WO1994028296A1

WO1994028296A1 - A method and an internal combustion engine

Info

Publication number: WO1994028296A1
Application number: PCT/DK1994/000167
Authority: WO
Inventors: Thomas Synnestvedt Knudsen; Allan ØSTERGAARD
Original assignee: Man B & W Diesel A/S
Priority date: 1993-05-26
Filing date: 1994-04-25
Publication date: 1994-12-08
Also published as: HRP940316A2; JPH08510523A; DK60293D0; DK170447B1

Abstract

A cylinder liner for a large two-stroke internal combustion engine has in its upper portion a number of groups of cooling surfaces, in which the cooling surfaces may groupwise be open or closed to through-flow of cooling water. In the first group the cooling surfaces (8) are provided by channels extending obliquely into the wall of the liner, and the cooling channels in the second group are likewise oblique bores, which at least at their upper section are positioned at a larger distance from the liner running surface (5) than the channels of the first group. The third group has a single cooling surface (18) at the external side of the liner. The intensity of the cooling may be varied in dependency of the thermal load on the liner by the cooling water being routed to selected cooling surfaces (8, 8', 18), the distance from the running surface and/or the number of which are adjusted to the current thermal load.

Description

A method and an internal combustion engine.

The invention relates to a method of cooling a cylinder liner in an internal combustion engine, particularly a large two-stroke main engine of a ship, wherein the liner in its upper portion has several cooling surfaces distributed along the circumference of the liner and cooled by cooling water to carry off heat from the running surface of the liner.

In a large two-stroke internal combustion engine, the upper portion of the liner, which normally projects upwards from the cylinder section and is clamped against it by means of a cover, is thermally and mechanically heavily loaded by the heat and pressure produced by the combustion. The temperature level on the internal running surface for the piston of the cylinder liner is of decisive importance to the life of the liner and thus also to the operating economy of the diesel engine. If the temperature of the running surface becomes too high, heat cracks will occur in the liner, and if the tempera- ture becomes too low, sulphuric acid from the combustion products may condense on the running surface, which results in increased wear owing to corrosive erosion of the material of the liner and decomposition of the lubricating oil film on the running surface. The temperature of the running surface will normally vary with the engine load, and as the engine has to be able to run for a long period at both high and low loads, the liners are conventionally made so that the temperature of the running surface at the maximum load of the engine is close to the highest permissible temperature. The high temperature level renders it possible at partial loads to maintain a sufficiently high temperature to prevent acids from condensing on the running surface. The cylinder lubricant and the material of the liner are affected by the high temperature at full engine load, and an increase of this temperature may lead to a decomposition of the lubricant and lasting damage to the liner material, among other things in the shape of the above heat cracks. The present cooling method thus in practice sets a limit to the output produced in the cylinder, unless a certain risk of acid condensation at low loads is accepted. An attempt has been made to solve this problem by controlling the temperature on the running surface through adjustment of the amount of cooling water flowing through. The cooling water and thus the cooling surfaces normally have a temperature of about 70°C. Tests with control of the water flow have shown that a 50 per cent reduction of the water flow may result in a temperature increase of about 10°C on the running surface. A temperature increase of only 10°C at low engine load gives very limited possibilities of increas- ing the carrying-off of heat at high loads, and there¬ fore the water flow at low loads has to be heavily restricted to have a noticeable effect at high loads. A small water flow involves a serious risk of the cooling water being largely stagnant over certain areas of the cooling surfaces, which results in micro-boilings in the water immediately outside of the cooling surface. The micro-boilings will fix the temperature of the cooling surface at a level which is dependent on the operating pressure of the cooling water, because the heat has to be carried off by steam. At a typical cooling water pressure of 2-3 bar, the temperature of the steam and thus also the cooling surface will be in the range of 120-130^CC. Such a temperature increase of 50-60^cC on the cooling surface results in, on one hand, a progressive expansion of the area with micro-boiling, on the other hand, local overheating of the adjacent area on the running surface. An adjustment of the water flow thus involves a risk of damages to the upper portion of the liner where the thermal load is greatest. The object of the invention is to provide a reliable cooling of the cylinder liner along its full height and over a wide range of loads for the engine.

