DK178078B8

DK178078B8 - A large slow running turbocharged two-stroke internal combustion engine with an exhaust gas receiver and a scavenge air receiver

Info

Publication number: DK178078B8
Application number: DK201400276A
Authority: DK
Inventors: Morten Vejlgaard-Laursen
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2014-05-22
Filing date: 2014-05-22
Publication date: 2015-05-18
Also published as: CN104863694B; JP2015222074A; CN104863694A; DK178078B1; KR101606786B1; KR20150135088A; JP5886456B2

Abstract

A large slow-running turbocharged two-stroke internal combustion line engine of the uniflow type with crossheads (41) The engine is provided with a turbocharger (5), an elongated scavenge air receiver (2) and an elongated exhaust gas receiver (3). The scavenge air receiver (2) is longitudinally divided into at least two scavenge air receiver sections, with a first scavenge air receiver section (2a) connected to one or more primary cylinders (1) and a second scavenge air receiver section (2b) connected to one or more secondary cylinders (1). The first scavenge air receiver section (2a) is provided with an outlet and the second scavenge air receiver section (2b) is provided with an outlet. The exhaust gas receiver (3) is longitudinally divided into at least two exhaust gas receiver sections, with a first exhaust gas receiver section (3a) connected to one or more primary cylinders (1) and a second exhaust gas receiver section (3b) connected to one or more secondary cylinders (1). The first exhaust gas receiver section (3a) is provided with an inlet and the second exhaust gas receiver section (3b) is provided with an inlet. The second scavenge air receiver section (2b) is selectively connectable to the first scavenge air receiver section (2a) and the second exhaust gas receiver section (3b) is selectively connectable to the first exhaust gas receiver section (3a).

Description

A LARGE SLOW RUNNING TURBOCHARGED TWO-STROKE INTERNAL COMBUSTION ENGINE WITH AN EXHAUST GAS RECEIVER AND A SCAVENGE AIR RECEIVER

FIELD OF THE INVENTION

The present invention relates to a large slow-running uniflow turbocharged two-stroke internal combustion engine with crossheads that is provided with exhaust gas receiver and scavenge air receiver.

BACKGROUND ART

Large slow running two-stroke internal combustion engines with crosshead are typically used in propulsion systems of large ships or as prime mover in power plants. These engines have a crosshead disposed between the piston and the crankshaft.

Emission requirements have been and will be increasingly difficult to meet, in particular with respect to mononitrogen oxides levels.

Exhaust Gas Recirculation is a measure that is known to assist in small fast running diesel engines to reduce N0X emissions. However, there are up to now no only very few commercially operating large two-stroke diesel engines that use exhaust gas recirculation. The reason is that it difficult to implement exhaust gas recirculation in a large two-stroke diesel engine.

One known approach is to route exhaust gas from the low-pressure side of a turbine through an EGR cooler to the inlet of an engine compressor. Unfortunately, this approach requires all of the exhaust to be both expanded and recompressed every time the gas is expanded and compressed, thereby resulting in efficiency losses. Furthermore, the EGR is routed through the intercoolers/aftercoolers, which are designed to cool clean air as opposed to the particulate-laden air that they are required to cool in this scenario. As a result, the particulates will foul the coolers, causing loss in their effectiveness.

Another known EGR approach is to pump exhaust gas from the exhaust receiver into the intake receiver, downstream of the fresh air intercoolers. While fouling of the intercoolers is mitigated, this approach requires an additional blower to pump the recirculated exhaust gas to the inlet side.

Yet another approach is to retain internal EGR in all cylinders of the engine. While this is a relatively simple approach, this method suffers from a shortcoming in that the EGR is not cooled and, thereby, less effective .

One reason that it has proven to be so challenging to implement exhaust gas recirculation in a large two-stroke diesel engine is the amount of power that is required to transport the recirculated exhaust gases from the exhaust gas receiver into the scavenge air flow. In a large two-stroke diesel engine, the scavenge air pressure is typically up to approximately 0.3 bar higher than the pressure in the exhaust gas receiver of large two-stroke diesel engines. Thus, a blower or other means is required for forcing the recirculated exhaust gases from the exhaust gas receiver into the scavenge air system. In a large bore 12 or 14 cylinder two-stroke diesel engine, such as the MAN B&W 12K98MC-C engine the power reguired to drive such a blower would be close to 0.5 MW. This is a significant amount of energy to use on an exhaust gas system and an electric drive motor for driving a blower with such large of power reguirements is extremely expensive. Further, any blower or means to overcome this pressure difference is placed on the "dirty" side of the combustion process and this poses significant reguirements on the blower materials.

