DK177700B1

DK177700B1 - A large slow running turbocharged two stroke internal combustion engine with crossheads and exhaust- or combustion gas recirculation

Info

Publication number: DK177700B1
Application number: DK201200272A
Authority: DK
Inventors: Jens Vilhelm Goertz
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2012-04-19
Filing date: 2012-04-19
Publication date: 2014-03-24
Also published as: DK201200272A; KR101467419B1; JP2013224653A; CN103375308A; JP5681742B2; CN103375308B; KR20130118237A

Abstract

A large slow running turbocharged two-stroke internal combustion engine (1) with crossheads and with and exhaust or combustion gas recirculation. The engine (1) has a predetermined maximum continuous rating and the engine (1) comprises an exhaust gas system, a charging air system and an EGR system connected to the exhaust gas system at a split point (17,20) and to the charging air system at an admixing point (10,16), the portion of the exhaust gas system downstream of the split point (17,20) having a specified capacity to handle at the most a mass flow of exhaust gas that is less than the mass flow of exhaust gas coming from the all the cylinders (4) at maximum continuous rating, the engine being configured to be operated with the lowest possible EGR ratio that is possible without the mass flow actually coming from the cylinders (4) minus the mass flow going through the EGR system exceeding the specified capacity.

Description

i DK 177700 B1

A LARGE SLOW RUNNING TURBOCHARGED TWO STROKE INTERNAL COMBUSTION ENGINE WITH CROSSHEADS AND EXHAUST- OR COMBUSTION GAS RECIRCULATION

5 FIELD OF THE INVENTION

The present invention relates to large slow running turbocharged two stroke internal combustion engines with crossheads and exhaust- or combustion gas recirculation.

10 Further, the invention relates to a method of operating a large slow running turbocharged internal combustion engines with crossheads and exhaust- or combustion gas recirculation. -

15 BACKGROUND OF THE INVENTION

Large slow running turbocharged two stroke internal combustion engines with crossheads are engines with at least one cylinder and a reciprocating piston received 20 therein. These engines have a crosshead disposed between the piston and the crankshaft. A combustion chamber is defined between the piston, the inner cylinder wall and by a cylinder cover at one end of the cylinder. The cylinder cover includes an exhaust valve that is 25 controllably and intermittently openable in order to expel combustion residues from the combustion chamber to an exhaust duct system. These engines also have means for intermittently establishing an opening in the combustion chamber near the cylinder's second end prior to a 30 combustion therein, for scavenging towards the first end by introduction through said opening of pressurized scavenge gas comprising oxygen, and these engines comprise means for fuel injection into the compressed

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2 DK 177700 B1 scavenge gas for internal combustion in said combustion chamber.

Engines according above definition are often referred to 5 as "large turbocharged 2-stroke uniflow crosshead diesel engines" or just a "large 2-stroker" although these terms may not be fully correct, and are often embodied with a plurality of standing cylinders in a row, their pistons working on a single crankshaft; These engines can have a 10 pure two-stroke working sequence and are normally of large physical size regarding cylinder diameter and piston stroke, often making a such engine high as a house, to at relatively low rotational speed deliver multiple megawatts of power for driving power plant 15 generators, for propulsion of sea vessels, or for satisfying like power requirements in the MW+ range.

Presently, a number of options exist to reduce NOx formation in large slow running turbocharged internal 20 combustion engine by changes to be applied to the engine process, in particular the following: • Exhaust- or combusted Gas Recirculation (EGR) • Use of water emulsified fuel.

25 · Humidification of the Fresh Charge, i.e. Scavenge

Air Moisterization - (SAM).

In the following of this document the term “exhaust- or combusted gas recirculation” will be referred to by the 30 term EGR.

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3 DK 177700 B1 WO 2010105620 discloses an engine according to the preamble of claim 1.

The most effective reduction method has been EGR.

5 Document DE 19809618 discloses a large two-stroke turbocharged diesel engine with exhaust gas recirculation (in this engine the gases are taken directly from the cylinders and therefore this form of EGR is also referred to as Combusted Gas Recirculation - CGR) . When a 10 reference is made to "exhaust gas recirculation" in this document this is meant to cover both recirculation of gases that are taken from the exhaust and gases that are directly taken from the individual combustion chambers.

15 In exhaust gas recirculation, exhaust gas is mixed with the clean scavenge air so as to reduce the oxygen content of the resulting gas mixture at the start of the combustion, whereby a reduction of the chance that NOx is formed during the combustion process is achieved.

20

From 2011, marine diesel engines installed on new ships must meet the IMO Tier II NOx emission requirements. For large slow running turbocharged internal combustion engine the limit will be 14.4 g/kWh. This can be achieved 25 by traditional engine modifications, but these result in increased fuel consumption.

