DK179313B1

DK179313B1 - Large turbocharged two-stroke compression-igniting engine with exhaust gas recirculation

Info

Publication number: DK179313B1
Application number: DKPA201671013A
Authority: DK
Inventors: Kim Jensen
Original assignee: Man Diesel & Turbo Filial Af Man Diesel & Turbo Se Tyskland
Priority date: 2016-12-21
Filing date: 2016-12-21
Publication date: 2018-04-30
Also published as: KR20180072552A; CN108223203A; JP6595571B2; DK201671013A1; CN108223203B; KR102019931B1; JP2018100669A

Abstract

A large turbocharged two-stroke compression-igniting combustion engine with crossheads (23) comprising a plurality of cylinders (1), each cylinder (1) being provided with scavenge ports (19) and with an exhaust valve (4),an exhaust gas receiver (3) connected to the cylinders (1) via their respective exhaust valves (4), a turbocharger (5), an exhaust gas conduit (18) connecting an outlet of the exhaust gas receiver (12) to a turbine (6) of the turbocharger (5), a compressor (9) of the turbocharger (5) driven by the turbine (17), a scavenge air conduit (11) connecting an outlet of the compressor (9) to an inlet of a scavenge air receiver (2), the scavenge air conduit (11) comprising a scavenge air cooler (12), the scavenge air receiver (2) being connected to the cylinders (1) via their respective scavenge ports (19), an exhaust gas recirculation conduit (30) for recirculating a portion of the exhaust gas back to the cylinders (1), the exhaust gas recirculation conduit (30) comprising a blower (32) or compressor for forcing recirculated exhaust gas back to the cylinders (1), a cylinder bypass conduit (40) for bypassing the cylinders (1) by conveying a portion of the hot scavenge air from the scavenge air conduit (11) upstream of the scavenge air cooler (22) to the turbine (6) of the turbocharger (5), and a boiler (36). The engine is configured to convey at least a first portion of the exhaust gas from the cylinders (1) through the boiler (36).

Description

<¹θ> DANMARK (10)

<¹²> PATENTSKRIFT

Patent- og

Varemærkestyrelsen (51) lnt.CI.: F02 M 26/05 (2016.01) (21) Ansøgningsnummer: PA 2016 71013 (22) Indleveringsdato: 2016-12-21 (24) Løbedag: 2016-12-21 (41) Aim. tilgængelig: 2018-04-30 (45) Patentets meddelelse bkg. den: 2018-04-30 (73) Patenthaver: MAN DIESEL & TURBO, FILIAL AF MAN DIESEL & TURBO SE, TYSKLAND, Teglholmsgade 41, 2450 København SV, Danmark (72) Opfinder: Kim Jensen, Tåstrup Valbyvej 52, 2635 Ishøj, Danmark (74) Fuldmægtig: NORDIC PATENT SERVICE A/S, Bredgade 30,1260 København K, Danmark (54) Benævnelse: LARGE TURBOCHARGED TWO-STROKE COMPRESSION-IGNITING ENGINE WITH EXHAUST GAS RECIRCULATION (56) Fremdragne publikationer:

DK 177388 B1 JP 2005273556 A DE 102010003002 A1 (57) Sammendrag:

Fortsættes ...

Fig. 7

LARGE TURBOCHARGED TWQ-STROKE COMPRESSION-IGNITING ENGINE

WITH EXHAUST GAS RECIRCULATION

TECHNICAL FIELD

The present invention relates to a large turbocharged twostroke compression-igniting internal combustion engine of crosshead type with an exhaust gas purification system.

BACKGROUND

Large two-stroke compression-igniting internal combustion engines of the crosshead type are typically used in propulsion systems of large ships or as engine in power plants. Emission requirements have been and will be increasingly difficult to meet, in particular with respect to oxides of nitrogen (NOx) levels.

Exhaust gas recirculation is a measure that is known to assist in combustion engines to reduce NOx.

These emission requirements such as the International Maritime Organization (IMO) Tier II and especially Tier III emission standards are difficult to meet without using an exhaust gas recirculation system. Preferably, the exhaust gas recirculation rate is variable.

DK 177388 discloses a large two-stroke compression-igniting internal combustion engine according to the preamble of claim 1.

