas control valve which allows a stable control of the combustion gas flow by creating a back pressure.

  According to a possible third embodiment of the first aspect, the combustion gas flow path comprises a wet scrubber for cleaning the combustion gas, preferably arranged downstream of the combustion gas receiver.

  According to a possible fourth embodiment of the first aspect, the combustion gas channel comprises a combustion gas cooler, preferably downstream of the wet scrubber, for cooling the combustion gas.

  According to a possible fifth embodiment of the first aspect, the combustion gas flow path comprises a shutoff valve.

  According to a possible sixth embodiment of the first aspect, the combustion gas passage comprises a combustion gas supply conduit connecting the combustion gas passage to the fuel valve or the combustion gas valve.

  According to a possible seventh embodiment of the first aspect, the combustion gas exhaust port is arranged either on the cylinder cover or on the upper part of the cylinder liner.

  According to a possible eighth embodiment of the first aspect, the engine is arranged to open the combustion gas valve prior to or simultaneously with the exhaust valve.

  According to a possible ninth embodiment of the first aspect, the gaseous fuel and the combustion gas are simultaneously injected as a mixture from the at least one fuel valve into the combustion chamber.

  According to a possible tenth embodiment of the first aspect, the gaseous fuel and the combustion gas are mixed inside at least one of the fuel valves.

  According to a possible eleventh embodiment of the first aspect, the gaseous fuel and the combustion gas are mixed upstream of at least one of the fuel valves.

  According to a possible twelfth embodiment of the first aspect, the gaseous fuel and the combustion gas are injected simultaneously from a plurality of nozzle holes of the nozzle of at least one of the fuel valves.

  According to a possible thirteenth embodiment of the first aspect, the engine comprises a combustion gas supply conduit for supplying the combustion gas to the fuel valve or the combustion gas injection valve, and a pressurized gas fuel supply for the gas fuel. A separate supply conduit for supplying the fuel valve from a source.

  According to a possible fourteenth embodiment of the first aspect, the engine comprises a control device arranged to control the amount of combustion gas injected into the combustion chamber during fuel injection.

  According to a possible fifteenth embodiment of the first aspect, the fuel valves are evenly arranged around the outer circumference of the cylinder liner.

  According to a possible sixteenth embodiment of the first aspect, the fuel valve is arranged at a central position in the longitudinal direction of the cylinder liner.

  According to a possible seventeenth embodiment of the first aspect, the simultaneous, sequential or overlapping injection of the gaseous fuel and the combustion gas is preferably performed during the stroke of the piston towards the cylinder cover. After the piston has passed through the scavenging air port, it is more preferably started when or just before the exhaust valve is closed.

  According to a possible eighteenth embodiment of the first aspect, the engine comprises an ignition device for initiating ignition, preferably at or near top dead center (TDC).

  According to a possible nineteenth embodiment of the first aspect, the engine includes a knock sensor and is configured to control the amount of combustion gas added in response to a signal from the knock sensor.

  According to a possible twentieth embodiment of the first aspect, the engine is arranged to increase the mass of combustion gas injected during fuel injection when pre-ignition or diesel knock is detected by the knock sensor. Composed.

  According to a possible twenty-first embodiment of the first aspect, the engine comprises combustion gas injected during fuel injection when knock is not detected by the knock sensor for a predetermined period or a predetermined engine speed. Configured to reduce the mass of.

  According to a possible twenty-third embodiment of the first aspect, each dedicated combustion gas valve is arranged in the cylinder liner proximate to any of the gas fuel valves.

  According to a possible twenty-fifth embodiment of the first aspect, each dedicated combustion gas injection valve has a nozzle with one or more nozzle holes.

  According to a possible twenty-sixth embodiment of the first aspect, scavenging air is added to the combustion gas and a mixture of scavenging air and combustion gas is injected during fuel injection.

  According to a possible twenty-seventh embodiment of the first aspect, the combustion gas injection valve is arranged at a central position in the longitudinal direction of the cylinder liner.

  According to a possible twenty-eighth embodiment of the first aspect, the engine supplies the gaseous fuel using the fuel supply opening and the combustion gas to the fuel supply opening or the dedicated combustion gas. The fuel is injected by using an injection valve, and the supply of the gas fuel to the combustion chamber and the injection of the combustion gas are performed simultaneously, sequentially, or at the time of fuel injection, whereby the fuel injection is performed. At this time, the momentum of the substance injected into the combustion chamber is increased.

  According to a possible twenty-ninth embodiment of the first aspect, the cylinder liner has one or more combustion gas injection openings connected to the combustion gas injection valve.