When sailing into dedicated Emission Control Area (ECA) engines installed on ships built after 1st of January 30 2016 must meet a far lower limit, Tier III, at 3.4 g/kWh for low speed engines. This limit cannot be reached by traditional engine modifications, and other methods, such as EGR, to lower the emission must be used.

35 The exhaust gas system can be provided with a SOx scrubber or other devices at the low pressure side of the

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4 DK 177700 B1 engine's one/more turbocharger's turbine. The SOx scrubber is a voluminous device since it must be able to process the large mass flow of exhaust gas that the engine produces at maximum continuous rating (MCR) power 5 delivery.

DISCLOSURE OF THE INVENTION

On this background, it is an object of the present 10 application to provide an engine that meets the various emission restrictions, and is able to do so economically from both a construction cost and an operation costs point of view.

15 This object is achieved by providing a large slow running multi cylinder turbocharged internal combustion engine with crossheads and with a defined maximum continuous rating, said engine comprising an exhaust gas system, a scavenge air system, a turbocharger with a compressor in 20 the scavenge air system and a turbine in the exhaust gas system, an EGR system connected to the exhaust system and to the scavenge air system, a controller, whereby the controller is configured to distribute the total mass flow rate of exhaust gas coming from the cylinder between 25 an EGR mass flow rate entering the EGR system, and an exhaust gas mass flow rate flowing in the exhaust gas system towards the turbine, with a selected EGR ratio of said ERG mass flow rate to said total mass flow rate of exhaust gas, said selected EGR ratio being selectable in 30 a range from zero to a predetermined maximum ratio, whereby the exhaust gas system has a specified maximum continuous capacity to handle exhaust gas mass flow rate, said specified maximum continuous capacity being less than the total exhaust gas mass flow rate coming from the

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5 DK 177700 B1 cylinders at said maximum continuous rating, and whereby the controller is configured to feed excess mass flow rate into the EGR system when the actual total exhaust gas mass flow rate coming from the cylinders exceeds said 5 specified maximum capacity of the exhaust gas system, regardless of the selected EGR ratio.

Thus, the maximum mass flow of exhaust gas flowing through the exhaust gas system towards the turbine of the 10 turbocharger can be significantly reduced, which provides large cost savings in both operation and construction of the engine.

In an embodiment the specified maximum capacity is in the 15 range of 50%-90% of the total exhaust gas mass flow rate coming from the cylinders at said maximum continuous rating.

In an embodiment the exhaust gas system comprises at 20 least an exhaust gas treatment component.

In an embodiment, the scavenge air system has a specified maximum capacity to handle a scavenge air mass flow rate, said specified maximum capacity being less than the 25 charging air mass flow rate of the total scavenge gas flowing to the scavenge gas receiver at said maximum continuous rating. Thus the components of the scavenge air system can be reduced in size, thereby saving costs in manufacturing and operation.

30

In an embodiment the scavenge air system comprises at least a scavenge air cooler.

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6 DK 177700 B1

In an embodiment the controller is configured to operate in at least two modes: a low emission mode, whereby the engine, depending on the 5 engine load, wherein the selected EGR ratio is selected to just meet emission requirements when there is no excess mass flow rate, and a reduced exhaust mode, whereby the engine, depending on the engine load, wherein the selected EGR ratio is 10 selected to be zero except when a higher than zero EGR ratio is required to avoid that the mass flow rate flowing through the exhaust gas system to the turbine of the turbocharger exceeds said specified maximum continuous capacity.

15

The object above is also achieved by providing method of operating a large slow running multi cylinder turbocharged internal combustion engine with crossheads engine and with a defined maximum continuous rating, said 20 engine comprising an exhaust gas system, a scavenge air system, a turbocharger with a compressor in the scavenge air system and a turbine in the exhaust gas system, an EGR system connected to the exhaust system and to the scavenge air system, and a controller, said method 25 comprising: distributing the total mass flow rate of exhaust gas coming from the cylinders between: an EGR mass flow rate entering the EGR system, and an exhaust gas mass flow rate flowing in the exhaust gas system towards the turbine, in accordance with a selected EGR 30 ratio of said ERG mass flow rate to said total mass flow rate of exhaust gas, selecting an EGR ratio in a range from zero to a predetermined maximum ratio, whereby the exhaust gas system has a specified maximum continuous capacity to handle exhaust gas mass flow rate, said

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7 DK 177700 B1 specified maximum continuous capacity being less than the total exhaust gas mass flow rate coming from the cylinders at said maximum continuous rating, and feeding excess mass flow rate into the EGR system when the actual 5 total exhaust gas mass flow rate coming from the cylinders exceeds said specified maximum capacity of the exhaust gas system, regardless of said selected EGR ratio.

10 Thus, the maximum mass flow of exhaust gas flowing through the exhaust gas system towards the turbine of the turbocharger can be significantly reduced, which provides large cost savings in both manufacturing and construction of the engine.