The energy system consisting of engine cylinders and turbocharger, must be carefully balanced in all operation conditions. If not balanced, the boundary conditions for the cycle process in the cylinders become un-acceptable, and/or the compressor of the turbocharger goes into either

02634-DK-P surge or choke. The compressor characteristic determines if the turbocharger is operating close to its maximum efficiency, but with enough surge margin to ensure compressor stability. The surge margin is needed as the turbocharger operating point could approach the surge line in the compressor map during a transient, e.g. a fast engine load reduction, or during an abnormal situation.

The balancing becomes significant more complicated, when engine must offer operating modes both with and without high pressure exhaust gas recirculation, and with fixed turbocharger components. The reason is that the exhaust gas recirculation line from exhaust gas receiver to scavenge air receiver includes a cooler, which removes very significant amounts of energy from the energy system. This energy is 'lost' in vessels central cooler. When running without exhaust gas recirculation active, this energy removal is not present. Thus, when switching from exhaust gas recirculation operation to non-exhaust gas recirculation operation and vice versa the balance in the energy system is significantly different.

Presently, the 'balance' is established by using a cylinder bypass from the compressor outlet to turbine inlet, and a turbine bypass. The control strategy of these bypasses is designed to compensate the energy removal in each operating mode. When running without exhaust gas recirculation, a turbine bypass reduces the power delivered to the turbine, and when running with exhaust gas recirculation, the cylinder bypass increases the power delivered to the turbine. Together, these measures compensate the effect of the exhaust gas recirculation line being active or inactive, while reducing the scavenging air flow through the cylinders.

02634-DK-P

Thus, there is a need for turbocharged two-stroke compression-igniting internal combustion engine in which the turbocharger is balanced for both operation with and without exhaust gas recirculation with minimum need to use bypasses and minimum energy loss in exhaust gas recirculation cooler.

SUMMARY

In view of the above it is an object of the present invention to a large two-stroke compression-igniting internal combustion engine with crossheads that overcomes or at least reduce the problem mentioned above.

The foregoing and other objects are achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, there is provided a large turbocharged two-stroke compression-igniting combustion engine with crossheads comprising a plurality of cylinders, each cylinder being provided with scavenge ports and with an exhaust valve, an exhaust gas receiver connected to the cylinders via their respective exhaust valves, a turbocharger, an exhaust gas conduit connecting an outlet of the exhaust gas receiver to a turbine of the turbocharger, a turbocharger compressor of the turbocharger driven by the turbine, a scavenge air conduit connecting an outlet of the turbocharger compressor to an inlet of a scavenge air receiver, the scavenge air conduit comprising a scavenge air cooler, the scavenge air receiver being connected to the cylinders via their respective scavenge ports, an exhaust gas recirculation conduit for

02634-DK-P recirculating a portion of the exhaust gas back to the cylinders, the exhaust gas recirculation conduit comprising a blower or compressor for forcing recirculated exhaust gas back to the cylinders, and a cylinder bypass conduit for bypassing the cylinders by conveying a portion of the hot scavenge air from the scavenge air conduit upstream of the scavenge air cooler to the turbine of the turbocharger, characterized by comprising and a boiler, and characterized in that the engine being is configured to convey at least a first portion of the exhaust gas from the cylinders through the boiler (36) and in that the engine has at least two modes of operation, the engine being configured in a first mode of operation to convey said first portion of the exhaust gas from the cylinders through the boiler (36) and from the boiler (36) through the exhaust gas recirculation conduit back to the cylinders and to convey a portion of hot scavenge air from the scavenge air conduit upstream of the scavenge air cooler through the bypass conduit to the turbine, and the engine being configured in a second mode of operation to prevent flow through the exhaust gas recirculation conduit, to prevent flow through the bypass conduit and to convey the first portion of exhaust gas conveyed through the boiler from the boiler to the turbine.

