WO2013029612A1

WO2013029612A1 - Method to reduce load to a sealing means circumfering a piston rod engine and such engine

Info

Publication number: WO2013029612A1
Application number: PCT/DK2012/000095
Authority: WO
Inventors: Erik Crone
Original assignee: Man Diesel & Turbo
Priority date: 2011-08-30
Filing date: 2012-08-24
Publication date: 2013-03-07
Also published as: CN103842696A; CN103842696B; JP2014531549A; KR101552184B1; JP6132212B2; KR20140056313A; WO2013029612A8

Abstract

At an engine of the crosshead type, especially a big sized two stroke diesel engine, having a crankcase (1) as well as at least one cylinder (3) containing a cylinder liner (4), which extends in a surrounding scavenge chamber (7) and is ending above a chamber bottom (8) of the scavenge chamber (7), and wherein a piston rod (11 ) is provided, which connects a piston (5) going up and down within the cylinder liner (4) with an associated crosshead (10) arranged in the crankcase (1 ), and which penetrates a seal packing (15) provided in the chamber bottom (8), pollution of the system oil of the crankcase (1 ) by cylinder oil and/or combustion residues can be prevented in that the blast generated during the start of the piston upstroke and passing the lower edge of the cylinder liner (4) is diverted from a radial direction to an at least mostly axial direction.

Description

MAN Diesel & Turbo

Filial af MAN Diesel & Turbo SE, Tyskland

Teglholmsgade 41

2450 COPENHAGEN SV

DENMARK

Method to reduce load to a sealing means circumfering a piston rod for an engine and such engine

The invention relates to a method to reduce load to a sealing means circumfering an axially movable piston rod, from substance deposited on said rod

for an engine having at least one piston reciprocating in a mating cylinder liner having it's end exposed to a scavenge chamber whose wall structure comprises said sealing means around said piston's rod moving synchroneously with the piston and axially through the sealing means separating the scavenge chamber from other space whereinto part of the piston rod also is exposed,

the cylinder liner's running face swept by the piston and/or by it's possible piston rings and possibly other related movable parts/surfaces being treated with a flowable substance, a surplus of which possibly also containing other adopted substances and/or imbedded particles is liberated from areas of the cylinder liner, a gassy medium in the scavenge chamber by its whirling streaming is forcing particles of liberated flowable substance to be directed towards the piston rod.

The invention relates further to a corresponding method for diverting a gassy medium in a running engine.

The invention relates further to an engine described above, preferably to an engine of the crosshead type, especially a big sized two stroke diesel engine, having a crankcase as well as at least one cylinder containing a cylinder liner, which extends in a surrounding scavenge chamber and is ending above a chamber bottom of the scavenge chamber, the chamber bottom separating the scavenge chamber from the crankcase, and wherein a piston rod is provided, which connects a piston going up and down within the cylinder liner with an associated crosshead arranged in the crankcase and which penetrates a seal packing provided in the chamber bottom.

In an engine of this type it can happen that cylinder oil dripping off the cylinder liner and polluted with combustion residues remains on the scavenge chamber bottom and that also exhaust gas containing combustion residues blows back into the scavenge chamber through the scavenge/inlet ports gradually opened to the combustion chamber by the downstroking piston. When during the start of the upstroke of the piston a suck is generated under the piston this suck can lead to a severe blast of the gas contained in the scavenge chamber passing the lower edge of the cylinder liner. This blast can carry along oil particles and combustion residues from the scavenge chamber bottom and from the cylinder liner's ports and lower edge and flows inwardly toward the piston rod thus propelling a lot of cylinder oil particles polluted with combustion residues to directly impinge the central piston rod. Therefore it can occur that the piston rod moving up and down feeds cylinder oil and combustion residues through the seal packing between the scavenge chamber and the crankcase into the crankcase what will lead to a pollution of the system oil contained in the crankcase so that this system oil which must be clean enough for bearing lubrication and hydraulics, needs a frequent filtration or even may require frequent replacement due to unfavorable mixing/reaction effects from the cylinder oil. Engines being charged by a turbocharger, a compressor or the like are more likely to be subject to the problems just described, as fresh air is delivered to the scavenge chamber with a pressure substantially over atmospheric pressure, so that the pressure difference between the inside of the cylinder liner and the outside is very high. This supports the occurrence of the blast.