15

In an embodiment the method further comprises determining the actual total mass flow rate coming from the cylinders, determining the difference between said actual mass flow rate and said specified capacity, when said 20 actual mass flow rate is smaller or egual to said specified capacity: applying a desired EGR ratio selected in a range between zero and a predetermined maximum ratio, and when said actual mass flow rate is larger than said specified capacity: applying an EGR ratio high 25 enough to ensure that that the mass flow flowing through the exhaust gas system to the turbine of the turbocharger does not exceed said specified capacity.

In an embodiment the method further comprises operating 30 said engine in one of at least two modes: a low emission mode, whereby the engine, depending on the engine load, operates with an EGR ratio needed to meet low emission requirements when there is no excess mass flow rate, and a reduced exhaust mode, whereby the engine, depending on

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8 DK 177700 B1 the engine load, operates with the lowest possible EGR ratio that is required to avoid that the mass flow rate flowing through the exhaust gas system to the turbine of the turbocharger exceeds said specified maximum 5 continuous capacity.

In an embodiment of the method the operation mode is either manually selected by an operator or automatically selected an electronic said controller unit.

10

In an embodiment of the method the controller decides on the operating mode on the basis of information regarding the geographic position of the engine.

15 Further objects, features, advantages and properties of the engine and method of operating an engine according to the present disclosure will become apparent from the detailed description.

20 BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more detail with reference to the exemplary embodiments shown 25 in the drawings, in which:

Fig. 1 is diagrammatic representation of an engine according to an exemplary embodiment,

Fig. 2 is a diagrammatic representation of an engine 30 according to another exemplary embodiment,

Fig. 3 is a flow chart illustrating an exemplary embodiment of a method of operating an engine.

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9 DK 177700 B1

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a diagrammatic representation of an engine, here in the form of a large low speed 5 turbocharged two-stroke internal combustion engine 1 with crossheads. In the exemplary embodiment the engine 1 has six cylinders 4 (illustrated by the interrupted circles) in line. Large turbocharged two-stroke diesel engines have typically between 5 and 16 cylinders in line, and 10 carried by an engine frame 2.

The engine 1 is of the two-stroke uniflow type with scavenge ports at the lower region of the cylinders 4 and an exhaust valve at the top of the cylinders 4. The 15 general operation principle of such engines is well-known and will not be described in detail here.

The engine 1 has a charging air system that includes an inlet 5 possibly with a silencer or a filtering unit 20 upstream of a compressor 7 of a turbocharger 6. The turbocharger 6 is also provided with a turbine 8 that is part of the exhaust gas system that will be described in greater detail further below. Only one turbocharger 6 is shown, but it is to understood that it is also possible 25 to operate the engine with a plurality of turbochargers.

The compressed and hot scavenging air leaves the compressor 7 through a pipe 9 that extends to a scavenging gas receiver 16. Before arriving at the scavenging gas receiver 16 the scavenging gas is first 30 passed through a first cooler 11, thereafter through a second air cooler 12 and then through a reversing chamber/water mist catcher 14.

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10 DK 177700 B1

In the first cooler 11, the scavenging air is humidified and slightly cooled. In the air cooler 12, the scavenging air is cooled down, typically from temperatures in the range of 190 degree Celsius to approximately 40 degree 5 Celsius.

At an admixing point 10, a flow of recirculated exhaust gas is added to the scavenge air stream. The amount of recirculated exhaust gas that is added to the scavenge 10 air stream is variable between zero and a predetermined maximum mass flow ratio depending on operation mode and engine load/operation conditions.

In Fig. 1, the components of the charging air system that 15 are upstream of the admixing point 10 are shown included within an interrupted line 42.

The reversing chamber/water mist catcher 14 ensures that any water droplets in the gaseous scavenging medium are 20 caught and removed to avoid that they end up in the combustion chambers.

From the reversing chamber/water mist catcher 14, the scavenging gas goes directly to the scavenging gas 25 receiver 16, except at low engine loads (typically below approximately 40% MCR) . At such low engine loads, the scavenging air pressure generated by the turbine 7 is normally insufficient, and therefore the scavenging pressure can be increased by the auxiliary blower 15, if 30 switched in to function at these low engine load conditions .

From the scavenging gas receiver 16, the scavenging gas enters the combustion chambers in the cylinders 4 through

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11 DK 177700 B1 the aforementioned scavenging ports, according to the defined sequence of operation for these cylinders 4.

