DK201500354A1

DK201500354A1 - Large two-stroke turbocharged compression ignited internal combustion engine with an exhaust gas purification system

Info

Publication number: DK201500354A1
Application number: DKPA201500354A
Authority: DK
Inventors: Peter Skjoldager
Original assignee: Man Diesel & Turbo Filial Af Man Diesel & Turbo Se Tyskland
Priority date: 2015-06-19
Filing date: 2015-06-19
Publication date: 2017-01-16
Also published as: KR101845487B1; DK178781B1; KR20160150056A; JP6235653B2; CN106050400A; JP2017008932A

Abstract

A large turbocharged two-stroke compression ignited internal combustion engine of the crosshead type with a turbocharger with an exhaust gas driven turbine connected to a compressor for delivering pressurized scavenge air, a plurality of cylinders connected to a scavenge air receiver and to an exhaust gas receiver, a selective catalytic reduction reactor with an inlet connected to an outlet of the exhaust gas receiver, an exhaust conduit connecting an outlet of the selective catalytic reduction reactor to an inlet of the turbine, a scavenge air conduit connecting an outlet of the compressor to an inlet of the scavenge air receiver via a scavenge air cooler, an auxiliary blower in the scavenge air conduit for assisting the compressor at low load conditions of the engine, a controllable by pass conduit extending from a position in the scavenge air conduit to a position in the exhaust conduit for bypassing the plurality of cylinders, an electronically controlled bypass blower for assisting a flow of scavenge air from the scavenge air conduit to the exhaust conduit, and an electronic control unit operably connected to the electronically controlled bypass blower, the electronic control unit being configured control the flow of scavenge air from the scavenge air conduit through the controllable bypass conduit to the exhaust conduit.

Description

LARGE TWO-STROKE TURBOCHARGED COMPRESSION IGNITED

INTERNAL COMBUSTION ENGINE WITH AN EXHAUST GAS PURIFICATION SYSTEM

The present invention relates to a large turbocharged two-stroke compression ignited internal combustion engine of crosshead type, preferably an engine with an exhaust gas purification system, in particular a large two-stroke diesel engine of the crosshead type with a selective catalytic reduction reactor.

BACKGROUND ART

Large two-stroke diesel 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 particular with respect to mono-nitrogen oxides (NOx) levels .

Using a selective catalytic reduction (SCR) reactor is a measure that is known to assist in diesel engines to reduce N0X emissions. A minimum temperature of approximately 300 to 350 °C for the exhaust gases entering the SCR converter is required for proper functioning of the SCR reactor.

However, due to the characteristics of the two-stroke turbocharged engine the exhaust gas temperature at low engine load (e.g. lower than 40% of the maximum continuous rating of the engine concerned) is relatively low, i.e. too low for the NOx in the exhaust gas to be converted in the SCR reactor. Thus, measures need to be taken to increase the temperature of the exhaust gas at low engine load conditions in order to ensure NOx removal at low engine load conditions.

At low load conditions it is also difficult to maintain sufficient scavenge pressure in a large turbocharged two-stroke diesel engine. Therefore, an auxiliary blower is used at these low load conditions to maintain the scavenge air pressure. Thus, any measures that are taken to increase the temperature of the exhaust gases at the inlet of the SCR reactor should not have a negative effect on the scavenge air pressure.

There is a need for a large turbocharged two-stroke compression ignited internal combustion engine that overcomes or at least reduces the above mentioned drawbacks .

DISCLOSURE

On this background, it is an object of the present invention to provide a large turbocharged two-stroke compression ignited internal combustion engine that can operate with an SCR reactor at a wide range of engine load conditions .

This object is achieved in accordance with a first aspect by providing a large turbocharged two-stroke compression ignited internal combustion engine of the crosshead type comprising: a turbocharger with an exhaust gas driven turbine connected to a compressor for delivering pressurized scavenge air, a plurality of cylinders connected to a scavenge air receiver and to an exhaust gas receiver, a selective catalytic reduction reactor with an inlet connected to an outlet of the exhaust gas receiver, an exhaust conduit connecting an outlet of the selective catalytic reduction reactor to an inlet of the turbine, a scavenge air conduit connecting an outlet of the compressor to an inlet of the scavenge air receiver via a scavenge air cooler, an auxiliary blower in the scavenge air conduit for assisting the compressor at low load conditions of the engine, a controllable bypass conduit extending from a position in the scavenge air conduit to a position in the exhaust conduit for bypassing the plurality of cylinders, an electronically controlled bypass blower in the controllable bypass conduit for assisting a flow of scavenge air from the scavenge air conduit to the exhaust conduit, and an electronic control unit operably connected to the electronically controlled bypass blower, the electronic control unit being configured control the flow of scavenge air from the scavenge air conduit through the controllable bypass conduit to the exhaust conduit.

