WO2024063685A1

WO2024063685A1 - An exhaust recirculation device for a 4-stroke compression ignition engine

Info

Publication number: WO2024063685A1
Application number: PCT/SE2023/050913
Authority: WO
Inventors: Jörgen SVENSSON; Mikael NEHVONEN
Original assignee: Cetech Ab
Priority date: 2022-09-19
Filing date: 2023-09-18
Publication date: 2024-03-28
Also published as: SE2251081A1; SE546328C2

Abstract

An exhaust gas recirculation (EGR) arrangement (100) for a single or multi-cylinder 4-stroke compression ignition engine, the EGR arrangement (100) comprising: an exhaust gas conduit in fluid communication between an EGR valve (51) and an EGR outlet (42), wherein the EGR scrubber (70) is a water scrubber comprising a chamber (76) having a chamber inlet (71) and a chamber outlet (72), the chamber outlet (72) being arranged in downstream fluid communication with the chamber inlet (71), and at least one water spraying device (60) comprising at least one nozzle (64), the at least one water spraying device (60) being arranged downstream the EGR valve (51) and upstream the chamber outlet (72), wherein the water spraying device (60) is connectable to a pressurized water source and configured to inject pressurized water into the exhaust gas conduit via the at least one nozzle (64), to increase a liquid surface area of the injected water coming into contact with the exhaust gases in the exhaust gas conduit.

Description

AN EXHAUST RECIRCULATION DEVICE FOR A 4-STROKE COMPRESSION IGNITION ENGINE

TECHNICAL FIELD

The present disclosure relates to the field of exhaust gas recirculation (EGR) for heavy and intermediate fuel oil or diesel (HFO/IFO/diesel) fuelled compression ignition engines for stationary on-land use, such as in backup power generators and for marine applications in propulsion of marine vessels and/or for onboard electric power generation.

BACKGROUND

Nitrous oxide gases in the form of nitric oxide (NO) and nitrogen dioxide (NO2), commonly referred to as NOx gases, are usually produced from the reaction of nitrogen and oxygen during combustion of fuels, in particular at high combustion temperatures, such as the combustion temperatures present in compression ignition combustion engines, also commonly referred to as Diesel engines. NOx gases are harmful to the environment and contribute to the formation of smog and acid rain, as well as affecting tropospheric ozone. Engine manufactures and manufacturers of engine exhaust cleaning apparatuses have therefore developed solutions for purifying engine exhaust gases by removal or reduction of NOx gases from the engine exhaust gas streams.

Exhaust gas recirculation (EGR) works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. This is commonly done by diverting exhaust gases from the exhaust manifold and injecting the diverted gases to the intake manifold of the engine. The EGR gases dilute the dioxygen (02) in the incoming air stream and provides the engine intake with gases having a lower oxygen content for combustion in the cylinder(s). The addition of lower oxygen content EGR gases helps reducing the combustion temperature, i.e. for a higher combustion temperature more NOx is produced and for a lower combustion temperature less NOx emissions is generated.

Another solution of reducing NOx formation in compression ignition engines is to adjust fuel injection timing in relation to a piston’s position relative to the top dead centre (TDC). Such adjustment may be made by retarding or delaying the injection to a point in time after the piston has reached TDC. Alternatively, an additional injection of fuel may take place after the main injection. This reduces combustion temperatures but results in increased fuel consumption, which is not desirable. Adjusting fuel injection may thus reduce NOx production. A problem with fuel injection adjustment is increased overall fuel consumption which in turn leads to an increased production of environmentally harmful combustion components, including CO2 and NOx. Thus, this solution is not a viable option for achieving higher than Tier II of the stringent International Maritime Organization (IMO) and its equivalent for land-based installations.

Another solution of reducing NOx gases is to implement a selective catalytic reduction device (SCR) in the exhaust conduit of the engine. An SCR works by converting NOx with the aid of a catalyst into diatomic nitrogen (N2), and water (H2O). A reductant, typically a hydrous ammonia (NH3), aqueous ammonia (NH4OH), or a urea (CO(NH2)2) solution, is added to the exhaust stream of flue or exhaust gas and is reacted onto a catalyst. As the reaction drives toward completion, nitrogen (N2), and carbon dioxide (CO2), in the case of urea use, are produced.

For the automotive industry, SCR technology is widely implemented for reducing NOx emissions. For larger engines, such as marine engines, the size needed for installing the SCR is large and the cost of the installation and the SCR unit itself is high. In addition, the cost of the reductant needed for the continuous operation of an engine having SCR technology, adds to the total engine operating costs. There is also a need for installing and/or maintaining tanks, pumps, compressors, and similar additional devices for the reductant, further increasing system and operational costs. Lastly, SCR technology depending on reductant, suffers from reductant slip, also known as ammonia slip, when reductant passes through the SCR unreacted. Reductant slip is undesirable and has a negative impact on the environment.

Increasingly stringent marine and land-based exhaust gas emission requirements for compression ignition engines from governmental and intergovernmental organizations, such as the International Maritime Organization (IMO), as well as requirements for land- based engine installations, requires that new technical solutions are developed and implemented for reducing NOx in the gas exhausted from the compression ignition combustion engines.

There is thus a desire to provide a solution for medium-speed and high-speed compression ignition engines for marine use, as well as for land-based engine installation, that improves the reduction of harmful NOx exhaust gases, and which is cost efficient to manufacture and install on new engine installations as well as able to retrofit to current engine installations. SUMMARY

The present invention at least partly solves the above problems by providing an exhaust gas recirculation (EGR) arrangement for a single or multi-cylinder 4-stroke compression combustion ignition engine, the EGR arrangement comprising: an exhaust gas conduit having an EGR inlet and an EGR outlet, wherein the EGR inlet is arranged to be connected to an engine exhaust manifold of an engine cylinder bank for receiving a portion of combustion gases from at least one cylinder of the cylinder bank, and wherein the EGR outlet is arranged to be connected to an intake of the engine upstream a turbocharger compressor inlet, at least one controllable EGR valve arranged in fluid communication between the EGR inlet and the EGR outlet, an EGR scrubber arranged in the exhaust gas conduit in fluid communication between the EGR valve and the EGR outlet, wherein the EGR scrubber is a water scrubber comprising a chamber having a chamber inlet and a chamber outlet, the chamber outlet being arranged in downstream fluid communication with the chamber inlet, and at least one water spraying device comprising at least one nozzle, the at least one water spraying device being arranged downstream the EGR valve and upstream the chamber outlet, wherein the water spraying device is connectable to a pressurized water source and configured to inject pressurized water into the exhaust gas conduit via the at least one nozzle to increase a liquid surface area of the injected water coming into contact with the exhaust gases in the exhaust gas conduit.

The EGR arrangement is adapted for use with compression ignition (Cl) engines, also referred to as compression ignition combustion engines. An engine may comprise engine cylinders in straight or inline configuration. For straight or inline engine configurations, the cylinders are aligned next to each other forming a straight line. The cylinders of the engine may then be said to form a common cylinder bank. Alternatively, engine cylinders may also be arranged in a V-configuration forming what is commonly referred to as a V engine. For a V engine the engine cylinders are divided into two separate cylinder banks wherein each cylinder bank is arranged at an angle in relation to the other cylinder bank, such as 90 degrees. The EGR arrangement may also be used with other less common engine configurations. The EGR arrangement of the present invention may be arranged to circulate exhaust gas from a single cylinder, a cylinder bank comprising a plurality of cylinders or from multiple cylinder banks such as the above-mentioned V-configuration engines.

Each cylinder bank may be connected to an exhaust manifold of an engine exhaust. The exhaust manifold typically comprises exhaust gas inlets adapted to be connected to the exhaust ports of a cylinder bank. The exhaust manifold further comprises an exhaust outlet for connecting to an exhaust system. The exhaust system may in turn comprise further devices such as exhaust silencers, exhaust gas aftertreatment devices, and piping for connecting such devices together. At the end of the exhaust system, the exhaust gases are discharged to ambient air through an exhaust system outlet, stack or funnel. The exhaust manifold joins the individual exhaust streams from the exhaust ports of engine cylinders of a cylinder bank into a common exhaust stream that flows out from the exhaust manifold outlet to the exhaust system. A technical advantage of the exhaust manifold is thus to collect and join multiple exhaust gas streams into one common exhaust gas stream. The exhaust manifold outlet may in turn be connected, directly or through piping, to a turbocharger exhaust turbine inlet.