After combustion, the exhaust gas leaves the combustion 5 chambers in the cylinders 4 through a respective exhaust valve and arrives in the exhaust gas receiver 17. The exhaust gas receiver 17 often is a large cylindrical vessel that extends along the full length of the engine 1. The exhaust gas receiver 17 has a volume that is large 10 enough to substantially dampen out the pressure fluctuations of the exhaust gas coming from the individual cylinders 4. The exhaust gas receiver 17 may be sectioned in discrete parts and may internally contain or comprise various functional elements to supplement the 15 overall function of the engine, e.g. for collecting valuable heat from the exhaust gas, or for adding various substances to improve the overall engine function.

A given engine 1 has at its maximum continuous rating, a 20 known mass flow rate of exhaust gas that leaves the cylinders 4 and enters the exhaust gas receiver 17.

The exhaust gas leaves the exhaust gas receiver 17 through a pipe 18. At a split point 20, a fraction 25 (percentage) of the total mass flow of exhaust gas coming from the cylinders 4 is led into an EGR system, whilst the remaining part of the total mass flow of exhaust gas coming from the cylinders is led through the portion of the exhaust gas system downstream of the split point 20.

30

Downstream of the split point 20, the exhaust gases continue in a pipe 31 to the turbine (s) 8 of the turbocharger (s) 6. Downstream of the turbine 8 the exhaust gases in this example continue through a pipe 32

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12 DK 177700 B1 via a waste heat recovery unit 33 and then through a SOx scrubber 34. Thereafter, the exhaust gases are led into the environment, i.e. the ambient air. The waste heat recovery unit 33, and especially the SOx scrubber 34, are 5 very voluminous devices for which it is hard to find space e.g. aboard a vessel where the engine is used as the propulsion unit. Supplementary or alternatively various other recovering or treating devices may be lined-in to the 31- & 32- exhaust duct downstream of the 10 split at point 20. The common rule that: the larger the exhaust gas mass flow rate, the larger the physical volume of the related device, is generally valid for all such devices inserted.

15 For ease of recognition, the components of the exhaust gas system downstream of the split point 20 are shown surrounded by an interrupted line 44 in Fig. 1.

From the split point 20, the recirculated exhaust gases 20 are passed through a pipe 28 via an electronically controlled valve 21, a pre-scrubber 22, a mix cooler 23, a wet scrubber 24, a water mist catcher 25 and an EGR blower 26 to the admixing point 10, where the recirculated exhaust gases are added to the scavenging 25 air stream.

A controller in the form of an electronic control unit 50 sends control signals to the electronically controlled valve 21, to the EGR blower 26, to the auxiliary blower 30 15 and to the unreferenced water pumps associated with the cooling units 11, 12, 23. The same electronic control unit may also be used to control other functions of the engine, such as e.g. the fuel injection system,

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13 DK 177700 B1 the engine cooling system, the engine lubrication system and the exhaust valve actuation system.

The electronic control unit 50 determines, through the 5 signals to the electronic valve 21 and to the EGR blower 26, the ratio of the recirculated exhaust gas.

The electronic control unit 50 determines the required EGR ratio on the basis of the selected operation mode and 10 on the engine running conditions, such as the engine load. The engine 1 and the electronic control unit 50 have been configured to be able to be operated in at least two different modes. One mode is the low emission mode (LEM) that provides for low NOx emission values. The 15 other mode is the reduced exhaust mode (REM) that provides better fuel efficiency at engine loads below maximum continuous rating with a tradeoff in the form of higher NOx emission levels at engine loads below maximum continuous rating.

20

The selection of the operating mode can be automatic, based on the geographic location of the engine 1, or it can be selected through input by an operator of the engine 1, or possibly automatically by coupling the 25 control to a GPS unit.

With the engine 1 according to the present exemplary embodiment, the NOx emission values can be kept safely below the crucial upper limits of ECA Tier III, in the 30 low emission mode. In the low exhaust mode the fuel efficiency is better and the NOx emission levels are significantly lower than required in non-ECA.

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14 DK 177700 B1

In order to meet the strictest emission restrictions that will apply in ECA under Tier III, the engine is operated with a relatively high EGR ratio in the low emission mode. This relatively high EGR ratio is often held 5 constant for all engine loads. Typically, the EGR ratio in the low emission mode is between approximately 32% to approximately 44%. In the example given in table 1 below, the EGR ratio in the reduced emission mode is 38%. Also in low emission mode the ERG ratio may be varied relative 10 to the engine load to compensate for specific engine "behavior" effects at specific part-load situations.

The table 1 below, lists the engine load as the percentage of the maximum continuous rating, the EGR 15 ratio and the NOx emission levels in g/kWh at different engine loads, namely at 25% MCR, 50% MCR, 75% MCR, and 100% MCR. The NOx values for use in the IMO NOx cycle as well as the combined NOx value according to the IMO cycle are also indicated. Table 1 also lists the mass flow 20 rate of exhaust gas through the portion of the exhaust gas system downstream of the split point 20 as a percentage of the mass flow rate of exhaust gas coming from all of the cylinders of the engine, when the engine is running at 100% maximum continuous rating.

