DK171975B1 - Fuel injector for a large two-stroke internal combustion engine - Google Patents

Description

DK 171975 B1

The invention relates to a fuel injector for a large two-stroke internal combustion engine, such as a ship propulsion diesel engine, with an elongated outer housing for mounting in a water-cooled cylinder cover in such a way that the valve has an upper cooled valve section and a lower substantially non-cooled valve section which at least comprises the lower portion of the nebulizer with transverse nebulizer holes starting from a central longitudinal nebulizer bore and wherein a valve slider has an upper 10 section carrying a movable valve member for a primary valve seat located in the refrigerated valve section for opening and closing the fuel injector; and a thin lower section extending into the nebulizer bore and carrying a secondary valve member located in the lower valve section for the fuel flow to the nebulizer holes.

For four stroke engines, fuel injectors are known, where the primary valve seat is immediately above the nebulizer holes, see for example EP-A-0 451 408. Here, the front part 20 of the injector with the valve seat is cooled by the cooling water in the cylinder cover, since it is so small in thickness and the injector housing is so short that the cooling works all the way down to the tip of the injector. As a result of the cooling, the nebulizer and valve seat may be of hardened 25 steel.

In large two stroke engines, the cylinder cover is so thick that the lower valve section of the injector extends so far from the injector's abutment surface to the cooling cover down to the nebulizer bores that the lower portion is substantially uncooled and heated to high temperature by the engine's combustion gases. Since the high temperatures can lead to failure of the primary valve seat, for example due to coking or material degradation, the primary valve seat in these injectors is located in the upper, cooled valve section. This means that the flow passage between the primary valve seat and the nebulizer holes becomes long and receives a large volume, typically amounting to 2-3% of the fuel volume injected during a motor cycle.

When the primary valve seat is closed at the end of the fuel injection, the amount of fuel in the passage between the valve seat and the nebulizer holes is cut off from the fuel delivery pressure. This amount of fuel can seep or drip through the atomizer bores during the period when the injector is closed by itself. Since this residual amount of fuel is not atomized into the combustion chamber, no or very little combustion of the fuel is obtained. The unburned fuel 15 leads to the boiling of the combustion chamber and of the flow components which follow, as well as to an environmentally unfavorable discharge of fuel with the exhaust gas and of course also to increased fuel consumption.

The majority of these disadvantages are remedied with the fuel injector described in WO 93/07386 which is of the type mentioned initially. Here, the valve slider carries a secondary closure member in the form of a ring which extends downwardly past the atomizer holes in the closed position of the injector so that the amount of oil in the passage below the primary valve seat is prevented from flowing through the atomizer holes when the injector is closed. At the injector open movement, the ring slides upwards into the nebulizer bore to expose the nebulizer holes.

The central nebulizer bore has a constant diameter to allow insertion and displacement of the sliding ring in the bore.

In practice, the secondary closure injector has been found to lead to greater fuel consumption especially at 35 high engine loads. This is probably due to changed injection conditions when the injector is open and the oil is atomized into the combustion chamber.

The invention has for its object to provide a fuel injector which, despite a relatively high temperature level in the area around the atomizer holes, is both capable of limiting the discharge of fuel when the injector is closed, and to provide an advantageous good injection and distribution of fuel when the injector is open.

To this end, the fuel injector according to the invention is characterized in that the nebulizer bore has a downwardly decreasing diameter downstream section, that the nebulizer holes extend from the smaller diameter bore section, and that the lower section of the valve slide ends in level above the upper nebulizer hole. and the secondary closure member is located at the region of the diameter reduction of the bore when the slider is in its closing position.

Surprisingly, it has been found that the fuel injector according to the invention fulfills the above purpose.

The secondary closure means prevents the excess amount of fuel from penetrating to the nebulizer holes when the injector is closed. An explanation of the reduced fuel consumption when the injector is open can be reasonably found in the fact that the bore section leading to the nebulizer holes has an advantageously small diameter, which gives uniform flow conditions to the nebulizer holes. Since the valve slider is completed in any position above the atomizer holes, the fuel flow to these holes is probably only slightly affected by the presence of a secondary closure.

In the closed position of the valve, the primary valve seat prevents the fuel pressure on the pump side from affecting the area around the secondary closing means. Thus, there is no appreciable pressure drop across the closure means, which gives freedom to design this in a way that the closure means in its closed position only affects the material of the atomizer with very small forces.

The end of the valve guide at a distance from the upper nebulizer hole also gives the advantage that the slider tip is not affected by the erosion forces that appear around the nebulizer holes when the valve opens.