Thus, the first cost for the machinery e.g. the blower and drive motor, in an exhaust gas recirculation system for a large two stroke combustion engine amounts to a substantial sum, due to the dimensions of these parts. Further, the changing from EGR operation to non-EGR operation has posed challenges, e.g. in relation to balancing of the turbocharger.

KR20110089074 A1 discloses an engine according to the preamble of claim 1.

DISCLOSURE OF THE INVENTION

On this background, it is an object of the present application to provide a large slow running turbocharged two-stroke internal combustion engine with exhaust gas recirculation system that overcomes or at least reduces the problems indicated above.

This object is achieved by providing a large slow-running turbocharged two-stroke internal combustion line engine of the uniflow type with crossheads, the engine comprising: a single line of cylinders, each cylinder being provided with scavenge ports at or near the lower end of the cylinder and with a single exhaust valve at the top of the cylinder, a turbocharger with a turbine that drives a compressor, an elongated scavenge air receiver extending along the line of cylinders, the scavenge air receiver being connected to the cylinders via the scavenge ports, an elongated exhaust gas receiver extending along the line of cylinders, the exhaust gas receive being connected to the cylinders via the exhaust valves, the scavenge air receiver being longitudinally divided into at least two scavenge air receiver sections, with a first scavenge air receiver section connected to one or more primary cylinders and a second scavenge air receiver section connected to one or more secondary cylinders, the first scavenge air receiver section being provided with an inlet and the second scavenge air receiver section being provided with an inlet, the second scavenge air receiver section being selectively connectable to the first scavenge air receiver section, the exhaust gas receiver being longitudinally divided into at least two exhaust gas receiver sections, with a first exhaust gas receiver section connected to one or more primary cylinders via one or more exhaust ducts and a second exhaust gas receiver section connected to one or more secondary cylinders via one or more exhaust ducts, the first exhaust gas receiver section being provided with an outlet and the second exhaust gas receiver section being provided with an outlet, the second exhaust gas receiver section being selectively connectable to the first exhaust gas receiver section.

By providing a divided exhaust gas receiver and a divided scavenge air receiver with the sections in the respective receiver being arranged to be selectively connectable to one another, it becomes possible to switch between running the engine conventionally with all the cylinders connected to one large scavenge air receiver and connected to one large scavenger receiver and running the engine non-conventionally, with a number of primary cylinders connected to a first section of the scavenge air receiver and to a first section of the exhaust gas receiver and a number of secondary cylinders connected to a second section of the scavenger receiver and to a second section of the exhaust gas receiver. By providing dedicated sections in the receivers for primary cylinders and for secondary cylinders, respectively, it becomes possible to operate the primary cylinders different from the secondary cylinders, e.g. on different fuel, and different EGR rates. By further providing selective connectivity between the sections in the receivers, it becomes possible to quickly or automatically switch between different operation modes, thus providing additional flexibility that can be required to switch between e.g. operating the engine as clean as possible in areas with restricted emission levels and operating the engine as fuel efficient as possible in areas with less restricted emission levels.

The secondary cylinders that produce the exhaust gas for the primary cylinders can be run on a different fuel /different process, that reduces the required amount of NOX reduction, e.g. these secondary cylinders can be operated on distillate or ethanol, while primary cylinders operate on heavy fuel oil.

Especially for engines operating with gas as fuel the solution seems favorable.

In embodiment the first exhaust gas receiver section is separated from the second exhaust gas receiver section by a transverse wall in the elongated exhaust gas receiver.

In another embodiment the first exhaust gas receiver section has a hollow interior space and wherein the second exhaust gas receiver section has a hollow interior space .

In another embodiment the elongated exhaust gas receiver has hollow cylindrical shape defining a cavity that is longitudinally split by traverse wall that extends across the interior of the exhaust gas receiver.