Further, the exhaust manifold may be connected to the exhaust ports of a cylinder through engine cylinder exhaust runners. Engine cylinder exhaust runners may be arranged in the form of pipe sections comprising mounting flanges at one end to mount to the engine cylinder head, wherein the pipe sections transport exhaust gases from individual engine cylinders to the exhaust manifold main body. At the opposite end of the mounting flanges, the exhaust runners may be welded or joined to the exhaust manifold body through further mounting flanges. This exemplified exhaust manifold arrangement may be referred to as an exhaust manifold with induvial exhaust runners.

The exhaust manifold may also be a solid cast iron structure spanning across all cylinders of a cylinder bank, in a manner such that the structure is absent of individual exhaust runners. For such an exhaust manifold, the exhaust manifold comprises a main body with exhaust gas inlet openings at one side matching the number of exhaust ports of the cylinder bank. The manifold has a machine surface adapted to mount against the cylinder head of the engine with inlet ports matching those of the exhaust ports of the engine cylinder head. The main body also comprises an exhaust gas outlet opening. The inlet opening side is arranged to be connected to the engine exhaust system through a mounting flange and the outlet is arranged to be connected to an engine exhaust system using a flange or similar connection.

The exhaust manifold may also be in the form of exhaust headers or simply headers. Headers comprise individual exhaust port exhaust runners often in the form of pipe or tubing with flanges for mounting to the individual exhaust ports of the cylinder bank. The individual exhaust runners are joined into one common exhaust pipe or tube at a point or position called a collector wherein exhaust gas from the individual exhaust ports of the cylinder bank are joined into a common exhaust stream. The exhaust manifold may also form an integral part with the cylinder bank.

The function of the EGR conduit is to transport the exhaust gases from the inlet of the EGR arrangement to the outlet of the EGR arrangement. The EGR conduit may be formed by a plurality of exhaust pipe sections that are bolted together through flanges, or the sections may be welded, or otherwise, bolted together. The sections may comprise the following pipe sections. A first pipe section comprising the EGR inlet and connecting the EGR inlet to the controllable EGR valve. A second pipe section connecting the controllable EGR valve to the EGR scrubber. A third section connecting the EGR scrubber to the engine intake through the EGR outlet. The EGR outlet is arranged to be connected to an intake of an engine, preferably to a position upstream a turbo compressor. This position may also be referred to as the low-pressure area of a turbo compressor. This allows for EGR gas recirculation in the EGR conduit without the need for an EGR pump thereby reducing the overall cost of the EGR arrangement.

As also described above, the EGR inlet is arranged to be connected to an engine exhaust manifold of an engine cylinder bank for receiving a portion of combustion gas from at least one cylinder of the cylinder bank. The EGR arrangement is adapted to receive exhaust gases from a relative low-pressure area within the exhaust manifold of an engine, having the effect of the gases being cleaner and having a lower temperature and pressure compared to diverting exhaust gases from a relatively more contaminated high temperature/pressure area of the exhaust manifold. As the exhaust gases from all of the cylinders of a cylinder bank are collected or joined into a common exhaust gas stream, the pressure, and the temperature of the exhaust gas increase. In addition, the level of exhaust particles and unburnt fuel also increase. Diverting exhaust gases from a position upstream the position where exhaust gases from all of the cylinders are collected to a common exhaust gas stream provides the EGR arrangement with exhaust gases having lower temperature, pressure and level of exhaust particles and unburnt fuel compared to conventional solutions wherein exhaust gases are diverted after the collection point, i.e. downstream the collection point. For example, the EGR inlet may be connected to an exhaust manifold at a longitudinal end portion of the manifold at a position opposite the exhaust manifold outlet. The amount of combustion gas received through the EGR inlet may be in the range of 5-10% of the total amount of exhaust gases from all cylinders of a cylinder bank. The amount of combustion gases received through the inlet may be controlled by controlling the opening degree of the EGR valve.

When the exhaust manifold comprises individual exhaust runners the exhaust gas may be diverted from a position in an individual exhaust runner by arranging the EGR inlet in the individual exhaust runner. This allows a portion of exhaust gas from a single cylinder to be diverted to the EGR inlet.

The at least one EGR valve is arranged in fluid communication between the EGR inlet and the EGR outlet. The EGR valve may be an electrically controllable EGR valve. The EGR valve controls the amount of exhaust gases flowing from the EGR inlet to the EGR outlet. The EGR valve may be controllable by a control unit to allow increasing or decreasing the exhaust gas flow depending on an engine load. The engine load or engine load factor is defined as the actual power output of the engine relative to its Maximum Continuous Rating (MCR). The Load factor is normally specified in percentage. For example, an engine working at 50% of its maximum load has a current load factor equal to 50%. The engine load signal may be received or read from an engine control unit (ECU) and represents the current engine load the engine is operating at.

The EGR valve may be controlled to assume a closed position to stop the operation of the EGR arrangement. The EGR valve is arranged downstream the EGR inlet and upstream the EGR scrubber and/or the water spraying device.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. The control unit may also, or instead, include an application specific integrated circuit, a programmable gate array or programmable array logic, a programmable logic device, or a digital signal processor. Where the control unit includes a programmable device such as the microprocessor, microcontroller or programmable digital signal processor mentioned above, the processor may further include computer executable code that controls operation of the programmable device.

The at least one EGR valve may also be set to a predetermined opening degree when the EGR system is connected to an engine that runs at a continuous and predetermined, or pre-set, engine load. An example of such a situation may be for land-based installations for backup power generation wherein the engine is operated at a predetermined load. The arrangement may further comprise a second controllable EGR valve arranged downstream the EGR scrubber and upstream the EGR outlet. This allows for the EGR arrangement to be isolated or disconnected from an engine by closing both EGR valves. Hereby, the engine may continue to be operated, albeit with increased NOx emission, and the EGR scrubber or EGR arrangement components may be repaired, cleaned or serviced. Additionally, if the first EGR valve mechanically fails and is stuck at a partly or fully opening degree, the second EGR valve may assume control of the amount of EGR gases flowing through the EGR arrangement by throttling or controlling the amount of gas flowing from the EGR arrangement to the EGR outlet. The second EGR valve is preferably arranged after the exhaust gases have been cleaned, thereby reducing the risk of fouling or soot build up on the second EGR valve. This also minimizes the risk of the second EGR valve malfunctioning.

By spraying or injecting the pressurized water into the exhaust stream from the nozzle, the water is divided into drops or droplets, forming a spray pattern, and the surface area of the water coming into contact with the exhaust gas stream is improved. Increasing a liquid surface area of the water injected into the exhaust stream improves the exhaust gas scrubbing effect by increasing the contact area between the water and the exhaust gas. The nozzle receives water from the water spraying device and divides the water into drops. A water drop of a first size and amount may be divided into a plurality of smaller sized drops, wherein the amount of water of the plurality of smaller sized drops together has the same volume of water as the water drop of the first size and volume. The total surface area of the plurality of water drops is thereby larger than the surface area for the water drop of the first size and volume. For any given volume of fluid being sprayed the surface area exposed is inversely proportional to the droplet size. Hence, if one halves the droplet radius one doubles the surface area of the fluid.

The at least one water spraying device may be arranged inside the EGR scrubber. The at least one water spraying device may be arranged to spray water into the chamber of the EGR scrubber. The at least one water spraying device may also be arranged upstream the EGR scrubber, and downstream the EGR valve, for spraying water into the exhaust gas conduit. The EGR arrangement may comprise a combination of at least one water spraying device arranged upstream the EGR scrubber as well as at least one water spraying device arranged to spray water inside the chamber. The water spraying device may comprise a single spray nozzle arranged inside the EGR conduit, or the nozzle may be arranged inside the EGR scrubber chamber. The EGR arrangement may comprise more than one water spraying device, such as, but not limited to, two or three water spraying devices.

The EGR arrangement may comprise at least one water spraying device arranged upstream the EGR scrubber chamber and at least one water spraying device arranged inside the EGR scrubber chamber. Arranging one or more water spraying devices upstream the chamber allows for decreasing the size of the EGR chamber, enabling for a reduction in the installation space needed for the EGR chamber. This provides for increased flexibility of installing the EGR arrangement on different types of engine installations and different types of engines.

