Turbocharged internal combustion engine and method for determining NOx reduction rate of engine

Abstract

A large two-stroke uniflow scavenging turbocharged multi-cylinder internal combustion engine and a method for controlling the NOx reduction rate in the engine, the engine having an SCR reactor (28) supplied with a flow of reductant and a controller (50), the controller is configured to calculate the NOx reduction rate of the SCR reactor (28) and to control the magnitude of the reductant flow accordingly.

Description

Technical Field

[0001] The present invention relates to a crosshead type large turbocharged two-stroke single-flow internal combustion piston engine, and in particular to a crosshead type large turbocharged two-stroke single-flow internal combustion piston engine with an SCR (Selective Catalytic Reduction) reactor for reducing NO in the exhaust gas. x Reduction is performed to purify exhaust gas generated by the engine. Background Art

[0002] Large two-stroke, uniflow, scavenged, turbocharged, crosshead, compression-ignition internal combustion engines are commonly used in the propulsion systems of large ships or as prime movers in power plants. Their enormous size, weight, and power output set them apart from conventional internal combustion engines and put them in a class of their own.

[0003] Emission requirements for these engines have become increasingly difficult to meet, and will continue to become increasingly difficult to meet, particularly with respect to nitrogen oxides (NO x This is especially true at the global level. General awareness of environmental issues is rapidly increasing. The IMO (International Maritime Organization) currently has emission limits for certain forms of marine air pollution. Authorities around the world are implementing similar measures. One example is the proposed EPA (U.S. Environmental Protection Agency).

[0004] NO in exhaust gas x Reduction can be achieved by primary and / or secondary reduction methods. Primary methods are those that directly affect the engine's combustion process. The actual degree of reduction depends on the engine type and the reduction method, but varies from 10% to over 80%. Secondary methods are measures to reduce emission levels without changing the engine's performance from its fuel-optimized settings, using equipment that does not form part of the engine itself. The most successful secondary method to date is the removal of NO x The SCR (Selective Catalytic Reduction) method, which reduces NO by adding a reducing agent such as ammonia or urea to the exhaust gas before it enters the catalytic converter, can be used to reduce NO x The level is reduced by more than 95%. Typically, the reducing agent is injected and atomized in the exhaust gas system at a location upstream of the SCR reactor or in the SCR reactor. The SCR reactor contains multiple layers of catalyst. The catalyst volume and therefore the size of the reactor depends on the activity of the catalyst and the required NO x The catalyst generally has a monolithic structure, which means that the catalyst comprises a catalyst block with a large number of parallel channels, the walls of which are catalytically active.

[0005] For example, when urea is added to an SCR reactor as a reducing agent, the urea acts as a reducing agent to reduce nitrogen oxide (NOx) emissions into nitrogen (N2) and water vapor (H2O), both of which are harmless byproducts. This process occurs in multiple steps:

[0006] 1. Urea injection: Urea (CO(NH2)2) is injected into the exhaust stream before it enters the SCR catalyst chamber. Urea is usually dissolved in water to form a urea aqueous solution (UWS), which is then sprayed into the exhaust gas.

[0007] 2. Thermal decomposition: When the urea aqueous solution enters the hot exhaust stream, the urea aqueous solution evaporates and decomposes into ammonia (NH3) and isocyanic acid (HNCO) through thermal decomposition. This reaction occurs when the exhaust gas is still hot, usually above 200°C.

[0008] 3. Hydrolysis: Isocyanic acid is further hydrolyzed to form additional ammonia and carbon dioxide (CO2). This step ensures that most of the urea is converted into ammonia, which is the actual reducing agent in the SCR process.

[0009] 4. Catalytic Reaction: Ammonia then reacts with nitrogen oxides present in the exhaust gas in the presence of a catalyst. Catalysts are typically made of materials such as vanadium, titanium oxide, zeolites, or various base metals that promote the reaction but are not consumed in the process. SCR catalysts facilitate the selective reduction of NOx to nitrogen and water vapor in the presence of oxygen, which is present in diesel exhaust.

[0010] This process effectively reduces the level of NOx in the exhaust gas. The efficiency of the SCR system depends on a number of factors, including the temperature of the exhaust gas, the concentration of NOx, the amount and distribution of the injected urea solution, and the design and material of the SCR catalyst.

