Method of combusting first and second liquid fuels in an internal combustion piston engine

Abstract

The invention relates to a method of combusting a first liquid fuel and a second liquid fuel in an internal combustion piston engine, the first liquid fuel having a lower heating value than the second liquid fuel, wherein - a first liquid fuel is injected into a cylinder of the engine as a main fuel, which brings most of the energy into the process, so that the total amount of first liquid fuel delivered to the cylinder for one combustion stage is divided into at least two partial injections, wherein - the main injection of the first liquid fuel accounts for 70-95% of the total amount of the first liquid fuel, and - the start of the main injection occurs at the latest at 20°CA before the top dead centre position of the piston in the cylinder, - the pre-injection of the first liquid fuel accounts for 5-30% of the total amount of the first liquid fuel, and wherein - the start of the pre-injection occurs at 20-55°CA before the top dead centre position of the piston in the cylinder, and the pre-injection is formed by one injection event, and - a second liquid fuel is injected into the cylinder of the engine as a fuel assisting compression ignition, so that the start of the injection of the second liquid fuel occurs at 1-23°CA before the start of the injection of the main injection of the first liquid fuel.

Description

Technical Field

[0001] This invention relates to a method for burning a first liquid fuel and a second liquid fuel in an internal combustion piston engine. Background Technology

[0002] There is a strong market demand for reducing emissions from internal combustion engines, particularly decarbonization. An effective solution for reducing emissions and lowering operating costs from large internal combustion engines in ships and power plants is the so-called dual- or even tri-fuel engine, which can operate on fuels that are carbon-free or contain less carbon, such as traditionally used fossil fuels. These multi-fuel engines offer the flexibility to select the most suitable fuel based on the availability and price of different fuels and / or emission restrictions in a particular place or at a particular time. For example, a ship's engine can operate on non-carbon fuels in areas with strict emission restrictions and on fossil fuel oils elsewhere.

[0003] Traditionally, when operating large diesel or gas engines intended for power generation in land-based power plants or ships, it is generally assumed that fuel injection to ignite the fuel occurs approximately at top dead center (TDC) after the compression stroke. For example, in a diesel engine using LFO as fuel, injection can occur from 25° crank angle (CA) before TDC to 5° CA after TDC, and the injection window is typically about 25° CA long.

[0004] When using generally known principles and experience to select the timing and duration of fuel injection for low-calorific-value fuels, these practices necessitate larger injectors for such fuels to maintain injection timing and duration within conventional ranges, resulting in corresponding power outputs for conventional fuels. This is because narrow injection windows and actual injection pressures require a significant increase in fuel flow rate as a function of time to achieve the desired power output per cylinder of the engine. It has been found that injecting such a large amount of fuel within a narrow window in the TDC region results in a diffuse flame that burns closer to the cylinder walls, increasing component thermal loads.

[0005] The large amount of fuel injected during the compression stroke can easily lead to problems such as increased fuel slip and cylinder liner wetting.

[0006] The purpose of this invention is to provide a method for burning a first liquid fuel and a second liquid fuel in an internal combustion piston engine, wherein the first liquid fuel has a lower calorific value than the second liquid fuel, which results in high combustion performance and low emissions. Summary of the Invention

[0007] The objectives of the invention can be substantially satisfied as disclosed in the independent claims and in other claims that describe various embodiments of the invention in more detail.

[0008] According to an embodiment of the present invention, a method for burning a first liquid fuel and a second liquid fuel in an internal combustion piston engine, wherein the first liquid fuel has a lower calorific value than the second liquid fuel, the method comprising the following steps: - A first liquid fuel is injected as the main fuel into the engine cylinders, which carries most of the energy to the process, such that the total amount of the first liquid fuel delivered to the cylinders for a combustion stage is divided into at least two partial injections, in which... o The main injection of the first liquid fuel accounts for 70-95% of the total amount of the first liquid fuel. The main injection begins as early as 20°CA before the piston reaches top dead center in the cylinder. o The pre-injection of the first liquid fuel includes 5-30% of the total first liquid fuel, and Pre-injection begins 20°–55°CA before the piston reaches top dead center in the cylinder, and is formed by a single injection event. - A second liquid fuel is injected into the engine cylinder as fuel-assisted compression ignition, such that the injection of the second liquid fuel begins at 1-23°CA before the main injection of the first liquid fuel begins.

[0009] This achieves a significant improvement in the thermal load of cylinder components, while still maintaining engine output at the desired level when burning low-calorific-value fuels as the primary fuel.