The water spraying device may also be pre-installed to a pipe section having pre-welded or pre-manufactured mounting flanges for connecting to pipe sections of the EGR conduit. This allows for simple installation of the water spray device and the pipe-section to the EGR conduit since no need for drilling or cutting is needed on site to mount the water spraying device itself to a pipe section. Both the water spraying device(s) and the EGR scrubber may be manufactured with pre-made mounting flanges in a modular fashion, reducing the time needed for installing the EGR arrangement.

The water spraying device may comprise more than one nozzle. Each nozzle may comprise at least one opening for spraying or injecting water into the exhaust gas stream. The openings of the nozzle may project water into a plurality of directions. The plurality of directions may form a water spray pattern such as a cone pattern. The openings of the nozzle may have a size adapted to provide a mist of water that mixes with the exhaust gas stream. Spraying or injecting the water using the nozzle increases the liquid surface area of the water coming into contact with the exhaust gases in the exhaust gas conduit. This provides for improved cooling of the exhaust gases as well as improved capturing and cleaning of combustion particles, such as soot. When the exhaust gases come into contact with the injected water, the water forms a mixture of exhaust gases and water vapor. When water vapor condensate, the water vapor turns back into liquid water in the form of water drops. The water drops are thus formed and grow in size. During this process, combustion particles adhere to the water drops and the drops grow in size and are collected at the bottom of the EGR chamber, and further transported away from the bottom of the EGR chamber and into the wastewater collection tank.

The water spray nozzle may be arranged in an opening of a wall of the EGR scrubber chamber or EGR conduit, such that the injection of water is made in a direction perpendicular to the flow of exhaust gases. Multiple nozzles may be arranged around the circumference or inner surface of the EGR conduit. For example, if the EGR conduit comprises pipe sections connecting the EGR valve to the EGR scrubber, multiple nozzles may be installed to slightly protrude into the inner volume of the EGR conduit pipe, wherein the nozzles are spaced around the circumference of the pipe. The water nozzle, or nozzles, may further be pre-installed to a pipe section having mounting flanges simplifying installation on-site of the EGR arrangement.

The water spray nozzle(s) may be arranged to inject or spray water against and/or along the exhaust gas flow. For example, one nozzle may be arranged to spray against the exhaust gas flow with another nozzle arranged to spray along the flow of the exhaust gas. The direction of the exhaust gas flow may be construed as along the EGR conduit, such as along a center axis of a pipe, when the EGR conduit is made up of pipe sections. The nozzle may be arranged in a central position, away from the walls of the chamber or EGR conduit. This may be achieved by arranging the nozzle on a pipe section protruding from the wall of the EGR conduit, or chamber, to a position centrally arranged in the pipe section, or chamber.

The water spraying device may be provided with pressurized water from a pressurized water source, at a pressure of between 2-20 bar, preferably between 4-10 bar. The pressure may also be higher. The water pressure may depend on the nozzle manufacturer specifications. The pressurized water source may be provided by a water pump or a hydrophore tank or similar source of pressurized water.

The at least one water spraying device may comprise a controllable water valve for controlling the pressure and/or flow amount of water provided to the nozzle. This allows for a plurality of different water sources having different pressure and flow to be connected to the water spraying device. It also allows for adapting the pressure and flow to the nozzle specifications. For example, when the pressurized water source provides water at a pressure of 10 bar and the nozzle is defined by the nozzle manufacturer to operate optimally at between 6-8 bar, the valve may be adjusted to meet the nozzle operating range of 6-8 bar. In addition, the controllable water valve may be adjusted based on the flow amount of the EGR gases flowing into the chamber of the scrubber. This is advantageous in that the system water usage may be reduced. The controllable valve may also be operated to close when the engine is turned off, thereby discontinuing the injection of water. Each water spraying device may comprise an individual controllable water valve or they may share a common controllable water valve. When the EGR arrangement comprises more than one water spraying device, of which each water spraying device comprises an individual controllable water valve, a water spraying device may be activated to spray water depending on the engine load. Additionally, the activation of an individual water spraying device may be done based on the humidity of the exhaust gas leaving the EGR scrubber. When the humidity is below a threshold value, additional water spraying devices may be activated by opening their respective controllable water valves. If the humidity is above a threshold value, the amount of injected water may be reduced by operating the controllable water valve.

Additionally, when the EGR arrangement comprises more than one water spraying device, each water spraying device may operate at different pressure and/or flow amount. This allows for reducing the amount of water needed to operate the EGR arrangement. In addition, it allows for a first water spraying device to provide the main part of water spray to the exhaust gas stream with a second water spraying device for fine tuning and optimizing water spray flow and pattern for the exhaust gas cleaning process. Additionally, the first controllable water valve may be selected to have a lower control resolution in terms of controlling pressure and/or flow. For example, the first valve may be controllable to set a degree of opening in increments of 10% whereas the second valve may be controllable to set a degree of opening in increments of 1-5%.

The EGR scrubber is arranged downstream the EGR valve and upstream the EGR outlet. The EGR scrubber comprises a chamber having an exhaust gas inlet and an exhaust gas outlet. The chamber may have a cylindrical shape, a box shape or any other shape that is beneficial for optimizing the flow through the chamber. The chamber may also have a shape conforming to the space constraints for an engine installation. Such as a cylindrical shape that tapers or widens between the chamber inlet and outlet. The chamber may be manufactured from multiple section allowing for easy disassembly and servicing. For example, the chamber may be manufactured in two halves that may subsequently be welded or bolted together.

The chamber inlet is arranged to receive exhaust gas flowing from the EGR valve towards the EGR scrubber. The chamber outlet is arranged upstream to the EGR outlet and in fluid communication with the EGR outlet. The chamber may also be construed as comprising an inlet portion, a middle portion, and an outlet portion. The inlet portion may have a cone shape that widens from the chamber inlet opening diameter to a diameter of the chamber middle section. In addition, the outlet portion may have a tapered cone shape compared to the middle section. The chamber diameter may be larger than the diameter of the chamber inlet and/or outlet. Having the inlet portion widening and the outlet portion tapering provides a connection interface of the EGR scrubber to use the same diameter EGR conduit piping with different diameter or width chamber middle portions. The same diameter EGR conduit piping may thus be used with different diameter or widths of the EGR scrubbers. In the case where the EGR chamber middle section is box shaped, the chamber inlet may have a widening truncated or frustum pyramid shape and the chamber outlet a tapered truncated or frustum pyramid shape. The chamber inlet portion widening shape helps with decreasing the speed of the exhaust gases entering the EGR scrubber. Slowing down the exhaust gas inside the chamber improves the water vapor condensation inside the chamber.

The EGR scrubber may further comprises a wastewater collection tank for collecting wastewater, and at least one controllable wastewater valve in fluid communication with a wastewater outlet of the wastewater collection tank, the valve configured to control removal of collected wastewater containing combustion particles, such as soot, from the chamber, by the opening of the at least one wastewater valve. The wastewater collection tank is connected and in fluid communication with the EGR scrubber chamber through a plurality of longitudinally extending, slits or openings in the bottom portion of the chamber. The slits or openings are preferably arranged parallel to each other and spaced apart to allow for water to pass from the chamber to the wastewater collection tank. The slits or openings are aligned with a central axis of the EGR chamber. As the water sprayed into the exhaust gas stream by the water spraying device nozzles condenses in the chamber, through gravity, the wastewater is collected in the bottom portion of the chamber. The water then flows through the slits or openings arranged in the bottom portion, into the wastewater collection tank.

The chamber may comprise at least one, or a plurality of perforated plates comprising a plurality of openings, the perforated plates being arranged inside the chamber downstream the at least one water spraying device. The perforated plates promote and improve condensation of the water vapor in the chamber as the water vapor comes into contact and is cooled down by the perforated plates.

The plates may be made from a material resistant to corrosion due to the water and water vapor mixture containing combustion particles. The perforated plates may be made from stainless steel, titanium, or other material resistant to corrosion. The plates may also be made from plastic or a composite material. The plates and the chamber may be 3D printed. This allows for the plates to be manufactured in place inside the chamber and removes the need for assembling the plates in the chamber which is required when the chamber and plates are manufactured using standard manufacturing techniques, such as e.g. high- pressure water cutting. The plates may be made from metal or plastic with stamped or drilled openings.