[0011] Emission regulations for engines operating on marine vessels (IMO regulations) require that the NOx reduction rate at each test point not differ by more than 5% from the reduction rate specified in the NOx Technical File (created on a test bench for the relevant engine type). However, establishing and monitoring the NOx reduction rate during engine operation is challenging because, when commercially available NOx sensors are positioned downstream of the SCR reactor, the PPM levels provided by these sensors do not correspond to either the NOx mass flow rate or the specific NOx level in g / kWh that the emission regulations are based on. Furthermore, to understand the reduction rate, the NOx mass flow rate or the specific NOx level in g / kWh in the exhaust gas upstream of the SCR reactor must be known. However, determining the NOx mass flow rate or the specific NOx level in g / kWh in the exhaust gas upstream of the SCR reactor using, for example, commercially available NOx sensors positioned upstream of the SCR reactor is also challenging because the measurements are performed in the high-pressure stream.

[0012] DK177462 discloses a large turbocharged two-stroke diesel engine with a crosshead, the engine having a plurality of cylinders, a turbocharger, and an SCR reactor located upstream of the turbocharger and downstream of the exhaust gas receiver. A reducing agent for the SCR reactor is introduced into the exhaust gas upstream of the SCR reactor.

[0013] DK180561 discloses a large turbocharged two-stroke internal combustion engine according to the preamble of claim 1 . Summary of the Invention

[0014] The object is to provide a large two-stroke uniflow scavenged turbocharged internal combustion engine which overcomes or at least reduces the above-mentioned problems.

[0015] These and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the drawings.

[0016] According to a first aspect, there is provided a large two-stroke uniflow scavenged turbocharged internal combustion engine comprising:

[0017] a plurality of cylinders that generate an exhaust gas flow containing NOx during operation of the engine,

[0018] a turbocharger system comprising a compressor and an exhaust gas driven turbine, the turbine being located in the exhaust gas system and the compressor being located in the scavenging air system for supplying scavenging air to cylinders of the engine,

[0019] a selective catalytic reduction reactor located in the exhaust gas system,

[0020] a reducing agent source configured to add a given metered reducing agent flow to the exhaust gas conduit for reacting with NOx in the SCR reactor,

[0021] an O2 sensor that generates a signal representative of O2 ppm in the exhaust gas downstream of both the SCR reactor and the turbine,

[0022] a NOx sensor generating a signal representative of NOx ppm in the exhaust gas downstream of both the SCR reactor and the turbine,

[0023] A controller is informed of the engine load and is configured to:

[0024] - The NOx mass flow rate in the exhaust gas downstream of the SCR reactor is calculated according to:

[0025] -O2 sensor signal,

[0026] - NOx sensor signal,

[0027] - thermal efficiency of the engine,

[0028] - engine load, and

[0029] - adjustment coefficient,

[0030] - Calculate the NOx mass flow in the exhaust gas upstream of the SCR reactor based on the size of the reducing agent flow,

[0031] - calculating the NOx reduction rate of the SCR reactor based on the NOx mass flow rate in the exhaust gas upstream of the SCR reactor and the NOx mass flow rate in the exhaust gas downstream of the SCR reactor, and

[0032] - Adjusting the size of the reductant flow based on comparing the calculated NOx reduction rate with the required NOx reduction rate.

[0033] By placing the O2 sensor and the NOx sensor downstream of the SCR reactor on the low-pressure side of the turbocharger and by calculating the NOx mass flow rate before and after the SCR reactor (for example in [g / s] or [kg / h]), the actual accurate NOx reduction rate can be determined, and thus by comparing with the required minimum reduction rate, the actual accurate NOx reduction rate can be used as a signal in a feedback loop, and accordingly, the size of the reducing agent flow to the SCR reactor can be accurately controlled to achieve the required NOx reduction rate required by law.

[0034] According to a possible implementation form of the first aspect, the adjustment coefficient is an adjustment coefficient related to the engine load.

[0035] According to a possible implementation form of the first aspect, the regulation coefficient is a function of the thermal efficiency of the engine and a fuel regulation coefficient, the fuel regulation coefficient preferably being a Thornton constant.

[0036] According to a possible implementation form of the first aspect, the adjustment coefficient is SFOC, Thornton constant, u for NOx gas and a function of the LHV of the fuel.

