DK174074B1 - Combustion engine with a coke scraping ring in a cylinder - Google Patents

Description

in DK 174074 B1

The invention relates to an internal combustion engine having a coke scraping ring in a cylinder and having a longitudinally displaceable piston with piston rings which, when displaced by the piston, slides along the substantially cylindrical inside of the cylinder and produces a pressure-sealing separation between the volume below the piston and the upper piston ring. a working chamber defined by the upper piston ring, the piston, the inside of the cylinder and the cylinder cover, wherein the coke scraping ring protrudes from the inside of the cylinder and extends around it in such an axial position that the upper piston ring is near the bottom of the the coke scraping ring when the piston is in the top dead center position.

Such an engine with a coke scraping ring is known from four-stroke engines, which in the cylinder cover have both an intake and an exhaust valve. The purpose of the coke scraping ring is to scrape coke deposits away from the cylindrical upper piston section above 20 the upper piston ring.

The upper piston ring forms the lower boundary of the combustion chamber in the annulus located between the upper piston section above the piston ring and the inside of the cylinder. Therefore, part of the combustion products 25 will penetrate into the annulus and deposit on the outside of the upper piston section. Lubricating oil from the inside of the cylinder can also splash onto this outside. The deposited oil residues and combustion products are subjected to severe heat stress from the combustion and, as the engine runs, will be transformed into a continuous capping stroke on the piston sound side. If a coke scraping ring is not used, the coke layer will grow in thickness until it touches the inside of the cylinder.

DK 174074 B1 2

In order to avoid damage to the cylinder and piston rings, it is essential that an appropriate lubricating oil film be maintained between these movable parts.

When the coke layer on the piston's periphery is built to the maximum thickness and comes into contact with the inside of the cylinder, it will interfere with the thin oil film and absorb or scrap part of the oil, adversely affecting the lubrication conditions. At worst, the lubrication can be locally deteriorated so that damage to the piston rings or the liner occurs.

The coke scraping ring of the known four-stroke engine limits the thickness of the coke stroke as the piston moves near its peak dead-end position, and the upper piston portion 15 moves up and down past the coke scraping ring whose upper and lower circumferential edges blunt the coke touching the edges. As the scraping ring protrudes from the inside of the cylinder, the coke layer is prevented from reaching a thickness which causes contact between the coke layer and the inside of the cylinder.

Because the known engine with the coke scraping ring is a four stroke engine and both the intake and exhaust valves of the four stroke engine are located in the cylinder cover, the other operating conditions of the engine are largely unaffected by the use of a coke scraping ring.

In the four-stroke engine the flushing of the cylinder takes place by a separate piston stroke between each working stroke, and the air supply to the combustion takes place from above down through the suction valve at the subsequent downward suction stroke. The coke scraping ring therefore has no influence on the rinse and charge of the cylinder.

A more significant relationship for the favorable results obtained with the coke scraping ring in the four-stroke engine is the piston's movements itself relative to the inside of the cylinder 35. The four-stroke cycle means that piston 3 DK 174074 B1 is loaded differently during every other upward stroke, and also in the downward stroke the load type changes every other time. This causes the radial position of the piston near the top dead center to constantly vary, so that the coke scraping ring scrapes the coke off at greater depth than corresponding to its own inner diameter, thereby creating clearance between the coke-coated upper piston portion and the coke scraping ring. In a long-rinsed two-stroke cross-head engine, the conditions are not as straightforward, and trials with the four-stroke coke scraping ring known from the four-stroke engine have shown generous operating problems in the form of increased specific fuel consumption and damage to, in particular, the top piston ring, which is surprising, as the coke scraping ring should be improved. lubrication conditions for the piston rings.

The invention has for its object to alleviate the above disadvantages and to enable an advantageous use of a coke scraping ring in a two-stroke cross-head motor.

To this end, the invention is characterized in that the motor is a longitudinally flush, two-stroke cross-head motor with flushing air ports located in a lower cylinder section, and that the coke scraping ring in its cylindrical interior has several leakage grooves which extend from the underside to the upper longitudinal axis of the cylinder. of the coke scraping ring.