In a preferred embodiment, the secondary closure member has a cylindrical portion which can slide sealingly into the smaller diameter section of the nebulizer bore. As the slider is moved downward toward the closing position, the cylindrical portion is displaced into the narrower lower portion of the nebulizer bore 15 so that the flow connection between the nebulizer holes and the overlying wider portion of the nebulizer bore is interrupted. The cylindrical portion only affects the nebulizer itself with the small frictional force that results when the surfaces slip past one another. In the closed position of the injector, the cylindrical portion is accommodated within the lower portion of the nebulizer bore without the nebulizer being affected by actual closing forces.

In a particularly simple embodiment, the thin lower section of the valve slide with the secondary closure means is a rigid extension of the upper section of the slide. The stiffness of the thin section causes the slider tip to be held coaxial with the upper section of the slider and thus also coaxial with the nebulizer bore.

In an alternative embodiment, the thin lower portion of the valve slider is a transverse extension of its upper portion, and the lower portion has a level above the secondary closure means centering the closure member of the nebulizer bore through abutment against the wall of the larger diameter bore 35. The separate guide for centering the slider tip is more difficult to manufacture than a cylindrical, smooth lower section, but on the other hand there is no need for the lower section of the slider to be created relative to the upper section, with the 5 tip of the slider is self-centering in the nebulizer bore. This significantly facilitates mounting of the slider in the injector and ensures good centering of the slider even after long periods of operation. The self-erecting slider tip is particularly advantageous in cases where the lower section of the slider is a separate, replaceable unit.

It is preferred that the guide is configured as a plurality of radially extending longitudinal tabs on the lower portion of the slider and that the upper and lower ends of the tabs are preferably tapered. The longitudinal tabs only slightly interfere with the downward flow of fuel when the injector is open. The flow disturbances can be further mitigated by the ends of the tabs being tapered so that the flow gets smooth drainage from the tabs. For best flow conditions in the lower section of the nebulizer, the lower free end of the slider may conveniently be tapered so that not too many swirls are set up in the fuel as it passes through the secondary closing means from flowing out of the slider to even fill the entire cross-section of the bore.

In particular, if the fuel is gaseous, it may be convenient to design the injector so that the secondary closure member in its closed position abuts a bevel surface in the bore of decreasing diameter, and that the closure member is slidable in the longitudinal direction of the slider and spring-loaded for movement away from the top of the slider. section. The inclined surface acts as a valve seat, but due to the secondary closure member's displacement relative to the upper section of the slider, the closure member can be pressed against the seat at the maximum with the force produced by the associated spring. The spring force can be adjusted to the strength of the material in the nebulizer, ie. for example, the spring force can be selected so small that the seat material is largely unloaded by the closing means.

It is preferred that the lower thin section of the valve slide with the secondary closure means be a separate unit which is removably attached to the upper section. This makes it possible to replace the secondary closure member independently of the upper section of the slider, and furthermore, the manufacturing advantage is obtained that the two sections can be manufactured separately, ie. also in its own material, if it is desired that the closing means be of a more temperature resistant material than the upper section of the slider.

In order to achieve the greatest possible reduction in the oil loss during periods when the injector is closed, it is preferred that the area of the nebulizer bores with diminishing diameter is substantially closer to the nebulizer holes than to the primary valve seat. Thus, the volume of nebulizer drilling is limited below the secondary closure means.

To obtain a good start on the fuel atomization by opening the injector, it may conveniently be designed so that the secondary closure means only opens to the smaller diameter section of the nebulizer bore when the slider movable valve portion is moved a predetermined distance away from the primary valve seat. Thus, the pressure of the fuel in the larger diameter section of the nebulizer bore can be built up to suitably high pressure before the closing means opens for the fuel's access to the bore leading to the nebulizer holes. Therefore, when the fuel starts to spray out through the nebulizer holes, this occurs at higher pressure, which promotes the nebulization. In one embodiment, the delay of the closing member can be adjusted by the length of the cylindrical portion which can slide sealingly into the nebulizer bore, and in another embodiment, the delay is adjusted by the location of a stop pulling a slidable closure member with it in the slider movement.

Examples of embodiments of the invention 5 will now be described in more detail with reference to the schematic drawing, in which 1 is a longitudinal section through a first embodiment of a fuel injector; FIG. 2 and 3, on a larger scale, the lower section of 10 shows another embodiment of the injector in the open and closed positions, respectively; 4 and 5 show similar views of a third embodiment mounted in a cylinder cover; and FIGS. 6 and 7 show similar images of a fourth embodiment.