The document US 1 ,506,835 shows an engine having two cylinders wherein a gassy medium can be sucked in a room under pistons contained in the cylinders. The document US 7,258,087 shows a cylinder with a piston. When the piston moves upward, air may be sucked in from a surrounding chamber. The document GB 290,153 shows a piston moving in a cylinder with a piston rod passing through a stuffing box. Besides the piston rod, a heat shielding ring is provided that delimits a chamber under the piston.

The document US 1 ,645,595 shows a piston rod having a cooling chamber around it. The cooling chamber delimits a combustion room having two fuel injection valves.

The document US 1 ,152,658 shows three embodiments of heat protection means for a piston rod going through a combustion chamber.

The document GB 527,208 shows a cylinder containing a piston with a piston rod. The piston rod is surrounded by a telescopic tube that goes through a stuffing box. Air is sucked in from a line during upward movement of the piston. The document US 1 ,645,169 shows an engine having two cylinders with a complex air guiding system, wherein air is sucked in a room under a piston during upward movement of the piston.

Starting from this point of view it is the object of the present invention to reduce load to sealing means circumfering an axially movable piston rod and to keep low the need for cleaning the system oil in crankcase.

It is a further object of the present invention to simplify mounting of means that help to reduce load to sealing means.

These and other objects are solved by an engine according to claim 1 and by a method according to claim 32. Preferred embodiments can inter alia be obtained from the dependent claims.

According a superposed idea of the invention this object is attained in that the particles of liberated flowable substance forced by the gassy medium are hindered deposition onto the piston rod due to effect of inertia preferably by means of an intermediate wall structure connected to the scavenge chamber, the wall stopping the substance particles by impingement while the carrying gassy medium is diverted preferably from said wall from a radial direction to an at least mostly axial direction.

A preferred embodiment of this idea can be seen in that as the intermediate wall structure a skirt is provided upstanding from the scavenge chamber bottom and surrounding the piston rod. Preferably, an intermediate wall structure is provided on the chamber bottom, wherein the piston rod, the seal packing and the wall structure define a clearance being open in a direction towards the interior of the cylinder liner, the wall structure being adapted such that the blast generated during the start of the piston upstroke and passing a lower edge of the cylinder liner, is diverted by the intermediate wall structure from a radial direction to an at least mostly axial direction.

With these measures the disadvantages of the known arrangements can be avoided. The skirt diverts the blast of scavenge gas surrounding the lower end of the cylinder liner from a more radial to a more axial direction and shields so the piston rod against deposition of cylinder oil particles and combustion residues. Due to the deviation of the blast of scavenge gas cylinder oil particles and combustion residues carried along in it are separated from the gas stream by inertia forces and caught on the outside of the skirt and the scavenge chamber bottom, so that the piston rod is protected from cylinder oil and combustion residues deposition and will not feed it into the crankcase.

The invention is preferably applicable to an engine being charged, e.g. by a turbocharger or a compressor.

In the following further advantageous developments of the generic measures are recited.

Usefully the blast of the scavenge gas containing cylinder oil particles can be directed at least partly to the inside running surface of the cylinder liner. This can easily be achieved in that the skirt at least in its upper area is funnel shaped i. e. being enlarged in the radially outward direction. This results in leading nonseparated oil particles onto the lower part of the running surface of the cylinder liner and thus to a reuse of cylinder oil and therefore to lowering the oil consumption.

In a further development of the superposed measures the height and/or the projection in the radially outward direction of the skirt can be adjustable. This gives the possibility for optimizing the operation of the skirt.

Usefully the skirt can be attached to the upper flange of a stuffing box building the seal packing or to the upper end of a socket enclosing the packing. Thus mounting can smartly be related.

A further preferred measure can be that the skirt contains at least two sections in circumference which sections are fixable to one another. This split-ring design enables smart mounting as well as demounting of the skirt without removal of the piston what makes possible service inspections, repair and retrofit activity much quicker and thereby cheaper to perform, by access from the scavenge chamber.

Advantageously the skirt can be provided with at least one exit opening associated to its lower end. Thus oil particles caught within the skirt can be discharged to outward and therefore prevented from getting into the gap between the piston rod and the packing. To hinder entry of parts of the gas blast into the inside of the skirt one or more or all exit openings can be protected by a hood arranged with radial clearance to a side face of the skirt.