It is believed that the disadvantages of using the known coke scraping ring in a two-stroke engine can be explained by the following mechanisms. In a two-stroke cross-head motor, the piston performs a compression stroke during each upward movement and a work stroke during each downward movement. This means that the piston is loaded in much the same way every time it passes up and down past the coke scraping ring, which is why the piston performs a similar, repeating movement pattern near the upper dead center position. The tendency for a uniform pattern of movement is enhanced by the crosshead, which controls the lower end of the piston rod in a clean translational motion along the longitudinal axis of the cylinder. Accordingly, the coke deposits on the piston periphery will be built up to a shape that fits neatly into the coke scraping ring, so that there is little clearance between this and the upper piston section. As the top of the piston passes the coke scraping ring in the compression stroke, an annular cavity between the outside of the piston with the coke layer and the inside of the cylinder is defined axially between the protruding coke scraping ring and the upper piston ring. The upward piston movement induces a rapid axial shortening of the annular cavity with consequent vigorous compression of the air therein, causing a greatly increased load on the upper piston ring.

The leakage grooves in the cylindrical inside of the coke scraping ring reduce or remove the pressure build-up in the annular cavity, the air therein being able to evade through the leakage grooves to the portion of the work chamber located above the piston top. This prevents the upper piston ring from being subjected to increased load due to the presence of the coke scraping ring. This ratio is of particular importance in today's large two-stroke 25 head motors, which are developed in the direction of very high effective compression ratios, such as 1:16 - 1:20, which in itself imposes large loads on the piston rings.

The sloping course of the leak grooves ensures that the coke is also scraped in the areas next to the leak grooves. The portions 30 of the coke coating which lie beyond the bottom openings of the leak grooves will not hit the bottom of the coke scraping ring, but will, during the continued upward piston movement, pass past the upper edges of the leak grooves and here be scraped to the desired dimension. The 35 coke particles scraped in the grooves are led up into the space 5 DK 174074 B1 over the piston of the leakage air which blows through the grooves.

The leakage tracks also counteract an increased fuel consumption. If there were no leaks, the effective piston area would be diminished during the first part of the combustion where the piston top is located above or above the coke scraping ring, as this would prevent the pressure rise in the working chamber from propagating down to the upper piston ring where it 10 effective piston areas cover the entire cylinder cross section. The leakage grooves reduce or eliminate the pressure drop across the coke scraping ring, both relieving the compression layer and during the working stroke, and the specific fuel consumption is therefore largely unaffected by the use of a coke scraping ring.

The coke scraping ring provides a further effect that is particularly advantageous in the large two-stroke diesel engines with high cylinder performance, such as from 1500 to 5500 kW, where the fuel is injected into the cylinder by 20 of two, three or four fuel injectors that emit directional clouds of atomized fuel. The burning of the fuel produces relatively concentrated heat effects, but as the coke scraping ring covers the upper piston ring, while the piston is 25 near its top dead center position, where the thermal load is greatest, and only the hot gas leads down to the piston ring through the leak grooves, the thermal load is distributed. more evenly over the upper piston ring, and thus the heat-sensitive lubricating oil film is also protected on the inside of the cylinder. Both contribute to better operating conditions of the piston ring package and increase the effect of preventing the coke on the piston from touching the lubricating oil film.

In one embodiment, the substantially cylindrical inside of the cylinder is constituted by an upper cover section 6 and a lower casing section, and the coke scraping ring is located at the top of the casing section. The coke scraping ring may be a ring that is shrunk into a recess on the inside of the casing or alternatively may be a protruding portion of the casing material itself, ie. an integral coherent part of the liner. In the latter case, the plunger with the plunger rod must be mounted before the liner is lowered into place in the engine at its assembly so that the plunger is guided from below through the liner. In the former case, the embodiment provides an advantageous option for retrofitting a coke scraping ring to preexisting engines.

In an alternative embodiment, the substantially cylindrical interior of the cylinder is constituted by an upper cover section and a lower casing section, and the coke scraping ring is located at the bottom of the cover section. Also in this case, the coke scraping ring may be a separate ring inserted into a recess in the upper cover section or may be formed integrally with the cover section, by rotating the lower portion of the cover section to a smaller internal diameter than the upper section, then machining the leak grooves into the the bottom piece. The alternative embodiment is particularly applicable to thermally particularly highly loaded cylinders, wherein the cylinder cover is made of more heat resistant material than the liner. By placing the coke scraping ring in the cover section, the interface between the casing and the cover can be moved down to the area immediately above the position of the top piston ring in the top dead center position.

It is preferred that the leakage grooves constitute from 0.25 to 50% of the axially directed area of the coke scraping ring projecting from the substantially cylindrical inside of the cylinder, preferably from 5 to 40% thereof, 35 and suitably from 20 to 30 V thereof. If the area of the leakage traces becomes less than 0.25%, the pressure drops across the coke scraping ring become too large, and at a leakage area of more than 50% no further positive effects are obtained. The 5% limit still gives a 5 pressure drop, but a noticeable improvement in operating conditions, while the 40% limit is usually fully sufficient to prevent pressure drop over the coke scraping ring. An area in the range of 20 to 30% represents a suitable compromise between the desire to achieve little or 10 no pressure drop and the desire to distribute the thermal load evenly.