Combustion particles such as soot is thereby removed from the exhaust gas stream and the amount of combustion particles or soot of the EGR outlet is reduced compared to the EGR inlet. The exhaust gases are thus both cleaned and cooled. The perforated plates may have an outer edge shape conforming to a cross-sectional shape of the chamber. The plates may be square, rectangular, elliptical, or circular shaped. In addition, the perforated plates may have a convex shape.

The chamber may comprise a plurality of perforated plates arranged in a stacked formation at a distance from each other. The distance between two plates may be defined and measured along a perforated plate surface normal of a plate. The distance is preferably the same at all positions of a plate.

The arrangement may comprise a plurality of perforated plates, and wherein a first and a second perforated plate are arranged at an angle to each other. However, the plates may be arranged at an angle in relation to each other such that the distance between two plates varies along the perforated plate surfaces of two plates. Alternatively, some plates may be mounted in a stacked and parallel orientation with intermediate plates arranged at an angle in relation to the stacked and parallel plates.

The perforations or openings of the perforated plate may be circular shaped. Alternatively, the openings may be of elliptical, square, or rectangular shaped. Other shapes are also possible, such as octagonal or hexagonal. Circular or elliptical shaped may be advantageous in that they reduce the risk of crack formation and propagation at the boundary edges of the opening caused by heat cycling. Exhaust gases mixed with water vapor are guided by the perforated plates and directed through the openings of the perforated plates to decrease the speed of the mixture as well as to cool and condensate the water vapor of the mixture. As the water vapor condensate into water drops, the water through gravity collects in the wastewater collection tank. The openings of a first perforated plate may be different from the opening of a second perforated plate in the stack of perforated plates in terms of shape and/or in dimensions. When the chamber comprises at least one first and second perforated plate, a diameter of the openings of the first perforated plate may be the same or different from a diameter of the openings of the second perforated plate. When the openings are of a different shape, the width of the openings of the first perforated plate may be different from the width of the openings of the second perforated plate. The diameter or width of the opening of the first perforated plate may be larger than the diameter or width of the openings of the second perforated plate. The openings of the first perforated plate may thereby be adapted to receive the higher exhaust flow speed of the exhaust entering the chamber.

Additionally, the chamber may comprise a first and a second perforated plate, the openings of the first perforated plate being radially offset from the openings of the second perforated plate. Radially offsetting the openings increases the distance the exhaust gas and water vapor needs to travel to pass the first and second perforated plates. By radially offsetting the openings of the first and second perforated plates, the openings of the first perforated plate do not align with the openings of the second perforated plate.

Additionally, the size or dimension, such as diameter, of a first perforated plate may be different from the size or dimension of a second perforated plate. Such an example would be when the chamber of the EGR scrubber has a widening or tapered shape, the diameter of a second perforated plate may be smaller or larger in order to conform with the shape of the chamber.

As also indicated above, the EGR arrangement may further comprise a control unit electrically connected to the EGR valve and configured to control the controllable EGR valve to assume a position to adjust the amount of exhaust gases recirculated from the EGR inlet to the EGR outlet based on an engine load signal. The control unit may comprise processing circuitry configured to control the controllable EGR valve to adjust the amount of exhaust gases recirculated from the EGR inlet to the EGR outlet based on an engine load signal. The control unit may comprise a predefined model or map for different amounts of opening of the EGR valve depending on the engine load signal.

The EGR arrangement may further comprise at least one humidity sensor arranged downstream the EGR chamber for determining the amount of water in the exhaust gas stream, wherein the at least one humidity sensor is electrically connected to the control unit. The humidity sensor measures or determines the water vapor or humidity of the exhaust gas downstream the EGR scrubber. One or more humidity sensors may be used to determine the humidity at different positions downstream the EGR scrubber. Two humidity sensors may be arranged to measure humidity at the same position of the EGR conduit. This provides for fallback humidity sensor data should one sensor fail and thereby increase system uptime. Alternatively, two humidity sensors using different sensing technology may be used, whereby the average of the two sensors may be calculated or determined by the control unit.

The EGR arrangement may further comprise at least one oxygen sensor arranged in the exhaust gas conduit between the chamber, or EGR scrubber, and the EGR outlet, the oxygen sensor being arranged to determine an oxygen amount in the exhaust gas stream, wherein the oxygen sensor is electrically connected to the control unit. One or more oxygen sensors may be arranged downstream the EGR scrubber for detecting the oxygen amount and the one or more sensors are connected to the control unit. The data from the one or more oxygen sensors may be stored or analyzed to determine EGR arrangement efficiency. Using an oxygen sensor allows to improve the efficiency of the EGR arrangement. The one or more oxygen sensor may be an optical oxygen sensor, such as a differential optical absorption spectroscopy (DOAS) sensor. Alternatively, the one or more sensors may be an oxygen sensor of the state of the art suitable for measuring oxygen amount in an exhaust gas stream.

The oxygen sensor may be arranged in the chamber of the scrubber at a position close to the chamber outlet, downstream the perforated plates. The oxygen sensor may also be arranged outside the chamber of the scrubber at a position of the EGR conduit arranged upstream the EGR outlet.

The EGR arrangement may further comprise at least one temperature sensor arranged in the exhaust gas conduit between the chamber and the EGR outlet, wherein the temperature sensor is electrically connected to the control unit. The temperature sensor may also be arranged outside the chamber of the scrubber at a position of the EGR conduit upstream the EGR outlet. The EGR arrangement may comprise additional temperature sensors, such that temperature of the exhaust gas stream may be measured upstream the scrubber. The data from the one or more temperature sensors may be sent to the control unit for analyzing performance of the EGR arrangement.

The control unit may comprise processing circuitry adapted for the purpose to run program executable code, read data from the sensors as well as send control signal to operate the controllable valves of the EGR arrangement. The control unit may also be connected to transfer operating data of the EGR arrangement to an engine management system. The control unit may also store data for later uses including analysis also known as data logging.

The control unit may comprise processing circuitry configured to control the water controllable valve for controlling the pressure and/or amount flow of water provided to the water spraying device based on the data from the sensor or sensors, including the humidity, temperature, and oxygen sensor(s). This allows for adapting the amount of injected water based on the amount of exhaust gases flowing through the EGR conduit as a function of the engine load signal optimizing water usage. The control unit may also be configured to control the water controllable valve for controlling the pressure and/or amount flow of water provided to the water spraying device based on data from the sensor or sensors and/or based on the EGR valve position or the engine load signal.

The control unit may further be connected to the controllable wastewater valve, for controlling the wastewater valve to assume a position allowing for wastewater to be removed from the chamber. This allows for controlling the removal of wastewater water from the chamber to prevent the chamber from overfilling with wastewater.

The chamber may comprise a low wastewater level sensor indicative of a low wastewater level in the chamber and a high wastewater level sensor indicative of a high wastewater level in the chamber, wherein the control unit is configured to control the controllable wastewater valve to assume an open position when the level of wastewater is above the high wastewater level to allow the removal of wastewater from the wastewater collection tank and to assume a closed position when the level of wastewater is below the low wastewater level to prevent removal of wastewater from the wastewater collection tank. When the wastewater level is below a minimum threshold wastewater level, or “low” level, the low wastewater level sensor sends a signal to the control unit, or similar hardware such as a programmable logic controller (PLC). In addition, the control unit or the sensor may send a signal to the wastewater valve to close the valve. When the wastewater level is above a threshold value indicating that the wastewater level is high, the high wastewater level sensor sends a signal to a control unit, or similar hardware such as a programmable logic controller (PLC). In addition, the control unit or the sensor may send a signal to the wastewater valve to open the valve to release wastewater from the wastewater collection tank. Maintaining the wastewater level within the range of a low level and a high level reduces the risk of exhaust gases escaping the chamber through the EGR scrubber chamber reducing the risk for overpressure in auxiliary equipment connected to the wastewater valve. In addition, it reduces the risk of exhaust gases escaping and harming onboard personnel. Using a low-level sensor and a high-level sensor also reduces a duty cycle of a wastewater removal pump, reducing energy consumption of the pump and prolonging pump life.

