DK177462B1

DK177462B1 - Large turbocharged two-stroke diesel engine with exhaust gas purification

Info

Publication number: DK177462B1
Application number: DKPA201200090A
Authority: DK
Inventors: Karl-Johan Nogenmyr
Original assignee: Man Diesel & Turbo Deutschland
Priority date: 2012-02-03
Filing date: 2012-02-03
Publication date: 2013-06-17
Also published as: KR101316080B1; JP2013160224A; CN103244241B; KR20130090330A; JP5349675B2; CN103244241A

Abstract

A large turbocharged two-stroke diesel engine with crossheads, said engine having a plurality of cylinders (1) in line, a turbocharger (5) and an SCR reactor (19) upstream of the turbocharger and downstream of an exhaust gas receiver (3) . The exhaust gas receiver (3) is connected to the individual cylinders (1) via respective exhaust ducts (35) that introduce the exhaust gas tangentially and cause a swirl in the exhaust gas inside the exhaust gas receiver (3) . The exhaust gas receiver (3) is provided with an outlet (33) . A unit (42) with plurality of vanes (43) around a central axial duct (47) divides the exhausts gas receiver (3) in a mixing section (48) downstream of the unit and an outlet section (49) upstream of the unit (42) The swirling exhaust gas passes along the vanes (43) on its way from the inixing section (48) to the outlet section (49) and the vanes (43) cause the exhaust gas to lose its swirl and gain pressure. The pressure gain causes a portion of the exhaust gas in the outlet section (49) to flow back to the mixing section (48) via said central duct (47) . The reductant is introduced in the flow in said central duct 47) . A large turbocharged two-stroke diesel engine with an exhaust gas receiver (3) with tangential inlets (35) and a tangential outlet (39) is also disclosed It is suggested that Fig. 4 is published with the abstract.

Description

i DK 177462 B1

A LARGE TURBOCHARGED TWO-STOKE DIESEL ENGINE WITH EXHAUST GAS PURIFICATION

FIELD OF THE INVENTION 5

The present invention relates to a large turbocharged two-stroke internal combustion piston engine of the crosshead type, preferably a diesel engine with an exhaust gas purification system, in particularly to a 10 large two-stroke diesel engine of the crosshead type with a SCR (Selective Catalytic Reduction) reactor for purifying exhaust gas from NOx.

BACKGROUND ART 15

Large two-stroke engines of the crosshead type are typically used in propulsion systems of large ships or as prime mover in power plants. Emission requirements have been and will be increasingly difficult to meet, in 20 particular with respect to nitrogen oxides (NOx) levels.

General awareness of environmental issues is increasing rapidly. Within the IMO (International Maritime Organisation) there are now discussions of emission 25 limitations in the form of air pollution at sea. Authorities in various parts of the world are taking similar steps. An example is the proposed EPA (US -Environmental Protection Agency) rules currently under discussion.

30 NOx in the exhaust gas can be reduced with primary and/or secondary reduction methods. Primary methods are methods that affect the engine combustion process directly. The actual degree of reduction depends on engine type and 2 DK 177462 B1 reduction method, but varies from 10% to more than 80%. Secondary methods are means of reducing the emission level without changing the engine performance from its fuel optimized setting, using equipment that does not 5 form part of the engine itself. The most successful secondary method so far is the SCR (Selective Catalytic Reduction) method of removing NO*. This method makes it possible to reduce the NO* level by more than 95% by adding ammonia or urea to the exhaust gas before it 10 enters a catalytic converter.

The SCR reactor contains several layers of catalyst. The catalyst volume and, consequently, the size of the reactor depend on the activity of the catalyst and the 15 desired degree of NO* reduction required. The catalyst has typically a monolithic structure, which means that it consists of blocks of catalyst with a large number of parallel channels, the walls of which are catalytically active.

20

The exhaust gas must have a temperature of at least 280-350°C, depending on fuel sulphur content, i.e. high sulphur content requires high temperatures and low sulphur content requires less high temperatures, at the 25 inlet of the SCR reactor for an effective conversion of NO* into N2 and H2O.

The exhaust gas at the high pressure side of the turbine of the turbocharger have a temperature of approximately 30 350-450°C, whilst the exhaust gas at the low pressure side of the turbine of the turbocharger typically have a temperature of approximately 250-300°C.

3 DK 177462 B1 ! Consequently, it is advantageous to fit the SCR reactor at the high pressure side of the turbine of the turbocharger. However, there have been a lot of

complications associated with the construction of SCR

5 reactors at the high pressure side of the turbine due to the fact that these reactors include very large pipes and containers that have to be able to resist a pressure of approximately 4 bar and are exposed to temperature changes between approximately 20 and 400°C. Heat 10 expansion and fixation have caused great design problems.