For long-rinsed engines, it is preferred that the flushing air ports be opened by the upper side of the piston, which means that the coke scraping ring must not protrude too far from the inside of the cylinder, as an excessive width of the annular space between the coke stroke and the inside of the cylinder causes the top of the gates at the end of the work stroke will open to the gates. Accordingly, for cylinder bores in the range of 20 250 to 1000 mm, it is preferred that the coke scraping ring protrudes from 0.5 to 5 mm from the inside of the cylinder. The lower value of 0.5 mm ensures complete blocking of the flushing air ports until the piston top has passed. In the case of the largest engines, the coke scraping ring may suitably project 2 or 3 mm forward, while 1 to 2 mm may be suitable for the smaller engines. If the ring protrudes less than 0.5 mm, it is more difficult to obtain security against the coke coating touching the lubricating oil film on the inside of the cylinder.

It is preferred that the upper piston section overlying the upper piston ring is smaller in diameter than the underlying piston section with the piston rings, and that the inner diameter of the coke scraping ring is from 2 to 6 mm larger than the diameter of the top piston section, suitably from 3 to 4. mm 8 DK 174074 B1 larger than this. With these diameter ratios, the coke layer can be built up to a thickness of from 1 to 3 mm, conveniently from 1.5 to 2 mm, which provides an adequate clearance for the radial positioning of the piston relative to the coke scraping ring without the risk of the piston periphery touching the scraping ring.

It is possible within the scope of the invention to allow the coke scraping ring to project farther from the inside of the cylinder than indicated above, while at the same time reducing the diameter of the upper piston section so that the annular space around this piston section and the inside of the cylinder is of great thickness. Such a design means that the flushing air ports will be opened earlier, namely at the passage of the upper piston ring at the end of the working stroke, and the timing of the exhaust valve opening and the other engine parameters which depend on the opening time of the flushing ports must then be changed in accordance with the previous supply of rinsing air.

The number of leakage grooves in the coke scraping ring depends on the desired leakage area and the desired leveling of the heat load on the upper piston ring, with greater leakage area and an even distribution of the heat load advocating the use of a greater number of leakage grooves. The coke scraping ring may conveniently have from 4 to 30 leaks.

Since there are significant advantages in smoothing the heat load on the upper piston ring, it is preferred that the coke scraping ring has more than 15 30 leaks.

As an alternative to placing the leakage grooves in the cylindrical inside of the coke scraping ring, it is also possible within the scope of the invention to design the initially mentioned internal combustion engine with a coke scraping ring in a cylinder in the peculiar way. cross head motor with purging air ports located in a lower cylinder section and the upper piston ring located above the upper piston ring in its cylindrical exterior has 5 more leakage grooves extending from the top of the piston section down to the area immediately above the recess with the upper piston ring. In this case, the cylindrical inner surface of the coke scraping ring can be formed as a coherent circular cylindrical surface * In every 10 engine cycles, the leakage grooves flow through both compressed air and combustion gas, preventing coke deposits in the grooves. If the leak grooves are formed in the periphery of the upper piston section, they may advantageously extend axis parallel to the cylinder so that any broken off coke pieces are not immediately trapped in a leak groove with the associated risk of clogging. Furthermore, the number and size of the leakage grooves can be selected in the same way as for the leakage grooves in the coke scraping ring, cf. the description below.

20 Examples of embodiments of the invention are explained in greater detail with reference to the highly schematic drawing, in which fig. 1 shows a simplified cross-section through a motor with a coke scraping ring according to the invention; FIG. 2 is an enlarged sectional view of the area around the coke scraping ring in the cylinder of the engine of FIG. In FIG. 3 is a side elevation of a portion of the coke scraping ring; and FIG. 4 is a top plan view of a section of the coke scraping ring.

The motor illustrated in FIG. Figure 1 is a large two-stroke, long-rinsed diesel engine capable of using oil, such as heavy fuel oil, which, during combustion 35, produces residual products which can be deposited as coke on the surfaces of the engine's work chamber. Depending on the cylinder size and number, the engine can develop power from 2000 to 70,000 kW, for example. Such an engine is traditionally used as the main engine of a ship 5 or as a stationary electric power producing engine. In both cases, it is important that the engine can be in operation for a very long time without the need for overhaul and overhaul of the engine components. It is desirable that the engine can be in continuous operation for more than 2 years without 10 overhaul, and this places great demands on the best possible operating condition of the cylinder elements.

