A fuel injector for an internal combustion engine

The present invention relates to a fuel injector for an internal combustion engine, comprising at least a housing, a valve seat, a valve spindle, an atomizer, and a cut-off element; which atomizer has a central bore from which a plurality of nozzle bores extend through a side wall of the atomizer; which valve spindle has a valve element and is dis- placeable between a closed position, in which the valve element abuts the valve seat, and an open position, in which fuel is admitted past the valve seat and to the nozzle bores; which cut-off element is carried by a shaft on the valve spindle and comprises a first cylindrical section located in the central bore of the atomizer to close fuel access to inlet openings of a first group of nozzle bores, when the valve spindle is in the closed position. JP3027191B2 corresponding to KR253673B describes a fuel injector for an internal combustion engine, comprising a displaceable valve spindle for opening and closing a flow passage to nozzle bores in a central bore of an atomizer. The valve spindle has a foremost section with a cut-off element carried by a shaft and fitting in the central bore of the atomizer. In the closed position of the valve spindle, the cut-off element covers the inlet openings of the nozzle bore in the central bore. In the open position of the valve spindle, the cut-off element exposes the inlet openings of the nozzle bores and fuel is supplied to the nozzle bores through one or more axial passages through the cut-off element. WO 99/53196 corresponding to JP3308551B2 and CN1093226C describes a similar fuel injection device for internal combustion engines, especially two-stroke diesel engines, comprising an atomized protruding into an associated combustion chamber. The conditions for fuel admission are approximately the same for all nozzle bores resulting in a stable jet. Admission chambers depart from the central bore in the atomizer and are located at least at a part of the nozzle bores. The diameter of the chambers is greater than the diameter of the nozzle bores. The admission chambers are designed in such a way that at least similar length ratios exist for all nozzle bores in the row of nozzle bores.

In the prior art fuel injectors provided with a cut-off element on a shaft extending on the forward side of the valve seat, the fuel is supplied to the nozzle bores via an internal flow passage in the cut-off element. The fuel is consequently flowing inside the lower part of the shaft and forward through the cut-off element and out through the free end where the fuel cools the forward end of the central bore in the nozzle and thus cools the nozzle tip. The fuel flows from the end of the central bore and towards the inlet openings to the nozzle bores.

It is the object of the present invention to provide a fuel injector having high reliability in use.

In view of this object, the fuel injector according to the present invention is characterized in that, in the open position of the valve spindle, fuel is supplied to at least a second group of the nozzle bores through a passage between the circumference of the cut-off element and the central bore of the atomizer, and in that the cut-off element has a second cylindrical section for closing off inlet openings of the second group of nozzle bores from the fuel volume present in the central bore in between the second cylindrical section and the valve seat, when the valve spindle is in the closed position. The flow of fuel through the internal flow passage in the cut-off element provides - as just mentioned in the above description - an important cooling effect to the nozzle tip. However, the fuel flowing from the end of the central bore and towards the inlet openings to the nozzle bores has already been warmed by heat from the tip area at the point in time when the fuel is flowing out through the nozzle bores, and the cooling effect at the area of the nozzle bores is smaller because of this warming. And the cooling effect on the nozzle wall from the flow of fuel inside the cut-off element and in the shaft bore leading to the cut-off element is quite small. The present invention provides an important cooling effect in the nozzle wall portion located on level with the cut-off element. By feeding the second group of nozzle bores through a passage between the circumference of the cut-off element and the side surface of the central bore, a part of the injected fuel flows directly into the passage and forward to the second group of nozzle bores and vigorously

cools the inside surface of the nozzle wall, and another part of the fuel flows into the shaft and forward through the internal passage in the cutoff element and out to cool the tip of the nozzle. The combined effects of this dual flow provide the heat-affected nozzle wall portions with effec- tive cooling also in the side wall area. Due to this latter cooling the risks of overheating of the side wall and of carbon formation on the inside of the side wall have been effectively diminished. And consequently the reliability in use and the durability of the fuel injector are increased.