According to the second aspect, a method for avoiding or reducing pre-ignition or diesel knock by promoting mixing of gas fuel and scavenging air in the combustion chamber of a large two-stroke turbocharged uniflow scavenging internal combustion engine. So, the engine is
A combustion chamber separated by a cylinder liner, a piston, and a cylinder cover;
A scavenging air port located on the cylinder liner,
An exhaust gas exhaust port arranged on the cylinder cover and controlled by an exhaust valve;
At least one gas fuel supply opening arranged in the cylinder liner for supplying gas fuel received from a supply source of pressurized gas fuel via a fuel valve into the combustion chamber;
A combustion gas exhaust port connected to the combustion chamber and controlled by a combustion gas valve;
A combustion gas flow path extending from an exhaust port of the combustion gas valve to an air supply port of the gas fuel valve, or to an air supply port of one or more dedicated combustion gas injection valves,
The method uses the charge opening to charge the gaseous fuel and simultaneously, sequentially, or overlap with the charge opening or the one or more dedicated combustion gas injection valves. Is used to increase the momentum of a substance injected into the combustion chamber during fuel injection by injecting the combustion gas into the combustion chamber.

  According to a first possible embodiment of the second aspect, only if the engine load is high, preferably only if the engine load is greater than 60% of the maximum continuous rating of the engine, more preferably the engine load is the maximum of the engine. The combustion gas is injected only if it is greater than 70% of the continuous rating.

  According to a possible second embodiment of the second aspect, each dedicated combustion gas valve is arranged in the cylinder liner proximate to any of the gas fuel valves.

  The above and other aspects will be apparent from the embodiments described below.

In the details of the disclosure set forth below, each aspect, each embodiment, and each implementation is described in more detail with reference to the example embodiments shown in the drawings.
FIG. 1 is a front view of a large two-stroke diesel engine according to an exemplary embodiment. FIG. 2 is a side view of the large two-stroke engine of FIG. FIG. 3 is a diagrammatic representation of the large two-stroke engine of FIG. FIG. 4 is a cross-sectional view showing a cylinder frame and a cylinder liner according to one embodiment, together with a cylinder cover, an exhaust valve fitted thereto, and a piston shown at both positions of TDC and BDC. FIG. 5 is a partial cross-sectional view of the cylinder liner of FIG. FIG. 6 is a cylinder liner along the line segment VI-VI ′ in FIG. 5, in which the fuel gas and the injected combustion gas are supplied to the combustion chamber from the same fuel valve. It is a cross-sectional view of a cylinder liner including. FIG. 7 is a side view of a fuel supply source and fuel valve arrangement according to an embodiment in which gaseous fuel and injected combustion gas are mixed prior to being supplied to the fuel valve. FIG. 8 is a side view of a fuel supply and fuel valve arrangement according to an embodiment in which gaseous fuel and injected combustion gas are mixed within a fuel valve. FIG. 9 is a side view of a fuel supply and fuel valve arrangement according to an embodiment in which the gaseous fuel and combustion gas are not mixed prior to being supplied to the nozzle of the fuel valve. FIG. 10 is a side view of the combustion gas injection valve. FIG. 11 is a cylinder liner taken along the line VI-VI ′ of FIG. 5, showing a fuel valve configuration according to another embodiment in which gas fuel and combustion gas are supplied to the combustion chamber from separate valves. It is sectional drawing of the cylinder liner provided. FIG. 12 is a graph showing gas exchange and fuel injection cycle.

Detailed description

  In the following detailed description, the internal combustion engine will be described with reference to the large two-stroke low speed turbocharged internal combustion crosshead engine of the example embodiment. 1, 2, and 3 show an embodiment of a large-sized low-speed turbocharged two-stroke diesel engine equipped with a crankshaft 8 and a crosshead 9. 1 and 2 are a front view and a side view, respectively. FIG. 3 schematically shows the large-sized low-speed turbocharged two-stroke diesel engine of FIGS. 1 and 2 together with its intake system and exhaust system. In this example embodiment, the engine has four cylinders in a row. A large low speed turbocharged two stroke diesel engine typically has 4 to 14 cylinders in a row supported by the engine frame 11. This engine is used, for example, as a main engine of a ship or a stationary engine for driving a generator of a power plant. The total output of this engine is, for example, in the range of 1,000 kW to 110,000 kW.