The stationary parts of the engine comprise a bottom frame 1 in which the crankshaft 2 is mounted and a motor frame 3 mounted on the bottom frame which carries on its upper side a cylinder portion 4. A cylinder liner 5 is clamped down to a top plate 6 in the cylinder portion by means of cover pin 7 and a cylinder cover 8. The cylinder liner has a high wall thickness upper section which rests on the top of the top plate via an annular intermediate piece 9, and an elongated lower section which projects down into the cylinder portion 4. At its lower end, the cylinder liner has a series of rinsing air ports 10. through which flushing and charging air from a flushing air receiver 11 flows into the cylinder as the piston is near the bottom dead center position. A 25 exhaust valve housing 12 with a hydraulically actuated exhaust valve is located centrally in the cylinder cover.

When the exhaust valve is open, flushing air from the flushing air ports can flow up through the cylinder, at the same time as the combustion gases flow out through the exhaust vent inlet and into an exhaust receiver 13, from which the gas flows into the exhaust pipe via a turbocharger. The motor is high-pressure charged to a charging pressure of, for example, 3.5 -4 bar.

A care rod rod 14 connects the crankshaft 2 to a 35 crosshead 15 which, by means of guide planes 16 in the motor stand, guides the lower end of a piston rod 17 in a translational motion back and forth along the longitudinal axis of the cylinder. A piston 18 is mounted at the top of the piston rod. As is most clearly seen in FIG.

5, the plunger carries several, such as four, piston rings 19, 19 'which slide along the inside of the cylinder liner and produce a pressure-sealing separation between the working chamber 20 and the volume located below the plunger which communicates with the rinsing air filled 10 cylinder section.

The combustion or working chamber 20 is bounded by the inside of the cylinder cover 8, the inside of the cylinder liner 5, the top of the piston 18, the upper piston ring 19 'and the periphery of a top piston section 21 extending from the upper piston ring. The upper piston section 21 is smaller in diameter than the underlying portion of the piston, so that between the outside of the upper piston section and the inside of the cylinder is an annulus 22 in which coke will be deposited on the 20 piston sound side.

A coke scraping ring 23 extending in the cylinder protrudes from the inside of the cylinder and scrapes the coke deposits on the outside of the upper piston section 21 so that these deposits can reach no more than a diameter corresponding to the inside diameter of the coke scraping ring. It is preferred that the coke scraping ring has such a position in the axial direction of the cylinder that the upper piston ring 19 'is less than a ring height below the coke scraping ring 23 when the piston is in its top dead center position shown in the drawing, which ensures that the coke layer is substantially scraped down completely. to the upper piston ring. However, a significant coke scraping effect will still be achieved, although the coke scraping ring is positioned somewhat higher up, e.g., 2 to 3 35 ring heights up.

12 DK 174074 B1

It can be seen from FIG. 3 and 4, that the inside of the coke scraping ring has several leaking grooves 24 which create gas flow connection between the portion of the annulus 22 located under the coke scraping ring and the remaining upper part of the working chamber 20. The leakage area of the leakage grooves is suitably adjusted so that the pressure drop across the coke scraping ring becomes suitable. Advantageously, the leakage grooves may be evenly distributed along the inner periphery of the coke scraping ring, providing the most uniform heat load on the upper piston ring 19 '. The depth of the leak grooves may correspond to the thickness of the coke scraping ring protrusion relative to the inside of the cylinder. This is particularly advantageous if the scraping ring only projects a small distance such as 0.5 to 3 mm from the inside.

If the piston and scraper ring are made such that the annular space 22 is wide and the purge air ports 10 are opened at the passage of the upper piston ring, the depth of the leakage grooves must be less than the thickness of the inwardly extending portion of the coke scraping ring.

It is preferred that the leakage grooves do not get deeper than from 3 to 4 mm, since the gas flows through the individual groove at greater depths can become so great that the heat loads on the upper piston ring locally become too high. A very even heat distribution can be achieved with grooves no deeper than 1.5-2 mm, combined with a suitably large number of leaks, for example 15 or more.

The width of the leakage grooves is selected based on the number of leakage grooves, the groove depth and the desired total flow area, ie. the axially facing total cross-sectional area of the groove ends. Track widths of from 5 to 30 mm will in most cases be suitable and a track width of 10 to 20 mm is preferred for achieving a uniform heat load.