[0010] According to one aspect of the invention, the pre-injection of the first liquid fuel begins at 25°-35°CA before the top dead center (bTDC) position, preferably at 25°-30°CA before the top dead center position, which provides a suitable environment in the cylinder for the first fuel to form a premixed mixture.

[0011] According to the present invention, the pre-injection portion of the first fuel has sufficient time to form a premixed air-fuel mixture, the combustion of which occurs primarily as premixed combustion in the combustion chamber after compression-promoted ignition. This premixed combustion of the pre-injection portion of the first fuel, which merges into the main injection of the first fuel after compression ignition, effectively ensures a phase pressure rise in the combustion chamber and high engine efficiency and low emissions.

[0012] According to one aspect of the invention, the main injection of the first liquid fuel begins at 10-0°CA before the top dead center position.

[0013] According to one aspect of the invention, the main injection of the first liquid fuel is formed by a single injection event.

[0014] According to an alternative aspect of the invention, the main injection of the first liquid fuel is formed by a plurality of injection events, the first of which begins as early as 15°CA bTDC.

[0015] According to one aspect of the invention, the second liquid fuel injection is formed by a single injection event, and its duration is 2 to 6°CA. Preferably, the injection of the second liquid fuel ends before the main injection of the first fuel begins, wherein the injection of the second liquid fuel begins 1-5°CA before the main injection of the first liquid fuel begins, and the injection duration of the second fuel is 1 to 3°CA.

[0016] According to one aspect of the invention, the main injection comprises 85%-90% of the total first liquid fuel, and the pre-injection comprises 10%-15% of the total first liquid fuel.

[0017] According to one aspect of the invention, the pre-injection comprises 10%-15% of the total first liquid fuel, and the pre-injection begins at 25°-30°CA bTDC.

[0018] According to one aspect of the invention, the pre-injection of the first liquid fuel begins at 25°-35°CA before the top dead center position, and the main injection comprises 85%-90% of the total first liquid fuel, while the pre-injection comprises 10%-15% of the total first liquid fuel.

[0019] According to one aspect of the invention, the pre-injection of the first liquid fuel begins at 25°-30°CA before the top dead center position, and the main injection comprises 85%-90% of the total first liquid fuel, while the pre-injection comprises 10%-15% of the total first liquid fuel.

[0020] According to one aspect of the invention, the main injection of the first liquid fuel is formed by a single injection event, and the main injection comprises 85%-90% of the total amount of the first liquid fuel, and the pre-injection comprises 10%-15% of the total amount of the first liquid fuel.

[0021] According to one aspect of the invention, the main injection of the first liquid fuel is formed by a single injection event, and the main injection comprises 85%-90% of the total amount of the first liquid fuel, and the pre-injection comprises 10%-15% of the total amount of the first liquid fuel.

[0022] According to one aspect of the invention, the main injection of the first liquid fuel is formed by a plurality of injection events, the first injection event of which begins as early as 15°CA bTDC, and the main injection comprises 85%-90% of the total amount of the first liquid fuel, and the pre-injection comprises 10%-15% of the total amount of the first liquid fuel.

[0023] According to one aspect of the invention, the lower heating value of the first liquid fuel is ≤33MJ / kg, and the lower heating value of the second liquid fuel is >33MJ / kg.

[0024] According to one aspect of the invention, the first liquid fuel contains at least 51% methanol, preferably methanol, and the injection of the second liquid fuel begins at 1-3°CA before the main injection of the first liquid fuel begins. Preferably, the injection begins at 1-2°CA before the main injection begins.

[0025] According to one aspect of the invention, the first liquid fuel contains at least 51% methanol, and the injection pressure of the first liquid fuel is 0.8 MPa-1.2 MPa.

[0026] According to one aspect of the invention, the first liquid fuel comprises at least 51% methanol, and the injection start of the main injection of the first fuel depends on the engine load, such that at a load greater than 50% of the engine's maximum nominal load, the injection start is delayed by at least 5% or 1°CA compared to the injection start at a load less than or equal to 50%.

[0027] This process minimizes what is known as fuel slip.

[0028] The aspects of the above-mentioned liquid fuels that mainly contain methanol can be successfully used in any combination to improve the operation of methanol.

[0029] According to one aspect of the invention, the first liquid fuel comprises NH3, and the injection of the second liquid fuel begins at a CA of 3-7° prior to the main injection of the first liquid fuel. Preferably, the injection begins at a CA of 4-5° prior to the main injection.