Typically, the reductant is injected and atomized at a position in the exhaust gas system upstream of the SCR reactor. The present invention deals with the problem of 15 mixing ammonia into exhaust gas to obtain a uniform mixing, while minimizing costs (in terms of pressure drop). The reductant is typically ammonia, which is obtained from injected urea as it evaporates and decomposes. This process needs time, and during 20 evaporation, contact with exhaust gas system walls should be avoided not to have deposition. The correct addition of a reductant such as ammonia or urea is critical since contact of liquid reductant with the walls of the exhaust gas system could cause undesirable deposition of the 25 reductant on the inner walls of the exhaust gas system.

On this background it has been proposed to provide SCR systems with sophisticated and thus expensive spray systems for homogeneous distribution of ammonia or urea 30 across the exhaust gas stream, and - in order to ensure sufficient mixing downstream - use dedicated so-called mixing units that typically are rather bulky. Further the mixing units contribute to the overall head loss (pressure loss) of the exhaust system, being equivalent 4 DK 177462 B1 to a decrease in turbocharger efficiency. In particular this loss in efficiency of the turbocharger is unacceptable from a fuel efficiency perspective. Further, this pressure loss limits the applicability of power 5 turbines driven by an exhaust gas bypass stream (Waste heat recovery - WHR).

DISCLOSURE OF THE INVENTION

10 On this background, it is an object of the present application to provide an engine with an SCR reactor that overcomes or at least reduces the problems indicated above.

15 This object is achieved by providing a large turbocharged two stoke diesel engine of the uniflow type with crossheads, the engine comprising a plurality of cylinders in line, a turbocharger having an exhaust gas-driven turbine and a compressor driven by the turbine for 20 supplying charging air to the engine cylinders, an elongated cylindrical exhaust gas receiver extending along the cylinders and connected to the cylinders via individual exhaust ducts that direct the exhaust gas coming from the cylinders tangentially into the 25 cylindrical exhaust gas receiver for causing a swirl in the exhaust gas in the exhaust gas receiver, a unit with a plurality of vanes arranged around a central and axial duct in the unit, the unit is placed in the exhaust gas receiver at a position downstream of the exhaust gas 30 ducts and the unit divides the exhaust gas receiver longitudinally into a mixing section at the longitudinal side of the unit where the exhaust gas ducts are located and an outlet section other longitudinal side of the unit, the outlet section including an outlet connected to 5 DK 177462 B1 an inlet of a selective catalytic reduction reactor that is external to the exhaust gas receiver, an outlet of the selective catalytic reduction reactor is connected to the inlet of the turbine of the turbocharger, the unit is 5 arranged such that the swirling exhaust gas flows along the vanes on its way from the mixing section to the outlet section, the unit is further configured to cause the exhaust gas passing along the vanes from the mixing area to the outlet area to lose its swirl and to gain 10 pressure, the pressure gain causing a portion of the exhaust gas that has passed along the vanes to flow back from the outlet area to the mixing area via the axial duct, whereby the other portion the exhaust gas that has passed along the vanes flows from the outlet area via the 15 outlet to the external selective catalytic reduction reactor, a source of reductant that is to be added to the exhaust gas at a reductant introduction point, the reductant introduction point being located in the axial duct, so that the reductant is allowed to mix with the 20 portion of exhaust gas flowing back from the outlet section to the mixing section.

By injecting the reductant in a central duct that is separated from the swirling flow in the exhaust gas 25 receiver the reductant evaporates before it can come into contact with a wall of the exhaust gas receiver.

According to an embodiment, the exhaust gas that has flowed back through the axial duct and to which reductant 30 has been added is allowed to mix with the swirling exhaust gas in the mixing section.

According to another embodiment, the axial duct extends axially into the mixing section.

6 DK 177462 B1

According to another embodiment, the axial duct is part of a concentric tube that extends into the mixing section with the exhaust gas swirling around the concentric tube.

5 Preferably, the tube is long enough to let the reductant evaporate before it leaves the tube.

According to another embodiment, the flow of exhaust gas in the concentric tube is non-swirling. io

According to another embodiment, the vanes are radially extending from the duct to the inner wall of the exhaust gas receiver.

i5 According to another embodiment, the vanes comprise an upstream curved section and a downstream straight section.

According to another embodiment, the blades are 20 configured to cause the swirling exhaust gas flowing past the blades to lose its swirl and gain pressure.

According to an embodiment the engine is provided with two or more exhaust gas receivers in line.

25

According to an embodiment the exhaust gas receiver comprises a bypass outlet that connects the mixing section to a bypass conduit that connects to the turbine of the turbocharger.