By including a boiler that removes energy from the exhaust gas both in exhaust gas recirculation operation and in nonexhaust gas recirculation operation the energy system is balanced in both modes of operation and does not use a turbine bypass for non—exhaust gas recirculation operation. Instead it uses a boiler, i.e. a high pressure boiler in parallel with exhaust gas receiver, in order to remove energy from the system. A significant advantage is that the gas temperature and density is high, resulting in an

02634-DK-P extremely efficient heat exchanger or high pressure boiler, providing useful steam for with significantly lower size and cost than traditional boiler after turbine outlet. This is particularly useful when the engine is used on a marine vessel, where steam is always required.

In a first possible implementation of the first aspect the engine is configured to convey a second portion of the exhaust gas from the cylinders to the turbine without passing through the boiler.

In a second possible implementation of the first aspect the engine comprises an auxiliary blower in the scavenge air conduit and the engine is configured to operate the auxiliary blower in order to maximize the steam production of the boiler.

In a third possible implementation of the first aspect the first portion of the exhaust gas and the second portion of the exhaust gas together make up the total exhaust gas from the cylinders.

In a fourth possible implementation of the first aspect the engine comprises a boiler conduit including the boiler, with an inlet of the boiler conduit being connected to the exhaust gas receiver or to the exhaust gas conduit at a first position.

In a fifth possible implementation of the first aspect an outlet of the boiler conduit is connected to the exhaust gas recirculation conduit at a third position, the third position preferably being upstream of the blower or compressor .

02634-DK-P

In in a sixth possible implementation of the first aspect an outlet of the boiler conduit is connected to the exhaust gas conduit at a second position downstream of the first position .

In a seventh possible implementation of the first aspect the engine comprises a first control valve in the exhaust gas recirculation conduit.

In an eighth possible implementation of the first aspect the engine comprises a second control valve in the bypass conduit.

In a ninth possible implementation of the first aspect the engine comprises a third control valve between the third position and the position where the exhaust gas recirculation conduit connects to the exhaust gas conduit.

In a tenth possible implementation of the first aspect the exhaust gas recirculation conduit comprises an exhaust gas recirculation cooler.

In an eleventh possible implementation of the first aspect the division of exhaust gas flow between the boiler and the exhaust gas conduit is controlled according to desired turbocharger balance.

In a twelfth possible implementation of the first aspect the boiler is integrated into the exhaust gas receiver.

In a thirteenth possible implementation of the first aspect the exhaust gas receiver has a large volume for equalizing pressure pulses from the exhaust of the individual

02634-DK-P cylinders to provide a substantially constant pressure at an outlet of the exhaust gas receiver,

In a fourteenth possible implementation of the first aspect the engine further comprises an auxiliary blower associated with the scavenge air conduit for assisting the turbocharger at relevant load conditions.

In a fifteenth possible implementation of the first aspect the scavenge air receiver has a large volume for reducing pressure surges caused by the inlet flow to the individual cylinders .

In a the sixteenth possible implementation of the first aspect the engine is configured to operate the auxiliary blower at all engine load levels with the aim to maximize the steam production of the boiler. Thus, the use of an oil burner or the like to increase steam production in low load areas of the main engine can be reduced or avoided.

In a seventeenth possible implementation of the first aspect the engine is not provided with a steam boiler on the low-pressure side of the turbine.

These and other aspects of the invention will be apparent from and the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

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

02634-DK-P

Fig. 1 is an elevated view showing the fore end and one lateral side of a large two-stroke compression-igniting turbocharged engine according to an example embodiment, Fig. 2 is an elevated view showing the aft end and the other lateral side of the engine of Fig. 1,

Fig. 3 is a diagrammatic representation the engine according to Fig. 1 with its intake and exhaust systems, Fig. 4 is a diagrammatic representation a prior art Tier III engine a prior art intake and exhaust system,

Fig. 5 is the diagrammatic representation of a prior art Tier III engine of Fig. 4 operating in Tier III mode, i.e. with exhaust gas recirculation,

Fig. 6 is a diagrammatic representation of a prior art Tier

II engine of Fig. 4 operating in Tier II mode, i.e. without exhaust gas recirculation,

Fig. 7 is a is a diagrammatic representation an example embodiment of a Tier III engine with intake and exhaust system according to the invention,

Fig. 8, is the diagrammatic representation of the Tier III engine of Fig. 7 operating in Tier III mode, i.e. with exhaust gas recirculation,

Fig. 9, is the diagrammatic representation of the Tier III engine of Fig. 7 operating in Tier II mode, i.e. without exhaust gas recirculation, and

Figs. 10 to 12 are another example embodiments of a Tier

III engine with intake and exhaust system according to the invention .