At low engine loads the temperature of the exhaust gas entering the selective catalytic reactor is too low for proper conversion the NOx in the exhaust gas. By using a bypass blower in the bypass conduit a controlled flow of scavenge air can be directed from the scavenge air conduit to the exhaust conduit at a position downstream of the selective catalytic reduction reactor and upstream of the turbine of the turbocharger. This measure increases the temperature of the exhaust gases entering the selective catalytic reduction reactor at low engine load conditions, without affecting the scavenge air pressure negatively whilst ensuring removal of NOx from the exhaust gas in the SCR reactor.

In a first implementation of the first aspect the controllable bypass conduit further comprises an electronic control valve controlled by the electronic control unit.

In a second implementation of the first aspect the electronic control unit is configured control the flow of scavenge air from the scavenge air conduit through the controllable bypass conduit to the exhaust conduit to ensure that the temperature of the exhaust gases entering the selective catalytic reduction reactor is above a given threshold.

In a third implementation of the first aspect electronic control unit is configured to activate the bypass blower when the auxiliary blower is active.

In a fourth implementation of the first aspect the electronic control unit is configured to activate the auxiliary blower when the engine load is below a predetermined threshold.

In a fifth implementation of the first aspect the electronic control valve can assume a plurality of positions between a fully closed position and a fully open position, and wherein the electronic control unit is configured to control the flow of scavenge air from the scavenge air conduit through the controllable bypass conduit to the exhaust conduit by adapting the position of the electronic control valve.

In a sixth implementation of the first aspect the engine further comprises a temperature sensor between the outlet of the exhaust gas receiver and the inlet of the selective catalytic reduction reactor, with the electronic control unit being in receipt of a signal from the temperature sensor).

In a seventh implementation of the first aspect the valve is of the proportional type and is preferably controlled in a closed loop by the electronic control unit.

In an eighth implementation of the first aspect the electronic control unit is configured to control the bypass blower in an on/off fashion and configured to adjust the flow of scavenge air through the controllable bypass conduit by a controlling the position of the electronic control valve.

In a ninth implementation of the first aspect the controllable bypass conduit connects to the scavenge air conduit at a position between the compressor and the auxiliary blower.

In tenth implementation of the first aspect the bypass blower is driven by an electric drive motor.

In an eleventh implementation of the first aspect the exhaust conduit includes a three port mixing point for mixing the bypassed scavenge air with the exhaust gas.

In a twelfth implementation of the first aspect the scavenge air cooler can be deactivated by the electronic control unit.

In a thirteenth implementation of the first aspect the electronic control unit is configured establish a flow of scavenge air through the bypass conduit as a first measure, and to deactivate the scavenge air cooler as a second measure.

In a fourteenth implementation of the first aspect the scavenge air cooler can be turned into a heater by the electronic control unit.

In a fifteenth implementation of the first aspect the electronic control unit is configured to turn the scavenge air cooler into a heater as a third measure.

In a sixteenth implementation of the first aspect the controllable bypass conduit extends from a position between the compressor and the auxiliary blower to a position between the outlet of the selective catalytic reduction reactor and the inlet of the turbine in the exhaust conduit.

Further objects, features, advantages and properties of the large turbocharged two-stroke compression ignited internal combustion engine according to the invention 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 diagrammatic view of an engine according to an embodiment of the present invention,

Fig. 2 is a diagrammatic view of an engine according to another embodiment,

Fig. 3 is a diagrammatic view of an engine according to another embodiment,

Fig. 4 is a diagrammatic view of an engine according to another embodiment,

Fig. 5 shows a diagrammatic view of a another embodiment, Figs. 6 to 10 show further embodiments using reduced cooling of the scavenge air, and

Figs. 11 to 15 show further embodiments using active heating of the scavenge air.