30

The object above is also achieved by providing an exhaust gas receiver for a large turbocharged two stoke diesel engine of the uniflow type with crossheads, the exhaust gas receiver comprising an elongated cylindrical exhaust DK 177462 B1 gas receiver housing, individual openings distributed along a portion of the length of the exhaust gas receiver for tangentially receiving exhaust gas from the cylinders of the engine, thereby causing a swirl in the 5 exhaust gas inside the exhaust gas receiver, a unit with a plurality of vanes arranged around a central and axial duct in the unit, the unit is placed in the exhaust gas receiver at a position downstream of the openings and the unit divides the exhaust gas receiver longitudinally into 10 a mixing section at the longitudinal side of the unit where the exhaust gas ducts are located and an outlet section other longitudinal side of the unit, the outlet section including an outlet to the exterior of the exhaust gas receiver, the unit is arranged such that the 15 swirling exhaust gas flows along the vanes on its way from the mixing section to the outlet section, the unit is further configured to cause the exhaust gas passing along the vanes from the mixing area to the outlet area to lose its swirl and to gain pressure, the pressure gain 20 causing a portion of the exhaust gas that has passed along the vanes to flow back from the outlet area to the mixing area via the axial duct, whereby the other portion the exhaust gas that has passed along the vanes flows leaves the outlet area via the outlet, a reductant 25 introduction point, the reductant introduction point being located in the axial duct, so that the reductant is allowed to mix with the exhaust gas flowing back from the outlet section to the mixing section.

30 By injecting the reductant in a central duct that is separated from the turbulent flow in the exhaust gas receiver the reductant evaporates before it can come into contact with a wall of the exhaust gas receiver.

8 DK 177462 B1

It is another object of the invention to provide an exhaust gas receiver that reduces energy losses in the flow of exhaust gas through the exhaust gas receiver.

This object is achieved by providing a large turbocharged 5 two stoke diesel engine of the uniflow type with crossheads, the engine comprising a plurality of cylinders in line, a turbocharger having an exhaust gas-driven turbine and a compressor driven by the turbine for supplying charging air to the engine cylinders, an 10 elongated cylindrical exhaust gas receiver extending along the cylinders and connected to the cylinders via individual exhaust ducts, whereby the interior of the exhaust gas receiver is configured such are no obstacles to flow inside the exhaust gas receiver, the individual 15 exhaust ducts being configured to direct the exhaust gas coming from the cylinders tangentially into the cylindrical exhaust gas receiver for causing a swirl in the exhaust gas in the exhaust gas receiver, a tangentially directed outlet connected to a conduit that 20 leads to the turbine of the turbocharger.

By providing tangential inlets to the exhaust gas receiver, that allow in the exhaust gas to make a swirling movement towards the outlet, and by arranging a 25 tangential outlet the exhaust gas flow can pass through the exhaust gas receiver with a minimum loss of energy in.

In an embodiment the tangentially directed outlet, is 30 placed and configured to allow the swirling exhaust gas to leave the exhaust gas receiver with a minimum change in flow direction.

9 DK 177462 B1

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

5

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, the invention will be explained in more lO 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, 15 Fig. 2 is a side view of the large two stroke engine of Fig. 1,

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

Fig. 4 is a sectional view of the exhaust gas receiver of 20 the large two stroke engine of fig. 1,

Fig. 5 is a cross-sectional view along the line V-V' in Fig. 4,

Fig. 6 is an elevated and transparent view of the exhaust gas receiver of Fig. 4, 25 Fig. 7 is a sectional view of an exhaust gas receiver according to another exemplary embodiment,

Fig. 8 is a sectional view of another embodiment of an exhaust gas receiver of a large two stroke engine,

Fig. 9 is a cross-sectional view along the line IX-IX' in 30 Fig. 8,

Fig. 10 is a sectional view of another embodiment of an exhaust gas receiver of a large two stroke engine, and Fig. 11 is a cross-sectional view along the line XI-XI' in Fig. 10.

10 DK 177462 B1

I DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following detailed description, the large two 5 stroke engine will be described by the exemplary embodiments. Figures 1 to 3 show a large low speed turbocharged two-stroke diesel engine with a crankshaft 52 and crossheads 43. Figure 3 shows a diagrammatic representation of a large low speed turbocharged two-10 stroke diesel engine with its intake and exhaust systems.

In this exemplary 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 an engine frame 45. The engine may e.g.

15 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.

20 The engine is of the two-stroke uniflow type with scavenge ports at the lower region of the cylinders 1 and an exhaust valve 4 at the top of the cylinders 1. The charging air is passed from the charging air receiver 2 to the scavenging air ports (not shown) of the individual 25 cylinders 1. A piston 51 in the cylinder 1 compresses the charging 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 35 associated with the cylinder 1 concerned into the exhaust 30 gas receiver 3 and onwards through a first exhaust conduit 18 that includes an SCR reactor 19 to a turbine 6 of the turbocharger 5, from which the exhaust gas flows away through a second exhaust conduit 7. Through a shaft 8, the turbine 6 drives a compressor 9 supplied via an 11 DK 177462 B1 air inlet 10. The compressor 9 delivers pressurized charging air to a charging air conduit 11 leading to the charging air receiver 2.