DETAILED DESCRIPTION

In the following detailed description, a large two-stroke compression-igniting internal combustion engine will be described by the example embodiments. Figs. 1 and 2 show a large low-speed turbocharged two-stroke compressionigniting internal combustion engine with a crankshaft 22

02634-DK-P and crossheads 23 in elevated views. Fig. 3 shows a diagrammatic representation engine with its intake and exhaust systems. In this example embodiment the engine has six cylinders 1 in line. Large turbocharged two-stroke diesel engines have typically between five and sixteen cylinders in line, carried by a cylinder frame 25 that is supported by an engine frame 24. 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 (compression-igniting) engine of the two-stroke uniflow type with scavenge ports 19 in the form a ring of piston-controlled ports at the lower region of the cylinders 1 and an exhaust valve 4 at the top of the cylinders 1. Thus, the flow in the combustion chamber is always from the bottom to the top and thus the engine is of the so called uniflow type. The scavenging air is passed from the scavenging air receiver 2 to the scavenging air ports 19 of the individual cylinders 1. A reciprocating piston 21 in the cylinder 1 compresses the scavenging air, fuel is injected via two or three fuel valves 27 that are arranged in the cylinder cover 26. Combustion follows and exhaust gas is generated. When an exhaust valve 4 is opened, the exhaust gas flows through an exhaust duct 20 associated with the cylinder 1 concerned into an exhaust gas receiver 3 and onwards through an exhaust gas conduit 18 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through exhaust conduit 7. Through a shaft 8, the turbine 6 drives a compressor 9 supplied via an air inlet 10 .

02634-DK-P

The compressor 9 delivers pressurized scavenging air to a scavenging air conduit 11 leading to the scavenging air receiver 2. The scavenging air in the conduit 11 passes through an intercooler 12 for cooling the scavenging air. The cooled scavenging air passes via an auxiliary blower 16 driven by an electric motor 17 that pressurizes the charging air flow in low or partial load conditions to the charging air receiver 2. At higher loads the turbocharger compressor 9 delivers sufficient compressed scavenging air and then the auxiliary blower 16 can be bypassed via a nonreturn valve 15.

The exhaust gas receiver 3 is a large elongated cylindrical container disposed parallel and in close proximity to the top of the row of cylinders 1. The exhaust gas receiver 3 has a large volume enabling the exhaust gas receiver to equalize the pressure pulses that are caused by the periodic inflow of the exhaust gas from the individual cylinders 1 at the opening of the exhaust valves 4. The equalization effect of the exhaust gas receiver 3 provides for a substantially constant pressure at the outlet of the exhaust gas receiver 3. A constant pressure at the outlet of the exhaust gas receiver 3 is advantageous since the exhaust gas driven turbocharger 5 or turbochargers 5 that are used in large two-stroke diesel engines benefit from a constant feed pressure.

From the exhaust gas receiver 3 the exhaust gases are guided towards the turbine 6 of the turbocharger 5 via an exhaust conduit 18 (there can be a plurality of turbochargers 5 and that can be a plurality of exhaust gas receivers 3). The exhaust gases are disposed into the atmosphere downstream of the turbine 6. The turbocharger 5 is a constant pressure turbocharger, i.e. the turbocharger 5 is not configured for

02634-DK-P operation with pressure pulses in the exhaust gas. The turbocharger 5 has an axial or radial turbine and is configured for exhaust gas temperatures of up to approximately 500 to 550 °C.

The turbocharger 5 also includes a compressor 9 driven by the turbine 6 via a shaft 8. The compressor 9 is connected to an air intake 10. The compressor 9 delivers high pressure scavenge air to a scavenge air receiver 2 via a scavenge air conduit 11 that includes a scavenge air cooler 12.

