Large two-stroke uniflow scavenged turbocharged internal combustion engine with SCR reactor for reducing NOX emission and method for controlling NOX reduction in such engine

Abstract

To provide a large two-stroke uniflow scavenged turbocharged multi-cylinder internal combustion engine and a method for controlling NOx reduction rate in such engine.SOLUTION: An engine has an SCR reactor provided with a stream of reductant and a controller 50. The controller 50 is configured to calculate the NOx reduction rate of the SCR reactor, as a function of the NOx mass flow in respective exhaust gases upstream and downstream of the SCR reactor, and to control the magnitude of the stream of reductant accordingly.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a crosshead type large turbocharged two-stroke uniflow internal combustion piston engine, and in particular to a method for reducing NO in exhaust gas. x The present invention relates to a large-scale, crosshead-type, turbocharged, two-stroke, uniflow internal combustion piston engine equipped with an SCR (selective catalytic reduction) reactor that reduces CO2 and purifies exhaust gases emitted from the engine.

[0002] Large two-stroke uniflow scavenged turbocharged internal combustion engines are typically used in the propulsion systems of large ships and as prime movers in power plants. Their size, weight, and power output set them apart from other combustion engines, placing this type of compression ignition engine in a unique category.

[0003] The exhaust gas regulations for these engines are aimed at reducing the amount of nitrogen oxides (NO x ) levels have been and will continue to be increasingly stringent. Public awareness of environmental issues is growing rapidly. The IMO (International Maritime Organization) currently has emission limits in the form of air pollution at sea. Authorities around the world are taking similar measures. One example is the proposal by the EPA (US Environmental Protection Agency).

[0004] NO in exhaust gas x can be reduced by primary and / or secondary abatement methods. Primary methods are those that directly affect the engine combustion process. The actual reduction varies depending on the engine type and abatement method, but can range from 10% to over 80%. Secondary methods use devices that are not part of the engine itself and are a means of reducing emission levels without altering engine performance from its fuel-optimized setting. The most successful secondary method to date has been the reduction of NOx by SCR (Selective Catalytic Reduction). x This method involves adding a reducing agent such as ammonia or urea to the exhaust gas before it enters the catalytic converter, thereby reducing NO xThe reductant can reduce NOx levels by more than 95%. Typically, the reductant is injected and atomized into the exhaust system upstream of the SCR reactor or into the SCR reactor itself. The SCR reactor has multiple catalyst layers. The amount of catalyst, and therefore the size of the reactor, determines the activity of the catalyst and the required NOx. x The catalyst usually has a monolithic structure and is composed of a catalyst block with many parallel channels, the walls of which are catalytically active.

[0005] When urea is added to the SCR reactor as a reducing agent, the nitrogen oxides (NO x ) into harmless by-products: nitrogen (N2) and water vapor (H2O). This process takes place in several steps. 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-water solution (UWS) which is then sprayed into the exhaust gas. 2. Thermal decomposition: When the urea solution enters the hot exhaust stream, it vaporizes and thermally decomposes into ammonia (NH3) and isocyanic acid (HNCO). This reaction occurs because the exhaust gas is still hot (usually above 200°C). 3. Hydrolysis: The isocyanic acid undergoes further hydrolysis to produce ammonia and carbon dioxide (CO2). This step converts most of the urea into ammonia, which is the actual reducing agent in the SCR process. 4. Catalytic Reaction: The ammonia then reacts with nitrogen oxides present in the exhaust gas in the presence of a catalyst. The catalyst is usually made of materials such as vanadium, titanium oxide, zeolites, or various base metals, which facilitate the reaction without being consumed in the process. SCR catalysts react with the oxygen present in diesel exhaust to produce NO x is selectively reduced to nitrogen and water vapor.

[0006] This process reduces NO in the exhaust gas. x The efficiency of the SCR system depends on the temperature of the exhaust gas, NO xIt depends on a number of factors, including the concentration of urea, the amount and distribution of the injected urea solution, and the design and material of the SCR catalyst.