[0030] According to one aspect of the invention, the first liquid fuel comprises at least 51% NH3, and the injection pressure of the first liquid fuel is 1.0 MPa-1.7 MPa.

[0031] According to one aspect of the invention, the first liquid fuel comprises at least 51% NH3, and the injection start of the main injection of the first fuel depends on the engine load, such that at loads outside the range of 25% to 60% of the engine's maximum nominal load, the injection start is advanced by 1-10°CA compared to the injection start at loads within that range.

[0032] This process minimizes what is known as fuel slip.

[0033] The above aspects regarding liquid fuels that primarily contain ammonia can be successfully used in any combination to improve ammonia handling.

[0034] According to one aspect of the invention, the main injection begins between 10° and 0° CA before the piston reaches top dead center in the cylinder.

[0035] According to one aspect of the invention, the main injection of the first liquid fuel begins before the injection of the second liquid fuel ends.

[0036] According to one aspect of the invention, for a cylinder of an engine to which the method is to be used, a desired cylinder-specific nominal maximum power is determined or set, and a first injection valve is provided for injecting at least the first fuel, the injection valve comprising...

[0037] • Fuel inlet • The fuel passage is arranged to flow in communication with the fuel inlet (102), • Fuel outlet in the fuel passage, which includes one or more injection orifices, • A valve needle used to close or open the fuel outlet, and • The area of ​​the fuel outlet is set to 2-8.5mm. 2 / MW, where MW is the cylinder-specific nominal maximum power when used with the first fuel.

[0038] According to one aspect of the invention, the method includes: determining or setting a desired cylinder-specific nominal maximum power of the engine cylinder for a cylinder of an engine to which the method is to be used; and providing a first injection valve for injecting at least the first fuel, the injection valve including...

[0039] • Fuel inlet • Fuel passage, which is arranged to flow in communication with the fuel inlet. • Fuel outlet in the fuel passage, which includes one or more injection orifices, • A valve needle used to close or open the fuel outlet, and • The area of ​​the fuel outlet is set to 2-8.5mm. 2 / MW, where MW is the cylinder-specific nominal maximum power when used with the first fuel. And the internal combustion engine is operated alternately using the following operating modes: A. A first operating mode, during which a first liquid fuel and a second liquid fuel are burned in the internal combustion piston engine, wherein: - A first liquid fuel is injected into the engine cylinders using a first injection valve as the main fuel. This main fuel carries most of the energy to the process, such that the total amount of the first liquid fuel delivered to the cylinders for a combustion stage is divided into at least two partial injections, in which... The main injection comprises 70%-95% of the total first liquid fuel, and The main injection begins as early as 20°CA before the piston reaches top dead center in the cylinder. o Pre-injection includes 5-30% of the total first liquid fuel volume, and Pre-injection begins 20°–55°CA before the piston reaches top dead center in the cylinder, and is formed by a single injection event. - A second liquid fuel is injected into the engine cylinders using a second fuel injection valve as fuel-assisted compression ignition, such that the injection of the second liquid fuel begins at 1-23°CA before the main injection of the first liquid fuel begins. as well as B. Second operating mode, during which the majority of the second liquid fuel is injected directly into the cylinder as a primary injection event through the first fuel injection valve and the second portion of the second liquid fuel is injected into the cylinder as a primary injection event through the second fuel injection valve, and the fuel is ignited by compression ignition, and the second liquid fuel is burned as the main fuel.

[0040] The first fuel, having a lower calorific value than the second fuel, is, according to a preferred embodiment, methanol, ammonia, or a mixture thereof. Furthermore, when the proportion of light fuel oil is 50% or less, the mixture of methanol and light fuel oil, or ammonia and light fuel oil, has a low calorific value of <33 MJ / kg.

[0041] The cylinder ratio, or nominal maximum power, refers to the power output that the engine manufacturer sets as the maximum output power of a single cylinder. The total output power of an engine is the sum of the power outputs of all its cylinders. For example, the nominal maximum power of a 6-cylinder engine is six times the nominal power of a single cylinder (power group).

[0042] This invention is particularly advantageous in large internal combustion piston engines operating at low or medium speeds, where absolute time and cylinder volume of a single combustion cycle affect combustion chemistry, thereby allowing for different types of injection phasing compared to smaller engines operating at higher speeds. This invention is also applicable to four-stroke and two-stroke engines.