The scavenge air receiver 2 is a large elongated cylindrical container disposed parallel and in close proximity to the bottom of the row of cylinders 1. The scavenge air receiver 2 has a large volume enabling the scavenge air receiver 2 to compensate for the pressure drops that are caused by the periodic outflow of the scavenge air to the individual cylinders 1 at the opening of the scavenge ports 19. The compensation effect of the scavenge air receiver 2 provides for a substantially constant pressure in the scavenge air receiver 2 so that substantially the same scavenge air pressure is available for each cylinder 1. A constant pressure in the scavenge air receiver 2 is required since the turbocharger or turbochargers 5 that are used in large two-stroke diesel engines are operated with constant feed pressure and deliver a constant feed pressure, i.e. there is no pressure pulse available for scavenging the individual cylinders 1.

The prior art engine is provided with an exhaust gas recirculation system that is illustrated in Fig. 4. The exhaust gas recirculation system is configured to convey a portion of the exhaust gases coming from the cylinders 1 into the scavenge air, e.g. for lowering combustion

02634-DK-P temperature and thereby reducing NO_X emissions. The exhaust gas recirculation system can be active or inactive or of a type that operates with varying exhaust gas recirculation rates. The exhaust gas recirculation system includes a conduit 30 extending from the exhaust gas receiver 3 or from the exhaust gas conduit 18 to the scavenge air conduit 11 or to the scavenge air receiver 2. Alternatively, the exhaust gases may be taken from the cylinders 1 directly via a valve or port (not shown).

In the prior art shown in Fig. 4 the exhaust gas recirculation conduit 30 connects the exhaust gas conduit 18 to the scavenge air conduit 11. The exhaust gas recirculation conduit 30 branches off from the exhaust gas conduit 18 at a position downstream of the exhaust gas receiver 3 and connects to the scavenge air conduit 11 at a position downstream or upstream of the scavenge air cooler 12.

The exhaust gas recirculation conduit 30 includes various components. These components include cleaning equipment such as a scrubber or filter, a suction blower 32 (driven by an electric motor or by a hydraulic motor), and a first control valve 34.

The blower 32 and the first control valve 34, i.e. the components of the exhaust gas recirculation conduit 30, are connected to an electronic control unit (not shown). The electronic control unit controls the activity of the exhaust gas recirculation system on the basis of operating conditions and/or on input from a human operator. The electronic control unit is configured to be able to activate and deactivate the exhaust gas recirculation system and if needed variably control the exhaust gas

02634-DK-P recirculation rate, i.e. the ratio between air and exhaust gas .

The prior art engine is provided with a cylinder bypass conduit 40 that connects the scavenge air conduit 11 to the exhaust gas conduit 18. One end of the cylinder bypass conduit 40 is connected to the scavenge air conduit 11 at a position downstream of the compressor 9 and upstream the scavenge air cooler 12. The other end of the cylinder bypass conduit 40 is connected to the exhaust gas conduit 18 at a position downstream of the position where the exhaust gas recirculation conduit 30 connects to the exhaust gas conduit 18 and upstream of the inlet of the turbine 6. Other connection positions along the exhaust gas conduit 18 are also possible.

The cylinder bypass conduit 40 includes a second control valve 41 that regulates the flow of scavenge air from the scavenge air flow path 11 to the exhaust conduit 18, e.g. under command of the electronic control unit or a human operator. The second control valve 41 has a variable and controllable degree of restriction to the flow through the valve .

Alternatively, the second control valve 4 is an on/off type that is controlled by the electronic control unit or by a human operator. In this embodiment the electronic control unit is configured to open the second control valve 41 when exhaust gas recirculation system is active, and configured to close the second control valve 41 when the exhaust gas recirculation system is inactive.

The exhaust gas recirculation system may be inactive for various reasons. One of the reasons can be a defect or

02634-DK-P malfunction of the exhaust gas recirculation system. Another reason for inactivity of the exhaust gas recirculation system could be the Opportunity to optimize the fuel consumption of the engine with respect to a Tier II NOx emission level. The exhaust gas recirculation rate may vary, e.g. between 0% and approximately 45%.

The turbocharger 5 does not operate well or does not operate at all when it is not well matched to the engine due to surging or choking. In a typical compressor characteristic, pressure ratio is plotted as a function of the mass flow rate and the speed of rotation and contours of efficiency are superimposed. When matching a turbo charger 5 to an engine, the aim is to place the operating points of the engine near or within the contours of highest efficiency but with a safe margin to the surge line.