[0037] According to a possible implementation form of the first aspect, the controller is configured to take into account the ambient O2 concentration when calculating the NOx mass flow in the exhaust gas downstream of the SCR reactor. Preferably, the ambient O2 concentration is assumed to be 20.95%.

[0038] According to a possible implementation form of the first aspect, the controller receives a humidity sensor configured to sense ambient humidity, and wherein the controller is configured to take into account the ambient humidity sensed by the humidity sensor when calculating the NOx mass flow in the exhaust gas downstream of the SCR reactor.

[0039] According to a possible implementation form of the first aspect, the controller is configured to take into account the ambient O2 concentration when calculating the NOx mass flow in the exhaust gas downstream of the SCR reactor, preferably by using a stored fixed value for the ambient O2 concentration.

[0040] According to a possible implementation form of the first aspect, the controller is configured to:

[0041] - calculation of the specific NOx downstream of the SCR reactor as the mass of NOx per unit of energy produced by the engine, and

[0042] - Calculation of the NOx mass flow upstream of the SCR reactor as a function of the size of the reducing agent flow, as the mass of NOx per unit of energy produced by the engine.

[0043] According to a possible implementation form of the first aspect, for each engine cycle a given metered amount of fuel is injected into the cylinder.

[0044] According to a possible implementation form of the first aspect, the controller is configured to calculate the engine load from the engine speed and a given metering of fuel, preferably assuming a constant SFOC.

[0045] According to a possible implementation form of the first aspect, the engine is provided with a tachometer for sensing the rotation speed of the crankshaft of the engine.

[0046] According to a possible implementation form of the first aspect, the controller is configured to adjust the size of the reducing agent flow using a closed loop.

[0047] According to a possible implementation form of the first aspect, the cylinder includes a cylinder liner, a reciprocating piston located in the cylinder liner, and a cylinder head covering the cylinder, wherein a combustion chamber is formed inside the cylinder between the reciprocating piston and the cylinder head.

[0048] According to a possible implementation form of the first aspect, the compressor is driven directly or indirectly by the turbine.

[0049] According to a second aspect, there is provided a method for determining the NOx reduction rate of a large two-stroke uniflow scavenged turbocharged multi-cylinder internal combustion engine, the engine comprising:

[0050] a plurality of cylinders that generate an exhaust gas flow containing NOx during operation of the engine,

[0051] a turbocharger system comprising a compressor and an exhaust gas driven turbine, the turbine being located in the exhaust gas system and the compressor being located in the scavenging air system for supplying scavenging air to cylinders of the engine,

[0052] a selective catalytic reduction reactor located in the exhaust gas system,

[0053] a reducing agent source configured to add a given metered reducing agent flow to the exhaust gas conduit for reacting with NOx in the SCR reactor,

[0054] an O2 sensor that generates a signal representative of O2 ppm in the exhaust gas downstream of both the SCR reactor and the turbine,

[0055] a NOx sensor generating a signal representative of NOx ppm in the exhaust gas downstream of both the SCR reactor and the turbine,

[0056] The method includes:

[0057] - The NOx mass flow rate in the exhaust gas downstream of the SCR reactor is calculated according to:

[0058] -O2 sensor signal,

[0059] - NOx sensor signal,

[0060] - thermal efficiency of the engine,

[0061] - engine load, and

[0062] - adjustment coefficient,

[0063] - Calculate the NOx mass flow in the exhaust gas upstream of the SCR reactor based on the size of the reducing agent flow,

[0064] - calculating the NOx reduction rate of the SCR reactor based on the NOx mass flow rate in the exhaust gas upstream of the SCR reactor and the NOx mass flow rate in the exhaust gas downstream of the SCR reactor, and

[0065] - Adjusting the size of the reductant flow based on comparing the calculated NOx reduction rate with the required NOx reduction rate.

[0066] These and other aspects will become apparent from and elucidate the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In the following detailed description of the present disclosure, various aspects, embodiments, and implementations will be described in more detail with reference to exemplary embodiments shown in the accompanying drawings, in which:

[0068] Figure 1 is a front elevational view of a large two-stroke diesel engine according to an embodiment.

[0069] Figure 2 yes Figure 1 A side elevation view of a large two-stroke engine.

[0070] Figure 3 is based on Figure 1 Schematic diagram of an embodiment of a large two-stroke engine.

[0071] Figure 4 is based on Figure 1 A schematic diagram of another embodiment of a large two-stroke engine.