[0043] The present invention can also avoid or at least minimize fuel slip, i.e., unburned fuel escaping into the environment and cylinder liners that are over-wetted by injected fuel.

[0044] It has been found that the combustion of both low-calorific-value and high-calorific-value fuels using the direct injection method according to the invention is highly efficient and clean, and also provides equal cylinder power ratios in medium-speed four-stroke engines having the following details: -rpm range: 300 to 1800rpm -Injection pressure range o Main fuel 600 to 2500 bar LFO as the main fuel bar, for example, 600-2300 bar LHV as the main fuel bar, 600-2500 bar o Ignition fuel pressure of 900 to 2500 bar, preferably higher than the main fuel pressure. - Cylinder bore should be at least 135mm, preferably 150mm-700mm. -Single-cylinder nominal power output: 80 to 2500 kW / cylinder In this invention, it has been surprisingly found that, as is generally understood by those skilled in the art, in the combustion of liquid fuels with significantly low calorific values, the duration of the combustion process does not have the same relationship with the injection duration compared to conventional diesel engines operating with fuels such as heavy, medium, or even light fuel oils. In fact, it has been found that in the combustion of low calorific value fuels, particularly ammonia and methanol, the duration of the combustion process is not directly related to the duration of the fuel injection period.

[0045] This leads to new solutions where the injection duration of this fuel can be extended beyond the conventional range without causing a decline in combustion efficiency or emissions levels. Thus, by properly setting the injection cycle and without requiring compensation operations via significantly different injection pressures, the same, smaller injector can be used for different fuels.

[0046] In this document, the term "main fuel" refers to the fuel that carries the majority of the energy to the combustion chamber. The crank angle presented in this application refers to the control value used to actuate the fuel injectors.

[0047] The exemplary embodiments of the invention presented in this patent application should not be construed as limiting the applicability of the appended claims. The verb "comprising" is used in this patent application as an open limitation that does not exclude the presence of features not yet described. Unless expressly stated otherwise, the features described in the dependent claims may be freely combined with each other. Novel features considered to be characteristics of the invention are specifically set forth in the appended claims. Attached Figure Description

[0048] In the following description, the invention will be illustrated with reference to the accompanying exemplary schematic diagrams, wherein...

[0049] Figure 1 A fuel injection scheme according to an embodiment of the present invention is shown, and

[0050] Figure 2 A fuel injector system according to an embodiment of the present invention is shown. Detailed Implementation

[0051] Reference Figure 1 This invention explains a method for burning a first liquid fuel and a second liquid fuel according to one aspect of the invention. The method involves so-called direct injection, which refers to the direct injection of fuel into the combustion chamber of a cylinder when the piston is near or approximately at its top dead center (TDC) position after the compression stroke in a four-stroke engine. In this method, for each combustion stage, predetermined amounts of the first and second fuels are injected into the cylinder. The first liquid fuel is injected into the engine cylinder as the primary fuel, which carries most of the energy to the combustion process. The first liquid fuel has a lower calorific value than the second liquid fuel. According to one aspect of the invention, the calorific value of the first fuel is <33 MJ / kg, and the calorific value of the second fuel is ≥33 MJ / kg, preferably ≥42 MJ / kg. Figure 1 It can be clearly seen that the total amount of the first liquid fuel delivered to the cylinder for a combustion stage is divided into two injection stages: the first is the pre-injection 12, and the second is the main injection 10. Figure 1 The crank angle for the preferred injection start range is disclosed on its horizontal axis, and the relative amount of fuel is disclosed on its vertical axis. Each region defines the range of the injection operating point (relative fuel amount and fuel injection start). The main injection 10 begins as early as 10°CA bTDC, and the injection start range is between 10°CA bTDC and TDC, and the main injection comprises 70%-95% of the total first liquid fuel. Pre-injection begins at 55°CA bTDC, and the range for which injection can begin is 35°CA, 55°CA bTDC to 20°CA bTDC. Pre-injection accounts for 5-30% of the total first liquid fuel.

[0052] In addition, a second fuel 14 is injected, which begins 1-5°CA before the main fuel injection 10. The amount of the second fuel injected corresponds to 3%-10% of the energy brought into the combustion process by the first fuel.