13 DK 174074 B1 The leakage grooves 24 extend obliquely to the longitudinal axis of the cylinder so that the upper groove 25 is offset in the circumferential direction relative to the lower groove 26. This gives the advantage that the coke layer 5 is scraped along the entire periphery of the upper piston section 21 The longitudinal axes of the leak grooves in the embodiment shown form an angle of 45 ° with the longitudinal axis of the cylinder.

Of course, it is possible to use other angular sizes, for example from 15 to .80 °. The angle is adjusted to 10 track width so that there is no overlap in the axial direction between the upper and lower tracks 25 and 26. It is preferred for manufacturing reasons that the leak grooves extend the straight line between the upper and lower tracks, but other designs that create a flow connection between the of course, the upper and lower tracking 25 and 26 will also work in practice, such as an L-shaped or otherwise non-linear course.

Claims (10)

14 DK 174074 B1 An internal combustion engine having a coke scraping ring in a cylinder and having a longitudinally displaceable piston (18) with piston rings (19, 19 ') which, at the displacement of the piston, slides along the substantially cylindrical inside of the cylinder and produces a pressure-sealing separation between the volume below the piston and the the working chamber (20) located above the piston upper piston ring, defined by the top 10 piston ring (19 '), the piston (18), the inside of the cylinder and the cylinder cover (8), where the coke scraping ring (23) protrudes from the inside of the cylinder and extends around along this in such an axial position that the upper piston ring is near the lower edge of the coke scraping ring when the piston is in the top dead center position, characterized in that the motor is a long-flush, two-stroke cross-head motor with purging air ports (10) located in a lower cylinder section, and the coke scraping ring (23) in its cylindrical interior 20 has several leakage grooves (24), is inclined relative to the longitudinal axis of the cylinder from the underside to the upper side of the coke scraping ring. Combustion engine according to claim 1, characterized in that the substantially cylindrical inner surface of the cylinder is constituted by an upper cover section and a lower casing section, and the coke scraping ring (23) is located at the top of the casing section (5). Combustion engine according to claim 1, characterized in that the substantially cylindrical inner surface of the cylinder is constituted by an upper cover section and a lower casing section, and the coke scraping ring (23) is located at the bottom of the cover section. An internal combustion engine according to claim 2 or 3, characterized in that the coke scraping ring (23) is an integral continuous part of the cylinder bushing 15 or of the upper cover section, being manufactured as a protruding part in the cylinder casing or the cover section itself. material. An internal combustion engine according to any one of the preceding claims, characterized in that the leakage grooves (24) comprise from 0.25 to 50% of the axially directed area of the coke scraping ring (23) projecting from the substantially cylindrical inside of the cylinder, preferably from 5 to 40% thereof, and suitably from 20 to 30 10% thereof. Internal combustion engine according to one of the preceding claims, characterized in that the cylinder bore is in the range of 250 to 1000 mm and that the coke scraping ring (23) protrudes from 0.5 to 5 mm from the inside of the cylinder. Combustion engine according to one of the preceding claims, characterized in that the upper piston section (21) located above the upper piston ring (19 ') has a smaller diameter than the underlying piston section with the piston rings and that the inner diameter of the coke scraping ring (23) is from 2 to 6 mm larger than the diameter of the upper piston section, conveniently from 3 to 4 mm larger than this. Internal combustion engine according to one of the preceding claims, characterized in that the coke scraping ring (23) has from 4 to 30 leakage grooves. Internal combustion engine according to one of the preceding claims, characterized in that the coke scraping ring (23) has more than 15 leakage grooves. An internal combustion engine having a coke scraping ring in a cylinder and having a longitudinally displaceable piston (18) with piston rings (19, 19 ') which, when displaced by the piston, slides along the substantially cylindrical inside of the cylinder and produces a pressure-sealing separation between the volume under the piston 16 DK 174074 B1 and the working chamber (20) located above the upper piston ring defined by the upper piston ring (19 ') / piston (18), the inside of the cylinder and the cylinder cover (8), where the coke scraping ring (23) protrudes from the inside of the cylinder and extends around it in such an axial position that the upper piston ring is near the lower edge of the coke scraping ring when the piston is in the top dead center position, characterized in that the motor is a long-decoiled, two-stroke cross-head motor with purging air ports (10) located in a lower cylinder section and the upper piston section located above the upper piston ring IT (21) in its cylindrical exterior has several leaking grooves extending from the top of the piston section down to the area immediately above the recess with the upper piston ring.