  In the present embodiment example, this engine is a two-stroke uniflow scavenging type engine having a scavenging port 18 at the bottom of the cylinder liner 1 and a central exhaust valve 4 at the top of the cylinder liner 1. Scavenging air is delivered from the scavenging air receiver 2 through the scavenging ports 18 of the individual cylinders 1 when the piston is below the scavenging ports 18. The gas fuel and the combustion gas are injected from the fuel valve 30 while the piston is rising and before passing through the fuel valve 30 or the combustion gas injection valve 36 (in one embodiment (FIG. 11), the combustion gas is exclusively used). Injected by combustion gas injection valves 36, each dedicated combustion gas injection valve 36 preferably being proximate to the fuel valve 30 in the cylinder liner 1). Preferably, both the fuel valve 30 and the combustion gas injection valve 36 are evenly arranged around the outer periphery of the cylinder liner, and are arranged substantially at the center of the cylinder liner 1 in the longitudinal direction. This causes the injection of gas fuel (and the injection of combustion gases) to occur at relatively low compression pressures, ie significantly below the compression pressure at which the piston reaches TDC.

  The piston 10 in the cylinder liner 1 compresses the filled gas fuel, the injected combustion gas, and the scavenging air. Compression occurs at or near TDC ignition and is triggered, for example, by injection of pilot oil (or any other suitable ignition fluid) from pilot oil fuel valve 50. The pilot oil fuel valve 50 is preferably located on the cylinder cover 22. Post-ignition combustion occurs and exhaust gas is produced. Instead of or in addition to the pilot oil fuel valve 50, it is also possible to start ignition by using another type of ignition device such as a pre-combustion chamber, laser ignition, or a glow plug (both not shown).

  When the exhaust valve 4 is opened, the exhaust gas flows into the exhaust gas receiver 3 through the exhaust duct attached to the cylinder 1, passes through the first exhaust conduit 19 and proceeds to the turbine 6 of the turbocharger 5, and the turbine 6 Through the second exhaust pipe, the economizer 20, and the exhaust port 21 into the atmosphere. The turbine 6 drives a compressor 7 supplied with outside air from an air intake 12 via a shaft. The compressor 7 supplies the pressurized scavenging air to the scavenging air conduit 13 leading to the scavenging air receiver 2. The scavenging air in the conduit 13 passes through an intercooler 14 for cooling the scavenging air.

  The cooled scavenging air travels through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 pressurizes the scavenging air flow when the compressor 7 of the turbocharger 5 does not supply sufficient pressure to the scavenging air receiver 2, that is, when the engine is in a low load or partial load state. When the engine load is high, the compressor 7 of the turbocharger supplies sufficient pressurized scavenging air, after which the auxiliary blower 16 is bypassed via the check valve 15.

  Combustion gas is extracted from the combustion chamber through an exhaust port controlled by the combustion gas valve 26. The exhaust port and the combustion gas valve 26 are preferably arranged in the cylinder cover 20. The combustion gas valve 26 is controlled by an electronic control unit (not shown), and the timing and length of opening the combustion gas valve 26 are determined according to operating conditions, that is, the amount of combustion gas that needs to be injected back into the combustion chamber. To be done. Preferably, the combustion gas valve 26 is opened simultaneously with or before the exhaust gas valve in order to extract the combustion gas at a pressure higher than the cylinder pressure at the time of injecting the combustion gas.

  The engine has a combustion gas passage extending from the exhaust port of the combustion gas valve 26 to the air supply port of the fuel valve 30 or the air supply port of the dedicated combustion gas injection valve 36.

  The combustion gas passage serves to supply the extracted combustion gas to the fuel valve 30 or the dedicated combustion gas injection valve 36. The dedicated combustion gas injection valve 36 injects the combustion gas into the combustion chamber at the same time as, or sequentially or overlapping with the injection of the gas fuel into the combustion chamber.