[0072] Figure 5 is a schematic diagram of an embodiment of a NOx control system for an engine, and

[0073] Figure 6 is a schematic diagram of another embodiment of a NOx control system for an engine. DETAILED DESCRIPTION

[0074] In the following detailed description, the internal combustion engine will be described with reference to a large, two-stroke, low-speed, uniflow, scavenged, turbocharged internal combustion engine with a crosshead in an embodiment. The large, two-stroke, low-speed, uniflow, scavenged, turbocharged internal combustion engine can be of the following (high-pressure) type: in which the fuel is injected at or near the top dead center of the piston, i.e., compression ignition, or it can be of the following (low-pressure) type: in which the fuel is mixed with the scavenged air before or during compression, i.e., spark ignition. In the case of the low-pressure type, there is usually a "pilot" ignition using an ignition fluid, such as fuel, to ensure reliable ignition.

[0075] Figure 1 、 Figure 2 、 Figure 3 and Figure 4 A large, low-speed, turbocharged, two-stroke diesel engine is shown having a crankshaft 8 and a crosshead 9 . Figure 3 and Figure 4 Schematic diagrams of a large, low-speed, turbocharged, two-stroke diesel engine and its intake and exhaust systems are shown in two embodiments. In these embodiments, the engine has six in-line cylinders. Large, low-speed, turbocharged, two-stroke diesel engines typically have between four and fourteen in-line cylinders supported by a cylinder frame 23, which is supported by the engine frame 11. The engine can be used, for example, as a main engine in a marine vessel or as a stationary engine in a power station to operate a generator. The total output of the engine can range from 1,000 kW to 110,000 kW, for example.

[0076] In these embodiments, the engine is a two-stroke, single-flow, compression-ignition engine having scavenging ports 18 in the lower region of the cylinder liners 1 and a central exhaust valve 4 at the top of each cylinder liner 1. The engine can be operated using different fuels, such as marine fuel oil, ethanol, methanol, natural gas, petroleum gas, or ammonia. The engine can be a dual-fuel engine that can switch between two different fuels, so that the engine has one operating mode related to the first fuel and another operating mode related to the second fuel.

[0077] During operation, scavenging air is delivered from the scavenging air receiver 2 to the scavenging ports 18 of each cylinder 1. The scavenging air is compressed by the piston 10, which reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1. Fuel is injected into the combustion chamber in the cylinder liner 1 at or near TDC via a (high-pressure) fuel valve 49 arranged in the cylinder head 22. Fuel then burns, producing exhaust gas. Each cylinder head 22 is provided with two or more fuel valves 49. The fuel valves 49 are arranged in the cylinder head 22 around the central exhaust valve 4 and receive fuel from the fuel supply system 30.

[0078] In an embodiment, a fuel valve 49' (indicated by a dashed line) is positioned along the cylinder liner 1 and admits fuel to the cylinder liner before the piston 10 passes through the fuel valve 49' on its way from BDC to TDC. Thus, the piston 10 compresses the scavenging air and fuel mixture. Timed ignition at or near TDC is triggered by a spark, laser, ignition fluid injection, or the like. In embodiments with the fuel valve 49', the pressure at which the fuel is admitted is significantly lower than the pressure at which the fuel is injected in embodiments where the fuel valve 49 is located in the cylinder head 22. Consequently, the pressure required to deliver fuel through the fuel supply system 30' can be significantly lower, and / or a supercharger, often used in the fuel valve 49 located in the cylinder head, can be avoided, which is particularly advantageous for gaseous fuels.

[0079] When the exhaust valve 4 is opened, the exhaust gas flows through the exhaust pipe associated with each cylinder to the exhaust gas receiver 3 and continues to flow through the first exhaust pipe 19 to the turbine 6 of the turbocharger 5 via the selective catalytic reduction (SCR) reactor 28. The exhaust gas flows out of the turbine 6 through the second exhaust pipe via the outlet 21 and into the atmosphere. The SCR reactor 28 reduces emissions, especially NOx emissions. Figure 3 In the embodiment, the SCR reactor 28 is arranged upstream of the turbine 6 of the turbocharger 5, that is, arranged on the high pressure side of the turbocharger 5, and Figure 4 In the embodiment of FIG. 5 , the SCR reactor 28 is arranged downstream of the turbine 6 of the turbocharger 5 , that is, on the low-pressure side of the turbocharger 5 .