In another embodiment the transverse wall is provided with a selectively closeable opening for establishing a selective fluid connection between the first exhaust gas receiver section and the second exhaust gas receiver section .

In another embodiment the selectively closeable opening is electronically controlled and operatively connected to an electronic control unit of the engine.

In another embodiment the first scavenge air receiver section is separated from the second scavenge air receiver section by a transverse wall in the elongated scavenge air receiver.

In another embodiment the first scavenge air receiver section has a hollow interior space and wherein the second scavenge air receiver section has a hollow interior space.

In another embodiment elongated scavenge air receiver has hollow cylindrical shape defining a cavity that is longitudinally split by traverse wall that extends across the interior of the exhaust gas receiver.

In another embodiment the transverse wall is provided with a selectively closeable opening for establishing a selective fluid connection between the first scavenge air receiver section and the second scavenge air receiver section .

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

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 in the drawings, in which:

Fig. 1 is a front view of a large two stroke diesel engine according to an exemplary embodiment,

Fig. 2 is a side view of the large two stroke engine of Fig. 1,

Fig. 3 is a cross-sectional diagrammatic representation the large two stroke engine according to Fig. 1,

Fig. 4 is a diagrammatic representation of the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 5 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 6 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 7 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 8 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 9 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 10 is a diagrammatic representation of the embodiment the engine of Fig. 9 illustrating another operation mode,

Fig. 11 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 12 is a diagrammatic representation of another embodiment the engine of Fig. 1 illustrating the intake and exhaust system in greater detail,

Fig. 13 is a diagrammatic representation of a valve for selectively connecting and disconnecting two sections of an exhaust gas receiver or of a scavenge receiver, and Fig. 14 is a diagrammatic representation of another valve for selectively connecting and disconnecting two sections of exhaust gas receiver or of a scavenge receiver.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following detailed description, the large low speed two stroke engine will be described by the example embodiments. Figures 1 to 3 show a large low speed turbocharged two-stroke diesel engine with a crankshaft 42 and crossheads 43. Figure 3 shows a diagrammatic representation of the large low speed turbocharged two-stroke diesel engine with its intake and exhaust systems in sectional view. In this example embodiment the engine has four cylinders 1 in line, e.g. the engine is a single line of cylinders. For illustration purposes only, Fig. 1 shows the engine having a quantity of four cylinders 1. It should be apparent that virtually any other quantity of cylinders 1 may be employed without departing from aspects of the present invention. Large turbocharged two-stroke diesel engines have typically between four and sixteen cylinders in line, carried by an engine frame 45. The engine may e.g. be used as the main engine in an ocean going vessel or as a stationary engine for operating a generator in a power station. The total output of the engine may, for example, range from 5,000 to 110,000 kW.

The engine is a diesel engine of the two-stroke uniflow type with scavenge ports 17 at the lower region of the cylinders 1 and an exhaust valve 4 at the top of the cylinders 1. The engine can be operated on various types of fuel, such as e.g. marine diesel, heavy fuel, or gas (LPG, LNG, Methanol, Ethanol). The scavenge air is passed from the scavenge air receiver 2 to the scavenge ports 17 of the individual cylinders 1. A piston 41 in the cylinder 1 compresses the scavenge air, fuel is injected and combustion follows and exhaust gas is generated. When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 6 associated with the cylinder 1 concerned into the exhaust gas receiver 3 and onwards through a first exhaust conduit to a turbine 8 of a primary turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 7. Through a shaft, the turbine 8 of the turbocharger 5 drives a compressor 9 supplied via an air inlet 10. The compressor 9 delivers pressurized scavenge air to a scavenge air conduit 11 leading to the scavenge air receiver 2. In an embodiment (not shown) engine has more than one primary turbocharger .

The scavenge air receiver 2 has an elongated hollow cylindrical body constructed from e.g. plate metal and an essentially circular cross-sectional outline to form a hollow cylinder. The scavenge air receiver 2 extends along the full length of the engine and supplies all of the cylinders 1 with scavenge air. The scavenge air receiver 2 has a substantial cross-sectional diameter and a large overall volume, which is necessary in order to prevent any pressure fluctuations caused by the scavenge ports 17 of the individual cylinders 1 opening and taking in scavenge air, i.e. to ensure constant pressure in the scavenge air receiver 2 despite the irregular consumption of scavenge air by the individual cylinders 1. Typically, the diameter of the scavenge air receiver 2 is larger than the diameter of the pistons 1.