5 The intake air in the conduit 11 passes through an intercooler 12 for cooling the charging air - that leaves the compressor at approximately 200 'C - to a temperature between 36 and 80 ’C.

10 The cooled charging 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 15 scavenging air and then the auxiliary blower 16 is bypassed via a non-return valve 15.

Fig. 3 shows the SCR system layout. The system comprises a Selective Catalytic Reduction (SCR) reactor 19. A 20 reductant, such as ammonia or urea is added to the exhaust gas before it enters the SCR reactor 19. The exhaust gas must be mixed with a reductant such as ammonia, before passing through the SCR reactor 19, and in order to encourage the chemical reaction in the SCR 25 reactor 19 the temperature level has to be between 200 and 400 °C, depending on the sulfur content of the exhaust gas. In the present embodiment the source of ammonia is a water based urea solution.

30 In the embodiment shown in figure 3 a tank 26 contains an aqueous urea solution. A conduit 25 connects the tank 26 with the inlet of a pump 24. The pump 24 is configured to provide a substantially constant pressure. The outlet of the pump 24 is connected to a feed conduit 22 that 12 DK 177462 B1 — delivers the pressurized aqueous urea solution via an electronic control valve 23 to an injection valve 21 (see Fig 4). The electronic control valve 23 is in the present embodiment of the on/off type, but a proportional valve 5 could also be used. The electronic control valve 23 is controlled by a signal from an electronic control unit (process computer) 50. The electronic control valve 23 can be a hydraulically or pneumatically actuated valve, or a purely electrically actuated valve. The injection 10 valve 21 is mounted inside the exhaust gas receiver 3 and the injection valve 21 is provided with a nozzle with nozzle holes for atomizing the aqueous urea solution when it is injected into the exhaust gas receiver 3. The injection valve 21 is configured to initiate an injection 15 event only when a pressure threshold is exceeded so as to ensure that the injection only takes place when there is sufficient pressure for atomizing the aqueous urea solution. A NOx and 02 analyzer 32 is connected to the second exhaust conduit 7 and the result of the analysis 20 is sent as a signal to the electronic control unit 50.

The sensor 32 could also measure the NOx content in the exhaust gas in conduit 18 upstream of the SCR reactor 19 or downstream of the SCR reactor but upstream of the turbocharger turbine 6.

25

The amount of reductant injected into the exhaust gas is controlled by the electronic control unit 50 and is based on the NOx production for the actual running conditions (load) derived from the NOx production at different 30 running conditions (loads) measured during test bed running of the engine. The amount of reductant injected into the exhaust gas is also based on the signal from the NOx and 02 analyzer 32 or on both an experience table and on the signal from sensor 32. The timing of the injection 13 DK 177462 B1 the reductant is done without considering the actual position of the crankshaft 52 of the engine since this is not necessary as there will always be an exhaust gas jet from an exhaust duct 35 for the mixing of the reductant 5 with the exhaust gas on the path of the reductant from the injection point to the outlet 33.

Referring now to Figures 4, 5 and 6, the construction of the elongated cylindrical exhaust gas receiver 3 and the 10 reductant introduction system are described in greater detail with reference to an exemplary embodiment. The exhaust gas receiver 3 is a large elongated cylindrical receiver with a large cross-sectional area, i.e. the exhaust gas receiver can be up to approximately 10 meter 15 long and have a diameter of up to 1 -2 meter.

The exhaust gas receiver 3 extends along the cylinders 1 in relatively close proximity thereto, near the top of the cylinders 1 where the exhaust valve 4 and the exhaust 20 ducts 35 are located. The exhaust ducts 35 open into the exhaust gas receiver 3. In many engines the exhaust gas receiver 3 extends along all of the cylinders 1 of the in line engine. However, it is also common to split the exhaust gas receiver 3 lengthwise in two or more 25 sections, for example for very larges engines with a high number of cylinders so that the size the exhaust gas receiver 3 does not exceed the dimensions that can be handled by production facilities. Another reason to split the exhaust gas receiver 3 lengthwise in several parts 30 can be the presence of a plurality of turbochargers 5, with each a section of the divided exhaust gas receiver 3 associated with a single turbocharger 5.

14 DK 177462 B1

Typically the cross-sectional area of the exhaust gas receiver 3 is equal to or larger than the cross-sectional area of a piston 51 of the engine. The resulting large volume of the exhaust gas receiver 3 ensures damping of 5 the pressure pulses generated by the exhaust gas jets coming from the exhaust ducts 35 of the individual cylinders 1 when the exhaust valve 4 associated with the cylinders concerned 1 opens.