[0080] The turbine 6 drives a compressor 7 via a shaft, and the compressor 7 is supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenging air to a scavenging air duct 13 leading to a scavenging air receiver 2. The scavenging air in the scavenging air duct 13 passes through an intercooler 14 to cool the scavenging air.

[0081] When the compressor 7 of the turbocharger 5 is unable to deliver sufficient pressure to the scavenging air receiver 2, i.e., at low or partial load of the engine, the cooled scavenging air is conveyed via an auxiliary blower 16 driven by an electric motor 17, which pressurizes the scavenging air flow. At higher engine loads, the compressor 7 of the turbocharger delivers sufficient compressed scavenging air, and the auxiliary blower 16 is then bypassed via the non-return valve 15 and the electric motor 17 is deactivated.

[0082] For each engine cycle, a precisely given metered amount of fuel is injected into the cylinder 1 via the fuel valve 49 , 49 ′ and, in an embodiment, the controller 50 is configured to calculate the engine load from the given metered amount of fuel.

[0083] In an embodiment, the engine is provided with a tachometer (not shown) for sensing the rotational speed of the crankshaft 8 , and in this embodiment, the controller 50 may be configured to determine the power output by the engine based on the product of the rotational speed and the engine load.

[0084] An engine has a specific fuel consumption (SFOC), which describes the mass of fuel consumed per unit of energy supplied at the engine output. The unit of SFOC is kilograms per kilowatt-hour (kg / kWh).

[0085] The exhaust gas generated in the cylinder liner 1 contains too high a concentration of NOx to be discharged directly into the atmosphere. Therefore, an SCR reactor 28 is required to reduce the NOx in the exhaust gas. In embodiments where the SCR reactor 28 is located on the high-pressure side of the turbocharger 5, the pressure and temperature are higher, so the SCR reactor 28 can be smaller. In embodiments where the SCR reactor 28 is located on the low-pressure side of the turbocharger 5, the temperature and pressure will be lower, and the SCR reactor will need to be correspondingly larger to achieve the same effect.

[0086] exist Figure 3 and Figure 4In the embodiment shown in FIG, a tank 26 contains a urea-water solution. A reductant conduit 25 connects the tank 26 to the inlet of a pump 24. The pump 24 is configured to provide substantially an adjustment factor pressure. The outlet of the pump 24 is connected to a feed conduit 22, which delivers pressurized reductant, such as a urea-water solution, to an injection module 20 via an electronically controlled valve 23 for mixing with the exhaust gas. In this embodiment, the electronically controlled valve 23 is an on / off type, but a proportional valve may also be used. The electronically controlled valve 23 is controlled by a signal from an electronic control unit including a processor (controller) 50. The electronically controlled valve 23 may be hydraulically or pneumatically actuated, or solely electrically actuated. The injection module 20 is installed in or upstream of the SCR reactor and may be disposed within the exhaust gas receiver 3. The injection module 20 is preferably provided with a nozzle having a nozzle hole for atomizing the reductant solution as it is injected into the exhaust gas stream. The controller 50 is configured to control the magnitude of the reductant flow to the injection module 20 , for example, by controlling the speed of the pump 24 .

[0087] Figure 3 The implementation method and Figure 4 The only difference from the embodiment of FIG. 5 is that the SCR reactor 28 and the reducing agent injection module 20 are arranged on the low-pressure side of the turbocharger 5 .

[0088] Emission regulations for engines operating in marine vessels (IMO regulations) require that the NOx reduction rate at each test point must not differ by more than 5% from the value specified in the NOx technical file (which is established on a test bench for the relevant engine type). The test points typically correspond to: 100% engine load, with a weighting factor of 0.2; 75% engine load, with a weighting factor of 0.5; 50% engine load, with a weighting factor of 0.15; and 25% engine load, with a weighting factor of 0.1. In the regulations, the NOx level in the exhaust gas is expressed as a specific NOx level in g / kWh, and the NOx reduction rate of the SCR reactor 28 during engine operation needs to be better than or equal to the value specified in the technical file. Therefore, the controller 50 is configured to ensure that the NOx reduction rate is equal to or higher than the value specified in the technical file for each operating point.