DETAILED DESCRIPTION

In the following detailed description of the large turbocharged two-stroke diesel engine of the crosshead type and the method for operating a large turbocharged two-stroke diesel engine of the crosshead type according to the invention will be described by the example embodiments .

The construction and operation of a large turbocharged two-stroke compression ignited internal combustion engine of the cross-head type is as such well-known and should not require further explanation in the present context. Further details regarding the operation of the exhaust gas purification system are provided below.

Fig. 1 shows a diagrammatic depiction of a first example embodiment of a large two-stroke compression ignited internal combustion engine 1 according to the invention. The engine 1 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 1 is provided with a plurality of cylinders arranged besides one another in line. Each cylinder is provided with an exhaust valve associated with their cylinder cover. The exhaust channels can be opened and closed by the exhaust valve. A cross-head of the engine connects the piston rod to a big end of the crankshaft. Exhaust bends connect to an exhaust gas receiver 6. The exhaust gas receiver 6 is disposed in parallel to the row of cylinders. The exhaust gas receiver 6 is a large container with dimensions that are specifically adapted to the characteristics of the engine for optimal gas flow, counter pressure and acoustical considerations. Typically, the exhaust gas receiver 6 is a large hollow cylindrical body made of steel plates. Due to its large size and weight the exhaust gas receiver is suspended from the engine construction with the aim of handling vibration aspects.

From outlet of the exhaust gas receiver 6 the exhaust gas stream is guided towards a turbine 12 of a turbocharger via a selective catalytic reactor 8 (SCR reactor) and from the outlet of the SCR reactor 8 via an exhaust conduit 10 to the turbine 12. Thus, the outlet of the exhaust gas receiver 6 is connected to the inlet of the SCR reactor 8. The exhaust gas flows through the SCR reactor 8 and NOx in the exhaust gas is removed in the SCR reactor or the amount is at least substantially reduced by converting NOx to nitrogen and oxygen. The outlet of the SCR reactor 8 is connected to the exhaust conduit 10 that leads the hot and pressurized exhaust gases to the turbine 12. The exhaust gas is disposed into the atmosphere downstream of the turbine 12.

The turbocharger also includes a compressor 14 driven by the turbine 12. The compressor 14 is connected to an air intake. The compressor 14 delivers pressurized scavenge air to a scavenge air receiver 22 via a scavenge air conduit 16 that includes a scavenge air cooler 18 for cooling the scavenge air and an auxiliary blower 20 for assisting the blower at low engine loads (typically below 40% of the maximum continues rating of the engine 1). The scavenge air cooler 18 is arranged upstream of the auxiliary blower 20.

The scavenge air cooler 18 is operated with water as a cooling medium. The scavenge air cooler 18 can be one of various types. One possibility is a plate cooler in which the cooling medium is not in direct physical contact with the scavenge air. Another possibly is a scrubber, in which the cooling medium is in direct contact with the scavenge air.

The auxiliary blower 20 is typically driven by an electric motor (could also be driven by a hydraulic motor) and kicks in at low load conditions (typically below 40% of the maximum continuous rating) to assist the compressor 14 in maintaining sufficient scavenging pressure. When the auxiliary blower 20 is not used it is bypassed via a not shown bypass. The auxiliary blower 20 is controlled by an electronic control unit 33 and is typically either active or inactive, i.e. the electronic control unit either activates the auxiliary blower 20 (at engine loads below a given first engine load threshold) or deactivates the auxiliary blower 20 (an engine loads above a given second engine load threshold).

The scavenge air receiver 22 is an elongated hollow cylindrical body extending along the cylinders of the engine. The scavenge air is passed from the scavenge air receiver 22 to the scavenge air ports of the individual cylinders and into the combustion chambers in the cylinders . A controllable bypass conduit 26 is branched off from the scavenge air conduit 16. The other end of the controllable bypass conduit 26 is connected to the exhaust conduit 10 at a three port mixing point 30. The mixing point 30 is located downstream of the outlet of the SCR reactor 8 and upstream of the inlet of the turbine 12.

The purpose of the controllable bypass conduit 26 is to provide a flow of scavenge air from the scavenge air conduit 16 to the exhaust conduit 10 that bypasses the cylinders and thereby increases the temperature of the exhaust gas that enters the SCR reactor 8 during low engine load conditions.