In an embodiment, e.g. for very large engines with a high number of cylinders 1 and a great overall engine length, the engine may be provided with two scavenge air receivers 2, each having its own housing, with one of the scavenge air receivers 2 covering approximately half of the cylinders 1 at one end of the line of cylinders 1 and the other scavenge air receiver 2 covering the other approximately half of the cylinders at the opposite end of the line of cylinders. In prior art engines the two scavenge air receivers 2 will be in fluid communication with one another. However, in the present invention, the two scavenge air receivers will serve significantly uneven number of cylinders and will not be in fluid communication with one another at all times.

The exhaust gas receiver 3 has an elongated hollow cylindrical body constructed from e.g. plate metal and an essentially circular cross-sectional outline. The plate metal is covered by a layer of insulation material to avoid heat loss. The exhaust gas receiver 3 extends along the full length of the engine and receives exhaust gas from all of the cylinders 1 via the individual exhaust ducts 6 that extend into the exhaust gas receiver 3. The exhaust gas receiver 2 has a considerable cross-sectional diameter and a large volume, which is necessary in order to prevent pressure fluctuations caused by the exhaust valves 4 of the individual cylinders 1 opening sending exhaust gas at high speed into the exhaust gas receiver 3, i.e. to ensure constant pressure in the exhaust gas receiver 3 despite the irregular delivery of exhaust gas by the individual cylinders 1. Typically, the diameter of the exhaust gas receiver 3 is larger than the diameter of the pistons 1.

In an embodiment, e.g. for very large engines with a high number of cylinders 1 and a great overall engine length, the engine may be provided with two exhaust gas receivers grocery, with one of the exhaust gas receivers 3 covering approximately half of the cylinders 1 at one end of the line of cylinders 1 and the other exhaust gas receiver 3 covering the other approximately half of the cylinders 1 at the opposite end of the line of cylinders. In prior art engines the two the two exhaust gas receivers will be in fluid communication with one another. However, in the present invention, the two exhaust gas receivers will serve significantly uneven number of cylinders and will not be in fluid communication with one another at all times .

In an embodiment (not shown) the engine comprises two exhaust gas receivers 3, each of them being split up in a primary section and a secondary section and that there could be two scavenger receivers, each of them being split up in a primary section and a secondary section. You agree to this aspect so that we positively cover a very long engine where it's not possible to have say a primary section covering 12 cylinders and a secondary section covering to cylinders because the 12 cylinder primary section would be too long to cover by a single housing.

The smaller scavenge air receiver and the smaller exhaust gas receiver will serve the secondary soundless whilst the larger scavenge air receiver and the larger exhaust gas receiver will serve the primary cylinders.

Referring now to Fig. 4 the intake- and exhaust system of the engine is shown in greater detail.

The scavenge air receiver 2 is longitudinally divided by a separation wall 21, which is in an embodiment a plate wall, into a first scavenge air receiver section 2a and a second scavenger receiver section 2b of unequal length. In another embodiment (not shown) the first scavenge air receiver section 2a and the second scavenge air receiver 2b are two completely separate volumes formed e.g. by two separate receiver housings.

Similarly, the exhaust gas receiver 3 is longitudinally divided into a first exhaust gas receiver section 3a and a second exhaust gas receiver section 3b of unequal length. In another embodiment (not shown) the first exhaust gas receiver section 3a and the second exhaust gas receiver 3b are two completely separate volumes formed e.g. by two separate receiver housings.

The cylinders 1 are divided into a number of primary cylinders 1 and a number of secondary cylinders one. There will typically be a larger number of primary cylinders 1 than secondary cylinders 1.

The first scavenge air receiver section 2a and the first exhaust gas receiver section 3a extend along- and are connected to a number of primary cylinders 1.

The first scavenge air receiver section 2a is provided with an inlet and the second scavenge air receiver section 2b is provided with an inlet.

The second scavenge air receiver section 2b and the second exhaust gas receiver section 3b extend along- and are connected to a number of secondary cylinders 1.

The first exhaust gas receiver section 3a is provided with an outlet and the second exhaust gas receiver section 3b is provided with an outlet.