[0007] Marine engine exhaust gas regulations (IMO law) are based on NO at each test point. x The reduction rate is NO x The reduction rate specified in the technical file (established for the engine type in the test bed) must not differ by more than 5%. x When placed downstream of the SCR reactor, the sensor detects NO x Mass flow or specific NO x Level (specific NO x Since the PPM level does not correspond to the NO level (both units are g / kWh), x Reduction rates are difficult to set and monitor.

[0008] In order to know the reduction rate, the NO in the exhaust gas upstream of the SCR reactor x Mass flow or specific NO x However, the NO level (g / kWh) in the exhaust gas upstream of the SCR reactor must be known. x Mass flow or specific NO x The level is expressed in g / kWh, e.g., for the commercially available NO x Using sensors upstream of the SCR reactor is also difficult to determine because the measurement is performed in the high-pressure flow.

[0009] DK177462 discloses a large, crosshead, turbocharged, two-stroke diesel engine having multiple cylinders, a turbocharger, and an SCR reactor upstream of the turbocharger and downstream of an exhaust gas receiver. A reductant for the SCR reactor is introduced into the exhaust gas upstream of the SCR reactor.

[0010] DK180561 discloses a large turbocharged two-stroke internal combustion engine according to the preamble of claim 1.

[0011] The object is to provide a large two-stroke uniflow scavenged turbocharged internal combustion engine which solves or at least mitigates the above-mentioned problems.

[0012] These and other problems are solved by the features of the independent claims. More specific implementations will become apparent from the dependent claims, the description and the drawings.

[0013] According to a first aspect, there is provided a large two-stroke uniflow scavenged internal combustion engine comprising: NO during engine operation x a plurality of cylinders generating an exhaust gas stream including: a turbocharging system including an exhaust gas driven turbine disposed in an exhaust system and a compressor disposed in a scavenging system for supplying scavenging air to the cylinder; a selective catalytic reduction (SCR) reactor disposed in the exhaust system; NO in the SCR reactor x a reducing agent source configured to add a reducing agent to the exhaust gas line at a desired flow rate to react with an O2 sensor disposed downstream of the SCR reactor and the turbine, the O2 sensor generating a signal representative of the O2 concentration (PPM) in the exhaust gas; A NOx reduction device for reducing NOx in exhaust gases, the NOx reduction device being disposed downstream of the SCR reactor and the turbine. x Generates a signal representing the concentration (PPM) of NO x A sensor, a control unit to which the load of the engine is notified; The control unit includes: NO in the exhaust gas downstream of the SCR reactor x Mass flow, the signal of said O2 sensor, The above-mentioned NO x Sensor signals, the thermal efficiency of said engine; the load on said engine, adjustment factor, Calculate as a function of NO in the exhaust gas upstream of the SCR reactor xCalculating a mass flow as a function of the reducing agent flow rate; NO in the exhaust gas upstream of the SCR reactor x Mass flow and NO in the exhaust gas downstream of the SCR reactor x NO emission through the SCR reactor as a function of mass flow x Calculate the reduction rate, Desired NO x Reduction rate compared to the NO x adjusting the flow rate of the reducing agent as a function of the calculated reduction rate; It is configured as follows.

[0014] O2 sensor and NO sensor downstream of the SCR reactor on the low pressure side of the turbocharger x Sensors are placed before and after the SCR reactor to measure NO x By calculating the mass flow (e.g., in [g / s] or [kg / h]), the actual and accurate NO x The reduction rate can be determined and used as a signal in a feedback loop by comparing it to a desired minimum reduction rate. x The reductant flow rate to the SCR reactor can be precisely controlled to achieve the reduction rate.

[0015] In one example of an implementation of the first aspect, the adjustment factor is an engine load dependent adjustment factor.

[0016] In one implementation of the first aspect, the adjustment factor is a function of engine thermal efficiency and a fuel adjustment factor, which is preferably a Thornton constant (also called a Thornton number).

[0017] In one example implementation of the first aspect, the adjustment factors are SFOC, Thornton constant, NO x Ugas is a function of the LHV of the fuel.

[0018] In one example implementation of the first aspect, the control unit detects NO in the exhaust gas downstream of the SCR reactor. x When calculating the mass flow, the ambient O2 concentration is taken into account, preferably assuming that the ambient O2 concentration is 20.95%.