The combustion gas passage collects the combustion gas and minimizes pressure fluctuations in the extraction process, and a control valve 28 that secures stable control of the amount of recirculated combustion gas by generating the necessary back pressure. And a wet scrubber 29 that cleans the recirculated combustion gas so that sulfur dioxide (SO ₂ ) and soot particles are removed to the required extent, and combustion gas cooling that cools the recirculated combustion gas to the same temperature as the scavenging air. A device 39, a shut-off valve 38 for closing the system during the pause of the combustion gas recirculation system 44 to close the system to the wet scrubber 29, water for cleaning scrubber water and separating soot particles and clean water. And a processing system 45. The combustion gas flow path further includes a combustion gas supply conduit 48 and a combustion gas supply conduit 37. In one embodiment, the combustion gas supply conduit 48 connects the exhaust port of the combustion gas valve 26 and the supply port of the combustion gas receiver 27, and the exhaust port of the combustion gas receiver 27 and the supply port of the wet scrubber 29. And connect. A control valve 28 is arranged in the combustion gas supply conduit 48 (preferably between the combustion gas receiver 27 and the wet scrubber 29). Further, the combustion gas flow path includes a combustion gas supply conduit 37. In one embodiment, the combustion gas supply conduit 37 connects the exhaust port of the wet scrubber 29 to the intake port of the combustion gas cooler 39, and connects the exhaust port of the combustion gas cooler 39 to the intake port of the fuel valve 30. Alternatively, it is connected to the air supply port of the dedicated combustion gas injection valve 36. In one embodiment, the shutoff valve 38 is installed in the combustion gas supply conduit 37 between the combustion gas cooler 39 and the fuel valve 30 or the air inlet of the dedicated combustion gas injection valve 36.

  Only one combustion gas valve 26 may be provided for each cylinder of the engine, or a plurality of combustion gas valves 26 may be provided for each cylinder.

  In one embodiment, the combustion gas receiver 27 is connected to the combustion gas valves 26 of all cylinders of the engine so that the combustion gas flow path is in series from the combustion gas receiver 27 to the shutoff valve 38. That is, the combustion gas passage includes only one of the combustion gas receiver 27, the control valve 28, the wet scrubber 29, the combustion gas cooler 39, and the shutoff valve 38.

  In order to obtain a stable pressure before the gas enters the cleaning system, a high-temperature combustion gas of about 700 ° C. is extracted from the combustion chamber by the combustion gas valve 26 and supplied into the combustion gas receiver 27, and inside the combustion gas receiver 27. Pressure fluctuations caused by opening and closing the combustion gas valve 26 are reduced. For efficient cleaning process, it is preferable that the pressure inside the scrubber is stable.

In the wet scrubber 29, the recirculated combustion gas is washed with recirculated clean water. The recycled clean water is preferably added with NaOH to neutralize the sulfuric acid formed during the reaction of water with SO ₂ and sulfur trioxide (SO ₃ ). Due to the evaporation of the scrubber water, the temperature reaches an equilibrium temperature in the wet scrubber 29 near 90 ° C. The amount of evaporated scrubber water is only 10% to 20%, and the remaining dirty scrubber water is discharged from the scrubber and collected in a buffer tank which is a part of the water treatment system 45. The water treatment system 45 cleans dirty scrubber water and supplies clean recirculating scrubber water to the scrubber. The water treatment system 45 includes a sludge discharge part 46 and a clean water discharge part 47, and the clean water may be supplied from the clean water discharge part 47 to the scrubber.

  The washed recirculated combustion gas is then cooled in the combustion gas cooler 39. During cooling a considerable amount of water condenses in the combustion gas cooler 39.

  In one embodiment, the recycle combustion gas is cooled to a scavenging air temperature of about 35 ° C to 40 ° C.

  In one embodiment, the recirculated combustion gas is mixed with the cooled scavenging air sent from the compressor 7, and the mixed combustion gas and the scavenging air are supplied to the fuel valve 30 or the dedicated combustion gas injection valve 36, and the fuel is injected. At the time of injection, it is injected simultaneously with the gas fuel, sequentially, or overlapping. Scavenging air is supplied through the scavenging air supply duct 52, and the amount of scavenging air is controlled by the scavenging air valve 53. The scavenging air valve 53 is used to shut off the supply of scavenging air to the combustion gas supply conduit 37. Alternatively, an independent shut-off valve (not shown) is provided in the scavenging air supply duct 52.

  The amount of recirculated combustion gas can be controlled by the timing of opening and closing the combustion gas valve 26. This allows operation in different modes (ie, International Maritime Organization (IMO) secondary and tertiary regulatory modes for combustion gas recirculation). Further, the amount of recirculated combustion gas can be varied over the entire load range.

  In one embodiment, the combustion gas valve 26 begins to open 35 to 50 degrees before the exhaust valve 4 begins to open. In a typical large two-stroke inflow scavenging crosshead internal combustion engine, the pressure at this time is in the range of about 15 to 30 bar.

  In one embodiment in which the engine operates on gas fuel, the amount of combustion gas needs to be low to avoid pre-combustion or diesel knock. That is, the combustion gas injection valve is opened later with a low cylinder pressure.

  The opening length of the combustion gas valve 26 depends on the size and number of the combustion gas valve 26. The valve opening time and duration will vary based on the recirculated combustion gas requirements.