During low engine load conditions, e.g. when the auxiliary blower 20 is active, there will typically not be a sufficient pressure drop from the scavenge air conduit 16 to the exhaust conduit 10 to ensure a sufficient flow through the controllable bypass conduit 26. A bypass blower 46 assists the flow of scavenge air through the controllable bypass conduit 26. The bypass blower 46 is driven by e.g. an electric drive motor and the bypass blower 46 is operated under control of the electronic control unit 33. In an embodiment the bypass blower 46 is controlled by the electronic control unit 33 in an on/off fashion, i.e. the electronic control unit 33 either activates the bypass blower 46 or deactivates the bypass blower 46.

An electronic control valve 28 is also used to regulate the flow of scavenge air from the scavenge air conduit 16 via the bypass conduit 16 to the exhaust conduit 10 under command of an electronic control unit 33.

In one embodiment the electronic control valve 28 is a valve that can assume a plurality of positions between a fully closed position and a fully open position. The position of the electronic control valve 28 is controlled by the electronic control unit 33.

The electronic control unit 33 is configured control the flow of scavenge air from the scavenge air conduit 16 through the controllable bypass conduit 26 to the exhaust conduit 10 to ensure that the temperature of the exhaust gases entering the SCR reactor 8 is above a given first threshold.

In an embodiment the electronic control unit 33 is configured to activate the bypass blower 46 when the auxiliary blower 20 is active.

The electronic control valve 28 can assume a plurality of positions between a fully closed position and a fully open position. In an embodiment the electronic control unit 33 is configured to control the flow of scavenge air from the scavenge air conduit 16 through the controllable bypass conduit 26 to the exhaust conduit 10 by adapting the position of the electronic control valve 28 whilst the auxiliary blower 46 is active (at constant level).

In an embodiment the engine 1 is provided a temperature sensor 35 between the outlet of the exhaust gas receiver 6 and the inlet of the SCR reactor 8. The electronic control unit 33 is in receipt of a signal from the temperature sensor 35.

In an embodiment the electronic control valve 28 is of the proportional type and is preferably controlled in a closed loop by the electronic control unit 33, e.g. in response to the signal from the temperature sensor 35.

In an embodiment the electronic control unit 33 is configured to control the bypass blower 46 in an on/off fashion and configured to adjust the flow of scavenge air through the controllable bypass conduit 26 by a controlling the position of the electronic control valve 28 .

In an embodiment the electronic control unit 33 is configured to activate the bypass blower 26 and to open the electronic control valve 28 when the engine load is or drops below a predetermined first engine load threshold and the electronic control unit 33 is configured to close the electronic control valve 28 when the engine load is or rises above a predetermined second engine threshold. The first and second engine load thresholds need not be the same and can be defined as a percentage of the maximum continuous rating of the engine .

In another embodiment the electronic control valve 28 is a proportional valve that is controlled by the electronic control unit 33 in a closed loop. Hereto, the controller receives information about the temperature of the exhaust gas at the inlet of the SCR reactor 8 from a temperature sensor 35 and the electronic control unit 33 is configured to control the degree of opening of the valve 28 in response to the measured temperature of the exhaust gas entering the SCR reactor 8. Thus, the electronic control unit 33 will increase the opening degree of the electronic control valve 28 to increase the temperature of the exhaust gases when the measured temperature is below a minimum desired temperature and will decrease the opening of the electronic control valve 28 when the measured exhaust gas temperature is above the minimum desired temperature.

In the embodiment of Fig. 1 the bypass conduit 26 branches off from the scavenge air conduit 16 at a position before (upstream) of the intercooler 18 and the auxiliary blower 20.

The embodiment of Fig. 2 is essentially identical to the embodiment of Fig. 1, except that the bypass conduit 2 6 branches off from the scavenge air conduit 16 at a position between the intercooler 18 and the auxiliary blower 20.

Fig. 3 shows another embodiment that is similar to the embodiment of Fig. 1, with identical reference numerals indicating identical components of the engine. A difference with the embodiment of Fig. 1 is that the scavenge air conduit 16 is provided with a second electronic control valve 48 and that there is no bypass blower in the bypass conduit 26.

In this embodiment the first electronic control valve 28 is a regulating valve that can assume positions between a closed and an open position and the second electronic control valve 48 is a regulating valve that can assume positions between a least open and a most open position.

The second electronic control valve 48 is arranged downstream of the position at which the bypass conduit 26 branches off from the scavenge air conduit 16. The second electronic control valve 48 is controlled by the electronic control unit 33.