25

The portion of the exhaust gas system downstream of the split point 20 (surrounded by the interrupted line 44) is dimensioned to be able to handle at the most a mass flow rate of exhaust gas that corresponds to the total mass 30 flow rate of exhaust gas coming from the cylinders 4, when the engine 1 is operating at maximum continuous rating, reduced by the value of the mass flow rate of exhaust gas that has to be passed through the EGR system

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15 DK 177700 B1 at maximum continuous rating, to respect the IMO Tier III ECA limitation for the engine in question.

This specified capacity C for mass flow rate of the exhaust gas system downstream of the split point 20 is 5 determined (i.e. limited) by the "sizes"/capacities of the components of the portion of the exhaust gas system inside the area surrounded by the interrupted line 44.

The term “dimensioned” in this document means that the 10 exhaust gas system downstream of the split point 20 and the components thereof are designed and constructed such that they result in an exhaust gas system downstream of the split point 20 that can deal with the specified capacity (mass flow rate) without any substantial 15 overcapacity, i.e. the system is not overdimensioned.

Exhaust gas flow rate from the cylinders 4 that exceeds this specified capacity C and that needs to be passed through EGR system is hereafter also referred to as 20 excess mass flow rate.

As an example, the total mass flow rate of the exhaust gas coming from the cylinders 4 at maximum continuous rating of a 6 cylinder engine with a 98 cm bore and 25 approx. 2.4 m stroke, such as the MAN B&W 6K98ME-C7, torqueing out approx. 36 MW @ approx. 100 revs per minute, will be approximately 300,000 kg/h. With EGR ratios as in table 1 below, the portion of the exhaust gas system downstream of the split point 20 will for this 30 engine be dimensioned to have a specified capacity to handle 62% thereof, i.e. only 186,000 kg/h. At maximum continuous rating the excess mass flow rate will then be 114 metric tons/h that is passed through the EGR system.

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16 DK 177700 B1

When the engine 1 is operated in the reduced exhaust mode, the EGR ratio is not held constant for all engine loads. Instead, the EGR ratio is kept as low as possible 5 without exceeding the specified capacity of the portion of the exhaust gas system downstream of the split point 20. As shown in table 1, the electronic control unit 50 keeps the EGR ratio at zero for all engine loads equal to and below 62% of the maximum continuous rating. For 10 engine loads above 62% of the maximum continuous rating, the electric control unit 50 applies the EGR ratio that results in a mass flow rate through the portion of the exhaust gas systems downstream of split point 20 that corresponds the specified capacity, i.e. to 62% of the 15 mass flow rate of exhaust gas coming from the cylinders at 100% maximum continuous rating. Thus, in the reduced emission mode, the engine 1 is operated with an EGR rate varying between zero and 38% for engine loads between 62% and 100%, and with an EGR rate of zero for engine loads 20 below 62%, unless it for other reasons is desired to still recirculate some exhausted gas through the EGR system.

Tier II ECA -Tier III mode (Low Emission Non ECA - Reduced Exhaust Mode engine Mode) MCR % 100% 75% 50% 25% 100% 75% 62% 50% 25% EGR % 38% 38% 38% 38% 38% 18% 0% 0% 0%

Flow value 62% 46% 31% 15% 62% 62% 62% 50% 25% NOx 3.4 3.4 3.4 3.4 3.4 9.3 14.4 14.4 14.4

Weighted value 0.7 1.7 0.5 0.5 0.7 4.7 2.2 2.2

NOx IMO

cycle 3.4 9.7

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17 DK 177700 B1

Table 1

The combination of an exhaust system downstream of the 5 split point 20 that is dimensioned (has a capacity) for handling a mass flow rate of exhaust gas lower than the total mass flow rate of exhaust gas coming from the cylinders 4 (at 100% maximum continuous rating with an REM operating mode that applies lowest possible EGR 10 ratios depending on engine load), provides for an overall economic engine concept from both a construction and an operation point of view.

The numbers in the table 1 above are exemplary. Other 15 values for the EGR ratio that is applied in the TIER III mode are possible. The percentage of the exhaust gas mass flow rate of the total exhaust gas coming from the cylinders used for EGR flow can be in the range of 10% to 50%, preferably in the range of 20% to 45% and even 20 more preferably between 36% and 40%.

Accordingly, the size of mass flow rate of exhaust gas that the portion of the exhaust gas system downstream of the split point 20 is dimensioned to be able to handle, 25 can be in the range of 50% to 90%, preferably in the range of 55% to 80% and even more preferably between 60% and 64% of the exhaust gas mass flow rate of the total exhaust gas flow rate coming from the cylinders at said maximum continuous rating.