[0053] In this method, the pre-ignition portion of the first fuel forms a premixed charge in the combustion chamber and is ignited and burned as premixed combustion. The second fuel is injected before the main fuel to ensure premixed charge and compression ignition and combustion, as well as diffusion combustion of the main fuel. Therefore, the first fuel partially burns, i.e., the pre-injection portion, as premixed combustion, and partially burns, i.e., the main injection portion, as diffusion combustion. The pre-injection is formed by a single injection event, i.e., not so-called fractional injection. Typically, the amount of the second fuel assisting compression ignition is such that it promotes and ensures compression ignition of the main fuel by influencing the environment within the main combustion chamber. Ignition occurs when the pressure, temperature, fuel mixture, and the presence of chemically active substances (free radicals) are suitable for ignition and support premixed and diffusion combustion.

[0054] This invention enables the combustion of a liquid fuel with a substantially low calorific value (i.e., calorific value <33 MJ / kg) as a first fuel, with the assistance of a second fuel having a calorific value ≥33 MJ / kg, preferably ≥42 MJ / kg, while still achieving a cylinder-ratio maximum nominal power comparable to, for example, diesel fuel combustion in the corresponding cylinder. The cylinder-ratio maximum nominal power refers to the power that the engine manufacturer sets as the maximum output power of a cylinder. The total output power of an engine is the sum of the power of each cylinder. For example, the nominal maximum power of a 6-cylinder engine is six times the nominal power of a single cylinder (power group).

[0055] In this method, the injection duration of the second fuel is selected such that the start of the main injection 10 of the first liquid fuel occurs before the end of the second liquid fuel injection. This ensures reliable compression ignition of the fuel allowed to enter the combustion chamber during the main injection.

[0056] Figure 1 The shaded areas 10' and 12' depict an aspect of the invention according to the invention, showing a specific range of pre-injection and main injection of the first liquid fuel. Thus, the specific range for the initial pre-injection of the first liquid fuel occurs at 25°-35°CA bTDC, and the proportion of the first liquid fuel to the total volume is 10%-15%. According to an aspect of the invention, the main injection of the first fuel accounts for 85%-90% of the total first liquid fuel volume.

[0057] According to a first embodiment of the present invention, the first fuel is methanol, and the second fuel is diesel fuel, such as light fuel oil or marine diesel.

[0058] According to a first embodiment of the present invention, the method includes the feature that the injection of the second liquid fuel begins 1-3°CA before the main injection of the first liquid fuel begins. That is, when methanol is used, in particular, as the first fuel, the injection of the compression ignition auxiliary fuel needs to be injected closer to the ignition start of the main fuel.

[0059] According to a second embodiment of the present invention, the first fuel is ammonia, and the second fuel is diesel fuel, such as light fuel oil or marine diesel.

[0060] According to a second embodiment of the invention, the method includes the feature that the injection of the second liquid fuel begins at 3-5°CA before the main injection of the first liquid fuel begins. That is, when ammonia is used, in particular, as the first fuel, the injection of the compression ignition auxiliary fuel needs to be performed before the main fuel ignition begins.

[0061] Figure 2A fuel injector system 10 is disclosed, configured to implement an engine-specific method for one cylinder. The cylinder is provided with a first injection valve 100 and a second liquid fuel injection valve 200. At least during normal operation using a first fuel, the first injection valve 100 is configured to inject the main fuel, and the second injection valve 200 is configured to inject fuel to assist compression ignition. The first injection valve 100 and the second liquid fuel injection valve 200 can be arranged as separate bodies or in a common injector body, which is preferred because this makes it easier to adapt the injection valves to the cylinder head.

[0062] The first injection valve 100 includes a fuel inlet 102 and a fuel passage 104, the fuel passage 104 being arranged via a connection to the injector body ( Figure 2 The flow path 106 (not shown) is in flow communication with the fuel inlet 102. The flow path is preferably provided with a so-called flow fuse 108, which prevents excessive fuel flow in the event of a malfunction of the injection valve 100. As a preferred feature, the flow path 106 is provided with an accumulator 110 disposed between the fuel passage 104 and the fuel inlet 102. The accumulator 110 is also disposed between the fuel inlet 102 and the flow fuse 108, such that the volume of the flow passage downstream of the flowing fuel (in the normal operating fuel flow direction) is small, and therefore the amount of fuel leakage that may occur in the event of a malfunction is small. The accumulator is used only for the first injection valve 100, thus ensuring fuel delivery during injection. The inlet 102 of the direct injection valve 100 is arranged in a controllable flow connection with the first fuel source 16 and the second fuel source 20, which is only used for... Figure 2 This is illustrated schematically. Thus, if needed, the fuel injected by the direct injection valve 100 can be selected between the first fuel and the second fuel, or even a mixture of the first fuel and the second fuel can be used.