Thus, the line of cylinders is divided into a number of primary cylinders 1 and a number of secondary cylinders 1. For illustration purposes only, Fig. 4 shows the engine having a quantity of three primary cylinders 1 and one secondary cylinder 1. It should though be apparent that virtually any other combination of quantities of primary and secondary cylinders may be employed without departing from aspects of the present invention.

Scavenge air is routed to the compressor 9 of the turbocharger 5 via an inlet conduit 10. The compressor 9 compresses the scavenge air and a scavenge air conduit 11 routes the compressed scavenge air to the scavenge air receiver 2. The scavenge air in the conduit 11 passes through an intercooler 12 for cooling the compressed scavenge air - that leaves the compressor 9 at approximately up to 200 °C - to a temperature between 5 and 80 °C. The cooled scavenge air passes via an auxiliary blower (not shown) driven by a drive motor that pressurizes the charging air flow in low or partial load conditions to the charging air receiver 2. At higher loads the compressor 9 delivers sufficient compressed scavenging air and then the auxiliary blower is bypassed via a non-return valve (not shown).

The scavenge air conduit 11 passes a summation point 28 where recirculated exhaust gas is added to the scavenge air and leads the scavenge air mixed with recirculated exhaust gas to the inlet of the first scavenge air receiver section 2a. From the first scavenge air receiver section 2a the mixture of scavenge air and recirculated exhaust gas takes part in the combustion process in one of the primary cylinders 1. The exhaust gas thus produced in the primary cylinders 1 is received in the first exhaust gas receiver section 3a. Thus, the combustion process in the primary cylinders 1 is performed with recirculated exhaust gas thereby allowing low NOx emission levels.

The exhaust gas that is received in the first exhaust gas receiver section 3a leaves the first exhaust gas receiver section 3a via the outlet of the latter and is routed by a first exhaust gas conduit 18 to the inlet of the turbine 8 of the turbocharger 5, thereby providing power to the turbocharger 5. The exhaust gas leaves the turbine 8 via a second exhaust conduit 7.

The first exhaust gas conduit 18 has a branch 20 that routes a portion of the exhaust gas to the turbine of a secondary turbocharger 15. The compressor of the secondary turbocharger 15 compresses the scavenge air and a conduit 16 routes the compressed scavenge air from the secondary turbocharger 15 to the inlet of the second scavenger receiver section 2b. An intercooler 52 cools down the scavenge air on its way from the secondary turbocharger 15 to the second scavenge air receiver section 2b. In an embodiment (not shown) is the engine comprised two for more secondary turbochargers

From the second scavenge air receiver section 2b the scavenge air takes part in the combustion process in one of the secondary cylinders 1 (in this embodiment one single secondary cylinder 1, but it is understood that that could be more than one secondary cylinder 1) . The exhaust gas thus produced in the secondary cylinders 1 is received in the second exhaust gas receiver section 3b. Thus, the combustion process in the secondary cylinders 1 is performed without recirculated exhaust gas. In an embodiment the secondary cylinders 1 can be configured for internal exhaust gas recirculation through the timing of the exhaust valve in order to reduce NOx emissions, In another embodiment the secondary cylinders are operated with water injection of water emulsified fuel for NOx reduction .

The exhaust gas that is received in the second exhaust gas receiver section 3b leaves the second exhaust gas receiver section 3b via the outlet of the latter and is routed by an exhaust gas recirculation conduit 19 to the summation point 28, where the recirculated exhaust gas is mixed with the scavenge air coming from the turbine 9 of the turbocharger 5.

A second outlet on the second exhaust gas receiver section 3b is connected to first exhaust gas conduit 18 via a controllable valve 33 to a bypass conduit. This provides a means to control the exhaust gas recirculation (EGR) rate by bypassing the two sections of the exhaust receiver with the controllable variable valve 33. Another way to control the EGR rate is to use a variable turbocharger .

Generally, in a large turbocharged two-stroke internal combustion engine the pressure in the scavenge air on the inlet side of a cylinder 1 will be higher than the pressure in the exhaust gas on the outlet side of the cylinder concerned, otherwise, scavenging could not take place because the pressure dictated flow direction would be in the wrong direction towards the inlet. This aspect of large turbocharged two-stroke internal combustion engines makes it not possible to simply allow exhaust gas flow through a conduit to the inlet side for exhaust gas recirculation without the assistance of blowers or the like .