  FIG. 12 shows the opening and closing periods of the scavenging port 18 (intake port), the exhaust valve 4, and the gas valve (gas fuel valve 30 and combustion gas injection valve 36) as a function of crank angle. It is the graph shown. As the graph shows, the injection period of the gas fuel and the combustion gas is very short, which results in the gas fuel being mixed with the scavenging air in the combustion chamber for a very short time. The gaseous fuel and the injected combustion gas must be injected within this very short period.

  The combustion gas injected is considerable and the injection pressure is high. This is to obtain a relatively large amount of combustion gas injected at a relatively high speed in order to obtain a large amount of momentum of the injected combustion gas.

  The momentum of the injected combustion gases combined with the momentum of the injected gas fuel results in a total momentum that is significantly greater than the momentum of the gas fuel alone.

  The combustion gas injected is a reactive substance, but has no calorific value at all, so the calorific value of all the substances injected into the combustion chamber is substantially the same as the calorific value of the gas fuel injected into the combustion chamber. No difference.

  The amount of gas fuel injected in one engine cycle is determined by the engine load. The amount of combustion gas injected in one engine cycle depends on the speed of the injected gas fuel (this speed is related to the injection pressure of the gas fuel, the nozzle of the fuel valve, and the shape of the nozzle hole). And depends on the need to prevent pre-ignition or diesel knock on a particular engine running on a particular type of gas fuel and can be determined by simple trial and error.

  The combustion gas is preferably injected every engine cycle. At low engine loads, the risk of preignition or diesel knock is usually very low. Therefore, in one embodiment, only the combustion gases are injected into the combustion chamber when the engine load is high (eg, above 60% to 70% of the engine's maximum continuous rating).

  In one embodiment, the engine comprises a knock sensor, not shown, and the amount of combustion gas added is controlled in response to a signal from the knock sensor. That is, the amount (mass) of combustion gas injected when pre-ignition or diesel knock is detected is increased (when pre-ignition or diesel knock is not detected, the amount of combustion gas is decreased after a while).

  In one embodiment, the combustion gas is injected simultaneously with the gas fuel as a mixture with the gas fuel. Alternatively, the gas fuel valve 30 separately injects through different nozzle holes of one nozzle or different nozzles of one fuel valve.

  In one embodiment, the combustion gas is injected from the dedicated combustion gas injection valve 36 alone, simultaneously with the gas fuel, sequentially or with overlap.

  4, 5, and 6 show a cylinder liner 1 commonly used in large two-stroke crosshead engines. The cylinder liner 1 is manufactured in various sizes depending on the engine size, with the cylinder inner diameter usually in the range of 250 mm to 1,000 mm, and the corresponding cylinder length usually in the range of 1,000 mm to 4,500 mm. It

  The cylinder liner 1 shown in FIG. 4 is mounted on the cylinder frame 23 with the cylinder cover 22 arranged on the top of the cylinder liner 1 via an airtight interface. In FIG. 4, the piston 10 is shown by a broken line at bottom dead center (BDC) and top dead center (TDC), but these two positions cannot occur at the same time, and the crankshaft 8 is rotated by 180 degrees. Needless to say The cylinder liner 1 is provided with a cylinder oil hole 25 and a cylinder oil passage 24. When the piston 10 passes through the cylinder oil passage 24, the cylinder lubricating oil is supplied by the cylinder oil passage 24 and the next piston ring ( (Not shown) spreads the cylinder lubricating oil over the sliding surface of the cylinder liner 1.

  In the illustrated embodiment, the thinnest portion of the wall 49 is the bottom of the cylinder liner 1, that is, the portion below the scavenging port 18. The thickest portion of the wall 49 of the cylinder liner 1 is the axially upper portion of the cylinder liner 1. The cylinder liner 1 has a sudden change in thickness around the central portion in the axial direction, and this changed portion functions as a shoulder for mounting the cylinder on the cylinder frame 23. The cylinder cover 22 is pressed against the upper surface of the cylinder liner 1 with a large force applied from the attracting bolt.

  A pilot oil valve 50 (normally two or more for each cylinder) or a pre-combustion chamber equipped with the pilot oil valve 50 is mounted on the cylinder cover 22 and connected to a pilot oil source (not shown). In one embodiment, the timing of pilot oil injection is controlled by an electronic controller, not shown.