10 The elongated exhaust gas receiver 3 is provided with an outlet 33 that connects to conduit 18 and the SCR reactor 19 and allows the exhaust gas collected in the exhaust gas receiver 3 to flow to the turbine 6 of the turbocharger 5 via the SCR reactor 19. In the present 15 embodiment the outlet 33 is located at one of the longitudinal ends of the exhaust gas receiver 3, so the main direction of the flow inside the exhaust gas receiver 3 is in one direction: towards the outlet 33.

20 The cylinders 1 of the engine fire individually in a predetermined firing sequence. Accordingly, the exhaust valves 4 also open in the same sequence and the high speed exhaust gas jets (initially over 100 m/s later in the exhaust valve opening phase slowing down) coming from 25 the exhaust ducts 35 enter the exhaust gas receiver 3 in the same sequence.

The exhaust ducts 35 are directed tangentially relative to the cylindrical exhausts gas receiver, so that the 30 exhaust gas (pulses) coming from the cylinders 1 enters the exhaust gas receiver 3 tangentially and causes a swirl or swirling motion of the exhaust gas in the exhaust gas receiver. The swirl takes place whilst the 15 DK 177462 B1 exhaust gas moves towards the outlet 33, and the swirl is indicated by the arrows in Fig. 5.

Δ unit 42 is placed in the exhaust gas receiver 3 at a 5 position downstream of the exhaust gas ducts 35 and the unit 42 divides the exhaust gas receiver 3 longitudinally into a mixing section 48 upstream of the unit 42 and an outlet section 49 downstream of the unit 42. The unit has an overall shape of a thick disk or ring with a diameter 10 that corresponds to the inner diameter of the exhaust gas receiver 3, The unit 42 is provided with a plurality of vanes 43 arranged around a central and axial duct 47 in the unit 42. The vanes extend radially from the duct into the outer area of the unit 42 and to the inner wall of 15 the exhaust gas receiver 3. The radially outer area of the unit forms a vane filled passage for the exhaust gas.

The vanes or blades 43 have a curved upstream section and a straight downstream section. The curved upstream section is at the end of the vane 43 nearest to the 20 mixing section 48 and receives the swirling exhaust gas and converts the swirling component of the exhaust gas into a pressure gain. The straight downstream section extends from the curved upstream section to the end of the vane 43 that is nearest to the mixing section 48.

25 The straight section stabilizes the direction of the flow of the exhaust gas into the outlet section 49 in a straight and non-swirling flow. Other shapes and arrangements of vanes or blades or the like can also be used as long as these shapes and arrangements are 30 configured to cause the swirling exhaust gas flowing through the radially outer section of the unit 42 to lose its swirl and gain pressure.

16 DK 177462 B1

The inner area of the unit is formed by the duct 47. In this embodiment the duct 47 is formed by a tube 40 and a reductant introduction point in the form of an injection nozzle 21 is placed in the duct 47, or slightly further 5 down in the tube 40. The axial duct 47 extends axially into the mixing section and extends over most of the length of the mixing section 48. The axial duct is part of a concentric tube 40 that extends into the mixing section 48 with the exhaust gas swirling around the 10 concentric tube 40. The proximate end of the tube 40 is formed by the duct 47 in the unit 42 and constitutes the inlet of the tube 40. The distal end of the tube 40 is open and spaced from the longitudinal end of the exhaust gas receiver 3 and constitutes the outlet of the tube 40.

15

The outlet section 49 of the exhaust gas receiver 3 includes an outlet 33 that is connected to the inlet of the selective catalytic reduction reactor 19 via conduit 18.

20

In operation, the exhaust gas coming from the cylinders 1 via the individual exhaust ducts 35 make a swirling movement around the tube 40 and towards unit 42. The unit 42 is arranged such that the swirling exhaust gas flows 25 along the vanes 43 in the radially outer section of the unit on its way from the mixing section 48 to the outlet section 49. In this process the exhaust gas loses its swirl and the exhaust gas gains pressure, i.e. the swirl component of the exhaust gas is converted to a pressure 30 gain in the exhaust gas. The pressure of the exhaust gas leaving the radially outer section of the unit 42 is higher than the pressure of the exhaust gas entering the radially outer section of the unit 42. Thus, also the pressure of the exhaust gas near the outlet of the tube 17 DK 177462 B1 40 is lower than the pressure of the exhaust gas leaving the radially outer section of the unit 42. Consequently, the pressure at the inlet of the tube 40 is higher than the pressure at the outlet of the tube and this pressure 5 difference will cause a flow of exhaust gas from the mixing section 48 through the duct 47 and tube 40 to the mixing section.

The mixing unit and the exhaust gas receiver are 10 configured such that the flow through the tube 40 back to the mixing section 48 is relatively slow non-swirling. Further, the mixing unit and the exhaust gas receiver are configured such that only a minor portion of the exhaust gas leaving the radially outer section of the unit 42 is 15 transported back to the mixing section 48.