With the engine according to the present embodiment, during normal engine operation the pressure in the second scavenger receiver section 2b will be higher than the pressure in the second scavenge air receiver section 3b, which will be higher than the pressure in the first scavenge air receiver section 2a, which in turn will be higher than the pressure in the first exhaust gas receiver section 3a, i.e. P_2b > P_3b > P_2a > P_3a.

Thus, this embodiment provides for an engine with exhaust gas recirculation without the need for a blower. At 100% load typical values for the gauge pressures in the intake and exhaust system could for example be: P_2b = 4.0 bar(g) P_3b = 3.9 bar(g) P_2a = 3.8 bar(g) P_3a = 3.7 bar(g)

Fig. 5 shows another embodiment that is essentially identical to the embodiment of Fig. 4, except that the embodiment operates without the controllable valve 33 and the single intercooler 12 displays between the summation point 28 and the inlet of the first scavenge air receiver section 2b and cools the mixture of scavenger and recirculated exhaust gas. The operation of the engine according to this embodiment is essentially identical to that of the embodiment of Fig. 4, except for the lack of the use of the control valve 33 and in this embodiment P_2b > P_3b > P_2a > P_3a, and typical operation pressures are as indicated for the embodiment of Fig. 4.

An advantage of this embodiment is that an EGR cooler is not needed - giving a significant cost down.

Fig. 6 shows an embodiment that is similar to the embodiment of Fig. 4, except that this embodiment does not use a secondary turbocharger. Instead, a blower 25 is used to increase the pressure of the compressed scavenge air in the scavenger conduit 11. A conduit 26 branches off from the scavenger conduit 11 and routes increased pressure scavenge air using the blower 25 to the second scavenge air receiver section 2b. Thus, the pressure in the second exhaust gas receiver section 3b is higher than the pressure in the first scavenge air receiver section 2a and thus the exhaust gas from the second exhaust gas receiver section 3b will flow through the exhaust gas conduit 19 and via the exhaust gas cooler 53 to the summation point 28. The operation of the engine according to this embodiment is essentially identical to that of the embodiment of Fig. 4, except for the lack of the use of the control valve 33 and in this embodiment P_2b > P_3b > P_2a > P_3a, and typical operation pressures are as indicated for the embodiment of Fig. 4. The advantage of this embodiment is that it does not need a secondary turbocharger and the blower 25 the selected deal with "dirty" exhaust gas and can operate with clean scavenge air .

Fig. 7 shows an embodiment that is similar to the embodiment of Fig. 5, except that the second turbocharger 15 is driven by the exhaust gas coming from the second exhaust gas receiver section 3b via a conduit 27, and a conduit 26 is branched off from the scavenge air conduit 11 and feeds the inlet of the compressor of the second turbocharger 15 with compressed scavenge air, so that the second turbocharger can further increase the pressure of the scavenge air to the level needed for sending it to the second scavenge air receiver section 2b. The operation of the engine according to this embodiment is essentially identical to that of the embodiment of Fig. 4, and in this embodiment P_2b > P_3b > P_2a > P_3a. At 100% - load typical values for the gauge pressures in the intake and exhaust system could for example be: P_2b = 4.0 - 6.0 bar(g P_3b = 3.9 - 5.9 bar(g P_2a = 3.8 bar(g) P_3a = 3.7 bar(g)

The advantage of this embodiment is that the energy in the EGR gas is re-used instead of lost in a cooler. Further the higher pressures allows for extreme engine tuning for lower NOx.

Fig. 8 shows an embodiment that is similar to the embodiment of Fig. 7, except that there is a greater number of cylinders in-line, namely eight cylinders in total with six primary cylinders 1 connected to the first scavenge air receiver section 2a and to the first exhaust gas receiver section 3b, respectively and two secondary cylinders connected to the second scavenge air receiver section 2b and the second exhaust gas receiver section 3b, respectively. Further, the intercooler 52 has been placed in conduit 16. The operation of the engine according to this embodiment is essentially identical to that of the embodiment of Fig. 7, and in this embodiment P_2b > P_3b > P_2a > P_3a. At 100% - load typical values for the gauge pressures in the intake and exhaust system could for example be: P_2b = 4.0 - 6.0 bar(g P_3b = 3.9 - 5.9 bar(g P_2a = 3.8 bar(g) P_3a = 3.7 bar(g)