[0063] The first injection valve 100 is provided with a valve needle 114, which is arranged to close or open the fuel outlet 112 by its axial movement. The valve needle 114 is controlled by a hydraulic control system 116. The hydraulic control system can be implemented in various ways, utilizing the principle of generating a biasing force against the force generated by the fuel injection pressure. Figure 1In this embodiment, the hydraulic control system is provided with an inlet 118 for pressurized working fluid, which is guided through the inlet 118 to the needle housing at the end of the needle opposite the fuel outlet 112. A pressure chamber 124 is present, defined by the end of the needle 114, such that the pressure of the working fluid exerts a force on the needle 114. An outlet flow passage 122 of the hydraulic control system 116 is provided with a valve 120, which, when open, releases pressure from the chamber 124, causing the needle to move upwards as shown in the figure, thereby opening the fuel outlet 112. When the valve 120 is closed, pressure builds up in the chamber 124, forcing the needle 114 back to the closed position. The working fluid also fills a sealed fluid chamber 126 surrounding the upper part of the needle 114 at a pressure higher than the fuel injection pressure to prevent the first fuel from flowing into the hydraulic control system 116 and mixing with the working fluid.

[0064] The valve also includes a fuel outlet 112 arranged to lead to a fuel passage 104. This outlet may include one or more injection orifices 112.1, 112.2. As clearly seen in the enlarged cross-section of the valve, the orifices may have a circular cross-section with a diameter defining the geometric cross-sectional area of ​​the orifice. In the case of multiple orifices, the area A of the outlet 112 is the sum of the areas Ao of each orifice, i.e. .

[0065] The total area A of the fuel outlet is designed to be 2-8.5 mm. 2 / MW, where MW is the nominal maximum power output per cylinder, determined based on the engine specifications for which the fuel injection valve is intended to be used. The first injection valve 100 is a multi-fuel injection device, sized to produce substantially equal nominal maximum power per cylinder of the engine by burning any of the used fuels in practical applications. In practice, the engine typically operates with two different liquid fuels. The fuel outlet area in the injection valve is sized based on a specific correlation between the expected maximum nominal power per cylinder and the fuel's lowest calorific value, ensuring that the injection valve can inject a sufficient amount of fuel when used with any of the expected fuels, including both low and high calorific value fuels. According to the invention, the area of ​​the fuel outlet 112 is designed based on the cylinder-specific nominal maximum power output when used with the fuel having the lowest calorific value among the different fuels. More precisely, the area A of the fuel outlet 112 is 2-8.5 mm. 2 / MW, where MW is the cylinder-specific nominal maximum power when used with a fuel with a low calorific value <33MJ / kg. The area of ​​region A is determined by considering fuel pressure, resulting in an injection pressure of 600-2500 bar. This pressure range covers the possible variations in fuel viscosity, and when used, the appropriate amount of fuel in each fill can be fine-tuned by the total injection duration. In multi-fuel engines, the fuel pressures of different fuels can be selected to be close to each other, making it easier for these fuels to be directed into the same direct injection valve operating as a multi-fuel injection valve. The fuel pressure of one of the fuel pressures, such as the second fuel (e.g., LFO) in the second fuel source 20, can be selected to be slightly higher than the fuel pressure of the first fuel (a fuel with a low calorific value), allowing the second fuel to be used to displace or flush portions of the fuel system shared by both fuels during fuel switching. This may be important from a safety and maintenance perspective, as some fuels with low calorific values ​​(e.g., ammonia or methanol) have toxic properties.

[0066] For example, an engine is designed to operate using at least two fuels, one of which has a lower calorific value than the other, and the direct injection valve is designed based on the fuel having the lowest calorific value of the first and second fuels. When applied to engines with smaller cylinder bores (such as 200mm), in this case, determining a cylinder-specific nominal maximum power of 150kW, the area A would be 0.300-1.275mm². 2 Accordingly, when applied to large-bore engines (such as 640mm), in this case, to determine a cylinder-specific nominal maximum power of 1300kW, the area A will be less than 2.60-11.05mm². 2 Preferably, the area is designed to be close to the upper end of the range of the obtained value A of the area to avoid unnecessarily long injection periods; however, some compromises may be acceptable in practice as long as they do not lead to degradation of the combustion process.