Due to the addition of the unit 42 and the outlet chamber 49 the overall length of the exhaust gas receiver 3 is increased relative to a conventional exhaust gas 20 receiver.

In operation, the reductant is injected via the injection valve 21 with nozzle into the laminar flow in duct 47/tube 40 so that the reductant is allowed to mix with 25 the exhaust gas flowing back from the outlet section 49 to the mixing section 48. The non-swirling flow ensures that the reductant does not come into contact with the inner walls of the tube 40 and the reductant, for example urea, has time enough to evaporate and decompose before 30 it can come into contact with any wall of the exhaust gas receiver so there is less risk for deposit of reductant.

If the reductant is urea, the high temperature of the exhaust gas in the tube 40 causes the urea to be hydrolyzed (thermal decomposition) into ammonia gas and 18 DK 177462 B1 the watery part of the injected aqueous urea solution ! will evaporate.

To further assure that the flow in the duct 47/tube 40 is 5 non-swirling, guiding vanes can be provided near the position where reductant is injected. Preferably the guiding vanes are straight and extend axially in the tube 40. The axial length of the guiding vanes is in an embodiment approximately equal to the diameter of tube 10 40.

The reductant introduction point is in this embodiment the injection valve 21, which is located in the duct 47.

The aqueous urea solution is injected into the duct 47 in the form of a spray or jets from the holes in nozzle of 15 the injection valve 21. The vaporized aqueous urea solution enters the exhaust gas receiver 3 at the start of the tube 48. From this point the vaporized aqueous urea solution is transported in the main direction of the laminar flow in the tube 48.

20

When the exhaust gas with the added reductant leaves the tube 40 it is allowed to mix with the swirling exhaust gas in said mixing section 48. Thus, the reductant is present in the swirling exhaust gas and most of the 25 exhaust gas properly mixed with the reductant will flow from the outlet section 49 via the outlet 33 to the inlet of the SCR reactor 19. The exhaust gas properly mixed with the reductant flows through the SCR reactor 19 to the outlet of the SCR reactor 19. During this process the 30 NOx is reduced to N2 and water with the help of the reductant. From the outlet of the SCR reactor 19 the exhaust gas with a reduced NOx amount flows to the inlet of the turbine 6 of the turbocharger 5 and from there to the second exhaust conduit 7. The second exhaust conduit 19 DK 177462 B1 7 leads the exhaust gas from the outlet of the turbine 6 to the inlet of a silencer 28. A third exhaust conduit 29 leads the exhaust gas from the outlet of the silencer 28 to the atmosphere.

5

The reductant (aqueous urea solution) can be injected as a steady stream. Alternatively, the reductant can be injected or intermittently since there is ample time and opportunity for the injected reductant to mix and be 10 evenly distributed with the exhaust gas in the exhaust gas receiver 3. Thus, the timing of the injection of the reductant is not critical. This allows the use of a dosage dosing system that is based on timing, in the present embodiment by the electronic control unit 50 15 controlling the opening time of the electronic control valve 23. Thus, a relatively simple, accurate and reliable dosing system is provided since timing control is an accurate process over a wide range of delivery rates. The fact that a single reductant introduction 20 point suffices further simplifies the system.

The fact that the reductant dosing can be controlled by timing makes it easy to provide a system that can maintain a substantially constant pressure for the 25 injection event and thereby ensure that the reductant is properly atomized with each injection event.

Alternatively, the reductant dosage system could operate with a steady stream with the control performed by 30 regulating the injection pressure, or/and by selectively activating a number of nozzle from a plurality of nozzles.

20 DK 177462 B1

The diameter of the duct 47 and the length of the tube 40 can be adapted according to need and circumstances. In an embodiment the tube can be very short or altogether omitted so that the duct only extends axially over the 5 thickness of the unit 42. The effect of the swirl in the mixing section 48 provides for a concentric area in the middle of the mixing section 48 with relatively low pressure and calm flow, which will give the reductant a calm environment distant from any walls for evaporating 10 and hydrolyzing. The flow in the central pipe 40 could be adjusted by a restrictor, e.g. near the outlet of the tube.

Instead of one injection vale 21/nozzle a plurality of 15 valves and/or nozzles can be used.

Figure 7 shows another exemplary embodiment. This embodiment is essentially identical to the embodiment of figure 4. However, in this embodiment the exhaust gas 20 receiver 3 is provided with two outlets 33, one at each longitudinal end. Accordingly, the exhaust gas receiver has two outlet chambers 49 at opposite longitudinal ends of the exhaust gas receiver with one mixing chamber 48 and two units 42 therebetween. Otherwise, operation and 25 construction is identical to the embodiment of Fig. 4.