In the following a working example of the invention is described by means of the drawings. shows a vertical cross section of a big sized diesel engine of the crosshead type, shows an enlarged view of the lower area of the scavenge chamber of the motor of Fig. 1 , shows a vertical cross section of a skirt adjustable in height, shows a horizontal cross section of a skirt with split ring design and shows a vertical cross section of a lower area of the skirt containing an exit opening.

A diesel engine like represented in Fig. 1 can be used for driving maritime objects or large sized power plants or the like. The basic structure and mode of operation of such reciprocating piston engines are known and are therefore in the following described only to the extent found necessary in order to understand the present invention. The engine showed in Fig. 1 contains in its lower part a crankcase 1 wherein a crankshaft 2 is borne by so called main bearings. On the upside of the crankcase 1 a row of cylinders 3 is arranged. Each cylinder 1 contains a cylinder liner 4 wherein a piston 5 is arranged which is movable up and down. The piston 5 functions as the lower movable delimitation of a combustion chamber 6 positioned inside the liner 4.

The cylinder liner 4 is supported on the surrounding housing of a scavenge chamber 7 which can be charged with scavenge air or gas. A turbocharger 35 is provided near the piston in order to deliver compressed gas.

The liner 4 extends with its lower part into the scavenge chamber 7 and is ending with clearance above the chamber bottom 8. In the area of the lower end of the liner 4 inlet ports 9 are provided. The inlet ports 9 are passed by the piston 5 when it is moving down and up whereby a communication between the scavenge chamber 7 and the combustion chamber 6 is opened and shut. The piston 5 is connected with an associated crosshead 10 by a piston rod 11 arranged along the axes of the cylinder liner 4 and the piston 5. The crosshead 10 is positioned within the crankcase 1 and is designed as a sledge moving up and down and guided by associated guides 12 parallel to the axis of the piston 5 and piston rod 11. The crosshead 10 contains a crosshead pin 13 fixed to the piston rod 11. On this pin 13 a connection rod 14 is borne which connects the crosshead 10 with the crankshaft 2. The scavenge chamber bottom 8 rests on the top of the crankcase 1. The piston rod 11 passes through the wall arrangement between the scavenge chamber 7 and the crankcase, that means the piston rod 11 passes through the scavenge chamber bottom 8 and other possible structure on the top of the crankcase 1 , whereby the piston rod 11 penetrates an associated seal packing

15 provided in the scavenge chamber bottom 8.

The cylinder liner is supplied with suitable lubrication oil (in the application named as cylinder oil) which together with combustion residues can drip down to the scavenge chamber bottom 8 as far as it isn't burned. For disposing this dripping down fluid a drain 16 communicating with the bottom area of the scavenge chamber 7 is provided. The chamber bottom 8 can be cleaned towards the drain

16 and/or provided with a ring channel surrounding the seal packing 15 and communicating with the drain 16. Also exhaust gas containing further combustion residues can enter into the scavenge chamber 7 when the inlet ports 9 are opened during the downstroke of the piston 5.

In the crankcase 1 oil of high cleanliness is present (in the application named as system oil) which oil is used for lubrication of the bearings as well as for hydraulic purposes. For filtering this oil a filtering station (not shown) is provided. For preventing pollution of the system oil by cylinder oil the crankcase 1 must be separated from the scavenge chamber 7. For these purposes the seal packing 15 is provided. The seal packing 15 can as shown in Fig. 2 be designed as a stuffing box and be assembled in a surrounding socket 17 of the chamber bottom 8. The separation work of the seal packing 15 can be improved if as less cylinder oil and combustion residues as possible are allowed to reach the packing 15. In this connection one must consider that during the start of the piston upstroke the piston 5 moving to upwards generates a severe suction in the area under it which leads to a severe blast of gas from in the scavenge chamber 7 to the inside area of the cylinder liner 4 under the piston 5 as is indicated in Fig. 2 by arrows 18a, b. This blast passes the lower edge of cylinder liner 4 with radially inward going streaming direction and is carrying along cylinder oil and combustion residues from the scavenge chamber lower area and/or bottom 8.

For preventing that this blast carrying cylinder oil particles and combustion residues with it hits on the centrally positioned piston rod 11 like the dotted arrow 18a in Fig. 2 means are provided for diverting the said blast from a more radial direction to an at least mostly axial direction like the continuous arrows 18b in Fig. 2. For building these means a skirt 19 surrounding the piston rod 11 and upstanding from the scavenge chamber bottom 8 can be provided as can be seen best from Fig. 2.