30

Fig. 2 shows another exemplary embodiment of the engine 1 that is essentially identical with the embodiment shown in Fig. 1, except that the EGR system is connected to the exhaust system at the exhaust gas receiver 17, and thus

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18 DK 177700 B1 the exhaust gas receiver 17 proper forms the split "poinf'/location and the EGR system is connected to the scavenging system at the scavenging gas receiver 16, thus forming the admixing point. In this embodiment also the 5 water mist catcher 14 and the auxiliary blower 15 are included in the portion of the scavenging air system upstream of the admixing point, and thus also allows these components to be dimensioned smaller. Otherwise, the operation and control of the engine according to Fig.

10 2 is the same as for the engine according to Fig. 1.

Another position for the admixing "point" or location like 10 is also possible. A group of embodiments defined in the claims comprise addition of recirculated exhaust 15 gas to a position upstream of the compressor 7. Hereby e.g. the requirement for the output from the EGR-string being pressurized is substantially reduced. However increased capacity of some of the components in the scavenge gas intake system 42 must be provided to handle 20 the full mass flow rate of charging gas at maximum continuous rating. Further, embodiments directly introducing exhaust gas for recirculation into a respective cylinder before or after closure of its opening(s) for scavenging are covered by the scope of the 25 claims. For such embodiments the EGR string has to be adapted correspondingly, especially re. valves for distribution to cylinders and required pressure level.

Fig. 3 illustrates an example of a method of operation of 30 an engine, in a simplified flowchart. The method includes a determination of the geographic position of the vessel/engine 1 through a GPS or other navigation signal to the electronic control unit 50. The electronic control unit 50 determines on the basis of information stored

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19 DK 177700 B1 therein if the determined geographic position falls in an ECA region or not. If the determined geographic position indeed is inside an ECA, the electronic control unit 50 selects the Low emission mode operational method here 5 having a fixed predetermined EGR ratio. If the determined geographic position falls outside the ECA the electronic control unit 50 selects the reduced exhaust mode and operates with the lowest possible EGR rate. With certain intervals, the electronic control unit 50 checks the 10 geographic position and automatically selects operating mode depending on the conclusion of being positioned inside or outside an ECA. It is in principle always possible for an engine operator to manually overrule the selection of the operation mode, e.g. if an emergency 15 situation should require so.

In order to determine the lowest possible EGR rate when operating in the reduced emission mode, the electronic control unit 50 determines the actual mass flow rate 20 coming from the cylinders. In an embodiment this is facilitated by using a lookup table stored in the electronic control unit 50, the table including the mass flow rate coming from the cylinders in relation to the engine load as a percentage of the maximum continuous 25 rating. Next the electronic control unit 50 establishes the difference between the determined actual mass flow rate and the specified capacity of the portion of the exhaust gas system downstream of the split "point" 20.

When the actual mass flow rate is smaller or equal to 30 said specified capacity the electronic control unit 50 applies zero EGR ratio. When the actual mass flow rate is larger than the specified capacity of the exhaust system path 31,32 downstream from the split point, the electronic control unit 50 opens for a split off of the

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20 DK 177700 B1 determined difference mass flow rate to pass downstream of EGR-valve 21, thus establishes an EGR ratio equal to the value of the split off difference mass flow rate divided by the actual mass flow rate from the cylinders.

5 As an example: when the mass flow rate coming from the cylinders is 100kg/s and the specified capacity is 80kg/s, the established EGR rate is (100-80)/100 = 0,2 or 20%, as 20 kg/s is led through the EGR valve 21.

10 Bearing in mind that the reduced maximum mass flow rate limit through the exhaust system also inevitably will result in a split-off positive contribution from the EGR string, to the total mass flow rate of scavenge gas for cylinder charging, when the according to the invention 15 engine is operated to produce more combusted gas than acceptable to the exhaust system limit, also the required mass flow rate capacity of the inlet/upstream (5-7-9-11-14) part of the scavenge air system is reduced. Therefore the invention also gives the beneficial combined 20 possibility to reduce the dimensions for both air inlet, and exhaust gas systems components, as e.g. turbo charger, scavenge air "treatment devices", engine room ventilation, SOx scrubber system, Waste Heat Recovery (WHR) system and other applications, to an extent allowed 25 by the EGR ratio. The reduction will significantly lower the hardware and installation cost of the components, and in case of a SOx scrubber and WHR installation, a significant gain of space in the machinery room can be expected.

30

The waste heat recovery unit 33 also profits from the reduced maximum mass flow rate limit through the exhaust system, since there will be a better heat transfer efficiency due to stable "saturating" relatively large

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21 DK 177700 B1 (•"•maximum) hot exhaust gas flow rate during a substantial large range of engine operation and time, compared to conventional engines that only occasionally at maximum continuous rating reach their respective exhaust maximum 5 to beneficially "saturate" their WHR-unit.