When the exhaust gas recirculation system changes from an active state to an inactive state, the operating conditions for the turbocharger change substantially. The turbocharger 5 is namely matched to the engine for operation with the exhaust gas recirculation system active (i.e. operation with an exhaust gas recirculation rate between e.g. approximately 20 and 45 % and a good match with the turbocharger 5. Without countermeasures the turbocharger 5 will not be matched well when the exhaust gas recirculation system is deactivated, since the scavenge air pressure and flow would increase by approximately 25%, which is unacceptable at high engine load and may lead to choking and overspeeding of the turbocharger and low efficiency.

Matching a turbocharger 5 for an exhaust gas recirculation engine fulfilling the IMO Tier III emission legislation or a Tier IT engine running without exhaust gas recirculation

02634-DK-P (or a small amount of exhaust gas recirculation) is a compromise between compressor stability (surge margin) and compressor/turbocharger efficiency/Fuel consumption of the engine 1. If a compressor of the turbocharger is matched with a optimal layout when running with no exhaust gas recirculation, there is an unnecessary large surge margin as exhaust gas recirculation reduces the flow rate through the compressor 9 (engine operating point moves towards the surge line). Conventional turbochargers or variable turbine area turbochargers do not have the flow range that is required to handle the variations in flow when switching between these two modes without compromising scavenge air pressure (boost pressure) and engine efficiency.

In an embodiment, the compressor 9 of the turbocharger 5 is matched for exhaust gas recirculation operation and open cylinder by-pass flow path 40. When switching to nonexhaust gas recirculation mode the cylinder by-pass flow path 40 is closed ensuring that the increase in flow and scavenge air pressure is reduced for avoiding that the compressor 9 of the turbocharger 5 chokes, and optimal running conditions in the compressor characteristic (map) are obtained. Another effect is that a lower absolute exhaust gas recirculation mass flow is required for achieving the envisaged NOx reduction, since the air flow through the cylinders 1 is reduced when the cylinder bypass flow path 40 is open. Yet another effect is that the capacity of the exhaust gas recirculation system itself can be reduced since less suction blower power and amount of circulated exhaust gas is needed. Thus, the electronic control unit can be configured to increase the opening of the second control valve 41 with increasing exhaust gas recirculation ratio and vice versa so that the turbocharger

02634-DK-P best matched to the engine in all exhaust gas recirculation ratios that the engine is operated with.

A negative effect of the cylinder bypass flow through the bypass conduit 40 is an increased heat load on the engine caused by a reduced amount of scavenge gas passing through the cylinders 1.

A turbine bypass conduit 50 is provided for blowing off excess exhaust gas from the exhaust gas conduit 18 during operation without exhaust gas recirculation. The flow through the turbine bypass conduit 50 is controlled by a fifth control valve 51. A steam boiler 52 in the exhaust conduit 7 converts heat in the exhaust gas coming from the outlet of the turbine and from the turbine bypass 50 into steam.

Fig. 5 illustrates the operation mode of the engine of Fig. 4 during operation with exhaust gas recirculation the first control valve 34 and the second control valve 41 both open. For illustrative purposes, the control valves are not shown in Fig. 5.

During operation without exhaust gas recirculation, the first control valve 34 and the second control valve 41 are both closed. This mode of operation is illustrated in Fig

6. For illustrative purposes the control valves are not shown in Fig 6. In the operation mode without exhaust gas recirculation some of the exhaust gas coming from the cylinders 1 needs to bypass the turbine 6 in order to balance the turbocharger 5. Hereto, the fifth control valve 51 is opened so that a portion of the exhaust gas coming from the cylinders 1 bypasses the turbine 6 via the turbine bypass conduit 50.

02634-DK-P

Fig. 7 illustrates a first example embodiment of the engine. The engine according to this embodiment includes all the features of the prior art engine, except the turbine bypass conduit 50, the fifth control valve 51 and the recirculated exhaust gas cooler 31. In an embodiment, the engine does not have or at least does not need to have a steam boiler 52 on the low-pressure side of the turbine 6, while still being able to produce sufficient steam and while still being able to sufficiently extract maximum energy from the combusted fuel.