[0019] In one example implementation of the first aspect, the controller receives a signal from a humidity sensor configured to sense ambient humidity and detects NO in the exhaust gas downstream of the SCR reactor. x The mass flow is calculated by taking into account the ambient humidity sensed by the humidity sensor.

[0020] In one example implementation of the first aspect, the control unit detects NO in the exhaust gas downstream of the SCR reactor. x The mass flow calculation is configured to take into account the ambient O2 concentration, preferably using a fixed stored value of the ambient O2 concentration.

[0021] In one example of implementation of the first aspect, the control unit: The NO ratio downstream of the SCR reactor x (specific NO x ) as the NO per unit energy produced in the engine x Calculate as mass, NO upstream of the SCR reactor x mass flow per unit energy produced in the engine as a function of the reductant flow rate. x Calculate as, It is configured as follows.

[0022] In one implementation of the first aspect, a dose of fuel is injected into the cylinder every engine cycle.

[0023] In one example implementation of the first aspect, the control unit is configured to calculate engine load as a function of engine speed and fuel input, preferably calculating the engine load assuming a constant SFOC.

[0024] In one implementation of the first aspect, the engine is equipped with a tachometer that senses the rotational speed of a crankshaft of the engine.

[0025] In one example implementation of the first aspect, the controller is configured to adjust the flow rate of the reducing agent using a closed loop.

[0026] In one example of an implementation form of the first aspect, the cylinder includes a cylinder liner, a reciprocating piston within the cylinder liner, and a cylinder cover that covers the cylinder, and includes a combustion chamber formed within the cylinder between the reciprocating piston and the cylinder cover.

[0027] In one implementation of the first aspect, the compressor is driven directly or indirectly by the turbine.

[0028] According to the second approach, the NOx emissions from large two-stroke uniflow scavenging turbocharged multi-cylinder internal combustion engines are x A method for determining a derating rate is provided, wherein the engine comprises: NO during engine operation x a plurality of cylinders generating an exhaust gas stream including: a turbocharging system including an exhaust gas driven turbine disposed in an exhaust system and a compressor disposed in a scavenging system for supplying scavenging air to the cylinder; a selective catalytic reduction (SCR) reactor disposed in the exhaust system; NO in the SCR reactor x a reducing agent source configured to add a reducing agent to the exhaust gas line at a desired flow rate to react with an O2 sensor disposed downstream of the SCR reactor and the turbine, the O2 sensor generating a signal representative of the O2 concentration (PPM) in the exhaust gas; A NOx reduction device for reducing NOx in exhaust gases, the NOx reduction device being disposed downstream of the SCR reactor and the turbine. x Generates a signal representing the concentration (PPM) of NO x A sensor, and the method further comprises: NO in the exhaust gas downstream of the SCR reactor x Mass flow, the signal of said O2 sensor, The above-mentioned NO x Sensor signals, the thermal efficiency of said engine; the load on said engine, adjustment factor, Calculating as a function of NO in the exhaust gas upstream of the SCR reactor x Calculating a mass flow as a function of the reducing agent flow rate; NO in the exhaust gas upstream of the SCR reactor x Mass flow and NO in the exhaust gas downstream of the SCR reactor x NO emission through the SCR reactor as a function of mass flow x Calculating a reduction rate; Desired NO x Reduction rate compared to the NO x adjusting the flow rate of the reducing agent as a function of the calculated reduction rate; Includes:

[0029] These and other aspects will become more apparent from the examples described below. [Brief explanation of the drawings]

[0030] Various aspects, embodiments, and implementations will be described in detail below with reference to exemplary embodiments shown in the drawings. [Figure 1] 1 is a diagram showing a front view of a large two-stroke diesel engine according to an embodiment; [Figure 2] Figure 1 shows an overview of the large two-stroke engine as seen from the rear. [Figure 3] 2 is a diagrammatic representation of an embodiment of the large two-stroke engine of FIG. 1; [Figure 4] 2 is a diagrammatic representation of another embodiment of the large two-stroke engine of FIG. 1; [Figure 5] 1 is a diagrammatic representation of an embodiment of an engine NOx control system. [Figure 6] 1 is a diagrammatic representation of another embodiment of an engine NOx control system. Detailed explanation