[0089] Figure 5Controller 50 and engine components associated with controller 50 are shown. O2 sensor 27 sends a signal to controller 50 indicating the molar PPM of O2 in the exhaust gas at a location downstream of turbine 6 of turbocharger 5 and downstream of SCR reactor 28. Similarly, NOx sensor 29 sends a signal to controller 50 indicating the molar PPM of NOx in the exhaust gas at a location downstream of turbine 6 of turbocharger 5 and downstream of SCR reactor 28.

[0090] The controller 50 is configured to calculate the NOx mass flow rate in the exhaust gas downstream of the SCR reactor 28 based on:

[0091] - the signal of the O2 sensor 27,

[0092] - the signal of the NOx sensor 29,

[0093] - engine load,

[0094] - the thermal efficiency of the engine, and

[0095] -Adjustment coefficient.

[0096] The controller includes a first module 51 configured to execute an algorithm to calculate the mass concentration of NOx in the exhaust gas at the outlet of the SCR reactor 28. The algorithm receives signals from the O2 sensor 27 and the NOx sensor 29, and obtains or determines the engine load, the engine thermal efficiency, and the adjustment factor.

[0097] The adjustment factor may be an engine load-dependent adjustment factor or an engine load-independent adjustment factor.

[0098] In this embodiment, the regulation factor is a function of the thermal efficiency of the engine and the fuel regulation factor, which is preferably the Thornton constant.

[0099] Measuring the heat release rate in fire testing is complex and previously impossible to measure with high accuracy until the development of oxygen consumption calorimetry in the late 1970s. The oxygen consumption technique is based on Thornton's observation that for complete combustion, the net heat released per unit mass of oxygen consumed is almost the regulation factor and is independent of the fuel. In most fire experiments, a commonly used value for Thornton's constant is 13.1 kJ / g O².

[0100] WM Thornton first mentioned this in his 1917 article, "The Relation of Oxygen to the Heat of Combustion of Organic Compounds." He explained how the heat (energy) released by the combustion of hydrocarbons depends on the amount of oxygen available for combustion, and how each unit of oxygen will release almost the same amount of energy regardless of the hydrocarbon being burned.

[0101] Furthermore, the controller 50 is configured to calculate the mass concentration of NOx in the exhaust gas upstream of the SCR reactor 28 based on the size of the reductant flow. To this end, the controller 50 is provided with a second module 52, which is provided with an algorithm for calculating the mass concentration of NOx at the inlet of the SCR reactor 28 based on the size of the reductant flow. The second module can be provided with an adjustment coefficient that provides a relationship between the size of the reductant flow and the mass of NOx generated.

[0102] The controller 50 is configured to calculate the NOx reduction rate of the SCR reactor 28 based on the NOx mass flow rate in the exhaust gas upstream of the SCR reactor 28 and the NOx mass flow rate in the exhaust gas downstream of the SCR reactor 28 in a third module 53, and the third module 53 receives the NOx mass flow rate in the exhaust gas downstream of the SCR reactor 28 from the first module and receives the NOx mass flow rate in the exhaust gas upstream of the SCR reactor 28 from the second module.

[0103] The controller 50 is configured to adjust the amount of the reductant flow based on a comparison of the calculated NOx reduction rate with the desired NOx reduction rate. The result of this comparison is sent to a fourth module 54, which acts as a dosing unit and provides a signal to the dosing pump 24 to adjust the amount of the reductant flow injected into the exhaust gas flow. Thus, the amount of the reductant flow injected into the exhaust gas flow is controlled in a closed-loop manner to ensure that the NOx reduction rate is at or above the desired level.

[0104] Since the exhaust gas mass flow rate through the exhaust gas system is substantially the same on both sides of the SCR reactor 28, the controller 50 does not absolutely need to calculate the mass concentration in the exhaust gas. Instead, the controller 50 can determine the NOx reduction rate of the SCR reactor 28 by simply determining the NOx mass flow rate in the exhaust gas before and after the SCR reactor 28.

[0105] In an embodiment, the controller 50 may be configured to take into account the ambient O 2 concentration when calculating the NO x mass flow rate in the exhaust gas downstream of the SCR reactor 28 , preferably assuming an ambient O 2 concentration of 20.95%.

[0106] In an embodiment, the controller 50 receives a humidity sensor configured to sense ambient humidity, and in this embodiment, the controller 50 is configured to consider the ambient humidity sensed by the humidity sensor when calculating the NOx mass flow rate in the exhaust gas downstream of the SCR reactor 28.