In FIG. 1, there is generally shown a fuel injector or fuel valve 1 with an upper flange 2 for clamping the injector in the engine. The flange has an upwardly extending studs 3 to which a pressure tube (not shown) can be clamped which supplies fuel under pressure from a suitable source, such as a fuel pump or a high pressure reservoir.

The injector has at its lower end a nebulizer 4. The fuel can be fed from the connection at the bore 3 down 25 to the nebulizer 4 through an upper flow passage 5 passing from a central bore 6 in the bore through a spring guide 7 and a circulation slide 8 down to a pressure chamber. 9 defined by the slider 8 and a guide 10 therefor. On the underside of a seat 11, fuel flow 30 may further descend toward the nebulizer through a central flow passage 12 in the form of a central bore in a pressure tube 13, a pressure member 14 and a valve slider 15, wherein the central bore is connected to a primary pressure chamber 16 through several diaphragm bores 17. The middle flow passage downwards is completed by a primary valve seat 18. Under this valve seat, the fuel in the open position of the injector can flow further through a lower flow passage 19 in the form of a central bore 20 (see Fig. 2) at the bottom of a slide guide 21 for the valve slide 15 and a coaxial nebulizer bore thereof.

The central longitudinal nebulizer bore comprises a larger diameter upper bore portion 22 which, through a diminishing diameter region 23, passes into a lower diameter lower bore portion from which 10 nebulizer holes 24 emerge as shown in the following figures.

When the injector is in its closed position shown in FIG. 1, the upper flow passage 5 is connected through a spring channel 7 not shown in the spring guide 7 to the cavity located around the spring guide, so that in the upper part of the injector well-known fuel can circulate in a well known manner. It may be noted here that the injector of FIG. 1 is intended for injection of oil, in particular heavy fuel oil. When the fuel injection is to be initiated, the oil pressure rises in the upper flow passage 5 and in the pressure chamber 9, so that the circulation slide 8 moves upwards and blocks the transverse circulation passage. At the same time, the flow passage past the seat 11 is opened and the pressure propagates down through the middle flow passage 12 and the inclined bores 17 to the primary pressure chamber 18. A pressure spring 25 abuts an upper spring plate 26 and presses through a lower spring plate 27 downwards on the valve slide 15, relative to the primary valve seat 18, movable valve member 28 in the form of an annular tapered surface of the valve slider is pressed tightly against the valve seat 18.

As the oil pressure in the primary pressure chamber 16 reaches the opening pressure of the valve, which is determined by biasing of the compression spring 25, the valve slider 15 is moved upward as the oil begins to flow past the primary valve seat 18.

9 DK 171975 B1

The movable valve member 28 defines the upper portion of the valve slide 15 from a thin lower portion 30 of the slide. In the embodiment shown in FIG. 1, the lower section 30 is cylindrical and has a diameter 5 slightly smaller than the diameter of the smaller diameter 29 section of the nebulizer bore, so that the lower section 30 of the slider can slide sealingly into the lower bore section 29.

As the lower section 30 projects a bit down into the bore section 29 when the injector is closed, the pressure 10 is built up by opening the valve in the upper bore section 22, before the lower section 30 of the slider is lifted up by the bore section 29, thereby opening up the oil flow to the nebulizer holes. The pressure buildup in the oil prior to final feeding to the nebulizer holes promotes fine atomization of the oil upon initiation of the nebulization.

The 1, nebulizer holes not shown at the end of bore section 29, i.e. several bore diameters spaced from the lower 20 tapered tip of the valve slide 15 as the slide is in its shown closure state. The lower section 30 of the valve slider is substantially constant in diameter, but only needs precise machining on the lower portion acting as a closing member 32 which slides into the lower section 25 29 of the nebulizer bore.

The lower portion 30 of the valve slide 15 is shown in the first embodiment in FIG. 1, integral with the upper section of the valve slider and as a rigid extension thereof, whereby the lower section 30 without further control than the bearing of the upper slide section in the slide guide 21 is centered relative to the nebulizer bore.

A abutment surface 31 at the front end of the injector housing 2a lies in the injector's mounted position clamped down against an upwardly tapered surface of the cylinder cover of the engine.

This abutment surface is the lower place where the injector 10 DK 171975 B1 is subjected to a significant cooling effect which results from the cover being cooled by a refrigerant circulating in the motor which at the abutment surface 31 maintains the cover temperature of, for example, 80 ° C. Above the tapered contact surface 31, the injector temperature corresponds substantially to the temperature of the oil circulating in the injector, which may be preheated to, for example, 120 ° C. The nebulizer section located beneath the inclined abutment surface 31 is at least in its lower part in contact with the 10 high temperatures in the combustion chamber of the cylinder. The lower part of the nebulizer is therefore in practice uncooled.