[0067] exist Figure 2In this design, the second fuel injection valve 200 includes a needle 204 for supplying a second fuel to the combustion chamber of the engine. A second fuel passage 206 is flowably connected to a second fuel inlet 201 via a second fuel supply passage 212. The fuel inlet is in fluid communication with a second fuel source 20. A second accumulator space 214 is provided between the second fuel passage and the second fuel inlet 201, preferably within the injector body. Thus, the second fuel passage 206 is flowably connected to the second fuel inlet 201 via the second accumulator space 214. The fuel injector unit 10 also includes a hydraulically operated second valve control section 210 located at the end of the second fuel injection valve needle 204 opposite to the needle tip. The second fuel supply section can be designed to deliver fuel to the engine's combustion chamber in an amount representing even up to 70-100% of its energy so that the engine can operate at its design load. However, the most important function of the second fuel is to facilitate or provide ignition for the first fuel, in which case it typically represents less than 10% of the total fuel energy entering the cylinder.

[0068] The second fuel is used as the control fluid for the second valve 202. In other words, the second fuel supply section 200 utilizes the second fuel as the control fluid for the valve. From Figure 2 It is clearly visible that the control fluid return lines from both valves are combined to a single outlet 122. This means that the pressurized working fluid and sealing fluid in the first fuel injection valve 100 are a second fuel; however, the second fuel is supplied to the first fuel injection valve 100 through a dedicated inlet 118. Thus, the working fluid flowing to the first valve can be at a different pressure than the second fuel. This also provides independent pressure control. The sealing fluid chamber 126 in the first fuel injection valve is in continuous flow connection to inlet 118. This ensures that the pressure in the sealing fluid chamber is substantially at a sufficient level and substantially free of pulsations.

[0069] When designing and / or manufacturing a fuel injection valve according to an embodiment of the invention, a fuel inlet 102 and a fuel passage 114 are provided to the injection valve. The fuel passage 114 is arranged in flow communication with the fuel inlet 102. A fuel outlet 112 is arranged at the opposite end of the injection valve 100, through which fuel is injected as a spray. The fuel outlet is arranged to the fuel passage, and the outlet may be provided with one or more injection holes 112.1, 112.2. A valve needle 114 is axially movable in the body to close or open the fuel outlet 112. The desired cylinder-specific nominal maximum power for a cylinder intended to use the fuel injection valve is determined, and the fuel outlet 112 is provided with a diameter of 2-8.5 mm. 2 / MW is the area where MW is the cylinder-specific nominal maximum power when used with the lowest calorific value of the fuels intended and / or designed for use in the engine. Specifically, MW is the cylinder-specific nominal maximum power when used with a liquid fuel with a low calorific value <33MJ / kg.

[0070] While the invention has been described by way of example with reference to embodiments currently considered to be the most preferred, it will be apparent to those skilled in the art that the basic idea of ​​the invention can be implemented in many ways, along with technological advancements. Therefore, the invention and its embodiments are not limited to the examples and samples described above, but can be varied within the scope of the patent claims and their legal equivalents. When such a combination is technically feasible, the details mentioned in any of the foregoing embodiments can be used in conjunction with another embodiment.

Claims

1. A method for burning a first liquid fuel and a second liquid fuel in an internal combustion piston engine, wherein the lower heating value of the first liquid fuel is lower than that of the second liquid fuel, wherein... - A first liquid fuel is injected as the main fuel into the cylinders of the engine, the main fuel carrying most of the energy into the process, such that the total amount of the first liquid fuel delivered to the cylinders for a combustion stage is divided into at least two partial injections, wherein... The main injection of the first liquid fuel accounts for 70-95% of the total amount of the first liquid fuel. The main injection begins as early as 20°CA before the piston reaches top dead center in the cylinder. The pre-injection of the first liquid fuel accounts for 5-30% of the total amount of the first liquid fuel, and wherein... The pre-injection begins at 20°–55° CA before the piston reaches top dead center in the cylinder, and the pre-injection is formed by a single injection event. - A second liquid fuel is injected into the cylinder of the engine as fuel-assisted compression ignition, so that... The injection of the second liquid fuel begins at 1-23° CA before the main injection of the first liquid fuel begins.

2. The method according to claim 1, characterized in that, The pre-injection of the first liquid fuel begins at 25°–35° CA before the top dead center position.

3. The method according to claim 2, characterized in that, The pre-injection of the first liquid fuel begins at 25°–30° CA before the top dead center position.