This object is obtained by a method which according to the invention is characterized in that the intensity of the cooling is varied in dependency of the thermal load on the liner by the cooling water being routed to selected cooling surfaces, the number and/or distance from the running surface of which are adjusted to the actual thermal load. If, for example, the load of the engine increases, the heat inflow on the running surface and thus the need for its cooling will grow so that the cooling intensity has to be increased, which may be effected by routing the cooling water to cooling surfaces closer to the running surface, so that the temperature gradient between the running surface and the cooling surface becomes larger and the amount of heat carried off increases. The cooling water may also or alternatively be routed to a larger number of cooling surfaces, which increases the carrying-off of heat. At decreasing engine loads, cooling surfaces may be selected which are at a greater distance from the running surface and/or the number of cooling surfaces may be reduced. This adjust¬ ment of the cooling intensity may be made without any change in the water flow, whereby the risk of micro- boilings is eliminated.

The variable cooling in dependency of the engine load also results in a very uniform temperature on the running surface over the whole range of loads of the engine. Consequently, the temperature of the running surface may be selected to be at a suitable distance from both the acid dewpoint and the temperature at which the lubricant or the liner material exhibits beginning damage. The uniform lubricating and temperature condi- tions cause a considerable increase in the life of the liner. Nor is it necessary, of course, to change the design of the liner, if the existing engine is modified for lasting operation at another load (derating or uprating). The load-dependent control of the cooling intensity also renders possible an increase of the thermal load on the liner beyond what is possible today, which permits a design of engines with a higher output per cylinder.

The cooling water is preferably routed to selected groups of cooling surfaces where the cooling surfaces in groups comprising several cooling surfaces have substantially the same course in relation to the running surface, and the cooling water flow is adjusted so that the individual group is either completely open or completely closed to through-flow. The thermal load on the liner decreases in a direction away from its upper end, and some of the cooling surfaces therefore have to extend obliquely in relation to the running surface so that in the downward direction they are positioned at a growing distance therefrom. The grouping of the cooling surfaces so that the surfaces in each group have the same course, counteracts imbalances in the cooling of the liner at connection or disconnection of a group. As the stresses in the material of the liner depend both on the thermal and the mechanical load, the grouping and the consequent uniform cooling of the liner will contribute to the fact that the ability of the liner to absorb mechanical loads does not vary substantially along cross sections at right angles to the longitudinal axis of the liner. By letting the individual group be either completely connected or disconnected, a well- defined predetermined cooling effect is obtained on the liner depending on the current combination of connected groups, which makes it easy to program a control of cooling flows in dependency of the engine load.

The heat inflow on the running surface decreases in a direction away from the upper portion of the liner because the pressure and temperature of the combustion gas drop during the downward working stroke of the piston. In a liner portion positioned below the upper portion, the cooling need may consequently become so small that there is no risk of micro-boilings on the associated cooling surface. Therefore, the cooling intensity at this surface may suitably be adjusted by a change of the amount of cooling water flowing through, which results in the advantage that the flow of cooling water to the cooling surfaces in the upper portion is not restricted by the relatively low cooling need at the cooling surface in the below portion. A compensation for abnormal operating conditions is suitably made by measuring and registering the current temperatures at the running surface, by compar¬ ing the registered temperatures with predetermined limit values, and by adjusting the intensity of the cooling to the closest new level if a limit value is exceeded. The limit values may be determined as an upper and a lower deviation from the desired mean temperature of the liner, and the measurement of the actual temperatures renders it possible to adjust for changed thermal loads in a simple manner, for example as a consequence of changed ambient conditions, such as air and cooling water temperatures, which may result in load-independent variations in the heat inflow on the running surface. With this method, the temperature control becomes more sensitive and accurate than what may be obtained from a predetermined cooling adjustment based on empirical values for the connection between the thermal influence and the load on the engine. The connection between the choice of active cooling surfaces and the intensity of the cooling has to be predetermined, however.

To prevent the automatic cooling adjustment from disguising proper error conditions in the engine, an alarm may be emitted if the adjustment of the intensity of the cooling is due to a local temperature change on the running surface. Such a local change may, for example, be due to the poor condition of a piston ring or another mechanical failure of an engine component. The alarm signal enables the operating personnel to make an independent evaluation to determine whether the failing component should be repaired or whether it is justifiable to continue with an increased cooling intensity.