In principle a simple upstanding tubular preferably being circular structure shielding the piston rod 11 can be sufficient, thus mainly deviating the blast direction towards the piston's downfacing structure. But as a useful measure it can be provided that the skirt 19 at least in the area of its upper end is funnel shaped enlarged in the radially outward direction. In Fig. 2 the skirt 19 is provided with a funnel shaped upper rim 20. Naturally also a rounded shape of the upper edge of the skirt 19 would be possible. These measures assure that the blast said above is directed at least partly to the lower part of the inside running surface of the cylinder liner 4 as show the arrows 18b in Fig. 2, instead of else mainly be directed to deposit residual particles onto the downfacing structure of the piston. This can lead to a direct re-use of cylinder oil still contained in the blast. Most of the particles carried by the blast are separated from it by inertia forces due to the change of flow direction as is indicated at 21 in Fig. 2. These particles are now according the invention mainly deposited onto the skirt 19, wherefrom they as a liquid substance are driven downwards to be collected on the scavenge chamber bottom 8 which can slope toward a discharge exit 22 leaving from the lowermost bottom level being connected to the drain 16. Usefully a ring channel 23 leading to the exit 22 can be carved in the bottom 8.

Between the piston rod 11 , the seal packing 15 and the skirt 19, a clearance 36 is defined, being open in a direction towards the interior of the cylinder liner 4. In the shown embodiment, this means that the clearance 36 is open in an upward direction.

The maximum height and outer diameter of the skirt 19 is restricted by the shape of the lower part of the piston 5 in its lowermost position whereby usefully some clearance should be given between the upper side of the skirt 19 and the underside of the piston 5. Usefully the skirt 19 can reach up to a level above the lower end of the cylinder liner 4. The diameter of the upper end of the skirt19 can lie usefully within the range of 1.5 - 2.5 of the diameter of the piston rod 11 and can preferably be twice of it. According a further useful measure the outer diameter of the upper end of the skirt 19 can be augmented and be up to 10% larger than the outer diameter at the skirt's lower end, to allow for funnel shape, etc.

Normally it is sufficient if the skirt 19 has a fix height. But in some cases it can be advisable if the height of the skirt is adjustable. An example for a such design is showed in Fig. 3. Herein the skirt 19 contains at least two sections 19a, b in height which can be moved against each other and fixed to one another. In the showed embodiment fixing screws 24 are indicated whereby one section 19b is provided with associated slots 25. Naturally also other adjustable structure could come in question for example that the several sections 19a, b, are screwed into one another. In the shown embodiment the radially outward projection of the skirt 19 resp. of its upper rim 20 is fix and not adjustable. But also here an adjustable structure could be provided so that the projecting of the skirt 19 resp. of its rim 20 is adjustable. Especially for retrofit purposes it can be beneficial to cover a large amount of various cylinder bores with a relatively smaller amount of skirt constructions. Therefore, preferably, the skirt can have a construction allowing the skirt (assembly) to be mounted with another characteristic (e.g. outer) perimeter. A spiral like one-piece construction is here an elegant solution, even allowing placement around a piston rod in situ.

For enabling a smart mounting of the skirt 19 it can be designed as a split-ring as indicated in Fig. 4. Herein the skirt 19 contains at least two section 19c, d, in circumference which can be fixed to one another. In the shown embodiment a flange connection is provided. For this purpose the ends of the sections 19c, d can be bent outwardly to build flanges 26 which can be connected by screws 27. Also other embodiments being suited for separate placement around the piston rod 11 without removal of piston 5 or piston rod 11 can be used, e.g. a spirally shaped version.

The stuffing box building the sealing packing 15 is provided with a top flange 15a. The skirt 19 can be mounted to this top flange 15a of the seal packing 15. Another possibility could be to mount the skirt 19 on the upper front end of a housing enclosing the packing 15 e.g. in the form of a socket 28 provided in the bottom 8. Further, the upstanding skirt structure can be shaped as integral parts of the stuffing box top 15a normally being vertically split for repair replacement after axial withdrawal, or may be an integral socket-like structure reaching up from the scavenge chamber bottom structure 8, 28. Usefully pre-installed and/or machined mounting means can be provided. In the embodiment shown in Fig. 3 the skirt 19 is attached to the mounting base by angle brackets 29 and screws 30. Cylinder oil which may enter into the ring chamber defined inside the skirt 19 must be led outside. For this purpose the skirt 19 is provided with at least one exit opening 31 associated to its lower edge as is indicated in Fig. 5. The exit opening 31 can be built by a slot or the like ending on the lower edge of the skirt 19. Usefully each exit opening 31 is protected by a hood 32 arranged with radial clearance before it or by other labyrinth shielding means, to either skirt side. Thereby penetration of the blast of scavenge gas into the inner chamber of the skirt 10 is prevented.