The embodiment of Fig. 7 is particularly useful for engines with a large number of cylinders in line, e.g. more than 5 cylinders that have more than one turbocharger 5, e.g. with a turbocharger associated with 30 each outlet 33. Such an engine would also have two SCR units 19, one between each outlet 33 and turbocharger 5.

Fig. 8 (in combination with Fig. 3 - interrupted line) shows another exemplary embodiment. This exemplary 21 DK 177462 B1 embodiment is essentially identical to the embodiment of Figs 4 to 6, except that an SCR bypass outlet 36 and an SCR bypass valve 37 in the bypass outlet 39 have been added. The bypass outlet 39 is connected to the mixing 5 section 48 and connects directly to the inlet of the turbine 6 turbocharger 5 via a bypass conduit 38 in order to bypass the SCR 19. The bypass outlet 36, the bypass valve 37 under control of the electronic control unit 50 and the bypass conduit 38 allow the exhaust gas to bypass

10 the SCR unit. This bypass valve 37 is closed when the SCR

19 is engaged. SCR is typically only be used in regions where it is required by law. When the SCR 19 is not in use, it is beneficial (less pressure loss, lower specific fuel consumption, etc.) to directly lead the exhaust gas 15 to the turbo charger 5. When the SCR 19 is to be engaged, it is necessary to slowly warm up the SCR 19 by slowly closing the bypass valve 37 (during an hour, or so) . The bypass pipe acts as a tangentially directed outlet, and it is is placed and configured to allow the swirling 20 exhaust gas to leave the exhaust gas receiver 3 with a minimum change in flow direction. The tangential entry of the exhaust gas into the exhaust gas receiver 3 combined with the tangential exit of the exhaust gas from the exhaust gas receiver in when the SCR is not engaged 25 provides for low energy losses in the exhaust gas when it passes the exhaust gas receiver. Thus, the amount of energy available for the turbine of the turbocharger is possibly higher than in conventional exhaust gas receivers.

30

Figs. 10 and 11 show another exemplary embodiment of an exhaust gas receiver for a large two stroke diesel engine. This embodiment is different from the embodiments described above, in that the exhaust gas receiver 3 is 22 DK 177462 B1 not provided with means for admixing a reductant, although some form of admixing system could be included.

In this embodiment the exhaust gas receiver 3 Is placed along the cylinders 1 of the large turbocharged two-stoke 5 diesel engine like in the embodiments above, connected to the cylinders 1 via individual exhaust ducts 35. The individual exhaust ducts 35 are configured to direct the exhaust gas coming from the cylinders 1 tangentially into the cylindrical exhaust gas receiver 3 for causing a 10 swirl in the exhaust gas in the exhaust gas receiver 3.

The exhaust gas receiver 3 is optimized for minimizing energy losses and there are no obstacles to flow in the exhaust gas receiver 3. Further, the outlet 36 is tangentially directed so that the swirling exhaust gas 15 can leave the exhaust gas receiver with a minimum of energy loss. The outlet 36 is connected to a conduit that leads to the turbine 6 of the turbocharger 5. The tangentially directed outlet 36, is placed and configured to allow the swirling exhaust gas to leave the exhaust 20 gas receiver 3 with a minimum change in flow direction.

Thus, the energy in the exhaust gas the leaving the exhaust gas receiver is high and a higher amount of energy can be delivered to the turbine of a turbocharger of the engine in which the exhaust gas receiver is used.

25

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 single processor or other unit may fulfill the functions 30 of several means recited in the claims.

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

23 DK 177462 B1

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 5 departing from the scope of the invention. For example it can also be practiced on a large two stroke engine that uses exhaust gas recirculation.

Claims

A large long-stroke turbocharged two-stroke diesel engine with cross heads (53), comprising: 10 a plurality of cylinders (1) in line, a turbocharger (5) with an exhaust gas turbine (6), and a compressor ( 9) driven by the turbine (6) for supplying charge air to the engine cylinders (1), an elongated cylindrical exhaust gas receiver (3) extending along the cylinders (1) and connected to the cylinders (1) via individual exhaust channels (35) directing the exhaust gas coming from the cylinders (1) 20 tangentially into the cylindrical exhaust gas receiver (3) to effect an exhaust gas vortex in the exhaust gas receiver (3); ) having a plurality of blades (43) provided about a central and axial duct (47) of the unit (42), which unit (42) is located in the exhaust gas receiver (3) in a position on the downstream side of the 30 ducts for exhaust gas (35) and which unit (42) divides the receiver into u longitudinal exhaust gas (3) in a mixing section (48) on the longitudinal side of the unit (42) where the exhaust gas ducts (35) are positioned and in an outlet section (49) on the other longitudinal side of the unit (42), said output section (49) including an output (33) associated with an input to a selective catalytic reduction reactor (19) external to the exhaust gas receiver, an output of the selective catalytic reduction reactor W is connected to the inlet of the turbocharger (5) to the turbine (6), which unit (42) is provided such that the swirling exhaust gas flows along the blades (43) on its path from the mixing section (48) to the outlet section (49), (42) is further designed to cause the exhaust gas to pass along the blades (43) from the mixing region to the outlet area to lose its vortex and to obtain a greater pressure, which pressure increase causes a portion of the exhaust gas the passage passed along the blades (43) flows back from the exit area to the mixing region (48) via the axial channel (47), whereby the second portion of the exhaust gas passed along the blades (43) flows from the exit area via the exit ( 33) to the external selective catalytic reduction reactor (19), a source (26) of reducing agent to be added to the exhaust gas at a reducing point supply point, which reducing point supply point is in the axial channel (47) so that the reducing agent can mix with the part of