Further savings can also be obtained by reduction of engine room ventilation due to the reduced maximum air intake for the engine. In particular the costs for 10 silencers and engine room blowers can be reduced.

Reduced Exhaust Mode (REM) is a dedicated running mode of a marine diesel engine applied with EGR. REM implies that the EGR ratio is controlled with the purpose of keeping a 15 permanent low/"reduced" maximum mass flow rate downstream of a split point/location, of gas to exhaust (to ambience), and it thereby offers the opportunity to reduce the dimensions and costs of components in the exhaust system.

20

When sailing outside Emission Control Areas, (ECA), the EGR ratio will be substantially higher than needed for compliance with the NOx criteria outside ECA. At 100% MCR the EGR ratio equals the ratio needed for compliance with 25 the NOx criteria within ECA. At lower loads the EGR ratio can be reduced while keeping NOx level below the local NOx criterion.

In particular, the reduced size of a SOx scrubber has a 30 significant economic impact for several reasons: A SOx scrubber at the low-pressure side of the turbocharger is a very voluminous and therefore costly and space occupying piece of equipment. Thus, any size reduction will reduce costs and provide space for other equipment.

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Further, typically, SOx scrubbers are operated with large amounts of sea water as the cleaning medium, and pumping this seawater is energy consuming. On top of that, chemicals like e.g. NaOH have to be added to the sea 5 water, thereby further increasing costs when the amount (mass flow rate) of exhaust gases to be treated is increased. Thus, the reduction in the maximum mass flow rate of exhaust gases that need to be transported through the exhaust system downstream of the split point, and 10 thereby through the SOx-scrubber, too, is of a significant economic advantage.

Of course the engine may also be operated in a mode falling between a LEM mode for operation within ECA, and 15 the REM mode, meaning that the EGR ratio is larger than needed to not compromise the exhaust system mass flow rate downstream of the split point. However, for fuel economy reasons, one normally will operate at lowest possible EGR ratio.

20

From the above is also clearly understood that for an engine according to the invention advantages re. both size, space reguirements, and costs can be obtained, from the components of the scavenge air intake and 25 "treatment/conditioning" group of devices and components upstream of the inlet of recirculated exhaust gas into the flow of scavenging/charging gas.

For a number of sea vessels hitherto being operated to 30 less stringent NOx emission criteria, there may be an interest in adaption of an existing engine to fulfill future more restrictive NOx emissions criteria, instead of replacing the existing engine, or scrapping the vessel. Existing engines that are modified in accordance

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23 DK 177700 B1 with the inventive concept are also covered by the attached claims .

The number and "version" of engine components used for a 5 such modification are substantially different from the parts used for the engine at original state, and may further differ from engine to engine - even for new engines, too. To quickly identify a new engine or an engine modified to be inventive and to inform of its 10 modification history etc., an electronically read-/write-able tag, preferably of remotely readable RFID-type, may beneficially be installed to an inventive engine.

The term "comprising" as used in the claims does not 15 exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality. The single processor, device or other unit may fulfill the functions of several means recited in the claims.

20 The reference signs used in the claims shall not be construed as limiting the scope.

Although the present invention has been described in detail for purpose of illustration, it is understood that 25 such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.

01198-DK-P

Claims

A large, slow-moving, multi-cylinder, internal combustion turbocharged engine and crossheads (1) with a defined maximum continuous output, comprising: an exhaust gas system (44), a purge air system (42), a turbocharger (6) with a compressor (7) in the purge air system (42) and a turbine (8) in the exhaust gas system (44), an EGR system connected to the exhaust system (44) and with the purge air system (42), a control unit (50), and ) is designed to distribute the total mass flow of exhaust gas coming from the cylinders (4) between: an EGR mass flow flowing into the EGR system and an exhaust gas flow flowing into the exhaust gas system (44) towards the turbine (8), with a defined EGR ratio between the EGR mass flow and the exhaust gas mass flow, which defined EGR ratio can be defined within a range from zero to a predetermined maximum ratio, characterized by that the exhaust gas system (44) has a specified maximum continuous capacity (C) for handling the exhaust gas flow, which - 2 - DK 177700 B1 specified maximum continuous capacity (C) is lower than the total exhaust gas flow coming directly from the cylinders at the maximum continuous and, in that the control device (50) is sized to supply an excess mass flow to the EGR system when the actual total exhaust gas flow coming from the cylinders exceeds the specified maximum capacity (C) of the exhaust gas system (44) regardless of the EGR selected. -relationship.

The engine (1) of claim 1, wherein the specified maximum capacity (C) of the exhaust gas system (44) after the sub-location is in the range of 50% -90%, preferably in the range of 55% -80% and even more preferably between 60% and 64% of the total exhaust gas flow coming from the cylinders at the maximum continuous output.

Engine (1) according to any one of the preceding claims, wherein the exhaust gas system (44) comprises at least one exhaust gas treatment component (33, 34).