The skirt 19 and/or its elements can be produced as sheet metal parts. Naturally also other kinds of manufacture would be possible, for example casting. Due to the difficulty to clearly and unambiguously directly read possible markings etc. from a mounted and very soiled inventive shirt, e.g. at a service inspection, such skirt in a useful embodiment can be provided with at least one tag (not shown) with contactless remote access to its contained information, the tag preferably being of the RFID-type, comprising stored data to unambiguously define this skirt 19. Usefully one said tag can be loaded with data specifying details to authenticate said skirt 19, such authenticating data preferably also comprise manufacturing-, approval-, historic and possible or planned future use-data for said skirt 19.

The main function of the invention is that cylinder oil and combustion residues are kept away from the piston rod 11 as well as from the seal packing 15 and that therefore a pollution of the system oil in the crankcase 1 with cylinder oil and combustion residues is prevented with the consequence of a substantially reduced need for filtration, cleaning, properties adjustment by addition, and/or replacement of the system oil.

Claims

1. Engine, especially of the crosshead type, preferably big sized two stroke diesel engine, having a crankcase (1) as well as at least one cylinder (3) containing a cylinder liner (4), which extends in a surrounding scavenge chamber (7) and is ending above a chamber bottom (8) of the scavenge chamber (7), the chamber bottom (8) separating the scavenge chamber (7) from the crankcase (1), and wherein a piston rod (11) is provided, which connects a piston (5) going up and down within the cylinder liner (4) with an associated crosshead (10) arranged in the crankcase (1) and which penetrates a seal packing (15) provided in the chamber bottom (8), characterized in that an intermediate wall structure (19) is provided on the chamber bottom (8), wherein the piston rod (11), the seal packing (15) and the wall structure (19) define a clearance (36) being open in a direction towards the interior of the cylinder liner (4), the wall structure (19) being adapted such that the blast generated during the start of the piston upstroke and passing a lower edge of the cylinder liner (4), is diverted by the intermediate wall structure (19) from a radial direction to an at least mostly axial direction.

2. Engine according claim 1 having at least one piston reciprocating in a mating cylinder liner having it's end exposed to a scavenge chamber whose wall structure comprises said sealing means around said piston's rod moving synchroneously with the piston and axially through the sealing means separating the scavenge chamber from other space whereinto part of the piston rod also is exposed,

the cylinder liner's running face swept and/or by it's possible piston rings and possibly other related movable parts/surfaces being treated with a flowable substance, a surplus of which possibly also containing other adopted substances and/or embedded particles is liberated from areas of the cylinder liner,

a gassy medium in the scavenge chamber by it's whirling streaming is forcing particles of liberated flowable substance to be directed towards the piston rod characterized in that particles of liberated flowable substance forced by the gassy medium are hindered deposition onto the piston rod due to effect of inertia, by means of an intermediate wall structure connected to the scavenge chamber, the wall structure thereby stopping the substance particles by impingement while the carrying gassy medium is diverted from said wall.

3. Engine according claim 1 or 2, characterized in that as said intermediate wall structure a skirt (19) is provided upstanding from the scavenge chamber bottom (8) and surrounding the piston rod (11).

4. Engine according one of the preceding claims, characterized in that the blast is diverted at least partly to the inside running surface of the cylinder liner

(4).

5. Engine according claim 3 or 4, characterized in that the skirt (19) at least in its upper area is funnel shaped enlarged in the radially outward direction.

6. Engine according one of the preceding claims 3-5, characterized in that the diameter of the upper end of the skirt (19) is within the range of 1.5 - 2.5 of the diameter of the piston rod (11).

7. Engine according claim 6, characterized in that the diameter of the upper end of the skirt (19) is twice the diameter of piston rod (11).

8. Engine according one of the preceding claims 3-7, characterized in that the outer diameter at the upper end of the skirt (19) is augmented and being up to

10% larger than the outer diameter at the skirt's lower end.