[0107] In an embodiment, the controller 50 is configured to take into account the ambient O2 concentration when calculating the NOx mass flow rate in the exhaust gas downstream of the SCR reactor 28, preferably by using a stored fixed value for the ambient O2 concentration. The fixed value may be selected to be 20.95%.

[0108] In an embodiment, the controller 50 is configured to calculate the specific NOx downstream of the SCR reactor 28 as the mass of NOx per unit energy produced by the engine, for example in g / kWh; and calculate the NOx mass flow upstream of the SCR reactor 28 based on the size of the reductant flow as the mass of NOx per unit energy produced by the engine, for example in g / kWh.

[0109] The specific NOx downstream of the SCR reactor 28 can be calculated, for example, as follows:

[0110] NOx molar PPM / (engine thermal efficiency x engine O2 molar consumption [%] x fuel coefficient).

[0111] The fuel coefficient is called the aforementioned Thornton constant and is expressed in [kWh / g].

[0112] Figure 6 Another embodiment of the controller 50 is shown. In this embodiment, for the purpose of simplicity, structures and features that are the same as or similar to corresponding structures and features previously described or shown herein are represented by the same reference numerals as previously used. Figure 5 The embodiment is substantially the same except that the first module 51 receives a signal corresponding to the engine load, is informed of the SFOC, is informed of the u for NOx gas , and the LHV of the fuel is informed, and the adjustment factors are SFOC, Thornton constant, u for NOx gas and a function of the LHV of the fuel.

[0113] u gasIt is defined in IMO NTC2008 (NOx Technical Code) as the standard density ratio between exhaust gas and NOx (or CO, HC, CO2, O2).

[0114] The lower heating value (also called net calorific value, net CV or LHV) of a fuel is defined as the amount of heat released by burning a specific amount of fuel (initially at 25°C or other reference state) and returning the temperature of the combustion products to 150°C.

[0115] In this embodiment, the adjustment factor may be an adjustment factor related to the engine load or an adjustment factor independent of the engine load.

[0116] Various aspects and implementations have been described herein with reference to various embodiments. However, other variations of the disclosed embodiments may be understood and implemented by those skilled in the art in practicing the claimed subject matter, by studying the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other units of the controller may perform the functions of multiple items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0117] The reference signs used in the claims should not be construed as limiting the scope. Unless otherwise indicated, the drawings are intended to be read together with the specification (e.g., section lines, arrangement of components, proportions, extent, etc.) and should be considered part of the entire written description of the present disclosure.

Claims

1. A large two-stroke single-flow scavenged turbocharged internal combustion engine, comprising: a plurality of cylinders (1) which, during operation of the engine, generate an exhaust gas flow containing NOx, A turbocharger system (5) comprising a compressor (7) and an exhaust gas driven turbine (6), the turbine (6) being located in the exhaust gas system, the compressor (7) being located in the scavenging air system for supplying scavenging air to the cylinders (1) of the engine, a selective catalytic reduction reactor (28), the selective catalytic reduction reactor (28) being located in the exhaust gas system, a reducing agent source (26) configured to add a given dose of reducing agent flow to the exhaust gas conduit for reacting with NOx in the SCR reactor (28), an O2 sensor (27) generating a signal representing O2 ppm in the exhaust gas downstream of both the SCR reactor (28) and the turbine (6), a NOx sensor (29) generating a signal representing NOx ppm in the exhaust gas downstream of both the SCR reactor (28) and the turbine (6), A controller (50) is informed of the engine load, wherein the controller (50) is configured to: - The NOx mass flow in the exhaust gas downstream of the SCR reactor (28) is calculated according to: - the signal of the O2 sensor (27), - the signal of the NOx sensor (29), - the thermal efficiency of the engine, - the engine load, and - adjustment coefficient, - calculating the NOx mass flow in the exhaust gas upstream of the SCR reactor (28) according to the size of the reducing agent flow, - calculating the NOx reduction rate of the SCR reactor (28) based on the NOx mass flow rate in the exhaust gas upstream of the SCR reactor (28) and the NOx mass flow rate in the exhaust gas downstream of the SCR reactor (28), and - adjusting the size of the reducing agent flow based on comparing the calculated NOx reduction rate with the desired NOx reduction rate.