Engine (1) according to any one of the preceding claims, wherein the purge air system (2) has a specified maximum capacity for handling a purge air mass flow (A), the specified maximum capacity being less than the proportion of compressed gas mass flow in the total purge air (B) flowing to the purge receiver (14) at the maximum continuous output.

The engine (1) of the preceding claim, wherein the flushing air system (42) comprises at least one flushing air cooler (12). - 3 - DK 177700 B1

An engine (1) according to any one of the preceding claims, wherein the control unit (50) is configured to operate in at least two modes: a low-emission mode wherein the engine, depending on engine load, defines the selected EGR ratio to exactly meeting the emission requirements when there is no excess mass flow, and a reduced exhaust mode where, depending on engine load, the engine is defined as zero EGR ratio, unless a higher EGR ratio is required than zero to avoid, the mass flow flowing through the exhaust gas system to the turbine (8) of the turbocharger (6) exceeds the specified maximum continuous capacity (C).

A method of operating a slow-moving, multi-cylinder, internal combustion engine with internal combustion and cross heads (1) and having a defined maximum continuous output, comprising: an exhaust gas system (44), a purge air system (42), a turbocharger (6) with a compressor (7) in the purge air system (42) and a turbine (8) in the exhaust gas system (44), an EGR system connected to the exhaust system (44) and with the air purge system (42), and a control unit (50), which method comprises: - 4 - dividing the total mass flow of the exhaust gas coming from the cylinders (4) into: an EGR mass flow flowing into the EGR system and an exhaust gas flow flowing into the exhaust gas system ( 44) and towards the turbine (8), in accordance with a selected EGR ratio between the EGR mass flow and the total mass flow in the exhaust gas, selection of an EGR ratio within a range of zero to one predetermined maximum ratio, characterized in that the exhaust gas system (44) has a specified maximum continuous capacity (C) for handling the exhaust gas flow, which specified maximum continuous capacity (C) is lower than the total exhaust gas flow coming directly from the cylinders at the maximum continuous output, and supply of excess mass flow to the EGR system when the actual total exhaust gas flow coming from the cylinders exceeds the specified maximum capacity (C) of the exhaust gas system (44) regardless of the EGR ratio selected.

The method of claim 7, further comprising: determining the current total mass flow coming from the cylinders (4), determining the difference between the current mass flow and the specified capacity (C) when the current mass flow is less than or equal to the specified capacity: use of a desired EGR ratio selected within a range between zero and a predetermined maximum ratio, and when the current mass flow is greater than the specified capacity: use of a EGR conditions large enough to ensure that the mass flow flowing through the exhaust gas system (44) to the turbine (8) of the turbocharger (6) does not exceed the specified capacity (C).

A method according to any one of claims 7 or 8, further comprising operating the motor (1) in one of at least two modes: a low-emission mode wherein, depending on the engine load, the engine operates at an EGR ratio, needed to meet the low emission requirements when there is no excess mass flow, and a reduced exhaust mode where, depending on the engine load, the engine operates at the lowest possible EGR ratio required to prevent the mass flow flowing through the exhaust gas system and to the turbine (8) of the turbocharger (6), exceeds the specified maximum continuous capacity (C).

The method of operating an engine (1) according to claim 9, wherein the operating mode is either manually selected by an operator or automatically selected by an electronic control unit.

The method of claim 10, wherein the control unit determines the mode of operation on the basis of information regarding the geographical position of the engine.

A method of operating an engine according to any one of claims 7 to 11, further comprising using in one mode of operation the lowest EGR ratio possible, without allowing the mass flow of exhaust gas flowing through the exhaust gas system to the turbine (8) in the turbocharger (6) exceeds the specified capacity.

A method according to any one of claims 7 to 12, further comprising: determining the actual mass flow coming from the cylinders (4), determining the difference between the current mass flow and the specified capacity, and when the current mass flow is less than or equal to the specified capacity: use of a zero EGR ratio and when the current mass flow is greater than the specified capacity: use of an EGR ratio corresponding to the difference between the current mass flow and the specified capacity; divided by the current mass flow.

The method of claim 7, further comprising operating the motor in a different mode, including - operating with a fixed EGR ratio at all engine loads.

The method of claim 7, further comprising operating the motor (1) in a second mode which includes operating with an EGR ratio which is adjusted depending on the current engine load.

The method of claim 9, further comprising adjusting the EGR ratio when sailing in low emission mode within an ECA.

Method for producing an engine (1) according to any one of claims 1 to 6, characterized by installation, modification, replacement or conversion of engine components on an existing engine.

Process for producing an engine (1) according to claim 17, characterized by replacing engine components to at least achieve a greater total mass flow of exhaust gas coming from the cylinders at a new correspondingly defined maximum continuous output.