The EGR arrangement may further comprise a critical wastewater level sensor indicative of the wastewater level being at a critical level, and wherein the control unit is configured to control the at least one EGR valve to assume a closed position and to control the at least one controllable water valve to assume a closed position to prevent injection of pressurized water into the exhaust gas conduit. The critical wastewater level sensor indicates that the wastewater level has increased to a level higher than the high level, “high-high” level. This may indicate a problem with the wastewater valve, such as clogging or blockage. In addition, the level being above the critical level may indicate a problem with the control unit controlling the wastewater valve. When the wastewater level is above a threshold value indicating that the wastewater level is critical, the critical wastewater level sensor sends a signal to the control unit or similar hardware such as a programmable logic controller (PLC). Additionally, the sensor or control unit may generate an audible alarm signal in an engine control room. In addition, the control unit or the critical level sensor may send a signal to the EGR inlet valve or valves to close in order to isolate the EGR arrangement from the engine. In addition, the controllable water valve of the water spraying device may operate to discontinue or stop the supply of pressurized water to the water spraying device nozzles.

In addition, removal of wastewater may be commanded by the control unit, to operate the wastewater valve to open after the engine is turned off to prevent wastewater from being left in the wastewater collection tank for longer durations of time, or for removal of wastewater water during scrubber maintenance or cleaning.

The at least one EGR scrubber may be arranged inside an outer housing, the outer housing comprising an inlet opening and an outlet opening and wherein the housing is fed with cooling fluid from outside the outer housing, through the inlet opening and the outer housing and out from the outlet opening, using at least one of a fan, blower or pump in order to cool the outer surface of the at least one EGR scrubber. The cooling fluid may be air or a liquid fluid such as water including sea water. Arranging the scrubber in a housing may reduce noise in an engine or machinery room. It may also allow for having ventilation to air cool the scrubber external surface, which in turn improves exhaust gas stream cooling and condensation inside the EGR scrubber. The cooling air may be fed from air fans or air blowers into the housing inlet. After cooling the external surface of the EGR scrubber, the now heated air may flow out from the housing from the housing outlet. The housing inlet and outlet may be connected through air ducts to a position external the ship/facility. This further allows for the removal of the heat from the engine room to a position external the ship/facility reducing heat soak in the engine room.

The EGR arrangement may further comprise at least a second EGR scrubber arranged in fluid communication between the first EGR scrubber and the EGR outlet. The second EGR scrubber may then operate in series with the first EGR scrubber. This allows for improved performance on larger sized engines since scrubbing of exhaust gases are made in two steps, a first primary step using the first EGR scrubber and a secondary step using the second EGR scrubber. Additionally, the EGR arrangement may comprise more than two EGR scrubbers arranged in series and EGR scrubbing of exhaust gases may be made in a number of steps corresponding to the number of EGR scrubbers of the EGR arrangement.

Using multiple EGR scrubbers in series allows for two smaller EGR scrubbers to replace one larger single EGR scrubber. Hereby, a greater flexibility when installing the EGR arrangement to current engine installations is achieved. In addition, two smaller EGR scrubbers may be less costly compared to one larger EGR scrubber. In addition, only manufacturing EGR scrubbers of one standard size may be cheaper than manufacturing a wide variety of different sized EGR scrubbers.

The EGR arrangement may also comprise a second or more EGR scrubber, arranged between the EGR inlet and the EGR outlet, operating in parallel with the first EGR scrubber.

When the EGR arrangement is installed on a V motor, each of the cylinder banks of the motor may comprise an individual EGR arrangement connected to each cylinder bank. Alternatively, only one of the cylinder banks may be connected to an EGR inlet for receiving exhaust gases and an EGR outlet of the EGR arrangement may be arranged to provide cleaned exhaust gases to the intake side of both cylinder banks, such as upstream a shared turbocharger compressor inlet. If separate turbochargers are used for the cylinder banks, the EGR outlet may be split into two outlets, each outlet connected to provide clean exhaust gases to a respective turbocharger compressor inlet.

For EGR scrubbers operating in parallel, a controllable diverter valve is arranged downstream the EGR valve and upstream the first and second EGR scrubber, the diverter valve is controllable to divert a portion of the EGR gas flow from the exhaust gas stream of the exhaust gas conduit to the second EGR scrubber. This arrangement allows for diverting all of the exhaust gas flow to either the first or the second scrubber, or divide the exhaust gas flow between the two EGR scrubbers. Operation of the EGR arrangement may then be done using one or more EGR scrubbers depending on the engine load. In addition, this allows for optimal engine uptime or operating time, since the exhaust gases entering the EGR conduit may be completely diverted to one of the EGR scrubbers allowing the EGR scrubbers not receiving exhaust gas to be serviced or repaired. In addition, for some engines running at low load, cylinders may be deactivated to save fuel by not injecting fuel into a subset of cylinders for an engine for what is also referred to as cylinder deactivation. During cylinder deactivation, the diverter valve may divert all of the exhaust flow to a single EGR scrubber. When two or more EGR scrubbers operate in parallel they may be joined downstream the EGR scrubbers to a common exhaust stream upstream the EGR outlet.

For the case when the EGR system comprises a plurality of EGR scrubbers, the size of the second EGR scrubber may be different from the size of the first scrubber.

A second aspect of the present invention relates to a 4-stroke compression engine comprising the exhaust gas recirculation (EGR) arrangement according to any one of the above described examples.

The engine may comprise at least one cylinder bank and an exhaust manifold mounted to the cylinder bank, wherein the EGR inlet is connected to the exhaust manifold at a position upstream of an exhaust gas collector point, the collector point being a point in the exhaust manifold wherein exhaust gas from the engine cylinder bank is joined to form a common exhaust gas stream comprising exhaust gas from each cylinder of the engine cylinder bank.

The engine comprising the above described EGR arrangement may have the EGR inlet connected to an individual cylinder engine exhaust gas runner of the exhaust manifold.

The engine comprising the EGR arrangement may comprise an exhaust manifold and the exhaust manifold may comprise a plurality of manifold inlets connected to a matching number of engine exhaust ports, and an exhaust manifold outlet connected to the engine exhaust system, wherein the EGR inlet is connected to the exhaust manifold upstream the exhaust manifold outlet and downstream the plurality of manifold inlets. The engine comprising the EGR arrangement may comprise the EGR outlet connected to the engine intake upstream a turbo compressor.

The engine comprising the EGR arrangement may comprise a control unit, and the control unit may control the EGR valve to divert 5-10% of combustion gases from the exhaust manifold to the EGR inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which:

Fig 1 shows a schematic view of the EGR arrangement installed on an engine according to an example embodiment;

Fig 2 shows an exhaust manifold with connection to the EGR inlet of the EGR arrangement according to an example embodiment;

Fig 3 shows the EGR arrangement with two EGR scrubbers and water spraying devices operating in series according to an example embodiment;

Fig 4 shows the EGR arrangement with two EGR scrubbers and water spraying devices operating in parallel according to an example embodiment;

Fig 5 shows an enlarged view of the exemplified water spraying device of Fig. 1 ;

Fig 6 shows an enlarged view of an example of a EGR scrubber comprising two water spraying devices;

Fig. 7 shows examples of arranging perforated plates inside the EGR scrubber chamber;

Fig. 8 shows the wastewater collection tank with wastewater valve and sensor arrangement;

Figs. 9 show examples of perforated plates; and

Fig. 10 shows one examples of the EGR arrangement arranged inside an outer housing. DETAILED DESCRIPTION

Aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these aspects and embodiments are provided by way of examples so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig. 1 , shows an example embodiment of an EGR arrangement 100 installed on an inline four-cylinder compression ignition engine 1. The engine 1 has one common cylinder bank 10 comprising the four cylinders of the engine 1. A first 11 , a second 12, a third 13 and a fourth cylinder 14 is shown in Fig. 1. The engine 1 comprises an intake side having an intake manifold 21 connected downstream of a turbocharger compressor 22. The engine 1 also comprises an exhaust side having an exhaust manifold 31 mounted to the engine. The exhaust manifold 31 is arranged upstream a turbocharger turbine 32. The exhaust manifold 31 comprises four exhaust gas inlets 33, each connected to an individual exhaust gas port of the first 11 , second 12, third 13 and fourth cylinder 14 of the engine 1. In addition, the exhaust manifold 31 comprises a common exhaust outlet 34 for connecting to an engine exhaust system (not shown). The manifold 31 joins the exhaust gas streams of the individual exhaust ports into one common exhaust gas stream at the outlet 34. The outlet 34 may also be referred to as a collector point 34. The EGR arrangement comprises an EGR inlet 41 . The EGR inlet is connected to a port or opening in the exhaust manifold 31 . The EGR inlet 41 is arranged to receive exhaust gas from a low-pressure area of the exhaust manifold 31 when the engine 1 is operating. Fig. 1 shows the EGR inlet 41 arranged in the exhaust manifold 31 at a short end of the exhaust manifold 31 opposite the short end of the exhaust manifold outlet 34. This provides for exhaust gases having a relative low pressure, temperature and soot and unburnt fuel amount, to enter the EGR inlet 41.