[0031] In the following detailed description, the internal combustion engine will be described with reference to an exemplary crosshead type large, low-speed, uniflow-scavenged, two-stroke, turbocharged internal combustion engine. Large, two-stroke, low-speed, uniflow-scavenged, turbocharged internal combustion engine can be a compression-ignition (i.e., high-pressure) engine, in which fuel is injected near or at top dead center of the piston, or a spark-ignition (i.e., low-pressure) engine, in which scavenging air is mixed with fuel before or during compression. In the latter case, a pilot ignition with an additive (e.g., fuel oil) is usually used to ensure ignition.

[0032] Figures 1 to 4 depict a turbocharged, large, low-speed, two-stroke diesel engine. The engine has a crankshaft 8 and a crosshead 9. Figures 3 and 4 show schematic representations of two embodiments of a turbocharged, large, low-speed, two-stroke diesel engine, together with their intake and exhaust systems. In these examples, the engine has six cylinders arranged in series. A turbocharged, large, low-speed, two-stroke diesel engine typically has four to fourteen cylinders arranged in series. These cylinders are supported on a cylinder frame 23, which is supported on an engine frame 11. Such an engine can also be used, for example, as a main engine on a ship or as a stationary engine for driving a generator in a power plant. The total power output of the engine can be, for example, in the range of 1,000 to 110,000 kW.

[0033] The engine in these embodiments is a two-stroke uniflow compression ignition engine, with scavenging ports 18 provided in the lower region of each cylinder liner 1 and an exhaust valve located in the top center of the cylinder liner 1. The engine can be operated with a variety of fuels, including marine fuel oil, ethanol, methanol, natural gas, petroleum gas, and ammonia. The engine can also be a dual-fuel engine, capable of operating on two different fuels. That is, it can be configured to have one operating mode using a first fuel and another operating mode using a second fuel.

[0034] During engine operation, scavenging air is guided through the scavenging air receiver 2 to the scavenging ports 18 of each cylinder 1. The piston 10 reciprocates between bottom dead center (BDC) and top dead center (TDC) in the cylinder liner 1, compressing the scavenging air. Fuel is injected into the combustion chamber in the cylinder liner 1 at or near TDC through a plurality of (high-pressure) fuel valves 49 arranged in the cylinder cover 22. Following fuel injection, combustion occurs and exhaust is generated. Two or more fuel valves 49 are provided in each cylinder cover 22. The fuel valves 49 are arranged in the cylinder cover 22 around the exhaust valve 4 arranged in the center of the cylinder cover 22. The fuel valves 49 receive fuel from the fuel supply system 30.

[0035] In some embodiments, a fuel valve 49' (shown in dashed lines) is positioned along the cylinder liner 1. The fuel valve 49' introduces fuel into the cylinder liner as the piston 10 moves from BDC to TDC before passing the fuel valve 49'. The piston 10 then compresses the scavenging air / fuel mixture. Ignition is timed at or near TDC. Ignition can be achieved by spark, laser, injected ignition fluid, or the like. In embodiments with the fuel valve 49', the pressure at which fuel is introduced is significantly lower than the pressure at which fuel is injected in embodiments with the fuel valve 49 on the cylinder cover 22. This allows the fuel supply system 30 to deliver fuel at a significantly lower pressure and / or eliminates the need for a pressure booster, which is often used with fuel valves 49 located on the cylinder cover 22. This is particularly advantageous when using gaseous fuels.

[0036] When the exhaust valves 4 open, the exhaust flows through exhaust ducts provided for each cylinder to the exhaust receiver 3, then through a selective catalytic reduction reactor (SCR reactor) 28, through the first exhaust pipe 19 and on to the turbine 6 of the turbocharger 5. From there, the exhaust passes through a second exhaust pipe 25 and out the outlet 21 into the atmosphere. The SCR reactor 28 reduces the emissions in the exhaust, particularly NO x In the embodiment of Figure 3, the SCR reactor 28 is located upstream of the turbine 6 of the turbocharger 5, i.e., on the high-pressure side of the turbocharger 5, and in the embodiment of Figure 4, the SCR reactor 28 is located downstream of the turbine 6 of the turbocharger 5, i.e., on the low-pressure side of the turbocharger 5.