An engine according to claim 1, wherein the exhaust gas flowed back through the axial duct (47) and to which reducing agent is added can be mixed with the swirling exhaust gas in the mixing section (48).

The motor of claim 1, wherein the axial channel (47) 10 extends axially into the mixing section.

3 DK 177462 B1 exhaust gas flowing back from the outlet section (49) to the mixing section (48) -

The engine of claim 3, wherein the axial duct is a portion of a concentric tube (40) extending into the mixing section (48) with the exhaust gas swirling about the concentric tube (40).

The engine of claim 3, wherein the flow of exhaust gas into the concentric tube (40) is non-swirling.

The engine of claim 1, wherein the blades (43) extend radially from the channel (47) to the inner wall of the exhaust gas receiver (3).

The motor of claim 6, wherein the blades comprise a curved section on the upstream side and a straight section on the downstream side.

The engine of claim 1, wherein the blades (43) are designed to cause the swirling exhaust gas to flow past the blades (43) to lose its swirl and achieve greater pressure.

The engine of claim 1, comprising two or more exhaust gas receivers (3) in line. 4 DK 177462 B1

The engine of claim 1, wherein the exhaust gas receiver (3) comprises a bypass outlet (36) connecting the mixing section (48) to a bypass duct (38) connected to the turbine (6) of the turbocharger (5).

Exhaust gas receiver (3) for a large, long-head turbocharged two-stroke diesel engine with cross heads (53), comprising exhaust gas receiver (3) 10: an oblong cylindrical exhaust gas housing housing with individual openings distributed along a portion of the length of the exhaust gas receiver (3) for tangentially receiving exhaust gas from the engine cylinders (1), causing a vortex in the exhaust gas inside the exhaust gas receiver (3), a unit (42) having a plurality of blades (43), there is provided about a central and axial duct (47) in the unit (42), which unit (42) is located in the exhaust gas receiver (3) in a position on the downstream side of the 25 openings, and which unit (42) divides the receiver for longitudinal exhaust gas (3) in a mixing section (48) on the longitudinal side of the unit (42) where the exhaust gas channels (35) are located, and in an outlet section (49) on another longitudinal side of the unit (42). ), which ones An outlet section (49) includes an outlet (33) for the exterior of the exhaust gas receiver (3), which unit (42) is provided such that the swirling exhaust gas flows along the blades (43) on its way from the mixing section (48) for the outlet section 5 (49), which unit (42) is further designed to cause the exhaust gas to pass along the blades (43) from the mixing region to the outlet area to lose its 10 swirl and obtain a greater pressure, which increases the pressure, a portion of the exhaust gas passed along the blades (43) flows back from the exit area to the mixing region (48) via the axial channel (47), leaving the other portion of the exhaust gas passed along the blades (43) the outlet area via the outlet (33), a reducing point supply point, which reducing point supply point is in the 20 axial channel (47) so that the reduction nozzle can be mixed with the exhaust gas which drums back from the starting section to the mixing section (48).

A large 25-length turbocharged two-stroke turbocharged diesel engine with cross heads (53), comprising: a plurality of cylinders (1) in line, a turbocharger (5) with an exhaust gas turbine (6), and a compressor (9) driven by the turbine, (6) for supplying charge air to the engine cylinders (1), c an oblong cylindrical exhaust gas receiver (3) extending along the cylinders (1) and connected to the cylinders (1). 1) via individual exhaust ducts (35), whereby the interior of the exhaust gas receiver (3) is formed such that there are no obstacles to flow inside the exhaust gas receiver 3, which individual exhaust ducts (35) are designed to direct the exhaust gas coming from the cylinders (1) tangentially into the cylindrical exhaust gas receiver 10 (3) to effect a vortex in the exhaust gas of the exhaust gas receiver (3), a tangentially oriented outlet (39) connected to a duct , as before is to turbocharger 15 (6) of turbocharger (5).

The engine of claim 12, wherein the tangentially oriented output is positioned and configured to allow the swirling exhaust gas to exit the exhaust gas receiver 20 (3) with a minimal change in flow direction.