The EGR arrangement 100 comprises an EGR conduit starting with the EGR inlet 41 for receiving exhaust gas from the exhaust manifold 31 of the engine 1 , and an EGR outlet 42 for providing cleaned exhaust gas to the turbocharger compressor inlet 23.

The EGR arrangement 100 comprises a pipe section 101 for connecting the EGR inlet 41 to a controllable EGR valve 51 arranged downstream the EGR inlet 41. The pipe section 101 may be provided with a cooling structure (not shown), such as an air or liquid cooling arrangement, reducing the temperature level of the exhaust gas in the pipe section 101. The controllable EGR valve 51 is also shown arranged upstream an EGR scrubber 70. The EGR valve 51 is controllable to adjust or control the amount of exhaust gas that is recirculated through the EGR arrangement and EGR conduit. A further pipe section 102 connects the EGR valve 51 to the EGR scrubber 70.

A water spraying device 60 is arranged between the EGR valve 51 and the EGR scrubber 70. The water spraying device 60 is arranged upstream the EGR scrubber 70 and downstream the EGR valve 51 . The water spraying device 60 is further disclosed below in relation to the description of Figs. 5-6. The water spraying device 60 injects or sprays a mist of water into the exhaust gas for cooling the exhaust gases and for promoting removal of exhaust gas combustion particles or soot from the exhaust gases. Fig. 1 shows the water spraying device arranged at a pipe section 67 that is widened in relation to the pipe section 102. The water spraying device 60 further comprises a controllable water valve 61 for controlling the water flow amount and/or pressure. The controllable water valve is in turn fluidly connected to a source of pressurized water (not shown).

The EGR scrubber 70 comprises an inlet 71 and an outlet 72. The inlet 71 is arranged downstream the water spraying device 60 and the EGR valve 51 . The outlet 72 is arranged downstream the EGR scrubber inlet 71 and upstream the EGR outlet 42. The EGR scrubber 70 is further shown having a chamber 76 extending between the EGR inlet 71 and the EGR outlet 71. The chamber 76 is shown as comprising a plurality of perforated plates 73 for cooling and cleaning of exhaust gas, by condensation of water vapor comprising suspended combustion particles. When the mixture of exhaust gases and water vapor cools down, the water vapor forms water droplets with combustion particles or soot attached. Fig. 1 shows that the EGR scrubber 70 comprises a wastewater collection tank 74 extending from the chamber 76 for collecting condensation water with combustion particles or soot attached. The water collected in the wastewater collection tank 74 may be referred to as wastewater. The wastewater collection tank 74 further comprises an opening 75 in the bottom of the tank 74, and a controllable wastewater valve 62 connected to the opening 75. The wastewater valve 62 is electrically or manually controllable to move into an open position for allowing wastewater to evacuate the wastewater collection tank 74 of the EGR scrubber 70. Downstream the EGR scrubber outlet 72, three sensors 81 , 82, 83 are arranged to measure properties of the cleaned exhaust gas stream. The sensors 81 , 82, 83 are shown as a humidity sensor 81 , for sensing the amount of water and/or water vapor in the exhaust stream downstream the EGR scrubber outlet 72, a temperature sensor 82 for sensing and determining the temperature of the cleaned exhaust gas, and an oxygen 83 for determining the oxygen amount of the cleaned exhaust gas.

Fig. 1 also shows an optional second EGR valve 52 arranged downstream the sensors 81 , 82, 83 disclosed above. The second EGR valve 52 is controllable to close and isolate, or block, the EGR arrangement 100 from providing exhaust gas, such as cleaned exhaust gas to the EGR outlet 42 and the engine intake 23 upstream the turbocharger compressor 22.

Fig. 1 further shows a control unit 200. The control unit 200 is electrically connected to the first EGR valve 51 as well as to the second EGR valve 52. The control unit 200 comprises processing circuitry adapted to run executable code configured to control the opening and closing of the EGR valves 51 , 52. The control unit 200 is also electrically connected to the controllable water valve 61 of the water spraying device 60. Thereby, the control unit 200 can control the opening and closing of the controllable water valve 61 to adjust the pressure and flow amount of injected water to the exhaust stream. The control unit 200 is also electrically connected to the controllable wastewater valve 62. Thus, the control unit 200 is able to control the removal of wastewater from the wastewater collection tank 74 and prevent the EGR scrubber 70 from overfilling with wastewater. Additionally, the control unit 200 is connected for receiving sensing data from the sensors 81 , 82, 83. The sensing data may be fed to the executable code to control injection of water to the exhaust gas stream, control removal of wastewater from the wastewater collection tank 74 of the EGR scrubber 70 and control the degree of opening of the first and second EGR valves 51 , 52. In particular, the injection of water may be controlled in response to the sensing data from e.g. the humidity sensor 81 to reduce the risk of water, or water condensate, entering the intake manifold 21 of the engine. The control unit 200 is also connectable to an engine control unit, ECU, 2. The control unit is able to receive engine operating data including engine load signal from the ECU 2 and input the data to the control program or executable code running on the control unit 200.

Fig. 2 shows an exemplified engine 1 according to Fig. 1 , comprising an alternative example of the exhaust manifold of Fig. 1 . An exhaust manifold 31 ' comprises individual exhaust gas port runners 33' connecting a respective exhaust port 33' of the cylinder bank 10 to the main body 37 of the exhaust manifold 31 Fig. 2 shows that the EGR inlet 41 ' is connected to the exhaust gas runner of the first cylinder 11 of the engine 1 . Dashed lines 39 in Fig. 2 show schematically the exhaust gas flow in the exhaust manifold and how a portion of the exhaust gas from the first cylinder 11 exhaust gas runner is diverted and provided to the EGR inlet 41 ' of the EGR arrangement. The exhaust gas provided to the EGR inlet 41 thereby primarily, or fully, comprise exhaust gas from the first cylinder 11 . The exhaust gas is thus diverted upstream a collection point 34 of the exhaust gas manifold 31 ' wherein exhaust gas from all of the cylinders is joined to form one common exhaust stream.

Fig. 3 shows a variation of the EGR arrangement 100 of Fig. 1. The EGR arrangement 100' of Fig. 3 comprises an additional second water spraying device 60' and EGR scrubber 70', arranged downstream the first EGR scrubber 70 and upstream the EGR outlet 42. The EGR scrubber arrangement 100' shown in Fig. 3 works in two cleaning stages wherein the EGR gasses are cleaned with two EGR scrubbers 70, 70' working in series configuration. The second EGR scrubber 70' is further shown comprising a plurality of perforated plates 73' as well as a wastewater valve 62'. Further, an EGR valve 52 is arranged downstream the second EGR scrubber 70'. Fig. 3 further shows that the second water spraying device 60' comprises a controllable water valve 61 '. Fig. 3 shows a first humidity sensor 81 arranged downstream the first EGR scrubber 70 and upstream the second EGR scrubber 70', as well as a second humidity sensor 81 ' arranged downstream the second EGR scrubber 70'. The temperature and humidity sensors are arranged downstream the second EGR scrubber 70'.