[0037] The turbine 6 drives the compressor 7 via a shaft. Outside air is supplied to the compressor 9 through an air intake 12. The compressor 7 sends compressed scavenging air into a scavenging pipe 13 connected to the scavenging air receiver 2. The scavenging air in the scavenging pipe 13 passes through an intercooler 14 to cool the scavenging air.

[0038] The cooled scavenging air passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging air flow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging air receiver 2, i.e. when the engine is at low or partial load. When the engine load is high, the turbocharger compressor 7 can provide sufficiently compressed scavenging air, so the auxiliary blower 16 is bypassed by the check valve 15 and the electric motor 17 is switched off.

[0039] The correct amount of fuel to be injected is injected into the cylinder (1) through the fuel valves 49, 49' for each engine cycle. In some embodiments, the control unit 50 is configured to calculate the engine load as a function of the amount of fuel dosed.

[0040] In some embodiments, the engine is equipped with a tachometer (not shown) for sensing the rotational speed of the crankshaft 8. In such an embodiment, the control unit 50 may be configured to determine the power delivered by the engine from the product of the rotational speed and the engine load.

[0041] An engine has a Specific Fuel Oil Consumption (SFOC), which expresses the mass of fuel oil consumed per unit of energy supplied by the engine output. The unit of fuel consumption is kg / kWh.

[0042] The exhaust gas generated in cylinder liner 1 contains NO at a concentration that is too high to be emitted directly into the atmosphere. x Therefore, the SCR reactor 28 is used to remove NO from the exhaust gas. x In embodiments where the SCR reactor 28 is located on the high-pressure side of the turbocharger 5, the pressures and temperatures are higher, allowing the SCR reactor 28 to be smaller. In embodiments where the SCR reactor 28 is located on the low-pressure side of the turbocharger 5, the temperatures and pressures are lower, requiring a correspondingly larger SCR reactor to achieve the same effect.

[0043] In the embodiment shown in FIGS. 3 and 4, a tank 26 contains the urea solution. A reductant conduit 25 connects the tank 26 to the inlet of a pump 24. The pump 24 is configured to provide a pressure substantially equal to the modulation factor. The outlet of the pump 24 is connected to a supply pipe 22. The supply pipe 22 delivers pressurized reductant, e.g., urea 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 of the on / off type, although a proportional valve could also be used. The electronically controlled valve 23 is controlled by a signal from an electronic control unit including a processor 50. The electronically controlled valve 23 could be a hydraulically or pneumatically operated valve or a purely electrically operated valve. An injection module 20 is provided within the SCR reactor or upstream of the SCR reactor. The injection module 20 can be located within the exhaust gas receiver 3. The injection module 20 preferably includes a nozzle with nozzle holes for atomizing the reductant solution as it is injected into the exhaust gas flow. The control unit 50 is configured to control the flow rate of reductant to the injection module 20, for example by controlling the speed of the pump 24.

[0044] The only difference between the embodiment of FIG. 3 and the embodiment of FIG. 4 is that the SCR reactor 28 and the reductant injection module 20 are located on the low pressure side of the turbocharger 5.

[0045] Marine engine exhaust gas regulations (IMO law) are based on NO at each test point. x The reduction rate is NO x It is required that the value should not differ by more than 5% from the value given in the technical file (as verified for the engine type on the test bed). Test points usually 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. The law requires that NO in the exhaust gas x Levels are in g / kWh ratios. x Level (specific NO x The NOx produced in the SCR reactor 28 during engine operation is shown as NOx level.x The reduction rate must be equal to or greater than the value indicated in the technical file. x The reduction rate is configured to be equal to or greater than the value specified in the technical file at each operating point.

[0046] 5 illustrates the control unit 50 and associated engine components. The O2 sensor 27 sends a signal to the control unit 50 representing the molar concentration (PPM) of O2 in the exhaust gas at a location downstream of the turbine 6 of the turbocharger 5 and downstream of the SCR reactor 28. Similarly, the NO x The sensor 29 detects NO in the exhaust gas at a position downstream of the turbine 6 of the turbocharger 5 and downstream of the SCR reactor 28. x The signal representing the molar concentration (PPM) of the ion is sent to the control unit 50.