The electronic control unit 33 is configured to operate the first electronic control valve 28 and the second electronic control valve 48 with the aim to create a controlled flow of scavenge air through the controllable bypass conduit 26 when the engine load is below a predetermined engine load threshold or when a measured or estimated temperature of the exhaust gas entering the SCR reactor 8 is below a predetermined threshold.

Hereto, the electronic control unit 33 throttles the flow through the second electronic control valve 48 and opens the first control valve 28 so that the pressure upstream of the electronic control valve increases and a control portion of the scavenge air will flow through the bypass conduit 16.

By adjusting the degree of throttling applied by the second electronic control valve 48, the electronic control unit 33 can adjust and control the flow of scavenge air through the bypass conduit 16. Preferably, the electronic control valve 28 is fully open when a flow of scavenge air through the bypass conduit 16 is required, but for a certain range of engine loads, the second electronic control valve 48 will be fully open and the first electronic control valve 28 will need to be partially open to throttle the flow through the bypass conduit 16 in order to avoid a too large flow through the bypass conduit 16.

When the temperature of the exhaust gas entering the SCR reactor 8 sufficiently high and no flow of scavenge air through the bypass conduit is required, the electronic control unit 33 will fully open the second control valve 48 so that it will apply the least possible amount of throttling through the scavenge air flowing there through and the electronic control unit 33 will close the first electronic control valve 28 to prevent flow of scavenge air through the bypass conduit 16.

In an embodiment the electronic control unit 33 is configured control the flow of scavenge air from the scavenge air conduit 16 through the controllable bypass conduit 26 to the exhaust conduit 10 to ensure that the temperature of the exhaust gases entering the SCR reactor 8 is above a given threshold.

The engine 1 comprises in an embodiment a temperature sensor 35 between the outlet of the exhaust gas receiver 6 and the inlet of the SCR reactor 8, with the electronic control unit 33 being in receipt of a signal from the temperature sensor 35.

In another embodiment the electronic control unit 33 is configured to move the first electronic control valve 28 towards the fully open position when the temperature of the exhaust gas entering the SCR reactor 8 is below a given first threshold and the electronic control unit is configured to move the second electronic control valve 48 towards the least open position when the temperature of the exhaust gas entering the SCR reactor 8 is below the given first threshold.

In an embodiment the electronic control unit 33 is configured to move the first electronic control valve 28 towards the fully closed position when the temperature of the exhaust gas entering the SCR reactor 8 is above a given second threshold and/or wherein the electronic control unit 33 is configured to move the second electronic control valve 48 towards the most open position when the temperature of the exhaust gas entering the SCR reactor 8 is above the given second threshold.

Fig. 5 shows a second exemplary embodiment of a large two-stroke diesel engine 1 according to the invention. The same reference numbers refer to the same parts as in Fig. 1. The embodiment according to Fig. 5 is largely identical to the embodiment of Fig. 1 except for the following aspects of the scavenge air cooler 18 in the scavenge air conduit 16. A supply conduit 40 delivers cool water to the scavenge air cooler 18 and a return conduit 42 transports warm water away from the scavenge air cooler 18. In the second embodiment an electronically controlled bypass valve 44 in a cooling medium bypass circuit 43 and an electronically controlled separation valve 46 under command of the controller 33 allow the supply of cool water in the supply conduit 40 to be deviated to the return conduit 42 without passing through the scavenge air cooler 18. A recirculation conduit 48 including a pump 50 and a heater (or heat exchanger) 52 ensure that water flows through the scavenge air cooler 18 that is now changed into a heater and functions effectively as a heat exchanger. The heater 52 is provided with a warm heating medium, such a as warm water form the engine cooling system and heats the medium circulating through the scavenge air cooler 18.

In the second embodiment the electronic control unit 33 can deactivate the cooler 18 via valves 44 and 46 by bypassing the cooling medium. At the same time the controller 33 will activate the pump 50 to ensure that a medium is circulating in the scavenge air cooler 18. Further, the control unit 33 can activate the heater 52 by delivering a heating medium to heater 52 and thereby change the scavenge air cooler 18 into a heater. The electronic control unit 33 is configured to take various measures to increase the temperature of the scavenge air in relation to the need for increasing the temperature of the exhaust gases entering the SCR reactor 8.