The optimum control of the temperature of the liners will only be obtained when the cooling intensity is adjusted individually for each cylinder liner, so that it is possible to compensate for individual variations in the working conditions of the cylinders. The invention also relates to an internal combus¬ tion engine, particularly a large two-stroke main engine in a ship, having several cylinder liners each being clamped down against the cylinder section by means of a cover delimiting a combustion chamber together with the liner and the associated piston, wherein the liner in its upper portion has several cooling surfaces distributed along its circumference for carrying-off of heat from the running surface of the liner, being characterized in that the cooling surfaces are divided into groups, each having a separate cooling water supply passage and an adjustment member for control of the water flow in the passage. The groups positioned in the upper portion of the liner will typically have an adjustment member in the form of a cut-off means, which can open or close the water flow completely, while groups positioned below the upper portion may have a valve for adjustment of the amount of flow.

In a preferred embodiment, the groups have a mutually different distance from the running surface over at least part of the extent of the cooling surfaces in the axial direction of the liner. This fact renders it possible to adjust the cooling intensity in relative¬ ly small steps, because the cooling effect of a group positioned at a larger distance from the running surface is restricted by the smaller temperature gradient between the running surface and the cooling surface in the group. For cooling surface groups positioned inside the material of the liner, the radial separation of the groups also results in the advantage that the mechanical strength of the liner is not weakened unsuitably by the cooling surfaces. In a preferred embodiment, the liner is designed so that a first group comprises several elongated cooling channels distributed along the circumference of the liner and extending substantially upwards and inwards from the external side of the liner towards the running surface, that a second group comprises several elongated cooling channels distributed along the circumference of the liner and extending substantially upwards and inwards from the external side of the liner towards the running surface, preferably so that the upper sections of the channels have a greater distance from the running surface than the corresponding sections of the channels in the first group, and that a third group comprises a single annular cooling surface at the external side of the liner, positioned radially on a level with the channels of the first and the second groups, and preferably a fourth group having a single annular cooling surface at the external side of the liner, positioned axially below the other groups.

It is known that in its upper portion, formed with a larger wall thickness, a cylinder liner for a large two-stroke internal combustion engine may have a single group of elongated cooling channels extending from the external side of the liner substantially upwards and inwards towards the running surface at such an angle in relation to the cylinder axis that the cooling channels as a whole form a hyperboloid. These channels are closest to the running surface in the upper portion of the liner where the thermal load is greatest, and the oblique course of the channels ensures that the cooling intensity in the downward direction decreases more or less in step with the thermal influence. The use of a further group of elongated cooling channels inside the wall of the liner renders it possible to obtain a large jump in the cooling intensity by connection of the second group. If the upper sections of the channels are positioned radially outside the channels of the first group, the change of the cooling intensity at connection becomes smaller. On designing a new cylinder liner for a defined cylinder output, the course of the channels may be determined so as to obtain exactly the desired difference in cooling intensity at connection of the channels.

Structurally, it is very simple to provide a single annular cooling surface at the external side of the liner, and such a cooling surface positioned as far as possible from the running surface renders possible a fine adjustment of the cooling intensity. As mentioned above, the cooling need is smaller at a greater distance from the upper portion of the liner, so if desired, the cooling may here be effected merely by means of a single annular cooling surface at the external side of the liner.

An example of an embodiment of the engine according to the invention will now be explained in further detail below with reference to the schematic drawing, in which

Figs. 1 and 2 show radial sectional views through the upper portion of a cylinder liner along the lines

I-I and II-II, respectively, of Fig. 3,

Fig. 3, on a smaller scale, is a cross-sectional view through the liner along the line III-III of Figs. 1 and 2, and

Fig. 4 shows a connection diagram for cooling surface groups in the liner.

Figs. 1 and 2 show a segment of an upper section 1 of a cylinder liner for a large two-stroke crosshead engine. Such an engine is extremely well-known both as the main engine of a ship and as a stationary power- producing engine and will not be described in further detail here, but may, for example, be of the make MAN B&W DIESEL and may typically have the type designation L60MC, where 60 indicates a cylinder bore of 60 cm. The upper section 1 is intended for clamping between a cylinder cover and the upper side of the engine cylinder section which is mounted on an engine frame and an underlying bedplate. The section 1 has a downward lower abutment surface 2 resting on an opposite abutment surface on the upper side of the cylinder section, and an upward annular upper abutment surface 3 for support of the cylinder cover, not shown, which is clamped against the cylinder section by means of cover studs by a force greater than the largest upward force against the cover occurring during combustion. The upper section 1 has a great wall thickness so that it can transmit the large axially directed compressive forces from the cover to the cylinder section and can resist the radially outward pressure in the combustion chamber and the temperature load from it. In an engine with a cylinder bore of 60 cm, the upper section 1 may have an axial length of about 70 cm, and a lower section 4 may have an axial length of about 1.8 m. If the bore is, for example, 90 cm, the corresponding lengths are about 105 cm for the upper section and 250 cm for the lower section.