Dividing the fuel flow to the inlet openings into two different pathways results in a better cooling effect in the atomizer, also because fuel is flowing on a larger internal area of the atomizer than the atomizer bores. The outside of the cut-off element is also cooled by the flow of fuel into the passage and this reduces the temperature level in the first cylindrical section. The resulting lower temperatures on the inside of the central bore reduce the risk of carbon formation on the parts, and consequently also the risk of sticking of the cut-off element is reduced.

The increased cooling effect is obtained without sacrificing the advantages of the cut-off element in relation to avoiding fuel leaks through the nozzle bores when the fuel injector is closed, because the second cylindrical section prevent fuel from seeping into the nozzle bores when the fuel injector is closed.

In an embodiment, nozzle bores in said first group have inlet openings arranged in a first row in the central bore of the atomizer; and the nozzle bores in said second group have inlet openings arranged in a second row in the central bore of the atomizer, which first and second rows are spaced apart in the axial direction of the atomizer. In this manner, the total number of nozzle bores arranged within a maximum angle of e.g. 120 degrees may be increased without compromising the strength of the side wall of the atomizer. In an embodiment, in the open position of the valve spindle, fuel is supplied to the first row of the inlet openings of the nozzle bores through at least one internal passage of the cut-off element and to the second row of the inlet openings of the nozzle bores through an annular recess in the circumference of the cut-off element. The recess in the cir-

cumference is also separating the periphery of the cut-off element form the inside of the central bore when the fuel valve is in the closed position, and this separation in the closed position results in even less risk of carbon formation in the atomizer. In an embodiment, in the open position of the valve spindle, fuel is supplied to the annular recess in the circumference of the cut-off element through a first section of the central bore of the atomizer having larger diameter than a second section of the central bore comprising both rows of the inlet openings of the nozzle bores. Thereby, the cooling effect may be further improved, because the larger diameter provides a larger internal area of the atomizer, and then the fuel flows across a larger surface area and provides a higher cooling effect. Consequently, the risk of carbon formation is further reduced.

In an advantageous embodiment in terms of manufacture, the first cylindrical section and the second cylindrical section of the cut-off element have equal outer diameter, and the first and second cylindrical sections fit sealingly into the second section of the central bore.

In an embodiment, in the closed position of the valve spindle, the annular recess in the circumference of the cut-off element covers the first and second rows of the inlet openings of the nozzle bores. Thereby, the axial dimension of the annular recess may be long compared to the total axial dimension of the cut-off element, whereby a good cooling effect may be obtained by fuel flowing in the annular recess, thereby further reducing the risk of carbon formation. In an advantageous embodiment in terms of manufacture, an axial bore extends through the first and second sections of the cut-off element and opens out at a free end of the first section, and said bore communicates with the central bore of the atomizer through side openings in the shaft. In an embodiment, the first row of the inlet openings of the nozzle bores is located at a distance in the axial direction of the atomizer from a shoulder between the first and second sections of the central bore of the atomizer, said distance equalling the distance from the second cylindrical section of the cut-off element to the free end of the first

cylindrical section of the cut-off element. In this manner it can be obtained that injection is performed simultaneously through the nozzle bores of either row.

In an embodiment, the nozzle bores are arranged in pairs of mutually parallel bores belonging to either row and having inlet openings at the same angular position of the central bore of the atomizer. This increases the strength of the nozzle for a given total number of nozzle bores.

In an embodiment, in the open position of the valve spindle, the cut-off element seals against the central bore between the first and the second rows of the inlet openings of the nozzle bores. Thereby, the separation by means of the cut-off element between the inlet openings of the two rows makes it possible to equalise parameters like the injection time, the flow conditions and the injection capacity of each row of nozzle bores, thereby further improving the combustion.