[0047] The control unit 50 detects NO in the exhaust gas downstream of the SCR reactor 28. x It is configured to calculate the mass flow as a function of: O2 sensor 27 signal NO x Sensor 29 signal Engine load Engine thermal efficiency Adjustment Factor

[0048] The control unit 50 detects NO in the exhaust gas at the outlet of the SCR reactor 28. x A first module 51 is provided for executing an algorithm for calculating the mass concentration. This algorithm is based on the signal of the O2 sensor 27 and the NO x The engine load, engine thermal efficiency, and adjustment factors are input, along with receiving the signal from sensor 29. In some embodiments, the algorithm is configured to determine the engine load.

[0049] The adjustment factor may be an adjustment factor that depends on the engine load, or may be an adjustment factor that does not depend on the engine load.

[0050] In this embodiment, the trim factor is a function of the engine's thermal efficiency and a fuel trim factor, which is preferably a Thornton constant.

[0051] Measurement of heat release rate in fire tests is complex and was first achieved in the late 1970s by oxygen consumption calorimetry (O x It was not possible to measure it with high accuracy until the development of oxygen consumption calorimetry. The oxygen consumption technique is based on Thornton's observation that the net heat released per unit mass of oxygen consumed for complete combustion is approximately a scaling factor and is independent of the fuel. A common value for the Thornton constant, 13.1 kJ / gO2, is used in most fire experiments.

[0052] W. M. Thornton described this in his 1917 paper "The Relation of O x He first described this in his book "The Heat of Combustion of Organic Compounds." He explains how the heat (energy) released from the combustion of hydrocarbons depends on the amount of oxygen available for combustion, and that a unit amount of oxygen always releases roughly the same amount of energy, regardless of the hydrocarbon being burned.

[0053] The control unit 50 further calculates the NO 2 in the exhaust gas upstream of the SCR reactor 28 as a function of the reductant flow rate. x The control unit 50 is further configured to calculate the mass concentration of NO at the inlet of the SCR reactor 28 as a function of the reductant flow rate. x The second module 52 has an algorithm for calculating the mass concentration of the reducing agent and the resulting NO x The weighting factor may include an adjustment factor that provides a relationship between the mass of the weighting factor and the weight of the

[0054] The control unit 50 controls the NO 2 in the exhaust gas downstream of the SCR reactor 28 in the third module 53. xNO in the exhaust gas upstream of the SCR reactor 28 relative to the mass flow x NO in the SCR reactor 28 as a function of mass flow x The third module 53 is configured to calculate a reduction rate of NO in the exhaust gas downstream of the SCR reactor 28 from the first module. x The second module receives the mass flow of NO in the exhaust gas upstream of the SCR reactor 28. x Receives mass flow.

[0055] The control unit 50 determines the desired NO x Reduction rate compared to NO x The result of this comparison is sent to a fourth module 54, which functions as a reductant dosing unit, and provides a signal to the dosing pump 24 to adjust the flow rate of the reductant injected into the exhaust gas stream. x The reduction rate is controlled in a closed loop manner to ensure that it is equal to or greater than the required level.

[0056] Because the mass flow of exhaust gas through the exhaust system is substantially the same before and after the SCR reactor 28, it is not absolutely necessary for the control unit 50 to calculate the mass concentration in the exhaust gas. Instead, the control unit 50 calculates the NO concentration in the SCR reactor 28. x To determine the reduction ratio, the NO in the exhaust gas before and after the SCR reactor 28 x It is sufficient to determine the mass flow of

[0057] In some embodiments, the control unit 50 may be configured to detect NO in the exhaust gas downstream of the SCR reactor. x When calculating the mass flow, the ambient O2 concentration is taken into account, preferably assuming that the ambient O2 concentration is 20.95%.

[0058] In some embodiments, the controller 50 receives a signal from a humidity sensor configured to sense ambient humidity. In some embodiments, the controller 50 detects NO 2 in the exhaust gas downstream of the SCR reactor 28. x The mass flow is calculated by taking into account the ambient humidity sensed by the humidity sensor.