The engine according to this embodiment is instead provided with a high pressure boiler 36. The high pressure boiler 36produces steam that can be used by various consumers associated with the engine or its environment, such as e.g. a marine vessel in which the engine is installed. The highpressure boiler 36 receives a first portion of the total flow of exhaust gas from the cylinders 1 through a boiler conduit 35. The boiler conduit 35 includes a fourth control valve 38.

In this embodiment the inlet of the boiler conduit 35 is connected to the exhaust gas receiver 3 and the outlet of the boiler conduit 35 is connected to the exhaust gas recirculation conduit 30. The exhaust gas circulation conduit 30 is provided with a third control valve 37.

The control valves can be manually operated or be connected to an electronic control unit (not shown).

In a first mode of operation, the engine operates with exhaust gas recirculation. In this mode the third control valve 37 is closed, the first control valve 34 is open and

02634-DK-P the second control valve 41 is open. The first mode is illustrated in Fig. 8, only showing the active conduits and without showing the control valves for rendering the illustration easier to comprehend. In the first mode a first portion of the exhaust gas coming from the cylinders 1 is conveyed through the boiler conduit 35, through the through the high-pressure boiler 36, through the exhaust gas recirculation conduit 30 and through the blower 32 to the scavenge air conduit 11, preferably at a position upstream of the scavenge air cooler 12 (alternatively the recirculated exhaust gas can be delivered directly to the scavenge air receiver 2).

Hot scavenge air bypasses the cylinders 1 by being conveyed from the scavenge air conduit 11 via the bypass conduit 40 to the exhaust gas conduit 18.

In a second mode of operation, the engine operates without exhaust recirculation. In this mode the third control valve 37 is open, the first control valve 34 is closed and the second control valve 41 is closed. The second mode is illustrated in Fig. 9, only showing the active conduits and without showing the control valves for rendering the illustration for easy to comprehend. In the second mode a first portion of the exhaust gas coming from the cylinders 1 this conveyed through the boiler conduit 35, through the high-pressure boiler 36, through the open third control valve 37 to the exhaust gas conduit 18 to join the second (remaining) portion of the exhaust flow coming from the cylinders 1. Thus, all of the exhaust gas coming from the cylinders 1 is conveyed to the turbine 6. However, when compared to the prior art the amount of energy in the total flow of exhaust gas conveyer towards the compressor 6 is lower since the high-pressure boiler 36 has removed the

02634-DK-P portion of the energy and converted the removed portion of energy into steam. Thus, the turbocharger 5 is perfectly balanced of the engine, despite the fact that the turbine 6 receives the complete flow of exhaust gas from the cylinders 1.

A portion of	the	total flow of	exhaust	gas from	the
cylinders is	conveyed to the inlet of the turbine	6,
preferably,	both	in operation	with	exhaust	gas
recirculation	and	an operation	without	exhaust	gas

recirculation.

Fig. 10 illustrates a second embodiment that is essentially identical with the first embodiment except that the exhaust gas recirculation conduit 30 is provided with a recirculated exhaust gas cooler (scrubber) 39.

Fig. 11 illustrates a third embodiment that is essentially identical with the first embodiment except that inlet of the boiler conduit 35 is directly connected to the cylinders and the outlet of the boiler conduit is connected to the exhaust gas conduit 18.

Fig. 12 illustrates a fourth embodiment that is essentially identical with the first embodiment except that inlet of the boiler conduit 35 is connected to the exhaust gas conduit 18.

In an embodiment the engine is configured to operate the auxiliary blower 16 at all engine load levels (low, medium and high engine levels) with the aim to maximize the steam production of the boiler 36. Thus, the use of an oil burner or the like to increase steam production in low load areas of the main engine can be reduced or avoided.

02634-DK-P

In an embodiment (not shown) the high-pressure boiler 36 disposed inside the exhaust gas receiver 3. This significantly reduces the forces exerted on to the boiler components by the pressure of the exhaust gas. By integrating the high-pressure boiler 36 into the exhaust gas receiver less space is used and the engine will be more compact.

The invention has been described in conjunction with various embodiments herein. However, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage .

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

02634-DK-P en indgang til en skylleluftkanal (11)

Claims

patent claims

A large, turbocharged two-stroke combustion engine with compression ignition and cross-heads (23) comprising: a plurality of cylinders (1), each cylinder (1) provided with flushing ports (19) and an exhaust valve (4), an exhaust gas receiver (3), connected to the cylinders (1) via their corresponding exhaust valves (4), a turbocharger (5), an exhaust gas duct (18) connecting an outlet from the exhaust gas receiver (12) to a turbine (6) to the turbocharger (5), and a turbocharger compressor (9) for the turbocharger (5) driven by the turbine (17), a purge air duct (11) connecting an output of the turbocharger compressor (9) to a purge receiver (2), which comprises a purge air cooler (12), which purge air receiver ( 2) is connected to the cylinders (1) via their corresponding flushing ports (19), an exhaust gas recirculation duct (30) for recirculating a portion of the exhaust gas back to the cylinders (1), comprising an exhaust gas recirculation duct (30) blower (32) or compressor to force recirculated exhaust gas back to cylinders (1) and a cylinder bypass (40) to bypass cylinders (1) by passing a portion of the warm flushing air from the flushing air duct (11) upstream of the flushing air cooler (22) to the turbine (6) of the turbocharger (5), and a boiler (36), characterized in that the engine is configured to pass at least a first portion of the exhaust gas from the cylinders (1) through the boiler, and at least two modes of operation wherein the engine is configured in a first mode of operation to conduct the first portion of the exhaust gas from the cylinders (1) passed through the boiler (36) from the boiler (36;

through

02634-GB-P exhaust gas recirculation duct (30) back to the cylinders (1) and to pass a portion of hot purge air from the purge duct (11) upstream of the purge cooler (12) through the bypass duct (40) to the turbine (6) and where the engine is configured in another mode of operation to prevent flow through the exhaust gas recirculation duct (30), to prevent flow through the bypass duct (40) and to conduct the first portion of exhaust gas passed through the boiler (36) from the boiler (36) to the turbine (6).

An engine according to claim 1, wherein the engine is configured to pass another portion of the exhaust gas from the cylinders (1) to the turbine (6) without passing through the boiler (36).

An engine according to claim 1 or 2, further comprising an auxiliary fan (16) in the purge air duct (11), and wherein the motor is configured to drive the auxiliary fan (16) to maximize the steam production of the boiler (36).

An engine according to any one of claims 1 to 3, wherein the first part of the exhaust gas and the second part of the exhaust gas together constitute the total exhaust gas from the cylinders (1).

An engine according to any one of claims 1 to 4, comprising a boiler duct (35) including the boiler (36), wherein an inlet to the boiler duct (35) is connected to the exhaust gas receiver (3) or to the exhaust gas duct (18). at a first position.

An engine according to any one of claims 1 to 5, wherein an outlet from the boiler duct (35) is connected to the exhaust gas recirculation duct (30) at a third

02634-DK-P position, which third position is preferably upstream of the fan (32) or compressor.

The engine of claim 5 or 6, wherein an outlet from the boiler duct (35) is connected to the exhaust gas duct (18) at a second position downstream of the first position.

An engine according to any one of claims 1 to 7, comprising a first control valve (34) in the exhaust gas recirculation duct (30).

An engine according to any one of claims 1 to 8, comprising a second control valve (41) in the bypass duct (40).

An engine according to any one of claims 6, 8 or 9, comprising a third control valve (37) between the third position and the position where the exhaust gas recirculation duct (30) is connected to the exhaust gas duct (18).

An engine according to any one of claims 1 to 10, wherein the exhaust gas recirculation duct (30) comprises an exhaust gas recirculation cooler (39).

An engine according to any one of claims 1 to 11, wherein the distribution of exhaust gas flow between the boiler (36) and the exhaust gas duct (18) is controlled according to a desired turbocharger balance when operating in the second state.

An engine according to any one of claims 1 to 12, wherein the boiler (36) is integrated into the exhaust gas receiver (3).

02634-EN-P

An engine according to any one of claims 3 to 13 configured to operate the auxiliary fan (16) at all engine load levels for the purpose of

5 maximize the steam production of the boiler (36).

02634-EN-P

1.5

CD

2.5