  Each fuel valve 30 is attached to the cylinder liner 1 with the nozzle of the valve 30 being substantially flush with the inner surface of the cylinder liner 1 and with its rear end protruding from the outer wall of the cylinder liner 1. Usually, one or two (in some cases, three or four) fuel valves 30 are provided in the cylinder liner 1 in such a manner that they are circumferentially arranged at appropriate positions in each cylinder liner 1. In one embodiment, the fuel valve 30 is arranged substantially at the center of the cylinder liner 1 in the longitudinal direction.

  5 and 6 show the cylinder liner 1 and the fuel valve 30 in more detail. In this embodiment, the cylinder liner 1 comprises four fuel valves 30. Although the fuel valve 30 shown in FIG. 6 is oriented radially, it is clear that the fuel valve 30 can be arranged at other angles with respect to the cylinder liner 1. In this embodiment, the engine does not have a dedicated combustion gas injection valve 36 and the combustion gas is injected by the gas fuel valve 30.

  FIG. 6 is a cross-sectional view of the cylinder liner 1 at the height of the fuel injection valve 30, and the pressurized gas fuel supply source connected to the air supply port of each gas fuel valve 30 via the gas fuel supply conduit 41. It is the figure which showed typically the gas fuel supply system containing 40. The air supply port of the gas fuel valve 30 is also connected to the combustion gas supply conduit 37.

  In one embodiment, the fuel valve 30 is connected to a common (mixed) source of gaseous fuel and combustion gas.

  The fuel valve 30 shown in FIG. 7 is connected to both the pressurized fuel source 40 and the combustion gas extraction / recirculation system 44 via one supply line 42. The supply line 42 is connected to a mixing point to which both the combustion gas supply conduit 37 and the gas fuel supply conduit 41 are connected. In one embodiment, a valve, not shown, is provided to ensure the desired ratio of gas fuel to combustion gas supplied to fuel valve 30. The air-fuel mixture is transferred to the air supply opening 34 of the gas fuel valve 30 by the common conduit 32. The air-fuel mixture is supplied into the combustion chamber through the air supply opening 34. The fuel valve 30 is provided with, for example, means for timely injecting the air-fuel mixture into the combustion chamber under the control of the electronic control unit.

  In a variation of the embodiment of FIG. 7, the gas fuel and the combustion gas are not mixed and either the gas fuel or the injected combustion gas is sequentially supplied to the fuel valve 30 first (without substantial interruption). Are sequentially ejected.

  In another embodiment shown in FIG. 8, a gas fuel source 40 is connected to a dedicated port of the fuel valve 30 by a dedicated supply line 41. Gas fuel is guided to the mixing point 33 in the fuel valve 30 by a dedicated conduit 31. A combustion gas extraction / recirculation system 44 is connected to a dedicated port of the fuel valve 30 by a combustion gas supply conduit 37. A dedicated conduit 35 guides the combustion gases to the mixing point 33 inside the fuel valve 30. The gas fuel and the combustion gas are mixed at the mixing point 33, and the mixture is transferred from the mixing point 33 to the air supply opening 34 by the common conduit 32. Gas fuel is supplied to the combustion chamber through the supply opening 34. The fuel valve 30 is equipped with, for example, means for time-injecting the air-fuel mixture into the combustion chamber under the control of the electronic control unit.

  In another embodiment shown in FIG. 9, a gas fuel source 40 is connected to a dedicated port of the fuel valve 30 by a dedicated supply line 41. The dedicated conduit 31 guides the gas fuel to the first nozzle 39. A combustion gas extraction / recirculation system 44 is connected to a dedicated port of the fuel valve 30 by a combustion gas supply conduit 37. The dedicated conduit 35 guides the combustion gas to the combustion gas supply opening 51. Gas fuel is supplied to the combustion chamber through the supply air opening 34, and combustion gas is injected into the combustion chamber through the combustion gas supply opening 51. The fuel valve 30 is provided with, for example, means for timely injecting a gas fuel and a combustion gas into the combustion chamber under the control of the electronic control unit.

  In another embodiment shown in FIG. 11, the cylinder liner 1 includes a dedicated fuel valve 30 for injecting gas fuel and a dedicated combustion gas injection valve 36 for injecting combustion gas into the combustion chamber.

  The exclusive combustion gas injection valve 36 is installed in the cylinder liner 1 with the combustion gas injection opening 51 of the valve 36 being substantially flush with the inner surface of the cylinder liner 1 and the rear end protruding from the outer wall of the cylinder liner 1. It is installed. Usually, one or two (in some cases, three or four) dedicated combustion gas injection valves 36 are provided in each cylinder liner 1 in such a manner that they are evenly arranged at appropriate places in each cylinder liner 1 in the circumferential direction. There is. In one embodiment, the dedicated combustion gas injection valve 36 is disposed substantially in the center of the cylinder liner 1 in the lengthwise direction, preferably adjacent to the dedicated gas fuel valve 30.