As a whole, the valve 1 can thus be said to be divided into an upper cooled valve section 1a located above the abutment surface 31 and a lower substantially uncooled valve section 1b extending from the lower end of the nebulizer 4 and up to the abutment surface 31.

The atomizer 4 is of a high temperature resistant material that can also withstand the erosion effects of the fuel in the area around the atomizer holes. Since 20 hardened steels are not able to withstand the high temperature level in the uncooled valve section 1b, the nebulizer is made of, for example, Stellite 6 or another high temperature resistant alloy such as INCONEL ALLOY ma758 as described in EP-A-0 569 655.

It will be seen that the primary valve seat is located in the cooled valve section, while both the closing member 32 and the upper portion of the bore section 29 are located in the uncooled valve section 1b. Since the closure member 32 does not substantially burden the nebulizer material with longitudinal forces 30, both the closure member and nebulizer have a long service life despite the high temperature level.

In the following description of other embodiments, the same reference numerals as above are used for 35 elements having the same function.

11 DK 171975 B1

The FIG. 2 and 3, the second embodiment of the fuel injector is also for an engine that uses oil as fuel. The thin lower section 30 of the valve slide is here a separate interchangeable unit having at its upper end an external thread screwed up into an inner thread in a central bore 40 at the lower end of the upper section of the valve slide until a collar 41 on it the lower section 30 abuts the end surface of the upper section. A locking pin 45 inserted into flushing 10 bores in the upper and lower sections of the slider rotates the lower section 30 to the upper section of the slider.

If the lower slide section 30 becomes worn or damaged, the lock pin 45 can be removed and the lower section 30 can be replaced with a new one. This avoids 15 replacement of the entire slide.

The lower section 30 is elongated, thin and flexible in the transverse direction judged in relation to the upper section of the valve slider. When the slider is in the closing position shown in FIG. 3, the closure member 32 formed by the front cylindrical portion of section 30 projects into the bore section 29 and prevents the oil in the upper bore section 22 from penetrating to the atomizer holes 24. The amount of oil in the bore section 29 below the tip of the valve slider constitutes about 10% of that. total oil volumes under the primary valve seat 18.

The closure means 32 is centered in the nebulizer bore by means of a guide 42 sliding along a guide surface 43 in the nebulizer bore. The guide 42 consists of several, for example, four radially extending longitudinal tabs 30, the upper and lower ends of which are pointed. The oil can flow past guide 42 through the longitudinal spaces between the tabs.

In FIG. 2, the valve slide 15 is seen in its fully open position where the oil flows past the primary valve seat 18 and down into the nebulizer bore, where the oil in the area of decreasing diameter passes past the tapered free end 44 of the valve slide and flows further down to the nebulizer holes 24 as a total flow covering the entire cross-section of the nebulizer bore. The distance between the free end 44 of the slider and the nebulizer holes is probably large enough that the oil flow into the nebulizer holes is substantially unaffected by the lower portion 30 of the slider extending far down into the nebulizer bore.

The number of nebulizer holes 24 at the tip of the nebulizer depends on the power that the working cylinder of the engine is to produce and the number of injectors per unit. cylinder. For example, there may be 4 or 5 nebulizer holes, all of which open on the same side of the nebulizer, so that the longitudinal axes of the two outer nebulizer holes form at most an angle of 100 ° and often of only 80 ° or less. Thus, the oil is atomized into a fan-shaped burst of finely divided oil particles.

Next, injectors for injecting 20 gaseous fuel are described. The injectors are in principle constructed in the same manner as described above except that the valve slide is lifted by means of control oil which affects a piston area thereon and the gas is fed laterally into the lower part of the valve housing through an inlet channel 50 in the cover. indicated at 51 and an inclined channel 52 in the valve body 33.

The oblique duct 52 opens into a pressure chamber 53 located immediately above the primary valve seat 18.

The construction and operation of such a gas injector is otherwise well known in the art. The injector must inject a relatively large volume of gas during a motor cycle. The flow passages in the injector must therefore have a suitably large cross-sectional area, which means that the nebulizer bore and thus also the nebulizer itself has a large diameter. The injector abutment surface 31 ', which is pressed against a cooling conical surface on the cover 51, is therefore formed on the nebulizer 4 itself, so that the outer diameter of the injector housing can be kept suitably small. It can be seen otherwise in FIG. 4, that the cover near the surface 54 has cooling ducts 55. The part of the nebulizer located below the abutment surface 31 'is affected by the very high temperature level in the combustion chamber 56 and is in practice uncooled.