[0059] In some embodiments, the control unit 50 may be configured to detect NO in the exhaust gas downstream of the SCR reactor 28. x The mass flow calculation is configured to take into account the ambient O2 concentration, preferably using a stored fixed value for the ambient O2 concentration, which may be selected as 20.95%.

[0060] In some embodiments, the control unit 50 may adjust the ratio NO x is the mass of NO per unit of energy produced by the engine. x , calculated in units of, for example, g / kWh, and the NO x Mass flow is the mass NO per unit of energy produced by the engine. x as a function of the flow rate of the reductant, for example in units of g / kWh.

[0061] The NO downstream of the SCR reactor 28 x can be calculated, for example, as follows: NO x Molar concentration (PPM) / (engine thermal efficiency x engine O2 molar consumption [%] x fuel factor) The fuel factor is known as the Thornton constant and is expressed in units of [kWh / g].

[0062] 6 shows another embodiment of the control unit 50. In this embodiment, components and features similar to those already described or shown are designated by the same reference numerals as previously used. This embodiment is essentially the same as the embodiment of FIG. 5, except that a first module 51 receives a signal corresponding to the engine load and controls the SFOC and NO x The difference is that the Ugas and LHV of the fuel are input. The adjustment coefficients are SFOC, Thornton constant, NO x Ugas is a function of the LHV of the fuel.

[0063] Ugas complies with IMO NTC2008 (NO x Technical Code) exhaust gas and NO x It is outlined as the standard density ratio of CO, HC, CO2, O2.

[0064] The lower heating value (also called net heating value, net CV, or LHV) of a fuel is defined as the amount of heat released when a specific quantity of both the fuel and its combustion products is burned, the specific quantity initially at 25°C or other reference condition.

[0065] In this embodiment, the adjustment factor may be an engine load dependent adjustment factor or an engine load independent adjustment factor.

[0066] Various aspects and implementations of the invention have been described with reference to several exemplary embodiments. However, upon reviewing the specification, drawings, and claims of this application, those skilled in the art will understand and be able to embody many variations of the claimed invention in addition to the described embodiments. The words "comprise," "have," and "include" in the claims do not exclude the presence of unrecited elements or steps. The absence of a claim expressly stating a plurality of elements does not exclude the presence of a plurality of such elements. The functions of several elements recited in the claims may be performed by a single processor or other unit of a control unit. The fact that several items are recited in separate dependent claims does not exclude them from being implemented in combination, and may be advantageously implemented in combination.

[0067] Any reference signs used in the claims should not be construed as limiting the scope of the invention. Unless otherwise noted, the drawings are intended to be read together with the specification, and are an integral part of this disclosure.

Claims

1. A large two-stroke uniflow scavenging turbocharged internal combustion engine, NO during engine operation x a plurality of cylinders generating an exhaust gas stream including: a turbocharging system including an exhaust gas driven turbine disposed in an exhaust system and a compressor disposed in a scavenging system for supplying scavenging air to the cylinder; a selective catalytic reduction (SCR) reactor disposed in the exhaust system; NO in the SCR reactor x a reducing agent source configured to add a reducing agent to the exhaust gas line at a desired flow rate to react with A device for reducing O in exhaust gas, disposed downstream of the SCR reactor and the turbine. 2 Generates a signal representing the concentration (PPM) of O 2 A sensor, A NOx reduction device for reducing NOx in exhaust gases, the NOx reduction device being disposed downstream of the SCR reactor and the turbine. x Generates a signal representing the concentration (PPM) of NO x A sensor, a control unit to which the load of the engine is notified; The control unit includes: NO in the exhaust gas downstream of the SCR reactor x Mass flow, ・ The above O 2 Sensor signals, ・ The above NO x Sensor signals, - the thermal efficiency of said engine; - the load on the engine; - adjustment factor, Calculate as a function of NO in the exhaust gas upstream of the SCR reactor x Calculating a mass flow as a function of the reducing agent flow rate; NO in the exhaust gas upstream of the SCR reactor x Mass flow and NO in the exhaust gas downstream of the SCR reactor x NO emission through the SCR reactor as a function of mass flow x Calculate the reduction rate, Desired NO x Reduction rate compared to the NO x adjusting the flow rate of the reducing agent as a function of the calculated reduction rate; An institution structured as follows:

2. 2. The engine of claim 1, wherein the adjustment factor is an engine load dependent adjustment factor.