Fig. 9 shows an embodiment that is similar to the embodiment of Fig. 5, except that there is a larger number of cylinders, like in the embodiments of Figs. 7 and 8 and a number of valves 77, 7 8 and 7 9 have been added to the system. Further, the compressor of the second turbocharger 15 receives compressed scavenge air from the branch conduit 26. The operation of the engine according to this embodiment is essentially identical to that of the embodiment of Fig. 4, and in this embodiment P_2b > P_3b > P_2a > P_3a. At 100% - load typical values for the gauge pressures in the intake and exhaust system could for example be: P_2b = 4.0 - 6.0 bar(g P_3b = 3.9 - 5.9 bar(g P_2a = 3.8 bar(g) P_3a = 3.7 bar(g)

Fig. 10 shows how the embodiment of the original figure 9 can be operated in a mode that does not use exhaust gas recirculation. Hereto, the valve 77 in the EGR conduit 19 is closed, valve 79 in conduit 26 is closed and valve 78 in the inlet conduit for the compressor of the second turbocharger 15 is opened. Further, the wall 21 that separates the first scavenge air receiver section 2a from the second scavenge air receiver section 2b is opened, and the wall 31 that separates the first exhaust gas receiver section 3a on the second exhaust gas receiver section 3b is also opened, thus there is one single through going cavity in the scavenge air receiver 2 and in the exhaust receiver 3.

In order to open the wall 21 or 31 the latter can include a large butterfly valve 45, as illustrated in Fig. 13. The circular plate of the butterfly valve 45 can move, preferably under the direction all the actuator between the two positions illustrated in Fig 13 in order to open or close the opening in the wall so that the two sections of the scavenge air receiver 2 on the exhaust gas receiver 3 are either connected or not connected..

In embodiment, illustrated in Fig. 14 the wall 21 or 31 in the scavenge air receiver 2 or in the exhaust gas receiver 3, respectively, is formed by a pair of closely spaced plates 41,42 with a corresponding hole 43 therein that can be covered by a movable middle plate 40 that is received between the pair of closely spaced outer plates 41,42. The hole is opened and closed by sliding the movable middle plate 40 in the desired position. The middle plate 40 is pivotally mounted at a pivot shaft 44 and operated like a so called swing gate valve. The movable middle plate 40 can be connected to an actuator so that the middle plate can be positioned in the control from an electronic control unit.

The selectively closeable opening is in an embodiment electronically controlled and operatively connected to an electronic control unit (not shown) of the engine.

The advantage of this embodiment is that it can be operated with and without exhaust gas recirculation, in accordance with needs, that can for example depend on the location of a vessel driven by the large two-stroke turbocharged internal combustion engine.

The embodiment of Fig. 11 is essentially identical to the embodiment of Fig. 10, except that the intercooler 12 is placed in conduit 26 and the intercooler 53 is placed between the summation point 28 and the inlet of the first scavenge air receiver section 2a.

Fig. 12 shows another embodiment that is similar to the embodiment of Fig. 5, except that it does not use a second turbocharger or a blower. Instead, all of the scavenge air is led to the inlet of the second scavenge air receiving section 2b. However, in this embodiment the second scavenge air receiver section 2b is not completely separated from the first scavenge air receiver section 2a. Instead, the reason opening in wall 21 that acts as a restriction that allows the scavenger in the second scavenge air receiver section 2b flow to the first scavenge air receiver section 2a with a pressure drop. Thus, the pressure in the first scavenge air receiver section 2a will be lower than the pressure in the second scavenge air receiver section 2b. Thus, the pressure in the second exhaust gas receiver section 3b is higher than the pressure in the first scavenge air receiver section 2a and thus all of the exhaust gas in the second exhaust gas receiver section 3b will flow through the exhaust gas circulation conduit 19 via the intercooler 53 to the first scavenge air receiver section 2a. All of the exhaust gas that is received in the first exhaust gas receiver section 3a is transported to the inlet of the turbine 8 of the turbocharger 5 via the first exhaust gas conduit 18. The advantage of this embodiment is that it suffices with a single turbocharger and does not need a blower or other means to increase pressure.