The lower section 4 is not loaded by the axial compressive forces from the cover, and the pressure influence from the combustion gasses is also smaller. The section 4 therefore has substantially smaller wall thickness than the upper section. The circularly cylindrical internal side of the liner forms a running surface 5 for the piston rings on the piston journalled in the liner. The wall thickness of the lower section is sufficient to absorb the guide forces from the piston, and at the bottom of the lower section along the periphery of the liner, there are a number of scavenging air ports which are uncovered when the piston is near its lower dead centre position, so that scavenging air may flow up through the combustion chamber and out through the exhaust passage in the cover, and charging air may fill the combustion chamber simultaneously with the beginning of the compression stroke.

The liner is thermally most heavily loaded in an upper portion 6 which extends axially from the upper abutment surface 3 to the upper edge of a recess 7 on the external side of the liner machined into the lower part of the upper section 1. A first group of cooling channels 8 are bored into the upper wall part of the liner from a projecting surface 9 at the upper end of the recess, so that the channels 8 extend obliquely inwards towards the running surface 5 and are inclined in relation to a radial cut through the liner. For the sake of simplicity, the channels 8 in Figs. 1 and 2 are shown as if they extended in the radial cut. Fig. 3 shows that the cooling channels are evenly distributed along the periphery of the liner, and that the number of bores is sufficiently large to result in a substan¬ tially even cooling of the running surface 5.

The cooling channels 8 are blind bores, and a tube 10 having a smaller external diameter than the internal diameter of the channel has been inserted in each bore, so that there is an annular cooling slot or channel between the tube and the channel wall. The lower end of the tube has a projecting flange abutting a shoulder portion 11 in the channel 8. The upper part of the tube is bent into a wavy shape so that the top opening 12 of the tube is centred in relation to the bore. The tube is retained in the liner by means of a spring bushing abutting the tube flange. After insertion of the tube 10, the channel 8 has been closed downwards by means of a body 13, which may be a plug or a cover screwed into a thread. The channel 8 communicates with a radially extending supply channel 14 and a radially extending discharge channel 15 positioned at a level above the shoulder 11. The supply channel opens into the lower section of the cooling channel 8 below the shoulder 11, and as the flange on the tube 10 abuts the shoulder and bars the annular channel surrounding the tube, the water inflow is forced to flow upwards inside the tube 10 and further through the annular space outside the tube 10 down to the discharge channel 15. Another group of elongated cooling channels 8' are formed in basically the same manner as the cooling channels of the first group, and the channel members of the second group shown in Fig. 2 have been given the same reference numeral as in Fig. 1, but with the addition of a mark. The cooling channels 8' of the second group are bored at a smaller angle in relation to the running surface 5, so that the upper sections 16' of the channels are at a larger distance from the running surface than the corresponding sections 16 of the channels 8 of the first group, which means that channels 8' effect a smaller cooling intensity than channels 8. A jacket 17 envelops the upper portion of the liner and is arranged at a distance from an annular cooling surface 18 extending in parallel with the axis of the liner, so that an annular cooling chamber 19 is formed between this surface and the jacket 17. As the cooling surface 18 acts at the outer periphery of the liner, it is farthest away from the running surface 5, and therefore, the temperature gradient to the surface 18 is as small as possible. The cooling surface 18 is the only surface of a third group.

As the thermal load is heaviest in the upper portion 6 of the liner, this is also the place where the greatest variations in the thermal load occur when the engine load is changed. The three groups of cooling surfaces of the upper portion with their respective cooling intensity render possible an accurate matching of the cooling intensity to the immediate need. In the area below the upper portion, the cooling need is substantially smaller, and therefore, the cooling may be managed by a single annular cooling surface 20 at the external side of the liner. This surface is the only cooling surface in a fourth group. The recess 7 is formed so that in the upward direction the cooling surface 20 inclines inwards towards the running surface 5. As the cooling intensity of the surface is dependent on the distance to the running surface 5, the inclined course of the surface 20 ensures that its cooling effect increases basically in step with the increase towards the upper end of the liner of the heat inflow on the running surface 5. In the upper portion 6, the inclined bores in the first and second groups ensure a corresponding adaptation to the heat inflow increasing in the upward direction.