Thus, if it is sufficient to let some scavenge air pass through the controllable bypass conduit 26 to the exhaust conduit 10, the electronic control unit 33 will not take any further measures. However, if this first measure is not sufficient, the electronic control unit 33 will deactivate the cooling function of the scavenge air cooler 18. If this second measure is not sufficient, the electronic control unit 33 will as a third measure turn the scavenge air cooler 18 into a heater to actively heat the scavenge air.

Fig. 5 shows an example of the temperatures of the scavenge air and of the exhaust gas at various positions in the system. The examples are for low engine load conditions, e.g. under 40% of the maximum continuous rating of the engine concerned. The figures without brackets are the temperatures with scavenge air being passed through the bypass conduit 26 and with heat being added to the scavenge air at the scavenge air cooler 18. The figures in brackets are the temperatures when the engine is conventionally operated without scavenge air passing through the bypass conduit 26 and with the scavenge air cooler 18 cooling the scavenge air. With the new measures the temperature of the exhaust gas entering the SCR reactor 8 is 325 deg. C and the exhaust gas is sufficiently hot for being converted in the SCR reactor 8. Without the new measures the temperature of the exhaust gas entering the SCR reactor 8 is 220 deg. C and the exhaust gas is not sufficiently hot for being converted in the SCR reactor 8.

Fig. 6 shows the supply and return of cooling medium to the scavenge air cooler 18 via a cooling medium supply conduit 40 and a cooling medium return conduit 42.

Figs. 7 to 10 show various embodiments for controlled reduction of the cooling capacity of the scavenge air cooler 18.

In Fig. 7 the engine is provided with a scavenge air bypass conduit 17 for bypassing the scavenge air cooler 18. The scavenge air bypass conduit 17 includes an electronically controlled valve 23 for opening and closing the scavenge air bypass conduit 17 under command of the electronic control unit 33. The scavenge air conduit 16 includes another electronically controlled valve 21 for opening and closing the scavenge air conduit 16 under command of the electronic control unit 33. Thus, the electronic control unit 33 can control the flow of scavenge air through the scavenge air bypass conduit 17 in accordance with the need to increase the temperature of the scavenge air and thereby increase the temperature of the exhaust gas entering the SCR reactor 8.

In Fig. 8 the cooling medium supply conduit 40 is provided with an electronically controlled separation valve 46 and a cooling medium bypass circuit 43 that includes an electronically controlled bypass valve 44 and connecting the cooling medium supply conduit 40 directly to the cooling medium return conduit 42. The electronic control unit 33 commands the electronic valves 44 and 46 and can thereby control the extent to which the cooling medium passes through the scavenge air cooler 18 (could be on/off or proportional control).

In Fig. 9 a recirculation conduit 48 including a recirculation pump 50 (under control of the electronic control unit 33) is added to the embodiment shown in Fig. 5 for enabling the cooling medium to circulate in the scavenge air cooler 18.

In Fig. 10 the engine is provided with an additional (second) scavenge air cooler 19. The electronic control unit 33 is configured to control the cooling capacity of at least one of the scavenge air coolers 18,19 as explained above.

Figs. 11 to 15 show various embodiments for controlled adding of heat to the scavenge air.

In Fig. 11 the engine is provided with a steam injection conduit 90 connected to the scavenge air conduit 16. The steam injection conduit 90 includes an electronically controlled steam injection control valve 92 under command of the electronic control unit 33. Thus, the temperature of the scavenge air and thereby the temperature of the exhaust gas entering the SCR reactor 8 can be increased as desired by controllably injecting steam without a drop in scavenge air pressure.

In Fig. 12 the engine is provided with an exhaust gas injection conduit 60 connected to the scavenge air conduit 16. The exhaust gas injection conduit 60 includes an electronically controlled exhaust gas injection control valve 62 under command of the electronic control unit 33. Thus, the temperature of the scavenge air and thereby the temperature of the exhaust gas entering the SCR reactor 8 can be increased as desired by controllably injecting exhaust gas without a drop in scavenge air pressure .

In Fig. 13 the engine is provided with a heater unit 27 in the scavenge air conduit 16. The heater unit 27 is supplied with a heating medium (such as hot water or hot air) via a heating medium supply conduit 70 and the return heating medium is transported away by a heating medium return conduit 72. The heating medium supply conduit 70 and the heating medium return conduit 72 are provided with electronically controlled valves that are under the command of the electronic control unit 33. Thus, the temperature of the scavenge air and thereby the temperature of the exhaust gas entering the SCR reactor 8 can be increased as desired without a drop in scavenge air pressure.