The cylinder or cylinders in the exhaust gas, generating section of the engine, i.e. the secondary cylinders 1, can be operated differently than the rest of the engine (e.g. 4 stroke process, less over scavenging, Otto process), especially when using the four-stroke process, the pumping effect of the four stroke process will be able to provide the support reguired pressure to force the exhaust gas into the scavenger receiver 2.

The exhaust gas generating section, i.e. the secondary cylinders 1, of the engine can operate on a different (cleaner) fuel than the rest of the engine - resulting on reduced reguirements for cleaning of the EGR gas.

For all the embodiments above, for operation without exhaust gases circulation, the separation walls 21, 31 in the scavenge air receiver 2 and in the exhaust gas receiver 3, respectively, can be removed.

The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality.

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 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.

Claims

A large slow-running two-stroke turbocharged internal combustion engine of the long-flush type with cross heads (43), comprising: a single row of cylinders (1), each cylinder (1) provided with flushing ports (17) at or near it. low end of the cylinder and with a single exhaust valve (4) at the top of the cylinder, a turbocharger (5) with a turbine (8) operating a compressor (9), an elongated purge air receiver (2) extending along the row of cylinders (1) which purge air receiver (2) is connected to the cylinders (1) via the purge ports (17), an elongated exhaust gas receiver (3) extending along the row of cylinders (1), which exhaust gas receiver (3) is connected to the cylinders (1). 1) via the exhaust valves (4), which purge air receiver (2) is separated longitudinally in at least two purge air receiver sections, with a first purge air receiver section (2a) connected to one or more primary cylinders (1) and a second scavenge air receiver section (2b) connected to one or more secondary cylinders (1), which first purge air receiver section (2a) is provided with an input and which second purge air receiver section (2b) is provided with an input, purge air receiver section (2b) can be selectively connected to the first purge air section (2a), characterized in that the exhaust gas receiver (3) is longitudinally divided into at least two exhaust gas receiver sections, with a first exhaust gas receiver section (3a) with one or more primary cylinders (1) via one or more exhaust ducts, and a second exhaust gas receiver section (3b) connected to one or more secondary cylinders (1), which first exhaust gas receiver section (3a) is provided having an outlet and which second exhaust gas receiver section (3b) is provided with an outlet, which second exhaust gas receiver section (3b) can be selectively connected to the first exhaust gas receiver section (3a) ).

The engine of claim 1, wherein the first exhaust gas receiver section (3a) is separated from the second exhaust gas receiver section (3b) by a transverse wall (31) of the elongated exhaust gas receiver (3).

The engine of claim 1, wherein the first exhaust gas section (3a) has a hollow interior space and the second exhaust gas section (3a) has a hollow interior space.

The engine of claim 1, wherein the elongated exhaust gas receiver (3) has a hollow cylindrical shape defining a cavity spaced long by a transverse wall (31) extending transversely to the interior of the exhaust gas receiver (3). .

The engine of claim 2, wherein the transverse wall (31) is provided with a selectively closable opening (40, 43, 45) to establish a selective fluid connection between the first exhaust gas receiver section (3a) and the second exhaust gas receiver section ( 3b).

The motor of claim 5, wherein the selectively closable aperture (40, 43, 45) is electronically controlled and operatively connected to an electronic control unit for the motor.

The engine of claim 1, wherein the first purge air receiver section (2a) is separated from the second purge air receiver section (2b) by a transverse wall (21) of the elongated purge air receiver (2).

The engine of claim 1, wherein the first purge air receiver section (2a) has a hollow interior space and the second purge air treceiver section (2a) has a hollow interior space.

The engine of claim 1, wherein the elongated purge air receiver (2) has a hollow cylindrical shape defining a cavity spaced long by a transverse wall (21) extending transversely to the interior of the exhaust gas receiver (2). .

The motor of claim 7, wherein the transverse wall (21) is provided with a selectively closable opening (40, 43, 45) to establish a selective fluid connection between the first purge air receiver section (3a) and the second purge air receiver section (2b). .

The motor of claim 10, wherein the selectively closable aperture (40, 43, 45) is electronically controlled and operatively connected to an electronic control unit for the motor.