Fig. 4 shows an alternative EGR arrangement 100" according to an example embodiment, The alternative EGR arrangement 100" comprises a first EGR scrubber 70 and a first water spraying device 60 according to the EGR arrangement disclosed in relation to Fig. 1. The EGR arrangement 100" further comprises a second EGR scrubber 70" and a second water spraying device 60". The first and second scrubbers 70, 70" are arranged downstream the EGR valve 51 and a diverter valve 80. The diverter valve 80 is a controllable three-way valve electrically connected to the control unit 200 disclosed in relation to Fig. 1. The three- way valve is controllable to control the amount of exhaust gases flowing into the first and second EGR scrubber 70, 70". Additionally, the second EGR scrubber 70" of Fig. 4 is disclosed as being smaller in size compared to the first scrubber 70. The second EGR scrubber 70" has a diameter approximately half the diameter of the first EGR scrubber 70. When the EGR arrangement 100" is operating on an engine at a low engine load, the diverter valve 80 is controllable to assume a position such that either of the two EGR scrubbers 70, 70" are not provided with exhaust gases. Thus, one of the EGR scrubbers 70, 70" are arranged in a non-operating mode. When the EGR arrangement 100" is operating on an engine at a high engine load, the diverter valve 80 can assume a position that provides both EGR scrubbers 70, 70" with exhaust gas. Downstream the EGR scrubbers 70, 70" and upstream the EGR valve 52 and EGR outlet 42, the two cleaned gas streams are joined at a joining point 84 to form a common cleaned exhaust gas stream provided to the turbocharger compressor inlet. Fig. 4 shows that each of the first and second EGR scrubbers 70. 70" comprises a respective humidity sensor 81 , a temperature sensor 82 and an oxygen sensor 83. Further, Fig. 4 shows that the second EGR scrubber comprises a wastewater valve 62'.

Fig. 5 shows an enlarged view of the water spraying device 60 shown in Fig. 1 according to an example embodiment. The water spraying device 60 comprises a controllable water valve 61. The controllable water valve 61 is connected to a source of pressurized water (not shown). The water spraying device 60 further comprises a pipe section 63 connecting the water controllable valve 61 to a first and a second nozzle 64, 65. Both nozzles 64, 65 are arranged aligned with the central axis A of the exhaust conduit. The first nozzle 64 is arranged facing against the exhaust gas flow. The second nozzle 65 is arranged facing a direction opposite the first nozzle 64, in a direction along the exhaust gas flow. Each nozzle is shown having a plurality of openings for spraying water into the exhaust gas stream through water jets forming a spray pattern 66. The patterns 66 formed by the first and second nozzle 64, 65 are shown as having a cone like shape. The injected water from the pattern 66 vaporizes and forms a mixture of exhaust gas and water vapor. Downstream the second spray nozzle 65, the mixture of exhaust gas and water vapor enters the EGR scrubber chamber inlet 71 .

Fig. 6 shows an enlarged view of an EGR scrubber 700 according to an example embodiment, wherein a first and a second water spraying device 60 is arranged inside the chamber 76. The EGR scrubber 700 comprises a chamber 76 having an inlet 71 and an outlet 72. A plurality of perforated plates 73 are arranged in the chamber 76, the plates 73 arranged downstream the inlet 71 and upstream the outlet 72. The chamber 76 preferably has a cylindrical shape or a box shape. The perforated plates 73 are shown arranged perpendicular to and extending from the chamber inner walls or surface 77. Fig. 6 shows that the chamber comprises perforated plates 73, wherein the openings 78 of the perforated plates are radially offset from the openings 78 of neighboring perforated plates 73. This increases the distance the exhaust gas must take to flow through the chamber 76 from the inlet 71 to the outlet 72 as well as slows down the velocity of the exhaust gases. This increases the cooling effect provided by the perforated plates and improves cleaning efficiency.

Fig. 6 further shows a wastewater collection tank 74 of the EGR scrubber 70 arranged to collect wastewater 90. As the mixture of water vapor and exhaust gases enter the chamber and comes into contact with the perforated plates 73, the mixture is cooled until the water vapor condensates into water drops comprising water and suspended combustion particles such as soot or unburnt fuel. The water then exits the chamber and flows into the wastewater collection tank through longitudinally extending slits or openings arranged in the bottom portion of chamber (not shown). The water drops are collected in the wastewater collection tank 74 through gravity. Connected to a bottom portion of the wastewater collection tank is a wastewater outlet 75. The wastewater outlet 75 is connected to a controllable wastewater valve 62 downstream the wastewater outlet 75. The wastewater valve 75 in turn is connected downstream of the valve 75 to onboard equipment (not shown) such as a bilge tank or other tank for collecting wastewater onboard a marine vessel that is unsafe to pump overboard.

Fig. 7 shows an EGR scrubber 700' with a plurality of perforated plates 730-734 according to an example embodiment. The EGR scrubber chamber 760 is shown having a cylindrical shape indicated by the central axis B. In addition, Fig. 7 shows alternative mountings of a first 730, second 731 , third 732, fourth 733 and fifth 734 perforated plates in the chamber 760 of the EGR scrubber 700'. The first and the second perforated plates 730, 731 are arranged at a distance d from each other. The distance d is measured from a surface normal from the first perforated plate 730 to the second perforated plate 731 . Additionally, the first perforated plate 730 is shown having four openings 78'and the second perforated plate 731 is shown having seven openings 78". The openings of the first perforated plate 78'are radially offset from the openings 78" of the second perforated plate 731. Fig. 7 further shows that the third perforated plate 732 is arranged at a distance d2 from the second perforated plate 731. The distance d2 is shown as being less than the distance d between the first and second perforated plate 730, 731 .

Fig. 7 also shows that the fourth 733 and fifth 734 perforated plates are arranged at an angle a from the first, second and third perforated plates 730, 731 , 732.

Fig. 8 shows the wastewater collection tank 74 of the EGR scrubber 70 disclosed in Figs. 1 and 3-7 according to an example embodiment. The wastewater collection tank 74 comprises an outlet 75 and a wastewater valve 62 arranged downstream the outlet 75. The control unit 200 of Fig. 1 is also illustrated in Fig. 8. The control unit 200 is electrically connected to a low wastewater level sensor 91 indicating a low wastewater level 91 ' in the wastewater collection tank 74 of the EGR scrubber 70. The control unit is also electrically connected to a high wastewater level sensor 92 indicating a high wastewater level 92' in the wastewater collection tank 74 of the EGR scrubber 70. For illustration purposes an example water level 90 is also shown in Fig. 8.

The control unit 200 is configured to control the controllable wastewater valve 62 to assume an open position when the level of wastewater is above the high wastewater level 92' to allow the removal of wastewater from wastewater collection tank 74. In addition, the control unit is configured to control the wastewater valve 62 to assume a closed position when the level of wastewater is below the low wastewater level 91 ' in the wastewater collection tank 74.

Fig. 8 further shows a critical wastewater level sensor 93 indicating that the wastewater level is at or above a critical level 93'. When the control unit 200 receives a signal from the critical wastewater level sensor 93 that the wastewater level is at or above the critical level, the control unit 200 or software running on the control unit isolates the EGR arrangement of Fig. 1 from the engine by closing of EGR valve 51 and EGR valve 52. The control unit 200 also operates the one or more water valves 61 , 62 to close and discontinue injecting water through the nozzle or nozzles of the water spraying devices 60.

Figs. 9 show examples of different types of perforated plates for use in an EGR scrubber. Fig. 9a shows a first example of a square shaped plate 900 comprising a plurality of even sized openings 908 arranged in a first pattern. All of the openings are shown with the same or equal diameters. The openings are arranged in first 918 and second groups 919 of openings, wherein the openings 908 of a first group 918 are arranged interleaved from the openings 908 of a second group 919.

Fig. 9b shows a perforated plate 920 comprising openings 921-923 having different diameters. The openings are arranged in first 929, second 930 and third groups 931.

Fig. 9c shows a circular perforated plate 940 comprising a plurality of openings 948 each with the same or equal diameter, the openings 948 evenly spaced on the perforated plate 940. Fig. 9d shows a circular perforated plate 960 comprising a plurality of opening 968, 969. The perforated plate 960 comprises a plurality of first openings 969 having a first diameter, and four openings 968 having a diameter larger than that of the first openings 969. Figs. 9a-9d shows openings having a round shape, but other shapes are possible such as square, start or hexagon shaped. Additionally, plates having openings in different patterns may be combined into a stack of perforated plates.

Fig. 10 shows an EGR arrangement 100 of Fig. 1 comprising a single EGR scrubber 70 and water spraying device 60 arranged inside an outer housing 111. The outer housing 111 comprises an inlet 112 and an outlet 110. The inlet 112 is arranged to receive a flow of cooling fluid such as water or air from a pump or fan arranged external to the housing (not shown). The cooling fluid flows from the pump or fan through the inlet 112, through the internal volume of the housing and out of the outlet 110. As the cooling fluid flows through the housing 111 the external surface of the EGR scrubber and piping is cooled to further help with cooling the exhaust gases flowing through the EGR conduit and EGR scrubber 70. The outlet 110 of the housing 111 may in turn be connected to piping to a point or position external to the room or space wherein the engine and EGR arrangement is installed, such as ambient air (not shown).