Since the gas is substantially more flowable than oil, 10 and the nebulizer bores are substantially larger in diameter than in the above embodiments, it is most convenient that the closure member of the lower section 30 of the valve slider abuts against a tapered bevel surface 57 in the downwardly decreasing diameter bore. The closure member 15 may be a valve needle 58, as shown in FIG. 4 and 5, or a spherical valve member 59, as shown in FIG. 6 and 7.

The closing means is not pressed against the inclined surface 57 with a valve closing force of the same magnitude as the closing force acting on the primary valve seat 18, but is only 20 actuated against the closed position by a weak compression spring. For example, it may be a compression spring 61 which is accommodated in a cavity in the upper section of the valve slide and presses the entire lower slide section 30 slidably mounted in a central bore in the upper 25 section, or it may be a compression spring 60 (see Figs. 6 and 7) located around the lower slider section 30 and actuates the valve member 59 longitudinally slidably mounted on the lower section 30.

The FIG. 4 and 5, slidably 30 sliding sections 30 shown carry one portion of a bayonet coupling, e.g., several projecting tabs at its upper end. These tabs can be brought up through corresponding notes at the end of the upper section of the valve slide. When the tabs are raised into the cavity, the lower section can be rotated to its mounted position, where the underside of the tabs upon abutment to the bottom 14 acts as a stop for the downward displacement of the section 30 relative to the upper section of the valve slide.

The valve member 59 shown in FIG. 6 and 7 are restricted in their displacement away from the upper portion of the valve slide by a stop in the form of a collar 62 which engages over a thickened lower portion of the slide section 30.

It is to be understood that elements of the various embodiments described can be combined in various ways for new embodiments.

Claims (10)

15 DK 171975 B1 A fuel injector (1) for a large two-stroke internal combustion engine, such as a diesel propulsion engine, with an elongated outer housing (33) for mounting 5. a water-cooled cylinder cover (51) in such a way that the valve (1) has a upper cooled valve section (1a) and a lower substantially uncooled valve section (1b) comprising at least the lower portion of the nebulizer (4) with transverse nebulizer holes (24) starting from a central longitudinal nebulizer bore and 15) has an upper section carrying a movable valve member (28) for a primary valve seat (18) located in the cooled valve section for opening and closing the fuel injector, and a thin lower section (30) extending into the nebulizer bore (22, 23, 29) and carries a secondary closing means for the fuel flow to the nebulizer holes, characterized in that the nebulizer bore has a 20 region located in the lower valve section (lb). the downwardly decreasing diameter (23), that the nebulizer holes (24) project from the smaller diameter bore portion (29) and that the lower portion (30) of the valve slide ends in level above the upper nebulizer hole and the secondary closure means (32; 58; 59) 25 is located at the area (23) for the diameter reduction of the bore when the slider (15) is in its closing position. Fuel injector according to claim 1, characterized in that the secondary closure means (32) has a cylindrical portion which can slide sealingly into the smaller diameter section (29) of the nebulizer bore. 3. A fuel injector according to claim 1 or 2, characterized in that the thin lower section (30) of the valve slider (30) with the secondary closing member (32) is a rigid extension of the upper section. Fuel injector according to claim 1 or 2, characterized in that the thin lower section (30) of the valve slider is a transverse extension of its upper section and that the lower section in level above the secondary closing member (32) has a guide ( 42) centering the closure member of the nebulizer bore through abutment against the wall of the larger diameter section (22). Fuel injector according to claim 4, characterized in that the guide (42) is a plurality of radially extending longitudinal tabs on the lower portion (30) of the slider and that the upper and lower ends of the tabs are preferably tapered. Fuel injector according to claim 1, characterized in that the secondary closure member (58; 59) in its closed position abuts on an inclined surface (57) in the diminishing diameter (23) of the bore and that the closure member is displaceable in the longitudinal direction of the slider. 20 and spring loaded for movement away from the upper portion of the slider (15). Fuel injector according to one of the preceding claims, characterized in that the lower thin section (30) of the valve slider with the secondary closure means 25 (32; 58; 59) is a separate unit which is removably attached to the upper section. Fuel injector according to one of the preceding claims, characterized in that the area of the nebulizer bore (23) of decreasing diameter is substantially 30 closer to the nebulizer holes (24) than to the primary valve seat (18). Fuel injector according to one of the preceding claims, characterized in that the secondary closure means only opens to the smaller diameter section 35 (29) of the nebulizer bore when the slider's movable part (28) is moved a predetermined distance away from the primary valve seat (18). Fuel injector according to one of the preceding claims, characterized in that the lower free end (44; 58) of the slider is tapered.