In an embodiment, the inlet openings of the nozzle bores in the first and the second row, respectively, are arranged at the same axial position of the atomizer, and in that the nozzle bores of a row are directed in different angles in relation to the axial direction of the atom- izer. Thereby, it is possible to control the injection time of the nozzle bores very accurately and at the same time cover a broad injection angle within the plane of the axis of the atomizer.

The invention will now be explained in more detail below by means of examples of embodiments with reference to the very sche- matic drawing, in which

Fig. 1 is a longitudinal sectional view of an embodiment of a fuel injector according to the present invention,

Figs. 2 and 3 are enlarged views of the forward end of the fuel injector in closed position and in open position, respectively, Fig. 4 is an even more enlarged view of the forward end of an atomizer,

Figs. 5a-5e are sectional views along centre axes of pairs of nozzle bores,

Fig. 5f is a cross-sectional view through the atomizer, and

Fig. 6 is an illustration of fuel injection into an engine cylinder provided with three fuel injectors.

Fig. 1 illustrates a fuel injector, generally designated 1, for injection of fuel, particularly heavy fuel oil. The fuel injector has a housing 2 of elongate shape and provided with an upper flange 3 for mounting fuel injector 1 onto the cylinder of the internal combustion engine and a connection 4 for a fuel supply pipe, not shown, supplying pressurized fuel from e. g. a fuel pump or a high-pressure reservoir.

The engine is typically a two-stroke crosshead engine for ship propulsion or for stationary power production to a grid. The engine can have a power per cylinder in the range from e.g. 150 kW to 7000 kW, and typically the individual cylinder is provided with several, such as two, three or four, fuel injectors.

An atomizer 5 projects through a forward end opening of the housing and extends into the combustion chamber of the engine cylinder, when fuel injector 1 is mounted on the engine.

Fuel delivered to the fuel injector can flow through a central bore 6 in connection 4 and a central channel 7 extending from bore 6 through a spring guide 8 and a circulation slider 9 to a pressure chamber 10 defined by circulation slider 9 and a guide 11 for the circulation slider. When circulation slider 9 is in its forward position illustrated in Fig. 1, a forward end of circulation slider 9 closes a passage 12 leading to a channel 13 extending centrally through a pressure pipe 14, a pressure member 15 and an upper section 30 of a valve spindle generally designated 16. In the valve spindle central channel 13 communicates with a primary pressure chamber 18 through inclined channels 17.

The primary pressure chamber 18 is defined by upper section 30 of valve spindle 16, and a spindle guide 19 for upper section 30. Valve spindle 16 has a valve element 20 with an annular valve seat area which abut a valve seat 21 when the valve spindle is in the closed position illustrated in Figs. 1 and 2. In this closed position there is no flow connection between primary pressure chamber 18 and a central bore 22 in the atomizer 5. A compression spring 23 abuts a spring disc 24 and presses forwards in the closing direction on the upper section 30 of valve

spindle 16 via a lower spring disc 25 so that valve element 20 is pressed sealingly against valve seat 21.

When fuel injector 1 is in the closed position just mentioned, the upper bore 6 communicates with the cavity located around spring guide 8 through a transverse channel (not shown) in spring guide 8 so that preheated fuel can circulate in the upper part of the valve 1 in a well- known manner. When fuel injection is to be initiated, the fuel pressure in central channel 7 and the pressure chamber 10 rises, making the circulation slider 9 move upwards and cut off the transverse channel in spring guide 8. The displacement of circulation slider 9 opens the passage 12, and the fuel pressure propagates through channel 13 and the inclined channels 17 to the primary pressure chamber 18.

When the fuel pressure in primary pressure chamber 18 reaches the opening pressure of the fuel injector, determined by the pre- tensioning of spring 23, the valve spindle is displaced upwards and away from valve seat 21, and the fuel begins to flow past the valve seat 21 and down into the central bore 22 in atomizer 5.