Claims

1 . An exhaust gas recirculation (EGR) arrangement (100) for a single or multi-cylinder 4-stroke compression ignition engine, the EGR arrangement (100) comprising: an exhaust gas conduit having an EGR inlet (41) and an EGR outlet (42), wherein the EGR inlet (41) is arranged to be connected to an engine exhaust manifold (31) of an engine cylinder bank for receiving a portion of combustion gases from at least one cylinder of the cylinder bank, and wherein the EGR outlet (42) is arranged to be connected to an intake of the engine upstream a turbocharger compressor inlet, at least one controllable EGR valve (51) arranged in fluid communication between the EGR inlet (41) and the EGR outlet (42), an EGR scrubber (70) arranged in the exhaust gas conduit in fluid communication between the EGR valve (51) and the EGR outlet (42), wherein the EGR scrubber (70) is a water scrubber comprising a chamber (76) having a chamber inlet (71) and a chamber outlet (72), the chamber outlet (72) being arranged in downstream fluid communication with the chamber inlet (71), and at least one water spraying device (60) comprising at least one nozzle (64), the at least one water spraying device (60) being arranged downstream the EGR valve (51) and upstream the chamber outlet (72), wherein the water spraying device (60) is connectable to a pressurized water source and configured to inject pressurized water into the exhaust gas conduit via the at least one nozzle (64), to increase a liquid surface area of the injected water coming into contact with the exhaust gases in the exhaust gas conduit.

2. The exhaust gas recirculation (EGR) arrangement (100) according to claim 1 , wherein at least one water spraying device (60) is arranged upstream the EGR scrubber (70) and downstream the EGR valve (51), for spraying water into the exhaust gas conduit.

3. The exhaust gas recirculation (EGR) arrangement (100) according to any preceding claim, wherein at least one water spraying device (60) is arranged to spray water inside the chamber (76).

4. The exhaust gas recirculation (EGR) arrangement (100) according to any preceding claim, wherein the at least one water spraying device (60) comprises a controllable water valve (61) for controlling the pressure and/or flow amount of water provided to the nozzle (64).

5. The exhaust gas recirculation (EGR) arrangement (100) according to any preceding claim, wherein the EGR scrubber (74) further comprises a wastewater collection tank (74) for collecting wastewater, and at least one controllable wastewater valve (62) in fluid communication with a wastewater outlet (75) of the wastewater collection tank (74), the wastewater valve (62) configured to control removal of collected wastewater containing combustion particles, such as soot, from the chamber, by the opening of the at least one wastewater valve (62).

6. The exhaust gas recirculation (EGR) arrangement (100) according to any one of the preceding claims, wherein the chamber (76) comprises at least one perforated plate (73) comprising a plurality of openings (78), the perforated plate being arranged inside the chamber (76) downstream the at least one water spraying device (60).

7. The exhaust gas recirculation (EGR) arrangement (100) according to claim 6, wherein the chamber (76) comprises a plurality of perforated plates (730, 731, 732) arranged in a stacked formation at a distance (d, d2) from each other.

8. The exhaust gas recirculation (EGR) arrangement (100) according to claim 6-7, wherein the chamber comprises a plurality of perforated plates, and wherein a first and a second perforated plate (732, 734) are arranged at an angle (a) to each other.

9. The exhaust gas recirculation (EGR) arrangement (100) according to any one of claims 6 to 8, wherein the chamber (76) comprises a first and a second perforated plate, a diameter of the openings of the first perforated plate are the same or different from a diameter of the openings of the second perforated plate.

10. The exhaust gas recirculation (EGR) arrangement (100) according to any one of claims 6 to 9, wherein the chamber comprises a first and a second perforated plate, the openings of the first perforated plate being radially offset from the openings of the second perforated plate.

11. The exhaust gas recirculation (EGR) arrangement (100) according to any preceding claim, further comprising a control unit (200) electrically connected to the EGR valve (51) and configured to control the EGR valve to assume a position to adjust the amount of exhaust gases recirculated from the EGR inlet to the EGR outlet based on an engine load signal.

12. The exhaust gas recirculation (EGR) arrangement (100) according to claim 11 , the EGR arrangement further comprising at least one humidity sensor (81) arranged downstream the EGR chamber for determining the amount of water in the exhaust gas stream, wherein the at least one humidity sensor is electrically connected to the control unit.

13. The exhaust gas recirculation (EGR) arrangement (100) according to claim 11-12, further comprising at least one oxygen sensor (83) arranged in the exhaust gas conduit between the chamber and the EGR outlet, the oxygen sensor arranged to determine an oxygen amount in the exhaust gas stream, wherein the oxygen sensor is electrically connected to the control unit.

14. The exhaust gas recirculation (EGR) arrangement (100) according to claims 11-13, further comprising at least one temperature sensor (82) arranged downstream the EGR chamber and upstream the EGR outlet, wherein the temperature sensor is electrically connected to the control unit (200).

15. The exhaust gas recirculation (EGR) arrangement (100) according to any one of claims 12-14, wherein the control unit (200) is configured to control the water controllable valve (61) for controlling the pressure and/or amount flow of water provided to the water spraying device (60) based on data from the sensor or sensors and/or based on the EGR valve position or an engine load signal.

16. The exhaust gas recirculation (EGR) arrangement (100) according to any one of claims 11 to 15, wherein the control unit (200) is further connected to the controllable wastewater valve (62), for controlling the wastewater valve to assume a position allowing for wastewater to be removed from the chamber (76).

17. The exhaust gas recirculation (EGR) arrangement (100) according to any one of the preceding claims, wherein at least one EGR scrubber(70) is arranged inside an outer housing (111), the outer housing comprising an inlet opening (112) and an outlet opening (110) and wherein the housing is fed with cooling fluid from outside the outer housing, through the inlet opening and the outer housing and out of the outlet opening, using at least one of a fan, a blower or a pump in order to cool the outer surface of the at least one EGR scrubber.

18. The exhaust gas recirculation (EGR) arrangement (100) according to any one of the preceding claims, further comprising at least a second EGR scrubber (70') arranged in fluid communication between the first EGR scrubber (70) and the EGR outlet (42).

19. The exhaust gas recirculation (EGR) arrangement (100) according to any one of claims 1-17, the EGR arrangement further comprising a second EGR scrubber (70"), arranged between the EGR inlet (41) and the EGR outlet (42), operating in parallel with the first EGR scrubber (70).

20. A 4-stroke compression engine (1) comprising the exhaust gas recirculation arrangement (100, 100', 100") according to any one of the preceding claims.

21 . The 4-stroke compression engine of claim 20, wherein the engine comprises at least one cylinder bank (10) and an exhaust manifold (31) mounted to the cylinder bank, wherein the EGR inlet (41) is connected to the exhaust manifold at a position upstream of an exhaust gas collector point (34), the collector point being a point in the exhaust manifold wherein exhaust gas from the engine cylinder bank is joined to form a common exhaust gas stream comprising exhaust gas from each cylinder (11 , 12, 13,14) of the engine cylinder bank (10).

22. The 4-stroke compression engine of claim 20, wherein the EGR inlet (41 ') is connected to an individual cylinder engine exhaust gas runner (33') of the exhaust manifold (31 ').

23. The 4-stroke compression engine of claim 20, wherein the exhaust manifold comprises a plurality of manifold inlets (33) connected to a matching number of engine exhaust ports, and an exhaust manifold outlet (34) connected to an engine exhaust system, wherein the EGR inlet (41) is connected to the exhaust manifold (31) upstream the exhaust manifold outlet (34) and downstream the plurality of manifold inlets (33).

24. The 4-stroke compression engine according to claim 20-23, wherein the EGR outlet (42) is connected to the engine intake upstream a turbo compressor (22).

25. The 4-stroke compression engine according to claim 22-24, wherein the control unit (200) controls the EGR valve (51) to divert 5-10% of combustion gases from the exhaust manifold (31) to the EGR inlet (41).