The embodiment of Fig. 14 is essentially identical to the embodiment of Fig. 9, but further including a heat exchanger 52 for adding heat to the medium circulating through he scavenge air cooler 18.

In the embodiment of Fig. 15 the engine is provided with a heat exchanger 80 in the a cooling medium supply conduit 40 for supplying heat to the medium flowing through the cooling medium supply conduit 40.

Although the teaching of this application 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 teaching of this application.

The embodiments described above may be combined in every possible way to improve the function of the engine.

It should also be noted that there are many alternative ways of implementing the apparatuses of the teaching of this invention.

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 of several means recited in the claims.

Claims

CLAIMS :

1. A large turbocharged two-stroke compression ignited internal combustion engine (1) of the crosshead type comprising: a turbocharger with an exhaust gas driven turbine (12) connected to a compressor (14) for delivering pressurized scavenge air, a plurality of cylinders connected to a scavenge air receiver (22) and to an exhaust gas receiver (6), a selective catalytic reduction reactor (8) with an inlet connected to an outlet of the exhaust gas receiver (6), an exhaust conduit (10) connecting an outlet of the selective catalytic reduction reactor (8) to an inlet of the turbine (12), a scavenge air conduit (16) connecting an outlet of the compressor (14) to an inlet of the scavenge air receiver (22) via a scavenge air cooler (18), an auxiliary blower (20) in the scavenge air conduit (16) for assisting the compressor (14) at low load conditions of the engine (1), a controllable by pass conduit (26) extending from a position in the scavenge air conduit (16) to a position in the exhaust conduit (10) for bypassing the plurality of cylinders, an electronically controlled bypass blower (46) in said controllable by pass conduit (26) for assisting a flow of scavenge air from the scavenge air conduit (16) to the exhaust conduit (10), and an electronic control unit (33) operably connected to the electronically controlled bypass blower (46) , the electronic control unit (33) being configured control the flow of scavenge air from the scavenge air conduit (16) through the controllable bypass conduit (26) to the exhaust conduit (10).
2. An engine according to claim 1, wherein the controllable bypass conduit (26) further comprises an electronic control valve (28) controlled by the electronic control unit (33).
3. An engine according to claim 1 or 2, wherein the electronic control unit (33) is configured control the flow of scavenge air from the scavenge air conduit (16) through the controllable bypass conduit (26) to the exhaust conduit (10) to ensure that the temperature of the exhaust gases entering the selective catalytic reduction reactor (8) is above a given threshold.
4. An engine according to any one of claims 1 to 3, wherein the electronic control unit (33) is configured to activate the bypass blower (46) when the auxiliary blower (20) is active.
5. An engine according to any one of claims 1 to 4, wherein the electronic control unit (33) is configured to activate the auxiliary blower (20) when the engine load is below a predetermined engine threshold.
6. A large turbocharged two-stroke combustion engine of the crosshead type according to any one of claims 2 to 5, wherein the electronic control valve (28) can assume a plurality of positions between a fully closed position and a fully open position, and wherein the electronic control unit (33) is configured to control the flow of scavenge air from the scavenge air conduit (16) through the controllable bypass conduit (26) to the exhaust conduit (10) by adapting the position of the electronic control valve (28).
7. An engine according to any one of claims 1 to 6, further comprising a temperature sensor (35) between the outlet of the exhaust gas receiver (6) and the inlet of the selective catalytic reduction reactor (8), with the electronic control unit (33) being in receipt of a signal from the temperature sensor (35).
8. An engine according to any one of claims 1 to 7, wherein the valve (28) is of the proportional type and is preferably controlled in a closed loop by the electronic control unit (33).
9. An engine according to any one of claims 6 to 8, wherein the electronic control unit (33) is configured to control the bypass blower (46) in an on/off fashion and configured to adjust the flow of scavenge air through the controllable bypass conduit (26) by a controlling the position of the electronic control valve (28).
10. An engine according to any one of claims 1 to 9, wherein the controllable bypass conduit (26) connects to the scavenge air conduit (16) at a position between the compressor (14) and the auxiliary blower (20).