2. The engine according to claim 1, wherein The adjustment factor is an engine load-related adjustment factor.

3. The engine according to claim 1, wherein The adjustment coefficient is a function of a fuel constant and a thermal efficiency of the engine. Preferably, the fuel constant is a Thornton constant.

4. The engine according to claim 1, wherein The adjustment coefficients are SFOC, Thornton constant, u for NOx gas and a function of the LHV of the fuel.

5. The engine according to claim 1, wherein The controller (50) is configured to take into account the ambient O2 concentration when calculating the NOx mass flow rate in the exhaust gas downstream of the SCR reactor (28), preferably the ambient O2 concentration is assumed to be 20.95%.

6. The engine according to claim 1, wherein The controller (50) receives a humidity sensor configured to sense ambient humidity, and wherein the controller (50) is configured to consider the ambient humidity sensed by the humidity sensor when calculating the NOx mass flow rate in the exhaust gas downstream of the SCR reactor (28).

7. The engine according to claim 1, wherein The controller (50) is configured to take into account the ambient O2 concentration when calculating the NOx mass flow in the exhaust gas downstream of the SCR reactor (28), preferably, the controller (50) is configured to take into account the ambient O2 concentration when calculating the NOx mass flow in the exhaust gas downstream of the SCR reactor (28) by using a stored fixed value for the ambient O2 concentration.

8. The engine according to claim 1, wherein The controller (50) is configured to: - calculating the specific NOx downstream of the SCR reactor (28) as the mass of NOx per unit of energy produced by the engine, and - calculating the NOx mass flow upstream of the SCR reactor (28) as a function of the size of the reducing agent flow as the NOx mass per unit of energy produced by the engine.

9. The engine according to claim 1, wherein: For each engine cycle, a given dose of fuel is injected into the cylinder (1).

10. The engine according to claim 9, wherein The controller (50) is configured to calculate the engine load based on the engine speed and a given dosage of fuel. Preferably, the controller (50) is configured to calculate the engine load based on the engine speed and the given dosage of fuel under the assumption that the SFOC is constant.

11. The engine according to claim 1, wherein The engine is provided with a tachometer for sensing the rotation speed of a crankshaft of the engine.

12. The engine according to claim 1, wherein The controller (50) is configured to regulate the size of the reductant flow using a closed loop.

13. The engine according to claim 1, wherein The cylinder (1) comprises a cylinder liner (1), a reciprocating piston (10) located in the cylinder liner (1), and a cylinder head (22) covering the cylinder, wherein a combustion chamber is formed inside the cylinder (1) between the reciprocating piston (10) and the cylinder head (22).

14. The engine according to claim 1, wherein The compressor (7) is driven directly or indirectly by the turbine (6).

15. A method for determining the NOx reduction rate of a large two-stroke, uniflow scavenged, turbocharged, multi-cylinder internal combustion engine, the engine comprising: a plurality of cylinders (1) which, during operation of the engine, generate an exhaust gas flow containing NOx, A turbocharger system (5) comprising a compressor (7) and an exhaust gas driven turbine (6), the turbine (6) being located in the exhaust gas system, the compressor (7) being located in the scavenging air system for supplying scavenging air to the cylinders (1) of the engine, a selective catalytic reduction reactor (28), the selective catalytic reduction reactor (28) being located in the exhaust gas system, a reducing agent source (26) configured to add a given dose of reducing agent flow to the exhaust gas conduit for reacting with NOx in the SCR reactor (28), an O2 sensor (27) generating a signal representative of O2 ppm in the exhaust gas downstream of both the SCR reactor (28) and the turbine (6), a NOx sensor (29) generating a signal representative of NOx ppm in the exhaust gas downstream of both the SCR reactor (28) and the turbine (6), The method comprises: - Calculation of the NOx mass flow in the exhaust gas downstream of the SCR reactor (28) according to: - the signal of the O2 sensor (27), - the signal of the NOx sensor (29), - the thermal efficiency of the engine, - engine load, and - adjustment coefficient, - calculating the NOx mass flow in the exhaust gas upstream of the SCR reactor (28) according to the size of the reducing agent flow, - calculating the NOx reduction rate of the SCR reactor (28) based on the NOx mass flow rate in the exhaust gas upstream of the SCR reactor (28) and the NOx mass flow rate in the exhaust gas downstream of the SCR reactor (28), and - adjusting the size of the reducing agent flow based on comparing the calculated NOx reduction rate with the desired NOx reduction rate.

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