In the various embodiments described the reference numerals are re-used for details having the same function. Fig. 2 illustrates an embodiment where the tubular part of pressure member 15 extends into the upper section 30 to a position near inclined channels 17. Valve spindle 16 continues on the forward side of valve element 20 in a shaft 26 extending into the central bore of the atomizer. Shaft 26 is elongate and carries at the foremost end a cut-off element generally designated 27. The cut-off element has a first cylindrical section 28 and a second cylindrical section 29, which cylindrical sections 28, 29 have a cylindrical outer surface fitting into the central bore of the atomizer in a fluid-sealing manner when the valve spindle is in the closed position. A plurality of nozzle bores 31 is provided in the wall of the atomizer. The nozzle bores are arranged with their inlet openings 32 in a first group and in a second group. The inlet openings of the two groups can be arranged in an irregular pattern when viewed in the circumferential direction of the nozzle, or they can be arranged generally on a row or

on several rows, or they can as illustrated on the drawings be arranged in a first row A and a second row B. When the valve spindle is in closed position the first cylindrical section 28 is positioned at the first row A of inlet openings 32 and extends into the end portion of the central bore 22 located between the first row A of inlet openings and the end bottom 33 of the central bore so that the first cylindrical section cuts off the flow connection between this end portion of the central bore and the first row A of inlet openings. When the valve spindle is displaced away from the valve seat to the open position the first cylindrical section 28 is lifted free of the first row A of inlet openings, as illustrated in Figs. 3 and 4.

With the valve spindle in this position the total amount of fuel flowing from primary pressure chamber 18 and across valve seat 21 into central bore 22 divides into a first partial flow D of fuel entering side openings 35 and flowing inside shaft 26 and out into the bottom of the central bore where the fuel flow meets end bottom 33 and turns around into an upward flow feeding inlet openings 32 in the first row A.

A second partial flow C of fuel continues to flow forward on the outside of shaft 26 into a passage 36 between the circumference of second cylindrical section 29 and the side wall of central bore 22. The pas- sage extends forward past cylindrical section 29 and into the area in between the first cylindrical section 28 and the second cylindrical section 29.

A central flow passage 34 extends centrally through the cut-off element to side openings 35 in the shaft. The central flow passage can be embodied as a single axial bore extending from the free end of the cut-off element to the side openings 35 in the shaft, or it can alternatively be embodied as several passages extending in the shaft from the free end of the cut-off element to side openings 35.

The central bore 22 of the atomizer has a first section 22' with a larger diameter than a second section 22" of the central bore. The two rows A and B are both located in the second section 22" in the embodiments illustrated in Figs. 2 to 4. The second section 22" has a diameter only slightly larger than the outer diameter of the first and second cylindrical sections 28, 29 so that the second section functions as a guide for

the cut-off element and the first and second cylindrical sections 28, 29 fit into the second section 22" in a manner preventing fluid flow.

When the valve spindle is displaced from the closed position to the open position, the second cylindrical section 29 is lifted free of the second section 22" to the open position illustrated in Figs. 3 and 4. The fuel flow in the central bore 22 past the outside of the second cylindrical section 29 is illustrated by arrow C in Fig. 4. From annular recess 36 the flow continues onwards to the second row B of inlet openings 32 and out through the nozzle bores having inlet openings arranged in the second row B.

It is possible to obtain completely simultaneously opening of the fluid flow to inlet openings 32 in both the first row A and the second row B by adapting the positioning of the first row A to the size of the cut-off element 27 so that the first row A of inlet openings 32 is located at a dis- tance d in the axial direction of the atomizer from a shoulder 39 between the first and second sections of the central bore of the atomizer, said distance d equalling a distance e from the second cylindrical section 29 to the free end of the cut-off element.

The flow of fuel down into annular recess 36 and out through the nozzle holes fed by inlet openings 32 in the second row B acts to cool the wall material of the atomizer. The flow past the second cylindrical section 29 and through recess 36 is in contact with the inner surface of the central bore 22 and thus acts to cool the material of the atomizer. This cooling effect is much larger than the cooling obtainable by the flow through the nozzle bores, because the area of the inner surface of central bore 22 is large.