  The pressurized gas fuel supply source 40 is connected to the (four in this embodiment) gas fuel valves 30, and the combustion gas extraction / recirculation system 44 is connected to (four in this embodiment) dedicated combustion gas injection valves 36. It The gas fuel valve 30 and the combustion gas injection valve 36 are provided with, for example, means for injecting the gas fuel and the combustion gas into the combustion chamber in a timed manner under the control of the electronic control unit. In FIG. 11, the fuel valve 30 and the combustion gas injection valve 36 are shown as a close pair, but this arrangement is merely an example, and the fuel valve 30 and the combustion gas injection valve 36 need to be arranged in a pair. Obviously, it is also possible to place them at wider intervals.

  FIG. 10 is a side view of the combustion gas injection valve 36 having at least one combustion gas injection opening 51 for injecting the combustion gas into the combustion chamber. The illustrated combustion gas injection valve 36 has its proximal end connected to a combustion gas supply conduit 37.

  In one embodiment, the pressure of the combustion gases is increased to a suitable injection pressure by a compressor not shown. Since the combustion gas is already pressurized, less energy is required to raise the pressure of the air or gas to the injection pressure than if the pressurization to this injection pressure was started from atmospheric pressure.

  In one embodiment, the gaseous fuel is provided before the exhaust valve closes to prolong the mixing time. The injection timing of the combustion gas is adjusted accordingly.

  In one embodiment, not shown, the cylinder comprises a pre-combustion chamber for ignition, which is refueled by pilot injection from an independent pilot fluid (pilot oil) injection system.

  In one embodiment (not shown), the gas fuel is supplied from one gas fuel valve to the plurality of gas fuel supply openings, and the gas fuel supply openings are further supplied to the combustion chamber.

  In one embodiment, the engine has multiple cylinders, one or more of which operates as defined in the claims, while the remaining cylinders inject combustion gas into the combustion chamber. Works without. Alternatively, the remaining cylinders operate on liquid fuel.

  Various aspects and implementations have been described herein in connection with various embodiments. However, upon studying the drawings, the specification, and the appended claims, various other variations of the embodiments of the present disclosure will be understood and effected by those skilled in the art in practicing the claimed subject matter. To be done. In the claims, the term "comprising" does not exclude other elements or steps. A single processor or other device may fulfill the functions of several items recited in the claims. The mere fact that several measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

  Reference signs used in the claims are not meant to limit the scope of the invention.

Claims (25)