3. 2. An engine according to claim 1, wherein the adjustment factor is a function of engine thermal efficiency and a fuel constant, the fuel constant being preferably a Thornton constant.

4. The adjustment coefficients are SFOC, Thornton constant, NO x 2. The engine of claim 1, wherein Ugas is a function of LHV of the fuel.

5. The control unit is configured to detect NO in the exhaust gas downstream of the SCR reactor. x When calculating mass flow, consider the ambient O 2 It is configured to take into account the concentration of 2 10. The engine of claim 1, configured to take into account an assumed concentration of 20.95%.

6. The control unit receives a signal from a humidity sensor configured to sense ambient humidity and detects NO in the exhaust gas downstream of the SCR reactor. x The engine of claim 1 , configured to take into account ambient humidity sensed by the humidity sensor when calculating mass flow.

7. The control unit is configured to detect NO in the exhaust gas downstream of the SCR reactor. x When calculating mass flow, consider the ambient O 2 It is configured to take into account the concentration of 2 10. The engine of claim 1, configured to use a fixed stored value of concentration to factor into the calculation.

8. The control unit specific NO downstream of the SCR reactor x (specific NO x ) as the NO per unit energy produced in the engine x Calculate as mass, NO upstream of the SCR reactor x mass flow per unit energy produced in the engine as a function of the reductant flow rate. x Calculate as, The engine of claim 1 , configured to:

9. 10. The engine of claim 1, wherein a dose of fuel is injected into the cylinder every engine cycle.

10. 10. The engine of claim 9, wherein the control unit is configured to calculate engine load as a function of engine speed and fuel input, preferably calculating the engine load assuming a constant SFOC.

11. 10. The engine of claim 1, equipped with a tachometer for sensing the rotational speed of a crankshaft of said engine.

12. The engine of claim 1 , wherein the control is configured to regulate the reductant flow rate using a closed loop.

13. 2. The engine of claim 1, wherein the cylinder includes a cylinder liner, a reciprocating piston within the cylinder liner, and a cylinder cover covering the cylinder, and a combustion chamber formed within the cylinder between the reciprocating piston and the cylinder cover.

14. 10. The engine of claim 1, wherein the compressor is driven directly or indirectly by the turbine.

15. Large 2-stroke uniflow scavenging turbocharged multi-cylinder internal combustion engine NO x 1. A method for determining a reduction rate, comprising: However, the said institution: NO during engine operation x a plurality of cylinders generating an exhaust gas stream including: a turbocharging system including an exhaust gas driven turbine disposed in an exhaust system and a compressor disposed in a scavenging system for supplying scavenging air to the cylinder; a selective catalytic reduction (SCR) reactor disposed in the exhaust system; NO in the SCR reactor x a reducing agent source configured to add a reducing agent to the exhaust gas line at a desired flow rate to react with A device for reducing O in exhaust gas, disposed downstream of the SCR reactor and the turbine. 2 Generates a signal representing the concentration (PPM) of O 2 A sensor, A NOx reduction device for reducing NOx in exhaust gases, the NOx reduction device being disposed downstream of the SCR reactor and the turbine. x Generates a signal representing the concentration (PPM) of NO x A sensor, and and the method further comprises: NO in the exhaust gas downstream of the SCR reactor x Mass flow, ・ The above O 2 Sensor signals, ・ The above NO x Sensor signals, the thermal efficiency of said engine; - the load on the engine; - adjustment factor, Calculating as a function of NO in the exhaust gas upstream of the SCR reactor x Calculating a mass flow as a function of the reducing agent flow rate; NO in the exhaust gas upstream of the SCR reactor x Mass flow and NO in the exhaust gas downstream of the SCR reactor x NO emission through the SCR reactor as a function of mass flow x Calculating a reduction rate; Desired NO x Reduction rate compared to the NO x adjusting the flow rate of the reducing agent as a function of the calculated reduction rate; A method comprising:

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