In addition, the cooling effect of the fluid flowing through recess 36 acts over the complete surface of the recess and not just in the angular sector where the nozzle bores are located. The highest heat input to the atomizer is located in the area opposite the angular sector where the nozzle bores are located. And this heavily heat affected zone is not cooled at all from nozzle bores because no nozzle bores are located in the zone. This will be more clearly explained in the below description relating to Fig. 6.

When the valve spindle is displaced to the closed position at the end of the injection sequence, the second cylindrical section 29 is displaced in direction towards the end bottom 33 of the central bore so that at least the forward portion of the second cylindrical section is located in the second section 22" and cuts off the flow connection between the first section 22' of the central bore 22 and the recess 36 with the second row B of inlet openings.

In Figs. 2 and 3 the combustion chamber in the engine cylinder is denoted 37, and a combustion chamber wall surface 38 is illustrated in broken line. The fuel injector housing 2 is located in a low temperature area cooled by the cylinder wall cooling, and the valve seat in side the housing is also located in this low temperature area. The free end of the atomizer 5 extending beyond combustion chamber wall surface 38 into the combustion chamber is located in a highly heat affected area. The nozzle bores 31 are oriented in different directions in order to produce the desired injection process. The different directions are relating to both the so-called horizontal direction, viz. an angular range of distributing fuel in the circumferential direction of the engine cylinder, and to the so-called vertical direction, viz. an angular range of distribut- ing the fuel in the height direction of the cylinder.

With respect to the vertical direction Fig. 5a to 5e illustrate an example of different vertical inclinations angles α of the nozzle bores. The vertical inclinations angle α indicated is measured as the angle between the longitudinal axis of the nozzle bore and the horizontal direc- tion (perpendicular to the central axis of the cylindrical bore). The vertical inclination angle can be different from one nozzle bore to another. To give examples on relevant variations, the nozzle bores indicated in Fig. 5a can have an angle α of 30°, the nozzle bores indicated in Fig. 5b can have an angle α of 20°, the nozzle bores indicated in Fig. 5c can have an angle α of 40°, the nozzle bores indicated in Fig. 5d can have an angle α of 10°, and the nozzle bores indicated in Fig. 5e can have an angle α of 30°. Although it is technically possible to use different vertical inclination angles for the nozzle bores located vertically above one another, it is preferred that the nozzle bores are arranged in pairs of mutually parallel

bores belonging to either row. The consequence of this is that in each pair of nozzle bores located vertically above one another the nozzle bores are mutually parallel.

As illustrated in Fig. 5f the nozzle bores are all located in an an- gular sector covering only a minor portion of the circumferential direction of the injector. The reason for this is illustrated in Fig. 6 showing a cylinder viewed from the above. The cylinder is provided with three fuel injectors 1 located close to the periphery of the engine cylinder. The individual fuel injector only injects fuel in a sector directed to the next fuel injector. And the hot combustion zone from the combustion of fuel injected from the previous injector acts on the atomizer in the area located in direction of the previous injector. As a result the atomizer is heated by the combustion from the previous injector and is cooled by the injection of fuel through nozzle bores directed towards the following fuel injector. The angular sector can be defined by the maximum horizontal angle β between the two nozzle bores extending in directions deviating the most from one another. This horizontal angle β is normally less than 120°, and preferably less than 100°.

Variations are possible within the scope of the appended patent claims. To give an example the fuel injector need not be of a type having a compression spring 23. Instead of a compression spring the movements of the valve spindle between the open and the closed positions can be controlled hydraulically by the fuel pressure or by the use of control oil in a known manner. If the fuel is not heavy fuel oil the circulation slider 9 can be dispensed with. And the central bore of the atomizer can have a uniform inner diameter along its entire length, and the inlet openings 32 can be arranged in a non-row pattern, such as evenly distributed over a cylindrical area of the central bore, or distributed in V- shape or another convenient non-linear shape.