An annular jacket 21 envelops the recess 7 so that a cooling chamber is formed between the jacket and the surface 20. The jacket 21 extends upwards past the surface 9 and over a middle section 22 provided with annular grooves for distribution of cooling water between the channels of the same group. The grooves are closed radially outwards by the jacket 21. A number of sealing means 23 positioned in associated grooves abut the internal side of the jackets and yield the required sealing between the cooling surfaces and the grooves in the periphery of the liner.

Supply and discharge of cooling water to the individual groups is effected through pipes fastened to the outside of the jackets 17 and 21 in alignment with through-going holes therein. The drawing only shows one supply pipe and one discharge pipe for each group, but it is naturally possible to use several sets of pipes for each group, as the sets may then be distributed along the periphery of the liner so that the flow route from a supply pipe to the supply channel of a cooling channel will not be long.

An annular distribution channel 24 at the periphery of the liner connects the supply channels 14 associated with the first group with each other and with a supply pipe 25. The discharge channels 15 communicate with a discharge pipe 27 through an annular collecting channel 26. Correspondingly, the supply channels 14' are flow- connected with a supply pipe 29 through a distribution channel 28, and the discharge channels 15' are flow- connected with a discharge pipe 31 through a collecting channel 30. The cooling chamber 19 is connected with a supply pipe 32 at the bottom of the chamber and a discharge pipe 33 at the top of the chamber. The cooling chamber in the recess 7 communicates with a supply pipe 34 and a discharge pipe 35, also positioned at the bottom and top, respectively, of the chamber.

The adjustment of the water flow in the four groups is effected by means of valves controlled by a computer unit 36 shown in Fig. 4 and being in controlling connection with each valve, as shown by broken lines. The three first groups of cooling surfaces positioned in the upper portion 6 may be connected or disconnected completely by means of 3/2-way valves 37, 38 and 39, i.e., valves with three connections and two positions, so the whole water flow runs either through or past the group. With the valve positions shown in Fig. 4, the whole water flow is routed through all three groups, so the cooling intensity in the upper portion 6 is maximum. Each discharge pipe 27, 31 and 33 comprises a nonreturn valve 40, 41 and 42, respectively, which prevents cooling water from flowing backwards into a disconnected group.

The fourth group with the cooling surface 20 is to carry off so relatively limited amounts of heat that there is only a slight risk of micro-boilings at the cooling surface, which renders possible an adjustment of the cooling intensity by means of a stepless adjust¬ ment valve 43 which may route part of the water flow past the fourth group. The discharge pipe 35 also comprises a nonreturn valve 47. It is possible to collect several of the valves in a single valve block where the valve has a suitable number of supplies and discharges and valve positions so as to obtain the above control of the water flow. Through a wire 44, the computer unit 36 may be provided with information on the current load of the engine and on this basis emit control signals to the valves in accordance with a predetermined connection between the load and the need for cooling. It is also possible to arrange temperature sensors 45 at the running surface 5 and via a wire 46 supply the computer unit with information on the actual temperatures of the liner at the selected measuring points. In the latter case, the computer unit comprises predetermined informa¬ tion on the cooling intensity levels occurring at the possible combinations of active cooling groups, and information on permissible deviations from the desired liner temperature. If the temperature measured exceeds one of these predetermined limit values, the computer unit readjusts the cooling system to the nearest level for the cooling intensity.

The sensors 45 may be at a different distance from the abutment surface 3 in the axial direction of the liner, and at the same axial level there may be several sensors distributed along the circumference of the liner. Preferably, some of the sensors are at such a large distance from the surface 3 that the running surface at a level with the sensors is swept by the piston rings. If these sensors distributed along the circumference measure mutually different temperatures, this may be an indication of failure of a piston ring. At least one sensor may also be positioned at the point of the liner which is known from experience to be exposed to the highest temperature.

Below is a description of an example of a load- dependent connection or disconnection of the three cooling surface groups in the upper portion 6 of the liner. Engine load in per cent Group 1 Group 2 Group 3

95-105 + + +

85-95 + +

75-85 + - + 60-75 +

40-60 - + +

20-40 + 0-20 +

In the table, a load of 100 per cent is equivalent to the engine running at a 100 per cent nominal mean pressure and a 100 per cent nominal number of revol¬ utions, which is normally called the nominal LI point of the engine. The MCR point of the engine must not be set higher than the LI point, but in case of derated engines, for example, it is well-known to set the MCR point at a load corresponding to 85 per cent, for example, of the LI point. It appears immediately from the table that it is not necessary to change the liner, merely because the engine is derated, as the cooling intensity is automatically adjusted in accordance with the power yielded by the engine.