A combustion chamber partitioned by a cylinder liner (1), a piston (10), and a cylinder cover (22);
A scavenging air port (18) located in the cylinder liner (1),
An exhaust gas exhaust port arranged on the cylinder cover (22) and controlled by an exhaust valve (4);
One or more gas fuel supplies arranged in the cylinder liner (1) for supplying gas fuel received from a supply source (40) of pressurized gas fuel into the combustion chamber via a gas fuel valve (30). An air opening (34),
A combustion gas outlet connected to the combustion chamber and controlled by a combustion gas valve (26);
A combustion gas passage extending from the exhaust port of the combustion gas valve (26) to the air supply port of the gas fuel valve (30) or the air supply port of the dedicated combustion gas injection valve (36);
The engine is
The gas fuel is supplied, and at the same time, sequentially, or overlapping, the combustion gas is injected into the combustion chamber during fuel injection, and is injected into the combustion chamber during the fuel injection. Configured to increase the momentum of a substance
Large 2-stroke turbocharged uniflow scavenging internal combustion engine.   The combustion gas flow path includes a combustion gas receiver (27) and a combustion gas supply conduit (48) connecting the combustion gas valve (26) and an air supply port of the combustion gas receiver (27). The engine according to claim 1.   An engine according to claim 1 or 2, wherein the combustion gas flow path comprises a combustion gas control valve (28) which ensures a stable control of the combustion gas flow by creating a back pressure.   Engine according to any one of the preceding claims, wherein the combustion gas flow path comprises a wet scrubber (29) for cleaning combustion gases, preferably arranged downstream of the combustion gas receiver (27). ..   The combustion gas flow path comprises a combustion gas cooler (39) for cooling the combustion gas, preferably a combustion gas cooler (39) arranged downstream of the wet scrubber (29). The engine according to any one of Items 1 to 4.   An engine according to any one of the preceding claims, wherein the combustion gas flow path comprises a shutoff valve (38).   The combustion gas flow passage comprises a combustion gas supply conduit (37) connecting the combustion gas flow passage to the air supply port of the fuel valve (30) or the air supply port of the combustion gas injection valve (36). An engine according to any one of claims 1 to 6, comprising:   The engine according to any one of claims 1 to 7, wherein the combustion gas exhaust port is arranged in either the cylinder cover (22) or an upper portion of the cylinder liner (1).   An engine according to any one of the preceding claims, wherein the engine is configured to open the combustion gas valve (26) prior to, concurrently with, or after the exhaust valve (4). ..   The engine according to any one of claims 1 to 9, wherein the gaseous fuel and the combustion gas are simultaneously injected as a mixture from the at least one fuel valve (30) into the combustion chamber.   The engine of claim 10, wherein the gaseous fuel and the combustion gas are mixed inside at least one of the fuel valves (30).   The engine of claim 10, wherein the gaseous fuel and combustion gas are mixed upstream of at least one of the fuel valves (30).   The engine according to claim 1, wherein the gaseous fuel and the combustion gas are simultaneously injected from a plurality of nozzle holes of a nozzle of at least one of the fuel valves (30).   A combustion gas supply conduit (37) for supplying the combustion gas to the fuel valve (30) or the combustion gas injection valve (36), and the gas fuel from the pressurized gas fuel supply source (40) to the fuel valve. Engine according to any one of claims 10 to 13, including an independent supply conduit (41) for supplying (30).   The engine according to any one of claims 1 to 14, comprising a control device configured to control the amount of combustion gas injected into the combustion chamber during fuel injection.   Engine according to any one of the preceding claims, wherein the fuel valves (30) are evenly arranged around the outer circumference of the cylinder liner (1).   The engine according to any one of claims 1 to 16, wherein the fuel valve (30) is arranged at a central position in the longitudinal direction of the cylinder liner (1).   Both the injection of the gaseous fuel and the injection of the combustion gas are between strokes of the piston (10) towards the cylinder cover (22), preferably after the piston (10) has passed the scavenging air port, Engine according to any one of claims 1 to 17, more preferably started when or shortly before the exhaust valve (4) is closed.   Engine according to any one of the preceding claims, having an ignition device for initiating ignition, preferably at or near top dead center (TDC).   The engine according to any one of claims 1 to 19, which has a knock sensor and is configured to control the amount of combustion gas added in response to a signal from the knock sensor.   21. The engine of claim 20, configured to increase the mass of combustion gas injected during fuel injection when pre-ignition or diesel knock is detected by the knock sensor.   A configuration for reducing the mass of combustion gas injected during fuel injection when pre-ignition or diesel knock is not detected by the knock sensor for a predetermined period of time or a predetermined engine speed. The engine according to 20 or 21.   The engine according to any one of the preceding claims, wherein each dedicated combustion gas injection valve (36) is located in the cylinder liner proximate to any of the gas fuel valves (30). A method of avoiding or reducing pre-ignition or diesel knock by promoting mixing of gas fuel and scavenging air in the combustion chamber of a large two-stroke turbocharged uniflow scavenging internal combustion engine, the engine comprising:
A combustion chamber partitioned by a cylinder liner (1), a piston (10), and a cylinder cover (22);
A scavenging air port (18) located on the cylinder liner (1),
An exhaust gas exhaust port arranged on the cylinder cover (22) and controlled by an exhaust valve (4);
At least one gas fuel supply opening (34) arranged in the cylinder liner (1) for supplying the gas fuel received from the supply source (40) of the pressurized gas fuel via the fuel valve into the combustion chamber. )When,
A combustion gas outlet connected to the combustion chamber and controlled by a combustion gas valve (26);
A combustion gas passage extending from the exhaust port of the combustion gas valve (26) to the air supply port of the gas fuel valve (30) or the air supply port of one or more dedicated combustion gas injection valves (36); Prepare,
The method uses the charge opening (34) to charge the gaseous fuel and simultaneously, sequentially, or overlapping the charge opening (34) or the one or more. Increasing the momentum of substances injected into the combustion chamber during fuel injection by injecting the combustion gas into the combustion chamber using a dedicated combustion gas injection valve (36) of.   Only if the engine load is high, preferably only if the engine load is greater than 60% of the engine's maximum continuous rating, and more preferably, the engine load is greater than 70% of the engine's maximum continuous rating. 25. The method of claim 24, which is jetted.