9. Engine according one of the preceding claims 3-8, characterized in that the upper end of the skirt (19) along it's circumference is positioned below the shaped volume face which from above is defined by the piston (5) in its lower most position.

10. Engine according claim 9, characterized in that the upper end of the skirt (19) reach up to a level above the lowermost end of the cylinder liner (4).

11. Engine according one of the preceding claims 3-10, characterized in that the height of the skirt (19) is adjustable.

12. Engine according claim 11, characterized in that the skirt (19) contains at least two sections (19a, b) in height movable against each other and fixable to one another.

13. Engine according one of the preceding claims 3-12, characterized in that the skirt's (19) projection in the radially outward direction is adjustable, whereby the skirt (19) preferably has a construction with one or more flexing, mutually displaceable or the like parts allowing the skirt (19) to be mounted with another resulting outer diameter.

14. Engine according one of the preceding claims, characterized in that the skirt (19) is produced at least partly as a sheet metal part.

15. Engine according claim 14, characterized in that the skirt (19) contains at least two sections (19c, d) in circumference which are fixable to one another.

16. Engine according one of the preceding claims 3-15, characterized in that the skirt (19) is attached to the upper flange (15a) of the seal packing (15) or to the upper front end of a socket (28) enclosing the seal packing (15).

17. Engine according claim 16, characterized in that the skirt (19) is attached to its base place by angle brackets (29).

18. Engine according one of the preceding claims 3-17, characterized in that the skirt (19) is provided with at least one exit opening (31) associated to its lower edge.

19. Engine according claim 18, characterized in that each exit opening (31) of the skirt (19) is protected by a hood (32) arranged with radial clearance before it or by other labyrinth shielding means, to either skirt side.

20. Engine according one of the preceding claims, characterized in that a drain outlet (22) for cylinder oil and possible other residual substance carried herewith is arranged in the area of the scavenge chamber bottom (8).

21. Engine according claim 20, characterized in that the scavenge chamber bottom (8) is provided with a ring channel communicating with the drain outlet (22).

22. Engine according claim 21, characterized in that the ring channel (23) being located radially outside the skirt (19) perimeter.

23. Skirt to function as intermediate wall according to one of the preceeding claims, characterized in that being of overall tubular shape having means for detachable fixing to a structure in/at the scavenge chamber wall.

24. Skirt according claim 23, characterized in that having a slit to allow positioning by being snapped around an in principle endless rod.

25. Skirt according claim 24, characterized in that in it's freestanding position and/or in it's mounted situation exhibiting a spiral form with overlapping areas.

26. Skirt according claim 23, characterized in that the tubular shape being realized by interconnection of at least two separate parts.

27. Skirt according claim 23, characterized in that having at least one opening (31) located near a first end of the tubularly shaped structure.

28. Skirt according one of the claims 23-27, characterized in that the tubular shape being generally circular.

29. Skirt according claim 28, characterized in that having a second end funnelshapedly opening to a larger diameter.

30. Skirt to function as intermediate wall according claim 1 or 2, characterized in that being shaped as an upstanding tubular (possible split) structure to surround a piston rod and being integral with the housing structure part(s) for the sealing means around said piston rod.

31. Skirt according one of the claims 23-30, characterized by at least one tag provided on the skirt (19), preferably a tag of a RFID-Type, comprising stored data to unambiguously define said skirt (19).

32. Method of diverting a gassy medium in a running engine,

the engine having at least one piston with a piston rod reciprocating in a mating cylinder liner having it's end exposed to a scavenge chamber whose wall structure comprises sealing means around said piston,

said piston rod moving synchroneously with the piston and axially through the sealing means separating the scavenge chamber from other space whereinto part of the piston rod also is exposed,

the cylinder liner's running face swept by the piston and/or by it's possible piston rings and possibly other related movable parts/surfaces being treated with a flowable substance, a surplus of which possibly also containing other adopted substances and/or embedded particles is liberated from areas of the cylinder liner,

a gassy medium in the scavenge chamber by its whirling streaming is forcing particles of liberated flowable substance to be directed towards the piston rod, characterized in that particles of liberated flowable substance forced by the gassy medium are hindered deposition onto the piston rod due to effect of inertia, by stopping the flowing substance particles by impingment while the carrying gassy medium is diverted from a radial direction to an at least mostly axial direction, and that the blast is diverted at least partly to the inside running surface of the cylinder liner.