4. The method according to claim 1, characterized in that, The main injection of the first liquid fuel begins at 10°-0°CA before the top dead center position.

5. The method according to claim 1, characterized in that, The main injection of the first liquid fuel is formed by a single injection event.

6. The method according to claim 1, characterized in that, The main injection of the first liquid fuel is formed by a plurality of injection events, the first of which begins as early as 15°CA bTDC.

7. The method according to claim 1, characterized in that, The second liquid fuel injection is formed by a single injection event, and its duration is 2 to 6°CA.

8. The method according to any one of claims 1 to 7, characterized in that, The main injection comprises 85% to 90% of the total amount of the first liquid fuel, and the pre-injection comprises 10% to 15% of the total amount of the first liquid fuel.

9. The method according to any one of claims 1 to 9, characterized in that, The first liquid fuel contains at least 51% methanol.

10. The method according to claim 10, characterized in that, The injection of the second liquid fuel begins at 1-3° CA before the main injection of the first liquid fuel begins.

11. The method according to claim 10, characterized in that, The injection pressure of the first liquid fuel is 0.8 MPa-1.2 MPa.

12. The method according to claim 10, characterized in that, The injection start of the main injection of the first fuel depends on the engine load, such that at a load greater than 50% of the engine's maximum nominal load, the injection start is delayed by at least 5% or 1°CA compared to the injection start at a load less than or equal to 50%.

13. The method according to any one of claims 10 to 13, characterized in that, The first liquid fuel is methanol.

14. The method according to any one of claims 1 to 9, characterized in that, The first liquid fuel contains at least 51% NH3.

15. The method according to claim 15, characterized in that, The injection of the second liquid fuel begins at 3-7° CA before the main injection of the first liquid fuel begins.

16. The method according to claim 15, characterized in that, The injection pressure of the first liquid fuel is 1.0 MPa-1.7 MPa.

17. The method according to claim 10, characterized in that, The injection start of the first fuel main injection depends on the engine load, such that at loads outside the range of 25% to 60% of the engine's maximum nominal load, the injection start is advanced by 1-10°CA compared to the injection start at loads within the range.

18. The method according to any one of claims 15 to 18, characterized in that, The first liquid fuel is NH3.

19. The method according to claim 1, characterized in that, The main injection of the first liquid fuel begins before the injection of the second liquid fuel ends.

20. The method according to any one of the preceding claims, characterized in that, For the cylinder of the engine to which the method is to be used, a desired cylinder-specific nominal maximum power is determined or set, and a first injection valve is provided for injecting at least the first fuel, the injection valve comprising... • Fuel inlet (102), • Fuel passage (104), the fuel passage being arranged in flow communication with the fuel inlet (102), • The fuel outlet (112) in the fuel passage (104) includes one or more injection orifices. • Valve needle (114), the valve needle being arranged to close or open the fuel outlet (112), and When used with the first fuel, the area of ​​the fuel outlet (112) is set to 2-8.5 mm. 2 / MW, where MW is the specific nominal maximum power of the cylinder.

21. The method according to claim 20, characterized in that, The method includes alternately operating the internal combustion engine using the following operating modes: A. A first operating mode, during which a first liquid fuel and a second liquid fuel are burned in the internal combustion piston engine, wherein... - A first liquid fuel is injected into the cylinder of the engine as main fuel using a first injection valve. This main fuel carries most of the energy into the process, such that the total amount of first liquid fuel delivered to the cylinder for a combustion stage is divided into at least two partial injections, wherein... The main injection of the first liquid fuel accounts for 70-95% of the total amount of the first liquid fuel. The main injection begins as early as 20°CA before the piston reaches top dead center in the cylinder. The pre-injection of the first liquid fuel accounts for 5-30% of the total amount of the first liquid fuel, and wherein... The pre-injection begins at 20°–55° CA before the piston reaches top dead center in the cylinder, and the pre-injection is formed by a single injection event. - A second liquid fuel is injected into the cylinder of the engine using a second fuel injection valve as fuel-assisted compression ignition, thereby... The injection of the second liquid fuel begins at 1-23° CA before the main injection of the first liquid fuel begins, and B. Second operating mode, in which a large portion of the second liquid fuel is injected directly into the cylinder as a single injection event through the first fuel injection valve and a second portion of the second liquid fuel is injected into the cylinder as a single injection event through the second fuel injection valve, and the fuel is ignited by compression ignition, wherein the second liquid fuel is burned as the main fuel.

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