Instead of blind bores with inner tubes, the cooling channels inside the upper portion 6 may be through-going channels which extend from a lower supply opening to an upper discharge opening. These channels may be manufactured by boring at least two intersecting channel sections into the wall material of the liner, but for reasons of avoiding stress concentrations in the liner, the channels are preferably made from shaped tubes which are cast into the liner. This also gives great freedom to choose an optimum course for the channels.

Claims

P A T E N T C L A I M S 1. A method of cooling a cylinder liner in an internal combustion engine, particularly a large two- stroke main engine of a ship, wherein the liner in its upper portion (6) has several cooling surfaces (8) distributed along the circumference of the liner and cooled by cooling water to carry off heat from the running surface (5) of the liner, c h a r a c t e r i z e d in that the intensity of the cooling is varied in dependency of the thermal load on the liner by the cooling water being routed to selected cooling surfaces (8, 8', 18), the number and/or distance from the running surface of which are adjusted to the actual thermal load.

2. A method according to claim 1, c h a r a c t e r i z e d in that the cooling water is routed to selected groups of cooling surfaces where the cooling surfaces (8, 8') in groups comprising several cooling surfaces have substantially the same course in relation to the running surface (5), and that the cooling water flow is adjusted so that the individual group is either completely open or completely closed to through-flow.

3. A method according to claim 2, c h a r a c t e r i z e d in that in a portion posi¬ tioned below the upper portion (6), the liner has a cooling surface (20) where the cooling intensity is adjusted by changing the amount of through-flowing cooling water.

4. A method according to any one of claims 1-3, c h a r a c t e r i z e d in that a compensation for abnormal operating conditions is made in that the current temperatures at the running surface (5) are measured and registered, that the registered tempera- tures are compared with predetermined limit values, and that the intensity of the cooling is adjusted to the closest new level if a limit value is exceeded.

5. A method according to claim 4, c h a r a c¬ t e r i z e d in that an alarm signal is emitted, if the adjustment of the intensity of the cooling is due to a local temperature change on the running surface.

6. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that the cooling intensity is adjusted individually for each cylinder liner.

7. An internal combustion engine, particularly a large two-stroke main engine in a ship, having several cylinder liners each being clamped down against the cylinder section by means of a cover delimiting a combustion chamber together with the liner and the associated piston, wherein the liner in its upper portion (6) has several cooling surfaces (8) distributed along its circumference for carrying-off of heat from the running surface (5) of the liner, c h a r a c t e r i z e d in that the cooling surfaces (8, 8', 18, 20) are divided into groups, each having a separate cooling water supply passage (25, 24, 29, 28, 32, 24) and an adjustment member (37-39, 43) for control of the water flow in the passage.

8. An internal combustion engine according to claim 7, c h a r a c t e r i z e d in that the groups have a mutually different distance from the running surface over at least part of the extent of the cooling surfaces in the axial direction of the liner.

9. An internal combustion engine according to claim 7 or 8, c h a r a c t e r i z e d in that a first group comprises several elongated cooling channels (8) distributed along the circumference of the liner and extending substantially upwards and inwards from the external side of the liner towards the running surface (5), that a second group comprises several elongated cooling channels (8' ) distributed along the circumfer- ence of the liner and extending substantially upwards and inwards from the external side of the liner towards the running surface (5), preferably so that the upper sections (16') of the channels (8') have a greater distance from the running surface than the corresponding sections (16) of the channels (8) in the first group, and that a third group comprises a single annular cooling surface (18) at the external side of the liner, positioned radially on a level with the channels (8, 8' ) of the first and the second groups, and preferably a fourth group having a single annular cooling surface (20) at the external side of the liner, positioned axially below the other groups.

10. An internal combustion engine according to any one of the claims 7-9, c h a r a c t e r i z e d in that each of the first, the second, and the third groups has a valve (37, 38, 39) which routes the circulating amount of cooling water either completely through or completely past the group in question, and that the valves are controlled so that the current combination of open cooling water groups produces a cooling inten¬ sity corresponding to the current thermal load on the liner.